Browsing by Subject "Habitat fragmentation"
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Item Effects of anthropogenic habitat fragmentation on silvery brown tamarin (Saguinus leucopus) dispersal and movement patterns : landscape genetics, habitat connectivity and conservation implications(2018-05) Valencia Rodríguez, Lina María; Di Fiore, Anthony, Ph. D.; Bolnick, Deborah; Reed, Denne; Jha, Shalene; Blair, Mary EHabitat fragmentation can restrict the dispersal of individuals from one population to another, which often results in the loss of genetic diversity due to reduced gene flow, inbreeding, and genetic drift. The stability and long-term survival of animal populations in fragmented landscapes largely depends on their ability to disperse among patches. The main goal of this dissertation is to evaluate how human-modified heterogeneous landscapes impact population structure, dispersal, and gene flow of the silvery brown tamarin (Saguinus leucopus), an endangered and endemic primate of Colombia. In this study I use a multidisciplinary approach and combine genomic data with spatial analysis and ecological modeling to determine how anthropogenic and natural landscape features shape tamarin genetic variation. I describe a cost-effective reduced representation method called ddRAD-seq developed to identify and genotype large numbers of genome-wide SNP loci for taxa from across the New World monkeys. I test the utility of this approach to resolve platyrrhine evolutionary relationships at different time scales and discuss the protocol's promise in molecular primatology. Using this method, I investigate population structure across the S. leucopus distribution. Using traditional and novel population genetic approaches, I detect population structure between geographic regions at different hierarchical levels and find population structure to be associated with geographic distance. In addition, using individual-based landscape genetic analyses in combination with spatial and ecological modeling, I also found that anthropogenic and natural landscape features - beyond simple Euclidean distance - have an effect on the genetic relationships and population structure of the silvery brown tamarin. Remnants of secondary forest in an agricultural matrix and water bodies represent moderate barriers to tamarin gene flow and have a significant effect on genetic relationships and population structure of the silvery brown tamarin. Lastly, I assess structural and functional connectivity throughout the silvery brown tamarin's distribution using least-cost paths and circuit theory. I identify potential patches of tamarin habitat and prioritize patches and corridors important in maintaining landscape connectivity. I discuss the conservation implications of these results and offer recommendations and management guidelines for conservation authorities regarding the conservation and management of S. leucopus populations in a human-dominated landscape.Item The effects of habitat fragmentation on the diversity of nekton inhabiting subtropical seagrass meadows(2011-05) Hensgen, Geoffrey Michael; Holt, G. Joan; Munguia, Pablo; Ojanguren, Alfredo F.; Stunz, Gregory W.Habitat fragmentation is often regarded as a biodiversity threat associated with habitat degradation; however, research has also revealed beneficial effects on biodiversity as well, depending on the ecosystem and species community. This study examined the biodiversity of small nekton residing in seagrass meadows characterized by three levels of habitat fragmentation, and as a habitat gradient comprised of measures such as habitat amount, connectivity, patch shape, and proximity. Landscapes were mapped using recent advances in GPS and GIS technology, and analyzed using established methods from research in terrestrial ecosystems. Species richness was not significantly different as a function of fragmentation regardless of season, suggesting that the amount of habitat and configuration of several patches in fragmented habitats is sufficient to support comparable numbers of species in several patches compared to communities in large, continuous seagrass meadows. Species evenness declined significantly in fragmented habitats versus continuous ones in both seasons. Within fragmented landscapes, evenness progressively declined as habitat amount and connectivity decreased and patch isolation and density increased, suggesting that changes in landscape qualities can differentially impact processes supporting metapopulations such as dispersal and reproduction in certain species, thereby influencing community structure. Analyses that included measures of habitat connectivity, proximity, and patch density in addition to habitat amount accounted for more variability in species evenness than those just containing percent cover, and showed that fragmentation’s impacts can differ geographically. These data suggest that community resilience to fragmentation can differ between similar animal communities residing in separate locations, and that landscape configuration plays an important role in determining how communities respond to fragmentation after a threshold of change in habitat amount has been exceeded.Item The effects of habitat loss and fragmentation caused by woody plant encroachment on native plant diversity and on an invasive grass(2010-05) Alofs, Karen Marie; Fowler, Norma L.; Leibold, Mathew; Parmesan, Camille; Keitt, Timothy; Young, KennethHabitat loss, habitat fragmentation and species invasions have been recognized as three of the leading threats to biodiversity. I examined the effects of habitat loss and fragmentation on native and invasive plants in central Texas. During the last century, the density and abundance of woody plants has been increasing in the savannas of eastern Edwards Plateau. This process, known as woody plant encroachment, not only reduces the amount of open herbaceous habitat but also fragments that habitat creating smaller and more isolated patches. In three studies, I investigated the consequences of this habitat loss and fragmentation for plants which do not occur under the cover of woody plants including native grasses and forbs and the invasive Eurasian bunchgrass, Bothriochloa ischaemum (King Ranch Bluestem). In the first study, I show that woody plant encroachment reduces native herbaceous species richness (the number of species in a given area). Using a collection of historical aerial photographs, I demonstrate that current native herbaceous species richness was most strongly related to recent habitat amount, but to the degree of habitat fragmentation at least 50 years ago. In a second study, I show that the presence of B. ischaemum was negatively related to the degree of fragmentation in the surrounding landscape. Finally, I found that B. ischaemum had higher rates of germination and growth in experimental plots where the species commonly lost with woody plant encroachment were removed than in unmanipulated control plots. Together, this work suggests that woody plant encroachment is directly slowing the spread of an invasive species while indirectly facilitating its establishment.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 What defines an edge? : quantifying edge effects across multiple trophic levels(2020-08-14) Estrada, Jenelle Marie; Erdner, Deana L.Habitat fragmentation is often cited as a primary driver of biodiversity loss across biomes. Spatial habitat fragmentation causes an increase in edge habitat relative to interior which may provide different value as they often vary in functionality. There is a general lack of consensus regarding the distance that delineates edge versus interior limiting the ability to accurately capture edge effects on seagrass ecological function. As fragmentation is accelerating, it is necessary to understand the factors driving edge effects to better predict the effect of changes in habitat configuration. My work measured community metrics in seagrass ecosystems at varying distances from the edge to understand edge effects driving organismal response to habitat fragmentation. First, I sampled seagrass beds in 2018 for a post-disturbance study one year after Hurricane Harvey hit Texas. I sampled along seagrass patch edges and interior to quantify seagrass morphometrics and biomass, benthic macrofauna and nekton communities. Next, I conducted a fine-scale study in 2019 sampling seagrass beds along 10 meter transects from the edge in towards bed interiors in the same region to quantify nekton and macrofaunal communities, seagrass metrics, predation risk, and flow at a precise scale. Across both studies, I found increased seagrass biomass in habitat interiors that was most pronounced around 2 meters in one study. I saw higher temperature and epiphyte biomass with increased distance from seagrass edge in the fine-scale study and across studies there were no demonstrated edge effects on benthic macrofaunal community composition, predation risk or flow. There was a positive effect on nekton diversity in the post-disturbance study driven by matrix spillover of species associated with soft muddy bottoms. Results suggest pronounced edge effect for seagrass itself, and ecologically defined edges may be larger than the edge sizes assumed in many past studies highlighting the need for edge designations to be scaled to the response variables tested in order to accurately capture edge effects. Multi-trophic and continued empirical measurement of habitat edges may help resolve differential responses across studies and predict the effects of anthropogenic habitat fragmentation on the ecological function of critical nearshore habitat like seagrass