How do mesocarnivores interact in an urban environment? And how did the SARS-CoV-2 lockdown affect it?

This blog post is provided by Julie Louvrier (Twitter: @LouvrierJulie) and tells the #StoryBehindThePaper for the paper “Spatiotemporal interactions of a novel mesocarnivore community in an urban environment before and during SARS-CoV-2 lockdown”, which was recently published in the Journal of Animal Ecology.

Cities represent a novel environment for wildlife species: human activities and disturbance happen during the day; a high density of buildings and roads; a highly heterogeneous landscape at small scale; invasive, domestic and other new species. These modifications are new in terms of evolutionary times and species have to rapidly adapt to them. Consequently, the communities that are formed in such a novel environment, also present novel characteristics, in terms of species composition, their interactions and niche segregation. Studying these communities brings important insights into community functioning in novel environments.

Here we looked at the novel mesocarnivore community of Berlin, composed of the red fox (Vulpes, vulpes), and the marten (Martes sp.) as native species, the raccoon (Procyon lotor) as an invasive species, and the cat (Felis catus) as a domestic species. During five sampling seasons (fall 2018, spring 2019, fall 2019, spring 2020 and fall 2020), citizens of Berlin voluntarily participated in the WTImpact project (http://www.wtimpact.de), consisting in setting camera-traps in their garden or private allotment, for four consecutive weeks. For each sampling season, new citizen scientists were chosen, and every time about 200 volunteers participated. For urban wildlife, private gardens and allotments can represent a crucial source of food and shelter.

Example of instructions given to citizens to help with species identification, from the project (WTimpact) platform. (Photo credit: Milena Stillfried)

During our study, the epidemic of the novel Coronavirus SARS-CoV2 reached Berlin, leading to lockdown during spring and fall 2020. This lockdown lead to a decrease of human activities, with recommendations to work from home and a closure of public places such as restaurants and bars. During this period of lockdown, an increase of wildlife sightings also occurred, probably representing a change in wildlife behaviour. These changes could be due to a decrease of human activities, but also a decrease of food sources, as urban wildlife may rely on human-sourced food to thrive.

Four pictures of the four mesocarnivores species of Berlin, from top left to bottom right: The red fox, the domestic cat, the raccoon and the marten, occurring in the same garden at different times. (Photo credit: Stephanie Kramer-Schadt)

Based on the camera-trap data obtained from the citizens, we first assessed the spatial overlap of foxes, raccoons and martens (we considered that cats were spatially associated with the garden of their owners). To do so, we first assessed the effect of environmental variables on their presence in gardens (i.e. if they were detected at least once during the sampling period) and use intensity of gardens (i.e. how many pictures of them were taken during the sampling period). We assessed whether the SARS-CoV-2 lockdown had an effect on presence and use intensity of gardens and found that species were more present in gardens and displayed a higher use intensity in gardens during the SARS-CoV-2 lockdown period. As domestic cats are an infamous source of disturbance for wildlife, we tested for the effect of cats on presence and use intensity of gardens, and found that raccoons, the invasive species, displayed a positive response to cats, while foxes, the native species, displayed a negative trend towards cats. After assessing the environmental effects on presence and use intensity of wildlife gardens, we estimated the association between each species and found that all three wild species were positively associated in both presence and use intensity of gardens.

Species association from our analyses. Colour and width of the arrows represent the correlation value between two species. (Animal silhouettes by Aimara Planillo and Milena Stillfried)

As it appeared the mesocarnivores were positively correlated in gardens, we wanted to look at how they were separating their activities in time. A first way to look at it is by assessing the activity patterns, which show, in a 24h day, the activity intensity of each species. As expected, given the fact that human activities are mostly concentrated during the day, we found that mesocarnivores escaped human activities by having their activity mostly at night. However, we found that during the SARS-CoV-2 lockdown period, mesocarnivores were even more nocturnal. Not only were they more present and used more gardens, but they also concentrated their activities during the night. This could seem counterintuitive at first, but could be explained by the fact that the camera-traps were set in private gardens, and that during the lockdown periods, as business and public spaces were closed, people were more present in their houses and could be more present in their gardens, forcing wildlife to use these gardens during the night.

Activity patterns of each species composing the mesocarnivore community of Berlin, before the SARS-CoV-2 lockdown measures were in place (Covid) and were not in place (No Covid).

As mesocarnivores displayed overlapping spatial requirements, and overlapping nocturnal activities, we made the hypothesis that the segregation between each species occurred at a smaller temporal scale: in hours. To test this hypothesis we compared the waiting time between the detection of two species A and B and compared it to the waiting time between two detections of the same species B and B, assuming that if species avoid each other the former time should be bigger than the latter. All species displayed a temporal delay, and a hierarchical system of avoidance, in which, cats appeared to be the species avoided the most by foxes and raccoons. During the lockdown period, as species appeared to be more present, increased their use of gardens, and had more nocturnal activity, the consequence appeared to be a shorter waiting time. To conclude, we found that although the wild species were positively associated in space, the avoidance occurred at a smaller temporal scale, and human pressure, in addition, led to higher spatio-temporal overlap.

Predicted values of time of delay (hours) for each of the four mesocarnivore species of Berlin, depending on the species after which they were detected, and whether the SARS-CoV-2 lockdown was in effect or not.
Read the paper

Read the full paper here: Louvrier, J. L. P., Planillo, A., Stillfried, M., Hagen, R., Börner, K., Kimmig, S., Ortmann, S., Schumann, A., Brandt, M., & Kramer-Schadt, S. (2021). Spatiotemporal interactions of a novel mesocarnivore community in an urban environment before and during SARS-CoV-2 lockdown. Journal of Animal Ecology, 00, 1– 14. https://doi.org/10.1111/1365-2656.13635

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