Year of Award


Document Type


Degree Type

Doctor of Philosophy (PhD)

Degree Name

Organismal Biology and Ecology

Department or School/College

Division of Biological Sciences

Committee Co-chair

Doug J. Emlen, Dean E. Pearson

Commitee Members

Ragan Callaway, Lisa Eby, John L. Maron, Art Woods


University of Montana


Introductions of exotic species commonly restructure native communities, but the mechanisms driving native species responses are poorly understood. Invasion biology has focused its research on the negative impacts of invaders, yet invaders can also have positive interactions. A holistic understanding of how biological invasions can have a full range of potential responses from negative to neutral to positive. Understanding the mechanics that underlie native species responses to invasions can help elucidate those factors structuring the native communities we see today. I used a combination of experimental and observational studies in the field and laboratory to determine the effects of spotted knapweed (Centaurea stoebe) invasion on native web spiders at the species and community levels while also testing key tenets of ecological and evolutionary theory.

I found that the invader trait of plant architecture could be linked to the native spider trait of web construction to explain differences in native web spider species’ population responses to C. stoebe invasion. Architectural changes associated with C. stoebe invasion favor irregular webspider populations over orb-weaver populations by providing greater release from substrate limitation. Phenotypic plasticity of web size and its relationship to fitness may also influence differences in species responses. The irregular web spider Dictyna exhibited substantial web size plasticity with larger webs linking to higher prey captures and increased reproduction, while the orb-weaving spider Aculepeira, demonstrated no plasticity in web size and showed no associated fitness benefits. Interestingly, the fitness benefits associated with web size plasticity in early stages of invasion do not persist into later stages of invasion. Plasticity was significantly reduced in later stage populations, suggesting selection for reduced web size plasticity due to increased competition for food. Lastly, I also found that C. stoebe invasion was associated with changes in host-parasitoid interactions between Dictyna and its egg sac parasitoid. Dictyna from invaded grasslands were much more likely to kill parasitoids, compared to individuals from uninvaded, native grasslands. The combination of these results show the diverse effects of invasion on native species and communities and also highlight the value in using biological invasions as natural experiments to study ecology and evolution.



© Copyright 2014 Jennifer Naomi Smith