Dissertationen: „Pasture ecology – Western Australia“

1

Doole, Graeme John. „Value of perennial pasture phases in dryland agricultural systems of the eastern-central wheat belt of Western Australia“. University of Western Australia. School of Agricultural and Resource Economics, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0213.

Der volle Inhalt der Quelle

Annotation:

Over the past thirty years, price relativities and technological development have motivated an increase in the area of land allocated to cropping, as opposed to pasture production, throughout the central wheat belt of Western Australia. Nevertheless, reducing the proportion of pasture in these rotations has challenged the future productivity of farming systems in this area. First, the frequent application of selective herbicides for weed control in extended cropping rotations has promoted the development of herbicide resistance in a number of major agricultural weeds. Second, the primary use of annual plants has promoted the development of soil salinisation by allowing a significant proportion of rainfall to recharge saline water tables. The inclusion of perennial pasture phases between extended periods of cropping may mitigate or delay these constraints to production through (a) allowing the use of costeffective forms of non-selective weed control, and (b) through creating a buffer of dry soil that absorbs leakage occurring beneath subsequent crops. This study consequently explores the value of including perennial pasture phases in dryland agricultural systems in the eastern-central wheat belt of Western Australia, accounting for benefits related to herbicide resistance and water table management. A novel computational algorithm for the solution of multiple-phase optimal control problems is developed and used to conduct a conceptual analysis of the value of lucerne (Medicago sativa L.) pasture for managing annual ryegrass (Lolium rigidum Gaudin), the primary weed in wheat belt cropping systems. The competitiveness and fecundity of annual ryegrass provide strong economic incentives to maintain a low weed population, irrespective of herbicide-resistance status. Consequently, the ineffectiveness of selective herbicides primarily reduces the profitability of cropping by motivating the adoption of more costly non-selective forms of weed control. The inclusion of lucerne in land-use rotations is only optimal in the presence of severe herbicide resistance given (a) the low efficiency of alternative weed-management practices available during the pasture phase, relative to selective-herbicide application; (b) the significant cost of establishing this perennial pasture; and (c) the high relative profitability of cereal production in the absence of resistance. The value of lucerne, relative to annual pastures, for weed management is explored in greater detail through the use of compressed annealing to optimise a sophisticated simulation model. The profitability of candidate rotations is also manipulated to account for the long-term production losses accruing to the recharge of saline groundwaters that occurs beneath them. Sequences incorporating lucerne are only more profitable than those that include annual pasture at the standard set of parameter values if (a) annual ryegrass is resistant to all selective herbicides, (b) the water table is so shallow (approximately less than 3.5 m deep) that frequent rotation with perennials is required to avert soil salinisation, or (c) sheep production is highly profitable. The value of perennial pasture is sufficient under these circumstances to overcome its high establishment cost. Consistent with intuition, these benefits are reinforced by lower discount rates and higher rates of leakage occurring beneath annual-based systems. Formulation of an effective communication strategy to report these results to producers is justified given the complexity involved in determining the true magnitude of these intertemporal benefits through alternative means, such as field trials.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

2

McDonald, Kathi. „Variation in morphology, salinity and waterlogging tolerance and resource allocation in strawberry clover (Trifolium fragiferum L.) : implications for its use in mildly saline soils in southern Australian farming systems“. University of Western Australia. School of Plant Biology, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0105.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] In southern Australian farming systems the replacement of deep-rooted perennial native vegetation with shallow-rooted annual crops and pastures has resulted in rising groundwater tables and an increased incidence of dryland salinity. It has been suggested that to address this issue by restoring hydrological balance, large areas of agricultural land need to be vegetated with perennial plants. One of the most agriculturally productive ways to do this is to introduce perennial pastures, both into upslope groundwater

APA, Harvard, Vancouver, ISO und andere Zitierweisen

3

Twomey, Luke J. „The phytoplankton ecology of Wilson Inlet, Western Australia“. Curtin University of Technology, School of Environmental Biology, 2000. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=9801.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

4

Ireland, Carolyn. „Sustaining the western myall woodlands : ecology and mangement“. Title page, contents and abstract only, 1997. http://web4.library.adelaide.edu.au/theses/09PH/09phi65.pdf.

Der volle Inhalt der Quelle

Annotation:

Bibliography: leaves 227-244. This study is conceived to address various aspects of western myall (Acacia papyrocarpa Benth) recruitment, lifespan, distribution and the effects of major vertebrates on the species' ecology over the major part of its range in South Australia. A study of the population dynamics of the species is done to assess the adequacy of net recruitment. Population structure is examined across the woodlands. The new concept of "fossil paddocks" is adopted to investigate the historical impact of introduced herbivores on the landscape.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

5

Sounness, Marcus Neil. „Alternative grazing systems and pasture types for the South West of Western Australia : a bio-economic analysis“. University of Western Australia. School of Agricultural and Resource Economics, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0054.

Der volle Inhalt der Quelle

Annotation:

Alternative grazing systems and pasture types for wool production in the south west of Western Australia were analysed using bio-economic modelling techniques in order to determine their relative productivity and profitability. After reviewing the experimental and modelling literature on perennial pastures and grazing systems, seven case studies of farmers were conducted in order to investigate the practical application of innovative grazing systems and use of perennial pastures. Together these case studies provided information for identifying relevant variables and for calibrating the modelling work which followed. The core of the work lies in a bio-economic model for investigating the comparative value of the three grazing systems and two pasture families mentioned above. A baseline scenario using currently available and reliable scientific data provides baseline results, after which a number of sensitivity analyses provide further insights using variations of four key parameters: persistence, heterogeneity, water soluble carbohydrates, and increased losses. Results show that perennial pastures are in the studied region more profitable than annual pastures. Under current baseline conditions, continuous grazing with perennial pastures is the most profitable enterprise, but this superiority is not robust under parameter variations defined by other scenarios. The more robust solution in terms of enterprise profitability is cell grazing with perennial pastures. The results indicate that intensive grazing systems such as cell grazing have the potential to substantially increase the profitability of grazing operations on perennial pasture. This result is an encouraging one in light of its implications for water uptake and salinity control. It means that economics and land care can go hand in hand, rather than be competitive. It is to be noted that it is the choice of the grazing system in combination with the pasture species, rather then the pasture species itself, that allows for such complementarity between economics and sustainable land use. This research shows that if farmers adopt practices such as cell grazing they may be able to increase the area that they can profitably plant to perennial pasture thus reducing the impacts of dryland salinity. This finding is consistent with the findings of the case studies where the farmers perceived that, provided grazing was planned, increasing the intensity of their grazing management and the perenniallity of their pastures would result in an increase in the profitability of their grazing operation. As a result this research helps to bridge a gap which has existed in this area of research, between the results of scientific research and those reported in practice.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

6

Burkett, Danny, und danny burkett@deakin edu au. „Nutrient contribution to hyper-eutrophic wetlands in Perth, Western Australia“. Deakin University. School of Life and Environmental Sciences, 2005. http://tux.lib.deakin.edu.au./adt-VDU/public/adt-VDU20071115.082506.

Der volle Inhalt der Quelle

Annotation:

This thesis investigates nutrient contribution to six hyper-eutrophic lakes located within close proximity of each other on the Swan Coastal Plain and 20 kilometres south of the Perth Central Business District, Western Australia. The lakes are located within a mixed land use setting and are under the management of a number of state and local government departments and organisations. These are a number of other lakes on the Swan Coastal Plain for which the majority are less than 3 metres in depth and considered as an expression of the groundwater as their base is below the regional groundwater table throughout most of the year. The limited amount of water quality data available for these six lakes and the surface water and groundwater flowing into them has restricted a thorough understanding of the processes influencing the water quality of the lakes. Various private and public companies and organisations have undertaken studies on some of the individual wetlands and there is a wide difference in scientific opinion as to the major source of the nutrients to those wetlands. These previous studies failed to consider regional surface water and groundwater effects on the nutrient fluxes and they predominantly only investigated single wetland systems. This study attempts for the first time to investigate the regional contribution of nutrients to this system of wetlands existing on the Swan Coastal plain. As such, it also includes new research on the nutrient contribution to some of the remaining wetlands. The research findings indicate that the lake sediments represent a considerable store of nutrients (nitrogen and phosphorus). These sediments in turn control the nutrient status of the lake's water column. Surface water is found to contribute on an event-basis load of nutrients to the lakes whilst the groundwater surprisingly appears to contribute a comparatively low input of nutrients but governs the water depth. Analysis of the regional groundwater shows efficient denitrifying abilities as a result of denitrifying bacteria and the transport is localised. Management recommendations for the remediation of the social and environmental value of the lakes include treatment of the lakes sediments via chemical bonding or atmospheric oxidation; utilising the regional groundwaters denitrifying abilities to treat the surface water via infiltration basins; and investigating the merits of managed or artificial aquifer recharge (MAR).

APA, Harvard, Vancouver, ISO und andere Zitierweisen

7

Loo, Christopher. „The ecology of naturalised silvergrass (Vulpia) populations in south-western Australia“. University of Western Australia. School of Plant Biology, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0093.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] Annual grasses have colonised a diverse range of environments in southern Australia. The “Silvergrasses” of the genus Vulpia are excellent examples being widely distributed, are prevalent weeds of agriculture and have had a long history to naturalise on the continent. Research was undertaken on Vulpia populations to identify if naturalising species have reproductive traits that provide propagules with the best chances of success. Furthermore, research aimed at investigating if these traits vary between species and their populations and how this variability related to the environment. A herbarium and field study was undertaken to establish what Vulpia species occur in SW Australia and to investigate environmental factors affecting their distribution. 169 herbaria specimens was examined and a botanical field survey of 189 sites was carried out in September 1998. Four species occur in the region: V. fasciculata, V. muralis, V. bromoides and two variants of V. myuros (V. myuros var. megalura and V. myuros var. myuros). V. bromoides and V. myuros were introduced early into the region while V. fasciculata and V. muralis more recently. It is plausible that Vulpia invaded the region via early seaport settlements and was spread by agricultural expansion. 96% of field sites contained V. myuros var. myuros, 79% V. myuros var. megalura, 50% V. bromoides, 6% V. fasciculata and 6% contained V. muralis. 90% of sites contained a mix of species and 9% of sites contained pure species stands. V. myuros var. myuros is the most widespread species and dominant form of V. myuros. It is found from high rainfall regions through to arid locations occurring on mostly light textured low fertility soils. V. muralis and V. fasciculata occur infrequently with the former widely dispersed and the later occurring predominantly on sands. V. bromoides occurs extensively in high rainfall regions but rarely extends to locations receiving less than 400-450mm annual rainfall and northward above 30°00’ latitude. It is predominantly on light to loamy textured soils that are fertile and acid. The most common species V. myuros and V. bromoides often coexist within sites but the dominance of one over the other is strongly correlated with growing season length and false break frequency. V. bromoides is positively correlated to growing season length and V. myuros is negatively related. The distribution of Vulpia species is strongly influenced by climate and soils. Variability in distribution is a reflection of the ecological differentiation between species to colonise different environments

APA, Harvard, Vancouver, ISO und andere Zitierweisen

8

Frost, William E. „The ecology of cereal rust mite Abacarus hystrix (Nalepa) in irrigated perennial dairy pastures in South Australia /“. Title page, contents and summary only, 1995. http://web4.library.adelaide.edu.au/theses/09PH/09phf9398.pdf.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

9

Fisher, Judith L. „Fundamental changes to ecosystem properties and processes linked to plant invasion and fire frequency in a biodiverse woodland“. University of Western Australia. School of Plant Biology, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0109.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] Mediterranean southwest Australia, a global biodiversity hotspot, has nutrient deficient soils, exacting climatic conditions and is species rich with 7380 native vascular plant species, of which 49% are endemic. The region is expected to experience one of the world's highest degrees of biodiversity loss and change in the coming decades, with introduced species presenting a major threat. Limited knowledge is available on the mechanisms of ecosystem change associated with invasion and fire in this biodiversity hotspot region. Banksia woodland, an iconic complex species-rich natural ecosystem is one of the major vegetation types of the coastal sandplain, extending from 15 to 90 km inland and 400 kms along the west coast. The following hypothesis was tested to explore the ecological impacts of invasion: Is invasion of Banksia woodland by the introduced species Ehrharta calycina and Pelargonium capitatum accompanied by an alteration in ecosystem properties and processes, whereby the degree of change is related to fire frequency and abundance of introduced species? Different vegetation conditions, i.e. Good Condition (GC), Medium Condition (MC), Poor Condition invaded by Ehrharta calycina (PCe) and Poor Condition invaded by Pelargonium capitatum (PCp) were utilized for field assessments. ... In the soil seed bank, species numbers and germinant density decreased significantly for native and seeder (fire sensitive) species between GC sites and invaded sites. Surprisingly 52% of germinants at GC sites were from introduced species, with much of the introduced soil seed bank being persistent. Native species were dominated by perennial shrubs, herbs and sedges, while introduced species were dominated by perennial and annual grasses and herbs. Invasion by introduced species, associated with frequency of fire, altered the ecosystem, thus disadvantaging native species and improving conditions for even greater invasion within the Banksia woodland. Significantly higher soil phosphorus P (total) and P (HCO3) were found at PCe and PCp sites compared to GC sites. Leaf nutrient concentrations of phosphorus were significantly higher, and potassium and copper significantly lower in PCe and PCp sites, with introduced species having significantly greater concentrations than native species (except Manganese). This study demonstrated the key role of phosphorus in the Banksia woodland, in contrast to other research which identified nitrogen as the major nutrient affected by invasion. Higher levels of soil and leaf phosphorus, loss of species diversity and function, changes in fire ecology and canopy cover and a limited native soil seed bank make restoration of a structural and functional Banksia woodland from the soil seed bank alone unlikely. Without management intervention, continuing future fire is likely to result in a transition of vegetation states from GC to MC and MC to PC. The knowledge gained from this study provides a better ecological understanding of the invasive process. This enhanced understanding will enable the development of adaptive management strategies to improve conservation practices within a biodiversity hotspot and reduce the impact of the key threatening process of invasion.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

