Hominid paleoecology and competitive exclusion: Limits to similarity, niche differentiation, and the effects of cultural behavior
Fossil evidence from the Plio-Pleistocene of Africa apparently has confirmed a multi-lineage interpretation of early hominid evolution. Empirical refutation of the single species hypothesis must now be matched to the evolutionary ecology theory, which can underwrite taxonomic assessment and help to explain sympatric hominid coexistence. This paper contributes to that goal by reassessing the ecological rationale provided for the single-species hypothesis. Limiting similarity concepts indicate that the allowable ecological overlap between sympatric competitors is greater than the degrees of metric overlap often advanced as standards for identifying fossil species. Optimal foraging theory and the compression hypothesis show that the initial ecological reaction of a hominid to a sympatric competitor would likely be micro-habitat divergence and possibly also temporal differentiation of resource use. The long-term, evolutionary response is niche divergence, probably involving diet as well. General niche partitioning studies suggest that diet and habitat are the most common dimensions of niche separation, although temporal separation is unusually frequent in carnivores. The equation of niche with culture, basic to the single-species hypothesis, has no analytic meaning. Finally, four minor points are discussed, suggesting that (a) extinction is not unlikely, even for a long-lived and competitively competent hominid lineage, (b)parsimony is fickle, (c)interspecific mutualism may jeopardize survival, and (d)generalists are subordinate competitors, but for hominids, seemingly, successful ones. I argue that analog models of hominid paleoecology should be replaced by the use of zoological and anthropological observations to assess the generality and reliability of ecological theory and comcepts that may encompass early hominids.