Eastern Arc Mountains and Coastal Forests of Tanzania and Kenya ...

Table 3. Numbers of sites with Critically Endangered, Endangered and Vulnerable species in fivemajor taxonomic groups in the Eastern Arc Mountains and Coastal Forests hotspotNumber of Sites*TotalTaxonomic Group Kenya Tanzania SitesMammals 14 26 40Birds 10 19 29Amphibians 2 17 19Gastropods 1 3 4Plants 52 87 140*The total number of site outcomes is 160.An alternative to a simple threatened species richness ranking is to examine the site data forcomplementarity and to determine: 1) the minimum set of sites that contain all globallythreatened species at least once; and 2) those sites that contain a species that occurs nowhere else(i.e. are irreplaceable, even if they only have one species). A preliminary analysis (Rodriguesand Langhammer pers. comm.) indicates that the minimum set consists of 35 sites and that, ofthese, 26 are irreplaceable. If the sites are ranked by species richness, the top 33 sites contain 97percent of all threatened species (although it takes 129 sites to capture 100 percent). This meansthat, except for a few species, the selection of sites by a simple threatened species richnessranking is not a bad prioritization strategy compared with the complementarity set. Among thetop 20 sites by species richness, only two (Bagomoya District Forests and North PareMountains) fail to make it into the complementarity set and only three are not irreplaceable(Bagomoya District Forests, North Pare Mountains and Mafia Island).It must be understood, however, that neither strategy should be applied exclusively. There aremany reasons for this. First, the survival of a threatened species is likely to require conservationinterventions at more than one site. For example, the best known population of Clarke’s weaveris in Arabuko-Sokoke Forest, but it doesn’t breed there. Second, a species found in several sitesmay only have viable populations in one or two of them and these critical sites may not becaptured by complementarity, or rank highly for species richness. Third, variation in the rawdata (numbers of threatened species per site) can be partly accounted for by large site differencesin area (over five orders of magnitude: Appendix 3) and/or research investment. Fourth, theoutcome analysis is based on a small number of taxonomic groups and in some of these groups(especially the plants) the Red Lists are in serious need of re-assessment. Fifth, prioritizing sitesmust take into account not only their relative biological importance, but also the degrees ofthreat to them and the current investments in them.22