Browsing by Subject "Community ecology"
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Item Biogeography of upland bird communities in the Peruvian Amazon(2009-12) Pomara, Lazarus Yates; Young, Kenneth R.; Barth, Robert H.; Dull, Robert A.; Miller, Jennifer A.; Ruokolainen, KalleThe western Amazon is known to be one of the most biologically diverse regions in the world, yet information about the spatial distribution of that biodiversity and the processes governing its distribution remains scarce. An improved understanding of those biogeographic patterns and processes can inform conservation and development planning in areas where anthropogenic landscape change is ongoing. Spatial components of biodiversity are known to be influenced by historical and present-day physical and human geographic processes. There is evidence that major Amazonian rivers form the boundaries of biological regions, at least for birds. Other factors that may influence bird species composition include the dispersal limitations of individual species, forest plant species composition and structure, topography, forest fragmentation, and hunting. Sites where bird species composition was measured in this study represented mature, upland forest on both sides of the Amazon River, and a range of non-flooded forest types, as indicated by soil and plant surveys. Bird species compositional variation was closely correlated with variation in plant species composition, human disturbance associated with forest fragmentation, and position north or south of the Amazon River. The strongest differences were between opposite sides of the river, even though local environments, including plant composition, were not different on the two sides. This strongly suggests that historical biogeographic factors, rather than present-day environmental gradients, are responsible for bioregional boundaries at Amazonian rivers. The difference between plant and bird distributions at this scale underscores the pressing need to re-evaluate general notions of bioregional complexity and pattern in the Amazon basin. Locally, the influence of habitat fragmentation on animal communities, including reduced species richness, was confirmed. The influence of local floristic variation is of particular importance due to its ubiquity across western Amazonia. Thus, understanding the distributions of soils and vegetation is critical for explaining Amazonian animal diversity. The use of these factors to model bird community heterogeneity contradicts assumptions that the processes shaping Amazonian animal community diversity are too complex to measure efficiently, and their use contributes a new understanding of the dimensions of that diversity.Item Brazilian central Cerrado lizards in introduced Eucalyptus plantations : human mediated habitat disturbance effects from community diversity to population divergence(2012-05) Gainsbury, Alison Melissa; Pianka, Eric R.; Hillis, David M.; Bell, Christopher J.; Simpson, Beryl B.; Bolnick, Daniel I.Approximately two thirds of the world’s land is directly supporting human population contributing to an accumulation of disturbed habitats. This dissertation investigates the impact of human mediated habitat disturbance, in introduced Eucalyptus plantations, on community diversity and population divergence using Brazilian Cerrado lizards as a model. Data was collected along a gradient from undisturbed cerrado to disturbed Eucalyptus plantations. Community diversity differences and indicator species were identified. Furthermore, the role of phenotypic divergences were determined based on populations able to persist in disturbed habitats. Dispersal, food availability (body condition), competition and predation (caudal autotomy) were tested as potential mechanisms driving phenotypic divergences. Additionally, I investigated phylogenetic community structure differences between habitats to test for a phylogenetic signal to disturbance. The evidence showed community diversity indices were significantly lower in Eucalyptus plantations with a decrease along the cerrado– Eucalyptus gradient. Furthermore, 29 % of the Cerrado species suffered local extinctions in the disturbed habitat and of these 80 % are endemic species. One indicator species was identified for the disturbed habitat and seven species were identified for the undisturbed habitat. Species able to persist in both habitats demonstrated morphological trait divergences. These species showed short dispersal distances with only two individuals dispersing between habitats indicating a mechanism driving the observed phenotypic divergences. Another mechanism is body condition, which was higher in the disturbed habitats, reflecting increased food availability possibly due to the decreased abundances. Caudal autotomy showed no difference between the habitats indicating that competition and predation are not driving phenotypic divergences. Phylogenetic community structure demonstrated a phylogenetic signal to disturbance. The undisturbed habitat consists of communities with more closely related species compared to the disturbed habitat: indicating evolutionary forces such as habitat filtering as the stronger process structuring these communities. Whereas, disturbed communities are structured by ecological forces such as competition. This research provides information for the preservation and maintenance of the Cerrado biodiversity and has an even broader impact since habitat change caused by human activities touches a plethora of ecosystems.Item Competition across space : from metacommunities to social body-snatching trematodes(2019-09-13) Resetarits, Emlyn