Economic well-being, the distribution of income and species imperilment

Mikkelson et al.'s (PLoS One 2(5):e444, 2007) empirical finding of a positive relationship between income inequality and species imperilment in an international context is less-than-compelling for 3 reasons: (a) findings for their limited sample size, which constitutes a relatively small fraction of all countries, may not hold in the context of a more encompassing sample of countries, (b) their aggregate analysis, which includes amphibians, birds, mammals, reptiles, and vascular plants, may mask important taxa-level differences, and (c) the absence of controls for spatial autocorrelation between countries. Using data from 133 countries, we estimate models of factors that influence species imperilment and, controlling for cross-border effects, we reproduce the Mikkelson et al. findings, then demonstrate that they are sensitive to inclusion of additional countries, model specification, and to data aggregation.