The Relative Importance of Population Size, Colonist Quality, and Colonist Arrival Frequency for Population Success

Abstract

Successful population establishment, subsequent population dynamics, and extinction have all repeatedly been shown to be affected by the quantity of initial colonists. However, there are other, less studied factors that could determine population success, including the physiological condition in which colonists arrive (‘quality’), and the frequency with which they arrive (‘arrival frequency’). While all of these factors can individually drive the dynamics and extinction of new populations, we do not understand which has the strongest influence, nor the circumstances under which their relative importance may change. In this thesis, I examined the importance of different combinations of colonizer characteristics for population success, and how their importance varied between species and individuals. In my first experiment, I showed that population size, not arrival frequency, was the primary factor determining the survival and performance of introduced populations of Hemimysis anomala. In my second experiment, I found that the population dynamics of Daphnia pulicaria were only influenced by colonist quality, while the establishment of Skistodiaptomus oregonensis was more strongly influenced by arrival frequency. Finally, I showed that the benefits of increasing colonist quantity and genetic diversity can change based on colonist identity. For some Daphnia pulex colonists, higher quantities or genetic diversities improved their success, while in others there was little effect. I also conducted an additional project that examined the mechanisms driving human-mediated dispersal. Colonization is a shared and integral process across ecological disciplines, and our current understanding of the mechanisms involved is founded on research of both ‘natural’ and ‘human-mediated’ colonization. This project integrates the biological- and human-based processes involved in human-mediated dispersal, and develops a general framework outlining the mechanisms that determine which individuals enter, survive, and exit from human vectors. Overall, my work highlights the necessity of considering multiple colonist characteristics, and pre-arrival processes, to understand, predict, and control colonization, and that the value of particular characteristics is not necessarily consistent across species and individuals.