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The challenge of delineating biogeographical regions: nestedness matters for Indo-Pacific coral reef fishes

Authors

  • David Mouillot,

    Corresponding author
    1. Laboratoire ECOSYM, UMR 5119 CNRS-UM2-IRD-IFREMER, Montpellier, France
    2. ARC Centre of Excellence for Coral Reef Studies, and School of Marine and Tropical Biology, James Cook University, Townsville, Qld, Australia
    • Correspondence: David Mouillot, UMR 5119 CNRS-UM2-IRD-IFREMER ECOSYM, Place Eugène Bataillon cc 93, 34095 Montpellier, France.

      E-mail: david.mouillot@univ-montp2.fr

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  • Julien De Bortoli,

    1. Laboratoire ECOSYM, UMR 5119 CNRS-UM2-IRD-IFREMER, Montpellier, France
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  • Fabien Leprieur,

    1. Laboratoire ECOSYM, UMR 5119 CNRS-UM2-IRD-IFREMER, Montpellier, France
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  • Valeriano Parravicini,

    1. CESAB- FRB Immeuble Henri Poincaré, Aix-en-Provence cedex 3, France
    2. IRD – UR 227 Coreus, Laboratoire Arago, Banyuls/mer, France
    3. LABEX ‘CORAIL’, Laboratoire Arago, Banyuls/mer, France
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  • Michel Kulbicki,

    1. IRD – UR 227 Coreus, Laboratoire Arago, Banyuls/mer, France
    2. LABEX ‘CORAIL’, Laboratoire Arago, Banyuls/mer, France
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  • David R. Bellwood

    1. ARC Centre of Excellence for Coral Reef Studies, and School of Marine and Tropical Biology, James Cook University, Townsville, Qld, Australia
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Abstract

Aim

The delineation of regions is a critical procedure in biogeography, but there is still no consensus about the best approach. Traditionally, a compositional dissimilarity index and a clustering algorithm are used to partition locations into regions. However, the choice of index and algorithm may have a profound impact on the final result, particularly when locations display different levels of species richness and when they are nested within each other. Our objective was to estimate the influence of species nestedness among locations on the delineation of biogeographical regions.

Location

As a case study, we used coral reef fishes (families Chaetodontidae, Pomacentridae and Labridae) from the Indo-Pacific, where a large richness gradient extends, often as a series of nested assemblages, from the species-rich Indo-Australian Archipelago (Coral Triangle) to species-poor peripheral locations.

Methods

We used the turnover and nestedness components of the Sørensen and Jaccard dissimilarity indices to estimate the effect of nestedness on the delineation of biogeographical regions. In addition, we compared the results with those obtained using a parsimony analysis of endemicity (PAE).

Results

Low Mantel correlation values revealed that the PAE method assembled locations in a very different way than methods based on dissimilarity indices for Indo-Pacific coral reef fishes. We also found that nestedness mattered when delineating biogeographical units because, for both the Sørensen and the Jaccard indices, reef fish assemblages were grouped differently depending on whether we used the turnover component of each index or the complete index, including the nestedness component. The turnover component ignored variation in species richness attributable to differences in habitat area between locations, and permitted a delineation based solely on species replacement.

Main conclusions

We demonstrate that the choice of the component used to measure dissimilarity between species assemblages is critical, because it may strongly influence regional delineations, at least for Indo-Pacific coral reef fishes. We conclude that the two components of the dissimilarity indices can reveal complementary insights into the role that history may have played in shaping extant patterns of biodiversity.

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