Jane; Jha, Shalene; Bolnick, Daniel; Farrior, Caroline E; Leibold, Mathew A; Mueller, Ulrich GThis dissertation is composed of two sections. The first section focuses on experimentally testing the keystone community concept using protist microcosms. I found that habitat loss can cause structural changes in how communities are assembled, even when diversity measures appear unchanged. This work has important implications for reserves management and conservation efforts. The second section is composed of three chapters on social body-snatching trematodes residing in the California horn snail. First, I investigated the tradeoff between reproduction and defense to determine if social trematode colonies increase their soldier investment in areas of high intraguild predation (IGP). I found that colonies appear to respond to IGP as predicted and do so at the site-level. Second, I conducted a reciprocal transplant experiment to determine if differences in soldier investment are due to phenotypic plasticity. Unfortunately, our results were inconclusive but provided us with valuable information on natural variation in these colonies within an estuary. Finally, I investigated how individual soldier attributes and colony composition might explain a linear competitive dominance hierarchy between six species of social body-snatching trematodes. I found that the dominance hierarchy was not explained by attributes of the colony that we measured. All totaled, there are over 20,000 trematode species, in league with the diversity of social insect groups, like ants. The trematode system is rich with opportunity to study the evolution and ecology of sociality outside of insects.Item Dispersal evolution in a community context(2019-06-25) Subramaniam, Shankari; Farrior, Caroline E.Ecologists have long been interested in the consequences of dispersal for species interactions, trait evolution, and community coexistence. Less is known, however, about the impact of community structure or species interactions on the evolution of dispersal. In this report, I highlight recent research that has addressed this question and discuss how species interactions such as predation and parasitism affect dispersal evolution. Some noteworthy results include the selection on greater host dispersal as parasite search efficiency increases; the reversal on selection for dispersal in host individuals when a third trophic level is considered; novel mechanisms such as maternal provisioning that mediate the trade-off between competition and dispersal in plants. I also discuss how predictions for the evolution of dispersal change when multiple species are considered simultaneously. In a world where habitat fragmentation and climate change are increasing the pressure on species to move towards more favorable habitats, a better understanding of how dispersal is likely to evolve will help us predict range shifts and the future of communities in a more precise manner.Item Evolution of Competitive Ability: An Adaptation Speed vs. Accuracy Tradeoff Rooted in Gene Network Size(Public Library of Science, 2011-04-25) Malcom, Jacob W.Ecologists have increasingly come to understand that evolutionary change on short time-scales can alter ecological dynamics (and vice-versa), and this idea is being incorporated into community ecology research programs. Previous research has suggested that the size and topology of the gene network underlying a quantitative trait should constrain or facilitate adaptation and thereby alter population dynamics. Here, I consider a scenario in which two species with different genetic architectures compete and evolve in fluctuating environments. An important trade-off emerges between adaptive accuracy and adaptive speed, driven by the size of the gene network underlying the ecologically-critical trait and the rate of environmental change. Smaller, scale-free networks confer a competitive advantage in rapidly-changing environments, but larger networks permit increased adaptive accuracy when environmental change is sufficiently slow to allow a species time to adapt. As the differences in network characteristics increase, the time-to-resolution of competition decreases. These results augment and refine previous conclusions about the ecological implications of the genetic architecture of quantitative traits, emphasizing a role of adaptive accuracy. Along with previous work, in particular that considering the role of gene network connectivity, these results provide a set of expectations for what we may observe as the field of ecological genomics develops.Item Multi-scalar drivers of native bee community composition and population genetic structure in human-altered landscapes(2019-02-11) Ballare, Kimberly Michelle; Jha, Shalene; Bolnick, Daniel; Farrior, Caroline; Keitt, Timothy; Young, KennethOne of the most well-documented ecological impacts of human-caused landscape change is the fragmentation of natural habitats by human infrastructure, with potential implications for 1) community composition, and 2) species-level gene flow patterns. By including quantifiable measurements of local habitat composition, regional land-use, and the composition of the landscape matrix in ecological studies, we can better understand how multi-scalar environmental factors drive changes in wildlife community composition and dispersal processes, and infer subsequent consequences for ecosystem functions and services across human-altered landscapes. Pollination is a critical ecosystem service driven in part by wildlife community composition and dispersal processes, but despite the importance of bee pollination for ecosystem function, very little is known about how land-use