Controlled competition experiments estimating the relative effects of inter- and intraspecific competition can help to resolve whether interspecific competition results in coexistence or exclusion. Analyzing and interpreting such experiments presents two difficulties: 1) typical experimental designs are well suited to compare inter- and intraspecific competitive responses, but what is theoretically most interesting is a comparison of inter- and intraspecific competitive effects; and 2) different investigators may use different conditions, and experimental outcomes can be context dependent, making synthesis of results difficult. Using the example of competition experiments on larval mosquitoes, focusing on invasive Aedes albopictus competing with resident Aedes, I conducted meta-analyses that addresses these difficulties. I specifically addressed the questions: 1) Is the effect of interspecific competition is greater than, less than, or equal to that of intraspecific competition? 2) Do tests of competitive effects and competitive responses yield the same conclusions? And 3) Are competitive outcomes context-dependent with respect to food quality?
Results/Conclusions
For A. albopictus and A. aegypti, there was significant context dependence, with interspecific competitive advantage for A. albopictus with low food quality, and competitive equivalence with high food quality. Meta-analysis yielded more significant results when survivorship was the dependent variable, rather than estimated rate of increase. Competitive effects and competitive responses of each species yielded similar conclusions. This meta-analysis suggests competitive exclusion of A. aegypti by A. albopictus, and is thus consistent with field sampling, qualitative reviews, and interpretations from individual publications. For A. albopictus and A. triseriatus, most results indicated competitive equivalence and no context dependence, and are thus contrary to previous qualitative reviews and to interpretations from individual publications. For both pairs of species published results suitable for meta-analysis remain scarce, and better experimental designs and improved analysis and reporting of statistical results are needed. Greater emphasis needs to be placed on estimating species’ inter- and intraspecific competitive effects, rather than the more common, but theoretically less interesting, competitive responses. Experiments without low-density controls (i.e., replacement series) are inadequate for comparing competitive effects and responses.
