10 Brown and Davidson 1977 Competition ants rodents

Although data are less complete the same patterns

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Unformatted text preview: ies of the two groups (810). These data are consistent with the hypothesis that the two taxa compete for limited food resources. When other environmental conditions remained relatively constant, the two taxa responded similarly to the increasing availability of seeds. However, when one taxon was unable to respond to increased productivity [in this case, presumably because low temperatures inhibit ant activity (11)], the other increased in density, biomass, and diversity. Since distributions of rodents and ants are limited by different environmental constraints and geographic barriers, this ability to compensate for the absence of competitors may result in the evolution of taxonomically divergent but function882 populations may attain high densities by consuming food resources which, in continental habitats, are utilized by competitors that disperse poorly across bodies of water. Additional fieldwork will be required to assess the general significance of competition between unrelated taxa, to determine the effects of such interactions on ecosystems, and to produce realistic models of these processes. 18.0 24.0 15/25* 16/25t JAMES H. BROWN Department of Ecology and Evolutionary Biology, University ofArizona, Tucson 85721 DIANE W. DAVIDSON tIn three comparisons, the experi- ally similar granivore communities in geographically isolated deserts. Preliminary data from our exclusion experiments indicate that the increase of rodents or ants in response to the absence of the other taxon may have a compensatory impact on seed resources and plant populations. Analyses of annual plants and seeds in the soil revealed 5.5 times greater densities of seeds and 2.0 times greater densities of annual grasses (Bouteloua barbata and B. aristidoides) on plots from which both rodents and ants were absent than on any others; there were no significant differences among plots in which rodents, ants, or both were present. This finding suggests that rodents and ants are the primary granivores in this ecosystem and that their competitive interaction results in a compensatory reduction of seed resources when one taxon is removed. Additional field work is required to document the effects of these and other seed eaters on the diversity, stability, and productivity of desert plant communities (12). Strong competitive interactions among distantly related organisms such as we have demonstrated here are probably widespread and important in natural ecosystems. In most habitats the important kinds of food resources are used by several major taxa of potentially competing consumers. Obvious examples include phytophagous insects and grazing mammals in temperate and tropical grasslands (2), frugivorous insects, birds and mammals in tropical forests (4), insect and avian nectar feeders in many habitats, and even insectivorous plants, arthropods (spiders), and vertebrates in areas of acid soils. Competition among distantly related taxa may account in part for the higher density of some populati...
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This document was uploaded on 02/26/2014 for the course BIOLOGY 4368 at University of Houston.

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