Niche availability in space and time: migration in Sylvia warblers

AimThe ecological niche of a species is dynamic at a variety of spatial and temporal scales; embracing this complexity is required for accurate assessment of species' niche requirements and to forecast how species will respond to novel and dynamic climates. In the context of recent advances in species distribution modelling, however, both the environment and the ecological niche of a species have often been treated and quantified as static entities. Here, our aim was to explore how species' realized niches and geographical ranges are dynamically shaped by the decoupled spatio-temporal availability of different environmental conditions, using the migration of Sylvia warblers as an example. LocationPalaearctic, Afrotropical and Indo-Malay ecozones. MethodsWe used a species distribution modelling approach to evaluate the niche characteristics of Sylvia warblers under their actual migration strategies as well as null models assuming resident behaviour. We focused on climate and land cover as niche dimensions, taking into account the spatial availability of environmental conditions during the peak breeding and non-breeding season for each Sylvia species. ResultsMigration did not increase the overlap between breeding and non-breeding niches compared with breeding and non-breeding niche overlap in resident null models. Sylvia warblers did not compensate for the costs of a longer migratory journey by tracking their climatic niche or land-cover niche more closely. Instead, Sylvia warblers migrated further than the closest available area with suitable climate and land cover. Main conclusionsClimatic niche tracking is unlikely to be the main driver of migration in Sylvia warblers. We suggest that taking dynamic environments into account and comparing actual niche characteristics to those resulting from alternative possible range dynamics enhances our understanding of the drivers behind organisms' movements and distributions.