Shared Responses to Resource Heterogeneity and the Origins of Foraging Behavior

This study was designed to test the hypothesis that variations in foraging ichnofossil morphology are largely a response to spatial patterns in the resource environment. Modern organisms which forage amongst patches, such as Antarctic petrels, pocket gophers and rattlesnakes, have two distinct modes of movement: within-patch and between-patch movement. These different movement styles likely result from a difference in the cost-benefit balance an organism experiences while foraging. Within-patch movement occurs as a forager exploits the resources within a patch, and can take the form of complex spiraling or meandering movements termed area-restricted searching. Between-patch movement represents the non-directed or directed movements as a forager travels from one patch to another, whether or not it has detected and oriented towards a new patch. It consists of longer, straighter paths and prevents a forager from retracing its steps as it searches for a new patch to exploit.

Three different invertebrate species (pond snails, shore crabs, and soil nematodes) were placed within an arena with a single patch of food. All three invertebrates shared similarities in movement styles, and exhibited a difference between within- and between-patch path morphologies. The foragers' pathways within a patch are consistent with area restricted searching. Within-patch movement often resulted in spiraling and meandering pathways. Paths between patches more closely resemble a straight line, with longer paths between turns and smaller turns than within-patch movements. That these behaviors are shared by disparate invertebrate and vertebrate taxa indicates that the behavior is strongly selected for and may have evolved early in metazoan evolution.