Transitive taxonomic systems (TTS) and speciation during range dynamics

Abstract

The system of views on the structure of geographic ranges of species (superspecies) and their dynamics as one of the key features of species and the basis of taxonomic differentiation and evolution is considered. The mechanisms leading to the formation of new taxa in several ways are analysed, including (1) the formation of transitive taxonomic systems (TTS), in which spatial differentiation leads to the formation of geographically differentiated races as ‘small’ species; (2) the formation of new geographical races in relation to the maternal species (plesions), distributed within the primary ranges; (3) the formation of sibling species as a result of dispersal of one ‘small’ species into the range of the sister species. All such groups of ‘small’ species coexist in time and illustrate models that correspond to E. E. Reclus’s view of ‘geography is history in space.’ A number of illustrative cases discovered in the analysis of the taxonomic heterogeneity of different groups of mammals of the European fauna or the Palaearctic as a whole are considered. In particular, there were analysed the features of spatial-taxonomic differentiation in allospecies complexes that fall under the definition of TTS, in which the distribution of allospecies reflects the patterns of spatial differentiation of the ‘large’ species over time (phylogeographic patterns). Similar complexes have been demonstrated on the example of ground squirrels, birch mice, and wood mice. The formation of TTS, as well as new forms as a result of invasions into new ranges (or dispersal to ranges of adjacent forms) is considered within the amplificative species concept (ASCo), according to which specialization occurs not as a result of reduction of both the range and variability (classic models with founder effect or bottleneck), but in the phase of flourishing of the species, in particular when new populations emerge outside the initial natural ranges due to expansions or invasions. The invasive model of speciation was formed based on this idea, and a partial example of it is the formation of sympatric pairs of sibling species formed as a result of secondary sympatry, i.e. expansion. Examples from other groups, in particular regarding the formation of compilospecies and other variants of hybridogenic taxa provoked by introductions or invasions, are considered. All this is viewed through the prism of the concept of speciesness as the level of achievement of evolutionary separateness.