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Predicting total global species richness using rates of species description and estimates of taxonomic effort.

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Systematic biology

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      Abstract

      We found that trends in the rate of description of 580,000 marine and terrestrial species, in the taxonomically authoritative World Register of Marine Species and Catalogue of Life databases, were similar until the 1950s. Since then, the relative number of marine to terrestrial species described per year has increased, reflecting the less explored nature of the oceans. From the mid-19th century, the cumulative number of species described has been linear, with the highest number of species described in the decade of 1900, and fewer species described and fewer authors active during the World Wars. There were more authors describing species since the 1960s, indicating greater taxonomic effort. There were fewer species described per author since the 1920s, suggesting it has become more difficult to discover new species. There was no evidence of any change in individual effort by taxonomists. Using a nonhomogeneous renewal process model we predicted that 24-31% to 21-29% more marine and terrestrial species remain to be discovered, respectively. We discuss why we consider that marine species comprise only 16% of all species on Earth although the oceans contain a greater phylogenetic diversity than occurs on land. We predict that there may be 1.8-2.0 million species on Earth, of which about 0.3 million are marine, significantly less than some previous estimates.

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      Global patterns in bacterial diversity.

      Microbes are difficult to culture. Consequently, the primary source of information about a fundamental evolutionary topic, life's diversity, is the environmental distribution of gene sequences. We report the most comprehensive analysis of the environmental distribution of bacteria to date, based on 21,752 16S rRNA sequences compiled from 111 studies of diverse physical environments. We clustered the samples based on similarities in the phylogenetic lineages that they contain and found that, surprisingly, the major environmental determinant of microbial community composition is salinity rather than extremes of temperature, pH, or other physical and chemical factors represented in our samples. We find that sediments are more phylogenetically diverse than any other environment type. Surprisingly, soil, which has high species-level diversity, has below-average phylogenetic diversity. This work provides a framework for understanding the impact of environmental factors on bacterial evolution and for the direction of future sequencing efforts to discover new lineages.
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        Body size, metabolic rate, generation time, and the molecular clock.

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          Why are there so many species of herbivorous insects in tropical rainforests?

          Despite recent progress in understanding mechanisms of tree species coexistence in tropical forests, a simple explanation for the even more extensive diversity of insects feeding on these plants has been missing. We compared folivorous insects from temperate and tropical trees to test the hypothesis that herbivore species coexistence in more diverse communities could reflect narrow host specificity relative to less diverse communities. Temperate and tropical tree species of comparable phylogenetic distribution supported similar numbers of folivorous insect species, 29.0 +/- 2.2 and 23.5 +/- 1.8 per 100 square meters of foliage, respectively. Host specificity did not differ significantly between community samples, indicating that food resources are not more finely partitioned among folivorous insects in tropical than in temperate forests. These findings suggest that the latitudinal gradient in insect species richness could be a direct function of plant diversity, which increased sevenfold from our temperate to tropical study sites.
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            Author and article information

            Affiliations
            [1 ] Leigh Marine Laboratory, University of Auckland, Warkworth, New Zealand. m.costello@auckland.ac.nz
            Journal
            Syst. Biol.
            Systematic biology
            1076-836X
            1063-5157
            Oct 2012
            : 61
            : 5
            syr080
            10.1093/sysbio/syr080
            21856630

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