‘How many species are there‘ is a question receiving more attention from biologists and reasons for this are suggested. Different methods of answering this question are examined and include: counting all species; extrapolations from known faunas and regions; extrapolations from samples; methods using ecological models; censusing taxonomists’ views. Most of these methods indicate that global totals of 5 to 15 million species are reasonable. The implications of much higher estimates of 30 million species or more are examined, particularly the question of where these millions of species might be found.
What is Species
The nature of species is controversial in biology and philosophy. Biologists disagree on the definition of the term ‘species,’ and philosophers disagree over the ontological status of species. Yet a proper understanding of species is important for a number of reasons. Species are the fundamental taxonomic units of biological classification. Environmental laws are framed in terms of species. Even our conception of human nature is affected by our understanding of species. In this entry, three issues concerning species are discussed. The first is the ontological status of species. The second is whether biologists should be species pluralists or species monists. The third is whether the theoretical term ‘species’ refers to a real category in nature.
Biodiversity and Conservation Volume 2, Number 3, 215-232, DOI: 10.1007/BF00056669