Academic literature on the topic 'Paratya australiensis'

Caridean shrimps are an integral component of lowland river ecosystems in south-eastern Australia, but their distributions may be affected by flow alteration. Monthly shrimp samples were collected from slackwaters in three hydrologically distinct sections of the heavily regulated Campaspe River and the less regulated Broken River for three consecutive years. The distributions of Paratya australiensis, Caridina mccullochi and Macrobrachium australiense, along with their life history in river sections with different hydrology are outlined. Paratya australiensis and M. australiense occurred in all sections, but C. mccullochi was absent from sections of the Campaspe River that received irrigation flows during summer/autumn. Shrimp larvae were most abundant in summer (December–February) and juvenile recruitment continued through to mid autumn (April). Breeding and recruitment of P. australiensis occurred for longer than other shrimps. Apart from large adult and berried M. australiense, all life stages of shrimps commonly occurred in slackwaters, particularly the larval and juvenile stages. Irrigation flows in summer/autumn probably adversely affect the size, extent and arrangement of slackwaters, at a time when they may be critical habitats for C. mccullochi larval development and recruitment. Dams and weirs in the Campaspe River may have influenced shrimp abundance and the timing of breeding.

Caridean shrimps are an important component of lowland river ecosystems and their distributions may be affected by river regulation. We studied the mesoscale distributions of Paratya australiensis, Caridina mccullochi and Macrobrachium australiense in five lowland rivers of the Murray–Darling Basin, south-eastern Australia. We distinguished habitat patches according to water-current velocity and channel location – still littoral (SL), slow-current-velocity littoral (SCVL) and moderate-current-velocity channel (MCVC) – and investigated ontogenetic shifts in habitat use. We sampled seven reaches for shrimp in March 2003 and December 2003 using a modified backpack electrofisher. Paratya australiensis occurred in all habitats but was mostly associated with SL. All life stages of C. mccullochi utilised SL and SCVL, and only a few adults were collected from areas with greater than slow current velocity. The habitat preference of M. australiense changed with development: larvae only occurred in SL, but adults and berried females strongly preferred MCVC. Low flows and slow water currents are characteristic of lowland rivers in southern Australia during summer and autumn (December–April), the period during which shrimps’ larval development and juvenile recruitment occurs. Caridina mccullochi and M. australiense may rely on still and slow-current-velocity habitats during larval development and juvenile recruitment and to facilitate upstream movements.

The abundance and richness of macroinvertebrates in the lower Murray and Darling rivers were examined at a macroscale (rivers), mesoscale (billabongs, backwaters, channel) and microscale (vegetation, snags, substrata). In the Darling, insects dominated (85% of taxa, 81% of individuals); the richest taxa were Diptera (26 taxa) and Coleoptera (15 taxa) and the most abundant were Hemiptera (47%) and Diptera (35%). In the Murray, insects again dominated (84% of taxa, 52% of individuals), particularly Diptera (22 taxa), Coleoptera (12 taxa) and Hemiptera (9 taxa), but there were more crustaceans (9% of taxa, 47% of individuals, particularly the atyid shrimp Paratya australiensis). Both assemblages were uneven: in the Darling, >50% of biomass was Micronecta spp. (Corixidae), Dicrotendipes sp. (Chironomidae) and Macrobrachium australiense (Palaemonidae); in the Murray, 70% of biomass was P. australiensis and Caridina mccullochi (Atyidae) and the insects Micronecta spp. (Corixidae) and Chironomus sp. (Chironomidae). Abundances generally were greatest in the Murray. Hydrologic and geomorphic factors influenced assemblages at the macroscale, whereas microhabitat diversity dominated at the mesoscale.

All life-cycle stages of Paratya australiensis, formerly thought to occur predominantly in freshwater environments, were found to be common in estuaries of western Victoria. Highest densities of larvae were found below the halocline in stable, open, well developed, salt-wedge estuaries. Larvae developed in the salt wedge, and juveniles recruited to littoral weed beds. Adults were most abundant in low salinities among submerged, leafy macrophytes. Although recruitment to estuaries permits the avoidance of fatal drift of larvae to sea, tolerance of saline conditions may permit rare dispersal of larvae between estuaries. A new model for the biogeography of Paratya is proposed.

