Preserving the information content of species: Genetic diversity, phylogeny, and conservation worth

A variety of phylogenetic measures have been proposed to quantify distinctiveness, often held to mark species of high conservation worth. However, distinctiveness of species and their numbers have different implications for conservation policy, depending on whether moral, esthetic, or utilitarian reasons are accepted as justifying conservation. The utilitarian position values species according to increasing numbers, and as they are more, as opposed to less, distinctive. The view is taken that conservation should seek to maximize the preserved information of the planet's biota, best expressed in terms of genetic information held in genes and not in portions of the genome of uncertain or no function. Gene number is thus an important component of assessing conservation value. Phylogenetic measures are better indicators of conservation worth than species richness, and measures using branch-lengths are better than procedures relying solely on topology. Distance measures estimating the differences between genomes are preferable to substitution distances. Higher-taxon richness is a promising surrogate for branch-length measures. Complete enumeration of biotas in terms of phylogeny is desirable to avoid uncertainties in the use of indicator groups, and this is achievable now for bacteria. Phylogenetic measures are already important for management of sets of populations within species and are applicable for sets of species. Measures incorporating extinction probabilities and decision costs are being developed, and these, in conjunction with the use of confidence limits on the conservation worth of alternative reserves, are vital for conservation decision-making.