Predictable Sequences of Species Loss with Decreasing Island Area - Land Birds in 2 Archipelagoes

We quantify the notion of predictable species loss from progressively smaller islands, and apply the quantification to the indigenous forest-dwelling birds of a series of New Zealand islands and to the passerines of the Cyclades Archipelago in the Aegean Sea. The analysis focuses on the reasons why the species-area relationship deviates from a perfect rank-correlation. For both avifaunas, most species are found remarkably predictably: they approximate a pattern in which each species occupies all those and only those islands larger than some species-specific minimum area. However, a minority of species in each avifauna do not conform to this pattern. Possible reasons for non-conformance include habitat differences among islands, anthropogenous extinctions, and equilibrium turnover. To the extent that the first two forces predominate, it would be far better to base conservation decisions on species lists from particular tracts that are potential refuges than on island occupancy patterns.