Ant community shifts over 60 years in a montane ecosystem

Background/Question/Methods

In response to climatic changes, some species have begun to shift their distributions along latitudinal and/or elevational gradients. Ants are ideal organisms to study these changes due to their widespread distribution and sensitivity to environmental variation. Since ants have established colonies their occurrence implies suitable environmental conditions at small-scales which allows us to understand mechanisms of distributional change. Browne & Gregg (1969) examined the distributions of ant species in Gregory Canyon near Boulder, CO in 1957-58. Due to the variable topography and elevation (750m range), sites differ in temperature and moisture. We resampled Browne & Gregg (1969) to examine changes in the ant community over a period of more than 60 years. Specifically, we ask, 1) have ant species elevations shifted locally; and 2) does ant species composition vary between timeframes and topography? To answer these questions we collected ants following the same methods of Browne & Gregg (1969).

Results/Conclusions

Of the 28 species that were found both in the historical and contemporary samples, only 3 exhibited elevational range shifts (Ps < 0.01). The majority (60.7%) of species have increased in their site occurrence and 39.3% of species decreased in their site occurrence. Overall, ant communities significantly varied between timeframes (PERMANOVA, F = 17.01, P < 0.001) as well as across topography (Contemporary PERMANOVA, F = 3.92, P = 0.002; Historical PERMANOVA, F = 4.81, P = 0.001). Additionally, close to half of the observed species in each timeframe were unique to that sampling period indicating a high level of species turnover. This study shows that ant communities are closely tied to environmental conditions. High local community turnover over 60 years may have implications for ecosystem services provided by ants, such as nutrient cycling, decomposition, and community regulation.