Predators choosing between patches with standing crop: the influence of switching rules and input types |
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Authors: | Markus Frischknecht |
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Institution: | Abteilung Verhaltens?kologie, Zoologisches Institut, Universit?t Bern, CH-3032 Hinterkappelen, Switzerland, CH
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Abstract: | Where prey arriving in a patch are not consumed immediately, they will accumulate. Predators are then presented with a prey
density or standing crop that increases through further input, and decreases through the consumption by predators. Firstly,
I show that the switching rule of predators has a significant influence on the expected predator equilibrium distribution
in such a dynamic system. Three rules are compared; for all rules, analytical solutions are calculated (where possible). To
test their plausibility for natural situations, predator distributions are simulated given the assumption that each predator
obtains individual patch profitability estimates by using a common learning rule. As long as prey arrive in the patches in
constant numbers per time unit, the first rule leads to input matching because predators stop switching when consumption in
the two patches is equal. The other two rules, where predators continue to sample both patches even in the equilibrium state,
lead to predator distributions where the more profitable patch is underused. The final equilibrium depends on the exact assumptions
of the switching rule; however, it is independent of interference. But if the input delivered into a patch is a function of
the current prey standing crop (for example in a reproducing prey population), predator and prey distributions will not reach
an equilibrium in most cases: either standing crops increase indefinitely, or they approach zero, with all predators concentrating
on the better patch. Only a small number of parameter sets show intermediate crops that are reasonably stable. With this input
type, only up to 54% of the simulations reach the expected distribution. In a system with competition for dynamic standing
crop, it is therefore essential to know the type of input and the switching-rule used by predators to be able to predict equilibrium
predator distributions.
Received: 17 March 1995/Accepted after revision: 5 November 1995 |
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Keywords: | Ideal free distribution Learning Switching-rule Standing crop Simulation |
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