Development of a Foraging Model for a Field Population of the South American Sun-Star Heliaster helianthus

Abstract

SUMMARY (1) The objective of this study is to examine analytically size-related predation in a population of Heliaster helianthus in an intertidal rocky shore habitat in central Peru. Among 11243 prey individuals recovered from a total of 1132 feeding predators, the mussel Semimytilus algosus was predominant with an average proportion of 85-5% and 85-7% by number and biomass, respectively. (2) A graph describing the patterns of energy/biomass distribution among different size-classes of mussel prey in the field was obtained and used for comparison with the patterns of prey-size utilization by the predator population. Larger individuals of H. helianthus fed on clumps of Semimytilus algosus containing larger mussels, but the biomass distribution of all S. algosus consumed closely resembled that of the natural prey population, except in the smallest predator size-group (< 109 cm) where small mussels were more strongly represented in the diet. (3) A model was developed to account for the selection of meal sizes in the H. helianthus population. Frequency distributions of observed meal sizes for four predator size categories were compared and the patterns observed were generally in agreement with the model. (4) The study suggests that 'energy maximization', the core assumption of classic optimal diet choice models, is not relevant to the choice of prey size and meal size in H. helianthus. Difficulties in applying optimal foraging models based on the energy maximization premise to the analysis of foraging patterns in field animal populations are discussed.