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Academic literature on the topic 'Weed invasion'

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Published: 4 June 2021
Last updated: 28 January 2023

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Journal articles on the topic "Weed invasion"

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Panetta, F. Dane. "Weed Eradication—An Economic Perspective." Invasive Plant Science and Management 2, no. 4 (October 2009): 360–68. http://dx.doi.org/10.1614/ipsm-09-003.1.

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AbstractThere has been recent interest in determining the upper limits to the feasibility of weed eradication. Although a number of disparate factors determine the success of an eradication program, ultimately eradication feasibility must be viewed in the context of the amount of investment that can be made. The latter should reflect the hazard posed by an invasion, with greater investment justified by greater threats. In simplest terms, the effort (and hence investment) to achieve weed eradication comprises the detection effort required to delimit an invasion plus the search and control effort required to prevent reproduction until extirpation occurs over the entire infested area. The difficulty of estimating the required investment at the commencement of a weed eradication program (as well as during periodic reviews) is a serious problem. Bioeconomics show promise in determining the optimal approach to managing weed invasions, notwithstanding ongoing difficulties in estimating the costs and benefits of eradication and alternative invasion management strategies. A flexible approach to the management of weed invasions is needed, allowing for the adoption of another strategy when it becomes clear that the probability of eradication is low, owing to resourcing or intractable technical issues. Whether the considerable progress that has been achieved towards eradication of the once massive witchweed invasion can be duplicated for other weeds of agricultural systems will depend to a large extent upon investment (> $250 million over 50 yr in this instance). Weeds of natural ecosystems seem destined to remain more difficult eradication targets for a variety of reasons, including higher impedance to eradication, more difficulty in valuing the benefits arising from eradication, and possibly less willingness to pay from society at large.
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Ohrtman, Michelle K., and Sharon A. Clay. "Using a Pervasive Invader for Weed Science Education." Weed Technology 27, no. 2 (June 2013): 395–400. http://dx.doi.org/10.1614/wt-d-12-00132.1.

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Students studying weed science would expand their knowledge by conducting targeted experiments on invasive weeds. Tamarix spp., some of the most problematic weeds known in the United States, have value for weed science education. Tamarix was used in an undergraduate laboratory course to demonstrate weed science principles for a minimal cost and with great potential for academic enhancement. The laboratory exercise was designed to teach weed science students about the difficulty associated with controlling invasive weeds even at a relatively young age in a region where plants have been detected but large-scale invasion has not occurred to emphasize the importance of early detection and rapid response. The successful execution of this exercise and the positive student response suggests that Tamarix and other weeds with similar reproductive capacities could be valuable additions to weed science curricula. Innovative approaches to teaching weed science facilitate greater learning of this complex subject by students from diverse backgrounds and academic disciplines.
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Rozefelds, A. C. F., L. Cave, D. I. Morris, and A. M. Buchanan. "The weed invasion in Tasmania since 1970." Australian Journal of Botany 47, no. 1 (1999): 23. http://dx.doi.org/10.1071/bt97054.

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Tasmanian Herbarium (HO) collections are shown to provide temporal and distributional data to monitor weed introductions into the State flora during the last 25 years. Information obtained from herbarium collections, the botanical literature, and anecdotal sources indicates that since 1970, 159 new plant taxa have been recorded as naturalised in Tasmania, bringing to a total over 740 weed species recorded from the State. Most of these species are from the families Poaceae (15.1%), Fabaceae (10.1%), Asteraceae (6.9%), Cyperaceae (5.7%), Rosaceae s.l. (5.0%), Caryophyllaceae and Liliaceae s.l. (3.8% each), Iridaceae (3.1%), and Juncaceae and Ranunculaceae (2.5% each). While for many taxa the mechanisms for introduction remain unknown, at least 35% were introduced as ornamentals, and some 5% arrived through agricultural practices. Of the 159 species, 19 are known only from Tasmania and have not been recorded from the Australian mainland. The majority of weeds are of European origin, with a high proportion being from Africa, North and South America, and mainland Australia, in that order. This study demonstrates that even with the current quarantine controls a large number of weed species have been introduced to the State flora in the last 25 years, and a considerable number of these species are recognised as potential environmental weeds. The number of new weed species recognised is also possibly due, in part, to more collections of weeds being undertaken in recent years. As a large percentage of the weeds identified are ornamentals, stricter controls on the introductions of new ornamentals may be needed. Some of the limitations of using herbarium collections to assess weed introductions are also discussed.
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Osunkoya, Olusegun O., Claire Lock, Joshua C. Buru, Brad Gray, and Moya Calvert. "Spatial extent of invasiveness and invasion stage categorisation of established weeds of Queensland, Australia." Australian Journal of Botany 68, no. 8 (2020): 557. http://dx.doi.org/10.1071/bt20066.

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The risk posed by invasive alien species is determined primarily by two factors: distribution (occupancy) and abundance (density). However, most ecological studies use distribution data for monitoring and assessment programs, but few incorporate abundance data due to financial and logistical constraints. Failure to take into account invaders’ abundance may lead to imprecise pest risk assessments. Since 2003 as part of the Annual Pest Distribution Survey (APDS) exercise in the state of Queensland, Australia, government biosecurity officials have collected data on distribution and abundance of more than 100 established and emerging weeds. This data acquisition was done at spatial grid sizes of 17–50 × 17–50 km and across a very broad and varied geographical land area of ~2 × 106 km2. The datasets provide an opportunity to compare weed dynamics at large-medium spatial scales. Analysis of the APDS datasets indicated that weed distributions were highest in regions along the southern and central, coastal parts of Queensland, and decreased in the less populated inland (i.e. western) and northern parts of the state. Weed abundance showed no discernible landscape or regional trends. Positive distribution–abundance relationships were also detected at multiple spatial scales. Using both traits of weed abundance and distribution, we derived a measure of invasion severity, and constructed, for several (64) weed species, ‘space-for-time’ invasion curves. State-wide and in each of Queensland’s 10 regions, we also categorised the invasion stages of these weeds. At the grassroots of local government area or regional levels, the derived invasion curves and stage categories can provide policy direction for long-term management planning of Queensland’s priority weeds.
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Szilágyi, Arnold, Tamás Tóth, and László Radócz. "New occurence of woolly cupgrass (Eriochloa villosa [Thunb.] Kunth) in Hajdúság area, East-Hungary." Acta Agraria Debreceniensis, no. 71 (June 14, 2017): 51–54. http://dx.doi.org/10.34101/actaagrar/71/1572.