10

Lalor, Briony Maree. „An assessment of the recovery of the microbial community in jarrah forest soils after bauxite mining and prescription burning“. University of Western Australia. School of Earth and Geographical Sciences, 2009. http://theses.library.uwa.edu.au/adt-WU2010.0037.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] Recovery of soil nutrients, microbial populations and carbon (C) and nitrogen (N) cycling processes are critical to the success of rehabilitation following major ecosystem disturbance. Bauxite mining represents a major ecosystem disturbance to the jarrah (Eucalyptus marginata) forest in the south-west of Western Australia. Mining has created a mosaic of mined areas in various stages of succession surrounded by non-mined forest areas. Initial site preparations within rehabilitation areas such as contour ripping alter soil structure (creation of mound and furrows) and over time also influence the distribution of vegetation and litter. Current performance criteria developed by industry, government and other stakeholders have determined that before post-bauxite mined areas of jarrah forest can be integrated back into normal forest management practises they should be functional and demonstrate resilience to normal forest disturbances such as fire. Furthermore, resilience should be of a manner comparable to non-mined analogue forest sites. Currently little is known of the resilience of microbial communities and C and N cycling in rehabilitation sites to normal forest disturbances such as prescription burning. As such, before rehabilitated jarrah forests can be successfully integrated into broad scale forest management regimes, a more thorough knowledge of the potential impacts of burning practises on the soil microbial community and C and N cycling processes in these systems is required. ... While there are similar rates of C and N cycling the underlying microbial community structure was distinctly different; implying a high degree of functional redundancy with respect to C and N cycling. Differences in the C and N cycling and structure of the microbial communities were likely to be due to differences in soil environmental conditions (i.e. soil alkalinity/acidity, soil moisture) and C substrate availability which influence the physiological status of the microbial community and in turn are related to successional age of the forests. Results also suggest that the measurement of CLPP can be a useful approach for assessment of changes in the functional ability of microbial communities. However, the interpretation of how well these rehabilitation forests have recovered heterotrophic abilities was greatly affected by the methodological approach used (e.g. MicroRespTM or Degens and Harris, 1997). Importantly, results from Chapter 4 and 5 suggested that the effects of a moderate prescription fire on C and N processes, CLPP and microbial community structure of 18 year old rehabilitation forests are likely to be short-lived (< 2 years). Furthermore, the effects of the moderate spring prescription fire were not large enough to decouple C and N cycling processes over the short-term (< 1 years) which suggests that by 18 years of age rehabilitation forests demonstrate comparable functional resilience to a moderate prescription burn.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

11

Dalby, Paul Reginald. „Competition between earthworms in high rainfall pastures in the Mt. Lofty Ranges, South Australia“. Title page, contents and summary only, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phd137.pdf.

Der volle Inhalt der Quelle

Annotation:

Copy of author's previously published work inserted. Bibliography: leaves 261-306. The objectives of the project were: i. to determine whether there are competitive interactions between Aporrectodea trapezoides and A. caliginosa and A. rosea.--ii. to investigate compeditive interactions between A. calignosa, Microscolex dubius and A. trapezoides.--iii . to determine the likely impact of A. longa on soil fauna, especially the native earthworm, Gemascolex lateralis, in native ecosystems.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

12

Sutcliffe, Karen. „The conservation status of aquatic insects in South-Western Australia /“. Access via Murdoch University Digital Theses Project, 2003. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20040430.153605.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

13

Vanderklift, Mathew Arie. „Interactions between sea urchins and macroalgae in south-western Australia : testing general predictions in a local context“. University of Western Australia. School of Plant Biology, 2002. http://theses.library.uwa.edu.au/adt-WU2004.0086.

Der volle Inhalt der Quelle

Annotation:

Generalist herbivores profoundly influence the biomass and species composition of macroalgae assemblages. In subtidal ecosystems of temperate latitudes, large invertebrates are usually the most influential herbivores. I tested the prediction that exclusion of invertebrate herbivores would lead to changes in the biomass and species composition of the macroalgae assemblages that are a prominent feature of the reefs in south-western Australia. The most abundant invertebrate herbivores were sea urchins (Heliocidaris erythrogramma, Phyllacanthus irregularis and Centrostephanus tenuispinus), and these occupied different trophic positions. Heliocidaris was present at virtually all reefs surveyed, and was particularly abundant in the Fremantle region. Analyses of stable isotopes and direct observations of gut contents revealed that it was almost exclusively herbivorous, and that it mainly ate foliose brown algae. In contrast, Phyllacanthus and Centrostephanus were omnivorous; while they consumed large proportions of algae, a substantial proportion of the diet of both species was animal tissue. Because Heliocidaris is a generalist herbivore that occurs at high densities, it could exert a large influence on the macroalgae assemblage. This prediction was tested by a series of press experiments. Contrary to the prediction, Heliocidaris exerted a very minor influence on the biomass, and no detectable influence on the species composition, of attached macroalgae. However, it exerted a major influence on the retention of drift macroalgae and seagrass by trapping and feeding on drift. It exerted a particularly strong influence on retention of the kelp Ecklonia radiata. This kelp was not abundant in the attached algae assemblage (when all plots were pooled it ranked 35th in biomass), but was abundant as drift (ranking 1st). Most of the drift Ecklonia was retained by sea urchins, rather than freely drifting.Herbivorous fish may also influence macroalgae assemblages. To compare the effects of sea urchins versus fish on recruiting and adult macroalgae a 13-month exclusion experiment was conducted. There were no detectable effects of sea urchins (mainly Heliocidaris) on either recruiting or adult macroalgae. There were some patterns in the biomass of recruiting algae consistent with an influence by herbivorous fish; however, these patterns were also consistent with the presence of artefacts (shading and reduced water flow) by fish exclusion devices. I began with the prediction that large invertebrate herbivores were a major influence on the macroalgae assemblages of subtidal reefs in south-western Australia. Overall, there was little evidence to support this prediction: within spatial extents of tens of square metres and over periods of 1-2 years, only minor effects were detected. However, it remains plausible that herbivores exert an influence over long time periods across large spatial extents in south-western Australia. I propose that trophic subsidies support the comparatively high densities of Heliocidaris that exist at some reefs. I further propose that these subsidies mediate the effects of sea urchins on the attached macroalgae assemblage, and that they might play an important role in energy and nutrient cycling in these nearshore ecosystems.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

14

Carver, Scott Stevenson. „Dryland salinity, mosquitoes, mammals and the ecology of Ross River virus“. University of Western Australia. School of Animal Biology, 2008. http://theses.library.uwa.edu.au/adt-WU2009.0100.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] In an era of emerging and resurging infectious diseases, understanding the ecological processes that influence pathogen activity and the influences of anthropogenic change to those are critical. Ross River virus (RRV, Togoviridae: Alphavirus) is a mosquito-borne zoonosis occurring in Australia with a significant human disease burden. In the southwest of Western Australia (WA) RRV is principally vectored by Aedes camptorhynchus Thomson (Diptera: Culicidae), which is halophilic. The inland southwest, the Wheatbelt region, of WA is substantially affected by an anthropogenic salinisation of agricultural land called dryland salinity, which threatens to influence transmission of this arbovirus. This study assessed the ecological impacts of dryland salinity on mosquitoes, mammalian hosts and their interactions to influence the potential for RRV transmission. Many aquatic insect taxa colonise ephemeral water bodies directly as adults or by oviposition. Using a manipulative experiment and sampling from ephemeral water bodies in the Wheatbelt, I demonstrated that salinity of water bodies can modify colonisation behaviour and the distribution of some organisms across the landscape. Halosensitive fauna selected less saline mesocosms for oviposition and colonisation. In particular, Culex australicus Dobrotworksy and Drummond and Anopheles annulipes Giles (Diptera: Culicidae), potential competitors with Ae. camptorhynchus, avoided ovipostion in saline mesocosms and water bodies in the field. This finding suggests salinity influences behaviour and may reduce interspecific interactions between these taxa and Ae. camptorhynchus at higher salinities. Using extensive field surveys of ephemeral water bodies in the Wheatbelt I found mosquitoes frequently colonised ephemeral water bodies, responded positively to rainfall, and populated smaller water bodies more densely than larger water bodies. The habitat characteristics of ephemeral water bodies changed in association with salinity. Consequently there were both direct and indirect associations between salinity and colonising mosquitoes. Ultimately the structure of mosquito assemblages changed with increasing salinity, favouring an increased regional distribution and abundance of Ae. camptorhynchus. The direct implication of this result is secondary salinisation has enhanced the vectorial potential for RRV transmission in the WA Wheatbelt. ... This thesis contributes to an emerging body of research aimed at delineating important ecological processes which determine transmission of infections disease. Collectively the findings in this study suggest dryland salinity enhances the potential for RRV activity in the Wheatbelt. Currently, human RRV notifications in the Wheatbelt do not reflect the salinity-RRV transmission potential in that area, but appear to be associated with dispersal of RRV from the enzootic coastal zone of southwest WA. I speculate dryland salinity is a determinant of potential for RRV transmission, but not activity. Dryland salinity is predicted to undergo a two to four fold expansion by 2050, which will increase the regional potential for RRV activity. Preservation and restoration of freshwater ecosystems may ameliorate the potential for transmission of RRV and, possibly, human disease incidence.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

15

Christensen, Joseph. „Shark Bay 1616-1991 : the spread of science and the emergence of ecology in a World Heritage area“. University of Western Australia. School of Humanities, 2008. http://theses.library.uwa.edu.au/adt-WU2009.0029.

Der volle Inhalt der Quelle

Annotation:

Shark Bay is an extensive marine embayment located on the central coast of Western Australia that is recognised as a World Heritage Property on the basis of the Outstanding Universal Value of the natural environment of the region. This thesis examines the history of science at Shark Bay between the arrival of the first European explorers in the seventeenth century through to the official recognition of Shark Bay as a World Heritage Area in 1991. Each of the seven chapters is devoted to a different period in the development of scientific investigations, beginning with Dutch and English mariners and naturalists, passing on to French scientific explorers and British surveyors naturalists, and explorers, continuing through a variety of investigations in marine science and research in biogeography and evolution carried out by foreign expeditions and Australian field-workers, and culminating in the transformation of scientific investigations as a result of the rise and development of modern ecological science in the second half of the twentieth century. This development of science at Shark Bay is considered in light of existing frameworks for the development or spread of science in Australia, and in relation to current literature concerning the development or emergence of ecology in Australia. After evaluating the history of science at Shark Bay relative to existing knowledge of the spread of science and the emergence of ecology, the thesis concludes by proposing a new framework for the development of science and the emergence of ecology based on the experience at Shark Bay and with wider application to the history of science in Western Australia.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

16

Havel, J. J. „Ecology of the forests of south western Australia in relation to climate and landforms /“. Access via Murdoch University Digital Theses Project, 2000. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20060815.114944.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

17

Kay, Winston Robert. „Population ecology of Crocodylus porosus (Schneider 1801) in the Kimberley Region of Western Australia /“. [St. Lucia, Qld.], 2004. http://adt.library.uq.edu.au/public/adt-QU20050401.125015/index.html.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

18

Havel, Jaroslav J. „Ecology of the forests of south western Australia in relation to climate and landforms“. Murdoch University, 2000. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20060815.114944.

