How Many Species Are There on Earth and in the Ocean?

Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
PLoS Biology (Impact Factor: 9.34). 08/2011; 9(8):e1001127. DOI: 10.1371/journal.pbio.1001127
Source: PubMed


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 precluded direct 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 be estimated. This approach was validated against well-known taxa, and when applied to all domains of life, it predicts ~8.7 million (± 1.3 million SE) eukaryotic species globally, of which ~2.2 million (± 0.18 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 on Earth 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.

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    • "Much of our knowledge of biodiversity patterns and changes comes from the data based on mammals, birds and vascular plants (e.g., Gillison et al., 2013). Yet these taxa represent only a fraction of biodiversity; the major component of terrestrial biodiversity comprises insects (Mora et al., 2011). A recent meta-analysis of biodiversity studies revealed the dearth of information about most of the world's tropical biota (Gillison et al., 2013), highlighting the fact that in order to decipher biodiversity patterns and change the major component can no longer be ignored. "
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    ABSTRACT: Metabarcoding, the coupling of DNA-based species identification and high-throughput sequencing, offers enormous promise for arthropod biodiversity studies but factors such as cost, speed and ease-of-use of bioinformatic pipelines, crucial for making the leapt from demonstration studies to a real-world application, have not yet been adequately addressed. Here, four published and one newly designed primer sets were tested across a diverse set of 80 arthropod species, representing 11 orders, to establish optimal protocols for Illumina-based metabarcoding of tropical Malaise trap samples. Two primer sets which showed the highest amplification success with individual specimen polymerase chain reaction (PCR, 98%) were used for bulk PCR and Illumina MiSeq sequencing. The sequencing outputs were subjected to both manual and simple metagenomics quality control and filtering pipelines. We obtained acceptable detection rates after bulk PCR and high-throughput sequencing (80-90% of input species) but analyses were complicated by putative heteroplasmic sequences and contamination. The manual pipeline produced similar or better outputs to the simple metagenomics pipeline (1.4 compared with 0.5 expected:unexpected Operational Taxonomic Units). Our study suggests that metabarcoding is slowly becoming as cheap, fast and easy as conventional DNA barcoding, and that Malaise trap metabarcoding may soon fulfill its potential, providing a thermometer for biodiversity.
    Bulletin of entomological research 09/2015; DOI:10.1017/S0007485315000681
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    • "non-marine; Mora et al. 2011). These numbers are doubtless underestimates of actual richness, but similar proportions of undescribed species have been estimated for each habitat (91% of species are estimated to be undescribed in marine habitats vs. 86% in non-marine habitats; Mora et al. 2011). However, some authors have suggested that Mora et al. (2011) overestimated marine richness (e.g. "
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    ABSTRACT: Terrestrial environments occupy ~ 30% of the Earth's surface yet contain ~ 80% of all species. The causes of this dramatic biodiversity gradient have remained relatively unstudied. Here, I test the fundamental prediction that predominantly non-marine clades have more rapid rates of diversification than marine clades, using a time-calibrated phylogeny of animal phyla. The results strongly support this hypothesis. This pattern helps explain the higher richness of terrestrial environments and the dramatic variation in species richness among animal phyla. The results show the importance of ecology in explaining large-scale patterns of clade richness and of diversification rates in explaining Earth's largest biodiversity patterns. The results also demonstrate remarkable niche conservatism in habitats, in some cases lasting > 800 million years. Finally, the results highlight the surprisingly high species richness of freshwater habitats, which are nearly equal to marine environments despite their much smaller area (~ 2% of Earth's surface vs. 70% for marine habitats).
    Ecology Letters 09/2015; 18(11). DOI:10.1111/ele.12503
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    • "Despite increasing sophistication in the methods used to arrive at these estimates, there is a lack of convergence in the values (Mora et al., 2013). One thing that these studies do agree on is that the deep sea, the deep pelagic realm in particular, is one of the largest sources of uncertainty in these calculations because less than 1% of this enormous habitat has been sampled (Webb et al., 2010; Mora et al., 2011; Appeltans et al., 2012; Costello et al., 2012). Deep-sea biology is a relatively young discipline, which began in earnest only ∼140 years ago. "
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    ABSTRACT: Calculating global estimates for total species richness is fraught by the uncertainty in estimating the number of species left to be discovered. The deep-sea is widely regarded as one of the largest sources of uncertainty in these calculations, since so much of this realm has not yet been explored. Most estimates of species left to be discovered are reliant on previous rates of species description, yet these rates are likely to be biased. One well-known bias from terrestrial studies is that wide-ranging species tend to be described earlier. To test this hypothesis for the deep sea, spatial data from the Ocean Biogeographic Information System (OBIS) were combined with taxonomic data from the World Register of Marine Species (WoRMS) to carry out a meta-analysis on all species records found below 300 m. Results show a historical bias in species descriptions, with wide-ranging species over-represented in our current catalogs of deep-sea species richness. This suggests that current estimates of deep-sea species richness underestimate the true proportion of narrow-ranged species and hence total species in the deep oceans.
    08/2015; 2. DOI:10.3389/fmars.2015.00061
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