DILEMMAS OF RARITY - BIOGEOGRAPHICAL INSIGHTS AND CONSERVATION PRIORITIES FOR LAND MOLLUSCA

Land molluscs do not feature prominently in general discussions of rar ity and conservation priorities. One national index for prioritization (Israel) is discussed in detail, and its range-size criterion for rar ity applied to other faunas. As in many other taxa, the majority of ra ve species are found in the tropics, but site diversities there are no t consistently higher than those elsewhere. Mean range sizes are small in the tropics. Consideration of various faunas highlights the occurr ence of local radiations of closely I elated species in some, but not all families and genera, and the contribution this makes to molluscan biodiversity. Prioritization of taxonomic isolation would devalue such radiations. In higher latitudes, by contrast, ranges are generally la rger, but sometimes intermittent. A 'hotspot' policy will be effective in such cases, but not in the tropics. A hierarchy of criteria for co nservation priorities is suggested, giving precedence to range-related rarity.