Atyid shrimps are often an abundant component in undisturbed tropical streams. Studies in coastal streams in Puerto Rico and Brazil have demonstrated the importance of this group in removing periphyton and sediment from hard substrates and their effects on the composition and quantity of periphytic algae. We used experimental exclosures to investigate the influence of the small atyid Paratya australiensis on periphyton accrual on hard substrates in a coastal stream in the subtropics of Australia. We measured organic and inorganic matter, chlorophyll and algal biovolume in the presence and absence of shrimps on natural and artificial substrates. We found a 5-fold increase in the amount of organic matter on natural substrate in the absence of P. australiensis and a two to 10-fold increase in total periphyton mass on artificial substrate. The natural substrates did not show differences in biovolume of algae, however, algal biovolume on the artificial substrates was significantly higher in the exclusion treatment and diatoms were most affected. We conclude that P. australiensis can be considered a strongly-interacting element of the stream biota and an important species for monitoring and conservation.

While the notion of species is central to our understanding of biological processes, it has been impossible to arrive at a consensus regarding a single, widely applicable or functional concept. This project provides insight into the progression through the speciation process by a widespread species of freshwater shrimp, Paratya australiensis. Using mate choice experiments and genetic analysis, multiple reproductive barriers were identified indicating strong divergence between two populations. These barriers are consistent with requirements for species separation under various species concepts, providing strong evidence to support taxonomic revision of this cryptic species complex.

Many species have been translocated from their native habitat into new environments. Some of these transfers have had negative impacts on the resident populations. Hybridization and introgression are some of the impacts that are associated with species incursions. These processes can potentially result in successful invasions and jeopardize the existence of native species and populations. It is thought that intraspecific hybridization can result in the loss of local adaptations and decrease adaptive divergence among populations. Understanding the factors affecting survival of the native species in altered landscapes is an important issue in species conservation. This study explores the processes that could lead to asymmetrical hybridization between two closely related lineages of freshwater shrimp Paratya australiensis. Selection pressure appears to be leading to extinction of one lineage in most of the sites adjacent to a pool where a translocation resulted in mixing of the two lineages (Hughes 2003). The aim of the thesis was to identify the processes and traits involved in the shaping of the current genetic structure of this shrimp following the translocation event; using genetic markers to identify what could have triggered the asymmetrical hybridization and almost complete extinction of the resident lineage. This is an ideal model system to study and understand interactions between recently (2-3 million years ago) diverged lineages. The translocated lineage 4 comes from Kilcoy Creek, which is at a higher altitude (cold temperatures) than Stony Creek, where the resident lineage 6 is situated (warm temperatures). The temperature differences and the fact that the two lineages were thought to have been isolated for 3million years, led to the expectation of some degree of reproductive isolation. Hughes et al. (2003) found that, after this translocation the reproductive isolation was asymmetrical, such that most of the males appeared to mate only with females from the introduced lineage 4. They noticed that lineage 4 was inducing lineage 6 to the edge of extinction in its local environment. This particular translocation event provides an ideal opportunity to test a number of hypotheses to explain asymmetrical hybridization. The sensory drive hypothesis focuses on how mating signals are effective for particular environments and may differ between environments (Endler, 1992). The second hypothesis proposed by Hughes et al. (2003), focuses on the fact that crosses between the resident females and translocated males lineages and vice versa may have differential viability.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

The speciation debate in evolutionary science is long and protracted, evidenced by the multitude of concepts regarding species and speciation. Understanding the nature of species however, is of central importance in the study of biology and ecology. The purpose of this study was to investigate the genetic architecture of freshwater shrimp (Paratya australiensis) from two distinct lineages and of individuals across a known hybrid zone to gain insight into the process of speciation at the molecular level. The results of this study indicate that P. australiensis lineages sit in an advanced position along the speciation continuum, thus warranting taxonomic revision.

