Predator-induced changes in metabolism cannot explain the growth/predation risk tradeoff

Area of Science:

• Ecology
• Animal Physiology
• Evolutionary Biology

Background:

• Organisms face a trade-off between predator defense and growth/development.
• Reduced activity is the assumed cause for growth decline under predation risk.
• However, physiological costs beyond reduced foraging or defense allocation are often observed.

Purpose of the Study:

• To investigate the physiological basis of defense costs in tadpoles (Rana temporaria) under predation risk.
• To measure oxygen consumption as an indicator of metabolic rate in response to predation risk.
• To determine if metabolic rate changes explain the growth decline associated with predator avoidance.

Main Methods:

• Tadpoles were exposed to predation risk for short-term and long-term periods.
• Oxygen consumption was measured to assess metabolic rates.
• Changes in oxygen consumption were analyzed in relation to predation risk exposure.

Main Results:

• Short-term exposure to predation risk resulted in increased oxygen consumption, indicative of a "fight-or-flight" stress response.
• Long-term exposure (three weeks) led to a decrease in oxygen consumption.
• This decrease in metabolic rate could potentially mitigate growth costs associated with predator defense.

Conclusions:

• The stress response to predation risk is instantaneous and reversible.
• The observed metabolic changes do not fully explain the growth cost associated with predator defense.
• Alternative behavioral or physiological mechanisms must be responsible for the growth/predation risk trade-off.