Investment in defense and cost of predator-induced defense along a resource gradient |
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Authors: | Ulrich K Steiner |
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Institution: | (1) Institute of Zoology, University of Zürich, 8057 Zürich, Switzerland;(2) Biological Sciences, Herrin Labs, Stanford University, Stanford, CA 94304-5020, USA |
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Abstract: | An organism’s investment in different traits to reduce predation is determined by the fitness benefit of the defense relative
to the fitness costs associated with the allocation of time and resources to the defense. Inherent tradeoffs in time and resource
allocation should result in differential investment in defense along a resource gradient, but competing models predict different
patterns of investment. There are currently insufficient empirical data on changes in investment in defensive traits or their
costs along resource gradients to differentiate between the competing allocation models. In this study, I exposed tadpoles
to caged predators along a resource gradient in order to estimate investment in defense and costs of defense by assessing
predator-induced plasticity. Induced defenses included increased tail depth, reduced feeding, and reduced swimming activity;
costs associated with these defenses were reduced developmental rate, reduced growth, and reduced survival. At low resource
availability, these costs predominately resulted in reduced survival, while at high resource availability the costs yielded
a reduced developmental rate. Defensive traits responded strongly to predation risk, but did not respond to resource availability
(with the exception of feeding activity), whereas traits construed as costs of defenses showed the opposite pattern. Therefore,
defensive traits were highly sensitive to predation risk, while traits construed as costs of defense were highly sensitive
to resource allocation tradeoffs. This difference in sensitivity between the two groups of traits may explain why the correlation
between the expression of defensive traits and the expression of the associated defense costs was weak. Furthermore, my results
indicate that genetic linkages and mechanistic integration of multiple defensive traits and their associated costs may constrain
time and resource allocation in ways that are not addressed in existing models.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Adaptive plasticity Phenotypic plasticity Rana temporaria Time allocation tradeoff Trait integration |
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