New article: Associations between species and groups of sites

Ecologists often face the task of studying the association between single species and one or several groups of sites representing habitat types, community types, or othercategories. Besides characterizing the ecological preference of the species, the strength of the association usually presents a lot of interest for conservation biology, landscape mapping andmanagement, and natural reserve design, among other applications. The indices most frequently employed to assess these relationships are the phi coefficient of association and theindicator value index (IndVal).

In this contribution in the journal Ecology, Miquel de Càceres and Pierre Legendre compare these two approaches by putting them into a broader framework of related measures, which includes several new indices.

They presentpermutation tests to assess the statistical significance of species–site group associations and bootstrap methods for obtaining confidence intervals. Two main types of measures exist: Correlation measures, such as the phi coefficient, are more context-dependent than indicator values but allow focusing on the preference of the species. In contrast, the two components of an indicator value index directly assess the value of the species as a bioindicator because they can be interpreted as its positive predictive value and sensitivity. Ecologists should select the most appropriate index of association strength according to their objective and then compute confidence intervals to determine the precision of the estimate.
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De Càceres, M. & Legendre, M. 2009. Associations between species and groups of sites: indices and statistical inference. Ecology, 90: 3566-3574.