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theses

As anthropogenic influences on biological communities increase around the world, understanding how community level processes interact to affect ecosystem functioning has become a critical area of current ecological research. Biological invasions are one of the major drivers in biodiversity losses on local scales. Where exotic species do not perform comparably to the native species that they replace, they can be expected to have important consequences for ecosystem functioning. The question of which traits contribute to improved invasion potential is still a major focus of the field of invasion biology. In the first chapter of my dissertation, I examined how exotic and native shrubby plant species found in New Jersey interact below ground to influence competitive interactions in a greenhouse experiment. I found that exotic plants did not uniformly outperform native plants for a contested patch of soil nitrogen, but instead the native Rubus allegheniensis and exotic R. phoenicolasius both grew to significantly larger size than other competing plants and reduced competitor growth by greater than 50 percent. These results indicate that while root competition appears to be important for these shrub species, exotic species do not routinely outcompete native ones, suggesting that root competition among shrubs may not be an important trait governing invasion success. To fully understand the consequences of biological invasions, we must also understand how biological invasions affect invaded communities over evolutionary time. The remaining chapters of my dissertation used laboratory microcosms to experimentally study how evolution among resident and invading species altered the consequences of biological invasions. In Chapter 2, I determined that evolution resulted in increased performance for one invader, Euplotes daidaleos, in an assemblage of protists and rotifers, while in a second assemblage, evolution resulted in the appearance of increased biotic resistance of resident species against an invader, Paramecium bursaria. Changes in performance of both resident and invading species also resulted in significant differences in community composition in both assemblages. In one assemblage, communities with evolved invaders were most similar in composition, while in the other assemblage, communities with evolved residents were most similar. In the third chapter of my dissertation, I examined how evolution altered the temporal variability in species abundances. I found that for E. daidaleos the pattern of temporal variability in abundance most closely matched predictions of evolution decreasing the attack rate of predators on E. daidaleos, implying that this invader may have evolved increased defense against predators that were resident species of the assemblage into which it invaded. Several resident species in this community experienced decreased abundances concurrent with increased temporal variability in abundance suggesting one mechanism by which evolution may predispose those populations to extinction, while decreased temporal variability in invader abundance could facilitate invader persistence. These effects on community dynamics may provide one mechanism to explain how evolution can exacerbate invasions in some communities and ameliorate invasions in others. In Chapter 4, I determined how ongoing evolution in invaded communities affected biomass production, a measure of ecosystem functioning. I determined that biomass production tended to mirror species performance in abundance, but evolution ultimately reduced ecosystem functioning below that observed in the uninvaded state for both communities. These effects highlight the risk inherent in assuming that the long-term consequences of invasions can be adequately predicted by the effects observed following initial invasions by naïve species into novel communities. Collectively, these chapters, though different in theoretical motivation and empirical approach, demonstrate the complex nature of biological invasions, highlighting the need to consider the consequences of biological invasions at multiple ecological scales and time scales. To truly understand the consequences of invasions we must remember that the contemporary interactions that we observe today represent a snapshot in time, and consequently may not adequately predict future interactions. This dissertation particularly illustrates the point that each new biological invasion is a process and urges caution in our interpretation of the outcome of that process.

ETD_7970

Ph.D.

Includes bibliographical references

by Cara Anne Faillace

doi:10.7282/T3BR8W11

ETD doctoral

The author owns the copyright to this work.