Browsing by Subject "Spatial scale"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
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 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.