The consequences of local adaptation in stream ecosystems: ecological roles and species distributions

Ecological and evolutionary processes are often assumed to operate at different temporal scales. Most ecological research assumes that species characteristics are static over scales of ecological interest (e.g. days, years, or even decades). However, a considerable amount of research now suggests that ecological and evolutionary processes operate on similar scales and often interact with implications for the role organisms play in an ecosystem. In this presentation, Dr. Thomas will highlight research results that illustrate how local adaptation (a) influences the phenotypic traits and ecological roles of fish in Trinidadian streams and (b) leads to higher species turnover of aquatic insects along tropical elevation gradients relative to temperate latitudes. The selective pressures on all species change as species are gained and loss and both invading and resident species can face intense selective pressures following community changes. As time since invasion progresses and phenotypes adjust to new selective regimes, trait-mediated interactions between organisms and their environment also change. We have been examining this process using Trinidadian guppies (Poecilia reticulata) and their native ecosystems on the island of Trinidad. This work builds upon extensive prior research demonstrating rapid phenotypic change in guppies in response to the presence or absence of predators. In this presentation, we summarize the results of a large collaborative effort to examine ecological consequences of these changes using a suite of approaches that vary in their complexity. The second portion of this presentation will examine whether aquatic insect taxa have great species turnover along elevation gradients in Ecuador versus Colorado and whether differences are predicted by the thermal biology of resident species. In essence, this works tests Janzen's classic hypothesis regarding "Why mountain passes are higher in the tropics" and whether it holds for aquatic insect populations. Briefly, our results indicate that tropical species have reduced thermal tolerance, narrower altitudinal ranges and greater species turnover with altitude than their temperate counterparts.