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Unformatted text preview: 5, 293 (1977).
7. H. Gaffron and J. Rubin, J. Gen. Physiol. 26,
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
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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