Interference competition, the spatial distribution of food and free-living foragers

• Main Authors: Wouter K. Vahl, Jaap Van, Der Meer, Kim Meijer, Theunis Piersma, Franz J. Weissing
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2007
• Subjects: Arenaria interpres
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.540.7378; http://dissertations.ub.rug.nl/FILES/faculties/science/2006/w.k.vahl/c4.pdf

Studies of interference competition among foraging animals generally assume that variation in the spatial distribution of food can be neglect-ed. This assumption may be problematic as resource defence experi-ments suggest that such variation is of the essence in some interference mechanisms. Interpretation of the results of field experiments on this topic, however, is hard because of the way these experiments have been analysed: variation in the abundance of foraging animals has consistent-ly been treated as nuisance or as a predictor variable, whereas it usually is one of the prime responses. We performed a field experiment in which we provided wild ruddy turnstones (Arenaria interpres) with experimental plots that varied in the distance between a fixed number of so-called food pits, and, using multivariate statistics, we studied effects on the combination of the turnstones ’ behaviour and abundance. We found that when food pits were more spaced out, turnstones were present in higher numbers, while interacting less with each other, but that they spent about the same time digging for food, our measure of intake rate, at each inter-pit distance. These findings imply that to reli-ably predict the combination of the number, intake rate and amount of aggression of turnstones, the spatial distribution of food has to be known. We would not have reached this conclusion if we had used uni-variate statistics or if we had treated variation in forager abundance as mere nuisance. Moreover, treating forager abundance as a response variable led to the insight that while experiments on captive foragers usually exclude patch choice decisions, experiments on free-living for-agers necessarily involve patch choice decisions.