Evol Ecol Res 8: 1301-1309 (2006)     Full PDF if your library subscribes.

A trophic polymorphism induced by both predators and prey

B.R. Schmidt,1,2* N. Ramer1‡ and J. Van Buskirk1

1Zoologisches Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich and 2KARCH, Passage Maximilien-de-Meuron 6, 2000 Neuchâtel, Switzerland

Address all correspondence to B.R. Schmidt, Zoologisches Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
e-mail: bschmidt@zool.unizh.ch


Problem: We tested whether plasticity in head shape of newt larvae represents a predator-induced resource polymorphism that may allow newts to compensate for costs of defence.

Organism: Larvae of European Triturus newts exhibit defensive behaviour and morphology when in ponds with predators. Predator-induced newt larvae also have large heads, although head shape does not have a direct influence on vulnerability to predation.

Methods: We surveyed the morphology and diet of T. alpestris larvae in 17 natural ponds. A laboratory experiment was used to assess the effects of predators and food size on trophic morphology.

Results: In natural ponds, individuals with relatively large heads had large prey, and a larger volume of prey, in their guts. In the experiment, a large head was induced by both prey size and predator cues, acting additively.

Conclusion: Even though the large head offers no protection from predation, it is directly induced by predators and enables newts to consume more profitable prey.

Keywords: inducible defence, morphology, phenotypic plasticity, prey size, resource polymorphism, Triturus.

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