Mass-dependent predation risk and lethal dolphin-porpoise interactions

Area of Science:

• Marine Ecology
• Animal Behaviour
• Predator-Prey Dynamics

Background:

• Mass-dependent predation risk (MDPR) theory posits that increased body mass, while reducing starvation risk, elevates predation risk due to impaired escape performance.
• This trade-off has primarily been studied in birds, with limited understanding of its applicability to other animal groups.

Purpose of the Study:

• To investigate if MDPR applies to non-avian species, specifically harbour porpoises (Phocoena phocoena).
• To examine the relationship between bottlenose dolphin (Tursiops truncatus) presence and porpoise energy reserves in coastal Britain.

Main Methods:

• Utilized a natural experiment in coastal Britain where dolphins pursue but do not consume porpoises.
• Compared energy reserve levels in harbour porpoise populations experiencing high versus low levels of dolphin 'predation' pressure.

Main Results:

• Harbour porpoises in areas with high dolphin activity exhibited significantly lower energy reserves than expected.
• This reduction in reserves decreased a porpoise's potential survival time without feeding by approximately 37%.

Conclusions:

• Provides the first evidence of a mass-dependent starvation-predation risk trade-off in a marine mammal.
• Suggests MDPR may be a general ecological principle applicable across diverse animal taxa, not exclusive to birds.