Predation yields greater population performance: what are the contributions of density- and trait-mediated effects?

1. Population responses to extrinsic mortality can yield no change in the number of survivors (compensation) or an increase in the number of survivors (overcompensation) when the population is regulated by negative density-dependence. This intriguing response has been the subject of theoretical studies, but few experiments have explored how the source of extrinsic mortality affects the response. 2. This study tests abilities of three functionally diverse predators, alone and combined, to induce (over)compensation of a prey population. LarvalAedes aegypti(Diptera: Culicidae) were exposed to predation byMesocyclops longisetus(Crustacea: Copepoda),Anopheles barberi(Diptera: Culicidae),Corethrella appendiculata(Diptera: Corethrellidae), all three in a substitutive design, or no predation. 3. Predator treatment had no significant effect on the total number of adult survivors, nor on numbers of surviving males or females. The female development rate and a composite index of performance (r ') were greater with predation relative to no-predator control. No differences were detected between diverse and single-species predator treatments. 4. Sensitivity analyses indicated predation effects on the number of female adults produced, despite not being affected significantly, was the largest contributing factor to significant treatment effects on the demographic indexr '. While predation did not significantly increase the production of adults, it did release survivors from density-dependent effects sufficiently to increase population performance. This study provides an empirical test of mechanisms by which predation may yield positive mortality effects on victim populations, a phenomenon predicted to occur across many taxa and food webs.

Automated summary

The predator treatment did not significantly affect the total number of adult survivors, but had a positive impact on female development rate and a composite index of performance. Sensitivity analyses showed that predation effects on the number of female adults produced was the largest contributing factor to significant treatment effects on the demographic index r'. Overall, predation released survivors from density-dependent effects and improved population performance.