Using historical and experimental data to uncover warming temperature effects on ant communities

Historical records of biotic communities can be compared to current records to suggest effects of recent climate change.  However, attribution of biotic changes to climate changes can be problematic due to confounding variables.  Experiments that manipulate projected climates can overcome the matter of attribution but long-term implications of observed community responses are uncertain.  Using a combined approach of historical comparison and experimental manipulation can provide a powerful approach to reveal the effects of climate change on biological communities that can overcome the limitations of each approach on its own.  Here we use this approach by combining observational and experimental data on the effects of warming temperatures on oak forest ant communities.  The observational component compares historical ant community data (1976 and 1977) to present-day data (2010 and 2011) from the same oak-scrub forests stands at Savannah River Site, South Carolina. Temperatures between the sampling periods have had an increasing trend and the summers of 2010 and 2011 were approximately 2 °C warmer than 1976 and 1977.  The experimental component comes from a warming experiment at Duke Forest, North Carolina.  In this experiment, warming chambers are heated to from 1.5 - 5.5 °C above ambient temperature. Results from both studies were congruent. Under experimental and natural warming ant communities changed in evenness caused by increased abundance of the dominant species, Crematogaster lineolata.  Foraging data under experimental warming suggests that C. lineolata benefits from higher temperatures by increasing active foraging hours while other species do not.   We conclude that community structure of southeastern oak forest ants has changed under recent warming and will continue to change under projected warming.