No city for wetland species: habitat associations affect mammal persistence in urban areas

Abstract

The fast rate of replacement of natural areas by expanding cities is a key threat to wildlife worldwide. Many wild species occur in cities, yet little is known on the dynamics of urban wildlife assemblages due to species' extinction and colonization that may occur in response to the rapidly evolving conditions within urban areas. Namely, species' ability to spread within urban areas, besides habitat preferences, is likely to shape the fate of species once they occur in a city. Here we use a long-term dataset on mammals occurring in one of the largest and most ancient cities in Europe to assess whether and how spatial spread and association with specific habitats drive the probability of local extinction within cities. Our analysis included mammalian records dating between years 1832 and 2023, and revealed that local extinctions in urban areas are biased towards species associated with wetlands and that were naturally rare within the city. Besides highlighting the role of wetlands within urban areas for conserving wildlife, our work also highlights the importance of long-term biodiversity monitoring in highly dynamic habitats such as cities, as a key asset to better understand wildlife trends and thus foster more sustainable and biodiversity-friendly cities.

Keywords: extinction; habitat; mammals; resampling; urban wildlife; wetlands.

Figure 1.

(a) Mean species' spatial spread (expressed as numbers of occupied 1 × 1 km square grid cells) of mammals in the city of Rome at three time intervals; (b) proportions of mammal records at each time interval according to different sources: bibliographic = record from literature or museum specimens; iNaturalist = record retrieved from the inaturalist.org citizen science platform; rescue = record from Rome's Wildlife Rescue Centre; sampling = record from targeted field sampling for the Atlas of Mammals of Rome project (unpublished); (c) numbers of species occurring in Rome at each time interval, according to their preferred habitat.

Figure 2.

Mean spatial species' spatial spread (numbers of 1 × 1 km square grid cells) of occurrence of mammal species (N = 51) occurring in Rome, Italy, between years 1832 and 2023 (a); temporal span (in years) of species occurrence in the study area, separately according to species’ preferred habitat type (b): brown = generalist; dark green = forests; light green = grasslands; light blue = wetlands. Species last recorded prior to 1990 (indicated by vertical dashed line) were considered as locally extinct in the last time interval. Outliers (entries out of the 95% confidence interval) not depicted.

Figure 3.

Alluvial plot depicting the numbers of mammal species that went locally extinct in the urban area of Rome between 1832 and 2023, according to taxonomic order and preferred habitat type.

Figure 4.

Probability of local mammal extinction as a function of maximum spatial spread (quantified as numbers of 1 × 1 square km grid cells) in the city of Rome between 1832 and 2023 according to generalized linear models on (a) all species ( N = 51) and (b) separately for species preferring different habitat types ( sample sizes: forest = 17, generalist = 22, grassland = 4, wetland = 9). Shaded area in (a) indicates 95% confidence interval.