Gastrointestinal parasitism and recursive movements in free-ranging mandrills

Understanding animal movements is a key prerequisite for deciphering ecological processes such as population dynamics, community structure or biological invasions. Many animals restrict their movements to certain areas (home ranges) by alternating visits among several suitable sites. The dynamics of these recursive movements are assumed to be primarily driven by food availability and predation risk. In contrast, environmental parasite pressures have rarely been considered as possible drivers of animals' ranging patterns. In this article, we present evidence that environmentally transmitted gastrointestinal parasites may shape recursive movement patterns of a group of free-ranging mandrills, Mandrillus sphinx. These rainforest-dwelling primates returned less frequently and after longer time lags to sites, including sleeping sites, they had contaminated than to sites with low contamination levels. This pattern was especially pronounced during the dry season, when contamination risk was highest. In contrast, rainfall shortened the time between visits, consistent with the hypothesis that rainfall may wash away parasites, allowing a more rapid return to previously used sites. Although resource distribution and predator threat could not be ruled out in this study, we suggest that the risk of acquiring environmentally transmitted parasites is possibly another factor influencing animal ranging patterns as well as habitat selection or species distribution. Consequently, parasites and their distribution in the environment, as well as the possible antiparasite strategy we document here, should be targets for future research on animal movement.