Population genetics provides a framework for understanding genetic drift, mutation, migration and selection in natural populations. In the past, population geneticists concentrated on a handful of markers due to limitations of technology. However, with the advancement of Next Generation Sequencing Techniques, the field of population genomics has emerged, which facilitates understanding of evolutionary processes at a genomic level. Any population genetic measure which used to be just a point estimate can now be estimated across the genome. In addition to calculating genome wide averages for genetic differentiation among populations, we can also identify specific regions of the genome under natural selection. It has been of great interest to study natural selection in populations adapted to different environmental conditions and with the development of the technology this has become more feasible. Due to global climate change, species need to adapt to the changing environment and this is only possible if there is sufficient adaptive genetic variation at the molecular level. Adaptive divergence among populations has been studied across different altitudes, in different host forms, along latitudinal clines and between different coastal thermal regimes. This thesis is focused on the species Paratya australiensis which consists of 9 highly divergent mtDNA lineages. Lineage 4 and Lineage 6 of this species have been observed to have preference for upstream and downstream respectively and have been suggested to be adapted to different temperature regimes. In order to evaluate this, I have used a genomic approach in this thesis to investigate population structuring and evidence of adaptation between upstream and downstream populations of P. australiensis in the Mary River catchment in south east Queensland, Australia. My thesis has focused on a single lineage, lineage 4. Three streams (Broken Bridge, Booloumba and Obi Obi Creek) within the Mary River catchment were selected for the study, each consisting of upstream and downstream sites (6 populations). There were three main parts to this research: (1) testing if the population structure followed the Stream Hierarchy Model (SHM) and to compare to past conclusions based on conventional genetic markers (2) to identify putative genomic regions under selection between up and downstream populations and (3) to examine the distribution of lineage 4 and lineage 6 and to determine if they co-occur and, if so, whether they interbreed. In the past, it was observed that there was restricted gene flow between upstream and confluence populations of P. australiensis. Also, it was observed that P. australiensis in the Conondale Range followed the Stream Hierarchy Model (SHM), particularly in the Brisbane River catchment. However, those studies employed allozyme and mtDNA markers. In Chapter 3, I used Single Nucleotide Polymorphism (SNP) markers produced by the technique of Restriction Site Associated DNA Sequencing (RAD-Seq). I found a high level of genetic divergence between up and downstream populations of Booloumba Creek, which is similar to the past findings and indicates that this high level of divergence has been maintained between populations of this stream (Booloumba) over the years. Populations in the other two streams (Broken Bridge and Obi Obi Creek) did not show such high levels of divergence. Also, population structure did not fit with the Stream Hierarchy Model (SHM) as there was more genetic divergence between sites within streams than between streams in the catchment. Such results were possibly due to large divergence between Booloumba Creek populations. So, this study was more robust utilizing a large genotype data set compared to previously used markers. Furthermore, the new set of markers was developed for the first time and was successfully utilized to evaluate the present condition of population structure and genetic diversity of P. australiensis in the Conondale Range. The high divergence in Booloumba Creek in my study suggests that long term isolation and restricted geneflow in Booloumba could lead to local adaptation. Based on previous findings on the preference for up and downstream locations in lineage 4 and 6 respectively, I tested for evidence of local adaptation in these streams and looked for parallel patterns of adaptation across all three streams in Chapter 4. There were 44 outliers identified across the 6 populations, indicating putative genomic regions under selection. Furthermore, there was fixation of alternate alleles for these outliers between up and downstream populations in one stream (Booloumba Creek). Some outlier loci were common across two streams indicating parallel pattern of adaptation to some degree. In addition to the neutral divergence, adaptive divergence was also observed among the populations based on the outliers. As the studied populations were selected based on altitude, it is suggested that the putative evidence of local adaptation could be due to environmental differences between altitudes, most probably temperature differences. So, there are putative genomic regions under selection in P. australiensis, which suggests that with climate change and changing environmental conditions this species may have enough adaptive genetic variation to enable some level of adaptation to future climate change conditions. Due to a past translocation event in the Brisbane River catchment, artificial sympatry was observed between lineage 4 and 6 of P. australiensis. Also, asymmetrical hybridization between the two lineages and introgression of lineage 4 genes into lineage 6 was observed in the translocation area. However, natural sympatry between these 2 lineages had not been reported, despite extensive sampling. It would be interesting to observe if the 2 lineages show hybridization or not if they co-occur naturally. In this thesis, I have identified a case of sympatry between L4 and L6 in the Mary River catchment which is described in Chapter 5. It was thought that lineage 6 was absent from the Mary River catchment. However, I found evidence of lineage 6 in one of the sites together with lineage 4. Based on phylogenetic analysis using COI gene (mtDNA), there was evidence of sympatric lineages in only one site (Broken Bridge High site) in the Mary River catchment. Haplotypes identified in the Mary River catchment were different from those in the Brisbane River catchment. Analysis of nuclear genes in the two lineages (L4 and L6) showed that there were no lineage 6 alleles based on the allozyme data, but microsatellite loci were all under Hardy Weinberg Equilibrium (HWE) expectations, indicating random mating between the lineages. Here I observed that the 2 lineages are interbreeding but we need further investigation to understand the nature of hybridization and if there is introgression or not. Overall the thesis has revealed that P. australienis still shows restricted gene flow and population divergence in some parts of the Conondale Range. Due to long term divergence, some populations have become locally adapted to some extent. Sympatric lineages of P. australiensis have been identified in the past, although sympatry between lineage 4 and 6 was not identified previously. So, in this thesis, I present evidence of co-occurrence of lineage 4 and 6 for the first time in the Conondale Region. Also, the thesis provides information regarding interbreeding status of these 2 lineages. The thesis presents development and utilization of genomic data for the very first time in this species and can benefit other studies dealing with genomics of crustaceans. In addition, this thesis provides an in depth knowledge on the technology and analytical techniques for genomic data.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

