Feeding behavior of carnivorous and herbivorous organisms is commonly explained in terms of nutritional requirements. However, feeding behavior of omnivorous organisms is difficult to predict and may not be based on nutritional requirements alone. To assess the plasticity of feeding behaviors exhibited by an omnivore, we conducted a feeding experiment using juvenile signal crayfish ( Pacifastacus leniusculus (Dana, 1852)), both alone and in the presence of conspecifics and predators. Crayfish were presented with three types of food (chironomids, mayflies, and woody debris) in experimental enclosures, and the food type consumed and time to consumption were recorded. Although the same overall food choice (chironomid larvae) was made in all trials, the time it took for the juvenile crayfish to make a food selection was longer in the presence of adult conspecifics (both male and female) and adult cutthroat trout ( Oncorhynchus clarkii (Richardson, 1836)). Food selection also took longer, although not significantly, in the presence of conspecific juvenile crayfish, and no changes in behavior were noted in the presence of young-of-the-year (YOY) cutthroat trout. The altered behavior of the juvenile crayfish observed in the presence of adult fish and crayfish can lead to context-dependent effects of this omnivore on its community. Ecologists must be increasingly aware that the feeding of omnivores may not be solely based on nutritional criteria.
