Permanent urban resident edges out an urban newcomer

Pieniążek, A., Sokół, M. and Kozawiewicz, M. (2017) Ecological characteristics of two closely related rodent species in urban environment-permanent inhabitant vs newcomer. Natural Resources, 8, 69-80.

Adjusting to life in the city has its advantages

Animals that encounter habitats dominated by human features can face many challenges that ultimately impact whether they can remain in that environment. Some of the challenges are dealing with human disturbances such as noise pollution, proximity to humans, movement through areas with traffic, etc. Some species are able to adjust to city life and end up gaining some advantages over life in the forest. For example, in some cases many of the natural predators are absent in cities, leading to less predation that results in greater population numbers. Animals may also have access to plentiful food, such as human trash, allowing them to reproduce more frequently or have more babies.  A study in Warsaw, Poland set out to test whether two species of field mice differed in how urban environments might affect their population size and reproduction throughout the year. One mouse species (striped field mouse) is a permanent urban resident and the other (yellow field mouse) is an urban newcomer

A tale of two urban mice

Fig 1: Left left panel: Permanent urban resident: Striped field mouse (Apodemus agrarius), right panel: Urban newcomer: Yellow-necked field mouse (Apodemus flavicollis). Photo by Wiki-media commons.

The striped field mouse naturally inhabits open areas such as terrains and fields, and frequents forest edges. It was described as a common species in the city of Warsaw by the early twentieth century, making it a permanent urban resident since then. The yellow field mouse favors areas with dense vegetation and was recorded in Warsaw less than 10 years ago, frequenting suburban areas. The authors of this paper set out to test differences in population size and reproduction of these two species. To do so, they captured mice around areas in Warsaw that differed in the degree of urbanization and at a forest outside of the city limits.

The permanent urban resident edges out the urban newcomer

The researchers found that the striped field mouse (permanent urban resident) has a greater population size in the city than in the forest. Urban residents of striped field mice population are also much larger than the city population of the yellow field mice. Males of the striped field mouse are more sexually active and bigger in the city than in the forest. The bigger size of urban striped field mouse is possibly achieved because of easier access to food. In the forest, the yellow-necked field mice (urban newcomer) females are more sexually active than the females of the striped field mice.

Fig 2.  Percent of sexually active adults (top: Males; bottom: Females) from rural and urban populations. Percent of sexually active adults shown in dark gray and sexually inactive adults shown in white. Lines connect populations that differed.

The effect of life in the city differs with length of urban residency

Overall the findings of this study show that time spent living in the city can lead to ecological differences within and between species. The striped field mouse has inhabited the city of Warsaw over 80 years longer than the yellow field mouse. In this time, the striped field mouse has become accustomed to city life and potentially exploits features of the city to achieve larger size which can influence reproduction. It’s unclear whether with enough time the yellow field mouse will also adjust to city life as well. What’s important is to continue monitoring these species and learning more about how urbanization can affect the ecology of animals and plants across the world.


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Kevin Aviles Rodriguez

I am in the process of completing my PhD in Ecology and Evolutionary Biology at the University of Massachusetts in Boston. I am interested in human environmental changes as natural experiments to test hypothesis about the evolution of animals. Specifically, I study small lizards known as anoles and how living near human households impacts their ecology and behavior. I love fieldwork because often it takes me away from the cold and towards the sunny beachy islands that I love the most.

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