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Because of the globalization and global warming the emergence of invasive weeds in Hungary are more common. The woolly cupgrass (Eriochloa villosa [Thunb.] Kunth) is published as an important invasive weed in Hungary. Woolly cupgrass is native in East Asia and it spreads into several parts of the World and causes difficulties in plant protection. It has been spreading extensively during the last few years,as the weed shows a very serious invasion potential.
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Liu, Hua, Yexuan Li, Yumei Wei, MA Ming, and Gang Ma. "Discrete Population Competition Model of Poisonous Weed Invasion and Spatial Distribution." Journal of Physics: Conference Series 2173, no. 1 (January 1, 2022): 012016. http://dx.doi.org/10.1088/1742-6596/2173/1/012016.

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Abstract Poisonous weeds invade ecosystems and compete with edible forage grassland, changing the population spatial distribution. In this paper, a discrete population competition model for the interaction between poisonous weeds and edible forage grass is established, and a diffusion coefficient to describe the invasion and diffusion effect of poisonous weeds is introduced. By using cellular automata methods, the influence of invasive diffusion of poisonous weeds on the spatial distribution of poisonous weed and edible forage populations is simulated. These findings indicated that the invasion of poisonous weeds affected the ecological distribution of grassland, and that the spatial distribution of poisonous weeds also changed from initial uniform distribution to aggregated distribution.
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CURRAN, P. L., and F. S. MACNAEIDHE. "Weed invasion of milled-over bog." Weed Research 26, no. 1 (February 1986): 45–50. http://dx.doi.org/10.1111/j.1365-3180.1986.tb00675.x.

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Richardson, David M., and Petr Pyšek. "Plant invasions: merging the concepts of species invasiveness and community invasibility." Progress in Physical Geography: Earth and Environment 30, no. 3 (July 2006): 409–31. http://dx.doi.org/10.1191/0309133306pp490pr.

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This paper considers key issues in plant invasion ecology, where findings published since 1990 have significantly improved our understanding of many aspects of invasions. The review focuses on vascular plants invading natural and semi-natural ecosystems, and on fundamental ecological issues relating to species invasiveness and community invasibility. Three big questions addressed by the SCOPE programme in the 1980s (which species invade; which habitats are invaded; and how can we manage invasions?) still underpin most work in invasion ecology. Some organizing and unifying themes in the field are organism-focused and relate to species invasiveness (the tens rule; the concept of residence time; taxonomic patterns and Darwin’s naturalization hypothesis; issues of phenotypic plasticity and rapid evolutionary change, including evolution of increased competitive ability hypothesis; the role of long-distance dispersal). Others are ecosystem-centred and deal with determinants of the invasibility of communities, habitats and regions (levels of invasion, invasibility and propagule pressure; the biotic resistance hypothesis and the links between diversity and invasibility; synergisms, mutualisms, and invasional meltdown). Some theories have taken an overarching approach to plant invasions by integrating the concepts of species invasiveness and community invasibility (a theory of seed plant invasiveness; fluctuating resources theory of invasibility). Concepts, hypotheses and theories reviewed here can be linked to the naturalization-invasion continuum concept, which relates invasion processes with a sequence of environmental and biotic barriers that an introduced species must negotiate to become casual, naturalized and invasive. New research tools and improved research links between invasion ecology and succession ecology, community ecology, conservation biology and weed science, respectively, have strengthened the conceptual pillars of invasion ecology.
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Pearson, Dean E., Yvette K. Ortega, Justin B. Runyon, and Jack L. Butler. "Secondary invasion: The bane of weed management." Biological Conservation 197 (May 2016): 8–17. http://dx.doi.org/10.1016/j.biocon.2016.02.029.

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Gordon, Doria R., S. Luke Flory, Aimee L. Cooper, and Sarah K. Morris. "Assessing the Invasion Risk ofEucalyptusin the United States Using the Australian Weed Risk Assessment." International Journal of Forestry Research 2012 (2012): 1–7. http://dx.doi.org/10.1155/2012/203768.

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Many agricultural species have undergone selection for traits that are consistent with those that increase the probability that a species will become invasive. However, the risk of invasion may be accurately predicted for the majority of plant species tested using the Australian Weed Risk Assessment (WRA). This system has been tested in multiple climates and geographies and, on average, correctly identifies 90% of the major plant invaders as having high invasion risk, and 70% of the noninvaders as having low risk. We used this tool to evaluate the invasion risk of 38Eucalyptustaxa currently being tested and cultivated in the USA for pulp, biofuel, and other purposes. We predict 15 taxa to have low risk of invasion, 14 taxa to have high risk, and 9 taxa to require further information. In addition to a history of naturalization and invasiveness elsewhere, the traits that significantly contribute to a high invasion risk conclusion include having prolific seed production and a short generation time. Selection against these traits should reduce the probability that eucalypts cultivated in the USA will become invasive threats to natural areas and agricultural systems.
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Dissertations / Theses on the topic "Weed invasion"

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Gosper, Carl R. "Consequences of weed invasion and control on plant-bird interactions and bird communities." Access electronically, 2004. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20050221.155953/index.html.

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Siderov, Kris, and kris siderov@rmit edu au. "An investigation of the invasion dynamics of Asparagus asparagoides at the habitat level using spatial analytical techniques." RMIT University. Mathematical and Geospatial Sciences, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20061010.095929.

