Trade-offs associated with dietary specialization in corallivorous butterflyfishes (Chaetodontidae: Chaetodon )

Abstract

Increasing dietary specialisation is an inherently risky strategy because it increases a species’ vulnerability to resource depletion. However, risks associated with dietary specialisation may be offset by increased performance when feeding on preferred prey. Though rarely demonstrated, highly specialised species are expected to outperform generalists when feeding on their preferred prey, whereas generalists are predicted to have more similar performance across a range of different prey. To test this theory, we compared growth rates of two obligate coral-feeding butterflyfishes (Chaetodon trifascialis and C. plebeius) maintained on exclusive diets of preferred versus non-preferred prey. In the field, C. trifascialis was the most specialised species, feeding almost exclusively on just one coral species, Acropora hyacinthus. Chaetodon plebeius meanwhile, was much less specialised, but fed predominantly on Pocillopora damicornis. During growth experiments, C. trifascialis grew fastest when feeding on A. hyacinthus and did not grow at all when feeding on less preferred prey (P. damicornis and Porites cylindrica). Chaetodon plebeius performed equally well on both A. hyacinthus and P. damicornis (its preferred prey), but performed poorly when feeding on P. cylindrica. Both butterflyfishes select coral species that maximise juvenile growth, but contrary to expectations, the more specialised species (C. trifascialis) did not outperform the generalist (C. plebeius) when both consumed their preferred prey. Increased dietary specialisation, therefore, appears to be a questionable strategy as there was no evidence of any increased benefits to offset increases in susceptibility to disturbance.