Detecting small environmental differences: risk-response curves for predator-induced behavior and morphology

Area of Science:

• Ecology
• Evolutionary Biology
• Developmental Biology

Background:

• Organisms possess plastic traits sensitive to environmental changes, leading to environmentally induced polymorphisms.
• Phenotypic plasticity is increasingly understood as a continuous response rather than a simple threshold switch.

Purpose of the Study:

• To investigate how larval anurans (wood frogs) respond to a gradient of predation risk.
• To determine the level of risk inducing specific phenotypic traits and maximal responses.
• To assess if responses plateau and if different risk manipulation methods yield similar results.

Main Methods:

• Exposed wood frog tadpoles (Rana sylvatica) to an increasing gradient of predation risk.
• Manipulated predation risk by altering prey consumption or predator numbers.
• Quantified predator-induced behavior, morphology, and mass.

Main Results:

• All quantified traits displayed fine-tuned, graded responses to predation risk.
• Most traits showed a plateauing response, indicating limits to plasticity or high defensive costs.
• Significant trait induction occurred at low predation risk levels.
• Behavioral and morphological changes were linked to total prey consumption, not predator numbers directly.

Conclusions:

• Organisms exhibit sophisticated, graded responses to environmental changes, even at low risk levels.
• Plasticity has limits, potentially due to high costs associated with defensive phenotypes.
• Findings impact models of plasticity evolution, optimal design, and ecological community dynamics via trait-mediated indirect effects.