drives native bee community composition and their population gene-flow patterns. This research addresses this literature gap by investigating native bee communities (Chapter 1) and native bee gene flow (Chapter 2) across heterogeneous human-altered landscapes in Texas, and proposes methods for expanding conservation genetic research of pollinators using curated bee specimens (Chapter 3). In Chapter 1, we conducted an extensive survey of bee communities across two urban landscape gradients in Austin and Dallas, Texas, USA comparing communities within agricultural and native grassland habitat types. In Chapter 2, we investigate the genetic structure and gene flow patterns of the native eastern carpenter bee, Xylocopa virginica across a 450 km corridor spanning multiple land-uses in Texas. In Chapter 3, we test the effects of sampling and curation methods on next-generation sequencing of three widespread North American native bee species. Our results indicate that the composition of regional land-use differentially impacts bee abundance and diversity depending on local habitat management and between bee functional groups, and that contemporary land-use as well as regional and fine-scale geographic distance influence the gene flow patterns of a large wood-nesting bee. Lastly, we find that sampling and storage method influence sequence assembly quality, and that curated and trapped specimens can be successfully utilized for next-generation sequencing research.Item Scale and process : primate and non-primate mammal community composition and diversity in Madagascar(2015-05) Bannar-Martin, Katherine Hilary; Lewis, Rebecca J., 1972-; Leibold, Mathew A; Reed, Denne N; Di Fiore, Anthony; Hopkins, Mariah EThe study of community assembly, or the processes that shape the occurrence of species in an ecological community, is a fundamental area of inquiry in ecology. Patterns in community composition and diversity are attributed to the combined operation of deterministic (e.g., environmental sorting), stochastic (e.g., dispersal limitation), and biogeographic (e.g., dispersal barriers) processes. Environmental sorting results in communities composed of species that are ecologically adapted to their environment. Dispersal limitation results in communities shaped by the dispersal distance between sites. Biogeographic dispersal barriers prevent species dispersal between sites, and community membership is dependent upon site isolation. Community assembly is also dependent upon diversity type (taxonomic, functional, or phylogenetic) and spatial scale. I investigated the processes shaping the diversity of primate and nonvolant mammal communities using taxonomic, functional and phylogenetic diversity measures and a spatially explicit modelling approach. I described mammal diversity patterns at ecoregional, regional, and inter-regional scales within and across Madagascar and Australia. I tested the relationship of mammal community diversity to environmental, spatial, and biogeographic variables, indicating deterministic, stochastic, and biogeographic processes, in Madagascar and Australia. First, I found that arboreal mammal communities in Madagascar were more dispersal-limited than terrestrial mammal communities. Second, a combination of environmental sorting and dispersal limitation best explained primate taxonomic and functional diversity. Third, I tested for convergent diversity and assembly patterns in Madagascar and Australia, due to similar biogeographic and evolutionary histories, and found non-convergent patterns. Overall, biogeographic dispersal barriers were weak predictors of mammal diversity in Madagascar and Australia. Phylogenetic and functional diversity measures were weakly correlated, and phylogenetic diversity provided models with weak explanatory power. Environmental and spatial variables indicating the combined operation of environmental sorting and dispersal limitation variably shaped the taxonomic and functional diversity of mammal communities in Madagascar and Australia. Mammal community diversity was regionally specific, shaped by the unique historical and landscape components of each region, including ecoregional effects and the extinction of sympatric species. Macroscale studies of diversity should carefully investigate the influence of spatial scale and regional factors that can result in varied assembly patterns and unique ecological communities, such as those present for the nonvolant mammals of Madagascar and Australia.Item Sex and social hierarchies affect populations across landscapes(2016-05) Shaw, Roger William; Leibold, Mathew A.; Bolnick, Daniel; Jha, Shalene; Keitt, Timothy; Rudolf, VolkerEcologists have long been interested in the factors that drive the species composition of ecological communities. I propose that variation within species, particularly in dispersal behavior, plays an underappreciated role, as it affects population distributions across landscapes. To study this in the field, I censused dragonflies in a north Texas metacommunity, differentiating between adult males, adult females, and larvae. I found that while adult males were not well-explained by any environmental or spatial variables, adult females and larvae were significantly explained by their environment. Therefore, considering variation within species (in this case, sex and life stage) can clarify our understanding of species distributions. This is one example of sex-biased dispersal, which is universal amongst animals. However, research has mostly been focused on its potential benefits, while its costs remain largely unexplored. I developed an individual-based simulation model, to see how