Group foraging, patch exploitation time and the finder's advantage |
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Authors: | Hannu Rita E Ranta Nina Peuhkuri |
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Institution: | (1) Integrative Ecology Unit, Department of Ecology and Systematics, Division of Population Biology, P.O. Box 17␣(Arkadiarkatu␣7), FIN-00014 University of Helsinki, Finland Fax: + 358-9-191-7492 E-mail: Esa.Ranta@Helsinki.Fi, FI |
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Abstract: | We use a combination of the marginal value theorem (MVT) of Charnov (1976), and a group foraging model featuring information
sharing to address patch residence in an environment where food occurs in discrete patches. We shall show that among equal
competitors the optimal patch time for the individual that finds the food patch is shorter than that for the non-finder among
equal competitors, T
E < T
N. This is the case if the patch-finder commences food harvesting in the patch earlier and manages to monopolise a fraction
of the prey items (finder's advantage) before the other individuals come to take their benefit. When individuals differ in
their food-searching abilities so that some of them (producers) contribute proportionally more to food-searching than others
(scroungers), and differ in ability to compete for the food found, a difference emerges between producer and scrounger individuals
in the optimal patch time. Within a patch we always have the finder's advantage (T
E < T
N) regardless of phenotype. Between patches a suite of optimal patch times for encountering individuals emerges depending on
the performance of producers and scroungers when changing from solitary feeding to feeding in a group. The optimal patch time
for individuals that are affected more severely by competition is shorter than that for individuals of the phenotype with
better competitive ability. When both phenotypes are affected similarly no difference in optimal patch times emerges.
Received: 13 February 1996 / Accepted after revision: 28 September 1996 |
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Keywords: | Group foraging Marginal value theorem Producers Scroungers Assorted foraging groups |
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