Dispersal-related traits of the snail Cornu aspersum along an urbanisation gradient: maintenance of mobility across life stages despite high costs
Résumé
The extreme fragmentation of natural habitats due to urbanisation can influence the evolution of dispersal strategies in species persisting in cities. The brown garden snail Cornu aspersum is an anthropophilic species, capable of maintaining its populations in highly fragmented habitats despite a high cost of movement. In this species, we studied the variation of dispersal-related behaviours and traits along an urbanisation gradient characterised at two biologically relevant spatial scales (10 and 50 m), in order to identify the effects of habitat fragmentation on movement. The olfactory perceptual range was low, between 1 and 2.5 m, meaning that snails should perceive a large range of landscapes as fragmented. In line with previous results, subadults were more prone to explore than adults in the least urbanised populations. The boundary-crossing behaviour of subadults was not affected by urbanisation, while exploration propensity of adult snails increased with urbanisation at the 50 m (long-distance dispersal) scale, to reach subadult levels in more urban sites. Foot mass (a correlate of movement speed) and perceptual range were not affected by urbanisation. These results are interpreted in relation to the different levels of competition snails are likely to experience in different environments, the high risk of local extinction in urban fragmented landscapes, and the available opportunities for reproduction. They indicate that benefits of dispersal still need to be considered even in situations where movement costs are extremely important. The maintenance of relatively high mobility and its extension to the adult stage in response to anthropogenic changes may thus play a major role in the success of Cornu aspersum in urban habitats.