Ecological and behavioral studies of the decorator crab, Microphrys bicornutus Latreille (Decapoda : Brachyura): A test of optimum foraging theory

Abstract

The food and camouflage selectivity of the decorator crab, Microphrys bicornutus Latreille, was studied in relation to resource availability on a Caribbean fringing reef in the Republic of Panama. We attempted to test the hypothesis that resource availability affects niche breadth. Seasonal aerial exposures of the reef-flat devastated plant-animal assemblages, facilitating foraging comparisons in high and low reef biomass. Resource availability altered niche breadth. As predicted, M. bicornutus consumed a wider variety of species, when resources were scarce, and fewer species, when resources were abundant. Decorating behavior served as a control for resource availability while measurements of potential resources controlled for the choice in sampling periods. The prediction that predators may consume less preferred food items with greater frequency than more preferred food items, if there is a greater abundance of the less preferred food, was confirmed. Also, food preference did not readily change in response to changes in the environment. While highly predictable resources appeared to comprise the bulk of the crab's annual diet, unpredictable resources dominated the crab's diet over shorter periods. This suggests that the predictability of a resource in promoting resource specialization or generalization may not be as important as the number or types of food necessary for the growth and reproduction of the organism. High “within-phenotype components” of niche breadth for feeding and for decorating showed that the population of M. bicornutus has one generalist phenotype. The diet and camouflage compositions consisted mainly of the seaweeds, Acanthophora spicifera (Vahl) Borgesen and Laurencia papillosa (Forsskal) Greville, with animal taxa comprising not > 10% of either assemblages.