Frequency of Batesian mimics

The presence of innocuous monarch butterflies flying with toxic ones raises interesting questions for mimicry. From the point of view of the predator automimics are perfect Batesian mimics if we assume that they differ in no way from their models except as a result of toxins in the diet of one and not the other. They therefore make a useful model for perfect Batesian mimicry, that is, where the predator cannot distinguish visually between model and mimic. 

Owen (1971, pp. 131-135) has presented data on several African associations of butterfly models Bematistes spp.) and mimics Pseudacraea eurytus). In most examples the mimic is considerably less frequent than its model, but it outnumbers it in one sample. As might be expected, the relative frequencies vary considerably depending on the nature of the model/mimic pair (relative palatability, closeness of resemblance, sex-limited or not) and on the presence or absence of other species in the mimicry ring. 

Sheppard (1959) has also discussed this correlation of mimics to models, as well as the related phenomenon of pattern breakdown in Batesian mimics. If for reasons unrelated to mimicry there is a sudden increase in the number of mimics or a sudden decrease in the number of models, the selective advantage of close mimicry declines, perhaps even becomes disadvantageous and the variability of the mimics increases. 

The limitations of numbers have been vexing to some who see a paradox in (i) the mimetic pattern must confer an advantage upon its possessor, otherwise it wouldn t exist (ii) the mimic must be rare , and a gene with a selective advantage should be common, shouldn t it The subtleties of advantage , selection , rare/common , etc., will be taken up in Section 10.7, but the following quote from E. B. Ford (1975) may help  

If the frequency of mimic is thus severely limited, polymorphism in the mimic species is strongly encouraged. Thus, while there are many species like the viceroy that consist of a single Batesian morph, many others consist of a cryptic 

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