Climate drives the long-term reproductive investment of a tropical ant community

Abstract

Forecasting insect responses to environmental variables at local and global spatial scales remains a crucial task in ecology. However, predicting future responses requires long-term datasets, which are rarely available for insects, especially in the tropics. From 2002 to 2017, we recorded male ant incidence, a measure of ant reproductive investment, of 155 ant species at ten sites on Barro Colorado Island. In this Panamanian tropical rainforest, Malaise traps were deployed for two weeks during the wet and dry seasons. Short-term changes in community structure were pronounced, and compositionally distinct assemblages flew during the wet and dry seasons. Notably, the composition of these distinct assemblages oscillated in a consistent 5-year cycle but did not change during the 16-y study period. Across time, a Seasonal Auto-Regressive Integrated Moving Average (SARIMAX) model explained 75% of long-term variability in male ant incidence, which responded negatively to monthly maximum temperature and positively to sea surface temperature, a surrogate for El Niño Southern Oscillation events. Establishing these relationships allowed us to forecast ant incidence for five years until 2022, when year-long local climate variables were available. Consistent with the data, the forecast indicated no significant changes in long-term temporal trends of male ant incidence between 2017 and 2022. However, simulations of probable changes in ant incidence given different scenarios of climatic variables showed that strong El Niño events and maximum temperature are the environmental factors that could impact ant incidence the most. Our results highlight the dependence of ant reproductive investment on both short- and long-term changes in temperature, which is critical under current global warming scenarios.