Theory 027/Life & Evolution /Behavioural ecology
Mimicry Needs a Model Frequency
Mimicry is described as a gradient of resemblance. The advantage may switch on only once the model is common enough to teach predators.
Batesian mimicry evolves only when the model species exceeds a frequency threshold, so mimics should appear suddenly in populations where the model is common and be selected against where it is rare.
01The evidence
Mimicry is common where models are abundant and rare where they are not, and imperfect mimics persist in some populations, which suggests a frequency-dependent advantage.
02The tension
Mimicry is modelled as a continuous advantage proportional to resemblance. That predicts gradual evolution everywhere, and cannot explain why some populations have no mimics despite available resemblance.
03The mechanism
A predator learns to avoid a pattern only if it encounters the model often enough. Below that rate, the predator samples the pattern and learns nothing, so a mimic gains no protection.
That makes mimicry a threshold phenomenon, and predicts that imperfect mimics should be common just above the threshold, where the advantage is real but weak.
04What this is not
Those models make advantage proportional to resemblance. This makes it conditional on model frequency, which explains absent mimics.
05Predictions
- P1Mimics should appear above a model-frequency threshold.
- P2Imperfect mimics should cluster just above it.
- P3Removing models should collapse mimicry.
06Refutation
Mimics persisting at low model frequency would weaken the threshold account.
07What it changes
It would make mimicry occurrence predictable from community composition.