Pleistocene extinctions: the pivotal role of megaherbivores

摘要: Two alternative hypotheses have been advanced to explain the demise of about half mammalian genera exceeding 5 kg in body mass later Pleistocene. One hypothesis invokes climatic change and resulting habitat transformations. This fails predict increased likelihood extinctions with increasing size, greater severity both North South America than Eurasia or Australia, lack simultaneous Africa tropical Asia, absence at end previous glacial periods. The other human predation as primary cause. a number avian species not obviously vulnerable overkill. I propose "keystone herbivore" hypothesis, based on ecology extant African megaherbivore, (i.e., animals 1,000 mass). Due their invul- nerability non-human adults, these attain saturation densities which they may radically transform vegetation structure composition. elephant can closed woodland thicket into open grassy savanna, create gaps colonized by rapidly-regenerating trees forests. Grazing white rhinoceros hippopotamus tall grasslands lawns more nutritious short grasses. elimination megaherbivores elsewhere world hunters Pleistocene would promoted reverse changes vegetation. conversion parklike woodlands mosaic typical much during uniform forests prairie we find today could be consequence. Such detrimental distribution abundance smaller herbivores dependent upon nutrient- rich spatially diverse created megaherbivore impact. At same time become predation. influence is major factor differentiating terminal glaciation from those occurring glacial-interglacial transitions.