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This thesis reports on research that examines the early stage invasion process of Asparagus asparagoides (L.) W. Wight (bridal creeper), primarily a bird-dispersed weed, in a remnant vegetation patch. The study site is on Phillip Island, approximately 100 kilometres south east of Melbourne, Victoria. Asparagus asparagoides invasion of the remnant vegetation reserve is a relatively recent phenomenon. Landscape elements that affect bird dispersal and vegetation types that affect seedling establishment may be important factors that limit or enhance the spread of A. asparagoides. A systematic sampling strategy was adopted and data collected for a variety of landscape and vegetative variables including cover and abundance of A. asparagoides and the data were presented in a Geographic Information System (GIS). Preliminary results show that the distribution of A. asparagoides within a remnant vegetation patch is not random. It appears to have entered the reserve from two boundaries, spreading toward the centre, which to date remains sparsely colonised despite the capacity of this weed to spread rapidly over long distances by birds. A number of other outcomes are noted. Asparagus asparagoides establishment is prevented in pasture where sheep and cattle graze, and paddocks subjected to tillage practices. The exclusion of grazing in fenced off vegetation in pastures demonstrates rapid weed establishment and colonisation several hundred metres from main infestation. Field observation and visual inspection of temporal progress of invasion (using above ground weed density with tuber appearance to infer age) appear to suggest that invasion into remnant is associated with the track network. This age/density assumption is strengthened when spatial distribution is examined using a data set where low-density values for A. asparagoides are removed and compared with a data set using all A. asparagoides density values. The mapping of A. asparagoides in fenced off farm remnants suggests that velocity of spread at 191m/yr is a considerable underestimate. Subsequent analysis shows that the spatial distribution of A. asparagoides is not completely spatially random while intensity surface analysis highlights regions of low and high intensity located near track network. Mapping a density surface within GIS provided confirmatory evidence for the establishment of satellite clusters along the track network. The change in the intensity surface observed using the two data sets (lowdensity values and all density values) is also consistent with an expanding invasion occurring between two time periods. Spatial point pattern analysis using K-function statistics shows that xxii the clustering observed using GIS appears to be occurring at two scales or distances (130m- 160m and 195m-205m). The association between tracks and the invasion process observed in the initial stages of the study is examined. There is a change in density as a function of distance from a track where the density of A. asparagoides appears to reduce the further away from the track a site is and this relationship holds regardless of track width. The final stages of the study look at the development of a predictive model. Visual exploration of the data through mapping in a GIS and field observation made during data collection provide the starting point for the development of logistic models to estimate the probability of A. asparagoides presence. Finally the best overall logistic model is applied to a second independent site to determine the general applicability of the model. A number of variables that impact on the presence of A. asparagoides, particularly during the initial stages of the invasion process, are identified. While all the identified variables and the overall model are statistically significant, the model is found to correctly predict presence/absence in only 67% of cases overall. The model however could be expected to correctly predict the presence of A. asparagoides in 74% of cases and has a false positive rate of 40%. The model is applied at a second independent site and found to have an overall percent correct rate of 80% and correctly predicted A. asparagoides presence in 94% of cases. The variables identified as influential in the early stage of invasion are relatively easy to acquire by simple field survey that does not require specialist skills. When considering the model as a tool for the management of remnant vegetation communities, high false positive rates may lead to limited resources being spent on searching sites where there is no weed. However, a high false negative rate would have a larger impact on the management of the weed since the undetected infestations would form sources for new propagules. The model performs well from this point of view in that it provided low false negative rates at both sites. The value of the predictive model is its ability to provide managers with information regarding specific areas to target for weed eradication and management can use the model to assess the effectiveness of any control measures by going back to obtain new cover density data, then using the model to examine the changes over time. The model also provides a starting point for the development of a generic model of A. asparagoides invasion at sites outside of Phillip Island and could also provide the starting point for developing models that could be used for other bird-dispersed fleshy-fruited weed species.
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Carruthers, Sandy. "The effects of weed invasion on native plants communities : a case study of the creekbank vegetation communities of Morialta Conservation Park /." Title page, contents and abstract only, 1990. http://web4.library.adelaide.edu.au/theses/09AR/09arc319.pdf.

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Rounsaville, Todd J. "INVASION DYNAMICS OF THE EXOTIC LIANA EUONYMUS FORTUNEI (TURCZ.) HAND.-MAZZ. (WINTERCREEPER)." UKnowledge, 2017. http://uknowledge.uky.edu/biology_etds/40.

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Elevated atmospheric CO2 has been implicated as a driver of increased liana abundance worldwide. Known as disturbance creators and beneficiaries, lianas possess the potential to significantly influence forest ecosystems. I investigated the early-invasion dynamics of Euonymus fortunei (wintercreeper), an evergreen liana that is invading forests in eastern North America, disrupting native plant communities and ecosystem functions. Wintercreeper is widely cultivated as an ornamental groundcover, frequently invading natural areas via asexual stem growth. Invasion of remote natural areas is dependent upon seed transport and may occur less frequently. I examined the mechanisms of seed dormancy by conducting a ‘move-along’ experiment using fresh and after-ripened seeds. Additionally, I sought to characterize the nature of seed dispersal by birds by deploying seed traps within an invaded forest in central Kentucky. Wintercreeper seeds displayed conditional nondeep physiological dormancy. Although germination occurs at high velocity following cold stratification, a cold period was only facultative to break dormancy. While fresh seeds had greater germination rates (98.6%) compared to after-ripened seeds (85.7%), after-ripened seeds experienced earlier germination (41 days across all treatments). My findings also indicate that bird-mediated seed dispersal occurs throughout the winter from seeds that after-ripen on maternal liana phanerophytes. Overall, these data suggest wintercreeper seeds are capable of dispersing and recruiting in areas with mild to non-existent winters. The invasion of natural areas by exotic invaders is regulated by biotic and abiotic processes, which influence the invader’s success or failure. I studied the vegetation and soil effects of paired invaded (INV), uninvaded (NAT), and ‘restored’ (RES) sites on the germination and survival of wintercreeper seeds and seedlings. The effect of aril (with vs. without) was also tested, both in the field and in vitro. In the field, total germination and first year survival were 55.6% and 24.2%, respectively, across treatments. Total germination was unaffected by treatments, yet vegetation (P = 0.0016) and aril (P = 0.001) treatments significantly influenced germination rates over time, including delayed germination of seeds with arils. The proportion of germinated seedlings that survived was significantly different based on vegetation (P = 0.054) and aril (P = 0.071) treatments after the first winter of growth, but not prior to the first winter. The proportion of seedling survival was significantly lower among seeds dispersed with an aril and seeds sown within INV treatments; there were no interactive effects. Finally, I examined how seedling density and growth habit (horizontal vs. vertical) influenced plant survival, growth, and allometry. I also tested extractable soil C, N, P, K, Ca, and Mg prior to planting and after 17 months of soil conditioning. I found evidence that increased planting density negatively influenced growth among individual plants (lower survival, basal diameter, shoot mass, root mass). At the plot level, high-density plantings yielded greater stem length, and shoot, root, and combined biomass, indicating positive frequency dependence for this species. Soil analyses indicated C, N, P, Ca, and Mg significantly increased (P < 0.05) over the course of the experiment. I conclude that in wintercreeper, prominent asexual propagation leads to aggregate populations whose total contributions to above- and belowground biomass are positively correlated with density, even though individual plant fitness is not. Altogether, this work provides insight into how wintercreeper invasions occur at broad and fine scales. This information will provide a foundation for future wintercreeper studies and aid land managers in their prevention and control strategies.
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Dunlop, Elizabeth A. "Mapping and modelling the invasion dynamics of Senna obtusifolia at different levels of scale in Australia." Thesis, Queensland University of Technology, 2007. https://eprints.qut.edu.au/16490/1/Elizabeth_Dunlop_Thesis.pdf.

