Range Expansion and Population Patterns on the Wave of Colonization: The Midday Gerbil (Meriones meridianus Pallas 1773, Muridae, Rodentia) in Kalmykia Taken as a Model.

The mechanisms of species dispersal and colonization that drive the process of range expansion have always been in the focus of fundamental ecology. Typically, species' ranges change slowly, but human activities through global processes (landscape transformations, climate warming, and biological invasions) have sped up changes in species distributions, thus providing opportunities to observe and study range shifts in real time. In Kalmykia, human-induced landscape transformations from desert to steppe and vice versa allowed us to study the colonization process during range expansion in a desert-dwelling rodent, the midday gerbil (Meriones meridianus). We studied the population dynamics and changes in the range of midday gerbils in the southern part of Kalmykia, their physical conditions, and infestation with fleas on the wave of colonization, as well as demographic properties of the population of colonists compared to the source population. We found that, in recent years, the species range has been rapidly expanding to the west, where gerbils have established new colonies. The colonists differed significantly from the residents of the source population in a lower average body weight, this being associated not with the poorer physical conditions but with the age structure: the fertility rates of female colonists were much higher, and the population of colonists was much younger compared to the source population. In addition, colonists were almost not infested by fleas in contrast to the residents of the source population. Our findings indicate that the population on the wave of colonization does not experience the negative effects of low numbers, and the high reproductive rates in the colonist population account for its rapid growth and expansion. [ABSTRACT FROM AUTHOR]