Cheating death: selection on digestive physiology overcomes expected growth costs of anti-predator defenses.

Abstract

Organisms often face a fundamental trade-off between growth and predator avoidance, where traits that enhance growth - such as higher activity rates - also increase predation risk. While many species reduce activity in response to predators, potentially constraining growth, this trade-off can be mitigated if alternative traits, such as resource digestive efficiency, compensate for reduced activity. Such trait compensation could enable organisms to minimize growth costs while evading predators. To test this idea, we combined a mesocosm experiment with lab-based digestive physiological assays to examine survival selection and plasticity in damselfly larvae exposed to fish predators. We found that selection favored less active individuals, yet this reduction in activity did not suppress growth. Instead, plastic increases in consumption rate, selection for greater assimilation efficiency, and weaker digestive stress responses allowed individuals to maintain growth despite reduced activity and elevated metabolic rates. Our results reveal that selection on digestive physiology can buffer organisms against the putative costs of predator avoidance, demonstrating how trait networks can decouple growth from predation risk in complex ecological systems.