Community Niches and Evolution of Generalist Primates: A Preliminary Assessment of Plio-Pleistocene Cercopithecidae in Africa

Niche construction theory has increasingly received attention in paleoanthropology as a new focus for considering the evolutionary consequences of hominin tool-use and cultural adaptation starting in the Pleistocene. Modern humans excel at dramatic landscape modification, allowing us to regulate the effects of natural selection on our own species while simultaneously imposing novel selective forces on other living organisms. The long-standing effects of this current and past niche construction by our species makes it challenging to explore the timing and effects of hominin behavioral adaptations using modern analogues alone. In this paper I employ a community ecological approach to address evolutionary trends within a group of generalist primates—the Cercopithecidae—from Pliocene and early Pleistocene localities in Ethiopia, Kenya, and South Africa. Principal component analysis is used to model the dental ecomorphological niches of fossil cercopithecid species and taxocenes (a closely related subset of the faunal community), along with a comparative sample of extant cercopithecids from sub-Saharan Africa. Differences in the dental morphological niches of modern cercopithecid taxocenes can be attributed to variation in habitat conditions. Taxocenes appear more similar at local scales and co-occurring cercopithecids are relatively evenly dispersed in their dental morphological niche space, suggesting that they are able to maximize their available niches while avoiding competition within these taxocenes. Fossil taxocenes in eastern Africa (Hadar, Shungura, and Koobi Fora formations) also tend to occupy similar niches to one another and exhibit minimal spatial or temporal variation in their dental morphological niches. These eastern African taxocenes are distinct from those in South Africa (Makapansgat, Sterkfontein, Swartkrans, and Kromdraai), both in their overall niche positions and in measures of dispersion. Despite high species richness, cercopithecid taxocenes in the early Pleistocene of South Africa occupied restricted niches with more closely packed species, a pattern with no modern African analogue. The loss of this South African niche and an overall niche shift between early Pleistocene and modern cercopithecid taxocenes in Africa likely reflects a combination of climatic and habitat factors along with increasing impacts from tool-using hominins during the later Pleistocene. These results provide an important comparative pattern for considering how Pliocene hominins may have responded to environmental and habitat variation. Further, given the challenges of interpreting hominin behavioral evolution during this period, community paleoecological approaches like the one taken here can be useful for identifying changes in other mammalian groups in response an expanded hominin niche.