Temporal dynamics and nestedness of an oceanic island bird fauna

Authors

  • Ermias T. Azeria,

    Corresponding author
    1. Swedish University of Agricultural Sciences, Department of Conservation Biology, Box 7002, SE-750 07 Uppsala, Sweden,
    2. McMaster University, Department of Biology, 1280 Main Street West, Hamilton, L8S 4K1, Canada and
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  • Allan Carlson,

    1. Swedish University of Agricultural Sciences, Department of Conservation Biology, Box 7002, SE-750 07 Uppsala, Sweden,
    2. WWF-Sweden, Ulriksdals Slott, SE-170 81 Solna, Sweden
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  • Tomas Pärt,

    1. Swedish University of Agricultural Sciences, Department of Conservation Biology, Box 7002, SE-750 07 Uppsala, Sweden,
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  • Christer G. Wiklund

    1. Swedish University of Agricultural Sciences, Department of Conservation Biology, Box 7002, SE-750 07 Uppsala, Sweden,
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*Correspondence: Ermias T. Azeria, Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4K1, Canada. E-mail: ermias.azeria@nvb.slu.se

ABSTRACT

Aim  To examine temporal variation in nestedness and whether nestedness patterns predict colonization, extinction and turnover across islands and species.

Location  Dahlak Archipelago, Red Sea.

Method  The distributions of land birds on 17 islands were recorded in two periods 30 years apart. Species and islands were reordered in the Nestedness Temperature Calculator, software for assessing degrees of nestedness in communities. The occupancy probability of each cell, i.e. species–island combinations, was calculated in the nested matrix and an extinction curve (boundary line) was specified. We tested whether historical and current nested ranks of species and islands were correlated, whether there was a relationship between occupancy probability (based on the historical data) and number of extinctions or colonizations (regression analyses) and whether the boundary line could predict extinctions and colonizations (chi-square analyses).

Results  Historical and current nested ranks of islands and species were correlated but changes in occupancy patterns were common, particularly among bird species with intermediate incidence. Extinction and turnover of species were higher for small than large islands, and colonization was negatively related to isolation. As expected, colonizations were more frequent above than below the boundary line. Probability of extinction was highest at intermediate occupancy probability, giving a quadratic relationship between extinction and occupancy probability. Species turnover was related to the historical nested ranks of islands. Colonization was related negatively while extinction and occupancy turnover were related quadratically to historical nested ranks of species.

Main conclusions  Some patterns of the temporal dynamics agreed with expectations from nested patterns. However, the accuracy of the predictions may be confounded by regional dynamics and distributions of idiosyncratic, resource-limited species. It is therefore necessary to combine nestedness analysis with adequate knowledge of the causal factors and ecology of targeted species to gain insight into the temporal dynamics of assemblages and for nestedness analyses to be helpful in conservation planning.

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