Effect of Fruit Scarcity on Use of Spatial Memory in a Seed Predator, White-faced Saki (Pithecia pithecia)
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Many studies have shown that primates use spatial memory to travel efficiently between important resources such as trees with ripe fruit or water holes. White-faced sakis (Pithecia pithecia) have shown strong evidence of spatial memory as they travel efficiently to feed on the seeds of highly productive fruit trees and the ripe fruit of a highly preferred tree species and to drink from natural cisterns in trees. Researchers theorize that primates rely less on memory when they feed on more evenly dispersed food. Here we examine the use of spatial memory in a group of wild white-faced sakis during a month of fruit scarcity when they foraged for desiccated seeds, leaves, insect material, and flowers. We used logistic regression and three computer models (the geometric model, the step model, and the change point model) to analyze their movement patterns. We find that the focal group does not demonstrate the use of memory. These results are in contrast to results from a study of spatial memory with the same focal group in the two immediately preceding months. The results conform to theories on the role of nutritionally dense and patchy foods in driving the use of memory during travel between feeding sites. They demonstrate that, within a short time, a group of primates can vary from a strong reliance on spatial memory to no demonstrable use of spatial memory.
KeywordsCognition Fallback foods Platyrrhine Ranging Scarcity White-faced saki
E. P. Cunningham is grateful to the City University of New York Graduate School, L. S. B. Leakey Foundation, W. G. Kinzey Fund, and Wenner-Gren Foundation for funding this research. E. Cunningham thanks Karyl Swartz whose support made this research possible. We are grateful to the administration of EDELCA for allowing us to study the primates of Guri Lake. We thank Marilyn Norconk for helping E. P. Cunningham work at the study site. E. Cunningham thanks Amy Levine for her hard work and friendship in the field. We also thank John Robinson, Eric Delson, and Sharon Himmanen for their comments and logistical support. E. P. Cunningham thanks Johanna Warshaw for helping her navigate Adobe Illustrator CS2. We are grateful to Joanna Setchell and two anonymous reviewers for insightful comments.
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