Factors influencing variation among states in the number of federally listed mammals in the United States

Abstract

We analyzed the relative importance of 12 extrinsic factors potentially influencing the number of federally listed and proposed mammalian taxa in individual states of the United States. We applied multiple regression analysis to four data sets: numbers of federally listed (threatened and endangered) mammals, federal candidate mammals, a combination of both lists, and for comparison, all federally threatened and endangered plants and animals in each state. Amount of area in state parks and percentage of forest cover were the only significant variables in regression models for all four data sets. Number of mammal species, latitude of state capital, and total human population were significant variables in three of the models. Three variables (percentage of original wetlands lost, human population density, and percentage of state in federal land) were not significant in any model. For federally listed mammals, four variables (landscape habitat diversity, loss of wetlands, area of state parks, and percent forest cover) were significant (R2 = 57.5%). Seven variables (number of mammal species, total human population, latitude, topography, area of state parks, and percentage forest cover lost prior to 1908, and percent forest cover) were significant in the model for federal candidate taxa (R2 = 80.7%). For combined listed and candidate mammals, the same seven variables were significant (R2 = 79.6%). For the overall list of federally threatened-endangered plants and animals, five variables (latitude, area of state parks, number of mammal species, percent forest cover, and total human population) were significant (R2 = 63.9%). Based on a positive relationship between the number of listed-proposed taxa and total human population, and negative relationship between number of listed-proposed taxa and latitude, we predict that substantial problems in conservation biology for mammals will be encountered in the southern United States, which are experiencing dramatic increases in human population.