THE GROWTH–PREDATION RISK TRADE-OFF UNDER A GROWING GAPE-LIMITED PREDATION THREAT

Mark C. Urban1

School of Forestry and Environmental Studies, Yale University, 370 Prospect Street, New Haven, Connecticut 06511 USA



Growth is a critical ecological trait because it can determine population demography, evolution, and community interactions. Predation risk frequently induces decreased foraging and slow growth in prey. However, such strategies may not always be favored when prey can outgrow a predator's hunting ability. At the same time, a growing gape-limited predator broadens its hunting ability through time by expanding its gape and thereby creates a moving size refuge for susceptible prey. Here, I explore the ramifications of growing gape-limited predators for adaptive prey growth. A discrete demographic model for optimal foraging/growth strategies was derived under the realistic scenario of gape-limited and gape-unconstrained predation threats. Analytic and numerical results demonstrate a novel fitness minimum just above the growth rate of the gape-limited predator. This local fitness minimum separates a slow growth strategy that forages infrequently and accumulates low but constant predation risk from a fast growth strategy that forages frequently and experiences a high early predation risk in return for lower future predation risk and enhanced fecundity. Slow strategies generally were advantageous in communities dominated by gape-unconstrained predators whereas fast strategies were advantageous in gape-limited predator communities. Results were sensitive to the assumed relationships between prey size and fecundity and between prey growth and predation risk. Predator growth increased the parameter space favoring fast prey strategies. The model makes the testable predictions that prey should not grow at the same rate as their gape-limited predator and generally should grow faster than the fastest growing gape-limited predator. By focusing on predator constraints on prey capture, these results integrate the ecological and evolutionary implications of prey growth in diverse predator communities and offer an explanation for empirical growth patterns previously viewed to be anomalies.

Keywords: demographic models, life history evolution, optimal growth, phenotypic plasticity, predator–prey interactions, prey size refuge

Received: November 22, 2006; Revised: March 5, 2007; Accepted: March 12, 2007

1Present address: National Center for Ecological Analysis and Synthesis, 735 State Street, Suite 300, Santa Barbara, California 93101 USA. E-mail:

Cited by

Mark C. Urban. (2008) Salamander evolution across a latitudinal cline in gape-limited predation risk. Oikos 117:7, 1037-1049
Online publication date: 1-Aug-2008.
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Mark C. Urban. (2008) The evolution of prey body size reaction norms in diverse communities. Journal of Animal Ecology 77:2, 346-355
Online publication date: 1-Apr-2008.
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