Freshwater ecosystems represent hotspots for the world’s total diversity and human well-being. However, they are also subjected to threats across the globe as a result of localised human activities, broad scale catchment clearance, climate change and invasive species. The increased degradation of freshwater habitats and their ecological functions as a consequence of these threats, at local and global scales, has led to significant freshwater problems for human existence and the world’s biodiversity. There is growing evidence that the loss of biodiversity is one of the most complex environmental issues facing the world; however, the importance of understanding species distribution patterns and the ecological differentiation among species that are reflected as species-specific responses or tolerances to environmental drivers is less well understood. In particular, when a morphological approach is used as a taxonomic tool for investigating species diversity and species level responses to environmental drivers, the diversity of responses hidden within species complexes may not be realized, and the conclusion of generality may mask specific cryptic species responses. In South-East Queensland, Australia, European occupation since the mid 1800’s has seen large scale clearing of native vegetation along streams and rivers in nearly all catchments. As a consequence of this land-use change catchment hydrology has been substantially altered, which, combined with the presence of dams and weirs, has resulted in a decline in water quality of streams in some catchments, which is of growing concern for conservation of species biodiversity. This study aimed to explore cryptic diversity in two species complexes of freshwater aytid shrimps common in South-East Queensland and elucidate species level responses to environmental variation that could explain their spatial distribution. This broad aim was met through three specific studies. First, using regional scale data of cryptic species diversity and water quality, the importance of species-specific responses to environmental conditions in determining spatial distribution patterns and environmental relationships of cryptic species in the Caridina indistincta and Paratya australiensis species complexes was examined. To accomplish this aim, DNA sequences were used to identify shrimp specimens from 89 sites in 17 catchments spanning the study area. In addition, an assessment of eight morphological traits was used to test whether these cryptic species could be morphologically identified. Use of these eight traits did allow species level identification, at least in South-East Queensland. However, caution is suggested in the use of these morphological traits for recognising species, due to the probability of morphological plasticity within a species across broad spatial scales. Ordination analysis of presence-absence data showed that the five cryptic species within the two species complexes showed spatially distinct distributions across streams in SEQ, with each cryptic species displaying different relationships with individual environmental variables. For species in the Caridina indistincta complex, C. indistincta sp. B was significantly associated with elevation, C. indistincta sp. D was significantly correlated with dissolved oxygen range, whilst, individuals of C. indistincta sp. A were negatively associated with elevation and dissolved oxygen range. This may indicate that C. indistincta sp. A tended to inhabit sites with low elevation and perhaps having a higher tolerance to a low range of dissolved oxygen. For the Paratya australiensis species complex, P. australiensis lineage 4 and 6 showed significant correlations with elevation and conductivity, respectively. The second broad aim of the study was to explore these spatial patterns at smaller geographical scales and with greater detail about water quality to understand and quantify the fundamental environmental factors (e.g., physical chemical water parameters and concentrations of heavy metals) that are potentially shaping the current distribution patterns and abundance of cryptic species within the two species complexes. To explore this aim, sediment samples from 22 sites in 13 catchments in SEQ were analysed to determine concentrations (mg/kg dry weight) of 11 heavy metals. Additionally, a number of water quality variables were measured in situ, including: elevation, stream width, stream temperature, dissolved oxygen, conductivity, pH, total dissolved solids, and turbidity. Also, a water sample was taken from each site for laboratory analysis of: Ammonium nitrogen (NH4-N), Dissolved oxidized nitrogen (Nitrate+Nitrite) (NOX-N), Total nitrogen (TN), Total kjeldahl nitrogen (TKN), Total kjeldahl phosphorus (TKP), Orthophosphate-P (PO4-P). Shrimps were collected from each site and identified to species using both morphology and DNA sequencing. The morphological identification of each adult individual (except juveniles which were genetically analysed) was used as a measure of absolute abundance and the genetic ‘checking’ of a set number of individuals in each sample was used to compute relative abundance. Redundancy analysis (RDA) showed that the spatial distribution and absolute and relative abundance of C. indistincta sp. D and sp. B were significantly positively influenced by elevation, while the relative abundance of P. australiensis Lin.6 was significantly positively affected by the concentration of manganese (Mn). Stream Total nitrogen (TN) was significantly positive driver of the spatial distribution and relative abundance of C. indistincta sp. A, while Orthophosphate-P (PO4-P) was significantly positive driver for the absolute and relative abundance of this species. Further analysis, this study confirms that P. australiensis Lin.6 was more tolerant of heavy metal concentrations compared with other cryptic species, as its distribution and absolute and relative abundance were significantly positively correlated with the concentrations of manganese, iron and cobalt. In contrast, C. indistincta sp. A was more sensitive to these metals than other study species. These results demonstrated that cryptic species of freshwater atyid shrimps of the C. indistincta and P. australiensis species complexes were different in their environmental requirements. As well, the cryptic species of both complexes were identified to have different associations with heavy metal concentrations, indicating that these species were different in their tolerance to toxicants. Finally, the third aim of the study was to further examine the differences in sensitivity to heavy metals (Copper and Zinc) among cryptic species of the two study complexes experimentally in the laboratory. Two cryptic species of each complex were used as study species, C. indistincta sp. A and sp. D and P. australiensis Lin.4 and Lin.6. The field studies showed differences among these species in their correlations with metal concentrations, and therefore they were seen as good candidate species for testing differences in the sensitivity to metal toxicants. Each cryptic species was exposed to six concentrations of each metal Cu or Zn using an acute (96-h) toxicity test. The results from this study were generally showed contrasting correlation between species and heavy metals; P. australiensis Lin.6 was the most tolerant species to both study metals, while C. indistincta sp. A was more sensitive to copper, and C. indistincta sp. D was more sensitive to Zn compared with the other tested species. Furthermore, the exposure of individuals of each species to the heavy metals caused changes in both their behaviour and their colour during exposure time. Overall, this study has shown cryptic species within broad species complexes can vary in their spatial distribution and their tolerance and response to water quality parameters. This highlights the advantage of using analyses of biotic and abiotic variables for ecological management and biodiversity conservation and the need to understand true species diversity when looking at species level responses to environmental degradation.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text

