Taxonomic homogenization in ungulates: Patterns and mechanisms at local and global scales
Aim: The aim of this paper is to examine taxonomic homogenization in ungulates globally and at the local scale in South Africa. Specifically, we aim to examine the roles of distance, scale, time, extinctions vs. introductions, and extralimital vs. extraregional introductions in the homogenization of ungulate biotas, and to determine pathways of introduction of ungulate species globally and the proximate explanatory variables of ungulate introductions in South Africa. Location: Forty-one countries globally and three spatial resolutions in South Africa. Methods: Indigenous, extirpated and established introduced ungulate species data were obtained for countries globally, and at a quarter-degree grid-cell resolution in South Africa. Homogenization was calculated using Jaccard's index of similarity (JI) for countries globally and for three spatial resolutions in South Africa. Zoo holdings and transfer data from the International Species Information System database were used to investigate the relationship between non-indigenous ungulate species introductions and the number of non-indigenous ungulate species in zoos. Relationships between JI and species richness, and between numbers of introductions and several environmental and social factors were examined using generalized linear models. Results: Homogenization in ungulates was 2% for countries globally and 8% at the coarsest resolution in South Africa. Homogenization increased with increasing resolution and with time, but it decreased with increasing percentage change in species richness. Globally, introductions contributed more to homogenization than did extinctions. Within South Africa, extralimital introductions contributed more to the homogenization of ungulate assemblages than did extraregional ones, and ungulates were typically introduced to high-income areas with high human population and livestock densities. The same was not true in the past, when ungulates were introduced to ungulate species-poor areas. The number of non-indigenous ungulate species established in a country is significantly related to the number of non-indigenous ungulate species in zoos in the country, possibly owing to sales of surplus animals from zoos. Main conclusions: Ungulate faunas are homogenized at both the global scale and in South Africa, with extralimital introductions being of considerable significance regionally. In consequence, increasing attention will have to be given to the conservation consequences of ungulate translocations, both within particular geopolitical regions and across the globe. © 2008 The Authors.