Effect of Competition on Foraging Activity in Desert Rodents: Theory and Experiments

• Published in: Ecology (Durham) Vol. 71; no. 3; pp. 844 - 854
• Format: Journal Article
• Language: English
• Published: Ecological Society of America 01.06.1990
• Subjects: Israel
• ISSN: 0012-9658; 1939-9170
• DOI: 10.2307/1937356

We studied, both theoretically and empirically, the effect of intra— and interspecific competition on the foraging effort of individuals. We considered two models, one for a time—minimizer satisfying an energy requirement, the other for an animal maximizing fitness as a function of multiple inputs subject to a time constraint. The goal of satisfying an energy constraint predicts that foraging effort should increase with increased competition. The goal of maximizing fitness subject to a time constraint on multiple inputs may also predict that foraging effort should increase with increased competition because of the missed opportunity cost that results when different inputs are complementary. However, if the fitness—maximizer with multiple inputs incurs an energy cost of foraging (in addition to missed opportunity costs), then it should often reduce foraging effort in response to an increase in competition. We experimentally tested the foraging response to increased competition by two species of gerbils, Gerbillus allenbyi and G. pyramidum, over a range of manipulated population densities in field enclosures located in the Negev Desert of Israel. Our results support the cost—benefit model when the additional energy cost of foraging is important. Per capita activity (as measured by spoor) declined as a function of intraspecific density for each species and as a function of interspecific density for G. allenbyi. We detected no interspecific effect, however, on G. pyramidum.