Der volle Inhalt der Quelle

Annotation:

This thesis sets out to test the hypothesis that the vegetational patterns in the forested region of south western Australia are primarily determined by the interaction of climate and landform. The region is an area of 4.25 million hectares subject to recent agreement between the Commonwealth of '4ustralia and the state of Western Australia regarding long-term protection and management of forest (Regional Forest Agreement). The climate of the South Western forest region is warm temperate and summer dry, matching Koeppen's category Cs, usually described as mediterranean. The dominant geological features of South Western Australia are crystalline and sedimentary plateaus and coastal plains. They are subject to a complex process of weathering, denudation and re-deposition, which is the key determinant of landforms and soil patterns. Deep but infertile soils are prevalent. The dominant vegetation formation of the region is open forest, which reduces to woodland in the drier north and east and increases to tall open forest in the moister south. Floristically the vegetation is very rich, comprising over 3000 vascular plant species. The richness resides in the forest and woodland understorey and in the shrublands, heathlands and sedgelands of edaphically extreme sites. By comparison, the forest overstorey is very simple, only one or two species being often dominant over extensive areas. The validation of the hypothesis that climate and landforms determine the vegetation patterns in South Western Australia is carried out in the following stages: 1) review of past studies of vegetation patterns in relation to the underlying environmental factors, relating them to one another in terms of floristics, 2) conversion of landform and climate maps for the region into vegetation maps by means of toposequences, that is gradients of topography, soils and vegetation within individual landform/climate combinations, 3) production of two sets of vegetation maps, namely six maps of vegetation complexes (1:250,000) and one map of vegetation systems (1:500,000), 4) testing the predictive capability of the resulting maps by comparing the occurrences of individual species of trees, shrubs and herbs predicted by map legends, with their records in FloraBase, the geographic information system of the Western Australian Herbarium, and 5) using the outcomes of the above studies to assess the validity of the hypothesis. Because the above hypothesis is so broad, it will be considered under seven headings: a) nature of the vegetation patterns (continuum or discrete categories), b) regional effect of climate and local effect of landform, c) effect of landforms on soil depth, texture and fertility, d) joint effect of slope, soil depth and texture on water balance, e) interactive effect of landform and climate on vegetation patterns, f) response of individual species to climate and landform, and g) effect of other factors of environment, such as fire, on vegetation patterns. The subsidiary hypotheses are defined in Chapter 5. It is concluded that the vegetation of the region forms a lumpy continuum from the wet south west to the dry north east. Within that broad continuum there are localised continua from waterlogged sites in depressions to drought-prone sites on steep stony slopes. However, the dominant vegetation of the region is open forest on plateau uplands with deep infertile soils. Although climate and landforms have a strong effect on vegetation patterns, they do not determine all vegetation patterns directly. Some tree species have ranges of occurrence that are too broad for that, and others have ranges that are too restricted. A more probable explanation is that climate and landforms, together with fire, set the stage on which the interplay of species takes place and determines the structure and composition of the vegetation. An attempt is made to predict the likely effect of climatic changes on vegetation patterns. The applicability of the methodology developed to the mapping of other regions, especially the adjacent ones, is examined. A review is made of how the products of the study, in particular the maps, are currently being used, and suggestions are made how they could be used in the future.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

19

Vaudo, Jeremy. „Habitat Use and Foraging Ecology of a Batoid Community in Shark Bay, Western Australia“. FIU Digital Commons, 2011. http://digitalcommons.fiu.edu/etd/367.

Der volle Inhalt der Quelle

Annotation:

Worldwide declines in populations of large elasmobranchs and the potential cascading effects on marine ecosystems have garnered considerable attention. Far less appreciated are the potential ecological impacts of changes in abundances of small to medium bodied elasmobranchs mesopredators. Crucial to elucidating the role of these elasmobranchs is an understanding of their habitat use and foraging ecology in pristine conditions. I investigated the trophic interactions and factors driving spatiotemporal variation in abundances of elasmobranch mesopredators in the relatively pristine ecosystem of Shark Bay, Australia. First, I describe the species composition and seasonal habitat use patterns of elasmobranch mesopredator on the sandflats of Shark Bay. Juvenile batoids dominated this diverse community and were extremely abundant in nearshore microhabitats during the warm season. Stomach content analysis and stable isotopic analysis revealed that there is a large degree of dietary overlap between common batoid species. Crustaceans, which tend to be found in seagrass habitats, dominated diets. Despite isotopic differences between many species, overlap in isotopic niche space was high and there was some degree of individual specialization. I then, investigated the importance of abiotic (temperature and water depth) and biotic (prey and predator abundance) factors in shaping batoid habitat use. Batoids were most abundant and tended to rest in shallow nearshore waters when temperatures were high. This pattern coincides with periods of large shark abundance suggesting batoids were seeking refuge from predators rather than selecting optimal temperatures. Finally, I used acoustic telemetry to examine batoid residency and diel use of the sandflats. Individual batoids were present on the sandflats during both the warm and cold seasons and throughout the diel cycle, suggesting lower sandflat densities during the cold season were a result of habitat shifts rather than migration out of Shark Bay. Combined, habitat use and dietary results suggest that batoids have the potential to seasonally impact sandflat dynamics through their presence, although foraging may be limited on the sandflats. Interestingly, my results suggest that elasmobranch mesopredators in pristine ecosystems probably are not regulated by food supply and their habitat use patterns and perhaps ecosystem impacts may be influenced by their predators.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

20

Florentine, Singarayer K. „Ecology of Eucalyptus victrix in grassland in the floodplain of the Fortescue River“. Curtin University of Technology, School of Environmental Biology, 1999. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=10260.

Der volle Inhalt der Quelle

Annotation:

The WA coolibah tree, Eucalyptus victrix L. Johnson & K. Hill forms an unique and pristine woodland in the Fortescue Valley, in the Pilbara district of Western Australia. Until recently, no research had been done on E. victrix ecology and concern had been expressed by pastoral managers and others about the condition of the woodland occupied by this species. This research was an attempt to understand the ecology of coolibah using a multi-disciplinary approach.A population demographic study of stands in E. victrix woodland reveals that the present tree populations occupy larger areas than saplings and seedlings. Soil moisture and warm summer temperatures are believed to be stimulating factors for seedling recruitment of E. victrix. Different size classes (height/diameter) reflect different recruitment events and these reflect past availability of seeds and adequate soil moisture in that particular area of the woodland. Occasional grasshopper outbreaks and drought cause canopy shrinkage. Presence of hollow boles, restrict dendrochronological examination of tree ages.An important population study was of a post-seedling cohort at Roy Hill, where height distribution reflected a typical single recruitment event. In subsequent years (1995 - 1998) height measurement showed several peaks, suggesting that seedlings were now growing at different rates. Uniform and steady height growth was observed on saplings found at the edges of gilgai. During May 1998 several saplings flowered, it was assumed that E. victrix attained its reproductive maturity at mean height of 2.50 m and with a stem diameter of 50 mm.Seedling recruitment and subsequent growth mainly depend on heavy rainfall flooding events. Seedling recruitment occurs only from current seed rain. Seed longevity reduces after 54 days of burial at 50 mm depth. Mortality (4 - 6 leaf stage) of newly recruited seedlings during ++
subsequent dry months is very high. Furthermore, allelopathic effects (root competition from established grass and insect herbivory) are additional causes of seedling mortality in the years of recruitment.Seedlings recruited at a burnt (disturbed) site, grew faster compared with undisturbed sites with less mortality. This suggested that fire created a suitable condition by reducing root competition, increasing soil nutrients and also creating a gap which providing sufficient solar radiation for seedlings to establish and develop into a healthy population. It is suggested that once newly recruited seedlings overcome the first summer, mortality rates during subsequent years are drastically reduced.Long-term waterlogging of E. victrix seedlings significantly increases seedling stem diameter. Large numbers of adventitious roots are developed and lenticels proliferate on the submerged portion of the stem. Flooding reduces each photosynthesis, transpiration and stomatal conductance. Flooding does not increase shoot fresh or dry weight on 4-, 8- or 17- week old seedlings. Leaf emergence may be stimulated on flooded seedlings compared with unflooded seedlings. While root dry weight is greater in 17-week old flooded plants than 13 - week seedlings, this difference is not significant. It is suggested that maintenance of a high root/shoot ratio is a drought adaptation. Furthermore, comparative study of flood tolerance in semi-arid eucalypt species suggests that those species intolerant of flooding seldom express morphological adaptations and fail to recover from physiological damage.The annual grass Setaria dielsii occurs under the canopy of mature E.victrix trees of the coolibah woodland. This species has probably displaced more palatable perennial grasses. Soil moisture under trees is slightly higher and soil temperatures are less extreme than away from the canopy. Growth of ++
S. dielsii appears to be more associated with soil nutrient status. Levels of total N, Mg, K, and of electrical conductivity (EC) under trees are significantly higher than those away from the tree. Levels of Ca, Na, Fe, and organic carbon do not differ. The under story sub-shrub Malvastrum americanum is an important competitor with S. dielsii. Light availability may determine relative biomass contributions of the two species.The effect of the density of grass species, growing space and time of establishment on E. victrix seedlings (inter-specific competition), and the effect of density and growing space within E. victrix seedling populations (intra-specific competition) were studied under controlled conditions. Results indicate resources necessary for growth of individual E. victrix seedlings were more limiting under increase density of neighbouring grass species than under intra-specific competition. In particular photosynthetic area was drastically reduced in mixed culture.Lack of ground cover beneath the canopy of isolated E. victrix trees was ascribed to toxic or phenolic substances present in leaf, bark and leaf litter of E. victrix. Lactuca sativa seed germination subjected to extracts and leachate demonstrate that the fresh leaf of E. victrix possesses toxic substances which cause deleterious effects on both germination and radicle development. Similarly, increasing concentrations of leaf and bark leachate show reduced germination percentage of L. sativa seeds. Shoot and root biomass of grass and eucalyptus treated with leaf leachate were reduced. E. victrix leaf leachate significantly reduced shoot and root biomass of its own seedlings. High Performance Liquid Chromatogram (HPLC) analysis separated 11 and 8 possible toxic substances from leaf and bark extract respectively.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

21

Chambers, Brian Kevan. „Human disturbance affects the ecology and population dynamics of the tammar wallaby, Macropus eugenii, on Garden Island, Western Australia“. University of Western Australia. School of Animal Biology, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0139.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] Understanding the effect that the disturbance of habitat by humans has on the population dynamics and ecology of wild animals is critical for the management of these populations. By understanding the demographic effects of disturbance the ways in which a population can be managed to increase or decrease its rate of change in size also become apparent. This thesis describes the effect that human disturbance, through the establishment of a large naval base, has had on the population dynamics and ecology of tammar wallabies (Macropus eugenii) on Garden Island, Western Australia. The disturbance of the environment on the HMAS Stirling Naval Base included the establishment of large areas of irrigated and fertilised couch grass (Cynodon dactylon) that increased and made virtually constant the amount of food available to the tammars in that area. In addition, traffic associated with the naval base resulted in large numbers of tammar wallabies being killed by vehicles. The effects of these disturbances were determined by comparing population dynamics, through vital rates of survival and fecundity and population growth rates, and spatial ecology, through the size of the animals' home ranges, in three areas of Garden Island. The three areas were the naval base (highly disturbed), southern bushland (adjacent to the naval base) and the northern bushland (undisturbed). The tammars on the naval base were in better body condition than those living in the two bushland areas of the island. ... When the impact of road-kills was removed, increased to 1.150.101 per year on the naval base and 0.960.076 per year in the southern bushland. Fecundity transitions, defined as the product of the rates of birth and pouch-young survival, and adult survival rates were lower in the bushland areas compared with the naval base in two of the three years, which were the main reasons for the lower estimates. There were no significant differences in the size of the tammars' home ranges between areas with modified or unmodified habitats or between the sexes (P>0.05). In summer the mean size of the home ranges was 3.90.66 ha, which was larger than winter when home ranges were 3.20.54 ha, but this difference failed to reach significance (P=0.058). These results indicate that the modification of the tammars' habitat has probably not caused significant changes in the size of the animals' home ranges. The size of the home ranges of tammar wallabies is likely to be determined by a complex interaction of many factors, and habitat modification alone has not been sufficient to cause substantial changes. The results presented in this thesis demonstrate that the disturbance caused by the establishment of the naval base on Garden Island has altered the population dynamics of the tammars wallabies, through increasing in the amount of food available to the tammars and through high numbers of road-kills. These results also demonstrate how gaining detailed knowledge of population dynamics can have direct application to managing the impact of disturbance on populations of wild animals.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

