VARIATION IN SPECIES INTERACTIONS AND THEIR EVOLUTIONARY CONSEQUENCES
Chamberlain, Scott A.
Whitney, Kenneth D.
Doctor of Philosophy
Species interactions restrict or promote population growth, structure communities, and contribute to evolution of diverse taxa. I seek to understand how multiple species interactions are maintained, how human altered species interactions influence evolution, and explore factors that contribute to variation in species interactions. In Chapter 1, I examine how plants interact with multiple guilds of mutualists, many of which are costly interactions. The evolution of traits used to attract different mutualist guilds may be constrained due to ecological or genetic mechanisms. I asked if two sets of plant traits that mediate interactions with two guilds of mutualists, pollinators and ant bodyguards, were positively or negatively correlated across 36 species of Gossypium (cotton). Traits to attract pollinators were positively correlated with traits to attract ant bodyguards. Rather than interaction with one mutualist guild limiting interactions with another mutualist guild, traits have evolved to increase attraction of multiple mutualist guilds simultaneously. In Chapters 2 and 3, motivated by the fact that agriculture covers nearly 50% of the global vegetated land surface, I explore the consequences of changes in plant mutualist and antagonist guilds in agriculture for selection on plant traits. I first explore how agriculture alters abundance and community structure of mutualist pollinators and antagonist seed predators of wild Helianthus annuus texanus. Mutualists were more abundant near crops, whereas antagonists were more abundant far from crops near natural habitat. In addition, mutualist pollinator communities were more diverse near sunflower crops. Plant mutualists and antagonists respond differently to agriculture. Next, I explore how these changes in abundance and community structure of mutualists and antagonists influenced natural selection on H. a. texanus floral traits. Natural selection on heritable floral traits differed near versus far from crop sunflowers, and overall selection was more heterogeneous near crop sunflowers. Furthermore, mutualist pollinators and antagonist seed predators mediated these differences in selection. Finally, in Chapter 4, I ask if variation in interaction outcomes differs across types of species interactions. Furthermore, I examined the relative importance of factors that create context-dependency in species interactions. Using meta-analysis of 353 papers, we found that mutualisms were more likely to change sign of the interaction outcome when compared across contexts than competition, and predation was the least likely to change sign. Overall, species identity caused the greatest variation in interaction outcomes: whom you interact with is more important for context-dependency than where or when the interaction occurs. Additionally, the most important factors driving context-dependency differed significantly among species interaction types. Altogether, my work makes progress in understanding how species maintain interactions with multiple guilds of mutualists, how agriculture alters species interactions and subsequent natural selection, and the variation in species interaction outcomes and their causes.
Ecology; Evolution; Meta-analysis; Agriculture