Michael Kaspari, Michael D. Weiser, Katie E. Marshall, Cameron D. Siler, Kirsten de Beurs. 2022. Temperature–habitat interactions constrain seasonal activity in a continental array of pitfall traps. Ecology
Activity Density (AD, the rate that animals collectively move through their environment) emerges as the product of a taxon’s local abundance and its velocity. We analyze drivers of seasonal AD using 47 localities from the National Ecological Observatory Network (NEON) both to better understand variation in ecosystem rates like pollination and seed dispersal as well as the constraints of using AD to monitor invertebrate populations. AD was measured as volume from biweekly pitfall trap arrays (mL trap-1 14 days-1). Pooled samples from 2017-2018 revealed AD extrema at most temperatures but with a strongly positive overall slope. However, habitat types varied widely in AD’s seasonal temperature sensitivity, from negative in Wetlands, to positive in Mixed Forest, Grassland, and Shrub habitats. The temperature of maximum AD varied 3-fold across the 47 localities; it tracked the 3-fold geographic variation in maximum growing season temperature with a consistent gap of ca. 3°C across habitats, a novel macroecological result. AD holds potential as an effective proxy for investigating rates driven by activity. However, our results suggest that its use for monitoring insect abundance is complicated by the many ways that both abundance and velocity are constrained by a locality’s temperature and plant physiognomy.