22

Hearman, Amy. „A modelling study into the effects of rainfall variability and vegetation patterns on surface runoff for semi-arid landscapes“. University of Western Australia. School of Earth and Geographical Sciences, 2008. http://theses.library.uwa.edu.au/adt-WU2009.0047.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] Generally hydrologic and ecologic models operate on arbitrary time and space scales, selected by the model developer or user based on the availability of field data. In reality rainfall is highly variable not only annually, seasonally and monthly but also the intensities within a rainfall event and infiltration properties on semi-arid hillslopes can also be highly variable as a result of discontinuous vegetation cover that form mosaics of areas with vegetation and areas of bare soil. This thesis is directed at improving our understanding of the impacts of the temporal representation of rainfall and spatial heterogeneity on model predictions of hydrologic thresholds and surface runoff coefficients on semi-arid landscapes at the point and hillslope scales. We firstly quantified within storm rainfall variability across a climate gradient in Western Australia by parameterizing the bounded random cascade rainfall model with one minute rainfall from 15 locations across Western Australia. This study revealed that rainfall activity generated in the tropics had more within storm variability and a larger proportion of the storm events received the majority of rain in the first half of the event. Rainfall generated from fontal activity in the south was less variable and more evenly distributed throughout the event. Parameters from the rainfall analysis were then used as inputs into a conceptual point scale surface runoff model to investigate the sensitivity of point scale surface runoff thresholds to the resolution of rainfall inputs. This study related maximum infiltration capacities to average storm intensities (k*) and showed where model predictions of infiltration excess were most sensitive to rainfall resolution (ln k* = 0.4) and where using time averaged rainfall data can lead to an under prediction of infiltration excess and an over prediction of the amount of water entering the soil (ln k* > 2). For soils susceptible to both infiltration excess and saturation excess, total runoff sensitivity was scaled by relating drainage coefficients to average storm intensities (g*) and parameter ranges where predicted runoff was dominated by infiltration excess or saturation excess depending on the resolution of rainfall data were determined (ln g* <2). The sensitivity of surface runoff predictions and the influence of specific within storm properties were then analysed on the hillslope scale. '...' It was found that using the flow model we still get threshold behaviour in surface runoff. Where conditions produce slow surface runoff velocities, spatial heterogeneity and temporal heterogeneity influences hillslope surface runoff amounts. Where conditions create higher surface runoff velocities, the temporal structure of within storm intensities has a larger influence on runoff amounts than spatial heterogeneity. Our results show that a general understanding of the prevailing rainfall conditions and the soil's infiltration capacity can help in deciding whether high rainfall resolutions (below 1 h) are required for accurate surface runoff predictions. The results of this study can be considered a contribution to understanding the way within storm properties effect the processes on the hillslope under a range of overall storm, slope and infiltration conditions as well as an improved understanding of how different vegetation patterns function to trap runoff at different total vegetation covers and rainfall intensities.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

23

Davis, Robert A. „Metapopulation structure of the Western Spotted Frog (Heleioporus albopunctatus) in the fragmented landscape of the Western Australian wheatbelt“. University of Western Australia. School of Animal Biology, 2004. http://theses.library.uwa.edu.au/adt-WU2005.0026.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] Amidst concern over the global phenomenon of declining amphibians, there is an increasing appreciation of the importance of understanding population dynamics at both local and regional scales. Data on the viability and persistence of species in landscapes altered by humans are scarce but an understanding of these dynamics is essential for enabling long-term species conservation in a modified world. Habitat loss, fragmentation and ensuing salinisation are of particular concern for species in Australia’s temperate agricultural regions where the rapid conversion of continuously vegetated landscapes to small fragments has occurred in less than 200 years. This thesis investigated the local and metapopulation structure of Heleioporus albopunctatus to determine the current population structure and likely future of this species in a highly degraded landscape: the wheat and sheep growing areas of southwestern Australia ... The life-history attributes of H. albopunctatus, including high fecundity, high adult longevity and low to moderate dispersal contribute to a robust regional metapopulation, responsive to changes, but with a strong chance of persistence over the long-term. H. albopunctatus appears to have adjusted to a radically modified landscape but its long-term persistence may be dependent on the existence of a small number of source populations that recruit in most years.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

24

Boggs, Dimity. „Playas of the Yarra Yarra drainage system, Western Australia“. University of Western Australia. School of Earth and Geographical Sciences, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0074.

Der volle Inhalt der Quelle

Annotation:

This thesis examines playas as integrated ecosystems, through investigation of long- and short-term processes associated with playa geomorphology, hydrology and diatom ecology, in playas of the Yarra Yarra drainage system of Western Australia. This landscape approach was conducted at a range of scales and consequently revealed a level of heterogeneity not previously described in Australian playas. The key result and common thread linking the three facets of the playas investigated is the importance of hydroperiod in defining the playa environment. The morphology and distribution of playas are described and the results presented of an examination of potential mechanisms determining intra-system variability. Measurements of the physical attributes of the playas, including length, area, shape, density and orientation, were made through Geographic Information System analysis and detailed interpretation of aerial photography. Two main morphological groups are distinguished: small (<10 ha), elliptical to circular playas with a NNW-SSE orientation; and large (>30 ha), elongated playas. Regional patterns in geomorphic attributes are markedly different between the west and east sides of the system. The boundary between the two regions coincides approximately with rainfall distribution. In this respect, climate is an overarching driver of geomorphological variation but sub-catchment characteristics are also critical determinants. Littoral drift and segmentation processes that are common to coastal lagoons but not commonly described in playas were identified from visual interpretation of aerial photographs of spits, bars and cuspate shorelines. Six small playas, representing an hydrological continuum from mostly wet to mostly dry, were selected for investigation of their hydrology and diatom ecology, enabling assessment ii of the variability of hydrology, hydrochemistry and of the effects of different hydrological environments on the distribution of taxa. Hydroperiod was highly variable and central to determining playa geomorphology and biology. In the six playas it ranged from 19 to over 211 days, and filling frequency from 1 to 3 cycles between 2002 and 2004, reflecting rainfall and sub-catchment variability. Monitoring a series of nested piezometers revealed that the playas were net discharge points for ground water over the period of survey. However, small local vertical head variations indicate ground water does not discharge at the same rate across the playa surfaces and that playas may have short-lived phases of ground water recharge. Hydrochemically, the playas are typical of salt lakes in Australia. They displayed a wide range of salinity values, neutral to alkaline pH and ionic composition similar to sea water. It is postulated that the geochemical evolution of waters in the playas follows a pathway where low salinity recharge waters with dilute sea water salts progress to Na-Cl dominated brines through evaporative concentration. Surface waters showed an ionic dominance consistent with sea water with minor variations attributed to transitional phases in the geochemical evolution of the waters. Shallow ground waters showed a common and consistent pattern of ionic dominance: Na+ >Mg2+ >K+ >Ca2+ : Cl- >SO4 2- >HCO3 ->CO3 2-.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

25

Farrell, Claire. „Leaf-litter and microsite on seedling recruitment in an alley-planted E. sargentii and Atriplex spp. saline agricultural system“. University of Western Australia. School of Plant Biology, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0110.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] In order to assess the sustainability of mixed plantings on saline land, this thesis examined the importance of leaf-litter trapping and microsites on recruitment in a salt affected alley-belted (tree/shrub) agricultural system in Western Australia. Located in the low rainfall region (MAR <330 mm) of the wheatbelt, the 60 ha site consists of concentric rows of Eucalyptus sargentii trees with mounded (6 - 11 cm high) 10 -15 m inter-rows of Atriplex spp. Sustainability of this system and fulfilment of productive and ameliorative functions is dependant on successful recruitment (perennials). Although the present study site was conducted on farmland in a Mediterranean-type climate, low annual rainfall and spatial arrangement of perennial shrubs and trees, allow useful comparisons to be made with naturally occurring banded semi-arid systems and vice-versa. Of key interest were leaf-litter redistribution and trapping by tree and shrub rows and whether litter-cover/microsites facilitated/interfered with seedling recruitment (establishment, growth and survival). Litter from the tree row, redistributed by prevailing winds and rain, accumulated adjacent to saltbush seeding mounds, creating a mosaic of bare and littered areas across the site (total litter 10 t/ha over 22 months). Accumulated litter was hypothesized to differentially influence seasonal soil abiotic parameters (depending on litter-cover density) including; salinity, water availability, infiltration rates, water repellency and temperature. These abiotic conditions were also hypothesized to vary between tree and shrub microsites. Biotically, recruitment at this site was also hypothesized to be determined by interactions (positive and negative) between perennial components and understorey annuals/perennial seedlings. Accumulation of litter and resultant heterogeneity was influenced by shrub morphology, microtopography, wind direction and distance from litter source, with increased litter on the leeward sides of hemispherical Atriplex undulata shrubs and shrubs closest to tree rows. ... The importance of tree/shrub microsites varied seasonally, with no influence in winter due to moderate temperatures and increased water availability. In warmer months saltbush mid-row microsites were most favourable for seedling recruitment due to moderate litter-cover; reducing salinity, temperatures and increasing infiltration; and reduced root-competition/shading by the tree row. Tree microsites also directly inhibited seedling recruitment through increased salinities and water repellency. However, trees also indirectly facilitated recruitment in adjacent areas through provision of leaf-litter. As litter-trapping and recruitment patterns at this site mirror those found in semi-arid natural and artificial systems, the results of this study provide useful insights into creating appropriate mimics of low rainfall natural banded woodland and chenopod shrublands. Saltbush seeding mounds, shrub morphology and litter were key components for litter trapping and recruitment heterogeneity at this site. In this tree/shrub alley planting, where litter quantities directly influence vegetation cover densities, future saline plantings need to consider appropriate tree/shrub row spacings and orientation for efficient resource (seeds, litter and water) capture.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

26

Borger, Catherine. „The biology and ecology of Salsola australis R.Br. (Chenopodiaceae) in southwest Australian cropping systems“. University of Western Australia. School of Plant Biology, 2007. http://theses.library.uwa.edu.au/adt-WU2008.0062.

Der volle Inhalt der Quelle

Annotation:

Salsola australis is an introduced weed of crop and pasture systems in the Western Australian broad acre cropping and pasture region (wheat-belt). This thesis investigated the classification, biology and ecology of the genus Salsola in southwest Australia, as well as modelling the effectiveness of possible weed control practices. Prior to this research, S. tragus was the only recognised species of the Salsola genus within Australia. However, genetic analysis revealed that four genetically distinct putative taxa of the genus Salsola were found in southwest Australia, none of which were S. tragus. The taxa that is the most prevalent agricultural weed was classified as S. australis, but the other three putative taxa could not be matched to recognised species. All four taxa were diploid (2n = 18), as opposed to tetraploid (2n = 36) S. tragus. Within the agricultural system of southwest Australia, S. australis plants established throughout the year, although the majority of seed production occurred in late summer and autumn. Total seed production (138-7734 seeds per plant) and seed viability (7.6-62.8%) of S. australis were lower than that reported for other agricultural weed species of the Salsola genus. Seed dispersal occurred when the senesced plants broke free of their root system to become mobile. Wind driven plants travelled and shed seed over distances of 1.6 to 1247.2 m. Movement of approximately half the plants was restricted to less than 100 m by entanglement with other S. australis plants within the stand. Some seed was retained on the senesced plants, but the germinability of this seed fell to less than 2% in the two month period following plant senescence (i.e. a decline of 79%). Once seed shed into the soil seed bank, anywhere from 32.3 to 80.7% of the viable seeds germinated in the year following seed production, with the rest remaining dormant or degrading. A model of the life cycle of S. australis based on the population ecology data indicated that the dormant seed bank had very little effect on annual seedling recruitment, but seed dispersal from neighbouring populations had a large impact on population growth rate. Therefore, the most successful weed control measures were those that restricted seed dispersal from neighbouring populations, or those that were applied to all populations in the region rather than to a single population. Weed control techniques applied to a single population, without reducing seed dispersal, could not reduce population size.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

27

Paterson, Harriet. „Microzooplankton from oligotrophic waters off south west Western Australia : biomass, diversity and impact on phytoplankton“. University of Western Australia. School of Animal Biology, 2006. http://theses.library.uwa.edu.au/adt-WU2007.0031.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] The role of marine microzooplankton in aquatic food webs has been studied in most regions of the world’s oceans, with the exception of the subtropical/temperate eastern Indian Ocean. This thesis addresses this gap in knowledge by investigating microzooplankton from five stations on a cross continental shelf transect and in two mesoscale features ∼300 km offshore of south west Western Australia. My primary focus was to measure and evaluate microzooplankton community change over space and time and their impact on phytoplankton on a cross shelf transect, sampling five stations from February 2002 December 2004 as part of a large multidisciplinary investigation into the pelagic ecosystem on the shelf (Chapter 2). This transect was named the Two Rocks transect. I also investigated an eddy pair (Chapter 5), which had originated from water in the vicinity of the Two Rocks transect, also undertaken as part of a larger study, investigating biophysical coupling within mesoscale eddies off south west Western Australia . . . The distribution of mixotrophic cells differed across the transect. Those mixotrophs that use photosynthesis as their primarily energy source exploited nutrient limited conditions inshore consuming particles, while mixotrophs that are primarily heterotrophic survived low prey conditions offshore by photosynthesizing. In the eddies, the grazing behaviour of microzooplankton was dependent on the specific phytoplankton assemblage in each eddy. The warm core eddy had a resident population of diatoms that were consumed by heterotrophic dinoflagellates present in high numbers. The cold core eddy had a warm cap which prevented upwelled water reaching the surface, resulting in stratification and a very active microbial food web, particularly in the surface.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

28

Bunny, Felicity J. „The biology, ecology and taxonomy of Phytophthora citricola in native plant communities in Western Australia“. Murdoch University, 1996. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20061122.122739.

