The farther, the closer: geographic proximity and niche overlap versus genetic divergence in Caucasian rock lizards

Abstract

Abstract Caucasian rock lizards (Darevskia) are a speciose group with 42 described species from the Caucasus Mountain region. We selected 11 species from Georgia and adjacent territories to explore whether their distribution depends on the distribution of congeneric taxa. We estimated two measures for each species pair: (1) niche overlap between all pairs of the studied species; (2) the extent of contact between the ranges of individual species. We then calculated the correlation between these measurements and the time of divergence between the species. The results showed that in sympatric and parapatric (but not allopatric) species, there is a highly significant correlation between the divergence time and the extent of the contact, as well as between the divergence time and the overlap of suitable habitats. The ranges of the evolutionarily closest species have the smallest extent of contact. Species separated later have overlapping ranges, although are separated by altitude. The most distant species, irrespective of their phenotype, are commonly found in the same location. We suggest that a gradual increase in the contact extent is compensated for by increasing the effectiveness of other mechanisms of niche shift or behavioural isolation and hence the frequency of potentially deleterious interspecific contacts is kept low.