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Are there latitudinal gradients in species turnover?


Patricia Koleff, Comisión Nacional para el Conocimiento y Uso de la Biodiversidad, Liga Periférico — Insurgentes Sur 4903, Parques del Pedregal, Tlalpan 14010 México, D.F., México. E-mail:


Aim  To examine the effect on the observed relationship between spatial turnover and latitude of both the measure of beta diversity used and the method of analysis.

Location  The empirical analyses presented herein are for the New World.

Methods  We take the spatial distributions of the owls of the New World as an exemplar data set to investigate the patterns of beta diversity across latitudes revealed by different analytical methods. To illustrate the strengths and weaknesses of alternative measures of beta diversity and different analytical approaches, we also use a simple random distribution model, focusing in particular on the influence of richness gradients and landmass geometry.

Results  Our simple spatial model of turnover demonstrates that different combinations of analytical approach and measure of beta diversity can give rise to strikingly different relationships between turnover and latitude. The analyses of the bird data for the owls of the New World demonstrate that this observation extends to real data.

Conclusions  For the particular assemblage considered, we present strong evidence that species richness declines at higher latitudes, and there is also some evidence that species turnover is greater nearer the equator, despite conceptual and practical difficulties involved in analysing spatial patterns of species turnover. We suggest some ways of overcoming these difficulties.