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| Aim
Researchers measuring beta diversity have rarely concerned themselves
with the problems of how complete the species lists of studied
communities are, and of how the varying degrees of completeness can
actually change estimates of beta diversity. No comprehensive
assessment has been made regarding the behaviour of most beta diversity
indices when applied to incomplete samples, a situation which is more
common than usually recognized. Our objective was to assess the
behaviour and robustness of a number of beta diversity measures for
incidence data from undersampled communities.
Location
Mainland Portugal and the Azorean archipelago (North Atlantic).
Methods
Data from intensive sampling of spiders in mainland Portugal and
arthropods in Azores were collected. We examined the properties of 15
beta diversity measures developed for incidence data. We simulated
varying degrees of completeness, whereas computing beta diversity for
selected pairs of samples. The robustness of these beta diversity
accumulation curves was assessed for the purpose of finding the best
measures for undersampled communities.
Results
The Harrison et al.beta(-2) and the Williams beta(-3) are particularly
robust to undersampling. These measures are also insensitive to
differences of alpha diversity (species richness) between communities,
and therefore to nestedness. Colwell \& Coddington beta(cc) and the
related Jaccard beta(j) and Gaston et al.beta(g) performed best of the
measures sensitive to alpha diversity. They performed poorly, however,
when compared communities exhibited very low values of beta diversity.
In such cases, the Routledge beta(r) performed the best.
Main conclusions
No index was found to perform without bias in all circumstances.
Overall, beta(-2), beta(-3) and beta(cc) (or related measures beta(j)
and beta(g)) are recommended as they seem to be the most robust to
undersampling. | |
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