The tradeoff between colonization and competitive ability has been proposed as a mechanism for ecological succession, and this tradeoff has been demonstrated in various ecological communities. The tradeoff between competitive ability and predator vulnerability is also an often-cited and tested phenomenon; however, this tradeoff is not usually postulated as a cause of ecological succession. Early successional species that arrive before the predator could be either (A) Less vulnerable to predation than their successors, by virtue of being poor competitors (direct competition-predation resistance tradeoff); (B) Equally or more vulnerable to predation, because they are not evolutionarily adapted to avoid a predator that they normally precede in succession (no competition-predation resistance tradeoff). To test these alternative hypotheses, we established water-filled containers in an oak-hickory forest. We allowed half of the containers to be naturally colonized by early-successional Culex mosquitoes, mid-successional Aedes mosquitoes, and the mosquito predator Toxorhynchites rutilus. In the other half of the containers we prevented Aedes colonization via systematic removal of Aedes eggs, but allowed Culex and T. rutilus to colonize.
After seven weeks, Culex were significantly more abundant in containers where Aedes had been removed, which suggests that Culex are competitively inferior to Aedes. Toxorhynchites rutilus abundance and colonization rate were unaffected by the removal of Aedes, and T. rutilus significantly reduced prey density in both treatments, which supports the hypothesis that Culex is no less vulnerable to predation than is Aedes. Interestingly, by week 7 T. rutilus also demonstrated prey switching behavior, significantly depleting only the most common prey genus in each treatment. These data support postulate that Culex and Aedes demonstrate a direct colonization-competition tradeoff, but no direct competition-predation resistance tradeoff.