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The invasion of natural environments by alien species is a significant threat to the ecological integrity of these systems. Senna obtusifolia is an aggressive invasive weed recently introduced to Australia that is having significant impacts on grassland ecosystems on the Cape York Peninsula. Currently the species is inadequately managed and so range expansion continues. The invasion potential of S. obtusifolia in Australia remains unknown, as does much about its behaviour and management in natural systems. This project undertakes extensive mapping and modelling of the current and future distributions and the invasion dynamics of S. obtusifolia in Australia to facilitate early detection of outbreak populations and the development of appropriate management strategies. The mapping and modelling of S. obtusifolia was conducted at three different scales: continental, landscape and local (population). To address these spatial scales, eco-climatic modelling, remote sensing analysis, field experimentation and creation of a model of seed fate was undertaken. Using the climatic preferences of S. obtusifolia displayed internationally, an eco-climatic model (using CLIMEX software) ascertained that S. obtusifolia has a very large invasive potential in Australia. The predicted geographic distribution comprised the entire eastern and northern Australian coastlines, with spread further inland being largely restricted by a lack of moisture. The regional distribution of S. obtusifolia was not successfully delineated using remote sensing technology. Despite possessing favourable traits for detection by remote sensors, poor data quality and inappropriate image scales prevented the weed from being distinguished from other vegetation by multi-spectral satellite imagery and aerial photography. However, the results indicated that refining the data and the techniques used, single S. obtusifolia populations may be detectable in the future. Investigation of the invasion dynamics of S. obtusifolia at the local scale involved multiple field surveys and manipulative experiments during 2002-2005. Field work indicated that little variation in population characteristics (e.g. stem density, soil seed reserve, seed production) existed within populations, but there was variability across populations and between years: the variation between years was very significant. The vegetation type adjacent to the weed population did not affect population attributes; however less competitive, more open and disturbed environments may better facilitate the invasion. The compartment model of seed fate reflecting S. obtusifolia population dynamics demonstrated that change in annual rainfall was unlikely to explain the variation evident between populations and years. Instead, the rate at which dormancy is broken in seeds and the intensity and regularity of fire provided a better explanation of the weed's population dynamics. Early detection of invaders and the prediction of likely sites of invasion provide the most effective means of preventing future invasions. How best to achieve these goals still remains largely unknown. The process undertaken in this study was a relatively quick and reliable method for assessing the seriousness of S. obtusifolia, predicting future outbreaks and for providing clues to long term management. The appropriate use of fire, maintaining high interspecific competition and shade, as well reducing the rate at which dormancy is broken in seeds are all possible methods of managing S. obtusifolia.
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Dunlop, Elizabeth A. "Mapping and modelling the invasion dynamics of Senna obtusifolia at different levels of scale in Australia." Queensland University of Technology, 2007. http://eprints.qut.edu.au/16490/.

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The invasion of natural environments by alien species is a significant threat to the ecological integrity of these systems. Senna obtusifolia is an aggressive invasive weed recently introduced to Australia that is having significant impacts on grassland ecosystems on the Cape York Peninsula. Currently the species is inadequately managed and so range expansion continues. The invasion potential of S. obtusifolia in Australia remains unknown, as does much about its behaviour and management in natural systems. This project undertakes extensive mapping and modelling of the current and future distributions and the invasion dynamics of S. obtusifolia in Australia to facilitate early detection of outbreak populations and the development of appropriate management strategies. The mapping and modelling of S. obtusifolia was conducted at three different scales: continental, landscape and local (population). To address these spatial scales, eco-climatic modelling, remote sensing analysis, field experimentation and creation of a model of seed fate was undertaken. Using the climatic preferences of S. obtusifolia displayed internationally, an eco-climatic model (using CLIMEX software) ascertained that S. obtusifolia has a very large invasive potential in Australia. The predicted geographic distribution comprised the entire eastern and northern Australian coastlines, with spread further inland being largely restricted by a lack of moisture. The regional distribution of S. obtusifolia was not successfully delineated using remote sensing technology. Despite possessing favourable traits for detection by remote sensors, poor data quality and inappropriate image scales prevented the weed from being distinguished from other vegetation by multi-spectral satellite imagery and aerial photography. However, the results indicated that refining the data and the techniques used, single S. obtusifolia populations may be detectable in the future. Investigation of the invasion dynamics of S. obtusifolia at the local scale involved multiple field surveys and manipulative experiments during 2002-2005. Field work indicated that little variation in population characteristics (e.g. stem density, soil seed reserve, seed production) existed within populations, but there was variability across populations and between years: the variation between years was very significant. The vegetation type adjacent to the weed population did not affect population attributes; however less competitive, more open and disturbed environments may better facilitate the invasion. The compartment model of seed fate reflecting S. obtusifolia population dynamics demonstrated that change in annual rainfall was unlikely to explain the variation evident between populations and years. Instead, the rate at which dormancy is broken in seeds and the intensity and regularity of fire provided a better explanation of the weed's population dynamics. Early detection of invaders and the prediction of likely sites of invasion provide the most effective means of preventing future invasions. How best to achieve these goals still remains largely unknown. The process undertaken in this study was a relatively quick and reliable method for assessing the seriousness of S. obtusifolia, predicting future outbreaks and for providing clues to long term management. The appropriate use of fire, maintaining high interspecific competition and shade, as well reducing the rate at which dormancy is broken in seeds are all possible methods of managing S. obtusifolia.
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Gatehouse, Hazel A. W. "Ecology of the naturalisation and geographic distribution of the non-indigenous seed plant species of New Zealand." Diss., Lincoln University, 2008. http://hdl.handle.net/10182/1009.

