10 Brown and Davidson 1977 Competition ants rodents

25 293 1977 7 h gaffron and j rubin j gen physiol

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Unformatted text preview: 5, 293 (1977). 7. H. Gaffron and J. Rubin, J. Gen. Physiol. 26, 219 (1942). 8. B. Diner and D. C. Mauzerall, Biochim. Biophys. Acta 305, 329 (1973). 9. Proceedings of the Workshop on Bio-Solar Conversion (NSF/RANN Report GI 40253, National Science Foundation, Washington, D.C., 1973). 10. S. Lien and A. San Pietro, An Inquiry into Biophotolysis of Water to Produce Hydrogen (NSF/ RANN Report GI 40253, National Science Foundation, Washington, D.C., 1973). 11. The Chlamydomonas reinhardtii used in this work was obtained through the courtesy of Drs. N.-H. Chua, G. Schmidt, and K. S. Matlin. I express my deep appreciation to D. Mauzerall for valuable discussions and critical reading of the manuscript. I also thank S. Beale, F. Hong, N. Kagan, and R. Piccioni for their comments. Supported in part by NSF grant PCM74-11747. 13 October 1976 Competition Between Seed-Eating Rodents and Ants in Desert Ecosystems Abstract. Three kinds of evidence indicate that desert rodents and ants compete for seeds: (i) extensive overlaps in diet, (ii) reciprocal increases when one taxon is experimentally excluded, and (iii) complementary patterns of diversity and biomass in geographic gradients of productivity. The effect on seed resources and annual plants seems to be similar whether rodents, ants, or both are foraging. A primary challenge of contemporary ecology is to understand the processes that determine the diversity, organization, and stability of natural ecosystems. Competition between species for food and other resources is thought to be an important determinant of ecosystem structure and dynamics. Empirical support for this conclusion comes almost exclusively from field and laboratory studies of a small number of closely related species (1). Taxonomic specialization has prevented most ecologists from recognizing and investigating the significance of competition among distantly related organisms. Several recent studies indicate that such distantly related taxa as insects, birds, and mammals eat similar foods and are potentially important competitors (24). We now report competition between seed-eating desert rodents and ants that affects the structure and dynamics of ecosystems. Seeds play a major role in the ecology SCIENCE, VOL. 196 o of desert regions. They constitute dormant, resistant life-history stages that maintain large populations of annual plants for the long, unpredictable intervals between short periods of vegetative growth. Seeds of annuals are the primary food of several distantly related taxa of specialized granivores such as rodents, birds, ants, and other insects (for example, bruchid and curculionid beetles). Rodents and ants are similar in their utilization of seed resources. Experiments in which domestic seeds were distributed in desert habitats demonstrated that these two taxa took most of the seeds, harvested the same sizes and species, and collected them from the same microhabitats (3). Foraging rodents and ants select overlapping sizes and species of native seeds (Fig. 1) (5...
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