Der volle Inhalt der Quelle

Annotation:

The objectives of the project were to develop an understanding of the disease dynamics caused by Phytophthora citricola in native plant communities in the south of Western Australia. Prior to 1983, the pathogen had only been reported twice from Australian forests. Since then, P. citricola has been extensively recorded from plant communities north and south of Perth, and is currently the second most frequently recovered Phytophthora species from the northern jarrah forest and the northern sandplains. The objectives were addressed by examining the biology, ecology and taxonomy of isolates of P. citricola local to the southwest. Examination of the intraspecific variation of P. citricola by isozyme analysis resolved three major electrophoretic subgroups (SG), and these were aligned with morphological and cultural variation within the species. One electrophoretic SG was confined to forested areas. This SG differed from other SGs in sporangial dimensions, growth rate on two media and in vitro sensitivity to phosphonate. A redescription of the species may be warranted. P. citricola was positively associated with two roads in the northern jarrah forest. Road surfaces were sampled, then soil overburden was removed and the surface of the concreted lateritic layer beneath was sampled. Isolation of P. citricola declined away from the road into the adjacent forest and was more frequently recovered from the caprock (up to 1 metre below soil surface) than from the soil surface. The most probable source of introduction was from infested soil on vehicles using the roads. Oospores were shown to be produced in two soils, a lateritic gravelly loam and sand, and in plants. In soil, the electrophoretic SG confined to the forest (loamy soil) produced only limited numbers of oospores in the sandy soil of the northern sandplain. The restriction of this SG to the forested areas is probably physiological, rather than limited dispersal, with the SG currently occupying the full extent of its range. Estimation of the relative persistence of oospores, zoospores and plant material colonised by P. citricola established that only oospores (either free in soil or in colonised plant material) were important in long tern survival in soil. Oospores were still viable after six months at two field sites, and after 18 months in soil in the laboratory. Phosphonate is currently the most promising method of control of Phytophthora induced disease in native plant cornmunites of the southwest. The efficacy of phosphonate against P. citricola was examined in vivo and in vitro against two SGs. Phosphonate successfully inhibited lesion growth of both SGs in vivo, but of only one electrophoretic subgroup in vitro. The ecological implications of infestation of native plant communities in the southwest of Australia are discussed.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

29

Hardman, Blair. „Reintroduction ecology of mala (Lagorchestes hirsutus) and merrnine (Lagostrophus fasciatus) at Shark Bay, Western Australia“. Connect to this title online, 2006. http://portal.ecu.edu.au/adt-public/adt-ECU2007.0024.html.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

30

Bunny, F. „The biology, ecology and taxonomy of Phytophthora citricola in native plant communities in Western Australia /“. Access via Murdoch University Digital Theses Project, 1996. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20061122.122739.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

31

Hardman, Blair D. „Reintroduction ecology of mala (Lagorchestes hirsutus) and merrnine (Lagostrophus fasciatus) at Shark Bay, Western Australia“. Connect to thesis, 2006. http://portal.ecu.edu.au/adt-public/adt-ECU2007.0024.html.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

32

Smith, Amanda Jessica. „Campsite impact monitoring in the temperate eucalypt forests of Western Australia : an integrated approach /“. Access via Murdoch University Digital Theses Project, 2003. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20040504.151201.

Der volle Inhalt der Quelle

Annotation:

Thesis (Ph.D.)--Murdoch University, 2003.
Thesis submitted to the Division of Science and Engineering. "Supported by CRC for Sustainable Tourism and Dept of Conservation and Land Management (Western Australia)". Bibliography: leaves 334-355.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

33

Setyawan, Dwi. „Soil development, plant colonization and landscape function analysis for disturbed lands under natural and assisted rehabilitation“. University of Western Australia. School of Earth and Geographical Sciences, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0117.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] Spontaneous plant growth and soil development occur at disturbed sites with their extent and nature being variously affected by soil fertility status, local climate and topographic conditions. Soil-plant interactions can be diverse and site-specific within a disturbed landscape. The main purpose of the present study is to evaluate soil characteristics and landscape indices in relation to natural plant growth and soil development under different conditions and for diverse materials. A comprehensive study has been carried out to evaluate spontaneous soil development and plant colonization on various regolith materials at a railway cutting near Jarrahdale bauxite mine and on various substrates comprising waste rock, weathered regolith and replaced topsoil at Scotia (Norseman, Western Australia) and Kelian (East Kalimantan, Indonesia). At Jarrahdale soil development has occurred slowly over 36 years in relation to morphological changes in surface horizons. Soils at several locations exhibit substantial changes in color, texture and structure. The slow soil development is primarily due to low biomass and litter contributions (˜1 Mg/ha) from colonizing plants (e.g. Dryandra sessilis, Eucalyptus marginata and low shrubs) on the cutting shelf and slow litter decomposition. Nutrient accumulation is up to 5 kg N/ha, and 0.5 kg/ha for P and K. Surface soil samples from Jarrahdale are generally acidic (pH < 5.1) and contain low concentrations of total soil carbon (20 g/kg) and nutrients of total nitrogen (0.73 g/kg), bicarbonate-extractable phosphorus (bic-P) (< 2 mg/kg), bic-K (37 mg/kg) and total exchangeable bases (<1.1 cmol/kg, with 24 % base saturation). Soil properties at the Scotia waste dump are mainly associated with alkaline (mean pH = 9) and saline conditions (EC1:5 = 1.01 dS/m). Exchangeable base values are high with average concentrations of exchangeable Ca of 18 cmol/kg and exchangeable Mg of 6 cmol/kg, thus these elements are not a limiting factor for plant nutrition. Patchy plant growth on the waste dump is mostly related to differences in water availability in the arid region and to salinity such that halophytes (saltbushes Maireana and Atriplex) colonize many parts of the waste dump together with some Melaleuca and Eucalyptus species

APA, Harvard, Vancouver, ISO und andere Zitierweisen

34

Eberhard, Stefan M. „Ecology and hydrology of a threatened groundwater-dependent ecosystem : the Jewel Cave karst system in Western Australia /“. Access via Murdoch University Digital Theses Project, 2004. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20051010.141551.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

35

Abdo, David A. „Maintenance and structuring of two temperate Haliclonid sponge populations“. University of Western Australia. School of Plant Biology, 2007. http://theses.library.uwa.edu.au/adt-WU2008.0197.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] Sponges have an invaluable ecological importance through the provision of shelter and habitat, consolidation of reefs, bio-erosion, and in benthic-pelagic coupling processes. In addition, sponges are known to be an incredible source of compounds with bio-medicinal and commercial applications. Despite their ecological and economic importance, our understanding of the processes which maintain and structure sponge populations is severely lacking compared to other sessile invertebrates (e.g. Cnidarians). This study examines the processes which help maintain and the factors which structure the populations of two sympatric Haliclona species (Demospongiae; Haplosclerida; Chalinidae) at Hamelin Bay on the south west coast of Australia. In addition, the importance of both species to the broader marine community is examined. The reproductive biology of both species was determined from histological sections taken from each species over two years at Hamelin Bay. No evidence of asexual reproduction was observed in either species. Sexual reproduction occurred from November to April in Haliclona sp. 1 (hereafter green Haliclona) and November to May in Haliclona sp. 2 (hereafter brown Haliclona). The green Haliclona is viviparous with both gonochoric and hermaphroditic individuals observed in the population. The brown Haliclona is also viviparous with separate sexes. The onset and progression of reproduction in both species corresponded to increases in water temperature and photoperiod, but only decreasing wave height showed a significant correlation to gametogenesis. ... A significant (P < 0.05) difference in concentration between seasons was also observed, suggesting environmental and physiological factors affect the production of salicylihalamide A in the green Haliclona. The importance of each species to the marine environment was assessed by investigating the endofauna inhabiting each species across their known range ( [approx. ]1000 km's). A total of 948 and 287 endofaunal individuals were found associated with the green and brown Haliclona, respectively. Twenty four endofaunal taxa were found (from mysid shrimps to teleost fish), and the endofaunal assemblages of each species were significantly different. However, only the endofaunal assemblage associated with the green Haliclona varied among locations. Overall, this study demonstrates that the populations of both species are maintained by limited sexual reproductive output and larval dispersal. Abiotic factors (e.g. water temperature, wave exposure) influence the growth and physiology of both species, which is intimately connected to their abilities to reproduce. This has important consequences for the species populations with regard to their resilience to environmental change, and potential for harvesting of biomass for supply of bioactive compounds. Additionally, both species provide important habitats for many other organisms. The findings highlight the need for a detailed understanding of the ecology of potentially exploitable sponge species, to ensure their conservation and limit the impact on the organisms which rely on the sponges.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

36

Jayawickrema, Jacintha. „A reconstruction of the ecological history of Longneck Lagoon New South Wales, Australia /“. View thesis, 2000. http://library.uws.edu.au/adt-NUWS/public/adt-NUWS20050720.135957/index.html.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

37

au, Stefan@calm wa gov, und Stefan Eberhard. „Ecology and Hydrology of a Threatened Groundwater-Dependent Ecosystem:The Jewel Cave Karst System in Western Australia“. Murdoch University, 2004. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20051010.141551.

Der volle Inhalt der Quelle

Annotation:

Groundwater is a significant component of the world's water balance and accounts for >90 % of usable freshwater. Around the world groundwater is an important source of water for major cities, towns, industries, agriculture and forestry. Groundwater plays a role in the ecological processes and 'health' of many surface ecosystems, and is the critical habitat for subterranean aquatic animals (stygofauna). Over-abstraction or contamination of groundwater resources may imperil the survival of stygofauna and other groundwater-dependent ecosystems (GDEs). In two karst areas in Western Australia (Yanchep and Leeuwin-Naturaliste Ridge), rich stygofauna communities occur in cave waters containing submerged tree roots. These aquatic root mat communities were listed as critically endangered because of declining groundwater levels, presumably caused by lower rainfall, groundwater abstraction, and/or forest plantations. Investigation of the hydrology and ecology of the cave systems was considered essential for the conservation and recovery of these threatened ecological communities (TECs). This thesis investigated the hydrology and ecology of one of the TECs, located in the Jewel Cave karst system in the Leeuwin-Naturaliste Ridge. A multi-disciplinary approach was used to explore aspects pertinent to the hydrology and ecology of the groundwater system. Thermoluminescence dating of the limestone suggested that development of the karst system dates from the Early Pleistocene and that caves have been available for colonisation by groundwater fauna since that time. Speleogenesis of the watertable maze caves occurred in a flank margin setting during earlier periods of wetter climate and/or elevated base levels. Field mapping and leveling were used to determine hydrologic relationships between caves and the boundaries of the karst aquifer. Monitoring of groundwater levels was undertaken to characterise the conditions of recharge, storage, flow and discharge. A hydrogeologic model of the karst system was developed. The groundwater hydrograph for the last 50 years was reconstructed from old photographs and records whilst radiometric dating and leveling of stratigraphic horizons enabled reconstruction of a history of watertable fluctuations spanning the Holocene to Late Pleistocene. The watertable fluctuations over the previous 50 years did not exceed the range of fluctuations experienced in the Quaternary history, including a period 11,000 to 13,000 years ago when the watertable was lower than the present level. The recent groundwater decline in Jewel Cave was not reflected in the annual rainfall trend, which was above average during the period (1 976 to 1988) when the major drop in water levels occurred. Groundwater abstraction and tree plantations in nearby catchments have not contributed to the groundwater decline as previously suggested. The period of major watertable decline coincided with a substantial reduction in fire frequency within the karst catchment. The resultant increase in understorey vegetation and ground litter may have contributed to a reduction in groundwater recharge, through increased evapotranspiration and interception of rainfall. To better understand the relationships between rainfall, vegetation and fire and their effects on groundwater recharge, an experiment is proposed that involves a prescribed burn of the cave catchment with before-after monitoring of rainfall, leaf-area, ground litter, soil moisture, vadose infiltration and groundwater levels. Molecular genetic techniques (allozyrne electrophoresis and mitochondria1 DNA) were used to assess the species and population boundaries of two genera and species of cave dwelling Amphipoda. Populations of both species were largely panrnictic which was consistent with the hydrogeologic model. The molecular data supported the conclusion that both species of amphipod have survived lower watertable levels experienced in the caves during the Late Pleistocene. A mechanism for the colonization and isolation of populations in caves is proposed. Multi Dimensional Scaling was used to investigate patterns in groundwater biodiversity including species diversity, species assemblages, habitat associations and biogeography. Faunal patterns were related to abiotic environmental parameters. Investigation of hydrochemistry and water quality characterized the ecological water requirements (EWR) of the TEC and established a baseline against which to evaluate potential impacts such as groundwater pollution. The conservation status of the listed TEC was significantly improved by increasing the number of known occurrences and distribution range of the community (from 10 m2 to > 2 x lo6 m2), and by showing that earlier perceived threatening processes (rainfall decline, groundwater pumping, tree plantations) were either ameliorated or inoperative within this catchment. The GDE in the Jewel Cave karst system may not have been endangered by the major phase of watertable decline experienced 1975-1987, or by the relatively stable level experienced up until 2000. However, if the present trend of declining rainfall in southwest Wester,,Australia continues, and the cave watertable declines > 0.5 m below the present level, then the GDE may become more vulnerable to extinction. The occurrence and distribution of aquatic root mat communities and related groundwater fauna in other karst catchments in the Leeuwin-Naturaliste Ridge is substantially greater than previously thought, however some of these are predicted to be threatened by groundwater pumping and pollution associated with increasing urban and rural developments. The taxonomy of most stygofauna taxa and the distribution of root mat communities is too poorly known to enable proper assessment of their conservation requirements. A regional-scale survey of stygofauna in southwest Western Australia is required to address this problem. In the interim, conservation actions for the listed TECs need to be focused at the most appropriate spatial scale, which is the karst drainage system and catchment area. Conservation of GDEs in Western Australia will benefit fi-om understanding and integration with abiotic groundwater system processes, especially hydrogeologic and geomorphic processes.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

