Seasonal or ecological differences in diet and molar microwear in Cebus nigrivittatus

Dental microwear analyses have raised new hopes and questions for functional morphologists. One hope is that analyses will allow insights into subtle dietary differences of extinct species. One major question is whether seasonal and/or habitat differences in dental microwear are reliably detectable. The extensive collections of Cebus nigrivittatus obtained by the Smithsonian Venezuelan Project allowed us to examine seasonal and habitat differences in dental microwear. Specimens were collected from three distinct ecological life zones that are distinguished by both the amount of rainfall and its seasonability. Environmental variation is generally correlated with variation in resource availability which, in C. nigrivittatus, affects diet. Published field studies indicate that these animals depend more on dry hard fruit and chitinous invertebrates during drier times and succulent fruits and caterpillars during wetter times of the year. As in previous microwear analyses, epoxy replicas were prepared from dental impressions, and the replicas were examined under a scanning electron microscope. Two micrographs were taken of facet 9 on M2 of each specimen. Mean values for the proportion of pits (vs. scratches), pit width, and scratch width were computed for each of 62 individuals and compared between ecological zones and collecting dates by using a multiple comparison test. Results indicate that, while seasonal differences in molar microwear in C. nigrivittatus are perhaps reliably detectable, 1) they are small in magnitude, 2) they are only detectable in certain ecological life zones, and 3) they are not of the order of magnitude that will obscure major interspecific differences in molar microwear such as those between C. apella and C. nigrivittatus.