How does species-specific mortality affect the populations of two competing species? An agent-based model, simulating mosquito lifecycles, was used to explore species-specific extrinsic mortality. Mosquitoes can experience high density-dependent mortality in the larval stage mediated by resource competition. Two mosquito species, Aedes aegypti and Aedes albopictus, are commonly found in similar larval habitats and compete for resources. A. aegypti and A. albopictus vector diseases such as dengue and Zika. Therefore, the two species are often the target of mosquito control, and several species-specific techniques have been developed to reduce their populations. Empirical and modelling studies have indicated that a higher number of adult mosquitoes may be produced if high densities of larvae are reduced by extrinsic mortality, compared to populations with a similar larval density where no extrinsic mortality occurred. Thus far, studies have investigated each species in isolation. To determine how species-specific extrinsic mortality may affect two competing species, one species was simulated as a “better resource competitor” and one species was simulated as a “worse resource competitor.” Each species underwent extrinsic mortality that was applied either early or late in the juvenile life-stage. The total number of adults produced for each species was reported.
Results/Conclusions
A higher number of adults in the non-target species were produced when early extrinsic mortality was applied, regardless of whether the better or worse competitor was targeted. However, when the better competitor was targeted, both the target and non-target species produced a higher number of adults. Additionally, a higher number of adults were produced in the non-target species when late extrinsic mortality was applied to the better competitor. The increase in adult number following late extrinsic mortality has not occurred in previous studies on singular species; the results are an indication that interspecific competition plays a significant role in population growth and regulation in the model system. The results indicate that species-specific extrinsic mortality approaches may have counter-productive results for the target species, and furthermore may increase the population size of a non-target competing species. Targeted extrinsic mortality is likely to have indirect effects on an ecological community, which need to be considered for management practices incorporating such techniques in their approach.