Are rare primate taxa specialists or simply less studied?

Abstract Aim Rare species are reported to be specialized. However, rare taxa are usually less studied than are common taxa. If so, the reported specialization might be just a result of paucity of records. We here test for this sampling artefact in primates, a taxon in which rarity has been explained by specialization. Location Tropical Africa, Madagascar, Asia, Americas. Methods We define rare and common species as those with geographical range sizes in the lower and upper quartiles, respectively, for primates in each realm. We conducted two independent searches of published literature to determine if there were significantly fewer studies on a common measure of specialization, diet, for rare vs. common species. We then tested for sampling artefact in reported diet breadth by comparing the number of references needed to obtain it for both rare and common species. Results We found, in both literature searches, significantly fewer studies on diet for rare primates – a mode of zero references for rare species, and one for common. By contrast, no significant difference existed for number of references needed to attain the full reported diet breadth: a median of one reference for both specialized, rare and generalized, common species. Main conclusions Rare species are indeed studied less. Nevertheless, the finding that rare primates are specialists is not necessarily mere sampling artefact.