Community disassembly is the nonrandom process of species loss following a disturbance. Pesticide contamination represents a novel anthropogenic disturbance, and one that produces gradients of impact across landscapes. While previous research has demonstrated evolved resistance to pesticides in mosquitoes, these studies do not place adaptive resistance in a broader, whole community setting. Here we examine how interspecific differences in the ability to adapt to pesticide contamination relate to community-level differences across landscapes.
The aquatic communities contained within bromeliads represent highly replicated, natural ecosystems that exist across gradients of pesticide contamination. We collected samples of the aquatic insect community from Costa Rican bromeliads. Two of the three sample sites were within the Area de Conservacion, Guanacaste Costa Rica and represent pristine, uncontaminated systems. The final site was within an orange plantation that has undergone regular pesticide application since before 2000. Larvae of mosquitoes and damselflies were collected, and exposed to increasing concentrations of the organophosphate pesticide dimethoate. From these bioassays resistance to pesticide was calculated. Differences in pesticide tolerance from these bioassays were compared to alterations in community composition observed in bromeliads collected across a contamination gradient.
Results/Conclusions
We found that predatory damselflies showed no adaptive ability in resistance between sites. Conversely, larvae of Wyeomyia mosquitoes showed signifcant increases in pesticide tolerance within the contaminated location compared to the pristine, indicating a large adaptive response. At the community level we found substantial differences in the types and abundances of insects inhabiting bromeliads within the pristine ecosystems versus bromeliads subjected to pesticides. The pristine communities had a higher species diversity, but a lower abundance of Wyeomyia mosquitoes. Repeated pesticide exposure therefore appears to produce a novel ecosystem in which the main bromeliad inhabiting predator, the damselfly, is removed through pesticide exposure. This pesticide-mediated extirpation of damselflies, coupled with Wyeomyia’s adaptive ability to withstand pesticide contamination appears to benefit Wyeomyia populations, causing them to become the dominant members of the community. Our investigations therefore highlight the interactions between ecological and evolutionary responses to pesticide contamination. Our results reveal that community disassembly patterns may be determined through multiple pathways. The ability of a species to tolerate a novel stressor will allow it to remain in modified ecosystems, but the full impact of the stressor will be determined by a combination of adaptive abilities, and changes to the strength of trophic interactions.