Evol Ecol Res 13: 665-679 (2011)     Full PDF with comment if your library subscribes.

Geographic range size and speciation in Mediterranean land birds

Julián Simón López-Villalta

Departamento Biología y Geología, IES Pedro Simón Abril, Alcaraz, Spain

Correspondence: J.S. López-Villalta, Departamento Biología y Geología, IES Pedro Simón Abril, P° San Francisco s/n, 02300 Alcaraz (Albacete), Spain.
e-mail: jsimon@edu.jccm.es


Background: Theory suggests that speciation rate should be a unimodal, monotonically decreasing or monotonically increasing function of range size. But few data exist to test these options adequately.

Goal: To develop and use a method to investigate the relationship between a species range size and its probability of speciation.

Data description: Extant species of Mediterranean land birds, their phylogeny, and their geographical distributions.

Method: For each endemic, select a candidate ancestor, i.e. its closest relative in the phylogeny. Accumulate a dataset of range sizes of all possible ancestors and their relatives within relatively broad clades (e.g. family). The point of the method is to compare the statistical distribution of ancestral range size with that of ancestral relatives to obtain the speciation–range size relationship. The method contains specific corrections for the following potential biases: (1) sampling from the macro-ecological distribution of range size (large ancestral ranges are expected to be more common in speciose clades); (2) phylogenetic inertia (clades may contain many ancestors, and so the analysis focuses at the clade level); (3) sampling effect of species diversity (more ancestors are expected from speciose range-size classes); and (4) wrongly assigned ancestors (since bird range size does not depend on phylogeny, the range size of wrong ancestors would be a random sample from the species pool, and so corrections 1 and 3 serve to erase any noise caused by wrong ancestors). The final outcome of the method is a plot that indicates the speciation–range size relationship. This plot can be tested for departure from a uniform distribution.

Conclusions: The speciation–range size relationship of these birds is unimodal and statistically different from a null, flat distribution. Speciation is more likely for species with intermediate range sizes. This pattern holds for absolute as well as relative range sizes.

Keywords: allopatric speciation, macroecology, macroevolution, Mediterranean region.

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