38

Frere, Celine Henria Biological Earth &amp Environmental Sciences Faculty of Science UNSW. „Interactions between behavioural ecology and relatedness of female bottlenose dolphins in East Shark Bay, Western Australia“. Awarded by:University of New South Wales. Biological, Earth & Environmental Sciences, 2009. http://handle.unsw.edu.au/1959.4/43776.

Der volle Inhalt der Quelle

Annotation:

Female mammals play a central role in determination of social structure and are thus central to understanding the overall fission-fusion grouping pattern characteristic of many delphinid societies. Focusing specifically on female-female relatedness and association patterns, I have analysed more than 17 years of group composition, behavioural data, and genetic information to investigate complex interactions between behavioural ecology and relatedness and to also examine the common social evolutionary theory, that variation in mammalian social systems is typically attributed to five main factors: inclusive fitness, predation pressure, sexual conflict and male harassment, inbreeding avoidance, and resource competition. Overall, I found that female bottlenose dolphin association patterns depend upon the interplay between matrilineal kinship, biparental relatedness and home range overlap, and that female bottlenose dolphins seem to adapt their social strategies to seasonal variation in levels of predation and male harassment. The presence of both high sexual conflict and bisexual philopatry lead me to investigate the extent of inbreeding avoidance. I found that more than 14% of the calves were most likely the product of mating between close relatives, and identified female fitness costs to inbreeding. We were able to show that the effect of inbreeding on females??? fitness occurs via two independent mechanisms: being inbred and having at least one inbred calf. Inbred calves are on average weaned later than non-inbred calves, and a female???s first calf has a higher probability to be an inbred than subsequent calves. Last, I examined whether sociality provides inclusive fitness to female bottlenose dolphins through an investigation of both the additive genetic and social variance components of female calving success using a pedigree-free animal model. I found that variance in calving success of female bottlenose dolphins is best explained by complex genetic and social interactions. Females with high calving success showed both high genetic and social merit; they not only have good genes but also prefer to associate with others of high fitness. This study reveals that both social and heritable genetic variance contribute to fitness trait variance in the wild.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

39

Beveridge, Maxine. „Molecular ecology of Dawson's burrowing bee Amegilla dawsoni (Hymenoptera: Anthophorini)“. University of Western Australia. School of Animal Biology, 2006. http://theses.library.uwa.edu.au/adt-WU2006.0091.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] In the last two decades, the use of microsatellites has revolutionized the study of ecology and evolution. Microsatellites, or short tandem repeats (STRs), are stretches of DNA repeats, 1 to 5 nucleotides long, where the number of repeats varies between individuals. They are co-dominant, highly variable, neutral markers, and are inherited in a Mendelian fashion. Microsatellite loci were isolated from Dawson’s burrowing bee, Amegilla dawsoni, a large, fast-flying solitary nesting bee endemic to the arid zone of Western Australia. Twelve polymorphic loci were found with an observed number of alleles ranging from two to 24 and observed heterozygosities between 0.17 and 0.85. These loci were used to examine two aspects of this bee’s molecular ecology; its population structure and mating system ... The molecular data were also used to show that the nesting female is the mother of all her offspring and that brood parasitism is unlikely in this species. The data indicate that females make daughters at the beginning of the season followed by large sons in the middle, and then small sons at the end. Females often place one brood cell directly above another. The distribution of sex and morph in these doublets follows a pattern with most containing a female on the bottom and a minor male on the top, followed by almost equal numbers of female on top of female and minor male on top of major male. This pattern is likely favoured by emergence patterns, with males emerging before females and minor males emerging before major males. I suggest that although minor males have low reproductive success, their production may nonetheless be beneficial in that minor males open up emergence tunnels for their larger and reproductively more valuable siblings. In addition, minor males may represent the ‘best of a bad job’ provisioning tactic arising from changes in the costs to nesting females of gathering brood provisions over the course of the flight season. This thesis demonstrates that microsatellites can be used to answer many questions regarding the molecular ecology of a species from the behaviour of the bees on a population scale to the mating behaviour of individual bees and how they allocate resources for the next generation. Many other aspects of the bee’s ecology could also be examined now that suitable molecular markers exist.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

40

Orr, Pia. „The biology of four commercial fish species in a seasonally closed estuary“. Murdoch University, 2000. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20060818.133418.

Der volle Inhalt der Quelle

Annotation:

The aim of this study was to determine the size and age compositions, growth rates, reproductive biology, dietary compositions and mesh selectivity of the King George whiting Sillaginodes punctata, the Australian herring Arripis georgiana, the yelloweye mullet Aldrichetta forsteri and the sea mullet Mugil cephalus in Wilson Inlet. These biological variables were chosen for analysis since the resultant data would be of use for managing these commercially important marine species in this seasonally closed estuary, which is located on the southern coast of Western Australia. Samples of each of the above species were typically collected, in at least every other month between April 1988 and April 1990, by using seine netting and gill netting at several sites, distributed at regular intervals throughout the 48 km2 basin of Wilson Inlet, and by gill netting at one site in each of two tributary rivers. The ages of Sillaginodes punctata, Aldrichetta forsteri and Mugil cephalus were determined using the annuli on scales, whereas those of Arripis georgiana were determined using the annuli on otoliths. The annuli on the above hard structures of the four species were shown to be formed annually before they were used for aging purposes. Although at least four year classes of each species were found in Wilson Inlet, the 0+ year class of none of the species was well represented in this estuary. The paucity of this age class was probably attributable, in most cases, to the spawning grounds of these species being located some distance away on the lower west coast of Australia. However, the absence of any 0+ S. punctata in one year was attributed to the mouth of Wilson Inlet being closed at a crucial time, which thereby prevented the recruitment of this species into this estuary. Virtually all of the S. punctata caught in Wilson Inlet were less than the LSo at first maturity, which implies that none of this species return to this estuary after they have emigrated to sea, matured and spawned. However, appreciable numbers of each of the other three species were found at lengths greater than their respective Lsos. There was clear evidence that large A. forsteri tended to leave the estuary soon after the bar at the estuary mouth was breached. In contrast, length-frequency distributions indicated that large A. georgiana often tended to remain in the estuary, even when they exceeded the LSo at first maturity and the estuary mouth was open. The maximum lengths attained by S. punctata, A. georgiana, A. forsteri and M. cephalus were 491,373,430 and 525 mm, respectively, while the maximum ages attained by these four species were 5+, 7+, 5+ and 4+, respectively. While there was no significant difference between the growth rates of the two sexes of either S. punctata or M. cephalus, the overall growth rates of the females of A. georgiana and A. forsteri were both greater than those of their males. Each fish was assigned a maturity stage using the criteria of Laevastu (1965). The maximum maturity stage recorded for the gonads of S. punctata was IV (maturing). The fact that no S. punctata with spawning (stage VI), spent (stage VII), recovering spent (stage VIII) or resorbing gonads were found provides overwhelming evidence that this whiting species neither spawns in Wilson Inlet nor returns to this estuary after it has spawned at sea. Furthermore, spawning and recently-spent gonads were never found in individuals of either A. georgiana, A. forsteri or M. cephalus, whch implies that these species also do not spawn in the estuary. However, some A. georgiana and A. forsteri with recovering spent gonads were found in Wilson Inlet, which indicates that some individuals of these two species enter the estuary after spawning at sea. There was no indication that this also applied with M. cephalus. Yet, the gonads of some individuals of this latter species and also of A. georgiana contained resorbing gonads, i. e gonads that had reached a reasonably advanced stage, but not maturity, and which were now undergoing regression. The fish with these gonads had presumably been trapped in the estuary at the time their gonads were developing and could not therefore emigrate out to their marine spawning areas. The dietary compositions of the four species were shown to be significantly different. Sillaginodes punctata and A. georgiana fed mainly on benthic macroinvertebrates, while all but the smallest M. cephalus were detritivores and A. forsteri was an omnivore. Furthermore, S. punctata fed mainly on errant polychaetes and nemerteans, whereas A. georgiana ingested decapods, mysids and other teleosts. The diets of each species underwent size-related changes. The differences in dietary compositions among and within species would reduce the likelihood of inter- and intraspecific competition for food resources. Comparisons have been made between traditional methods for estimating the selectivity of S. punctata, A. georgiana, A. forsteri and M. cephalus in gill nets and a new method of analysis developed (with Dr. N. Hall), which incorporates the best features of the traditional methods.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

41

Michael, Pippa J. „Agro-ecology of Malva parviflora (small-flowered mallow) in the Mediterranean-climatic agricultural region of Western Australia“. University of Western Australia. Faculty of Natural and Agricultural Sciences, 2006. http://theses.library.uwa.edu.au/adt-WU2006.0076.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] Malva parviflora L. (small-flowered mallow) (Malvaceae) is a common weed of pastures and wastelands and its distribution has increased rapidly throughout Australia during the last decade. Control of M. parviflora with herbicides, such as glyphosate, is often unsatisfactory and changing farming practices, such as minimum tillage, have facilitated its spread. Yet there has been little research on M. parviflora in the past and many aspects of its biology and ecology are unknown. Hence, there exists a need to examine these aspects in order to investigate and develop suitable integrated weed management strategies. Weed identification is the first and probably the most important step in the management of weeds. Here it is shown that the weedy Malva species in Western Australian farming systems is M. parviflora, and not a morphologically similar Malva species or hybrid of two species. A common garden study of 24 populations collected across the agricultural region of south-west Western Australia revealed that since its introduction over 140 years ago M. parviflora has successfully adapted to a wide range of distinct environments. The species is able to thrive in areas that vary in annual rainfall from 315 to 496 mm, maximum average temperatures from 21.9 to 26.8oC and minimum average temperatures from 9 to 13.6oC. However, there was limited broad scale ecoclinal differentiation and low genetic variation within the common garden study with only length of time between sowing and flowering differing between populations. As the species was shown to possess a predominately inbreeding system, which typically would create ecotypes/ecoclines due to limited gene flow, it was suggested that seed dispersal by sheep is likely to have increased gene flow thus suppressing population differentiation. A considerable proportion of mature hardseeded M. parviflora can survive rumen digestion and mastication by sheep. ... With origins thought to be in the Mediterranean region, it is not surprising that M. parviflora has thrived and prospered in south-west Western Australia. This thesis has determined several aspects that have enabled it to flourish in this Mediterranean-type environment and most of these attributes, including autogamous reproduction, ecoclinal/ecotypic formation, dormancy and asynchronous germination and rapid seed development, are commonly found in successful weeds world-wide.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

42

Eberhard, Stefan. „Ecology and hydrology of a threatened groundwater-dependent ecosystem: the Jewel Cave karst system in Western Australia“. Eberhard, Stefan (2004) Ecology and hydrology of a threatened groundwater-dependent ecosystem: the Jewel Cave karst system in Western Australia. PhD thesis, Murdoch University, 2004. http://researchrepository.murdoch.edu.au/61/.

