A comparative analysis of the avifaunas of different zoogeographical regions

Abstract

This paper provides a comparison of the landbirds of all main zoogeographical regions, based on the most recent (Sibley–Monroe) listing and classification of the world's birds. This classification arranges 9416 landbird species (i.e. excluding seabirds) into 2002 genera, 140 families and 23 orders. On this basis, the Neotropical region holds 36% of all known landbird species and 45% of genera, the Afrotropical region holds 21% of species and 24% of genera, the Indomalayan region 18% of species and 22% of genera, the Australasian region 17% of species and 23% of genera, the Palaearctic region 10% of species and 14% of genera and the Nearctic region 8% of species and 15% of genera. These major continental regions thus show 4.6-fold variation in species numbers or 9.1-fold variation in species numbers per unit area. The region of Oceania, comprising many Pacific Islands, holds only 2% of the world's bird species and 4% of genera. About 92% of all bird species on the continental parts of the Neotropical, Afrotropical and Australasian regions are endemic to those regions, compared to 64% of the Indomalayan, 54% of the Nearctic and 46% of the Palaearctic species. The Oceania region has the smallest number of endemics, but these form 87% of all species occurring naturally in this region. About 91% of all landbird species breed in only one zoogeographic region, another 8% in two regions, with the remaining 1% in three to seven regions. Only four species breed in all seven regions. Similarities in the species composition of different regions were compared using Jaccard and Simpson indices. As expected, each region shares the greatest number of species with the closest other region and the fewest species with the most remote region. As in previous analyses, the Neotropical and Australasian regions emerged as having the most distinctive avifaunas. Regions that hold large numbers of landbird species also hold large numbers of genera and families, as well as high species-per-genus and species-per-family ratios. Comparable levels of diversity thus extend through all these taxonomic categories. This implies that, whatever factors have promoted particular levels of avian diversity in the different regions, they are of long standing. As found in previous studies, species-per-genus and species-per-family ratios are lower in island than in continental avifaunas. No relationship is apparent between the size of each zoogeographical region and the numbers of species, genera and families found there; rather those regions with tropical forest have many more bird taxa overall than those without.