Primate evolution: a biology of holocene extinction and survival on the southeast Asian Sunda Shelf islands

What biological traits distinguish taxa susceptible to extinction from less susceptible taxa? Substantiated island biogeographic theory suggests that after insularization, small islands lose more species than do large islands. Thus, susceptible taxa are those now found on only large islands. The traits of susceptible taxa can thus be found by comparing the biology of species found only on large islands with those also found on small islands. The islands examined here are those of the Sunda Shelf, created as a result of the Holocene rise in sea levels of 120 m. We use four statistical comparisons: comparative analysis by (phylogenetically) independent contrasts (N = 8 contrasts at the subgeneric or deeper level), Spearman correlations, stepwise regression, and principle components analysis (N = 9 subgenera/genera). The genera and one subgenus considered are: Hylobates, Macaca, Nasalis, Nycticebus, Pongo, Presbytis, Symphalangus, Tarsius, and Trachypithecus. Traits of risk appear to be large body mass, low density, large annual home range, and low maximum latitude. Expected traits that did not correlate with susceptibility were low interbirth interval, high percent frugivory, high group mass, low altitudinal range, and small geographic range. The risky traits also apply to just the anthropoids (i.e., prosimians excluded). The risky traits are explained if susceptibility is induced by requirements for a large extent of habitat, a small population size, and specialization. These findings, which indicate that efficiency and plasticity of use of the environment separate susceptible from successful primate taxa, might be relevant to an understanding of hominoid evolution.