Résumé
Urban ecosystems are relatively recent and heavily human-altered
terrestrial ecosystems with a surprisingly high diversity of animals,
plants and other organisms. Urban habitats are also strongly fragmented
and subject to higher temperatures, providing a compelling model for
studying adaptation to global change. Crepis sancta (Asteraceae), an
annual Mediterranean wasteland weed, occupies fragmented urban
environments as well as certain unfragmented landscapes in southern
France. We tested for shifts in dispersal, reproductive traits and size
across a rural–urban gradient to learn whether and how selection may be
driving changes in life history in urban and fragmented habitats. We
specifically compared the structure of quantitative genetic variation and
of neutral markers (microsatellites) between urban and rural and between
fragmented and unfragmented habitats. We showed that fragmentation
provides a better descriptor of trait variation than urbanization per se
for dispersal traits. Fragmentation also affected reproductive traits and
plant size though one rural population did conform to this scheme. Our
study shows the role of fragmentation for dispersal traits shift in urban
environments and a more complex pattern for other traits. We discuss the
role of pollinator scarcity and an inhospitable matrix as drivers of
adaptation.