Print PagePesticides are widely applied in intensive agroecosystems and may have adverse effects on non-target organisms in waterbodies adjacent to crops. European pesticide registration process allows for small effects on non-target species if timely population recovery after pesticide applications is demonstrated. Population recovery is dependent on species specific life-history, pesticide fate and effects in the environment and habitat characteristics. Aquatic insects, due to their aerially dispersing stages, are assumed to efficiently recolonize aquatic habitats after stress events. However, just how effective dispersal is in aquatic insects is not well understood as the recolonization of waterbodies depends on species’ flying ability (weak or strong flyers) as well as landscape characteristics. In weak flyers, riparian vegetation forms a barrier for dispersal, but offers ample opportunities to rest and find mates. We developed an individual-based model of a weakly flying insect, the non-biting midge, Chironomus riparius, to understand the potential trade-off between dispersal and recolonization of stressed habitats versus higher local reproductive output.
Results/Conclusions
We looked into the population recovery time in stressed habitats, and the overall abundance and metapopulation dynamics. The modeled landscape is composed of two ditches (representing the available aquatic habitats) separated by terrestrial habitat whose permeability for chironomids is based on smaller or larger step sizes each individual can attain and results in closed, open or habitats whose permeability is season dependent. The simulation results indicate that metapopulation size in closed habitats is, on average, 42% larger than in open, permeable habitats. This is the result of individuals being restricted in their dispersal which, consequently, increases their chances to find mates. However, after an extreme stress event (100% mortality), population recovery does not occur in the treated ditch in closed habitats. Ditches in open habitats are recolonized faster than in seasonally permeable ones, and after elimination, it takes around 500 days to reach 95% abundance of the reference population. At least 40% of the ditch in closed habitats needs to be left untreated if populations are to recover within the same year after stress. Only 1% of the population needs to survive if recovery is to be accomplished in the following year. These findings will be discussed in detail because they have important implications for ecological risk assessment, as they show the need to go beyond overly simplistic assumptions that flying insects rapidly recolonize and recover their populations and take into account species’ dispersal abilities and landscape features.