Der volle Inhalt der Quelle

Annotation:

Groundwater is a significant component of the world's water balance and accounts for >90 % of usable freshwater. Around the world groundwater is an important source of water for major cities, towns, industries, agriculture and forestry. Groundwater plays a role in the ecological processes and 'health' of many surface ecosystems, and is the critical habitat for subterranean aquatic animals (stygofauna). Over-abstraction or contamination of groundwater resources may imperil the survival of stygofauna and other groundwater-dependent ecosystems (GDEs). In two karst areas in Western Australia (Yanchep and Leeuwin-Naturaliste Ridge), rich stygofauna communities occur in cave waters containing submerged tree roots. These aquatic root mat communities were listed as critically endangered because of declining groundwater levels, presumably caused by lower rainfall, groundwater abstraction, and/or forest plantations. Investigation of the hydrology and ecology of the cave systems was considered essential for the conservation and recovery of these threatened ecological communities (TECs). This thesis investigated the hydrology and ecology of one of the TECs, located in the Jewel Cave karst system in the Leeuwin-Naturaliste Ridge. A multi-disciplinary approach was used to explore aspects pertinent to the hydrology and ecology of the groundwater system. Thermoluminescence dating of the limestone suggested that development of the karst system dates from the Early Pleistocene and that caves have been available for colonisation by groundwater fauna since that time. Speleogenesis of the watertable maze caves occurred in a flank margin setting during earlier periods of wetter climate and/or elevated base levels. Field mapping and leveling were used to determine hydrologic relationships between caves and the boundaries of the karst aquifer. Monitoring of groundwater levels was undertaken to characterise the conditions of recharge, storage, flow and discharge. A hydrogeologic model of the karst system was developed. The groundwater hydrograph for the last 50 years was reconstructed from old photographs and records whilst radiometric dating and leveling of stratigraphic horizons enabled reconstruction of a history of watertable fluctuations spanning the Holocene to Late Pleistocene. The watertable fluctuations over the previous 50 years did not exceed the range of fluctuations experienced in the Quaternary history, including a period 11,000 to 13,000 years ago when the watertable was lower than the present level. The recent groundwater decline in Jewel Cave was not reflected in the annual rainfall trend, which was above average during the period (1976 to 1988) when the major drop in water levels occurred. Groundwater abstraction and tree plantations in nearby catchments have not contributed to the groundwater decline as previously suggested. The period of major watertable decline coincided with a substantial reduction in fire frequency within the karst catchment. The resultant increase in understorey vegetation and ground litter may have contributed to a reduction in groundwater recharge, through increased evapotranspiration and interception of rainfall. To better understand the relationships between rainfall, vegetation and fire and their effects on groundwater recharge, an experiment is proposed that involves a prescribed burn of the cave catchment with before-after monitoring of rainfall, leaf-area, ground litter, soil moisture, vadose infiltration and groundwater levels. Molecular genetic techniques (allozyrne electrophoresis and mitochondria1 DNA) were used to assess the species and population boundaries of two genera and species of cave dwelling Amphipoda. Populations of both species were largely panrnictic which was consistent with the hydrogeologic model. The molecular data supported the conclusion that both species of amphipod have survived lower watertable levels experienced in the caves during the Late Pleistocene. A mechanism for the colonization and isolation of populations in caves is proposed. Multi Dimensional Scaling was used to investigate patterns in groundwater biodiversity including species diversity, species assemblages, habitat associations and biogeography. Faunal patterns were related to abiotic environmental parameters. Investigation of hydrochemistry and water quality characterized the ecological water requirements (EWR) of the TEC and established a baseline against which to evaluate potential impacts such as groundwater pollution. The conservation status of the listed TEC was significantly improved by increasing the number of known occurrences and distribution range of the community (from 10 m2 to > 2 x lo6 m2), and by showing that earlier perceived threatening processes (rainfall decline, groundwater pumping, tree plantations) were either ameliorated or inoperative within this catchment. The GDE in the Jewel Cave karst system may not have been endangered by the major phase of watertable decline experienced 1975-1987, or by the relatively stable level experienced up until 2000. However, if the present trend of declining rainfall in southwest Wester,,Australia continues, and the cave watertable declines > 0.5 m below the present level, then the GDE may become more vulnerable to extinction. The occurrence and distribution of aquatic root mat communities and related groundwater fauna in other karst catchments in the Leeuwin-Naturaliste Ridge is substantially greater than previously thought, however some of these are predicted to be threatened by groundwater pumping and pollution associated with increasing urban and rural developments. The taxonomy of most stygofauna taxa and the distribution of root mat communities is too poorly known to enable proper assessment of their conservation requirements. A regional-scale survey of stygofauna in southwest Western Australia is required to address this problem. In the interim, conservation actions for the listed TECs need to be focused at the most appropriate spatial scale, which is the karst drainage system and catchment area. Conservation of GDEs in Western Australia will benefit fi-om understanding and integration with abiotic groundwater system processes, especially hydrogeologic and geomorphic processes.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

43

Everaardt, Annika. „The impact of fire on the honey possum Tarsipes rostratus in the Fitzgerald River National Park, Western Australia“. Everaardt, Annika (2003) The impact of fire on the honey possum Tarsipes rostratus in the Fitzgerald River National Park, Western Australia. PhD thesis, Murdoch University, 2003. http://researchrepository.murdoch.edu.au/66/.

Der volle Inhalt der Quelle

Annotation:

The honey possum Tarsipes rostratus is a tiny (7 - 12 g) highly specialised flower-feeding marsupial endemic to the south-western corner of Australia. The impact of fire on this small mammal was studied, over a 19-year period, in the Fitzgerald River National Park, a large (330,000 ha) area of relatively undisturbed heathland/shrubland, rich in the proteaceous and myrtaceous plants upon which the honey possum appears to rely for food. The honey possum is the most abundant and widespread mammal in this Park. Capture rates of honey possums were significantly related to the years since the vegetation was last burnt, annual rainfall in the preceding (but not the current) year, the season when trapping occurred, and the trapping grid operated. Capture rates declined markedly after fire and remained low (less than one third of those in long unburnt vegetation) for about 4 - 5 years following a fire. Rates of capture then increased steadily over the next 20 - 25 years, with maximal abundance recorded about 30 years after fire. Thereafter, there appeared to be a slight decline in capture rates, but even in the vegetation unburnt for longest (> 50 years since fire), honey possum abundance was substantial and relatively stable. In contrast to these changes in abundance, the structure of the honey possum population, with 79 % adults and 57 % males, appeared little influenced by fire history, annual rainfall, season or grid. The increase in the rates of capture of honey possums following fire paralleled the pattern of availability of cover in the vertical and, to a lesser extent, horizontal plane. Indeed, projective foliage cover took around 20 years after fire to reach levels similar to those available in areas unburnt for even longer. The trend in capture rates was also congruent with the maturation of the most frequently visited foodplants of honey possums, particularly Banksia nutans (summer flowering) and B. baueri (winter flowering). Areas long unburnt still contained shelter and foodplants adequate for honey possums even 50 years or more after fire, with only slight evidence of senescence. Pollen loads indicated that honey possums caught in burnt areas, where their preferred foodplants were absent, continued to feed on these favoured foodplants (Banksia and Dryandra spp.) at nearby unburnt areas. In addition, they also fed, in both burnt and long unburnt areas, upon a suite of other plant species that regenerated more rapidly from lignotubers and epicormic buds, as well as from seeds (e.g. Eucalyptus and Calothamnus spp.). Thus, honey possums appeared to persist with their preferences for feeding from a limited number of flowering plants despite some of these species not being available in recently burnt areas for many years. Nearby patches of unburnt vegetation can clearly be important refuges, feeding grounds and shelter for the few honey possums that visit recently burnt areas, and appear to be the source of honey possum colonists in the years following a fire. Capture rates were also greater following years when rainfall was higher than average. Indeed, rainfall had as great an influence upon capture rates as time since fire. Capture rates were also consistently higher over winter, and to a lesser extent over summer, than in either autumn or spring. Individual grids, even those close together in apparently similar vegetation with a similar fire history, still differed significantly overall in their capture rates of honey possums. This last finding has implications for the use of chronosequences in the study of post-fire changes in biota. Although not the primary focus of the study, data on the limited suite of other, far less abundant, small mammals present indicated that house mouse Mus musculus domesticus numbers peak soon after fire (about two years after fire), grey-bellied dunnart Sminthopsis griseoventer numbers somewhat later (about eight years after fire) and that southern bush rats Rattus fuscipes fiuscipes, like honey possums, are later successional species. Most species were present in vegetation over a range of post-fire ages, with data consistent with models based on sequential changes in relative abundance. Like many Australian mammals, the range of the honey possum has contracted substantially over the last 200 years and the coastal heathlands of the south-west are its last stronghold. In terms of its conservation, this study indicates that, if possible, management burns in these heathlands should be separated by intervals of at least 20 years between successive burns, and preferably even longer. If burns are required more frequently to meet other management priorities, it is highly preferable that they are small and patchy, rather than large scale. Such practices may help ensure the long-term survival of this unique, highly specialised and endemic marsupial.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

44

Toohey, Benjamin D. „Recovery of algal assemblages from canopy disturbance : patterns and processes over a range of reef structures“. University of Western Australia. School of Plant Biology, 2006. http://theses.library.uwa.edu.au/adt-WU2006.0135.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] Kelp beds of South-Western Australia have high alpha (within habitat) diversity, through high species turnover at small spatial scales. The E. radiata canopy has a strong negative influence on the diversity of the understorey through intense interspecific competition for light. Literature suggests that when the competitively dominant species such as E. radiata are physically removed, diversity will increase, as less competitive species become more abundant. Apart from disturbance, evidence suggests that reef topography at the 1-10 m vertical scale also has an influence on the structure of the kelp beds, particularly in reference to relative abundance of canopy algae and species richness of the assemblage. In this thesis, I explore the role of algal assemblage recovery from physical disturbance to maintain high diversity. I also investigate the influence of reef structure (in terms of topography at the 1-10 m vertical scale) on assemblage recovery. This thesis provides a valuable functional explanation for the high diversity observed in South-Western algal assemblages. In addition, it explores the influence of reef topography which has received little attention to date . . . Overall, this thesis argues that the high alpha diversity in algal assemblages of South-Western Australia is due to local scale processes including disturbance and assemblage recovery which generate diversity by the creation of species rich gap states and by phase-shifts during the recovery process, creating a mosaic of different patch types. Assemblage recovery is composed of several processes, including survival of juvenile kelp sporophytes and canopy shading, added to macroalgal diversity through spatial and temporal variation in their outcomes. Reef topography contributed to algal diversity by influencing the processes associated with assemblage recovery through alteration of key physical variables including light levels and water motion.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

45

Ryan, Kylie A. „Small, no-take marine protected areas and wave exposure affect temperate, subtidal reef communities at Marmion Marine Park, Western Australia“. University of Western Australia. School of Plant Biology, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0130.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] The ecological effects of marine protected areas (MPAs) in temperate ecosystems are poorly understood relative to their tropical counterparts. The limited number of rigorous empirical studies supporting existing theoretical models, increasing public awareness of the importance of marine conservation strategies and legislative requirements to review management effectiveness provide further impetus to study temperate MPAs. Investigations should consider confounding effects of natural variability if MPA effects are to be clearly demonstrated. This research helps to address these needs by investigating the short term effects of sanctuary zones (no-take MPAs where fishing is prohibited) and wave exposure at Marmion Marine Park, Western Australia. The three sanctuary zones at Marmion Marine Park are extremely small (0.061 0.279 km2) compared to most reported in the literature. The sanctuary zones are nested within a larger, fished zone (94.95 km2). The sanctuary zones have been protected from fishing since the year 2000. A post-hoc, asymmetrical sampling design was used in this study and involved surveys of fishes, mobile invertebrates and macroalgae at one sanctuary zone and two fished sites (controls) at each of three successive, subtidal reef lines. The three reef lines are exposed to a gradient in wave energy. The size structure and abundance of the heavily exploited Panulirus cygnus (Western Rock Lobster) were positively affected by protection from fishing in sanctuary zones, despite the highly mobile nature of this migratory species. The mean abundance of legal size lobsters was higher in sanctuary zones compared to fished sites during an interannual study (2003, 2005 and 2006). The total abundance of lobsters and the mean abundance of legal size lobsters were higher at inshore and offshore sanctuary zones compared to fished control sites during a 2005/2006 fishing season study. These zoning effects did not vary with the time of survey. ... Furthermore, the abundance of large lobsters in sanctuary zones decreased with the duration of the 2005/2006 fishing season. Similarly, it is likely that sanctuary zones are too small relative to the movement of fishes to adequately protect stocks of some targeted species. The small sanctuary zones at Marmion are unlikely to offer protection to highly mobile species over the long term. And finally, ecological assemblages within each level of wave exposure are distinct. Consequently for each assemblage type, the current reserve design does not include replication of sanctuary zones and does not offer any 'insurance' in the event of isolated impacts affecting a particular zone. This study has identified the benefits and deficiencies of the design and function of small no-take temperate MPAs in Western Australia. An increase in the size and number of sanctuary zones within each wave exposure level will help to address the v shortfalls of the zoning scheme and enhance the conservation benefits of management at Marmion Marine Park. More generally, this study demonstrates that the mobility of the species to be protected from fishing should be considered when designing MPAs. Lessons learned from this work will be beneficial for the future management and conservation of resources in the region and elsewhere.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

46

Delacy, Caine Robert. „Latitudinal patterns in reef fish assemblage structure : the influence of long-term and short-term processes“. University of Western Australia. School of Plant Biology, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0097.