populations with varying degrees of sex-biased dispersal were able to persist in the face of frequent disturbances. I found that increasing sex-biased dispersal made it difficult for individuals to find mating partners in suitable habitat, and so these populations did not persist very long, in comparison to populations with equal dispersal. These heavy costs may be alleviated by habitat selection or alternative mating systems, however these costs should remain in the discussion of understanding sex-biased dispersal. Even within males, there may be significant variation in social status and physical condition, which can then affect dispersal strategies; these differences could then produce unique signatures in the distributions of populations. I developed another individual-based simulation model, in which individuals were sensitive to crowds, to environment, to both, or to neither. In comparison to passive dispersal, I found that crowd-sensitive populations were disproportionately abundant in medium-quality patches. In contrast, environment- sensitive populations were scarce in these patches. This approach requires fine-scale environmental data, but may be easier to acquire than the fine-scale demographic data that would otherwise be required. Overall, considering variation between individuals, particularly in their dispersal behavior, can improve our understanding of species distributions.Item The ecology of amphibian-associated bacterial communities(2020-03-03) Correa Filho, Decio Tadeu; Matz, Mikhail V.; Leibold, Mathew A.; Bolnick, Daniel; Rodriguez, David; Ryan, Michael; Mueller, UlrichMulticellular organisms are habitat for a diverse bacterial community (microbiome) that can often be associated with host health and well-being. To better understand that relationship I explored several ecological aspects of the host-associated microbiomes using pre- and post-metamorphic amphibians. First, I investigated the relative roles of local selection (due to host species identity) and regional effects (due to water body identity) on the community structure of the gut microbiome of tadpoles. I found that each water body represents a relatively distinct species pool of bacteria available for community assembly, making the water body more important in shaping the microbiome of tadpoles than their species identity. I then showed that the gut microbiome of tadpoles is not homogeneous throughout its gut length as there are changes in composition, abundance, richness, and diversity from the anterior to the posterior parts of the gut. Moreover, the gut microbiome of the anterior portion is unstable, i.e., it is highly influenced by exposition to external bacteria, while the microbiome of the posterior gut has higher stability. The posterior part harbors the functional microbiome that helps tadpoles with digestion. In fact, I found that most of the essential amino acids in the tadpole tissue are derived from bacteria. I then manipulated their gut microbiome and diet and found that the composition of the microbiome can have profound impacts on the performance and fitness of the tadpole, as distinct microbiomes affect growth, development, and mortality of the host. Finally, as tadpoles metamorphose and leave the water, their microbiome is reshaped due to changes in conditions related to both the environment and the host. I tested and showed that closely related species of adult amphibians have a tendency to harbor similar skin microbiome, but the same signal was not found for their gut microbiome. In summary, I found that the gut of tadpoles harbor several distinct but connected microbiomes that vary in composition, diversity, and stability and that can profoundly affect the fitness of the host. Its composition is ultimately determined by the environmental bacteria tadpoles were exposed to. For adult amphibians, closely related species have more similar skin but not gut microbiome.Item Variation in diet and habitat resource use in desert adapted lizards in Western Australia(2011-08) Goodyear, Stephen Edward; Pianka, Eric R.; Fowler, Norma L.Impacts of ecological competition are reduced when organisms play different roles in their environment. More individuals can survive on varied but finite sets of resources when organisms eat different kinds of prey, live in different places, or are active at different times. Species within an assemblage of small fossorial snakes have ecologies that vary mostly by diet. Different species eat very different things. Species live in different habitats on sand ridges, but the differences are less dramatic than in diet. Disparity in resource use typically varies the most according to species, so that individuals of the same species are more similar to each other than they are to individuals of other species. However, variation exists in resource use within species over time and space. Wide variation exists in dietary resource use in four well-sampled species of comb-eared skinks. However, where species occur at the same study site there are clear distinctions in resource use between species despite the wide variation in diets observed between individuals of the same species. Additionally, strict ecological distances in diet between species are maintained during five censuses that were conducted over a 16-year period. These results illustrate the basic ecological principals of fundamental and realized niches. Here, individuals ate many different food items and species have the potential to overlap in diet but that overlap is reduced because of realized ecological boundaries between species within a single place and time, which result in decreased competition for resources.