Wesner, JS, EJ Billman, and MC Belk. 2012. Multiple predators indirectly alter community assembly across ecological boundaries. Ecology 93: 1674-1682. (see Publications for a .pdf).
Choosing where to lay eggs is critical to an organism’s fitness. Make the wrong choice, and your offspring are toast. It’s no surprise, then, that variation in habitat quality can often lead to variation in colonization, which is a key process during community assembly. Quality is defined in various ways, but one of the most obvious is the presence of predators, and organisms will often avoid colonizing habitats with predators when given the choice. But two features may complicate this choice, 1) predator diversity, and 2) the location of predator-free habitats in the landscape.
We measured insect colonization of aquatic mesocosms that contained predatory trout, dragonflies, or both. In addition, we varied the position of predator-free controls; some were adjacent to mesocosms with predators, while others were isolated. Based on previous research, we expected colonization in the adjacent controls to be intermediate between colonization in the predator treatments and isolated controls. We also expected colonization in the treatment with two predator species to be lower than colonization in treatments with single species.
Surprisingly, rather than showing intermediate preferences, we found that egg-laying insects (mostly chironomids) did not distinguish between treatments with single predator species, multiple predator species, or adjacent controls. They avoided all of these in favor of isolated predator-free mesocosms. This occurred despite the fact that adjacent and isolated predator-free controls were identical. Thus, colonization did not vary solely as a result of intrinsic habitat quality, but also as a result of the quality of adjacent habitats. This means that habitats that might appear identical to us based on intrinsic sampling may be perceived differently by organisms that colonize them. If these response scale-up, our results have consequences for traditional habitat models, as well as the design of conservation reserves.
The Wesner Lab 