Seasonal changes in arthropod diversity patterns along an Alpine elevation gradient

Deciphering patterns in species distributions and species interactions along ecological gradients are fundamental topics in ecology. Theory holds that species diversity is greater and interactions are stronger under warmer and more stable environments, such as low elevations and latitudes. However, recent findings have shown conflicting evidence, potentially due to seasonal effects. We aimed to address this gap by studying seasonal changes in arthropod communities over an elevation gradient in the Swiss Alps, as well as herbivore-predator interactions and their resulting consequences on plant herbivory levels. Overall, we found hump-shaped patterns in arthropod abundance, richness and diversity with increasing elevation, with all factors peaking below the tree line. However, these patterns varied seasonally, with strong mid-elevation peaks at the beginning of the summer, shifting to a pattern of linear decrease at the beginning of the fall. In searching for mechanisms explaining these changes, we found that shifts in arthropod communities over elevation and seasons usually followed shifts in vegetation productivity estimates. Other factors, such as top-down control by natural enemies, which was generally stronger at low elevations, and plant species-specific resistance rates along elevation gradients were also implicated as drivers of diversity and herbivory rates. These results highlight the complexity of arthropod communities' responses to environmental gradients, which vary during the season in response to relative changes in both bottom-up and top-down forces.