Content area
Full Text
Hum Ecol (2013) 41:773778 DOI 10.1007/s10745-013-9586-8
Human Population Density and Growth Validated as Extinction Threats to Mammal and Bird Species
Jeffrey McKee & Erica Chambers & Julie Guseman
Published online: 18 June 2013# Springer Science+Business Media New York 2013
Introduction
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. Factors of human behavior and economics are certainly involved as well (e.g. Smith et al. 2003; Mikkelson et al. 2007; Holland et al. 2009; McKee 2009; McKee and Chambers 2011), but as the exponential growth of the human population continues it is worth understanding the potential impact of that factor alone on global levels of threatened species.
On the basis of data on nation by nation human population densities and International Union for Conservation of Nature (IUCN) Red List threatened species from the year 2000, McKee et al. (2004) proposed a multiple regression model to explain threats to mammals and birds on continental nations, and forecast future threatened species based upon human population growth projections. It was found that the sum of threatened species per unit area could be best
explained by two variables: human population density and species richness (number of species per unit area); all variables were log-transformed. The model was statistically significant (p<0.001, r2=87.3 %, n=114). Ecological variables such as temperature and precipitation added no further contributions to explaining the variability. Further tests (McKee 2003b) initially showed no such correlation with per capita...