Going Wild in the City—Animal Feralization and Its Impacts on Biodiversity in Urban Environments

SIMPLE SUMMARY: Understanding the impact of urbanization on biodiversity is a crucial task of our time. Here, we reflect on the importance of feralization in the relationship between ongoing urbanization and the worsening biodiversity crisis. Feralization is often viewed as the exact opposite of a domestication process—a perception that we argue is too simplistic. The interrelations between domestication, feralization, and the adaptation of taxa to novel, human-made environments such as cities are complex. Given their unique traits, feral(izing) taxa can play key roles in sustainability, sometimes problematic (i.e., invasive species) but at other times, improving human well-being in urban settings. ABSTRACT: Domestication describes a range of changes to wild species as they are increasingly brought under human selection and husbandry. Feralization is the process whereby a species leaves the human sphere and undergoes increasing natural selection in a wild context, which may or may not be geographically adjacent to where the originator wild species evolved prior to domestication. Distinguishing between domestic, feral, and wild species can be difficult, since some populations of so-called “wild species” are at least partly descended from domesticated “populations” (e.g., junglefowl, European wild sheep) and because transitions in both directions are gradual rather than abrupt. In urban settings, prior selection for coexistence with humans provides particular benefit for a domestic organism that undergoes feralization. One risk is that such taxa can become invasive not just at the site of release/escape but far away. As humanity becomes increasingly urban and pristine environments rapidly diminish, we believe that feralized populations also hold conservation value.