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The naturalisation and subsequent spread of non-indigenous plant species (NIPS) is a major problem for most regions of the world. Managing plant invasions requires greater understanding of factors that determine initial naturalisation and distribution of wild NIPS. By the year 2000, 2252 NIPS were recorded as wild (1773 fully naturalised and 479 casual) in New Zealand. From published literature and electronic herbaria records, I recorded year of discovery of wild populations, and regional distribution of these wild NIPS. I also recorded species related attributes hypothesised to affect naturalisation and/or distribution, including global trade, human activities, native range and biological data; and regional attributes hypothesised to affect distribution, including human population densities, land use/cover, and environmental data. I used interval-censored time-to-event analyses to estimate year of naturalisation from discovery records, then analysed the importance of historical, human activity, biogeographical and biological attributes in determining patterns of naturalisation. Typically, NIPS that naturalised earlier were herbaceous, utilitarian species that were also accidentally introduced and/or distributed, with a wide native range that included Eurasia, naturalised elsewhere, with a native congener in New Zealand. In the year 2000, 28% of wild NIPS occupied only one region, 18% occupied two regions, decreasing incrementally to 2.5 % for nine regions, but with 13.5% occupying all ten regions. I used generalised linear models (GLMs) with binomial distribution to determine predictors of whether a wild NIPS occupied ten regions or not, and GLMs with Poisson distribution for wild NIPS occupying 0 – 9 regions. As expected, the dominant effect was that species discovered earlier occupied more regions. Utilitarian wild NIPS that were also accidentally introduced and/or distributed, and wild NIPS with a native congener tended to be more widely distributed, but results for other attributes varied between datasets. Although numbers of wild NIPS recorded in regions of New Zealand were sometimes similar, composition of wild NIPS was often very different. I used nonmetric multidimensional scaling (NMDS) to determine dissimilarity in composition between regions. Then, after reducing correlation between predictor variables using principal components analyses (PCAs), I tested the importance of regional variables in determining the regional composition of wild NIPS using metaMDS. The density of human populations best explained the dissimilarity in composition, but temperature gradients and water availability gradients were also important. In the year 2000 more than 1100 (60%) of the 1773 fully naturalised NIPS in mainland New Zealand had each been recorded in Northland/Auckland and Canterbury, and at the other end of the scale, Southland and Westland each had fewer than 500 (30%). I used GLMs to analyse the importance of people and environment in determining the numbers of wild NIPS in each region. Because I conducted multiple tests on the same dataset I used sequential Bonferroni procedures to adjust the critical P-value. Only human population density was important in explaining the numbers of NIPS in the regions. Overall, humans were the dominant drivers in determining the patterns of naturalisation and spread, although environment helps determine the composition of NIPS in regions. Incorporating human associated factors into studies of wild NIPS helps improve the understanding of the stages in the naturalisation and spread process.
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Liutkus, Dainius. "Ilgalaikio skirtingo intensyvumo žemės dirbimo poveikis miežių agrocenozei taikant intensyvias technologijas." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130621_111609-10533.

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Agronomijos studijų programos magistro baigiamasis darbas 40 puslapių, 10 paveikslų, 2 lentelės, lietuvių kalba. Tyrimo objektas: paprastojo miežio (Hordeum vulgare L.) vasarinės veislės ,,Simba'' agrocenozė. Tyrimo tikslas: Įvertinti ilgalaikio skirtingo intensyvumo žemės dirbimo poveikį miežių agrocenozei, taikant intensyvias technologijas. Tyrimo uždaviniai: 1. Apžvelgti mokslinę literatūrą ir atlikti sisteminę analizę tiriamuoju klausimu. 2. Aprašyti atlikto eksperimento vykdymo sąlygas ir metodus. 3. Tyrimais nustatyti ir įvertinti ilgalaikio skirtingo intensyvumo žemės dirbimo poveikį struktūros patvarumui, miežių sudygimui, pasėlių piktžolėtumui ir miežių produktyvumui. Tyrimo metodai: mokslinės literatūros apžvalga, loginė analizė ir sintezė, statistinė analizė, palyginamoji analizė, grafinio modeliavimo technikos. Tyrimo rezultatai: • Pirmoji dalis pristato Lietuvos ir užsienio autorių mokslinės literatūros analizę. Mokslinė medžiaga atrinkta, susisteminta ir analizuota. • Antroje dalyje aprašyti koncentruojamasi ties bandymo schema ir parametrais, mokslinio eksperimento variantais ir duomenų analizės stebėjimais ir metodais. • Trečioji dalis identifikuoja dirvožemio struktūros patvarumą, miežių sudygimą ir stiebų produktyvumą, miežių derlių, pasėlių piktžolėtumą bei miežių produktyvumą. Nustatyta, kad ilgalaikis skirtingo intensyvumo žemės dirbimas neturėjo esminės įtakos dirvožemio struktūros patvarumui. Nenustatyta esminės įtakos ir miežių produktyvumui... [toliau žr. visą tekstą]
Final work of University Undergraduate/Master Studies 47 pages, 9 figures, 2 tables, the Lithuanian language. Object of the research: barley (Hordeum vulgare L.) spring variety Simba'' agrocenoses. Aim of the research: to evaluate the long-term effect of different soil tillage intensity on barley agrocenosis applying intensive technologies. Objectives of the research: 1. Review of the literature and perform a systematic analysis of the relevant issue. 2. Describe an experiment carried out with the conditions and methods. 3. Studies to identify and evaluate the long-term differences in the intensity of tillage effects on structural stability, barley germination, weed infestation and barley productivity. Research methods: review of scientific literature logical analysis and synthesis, statistical analysis, comparative analysis, graphical modelling techniques. Research results: • Part One presents Lithuanian and foreign scientific literature. Scientific material selected, structured and analysed. • Part Two describe the focus is on testing scheme and the parameters of the scientific variants of the experiment and data analysis methods and observations. • Part Three identifies the soil structure stability, barley germination and stem productivity of barley harvest, weed and barley crop productivity. It was established, that tillage intensity had no significant effect on soil aggregate stability and on barley productivity parameters except the number of germinating barley... [to full text]
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Babin, Courtney H. "Size-dependent patterns of reproductive investment in the North American invasive plant species Triadica sebifera (L.) Small (Euphorbiaceae)." ScholarWorks@UNO, 2017. http://scholarworks.uno.edu/td/2295.

