Contrasting short‐ and long‐term outcomes of pairwise interactions between caddisflies at a hydrologically heterogeneous range margin

Abstract

Abstract Climate change is leading many species to shift their geographical ranges. Species undergoing these range shifts often are moving into areas with heterogeneous abiotic conditions. Additionally, these range‐shifting species will encounter resident species with whom they will compete for space and/or resources. However, the ways that these abiotic and biotic factors interact to influence the establishment and persistence of range‐shifting species has received little attention. Here, we conduct anin situcage experiment examining how a local wetland hydroperiod gradient (i.e., temporary and semi‐permanent ponds) and competition with a resident caddisfly species,Asynarchus nigriculus, influences the survival of the range‐shifting speciesLimnephilus picturatus. We then use long‐term survey data of population densities of these two species to determine whether pairwise interactions observed in the cage experiment translated into long‐term dynamics. The cage experiment revealed thatA. nigriculushad a strong, negative effect on the survival of the range‐shifting speciesL. picturatus, regardless of hydroperiod. However, we observed no relationship between the densities or occurrence ofL. picturatusandA. nigriculusin long‐term data for either temporary or semi‐permanent ponds. Our results suggest that landscape‐level abiotic heterogeneity at range margins may not always be important for mediating antagonistic interactions between resident and range‐shifting species. However, although an interaction appears ecologically significant in short‐term field studies, broader context is needed to understand whether those types of interactions mediate species' distributions and abundance through time. At face‐value, our results from the field experiment and long‐term data analysis did not align. This suggests that other factors such as additional competitive or trophic interactions may be more important drivers behind the population dynamics of this range‐shifting species at its new upper‐elevational limit.