Previous research has shown that a range of physical and biological drivers can influence the composition of faunal assemblages occupying localities within streams. There is much debate in the literature about which of these is more important. Descriptive and experimental field studies were conducted in two relatively undisturbed, second order rainforest streams in southeast Queensland, Australia. The principal objectives were to describe spatial and temporal patterns in pool fauna and explore relationships between these patterns and physical attributes of habitat, disturbance and biotic interactions. The macroinvertebrate and vertebrate fauna of 12 small stream pools were sampled approximately monthly over a period of 15 months. Samples were collected from all major within-pool habitat types and concurrent measurements of potentially important environmental parameters were made at landscape scales of stream, pool and habitat patch. Faunal assemblages were consistently different between the two streams and between the various within-pool habitat types, although the latter may partially be explained by differences in sampling protocols applied in the different habitat types. However, spatial and temporal variation in faunal assemblages within habitat types was large at the scales of whole pools and within-pool habitats, and this variation occurred apparently independently of variation in physical habitat attributes. These results indicated that very little of the local scale faunal variation could be explained by abiotic drivers and that some other factors must be responsible for the observed faunal patterns. Previous research had indicated that atyid shrimps can play a significant ecological role in rainforest streams, where they act as 'ecosystem engineers' by removing fine sediment from hard surfaces. This subsequently alters algal dynamics and faunal composition in streams. A pool-scale manipulative experiment was conducted to investigate the role of the atyid Paratya australiensis, which is an abundant and conspicuous component of the fauna. Removal of shrimp from pools had no effect on sediment accrual on hard surfaces and consequently did not affect algal biomass or faunal assemblages. The lack of effect on sediment accumulation was attributed to the low rate of deposition in these streams, which was an order of magnitude lower than in streams where atyids have been demonstrated to play a keystone role. The fish Mogurnda adspersa was found to be the primary predator of pool fauna in the study streams, where it preyed on a wide variety of taxa. Dietary analyses revealed that an ontogenetic shift occurred in both diet and the within-pool habitat where fish fed. Within this general framework, individual fish had strong individual prey preferences. Significant correlations were found between the natural abundance of Mogurnda in pools and faunal assemblage patterns in both gravel habitat and pools in general, indicating that predation had an effect on pool fauna. The nature of this effect varied between habitats. A direct density dependent response was observed in gravel habitat. In contrast, the response in pools varied considerably between individual pools, perhaps reflecting the differing prey preferences of individual fish. Despite these correlations, an experimental manipulation of the density of Mogurnda at a whole-pool scale did not conclusively identify a predation effect. This may have been due to problems with fish moving between treatments, despite attempts to constrain them, and low experimental power due to the inherent high variability of pool fauna. Overall, the results of the study indicated that there was considerable spatial and temporal variation in pool fauna despite similarities in the physical attributes of pools and their close proximity. This variation appeared to occur at random and could not be explained by abiotic or biotic factors. Predation had a small effect, but could not explain the overall patterns, whereas disturbance by spates had very little effect at all. Stochastic processes associated with low level random recruitment were identified as a possible and plausible explanation for observed patterns. These conclusions are discussed in terms of their implications for our understanding of the ecology and management of streams.

