Interactive effects of habitat fragmentation and microclimate on trap-nesting Hymenoptera and their trophic interactions in small secondary rainforest remnants

The combined effects of habitat fragmentation and climate change on biodiversity and biotic interactions are poorly understood. In the context of ongoing deforestation and agricultural intensification in the tropics secondary rainforest fragments might contribute to biodiversity conservation and mitigation of climate warming. This study investigated the interactive effects of habitat fragmentation and microclimate on the abundance and biotic interactions of trap-nesting bees and wasps in secondary forest fragments in the northwestern lowlands of Costa Rica. Fragment size did not affect hymenopteran abundance, parasitism and mortality rates, but all variables differed between edge and interior locations in the forest fragments. Interactive effects between size and location indicate higher mortality rates at interior locations in larger fragments. Microclimatic differences at edge and interior locations led to significant effects on all tested response variables. Abundance at interior locations was significantly higher with increasing temperatures. Mortality rates at interior location increased at lower mean temperatures, whereas higher temperatures at edges marginally increased mortality rates. Our results indicate that edge effects, mediated by altered microclimatic conditions, significantly change biotic interactions of trap-nesting hymenopterans in small secondary fragments.