Co-mimics have a mutualistic relationship despite unequal defences

Area of Science:

• Evolutionary Biology
• Ecology
• Behavioral Ecology

Background:

• Müller's mathematical treatment of natural selection proposed mimicry benefits defended prey by sharing mortality during predator education.
• Debate exists on whether mimicry between unequally defended species is mutualistic or parasitic.

Purpose of the Study:

• To investigate the relationship between unequally defended co-mimic species.
• To determine if mimicry confers mutualistic benefits under varying defense levels.

Main Methods:

• Utilized artificial prey and wild predators (great tit, Parus major) in a novel world experiment.
• Manipulated the density of moderately defended mimics (perfect or imperfect resemblance) relative to a constant abundance of highly defended models.
• Controlled for density-dependent dilution effects.

Main Results:

• Both model and defended mimics experienced a net benefit from decreased per capita mortality due to increased density.
• Defended mimics did not increase attacks on models when density effects were controlled.
• Accurate signal mimicry was favored by selection.
• Edible (Batesian) mimics increased attacks on models, but dilution negated overall mortality increase.

Conclusions:

• The relationship between unequally defended mimics is mutualistic.
• Current theories may overestimate parasitic costs by overlooking density-dependent benefits.
• Accurate mimicry is selected for, even between species with unequal defenses.