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Knowledge of sex allocation trade-offs with tree growth in insect-pollinated woody plants is limited, particularly in invasive plants. This study examined patterns of growth and reproductive investment in a North American invasive plant species, Triadica sebifera, I hypothesized that the energy limitations of smaller trees may result in the production of more male reproductive structures that are energetically less costly. Diameter at breast height was a significant predictor of seed and catkin mass and regression can describe these relationships across sites. Seed and catkin mass were positively correlated across sites. The relationship between the seed mass:catkin mass ratio and DBH was not significant, nor was seed mass:catkin mass and total investment. Results showed a significant positive relationship between total reproductive investment and tree size across sites. Seed mass:catkin mass ratio and reproduction investment showed substantial variation among individual trees of similar size within sites.
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Lucero, Jacob Elias. "Cheatgrass (Bromus tectorum), Native Grasses, and Small Mammals in the Great Basin: a Test of the Apparent Competition Hypothesis Facilitated by a Novel Method of Decanting Seeds from a Flotation Solution." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3405.

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The effect of shared enemies between invasive and native species has been argued to facilitate biological invasions (i.e., the apparent competition hypothesis or ACH). This study investigated a previously untested possibility: whether granivorous small mammals facilitate cheatgrass (Bromus tectorum) invasion by driving food-mediated apparent competition between cheatgrass and native grasses. Specifically, we tested three predictions that must be true if such apparent competition occurs. First, cheatgrass invasion augments total seeds available to granivorous small mammals. Second, density of granivorous small mammals increases in response to increased seed availability (simulated with experimental additions of cheatgrass seeds). Third, granivorous small mammals prefer seeds from native grasses over cheatgrass seeds. We tested these predictions in the Great Basin Desert of Utah, USA. Cheatgrass invasion augmented total yearly seed production. Granivorous small mammals preferred native seeds over cheatgrass seeds. However, neither abundance, richness, nor diversity of granivorous small mammals increased in response to experimental additions of cheatgrass seed. We therefore conclude that granivorous small mammals did not drive food-mediated apparent competition during the study period. The lack of support for the ACH in this study may suggest that the role of small mammal-driven apparent competition is either unimportant in the Great Basin, or that the appropriate indirect interactions between small mammals, cheatgrass, and native grasses have yet to be evaluated. Testing the third prediction required the separation of seeds from the soil matrix. We employed a chemical flotation methodology to recover target seeds from soil, and developed a novel method of decanting target material from the flotation solution. We compared the utility of the novel method to that of a traditional decantation method. Specifically, we compared effectiveness (the proportion of seeds recovered from a known sample), rapidity (the time required to decant that sample), efficiency (the number of seeds decanted per second), and recovery bias (the effect of relative density on seed recovery) between methods. Our proposed method was more effective, more rapid, more efficient, and less biased than the traditional method. Therefore, any future work relying on flotation to analyze seed banks should clearly describe how samples are decanted and should consider the proposed method as a potential means of enhancing the efficiency of chemical flotation.
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Books on the topic "Weed invasion"

1

M, Randall John, Marinelli Janet, and Brooklyn Botanic Garden, eds. Invasive plants: Weeds of the global garden. Brooklyn, NY: Brooklyn Botanic Garden, 1996.

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Westbrooks, Randy G. Invasive plants: Changing the landscape of America : fact book. Washington, D.C: Federal Interagency Committee for the Management of Noxious and Exotic Weeds, 1998.

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Westbrooks, Randy G. Invasive plants: Changing the landscape of America : fact book. Washington, D.C: Federal Interagency Committee for the Management of Noxious and Exotic Weeds, 1998.

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Westbrooks, Randy G. Invasive plants: Changing the landscape of America : fact book. Washington, D.C: Federal Interagency Committee for the Management of Noxious and Exotic Weeds, 1998.

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Westbrooks, Randy G. Invasive plants: Changing the landscape of America : fact book. Washington, D.C: Federal Interagency Committee for the Management of Noxious and Exotic Weeds, 1998.

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Westbrooks, Randy G. Invasive plants: Changing the landscape of America : fact book. Washington, D.C: Federal Interagency Committee for the Management of Noxious and Exotic Weeds, 1998.

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Williams, P. A. A weed risk assessment system for new conservation weeds in New Zealand. Wellington, N.Z: Dept. of Conservation, 2002.

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Inderjit, ed. Management of Invasive Weeds. Dordrecht: Springer Netherlands, 2009. http://dx.doi.org/10.1007/978-1-4020-9202-2.

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1963-, Inderjit, and SpringerLink (Online service), eds. Management of Invasive Weeds. Dordrecht: Springer Netherlands, 2009.

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Lesley, Henderson. Alien weeds and invasive plants: A complete guide to declared weeds and invaders in South Africa, including another 36 species invasive in that region. Pretoria: Plant Protection Research Institute, 2001.

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Book chapters on the topic "Weed invasion"

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Bohren, Christian. "Invasive Plants." In Weed Research, 271–312. Chichester, UK: John Wiley & Sons, Ltd, 2017. http://dx.doi.org/10.1002/9781119380702.ch10.

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Mashhadi, Hamid R., and Steven R. Radosevich. "Invasive Plants." In Weed Biology and Management, 1–28. Dordrecht: Springer Netherlands, 2004. http://dx.doi.org/10.1007/978-94-017-0552-3_1.

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Xing, Bo, and Wen-Jing Gao. "Invasive Weed Optimization Algorithm." In Innovative Computational Intelligence: A Rough Guide to 134 Clever Algorithms, 177–81. Cham: Springer International Publishing, 2013. http://dx.doi.org/10.1007/978-3-319-03404-1_13.

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Booth, Barbara D., Stephen D. Murphy, and Clarence J. Swanton. "Invasive Ecology of Weeds in Agricultural Systems." In Weed Biology and Management, 29–45. Dordrecht: Springer Netherlands, 2004. http://dx.doi.org/10.1007/978-94-017-0552-3_2.

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Yang, Guoqing, Furong Gui, Wanxue Liu, and Fanghao Wan. "Crofton Weed Ageratina adenophora (Sprengel)." In Biological Invasions and Its Management in China, 111–29. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-3427-5_8.

