Responses to global change in a river passerine

Abstract

Human-induced environmental change is affecting biodiversity across the world. River systems and species associated with these habtitats are particularly vulnerable to the different drivers of global change (e.g. land use, climate change, pollution). Understanding how species respond to these drivers is key for any attempts to address and minimise the effects of global change. In this thesis I focus on a river passerine, the white-throated dipper Cinclus cinclus, as a model to assess the effects of two of the main drivers affecting river ecosystems (land use and climate change) on different ecological traits across multiple scales and life stages. Breeding phenology (Chapter 2) was influenced by climate and land use at different scales, but the interactive effect of climate and land use was significant only at local scales. Lay dates were advanced for nests in areas dominated by farmland and under conditions of increased rainfall and warmer temperatures. Land use also affected stress hormones in developing nestlings (Chapter 3): higher forest cover in the riparian area was linked to lower nestling stress hormone levels but had no apparent effect on morphological traits traditionally associated with nestling development. This land use signal on stress hormones however, was no longer evident in later life (Chapter 4), when stress hormone variation had a strong year component, likely due to weather patterns. Climate also appeared to be associated with long-term morphological change (Chapter 5). Female and male dippers experienced a relative shortening of the wing in relation to body size, reducing dimorphism between the sexes during a period concurrent with increased magnitude and fluctuations in river flow conditions. Overall, these findings suggest that dippers are adjusting their phenology, physiology and morphology in response to global change. However, adjustments in one trait may have adverse consequences for other traits. This thesis highlights the value of using multiple approaches to understand how species respond to global change, and the importance of considering multiple drivers of environmental change.