The diversity of land molluscs-Questions unanswered and questions unasked

摘要

Studies on the diversity of land molluscs raise a number of crucial questions that remain unanswered, or in some cases have not been asked. At the most fundamental level, we need to question the comparability of species concepts used in different studies, which influence our assessment of overall diversity and of regional differentiation. Current estimates of global diversity are likely to be too low. Beyond that, the assumption that all species can be represented by equivalent digits needs to be challenged: the range of size, habits and trophic levels needs to be taken into account. While higher taxonomic categories can be used as rough proxies for similar ecology, we have very little detailed information other than for shell size and shape, where the huge range suggests some radical differences within and among faunas. The range of niches occupied may differ among faunas: are we dealing with comparable taxonomic entities? Our knowledge of microhabitat requirements is severely deficient.