AGE, AREA AND AVIAN DIVERSIFICATION

Using coarse resolution data on the spatial distribution of the entire New World avifauna, we test fbr phylogenetic patterns in the mean and total geographic range sizes of taxa. The analyses reveal that (i) th e species-range size distribution is only approximately normalized, an d remains significantly left-skewed, under logarithmic transformation. Most variance in range sixes is explained at the level of species wit hin genera; (ii) there is no effect of the age of taxa on mean clade r ange size, although older taxa are more likely to have larger total ra nge sizes; (iii) there is some evidence that taxa comprising more spec ies have larger total range sizes; (iv) there is little or no evidence for a relationship between rate of cladogenesis and range size. The r esults suggest that geographic range size is a labile trait, at least for New World birds, and that the influence of evolutionary history is only weakly detectable in the range size variation of extant taxa; at least at the scale of analysis used here. In addition to these conclu sions, two general and important procedural issues emerge. (C) 1997 Th e Linnean Society of London.