Connectivity analyses accounting for stepping-stone patches in fragmented landscapes
Presenter: Marie-Josée Fortin (S. Saura and A. Watts), Department of Ecology and Evolutionary Biology, University of Toronto, Canada
Climate and land-use changes will require species to move large distances following shifts in their suitable habitats, which will frequently involve traversing intensively human-modified landscapes. Practitioners will therefore need to evaluate and act to enhance the degree to which habitat patches scattered throughout the landscape may function as stepping stones facilitating dispersal among otherwise isolated habitat areas. We formulate a new generalized network model of habitat connectivity that accounts for the number of dispersing individuals and for long-distance dispersal processes across generations. We find that the loss of intermediate and sufficiently large stepping-stone habitat patches can cause a sharp decline in the distance that can be traversed by species (critical spatial thresholds) that cannot be effectively compensated by other factors previously regarded as crucial for long-distance dispersal (fat-tailed dispersal kernels, source population size). We illustrate how this generalized network model can be used to test how stepping-stones are important to promote species range expansion (Black Woodpecker, Spain) and the spread of vector-borne disease (Lyme disease, Ontario) in fragmented landscapes based on wildlife-host movement. For the Black Woodpecker range expansion example, we show that the loss of intermediate and sufficiently large stepping-stone habitat patches can cause a sharp decline in the distance that can be traversed by species (critical spatial thresholds) that cannot be effectively compensated by other factors previously regarded as crucial for long-distancedispersal (fat-tailed dispersal kernels, source population size). Then for the Lyme disease spread example, we estimate the probability of infected-tick (I. scapularis) spread comparing a suite of hosts (white-footed mice, American robins and white-tailed deer) in a Lyme-endemic island landscape in Thousand Islands National Park. We show that stepping-stone habitat is critical for short- and long-distance invasion of both the tick vector and the pathogen by mice and deer. Overall the novel network modeling tools can be extended to various disease systems with applications to anticipating the impact of land use changes on the wildlife disease spread. Findings from our new generalized network model stress that stepping stones must be of sufficient size to be of conservation value and are particularly crucial for the spread of species over long distances.
Publications referenced in this webinar can be found at: http://labs.eeb.utoronto.ca/fortin/publications.html