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Simberloff, Daniel. "A Future Planet of Weeds?" In Global Plant Invasions, 361–73. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-89684-3_17.

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Rees, Paul A. "Pest, weed and disease management." In Key questions in applied ecology and conservation: a study and revision guide, 90–105. Wallingford: CABI, 2021. http://dx.doi.org/10.1079/9781789248494.0090.

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Abstract This chapter contains questions about pests and weeds and their control, invasive species, parasites, and animal and plant diseases. The questions are arranged by topic and divided into three levels: foundation, intermediate and advanced.
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Shi, Mengzhu, and Jianwei Fu. "Alligator Weed Alternanthera philoxeroides (Mart.) Griseb." In Biological Invasions and Its Management in China, 163–73. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-3427-5_12.

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O'Keeffe, Catherina M., Gary W. Stutte, and Michelle McKeon-Bennett. "Ragwort: Invasive Weed and Potential Pharmaceutical." In Horticultural Reviews: Volume 43, 145–84. Hoboken, New Jersey: John Wiley & Sons, Inc., 2015. http://dx.doi.org/10.1002/9781119107781.ch03.

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Kumar, Dilip, B. G. Rajeev Gandhi, and Rajib Kumar Bhattacharjya. "Introduction to Invasive Weed Optimization Method." In Nature-Inspired Methods for Metaheuristics Optimization, 203–14. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-26458-1_12.

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Conference papers on the topic "Weed invasion"

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Veenhuis, C. "Binary Invasive Weed Optimization." In 2010 Second World Congress on Nature and Biologically Inspired Computing (NaBIC 2010). IEEE, 2010. http://dx.doi.org/10.1109/nabic.2010.5716311.

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Affolter, K., D. Schweizer, T. Hanne, and R. Dornberger. "Index Tracking with Invasive Weed Optimization." In 2014 International Conference on Soft Computing & Machine Intelligence (ISCMI). IEEE, 2014. http://dx.doi.org/10.1109/iscmi.2014.9.

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Ren, Zhigang, Wen Chen, Aimin Zhang, and Chao Zhang. "Enhancing invasive weed optimization with taboo strategy." In Proceeding of the fifteenth annual conference companion. New York, New York, USA: ACM Press, 2013. http://dx.doi.org/10.1145/2464576.2466815.

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Nath, Subhrapratim, Avik Kumar Chakravarty, Subinoy Ghosh, and Subir Kumar Sarkar. "Invasive weed optimization approach to VLSI routing." In 2017 Devices for Integrated Circuit (DevIC). IEEE, 2017. http://dx.doi.org/10.1109/devic.2017.8074024.

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Pappula, Lakshman, and Debalina Ghosh. "Large array synthesis using Invasive Weed Optimization." In 2013 International Conference on Microwave and Photonics (ICMAP). IEEE, 2013. http://dx.doi.org/10.1109/icmap.2013.6733486.

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Xuncai Zhang, Ying Niu, Guangzhao Cui, and Yanfeng Wang. "A modified invasive weed optimization with crossover operation." In 2010 8th World Congress on Intelligent Control and Automation (WCICA 2010). IEEE, 2010. http://dx.doi.org/10.1109/wcica.2010.5553805.

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Guo, Qian, Yanpeng Qu, and Ansheng Deng. "Invasive weed optimisation inspired fuzzy-rough feature selection." In 2016 IEEE International Conference on Fuzzy Systems (FUZZ-IEEE). IEEE, 2016. http://dx.doi.org/10.1109/fuzz-ieee.2016.7737929.

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Ruochen Liu, Xiao Wang, Yangyang Li, and Xiangrong Zhang. "Multi-objective Invasive Weed Optimization algortihm for clustering." In 2012 IEEE Congress on Evolutionary Computation (CEC). IEEE, 2012. http://dx.doi.org/10.1109/cec.2012.6256540.

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Ren, Zhigang, Shanshan Huang, Chenlin Sun, and Yongsheng Liang. "Improved invasive weed optimization based on clustering strategy." In 2016 Chinese Control and Decision Conference (CCDC). IEEE, 2016. http://dx.doi.org/10.1109/ccdc.2016.7531853.

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Nagib, M. M., Mahmoud M. Othman, Adel A. Naiem, and Y. G. Hegazy. "Invasive weed optimization algorithm for solving economic load dispatch." In 2016 IEEE 16th International Conference on Environment and Electrical Engineering (EEEIC). IEEE, 2016. http://dx.doi.org/10.1109/eeeic.2016.7555491.

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Reports on the topic "Weed invasion"

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Wilsey, Brian J., and Andrea Blong. Native Cover Crops: Effects on Weed Invasion and Prairie Establishment. Ames: Iowa State University, Digital Repository, 2006. http://dx.doi.org/10.31274/farmprogressreports-180814-2794.

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Wilsey, Brian J., and Andrea Blong. Native Cover Crops: Effects on Weed Invasion and Prairie Establishment. Ames: Iowa State University, Digital Repository, 2007. http://dx.doi.org/10.31274/farmprogressreports-180814-610.

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Wilsey, Brian J., and Andrea Blong. Native Cover Crops: Effects on Weed Invasion and Prairie Establishment. Ames: Iowa State University, Digital Repository, 2007. http://dx.doi.org/10.31274/farmprogressreports-180814-711.

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Wilsey, Brian J., and David Losure. Plant Species Effects on Diversity and Weed Invasion Resistance in Restored Grasslands. Ames: Iowa State University, Digital Repository, 2005. http://dx.doi.org/10.31274/farmprogressreports-180814-2558.

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Wilsey, Brian J., and David Losure. Plant Species Effects on Diversity and Weed Invasion Resistance in Restored Grasslands. Ames: Iowa State University, Digital Repository, 2006. http://dx.doi.org/10.31274/farmprogressreports-180814-710.

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Wilsey, Brian J., and Andrea Blong. Native Cover Crops and Timing of Planting: Effects on Weed Invasion and Prairie Establishment. Ames: Iowa State University, Digital Repository, 2008. http://dx.doi.org/10.31274/farmprogressreports-180814-2414.

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Hardy, Susan E., and Antonio J. Palazzo. Report on the Workshop on New Grass Germplasms and Invasive Weed Control. Fort Belvoir, VA: Defense Technical Information Center, October 2002. http://dx.doi.org/10.21236/ada408310.