Der volle Inhalt der Quelle

Annotation:

Latitudinal patterns in reef fish assemblages reflect the influence of long-term environmental conditions, evolutionary processes and the recent, short-term influence of fishing. Long-term processes generate the typically common latitudinal patterns in reef fish assemblages, such as decreases in diversity and herbivory towards higher latitudes. These patterns reflect the global gradient in water temperature and the isolation of temperate regions from the tropics. Fishing also influences reef fish assemblages in that it decreases the abundance of large-bodied carnivore species on reefs, often leading to over-exploitation, depletion and in some cases the extirpation of populations. Indirectly, the removal of these large-bodied carnivores can influence the abundance of their prey, leading to an increase in non-target species. This study examines the latitudinal patterns in reef fish assemblages across a unique biogeographic region, the temperate Western Australian coast, and incorporates an investigation of the influence of fishing on the structure of these assemblages. Seven regions across seven degrees of latitude and seven degrees of longitude covering approximately 1500 km of coastline were sampled. Fish assemblages were characterised at each region using diver operated stereo-video transects. At each region, four locations, and within each location, four reefs were surveyed totalling 1344 transects. A significant gradient in water temperature exists with latitude and longitude. Along the Western Australian coast, and in contrast to other regions species diversity of reef fish increased towards higher latitudes and there was no evidence for a decrease in the biomass and abundance of herbivorous reef fish. The presence of the poleward flowing warm water Leeuwin current combined with the absence of major extinction events means the temperate Western Australian coast contrasts with global latitudinal trends in reef fish assemblage structure. The unique biogeographic history of temperate Western Australia has also generated a high degree of endemism among reef fish. Nearly 30 % of the species found along the west coast in this study are endemic to Western Australia, with the narrow range of these species playing an important role in the large scale patterns and spatial vi heterogeneity in reef fish assemblage structure. Furthermore, many of these endemic species are large-bodied carnivores and targeted by fishers. The impact of fishing on the abundance of large-bodied carnivores throughout the Western Australian temperate region is clear both spatially and temporally. The distribution of fishing effort is greatest along the west coast and decreases towards the south following the gradient in SST. Along the west coast, high levels of fishing effort have reduced the biomass and abundance of target carnivores to well below the standing biomass of the south coast where a low level of fishing effort occurs. This reduction in biomass is related to the historical declines in catch per unit effort (CPUE) of many key target species. These target species include endemic species such as Choerodon rubescens, Glaucosoma herbraicum, Epinephilides armatus Nemadactylus valenciennesi and Achoerodus gouldii.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

47

Harrison, Sofie Alice. „The influence of seabird-derived nutrients on island ecosystems in the oligotrophic marine waters of south-western Australia“. Connect to thesis, 2006. http://portal.ecu.edu.au/adt-public/adt-ECU2007.0010.html.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

48

Hayward, Matt School of Biological Earth &amp Environmental Science UNSW. „The ecology of the quokka (Setonix brachyurus) (Macropodidae: Marsupialia) in the Northern Jarrah Forest of Australia“. Awarded by:University of New South Wales. School of Biological, Earth and Environmental Science, 2002. http://handle.unsw.edu.au/1959.4/18768.

Der volle Inhalt der Quelle

Annotation:

The quokka (Setonix brachyurus Quoy & Gaimard 1830) is a medium-sized, macropodid marsupial that is endemic to the mesic, south-western corner of Australia. While being a tourist icon on Rottnest Island, the species is threatened with extinction. It has been intensively studied on Rottnest Island in the 1960s and 1970s, however very little is known of its ecology on the mainland. Additionally the insular and mainland environments are extremely different suggesting that ecological differences between the two populations are likely. Consequently, this study sought to determine the basic autecology of the quokka and identify what factors have attributed to its threatened conservation status. The northern jarrah forest of Western Australia was selected as the study region due to it being at the northern limit of extant quokka distribution and because it was thought that the factors threatening the quokka would be exacerbated there. Fossil deposits suggest that the quokka originally occupied an area of approximately 49,000 km2 in the south-western corner of Australia. Historical literature show that they were widespread and abundant when Europeans colonised the region in 1829 but a noticeable and dramatic decline occurred a century later. The arrival of the red fox to the region coincided almost exactly with this decline and so it was probably ultimately responsible. Continued predation by both it and the feral cat are likely to have continued the decline, along with habitat destruction and modification through altered fire regimes. Specific surveys and literature searches show that since the 1950s, the area occupied by the quokka has declined by 45% and since 1990 by 29%. Based on the criteria of the IUCN (Hilton-Taylor 2000), the conservation status of the quokka should remain as vulnerable. An endangered status may be more applicable if the quokkas restriction to patches through its existence as a metapopulation is considered. Trapping of eight sites supporting quokka populations in the mid-1990s revealed three sites now locally extinct despite the ongoing, six year old, fox control programme. Another three are at serious risk of extinction. Extant population sizes ranged from one to 36 and population density ranged from 0.07 to 4.3 individuals per hectare. This is considered to be below the carrying capacity of each site. The overall quokka population size in the northern jarrah forest may be as low as 150 adult individuals, of which half are likely to be female. Even the largest extant populations are highly susceptible to stochastic extinction events. This small size was surprising considering the six year old, introduced predator control programme. Historically, the restriction to discrete habitat patches, the occasional inter-patch movement, the lack of correlation between the dynamics of each population and reports of frequent localised extinctions and colonisations suggest that the quokka population once existed as part of a classic metapopulation. The massive decline of the quokka in the 1930s pushed the metapopulation structure into a non-equilibrium state such that today, the extant populations are the terminal remnants of the original classic metapopulation. Wild mainland quokkas breed throughout the year. A significant reduction in the number of births occurs over summer and this coincides with a decline in female body weight. Despite this, the mainland quokka is relatively fecund and is able to wean two offspring per year. The level of recruitment from pouch young to independence was low and this may explain the apparent lack of population increase following the initiation of fox control. A total of 56 trapped quokkas were fitted with a radio collar. Mean home range size for quokkas was 6.39 ha with a core range of 1.21 ha and this was negatively related to population density. Male home ranges were larger than females but not significantly when the sexual size dimorphism was considered. Nocturnal ranges were larger than diurnal ranges reflecting nocturnal departures from the swamp refugia. Home range sizes varied seasonally, probably due to changes in the distance required to move to obtain sufficient nutrients and water over the dry summer compared to the wet winter and spring. Telemetry confirmed trapping results that showed no movement between swamps or populations. Home range centres shifted to the periphery of the swamp following the winter inundation and this may increase the species susceptibility to predation. The lack of dispersal is probably caused by quokka populations existing below carrying capacity and following selection for philopatry under the threat of predation for dispersing individuals. Without dispersal to recolonise or rescue unpopulated patches, the collapse of the original quokka metapopulation appears to have occurred. On a macrohabitat scale, the quokka in the northern jarrah forest is restricted to Agonis swamp shrubland habitats that form in the open, upper reaches of creek systems on the western side of the forest. This restriction was probably initially due to the high water requirements of the quokka but is likely to have been exacerbated by increased predation pressure since the arrival of the fox. On a microhabitat scale, the quokka is a habitat specialist, preferring early seral stage swamp habitats, probably for foraging, as part of a mosaic of old age swamp that provides refuge. Despite the six year old, introduced predator control programme, foxes and cats are still the major cause of mortality to quokkas. Road kills was the other identifiable cause. Individuals alive at the start of the study had an 81% chance of staying alive until the end. The likelihood of dying was minimised by grouping together with conspecifics, maximising home range size and maximising the time spent within the swampy refuge. Current rates of adult and juvenile survivorship should allow population recovery and so it seems pouch young mortality, reflected by low recruitment, has inhibited the anticipated population increase following predator control. The confounding effect of inadequate unbaited controls meant that little statistical evidence was available on the impact of introduced predators on the quokka, however the models provided support for earlier hypotheses of these. The presence of a quokka population at a site was related to the amount of poison baits delivered ??? reflecting predation pressure, the average age of the swamp and a mosaic of early and late seral stages within the swamp habitat. Recently burnt habitat is thought to provide food for quokkas and long unburnt habitat provides refuge from predation.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

49

O'Brien, Eleanor K. „Local adaptation and genetic variation in south-western Australian forest trees : implications for restoration“. University of Western Australia. School of Animal Biology, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0132.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] Spatial structuring of genetic variation is commonly observed in plant species due to limited dispersal and local adaptation. Intraspecific genetic variation has significant implications for ecological restoration because the source of seed or plants influences patterns of gene flow, and may affect performance if there is adaptive divergence among source populations. This study assessed quantitative trait variation, local adaptation and molecular variation within three common, widespread, long-lived forest tree species from south-western Australia to understand the distribution of intraspecific genetic variation and predict the consequences of seed transfer for restoration. The geographic distribution of quantitative trait variation of jarrah Eucalyptus marginata was assessed through measurement of 15-year-old trees grown in a provenance trial. Survival of trees from the northern jarrah forest was significantly higher than that of trees from southern jarrah forest provenances, where mean annual rainfall is much higher, but stem diameter at breast height (d.b.h.) of southern jarrah forest trees was greater, implying faster growth. D.b.h. of trees from within the northern jarrah forest also exhibited a positive relationship with mean annual rainfall, with maximum d.b.h. observed in trees from provenances in the high rainfall zone. These patterns may reflect selection for faster growth under high rainfall conditions or environmentally-induced parental effects. The percentage of trees bearing buds and flowers varied among latitudinal divisions. ... Neither genetic variation within nor among populations of any species could explain variation of emergence and establishment in reciprocal transplant trials. Collectively, the findings of this study suggest structuring of genetic variation in these species at a broad, rather than a very local, scale. This is expected for widespread, long-lived species, where extensive gene flow and temporal variation are likely to favour high within, relative to among, population genetic variation. However, there is evidence that the source of seed may have a significant influence on the success of restoration of these species, whether as a result of genetic variation among populations or due to other factors affecting seed quality. These results highlight the importance of integrating studies of molecular and adaptive trait variation when seeking to understand the causes and consequences of genetic variation within plant species and contribute to the development of seed sourcing practices for improved restoration success.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

50

Whitehead, Ayesha L. „The effects of isolation and environmental heterogeneity on intraspecific variation in Calamoecia clitellata, a salt lake-inhabiting copepod“. University of Western Australia. School of Animal Biology, 2006. http://theses.library.uwa.edu.au/adt-WU2006.0092.

Der volle Inhalt der Quelle

Annotation:

[Truncated abstract] This study focussed on how isolation and environmental heterogeneity in salt lakes has influenced intraspecific variation in the calanoid copepod Calamoecia clitellata. Calamoecia clitellata relies on passive vectors for dispersal, and this, coupled with the insular nature of salt lakes, may promote genetic divergence at a molecular level. When contrasting environments are involved, genetic divergence may also occur at the life history level, possibly due to local adaptation. I examined the distribution of genetic variation among 14 populations in Western Australia using molecular genetic markers, and examined variation in life history traits among contrasting environments. To ascertain how isolation had influenced molecular genetic variation, I determined population genetic structure and used a phylogeographic approach to infer the impact of historical events. Environmentally induced variation was also evident in the field, with a switch from subitaneous egg production to resting egg production coinciding with changing environmental conditions. It is proposed that plasticity in life history traits has evolved in response to temporal environmental heterogeneity … It can be concluded that isolation in salt lakes in Western Australia has influenced molecular and phenotypic variation in C. clitellata in contrasting ways. At the molecular level, contemporary and historical isolation have promoted genetic divergence of populations, yet when coupled with environmental heterogeneity, marked phenotype plasticity has arisen. This study raises questions as to whether phenotype plasticity is a widespread phenomena in zooplankton found in temporary saline waters and an adaptive strategy to tolerate marked temporal environmental heterogeneity

APA, Harvard, Vancouver, ISO und andere Zitierweisen

Dissertationen zum Thema „Pasture ecology – Western Australia“

Geben Sie eine Quelle nach APA, MLA, Chicago, Harvard und anderen Zitierweisen an