Andrey Yu. Puzachenko

Species Co-Existence and Morphological Divergence in West Siberian Mustelids (Carnivora, Mustelidae)

Common ecological observations testify that natural selection acts to reduce both morphological and behavioral similarities between competing animal species, thus lessening their niche overlap. Such reduction in similarity is termed “character displacement” (see Brown and Wilson 1956). Character displacement, or divergence of characters, is a commonly observed pattern in animals (see Dayan and Simberloff 1998, 2005; Henderson 1998; Rice and Pfennig 2007). Populations of closely related species often differ phenotypically where the species occur sympatrically; if they are morphologically indistinguishable when each occurs in its own range (allopatrically). The diversification of morphological characters (body size, cranial and dental characters) is often the first-order response to competitive situations among mammals, notably among carnivorans (Dayan et al. 1989, 1990; Brown 1995; McDonald 2002). As far as the literature devoted to character displacement is concerned, carnivores predominate among mammals. By investigating morphological relationships between species, we can examine how congeneric members of the same guild coexist in a local community. We have analyzed a degree of morphological differentiation between four sympatric species from a species-rich group of small-bodied mustelids (Mustela spp.). In the north-temperate zone, the majority of Mustela species is sympatric, but occurs in slightly different habitats (Nowak 1999). Yet, there are regions where closely related species co-occurs in the same habitats. One of these is the central part of the Baraba forest-steppe (West Siberia, Novosibirsk Province, Russia), where the four species—the Siberian weasel (Mustela sibirica), the steppe polecat (M. eversmanii), the ermine (M. erminea) and the least weasel (M. nivalis)—inhabit the same biotopes (Ternovsky and Danilov 1965; Ternovsky and Ternovskaya 1994). The weasels of Baraba form a guild that is specialized in locating, killing, and ingesting animal prey. Based on overall similarity of morphology and diet within the guild, we have examined patterns of morphological differentiation within the Baraba weasel assemblage. Reasoning from Dayan and Simberloff (1998), it is assumed that morphological differences should be very high in the Baraba’ species-rich fauna. Overwhelming majority of classic studies of character displacement in Carnivora (particularly, in Mustelidae) have been based on the combined samples (Rosenzweig 1968; McNab 1971; Dayan et al. 1989, 1990, 1992; Dayan and Simberloff 2005; Davies et al. 2007). Specimens used in the present analysis were collected from different localities and at different time but are compared as a unified sample. However significant spatial variation is known for many mustelid species including Mustela spp. (Ralls and Harvey 1985; Reig 1997; Abramov and Baryshnikov 2000; Abramov and Puzachenko 2009). This variation certainly affects results of the analysis. Another source of possible bias is temporal variation reported for Carnivora as well as for other mammalian species (Yom-Tov 2003; Yom-Tov et al. 2003, 2007). Thus body and skull size may vary geographically and over time and is influenced by several factors. It is very difficult to remove or estimate all of these impacts in the study of character displacement in Carnivora, but it is not considered in most of the published studies on this topic. Our study is a first attempt to analyze this phenomenon excluding the impact of most secondary factors.