Print PageSpecies that compete strongly for resources coexist in nature more often than classic Lotka-Volterra models of competition would predict. Intraguild predation can facilitate the coexistence of competing species, especially when the weaker competitor is the more effective predator. As part of a larger study of the feedbacks between ecology and evolution in Trinidadian streams, we investigated the response of a killifish, Rivulus hartii, to the introduction of a suspected intraguild predator, Poecilia reticulata, using mesocosm experiments and replicated field introductions.
Results/Conclusions
Mesocosm trials strongly supported the potential for mutual competitive and predatory interactions between Rivulus and Poecilia. Observations from the field introductions were also consistent with the Rivulus and Poecilia being intraguild predators, though the details of the Rivulus’ response have so far varied across the introduction streams. Most notably, Rivulus populations in introduction reaches have exhibited distinct trajectories, with some experiencing substantial declines in population size while others have not. Moreover, changes in individual growth rates and morphology have also varied across the introductions. Together, these results indicate that the local environmental context mediates the selection pressure that Poecilia imposes upon the native Rivulus. Specifically, Poecilia appears to limit Rivulus recruitment in some environments but not others, creating the potential for divergent phenotypic and evolutionary responses by Rivulus. While the divergence among populations may be a transient phenomenon on the path to a common equilibrium, it might instead represent the first steps toward distinct endpoints (i.e., alternate stable states).
