© 1979 by The Society for Integrative and Comparative Biology
An Experimental Study of Competition Between Seed-eating Desert Rodents and Ants
Department of Ecology and Evolutionary Biology, University of Arizona Tucson, Arizona 85721
Department of Biological Sciences, Purdue University West Lafayette, Indiana 46207
Department of Biology, Museum of Northern Arizona Flagstaff, Arizona 86001
Reciprocal increases in rodent and ant densities on 0.1 ha plots from which the other taxon had been excluded demonstrate that these distantly related desert granivores compete for seeds. Relative to unmanipulated control plots, numbers of ant colonies increased 71% on plots where rodents were excluded; rodents increased 20% in numbers of individuals and 29% in biomass in the absence of ants. Comparisons of seed levels in the soil and of annual plant densities on experimental and control plots provide evidence that the rodent and ant populations are limited by and compete for food. Greater numbers of seeds and annuals occurred on plots where rodents and ants had been excluded than on plots where both taxa were present. Particular species of annuals were reduced in density by foraging of rodents. Ants increased species diversity by differentially harvesting seeds of the most common species. Results of these and other recent studies suggest that competition among distantly related organisms plays a major role in the organization of ecological communities.