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Despite decades of research, we still have only a rudimentary understanding of the relative influence of the factors that shape the structure of local communities and whether those factors vary geographically. What we do know about community structure comes from detailed long-term observations at single sites or experimental manipulations. Whether what we have learned about single sites applies more generally to other sites, or whether there are even general laws governing the structure of communities is an open, and contested, question. Here, we report on a globally coordinated set of experiments to examine the factors that structure local ant assemblages. With dozens of other ant ecologists around the globe, we have examined the effects of resource availability on ant assemblages at 37 sites along a 47º latitudinal extent, from Ecuador to Maine. Along a transect at each site, we place 5 50-ml centrifuge tubes stocked with each of the following: water (as a control), 20% sucrose solution, 1% salt solution, 20% amino acid solution, olive oil, or a solution to mimic honeydew. After 2 hours, we collect the tubes and identify and enumerate the ants. We then use these data to ask whether there is systematic variation in the response of ant assemblages to resource availability.
Results/Conclusions
The number of species sampled from any community varied from 0 in some assemblages in northern New England to more than 20 in forests in Ecuador. The proportion of resource tubes occupied varied from 0 in New England to >50% at several sites in tropical and subtropical forests. Surprisingly, there were no strong responses, at any of the 37 sites, to salt, suggesting that these ant assemblages are not sodium limited. The responses of the ant assemblages to the other resources were idiosyncratic and varied dramatically along the latitudinal gradient and even among sites within the same region at the same latitude. Such a result suggests one of two possibilities. First, if resources are limiting and affect recruitment behavior of ants, then resources may be differentially limiting among sites. Second, perhaps food resources are not limiting and the behavioral responses documented here are simply the outcome of decisions that individual foragers make among possible resources. The continued addition of more sites to the experiment, ideally coupled with other manipulations, could assess whether the effects of limiting resources on ant assemblages are general, or nonexistent.
