Carcass predictability but not domestic pet introduction affects functional response of scavenger assemblage in urbanized habitats

1. Urbanization alters species richness and composition, but studies of urbanization effects on ecological functions have often quantified variation in functional traits and changes in functional diversity rather than measuring directly how ecological functions vary between rural and urban assemblages.
2. Consuming dead animal matter and recycling its nutrients stabilizes and structures food webs and therefore represents a key component of ecosystem functioning. Introduction of free-ranging domestic pet animals adds additional scavenger species to urban habitats, and increased predictability of carcass resources produced by human activities characterizes urban habitats.
3. Here, we investigate the effect of urbanization on the composition of diurnal and nocturnal scavenger assemblages and on the ecological function of carcass removal by using a carcass placement experiment in Swiss urban and adjacent rural habitats.
4. While diurnal and nocturnal scavenger assemblages changed considerably from rural to urban areas by comprising particularly more domestic cats in the latter, carrion consumption rate did not differ between the two habitats. Predictability of carcass occurrence increased carrion consumption rate in both urban and rural habitats but mainly native scavengers and not introduced domestic pets responded to the repeated placements.
5. These results suggest that urbanization shapes scavenger assemblage compositions without affecting their ecological function. The mechanism is likely due to a behavioural change of native scavengers in response to the occurrence of domestic pets resulting in functional plasticity of urban scavenger assemblages. The functional plasticity might be facilitated by the increased carcass predictability and additional anthropogenic food resources in urban habitats exploited by nutritionally flexible native scavenger species.

Keywords: carrion, domestic cat, ecological functioning, ecosystem services, functional equivalency, urbanization