Ecological Characteristics of Two Closely Related Rodent Species in Urban Environment—Permanent Inhabitant vs Newcomer

Abstract

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.