Do commonly used indices of beta-diversity measure species turnover?

Indices of beta -diversity are of two major types. (1) those that measure a mong-plot variability in species composition independently of the position of individual plots on spatial or environmental gradients, and (2) those th at measure the extent of change in species composition along predefined gra dients, i.e. species turnover. Failure to recognize this distinction can le ad to the inappropriate use of some beta -diversity indices to measure spec ies turnover. Several commonly-used indices of)beta -diversity are based on Whittaker's b eta (W) (beta (W) = gamma/alpha, where gamma is the number of species in an entire study area and a is the number of species per plot within the study area). It is demonstrated that these indices do not take into account the distribution of species on spatial or environmental gradients, and should t herefore not be used to measure species turnover. The terms 'beta -diversit y' and 'species turnover' should not be used interchangeably. Species turno ver can be measured using matrices of compositional similarity and physical or environmental distances among pairs of study plots. The use of indices of P-diversity and similarity-distance curves is demonstrated using simulat ed data sets.