Resource Characteristics and the Evolution of Information Centers

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Abstract
Avian nesting colonies previously have been explained as information centers, which allow unsuccessful foragers to follow successful neighbors to profitable feeding areas. A simple geometric model is developed to quantify the ecological parameters favoring information-based colonial nesting and communal roosting behavior in a variety of animal taxa. Unsuccessful foragers should act to maximize their probability of finding a better area, while minimizing their travel time to that site. Two parameters, affected principally by environmental factors, are central to the model: the distance between food patches relative to the average distance between the nest and food patches (the distance ratio) and the probability of a forager moving to a better feeding area by chance (ppat). Several ecological parameters affect ppat: patch quality distribution, patch quality assessability, prey mobility and patch duration. The advantages of information centers are greatest when ppat is low and the distance ratio is high, and when foragers can preferentially follow neighbors to high quality patches. Even if foragers cannot distinguish successful neighbors, information centers still can function if the effective distance ratio is > 2. Information centers can function at lower ratio values if foragers return to high quality patches or if successful foragers can be distinguished and followed. The model''s general predictions are supported by evidence from colonial seabirds and seed-gathering ants. The benefits of obtaining feeding success information from neighbors increase as ppat decreases. Low ppat values should favor deception or masking of information in foragers nesting among nonrelatives. Overt communication is favored in groups of relatives feeding in environments with low ppat values. Within colony variation in recruitment behavior of seed-gathering ants supports this prediction. The genetic ramifications of involuntary assistance to neighbors suggest that colonial individuals may preferentially nest among relatives to avoid aiding genetic competitors.