Evol Ecol Res 5: 653-670 (2003)     Full PDF if your library subscribes.

Can adaptive evolution or behaviour lead to diversification of traits determining a trade-off between foraging gain and predation risk?

Peter A. Abrams*

Department of Zoology, University of Toronto, 25 Harbord Street, Toronto, Ontario M5S 3G5, Canada

e-mail: abrams@zoo.utoronto.ca


In this article, I examine the population-level consequences of adaptive change in a trait that determines both the ability of a species to capture food and its ability to avoid predation. I assume that the foraging trait of a focal species has an equilibrium that minimizes fitness, but which can be maintained by frequency-dependent selection (i.e. a ‘branching point’ equilibrium). Such a scenario has the potential for selection to favour diversification into a well-defended type with low food consumption ability and a poorly defended type with high food consumption. Population and trait dynamics are examined using models of a three-species food chain in which the middle species has a foraging/vulnerability trait that changes adaptively at a rate proportional to the rate of change in fitness with a unit change in the value of the trait. Conditions favouring evolutionary diversification at a fitness minimizing trait are: (1) weak density dependence in the food species and (2) a moderately decelerating relationship between the foraging trait and vulnerability to the predator. If these conditions are satisfied, diversification occurs when the rate of adaptive change is sufficiently low. However, rapid change, such as that which occurs when the trait is behaviourally determined, often generates population cycles that may prevent diversification. Fitness minimization at a branching point implies that, when the rate of adaptive change is sufficiently high, population and trait cycles will either be produced or altered. Thus, it is possible that there are many ecological scenarios under which adaptive behaviour frequently fails to produce polymorphism when analogous evolutionary models predict such diversification.

Keywords: adaptive foraging, anti-predator behaviour, behavioural dynamics, branching point, diversification, food chain, predation.

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