Overcompensatory response to additional mortality as an effect of behavioral change

Background/Question/Methods

The addition to a population of a mortality source that results in increased rate of population change or population size is deemed “overcompensation”.  The traditional hypothesis explaining overcompensation is that mortality provides release from density-dependent effects. An alternative hypothesis postulates behavioral mediation if overcompensation. For Behavior-Mediated Overcompensation, the threat of mortality (e.g., via predation) causes a change in individual behavior toward reduced risk, resulting in more limited resource exploitation, greater resource regeneration, and ultimately greater growth and overcompensation of the consumer population. The hypothesis that overcompensation by the larval mosquito, Aedes triseriatus, arises in part due to change in individual larval behavior in response to cues from predation causing more prudent resource exploitation was tested. In the absence of cues from predation, larvae were predicted to forage more actively. To test this, cohorts of larvae, subject to either density relief (simulating predator removal of 50% of the cohort) or no relief, and either predation cues or no cues, were video recorded and cohort production of adults determined. Larval behavior was scored for activity and location.

Results/Conclusions

Both results of survivorship to adulthood and larval behavior are consistent with the predictions of behaviorally-mediated overcompensation. Survivorship data indicate an interaction between predation cue and density relief, such that without relief, predation cues induce greater adult production, and without cues, density relief induces greater adult production. Larval behavior data indicate that predation cues induce greater time resting and less time actively feeding, when compared to no predation cues. These results provide support for the hypothesis that individual behavior change in response to a predation threat contributes to population overcompensation. An understanding of the mechanisms creating the counter-intuitive outcome of overcompensation in response to mortality could prove useful in management of this medically important disease vector.