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Large, M., and L. Farrington. The Nephrolepis Boston fern complex (including Nephrolepis exaltata [L.] Schott), Nephrolepidaceae, naturalised in New Zealand. Unitec ePress, December 2016. http://dx.doi.org/10.34074/pibs.rs22016.

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Nephrolepis cordifolia (ladder fern) is widely recorded as an invasive weed, and is naturalised in New Zealand. The first records of this plant being wild date from the 1970s. The presence of other native species of Nephrolepis (in particular N. flexuosa Colenso) potentially complicates the recognition of the naturalised species. However, N. cordifolia has been easily distinguished by the presence of ‘bulbils’ or ‘tubers’ that appear along wire-like runners. In this paper we report the presence of the Boston fern complex (including N. exaltata) now apparently wild in the Auckland region. This aggregate is without bulbils and may superficially be confused with the other native and non-native species.
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Harms, Nathan, Judy Shearer, James Cronin, and John Gaskin. Geographic and genetic variation in susceptibility of Butomus umbellatus to foliar fungal pathogens. Engineer Research and Development Center (U.S.), August 2021. http://dx.doi.org/10.21079/11681/41662.

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Large-scale patterns of plant invasions may reflect regional heterogeneity in biotic and abiotic factors and genetic variation within and between invading populations. Having information on how effects of biotic resistance vary spatially can be especially important when implementing biological control because introduced agents may have different Impacts through interactions with host-plant genotype, local environment, or other novel enemies. We conducted a series of field surveys and laboratory studies to determine whether there was evidence of biotic resistance, as foliar fungal pathogens, in two introduced genotypes (triploid G1, diploid G4) of the Eurasian wetland weed, Butomus umbellatus L. in the USA. We tested whether genotypes differed in disease attack and whether spatial patterns in disease incidence were related to geographic location or climate for either genotype. After accounting for location (latitude, climate), G1 plants had lower disease incidence than G4 plants in the field (38% vs. 70%) but similar pathogen richness. In contrast, bioassays revealed G1 plants consistently received a higher damage score and had larger leaf lesions regardless of pathogen. These results demonstrate that two widespread B. umbellatus genotypes exhibit different susceptibility to pathogens and effectiveness of pathogen biological controls may depend on local conditions.
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Wideman, Jr., Robert F., Nicholas B. Anthony, Avigdor Cahaner, Alan Shlosberg, Michel Bellaiche, and William B. Roush. Integrated Approach to Evaluating Inherited Predictors of Resistance to Pulmonary Hypertension Syndrome (Ascites) in Fast Growing Broiler Chickens. United States Department of Agriculture, December 2000. http://dx.doi.org/10.32747/2000.7575287.bard.

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Background PHS (pulmonary hypertension syndrome, ascites syndrome) is a serious cause of loss in the broiler industry, and is a prime example of an undesirable side effect of successful genetic development that may be deleteriously manifested by factors in the environment of growing broilers. Basically, continuous and pinpointed selection for rapid growth in broilers has led to higher oxygen demand and consequently to more frequent manifestation of an inherent potential cardiopulmonary incapability to sufficiently oxygenate the arterial blood. The multifaceted causes and modifiers of PHS make research into finding solutions to the syndrome a complex and multi threaded challenge. This research used several directions to better understand the development of PHS and to probe possible means of achieving a goal of monitoring and increasing resistance to the syndrome. Research Objectives (1) To evaluate the growth dynamics of individuals within breeding stocks and their correlation with individual susceptibility or resistance to PHS; (2) To compile data on diagnostic indices found in this work to be predictive for PHS, during exposure to experimental protocols known to trigger PHS; (3) To conduct detailed physiological evaluations of cardiopulmonary function in broilers; (4) To compile data on growth dynamics and other diagnostic indices in existing lines selected for susceptibility or resistance to PHS; (5) To integrate growth dynamics and other diagnostic data within appropriate statistical procedures to provide geneticists with predictive indices that characterize resistance or susceptibility to PHS. Revisions In the first year, the US team acquired the costly Peckode weigh platform / individual bird I.D. system that was to provide the continuous (several times each day), automated weighing of birds, for a comprehensive monitoring of growth dynamics. However, data generated were found to be inaccurate and irreproducible, so making its use implausible. Henceforth, weighing was manual, this highly labor intensive work precluding some of the original objectives of using such a strategy of growth dynamics in selection procedures involving thousands of birds. Major conclusions, solutions, achievements 1. Healthy broilers were found to have greater oscillations in growth velocity and acceleration than PHS susceptible birds. This proved the scientific validity of our original hypothesis that such differences occur. 2. Growth rate in the first week is higher in PHS-susceptible than in PHS-resistant chicks. Artificial neural network accurately distinguished differences between the two groups based on growth patterns in this period. 3. In the US, the unilateral pulmonary occlusion technique was used in collaboration with a major broiler breeding company to create a commercial broiler line that is highly resistant to PHS induced by fast growth and low ambient temperatures. 4. In Israel, lines were obtained by genetic selection on PHS mortality after cold exposure in a dam-line population comprising of 85 sire families. The wide range of PHS incidence per family (0-50%), high heritability (about 0.6), and the results in cold challenged progeny, suggested a highly effective and relatively easy means for selection for PHS resistance 5. The best minimally-invasive diagnostic indices for prediction of PHS resistance were found to be oximetry, hematocrit values, heart rate and electrocardiographic (ECG) lead II waves. Some differences in results were found between the US and Israeli teams, probably reflecting genetic differences in the broiler strains used in the two countries. For instance the US team found the S wave amplitude to predict PHS susceptibility well, whereas the Israeli team found the P wave amplitude to be a better valid predictor. 6. Comprehensive physiological studies further increased knowledge on the development of PHS cardiopulmonary characteristics of pre-ascitic birds, pulmonary arterial wedge pressures, hypotension/kidney response, pulmonary hemodynamic responses to vasoactive mediators were all examined in depth. Implications, scientific and agricultural Substantial progress has been made in understanding the genetic and environmental factors involved in PHS, and their interaction. The two teams each successfully developed different selection programs, by surgical means and by divergent selection under cold challenge. Monitoring of the progress and success of the programs was done be using the in-depth estimations that this research engendered on the reliability and value of non-invasive predictive parameters. These findings helped corroborate the validity of practical means to improve PHT resistance by research-based programs of selection.
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