Species-area relationship and its determinants for mammals in western North American national parks

The relationship between non-volant mammalian species richness and area in 24 western North American national parks is examined. The exponential and the power function models are concluded to be the ‘best' models and account for nearly an identical proportion of the total variance (˜ 69%). Two principal hypotheses, the urea per se and the habitat diversity hypotheses, have been proposed to explain the species-area relationship. Support exists for both hypotheses based upon partial correlation analysis of non-volant mammalian species richness with area, elevational range, latitude, number of vegetative cover types and index of vegetative cover diversity. I conclude that area per se and habitat diversity defined as environmental heterogeneity are the best predictors of non-volant mammalian species richness in western North American national parks. I also conclude that vegetative cover diversity is a poor predictor of mammalian species richness in western North American national parks. Several problems with assessing the area per se and habitat diversity hypotheses are noted. These are: (1) the definition of the term ‘habitat'; (2) the predictions of these two hypotheses may not be mutually exclusive; and (3) area and habitat diversity tend to be intercorrelated. The slope (z) of the power function is equal to 0.12. The hypothesis that variation in the slope of the power function for nature reserves worldwide is a result of the comparative sizes of the nature reserves cannot be excluded. There has been considerable discussion in recent years about the conservation implications of the species-area relationship. Much of this discussion has been concerned with whether a single large reserve contains more species than several small reserves (SLOSS). The answer to SLOSS is heavily dependent upon the objectives of a reserve, the autecology of the species, and the ecological independence of the reserves. It is suggested that particular attention be given to area and elevation when designing nature reserves.