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A high-resolution map of ant diversity allows an assessment of how well biodiversity centers overlap across taxa. 

Abstract Activity density (AD), the rate at which 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⁻¹14 days⁻¹). Pooled samples from 2017 to 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 threefold across the 47 localities; it tracked the threefold geographic variation in maximum growing season temperature with a consistent gap ofca. 3°C across habitats, a novel macroecological result. AD holds potential as an effective proxy for investigating ecosystem 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. 

Abstract Activity density (AD), the rate that an individual taxon or its biomass moves through the environment, is used both to monitor communities and quantify the potential for ecosystem work. The Abundance Velocity Hypothesis posited that AD increases with aboveground net primary productivity (ANPP) and is a unimodal function of temperature. Here we show that, at continental extents, increasing ANPP may have nonlinear effects on AD: increasing abundance, but decreasing velocity as accumulating vegetation interferes with movement. We use 5 yr of data from the NEON invertebrate pitfall trap arrays including 43 locations and four habitat types for a total of 77 habitat–site combinations to evaluate continental drivers of invertebrate AD. ANPP and temperature accounted for one‐third to 92% of variation in AD. As predicted, AD was a unimodal function of temperature in forests and grasslands but increased linearly in open scrublands. ANPP yielded further nonlinear effects, generating unimodal AD curves in wetlands, and bimodal curves in forests. While all four habitats showed no AD trends over 5 yr of sampling, these nonlinearities suggest that trends in AD, often used to infer changes in insect abundance, will vary qualitatively across ecoregions. 

Abstract Across the globe, temperatures are predicted to increase with consequences for many taxonomic groups. Arthropods are particularly at risk as temperature imposes physiological constraints on growth, survival, and reproduction. Given that arthropods may be disproportionately affected in a warmer climate—the question becomes which taxa are vulnerable and can we predict the supposed winners and losers of climate change? To address this question, we resurveyed 33 ant communities, quantifying 20‐yr differences in the incidence of 28 genera. Each North American ant community was surveyed with 30 1‐m²plots, and the incidence of each genus across the 30 plots was used to estimate change. From the original surveys in 1994–1997 to the resurveys in 2016–2017, temperature increased on average 1°C (range, −0.4°C to 2.5°C) and ~64% of ant genera increased in more than half of the sampled communities. To test Thermal Performance Theory's prediction that genera with higher average thermal limits will tend to accumulate at the expense of those with lower limits, we quantified critical thermal maxima (CT_max: the high temperatures at which they lose muscle control) and minima (CT_min: the low temperatures at which ants first become inactive) for common genera at each site. Consistent with prediction, we found a positive decelerating relationship between CT_maxand the proportion of sites in which a genus had increased. CT_min, by contrast, was not a useful predictor of change. There was a strong positive correlation (r = 0.85) between the proportion of sites where a genus was found with higher incidence after 20 yr and the average difference in number of plots occupied per site, suggesting genera with high CT_maxvalues tended to occupy more plots at more sites after 20 yr. Thermal functional traits like CT_maxhave thus proved useful in predicting patterns of long‐term community change in a dominant, diverse insect taxon.