Biologia Y Medio Ambiente

How Many Species Are There on Earth and in the Ocean?
Camilo Mora1,2*, Derek P. Tittensor1,3,4, Sina Adl1, Alastair G. B. Simpson1, Boris Worm1
1 Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada, 2 Department of Geography, University of Hawaii, Honolulu, Hawaii, United States of America, 3 United Nations Environment Programme World Conservation Monitoring Centre,Cambridge, United Kingdom, 4 Microsoft Research, Cambridge, United Kingdom

Abstract
The diversity of life is one of the most striking aspects of our planet; hence knowing how many species inhabit Earth is among the most fundamental questions in science. Yet the answer to this question remains enigmatic, as efforts to sample the world’s biodiversity to date have been limited and thus have precludeddirect quantification of global species richness, and because indirect estimates rely on assumptions that have proven highly controversial. Here we show that the higher taxonomic classification of species (i.e., the assignment of species to phylum, class, order, family, and genus) follows a consistent and predictable pattern from which the total number of species in a taxonomic group can beestimated. This approach was validated against well-known taxa, and when applied to all domains of life, it predicts ,8.7 million (61.3 million SE) eukaryotic species globally, of which ,2.2 million (60.18 million SE) are marine. In spite of 250 years of taxonomic classification and over 1.2 million species already catalogued in a central database, our results suggest that some 86% of existing species onEarth and 91% of species in the ocean still await description. Renewed interest in further exploration and taxonomy is required if this significant gap in our knowledge of life on Earth is to be closed.
Citation: Mora C, Tittensor DP, Adl S, Simpson AGB, Worm B (2011) How Many Species Are There on Earth and in the Ocean? PLoS Biol 9(8): e1001127. doi:10.1371/journal.pbio.1001127 Academic Editor:Georgina M. Mace, Imperial College London, United Kingdom Received November 12, 2010; Accepted July 13, 2011; Published August 23, 2011 Copyright: ß 2011 Mora et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source arecredited. Funding: Funding was provided by the Sloan Foundation through the Census of Marine Life Program, Future of Marine Animal Populations project. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: moracamilo@hotmail.comIntroduction
Robert May [1] recently noted that if aliens visited our planet, one of their first questions would be, ‘‘How many distinct life forms—species—does your planet have?’’ He also pointed out that we would be ‘‘embarrassed’’ by the uncertainty in our answer. This narrative illustrates the fundamental nature of knowing how many species there are on Earth, and our limited progress with this researchtopic thus far [1–4]. Unfortunately, limited sampling of the world’s biodiversity to date has prevented a direct quantification of the number of species on Earth, while indirect estimates remain uncertain due to the use of controversial approaches (see detailed review of available methods, estimates, and limitations in Table 1). Globally, our best approximation to the total number of species isbased on the opinion of taxonomic experts, whose estimates range between 3 and 100 million species [1]; although these estimations likely represent the outer bounds of the total number of species, expert-opinion approaches have been questioned due to their limited empirical basis [5] and subjectivity [5– 6] (Table 1). Other studies have used macroecological patterns and biodiversity ratios in...