In response to human impact on the environment—from increased light, sound, air, and water pollution, to higher levels of interaction with humans—organisms must adapt to novel conditions in order to survive. One area in which organisms adapt is behavior.
von Merton et. al. (2022) explores how the behavior and personality of two shrew species (Crocidura russula and Sorex araneus) differs between urban and rural populations of each species, as well as how it varies within each respective population. They did this by testing the personality of the shrews in terms of boldness and antipredator aggression. First, to survey boldness, described as proactiveness and a desire to explore, they measured the amount of time it took for the shrews to leave a jar placed inside a shelter. The faster the shrews leave the jar to explore the shelter, the bolder they are. Next, to measure aggression, the experimenters held onto the base of the shrew’s tail and counted how many times the shrew bit them, simulating how the shrew might respond to a predatory situation. The more bites, the more willing the shrew is to fight against a predator, and thus, the more aggressive the shrew.
In both species, urban shrews left the shelter more often and faster, indicating a higher level of boldness compared to rural shrews. This makes sense because exploration is important to find food, shelter, etc. in the novel and ever-changing urban environments. Furthermore, bold individuals are more likely to disperse into urban areas to begin with, in comparison to shy individuals of the same species. In C. russula, urban shrews were also more aggressive than the rural shrews. This also makes sense, in that boldness is often connected with aggression towards predators. Of the two species, the behavioral differences were more pronounced in C. russula, possibly because they occupy more urbanized environments than S. araneus.
These differences between urban and rural populations of the same species confirm the authors’ hypotheses. However, the researchers were also interested in how personality varied within populations (e.g., personality differences between shrews that live in an urban area), an idea called behavioral heterogeneity. They found urban populations of shrews have greater behavioral heterogeneity than rural populations, meaning that urban individuals show more differences in personality from other urban individuals than rural individuals do with other rural individuals. Such differences between urban individuals could reflect the large amount of variation within urban environments. Food source distribution, availability of shelter, and types of disturbance (like cars or foot traffic) change often in urban areas and can be highly variable from one part of a city to another even over very short distances.
Together, these findings demonstrate that urban shrews behaviorally adapt to environmental variation in terms of boldness and aggression, resulting in personality differences between urban and rural populations as well as increased variation among urban individuals within a population. The behavioral differences between urban and rural populations are in line with findings in other organisms, supporting this type of behavior as a key component of adapting to urban environments. In addition, variation in behavioral responses might allow shrews to cope with the unpredictable and highly variable urban landscapes.
The information gathered with this study is important because it illustrates how the increased human impact on organisms could have long term effects on ecological and evolutionary dynamics. With urbanization continuing to rise, animals like the shrews in this study must adapt in order to survive the ever changing environment.
Read more:
- Behavioral Differences Among Individuals of Rural and Urban Shrews - September 6, 2023
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