Integrating demographic and genetic effects of connections on the viability of an endangered plant in a highly fragmented habitat

Abstract

Classical ecological theories state that the viability of small metapopulations is critically related to: (1) the correlation of local population dynamics, (2) the possibility of extinct patch re-colonisation, and (3) the effects of genetic deterioration. Recent works suggested that these factors are not independent because dispersal might affect both re-colonisation and genetic rescue processes and because connectivity between habitat patches may be related to their environmental synchrony. Close patches may exhibit both high connectivity and synchronisation of their environments.Here, we examined these effects in the endangered plant Ranunculus nodiflorus that inhabits temporary water puddles, where water corridors constitute the vector (1) allowing seed dispersal throughout puddle networks and (2) leading to synchrony of local environmental factors. We utilised a demo-genetic metapopulation model to show how the antagonistic effects of connectivity and synchrony lead to complex interactions between the species’ biology and network configuration. We specifically demonstrated that (1) when an effective seed bank occurs, viability is maximised either for systems of numerous small independent networks (not connected and not synchronised), or for one single large network, while intermediate situations lead to a dramatic increase of the extinction risk; (2) genetic deterioration has notable negative effects on viability only in situations where environmentally driven extinction is buffered by the presence of a seed bank and network configuration; and (3) temporary connections among networks lead to a dramatic reduction of the extinction risk. The implementation of such connections is an efficient management option for the species.