Human Population Density and Growth Validated as Extinction Threats to Mammal and Bird Species
Past extinctions of mammals are well correlated with the expansion of the human enterprise during the Holocene, and probably earlier (e.g. Klein 2000; Alroy 2001; McKee 2003a). It had long been suspected that the quantity of threatened species today could be linked to the size, density, and growth of the human population. Several studies have attempted to test and quantify this notion on a contemporary global scale (Kerr and Currie, 1995; Forester and Machlis 1996; Kirkland and Ostfeld 1999; Thompson and Jones 1999; Cincotta and Engelman 2000; Cincotta et al. 2000; McKinney 2001; Harcourt et al. 2001; Ceballos and Ehrlich 2006; McKee 2003a; McKee et al. 2004; Gaston 2005; Burgess et al. 2007; Luck 2007a, b; McKee and Chambers 2011). Whereas specific conclusions have varied, overall support has emerged for a strong correlation between human population density and the relative number of threatened species, if not direct causation.