Phylogenetic autocorrelation and evolutionary interpretation of the higher-taxon approach for biodiversity analyses

J A F Diniz-Filho,N M Tôrres

doi:10.1590/s1519-69842006000500013

Abstract

Although in most recent broad-scale analyses, diversity is measured by counting the number of species in a given area or spatial unity (species richness), a 'top-down' approach has been used sometimes, counting higher-taxon (genera, family) instead of species with some advantages. However, this higher-taxon approach is quite empirical and the cut-off level is usually arbitrarily defined. In this work, we show that the higher-taxon approach could be theoretically linked with models of phenotypic diversification by means of phylogenetic autocorrelation analysis in such a way that the taxonomic (or phylogenetic) rank to be used could not be necessarily arbitrary. This rank expresses past time in which taxa became independent for a given phenotypic trait or for the evolution of average phenotypes across different traits. We illustrated the approach by evaluating phylogenetic patches for 23 morphological, ecological and behavioural characters in New World terrestrial Carnivora. The higher-taxon counts at 18.8 mya (S(L)) defined by phylogenetic correlograms are highly correlated with species richness (r = 0.899; P < 0.001 with ca. 13 degrees of freedom by taking spatial autocorrelation into account). However, S(L) in North America is usually larger than in South America. Thus, although there are more species in South and Central America, the fast recent diversification that occurred in this region generated species that are "redundant" in relation to lineages that were present at 18.8 my. BP. Therefore, the number of lineages can be comparatively used as a measure of evolutionary diversity under a given model of phenotypic divergence among lower taxonomic units.

Highlights

In most recent broad-scale analyses, diversity is measured by counting the number of species in a given area or spatial unity
The average patch for all profiles was estimated as 18.8 million years before the present (BP), and so this was the level used to cut the Carnivore supertree to obtain a higher-taxon counts
Species richness in Carnivora across the New World followed the expected pattern, with more species concentrated in Tropical regions, decreasing in directions to higher latitudes (Fig. 1)

Summary

Introduction

In most recent broad-scale analyses, diversity is measured by counting the number of species in a given area or spatial unity (species richness). Many previous studies (e.g., Balmford et al, 2000; Grelle, 2002, and references therein) showed that these counts are a good surrogate for species richness in such a way that higher-taxon estimates of biodiversity could be used for understanding broad-scale diversity patterns and for conservation applications. There is a well-known problem in that taxonomic ranks in different groups of organisms do not necessarily have the same evolutionary information in terms of measuring time from divergence between lineages and the rates of character evolution. As expected by models of evolutionary diversification, the correlation between species richness and highertaxon counts tends to decrease when increasing the taxonomic rank, both because of a simple statistical effect of reduced variance (because lineages coalesce toward a single common ancestor in the past) and because explanations to variation in spatial patterns of diversity are shifted from current processes to past (historical) explanations, with some loss of information. The main problem with this higher-taxon approach is the choice of the rank, that is completely arbitrary most of the time, and interpretations should be made carefully (Williams & Gaston, 1994)

Methods

Results

Conclusion