Previous research has shown that a range of physical and biological drivers can influence the composition of faunal assemblages occupying localities within streams. There is much debate in the literature about which of these is more important. Descriptive and experimental field studies were conducted in two relatively undisturbed, second order rainforest streams in southeast Queensland, Australia. The principal objectives were to describe spatial and temporal patterns in pool fauna and explore relationships between these patterns and physical attributes of habitat, disturbance and biotic interactions. The macroinvertebrate and vertebrate fauna of 12 small stream pools were sampled approximately monthly over a period of 15 months. Samples were collected from all major within-pool habitat types and concurrent measurements of potentially important environmental parameters were made at landscape scales of stream, pool and habitat patch. Faunal assemblages were consistently different between the two streams and between the various within-pool habitat types, although the latter may partially be explained by differences in sampling protocols applied in the different habitat types. However, spatial and temporal variation in faunal assemblages within habitat types was large at the scales of whole pools and within-pool habitats, and this variation occurred apparently independently of variation in physical habitat attributes. These results indicated that very little of the local scale faunal variation could be explained by abiotic drivers and that some other factors must be responsible for the observed faunal patterns. Previous research had indicated that atyid shrimps can play a significant ecological role in rainforest streams, where they act as 'ecosystem engineers' by removing fine sediment from hard surfaces. This subsequently alters algal dynamics and faunal composition in streams. A pool-scale manipulative experiment was conducted to investigate the role of the atyid Paratya australiensis, which is an abundant and conspicuous component of the fauna. Removal of shrimp from pools had no effect on sediment accrual on hard surfaces and consequently did not affect algal biomass or faunal assemblages. The lack of effect on sediment accumulation was attributed to the low rate of deposition in these streams, which was an order of magnitude lower than in streams where atyids have been demonstrated to play a keystone role. The fish Mogurnda adspersa was found to be the primary predator of pool fauna in the study streams, where it preyed on a wide variety of taxa. Dietary analyses revealed that an ontogenetic shift occurred in both diet and the within-pool habitat where fish fed. Within this general framework, individual fish had strong individual prey preferences. Significant correlations were found between the natural abundance of Mogurnda in pools and faunal assemblage patterns in both gravel habitat and pools in general, indicating that predation had an effect on pool fauna. The nature of this effect varied between habitats. A direct density dependent response was observed in gravel habitat. In contrast, the response in pools varied considerably between individual pools, perhaps reflecting the differing prey preferences of individual fish. Despite these correlations, an experimental manipulation of the density of Mogurnda at a whole-pool scale did not conclusively identify a predation effect. This may have been due to problems with fish moving between treatments, despite attempts to constrain them, and low experimental power due to the inherent high variability of pool fauna. Overall, the results of the study indicated that there was considerable spatial and temporal variation in pool fauna despite similarities in the physical attributes of pools and their close proximity. This variation appeared to occur at random and could not be explained by abiotic or biotic factors. Predation had a small effect, but could not explain the overall patterns, whereas disturbance by spates had very little effect at all. Stochastic processes associated with low level random recruitment were identified as a possible and plausible explanation for observed patterns. These conclusions are discussed in terms of their implications for our understanding of the ecology and management of streams.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Australian School of Environmental Studies
Full Text