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| Historical records of species are compared with current records to elucidate effects of recent climate change. However,
confounding variables such as succession, land-use change, and species invasions make it difficult to demonstrate a causal
link between changes in biota and changes in climate. Experiments that manipulate temperature can overcome this issue of
attribution, but long-term impacts of warming are difficult to test directly. Here we combine historical and experimental
data to explore effects of warming on ant assemblages in southeastern US. Observational data span a 35-year period (1976–
2011), during which mean annual temperatures had an increasing trend. Mean summer temperatures in 2010–2011 were
,2.7uC warmer than in 1976. Experimental data come from an ongoing study in the same region, for which temperatures
have been increased ,1.5–5.5uC above ambient from 2010 to 2012. Ant species richness and evenness decreased with
warming under natural but not experimental warming. These discrepancies could have resulted from differences in
timescales of warming, abiotic or biotic factors, or initial species pools. Species turnover tended to increase with
temperature in observational and experimental datasets. At the species level, the observational and experimental datasets
had four species in common, two of which exhibited consistent patterns between datasets. With natural and experimental
warming, collections of the numerically dominant, thermophilic species, Crematogaster lineolata, increased roughly twofold.
Myrmecina americana, a relatively heat intolerant species, decreased with temperature in natural and experimental
warming. In contrast, species in the Solenopsis molesta group did not show consistent responses to warming, and
Temenothorax pergandei was rare across temperatures. Our results highlight the difficulty of interpreting community
responses to warming based on historical records or experiments alone. Because some species showed consistent
responses to warming based on thermal tolerances, understanding functional traits may prove useful in explaining
responses of species to warming. | |
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