UCLA

Species invasions present a major environmental challenge due to their negative impacts on biodiversity, natural and agricultural ecosystems, and human health. Climate warming increases rates of invasion, but the field lacks a full understanding of the processes generating this pattern. To mitigate the negative effects of warming-facilitated invasions, we must understand the role that temperature plays in invasion success. A critical component of this agenda is to understand the effects of temperature on the invasion of ectothermic species in particular, as a large proportion of high-impacting pest and pathogen invaders are ectotherms. A successful invasion requires that an invader colonize the thermal environment, as well as establish into the biotic environment, the latter of which exposes the invader to competitive and antagonistic interactions with native residents. Because temperature affects both invader colonization and establishment, ectotherm invasions represent a complex interplay between temperature, invader persistence, and biotic interactions.

Here we develop a conceptual framework for predicting the outcome of such complexity. The framework links the thermal environment to ectotherm population dynamics and interactions through impacts of temperature on life history and interaction traits. We integrate the temperature response of these traits into delay differential equations to make mechanistic predictions regarding the effects of warming on stage-structured populations and community-level dynamics. We use the framework to examine the effect of temperature on exotic invasion success by characterizing the fundamental thermal niche of an invader and the ways in which a resident competitor might constrain the thermal niche. We then ask how climate warming impacts these invasions.

Within the fundamental thermal niche of ectotherms, we find that high temperatures maximize the probability of colonization, but low temperatures maximize invader abundance. We find that ectotherms adapted to low latitudes (tropical climates) are more successful invaders of high latitudes (temperate climates) as compared to the other way around. Further, we find that warming can allow tropical invaders to establish when they could not under ambient temperate climates. Taken together, the dissertation clarifies our understanding of the mechanisms by which exotic species insert themselves into native communities under ambient and warming climates.