New indices for ranking conservation sites using ‘relative endemism’

Conservation requires decisions about which sites to protect. Choices are frequently made using distributions or occurrences of rare or endemic species, or species richness. For many assemblages, such data do not exist, may be semi-quantitative, or the scale at which the information available is not the scale at which sites need to be protected. The number of observed species does not contain information on identity, abundances or frequencies of occurrence. Incorporating data on abundances or frequency of occupation of habitat into indices to prioritize sites would allow greater emphasis to be placed sites that have disproportionate numbers of species with limited dispersion. This manuscript describes two indices, which combine information about species identity and abundances (cover/biomass) or occurrences in each site, relative to all other sites. They are applicable to any set of species for which information on abundances throughout their range do not exist, but for which there are data on abundances and/or occurrences in replicate representative samples. They allow sites to be ranked according to their importance for numbers/relative amounts of species, or the frequencies with which they are sampled. They are illustrated using simulations and data from sessile and mobile assemblages on boulders. The indices ranked sites in importance in ways not possible from species counts, ranking sites differently, depending on which assemblage was examined. The appropriate index for any situation depends on the biologies of the organisms and whether abundances or occupancy of patches of habitat within a site was considered most important.