Community composition modifies direct and indirect effects of pesticides in freshwater food webs

How Do Indirect Effects of Contaminants Inform Ecotoxicology? A Review

“…Biodiversity may also affect the frequency and strength of indirect effects. Low diversity systems with few species (and therefore few tolerant species, [4,15]) and with a simple food chain structure (e.g., few trophic levels) may be more prone to pronounced indirect effects than high diversity systems with complex food webs with many functionally redundant species. Therefore, indirect effects in diverse communities with complex trophic relationships may be more difficult to characterize, anticipate, and model.…”

“…Although rarely studied explicitly, the magnitude and frequency of indirect effects will undoubtedly differ as biodiversity and species composition vary over space and time within communities. Zhao et al [15] performed a mesocosm experiment to test for direct and indirect effects of herbicides and pesticides by manipulating the species number within trophic levels and the number of trophic levels within the experimental community. Direct effects of herbicides and pesticides were both reduced in treatments with a higher diversity of primary producers and herbivores, respectively, because more relatively tolerant species were present in high diversity treatments.…”

“…For pesticide exposure in a diverse community, the direct effect on relatively sensitive herbivore species reduces density, and a positive indirect effect is exerted on primary producers as herbivory is reduced ( Figure 4). However, a possible positive indirect effect on relatively tolerant herbivores could follow as competition among consumer species is reduced and as the basal food resource is increased [15,18]. Of course, indirect effects will be much more complex and context dependent if herbicide and pesticide exposures occur simultaneously, and it is possible that indirect effects could enhance or mask each other [4,15].…”

“…However, a possible positive indirect effect on relatively tolerant herbivores could follow as competition among consumer species is reduced and as the basal food resource is increased [15,18]. Of course, indirect effects will be much more complex and context dependent if herbicide and pesticide exposures occur simultaneously, and it is possible that indirect effects could enhance or mask each other [4,15]. Indirect effects in areas with complex mixtures of contaminants are especially difficult to study and predict for these reasons, adding uncertainty to estimates of chemical risk [4,19,20].…”

“…Indirect effects in areas with complex mixtures of contaminants are especially difficult to study and predict for these reasons, adding uncertainty to estimates of chemical risk [4,19,20]. However, given the wide ranges in tolerance among species within ecosystems [13,14], the potential for an asymmetrical response increases with increasing species diversity [4,15]. Interaction networks [16,17] and feedback loops [8] also tend to become more complex as diversity increases.…”