Date of Award

5-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Nathan J. Sanders

Committee Members

James Fordyce, William Hargrove, Daniel Simberloff

Abstract

Species distribution models are increasingly being applied to questions in ecology, biogeography and evolution, and in particular to the problem of predicting the potential spread of invasive species and the potential impacts of climatic change on biodiversity. However, despite their broad application, several conceptual limitations still preclude the use of species distribution models in many theoretical and practical applications. Chief among these is the assumption that climate alone determines the geographic ranges of species, as opposed to biotic interactions and dispersal limitations, and that such species-climate relationships remain largely unchanged across space and time. In this context, I explore the degree to which climate constrains the distributions of species and how such relationships change during biological invasions and under climate change. I first examine whether species-climate relationships are conserved during the invasion of the red imported fire ant (Solenopsis invicta) and find evidence, in contrast to model assumptions, that invasive species can undergo rapid niche shifts during invasive spread and that this result is robust to variable selection. Next, I explore the degree to which migration constraints may limit the ability of Banksia (Proteaceae) species endemic to southwestern Australia to respond to climate change. I find that migration constraints may not represent a major factor in determining future patterns of biodiversity in this region as ranges of most species were projected to collapse rather than shift and that this result was consistent across different scenarios of future climate. Finally, I investigate the relative importance of dispersal limitation (as implied by seed dispersal mode) and contemporary climate in determining of patterns of biodiversity for 2543 species of plants in southwestern Australia. In contrast to the predicted relationship, I find that the distributions of dispersal-limited species were less constrained by dispersal and more constrained by climate than the distributions of ostensibly more vagile species. Taken together, these studies suggest, in strong contrast with model assumptions, that species climate-relationships can change, sometimes rapidly, under environmental change such that future patterns of biodiversity and biological invasions may not be readily predictable from current distributions of species.

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