Use and usefulness of measures of marine endemicity in South Africa

Abstract

Numerous authors have cited numbers, or proportions, of endemic species within South(ern) African marine taxa, but comparisons between these statistics are confounded by differing definitions of regional boundaries and differences among data sets analysed. These have resulted in considerable variations in published endemicity data, even within the same taxonomic group. We tabulated and compared key endemicity statistics for regional marine taxa and explained biases in the data sets. The most comprehensive data sets available give overall marine endemicity within the national boundaries of South Africa as 28–33%, but estimates within individual taxa making up these totals vary enormously, from 0% (Aves, Mammalia) to over 90% (Polyplacophora). We also examined published data documenting localised endemicity patterns around the coastline. These consistently show the highest numbers of endemics occurring along the South Coast. There are logical biogeographical reasons to expect this trend, but endemicity rates are also inherently biased by distance from defined political boundaries and by differing sampling effort locally and in neighbouring countries. Range restriction is considered a better measure of conservation status than endemicity, although it is far less often used and yields very different patterns. Properly and consistently calculated measures of national endemicity do, however, retain significant conservation value, and the rates for South Africa marine biota are high relative to other regions globally, being exceeded only by New Zealand and Antarctica. It is important that when citing endemicity statistics, researchers and conservation managers understand the definitions used and the many constraints under which these measures are derived.