The mid-distance dispersal optimum, evidence from a mixed-model climate vulnerability analysis of an edaphic endemic shrub

Aim: Predicting accurate species responses to climate change in fragmented landscapes is challenging in conservation biogeography. We assessed the role of dispersal, including long-distance dispersal (LDD), for the long-term persistence of a rare plant species (Vella pseudocytisus subsp. paui) under current climate conditions and four future climate scenarios; and analysed the effect of competition for its regional survival. Location: Ester Iberian system, Aragón, Spain. Methods: We used BioMove, a linked modelling platform that integrates demographic, dispersal and competition features with biogeographic predictions of range dynamics, and whose results can inform risk assessments and conservation planning. We linked Vella's population dynamics and habitat suitability models with its well-documented life history traits and ecological characteristics to enhance our understanding of its inherent vulnerability to dispersal, competitive interactions and climate change. Results: We found thresholds in the effect of long dispersal distances on population persistence, suggesting a mid-distance optimum, which reduces mortality risk associated with the increasing proportion of LDD seeds. Moreover, increasing the proportion of LDD propagules reduces Vella's ability to compete in currently occupied and nearby unoccupied habitats by reducing the number of local recruitments. Main conclusions: Whereas LDD ability is generally assumed to be beneficial for the long-term persistence of plant species in fragmented landscapes, our results suggest that moderate to high distances between new colonization increase the species’ dispersal-related mortality. Higher numbers of LDD events reduce the number of local propagules in established populations, reducing regional survival for Vella. Moreover, associated range shifts of potentially better climate-adapted competitors could prevent Vella individuals from colonizing new climatically suitable habitats. These findings can support development of more efficient conservation management strategies for establishing new population patches to mitigate population losses due to climate change. Our findings may also apply as a framework for other narrowly distributed endemic shrub species, particularly edaphic endemics