CROSS-PHYLUM BEHAVIORAL ADAPTATIONS TO HETEROGENEOUS DISTRIBUTION OF RESOURCES IN THE SUBSTRATE

One of the most important characteristics of resource distribution in modern ecosystems is its heterogeneous nature. Patchy distribution of food most likely first arose during the Precambrian-Cambrian transition, in what is known as the ‘Agronomic Revolution'. At this time, the appearance and diversification of burrowing and bioturbating organisms stirred up the sediments, disrupting algal and bacterial matgrounds. This disruption of the substrate changed the landscape from one of evenly distributed resources, to one of patchily distributed resources. The organisms that lived during this time period had to have evolved behavioral adaptations to this new, patchy food distribution in order to survive. These adaptations may be linked to a coincident increase in trace fossil complexity and diversity.

The effects of the ‘Agronomic Revolution' can be seen in the widely distributed nature of optimal foraging and patch-foraging behaviors in modern ecosystems. Modern vertebrates exhibit a suite of similar behaviors in response to food patches. A series of experiments were conducted to see if species from different phyla, including the Mollusca, Arthropoda and Nematoda, share this same suite of behaviors. The density of the food patches, the distance of the forager from a patch, and the presence or absence of predation cues and shelter were manipulated during the experiments. Time spent foraging within a patch, moving about between patches, the order of patch choice, patch preference, the amount of food consumed and a forager's movement style within patches were measured in order to highlight the similarities and differences in the foraging behavior of these different organisms. The foraging behaviors shared by these three phyla reflect the evolution of foraging behavior in a common ancestor. The evolution of these behavioral adaptations may also be reflected in changes in trace fossil complexity, abundance and diversity that occurred at the same time as the ‘Agronomic Revolution'.