No abstract

We have attempted to describe the genetic structure and variability of the striped field mouse population inhabiting 17 locations in and around Warsaw, Poland, within a gradient of anthropopressure and discuss the possible factors that could potentially form the observed pattern. Ecological characteristics of the striped field mouse prevent decreases in genetic variability within local urban populations. High population density, ability to cross environmental barriers and to use ''green corridors'' allows this species to maintain gene flow in fragmented urban landscape. However, genetic variability and gene flow were efficiently reduced in the central part of the city. The results indicated that the degree of human pressure, defined based on the level of vegetation cover, is a good indicator of isolation. In the studied striped field mouse population, genetic interactions among particular locations (local populations) are modified in comparison with populations inhabiting natural areas, by replacement of the isolation-by-distance pattern of differentiation with the ''isolation-by-infrastructure'' pattern. As indicated by Bayesian analysis, the urban population from the right side of the Vistula river form common genetic cluster with exurban population located northward from the city, while the population from the left side of the river probably exchanges genes with neighbouring northern and southern ex-urban populations. However local populations at locations within the highest zone of anthropopressure are clearly isolated, and presently constitute separate genetic units.

The aim of the study was to characterize natural and urban populations of two Apodemus species-the striped field mouse (Apodemus agrarius) and the yellow-necked mouse (Apodemus flavicollis)-seeking to verify whether the different durations of synurbization have led populations of the two species to exhibit differing characteristics. The study was conducted in central Poland (in Warsaw and its surrounds, in urban parks in the city center and in natural habitats outside the city) over two seasons, during which a total of 1751 striped field mice and 454 yellow-necked mice were live-trapped (using the catch-mark-release method). We found altered characteristics of urban populations of striped field mice, which we interpret as the result of the relatively lengthy synurbization of the species over the last hundred years and its adaptation to the highly modified urban environment. A significantly higher percentage of sexually-active males and a higher average body mass were observed for the urban population of striped field mice, suggesting that the species is in better condition in urban habitats. We found urban populations of yellow-necked mice, in turn, to be unstable (as reflected in a high turn-over rate and a low percentage of retrapped mice), their survival in urban habitats only being made possible by ongoing attempts at colonization. We conclude that, in urban habitats, the system of competition between the two species exhibits a certain shift in favor of striped field mice-typically a weaker species, but the first to colonize cities. Overall, we conclude that the conditions present in urban habitats act as a strong factor shaping populations with characteristics different from those found in natural habitats. This is further enhanced by the priority effect, resulting from differing durations of urban habitation and adaptation, leading to changes in the system of competition between species.

Traffic noise was tested as a stress factor in an open-field study of urban and non-urban populations of two species belonging to the genus Apodemus: the striped field mouse and the yellow-necked mouse. The striped field mouse has inhabited green areas in cities for years, whereas the yellow-necked mouse was first observed in such areas relatively recently. Behavioral reactions to noise in the urban population of striped field mice were the same as the reactions observed in the non-urban population of the species. As for the yellow-necked mouse, behavior in response to noise in the non-urban population differed from that observed in the urban population. We see such differences as being related to the fact that striped field mice, which have inhabited urban areas for many generations, form a stable population in urban areas, and specific individuals are adapted to urban conditions. Yellow-necked mice, in turn, form no stable urban population and the individuals found in cities are most probably migrants, not adapted to urban conditions, which is the reason why their reaction to noise differs from the typical response.