The impact of taxonomic change on conservation: Does it kill, can it save, or is it just irrelevant?

Species numbers are increasing rapidly. This is due mostly to taxonomic inflation, where known subspecies are raised to species as a result in a change in species concept, rather than to new discoveries. Yet macroecologists and conservation biologists depend heavily on species lists, treating them as accurate and stable measures of biodiversity. Deciding on a standardized, universal species list might ameliorate the mismatch between taxonomy and the uses to which it is put. However, taxonomic uncertainty is ultimately due to the evolutionary nature of species, and is unlikely to be solved completely by standardization. For the moment, at least, users must acknowledge the limitations of taxonomic species and avoid unrealistic expectations of species lists.

Taxonomy and species conservation are often assumed to be completely interdependent activities. However, a shortage of taxonomic information and skills, and confusion over where the limits to 'species' should be set, both cause problems for conservationists. There is no simple solution because species lists used for conservation planning (e.g. threatened species, species richness estimates, species covered by legislation) are often also used to determine which units should be the focus of conservation actions; this despite the fact that the two processes have such different goals and information needs. Species conservation needs two kinds of taxonomic solution: (i) a set of practical rules to standardize the species units included on lists; and (ii) an approach to the units chosen for conservation recovery planning which recognizes the dynamic nature of natural systems and the differences from the units in listing processes that result. These solutions are well within our grasp but require a new kind of collaboration among conservation biologists, taxonomists and legislators, as well as an increased resource of taxonomists with relevant and high-quality skills.

Species are defined using a variety of different operational techniques. While discussion of the various methodologies has previously been restricted mostly to taxonomists, the demarcation of species is also crucial for conservation biology. Unfortunately, different methods of diagnosing species can arrive at different entities. Most prominently, it is widely thought that use of a phylogenetic species concept may lead to recognition of a far greater number of much less inclusive units. As a result, studies of the same group of organisms can produce not only different species identities but also different species range and number of individuals. To assess the impact of different definitions on conservation issues, we collected instances from the literature where a group of organisms was categorized both under phylogenetic and nonphylogenetic concepts. Our results show a marked difference, with surveys based on a phylogenetic species concept showing more species (48%) and an associated decrease in population size and range. We discuss the serious consequences of this trend for conservation, including an apparent change in the number of endangered species, potential political fallout, and the difficulty of deciding what should be conserved.