Long-Distant plant dispersal and habitat fragmentation: identifying conservation targets for spatial landscape planning under climate chagne

DOI: http://doi.org/10.1016/j.biocon.2004.12.006

Background:

As the global climate continues to change, plant species responses are expected to either perish, adapt to new local regimes, or track changing environmental conditions suitable to their contemporary niche. However, in some situations the climate may change at a faster rate that species local dispersal would serve as an unsuitable method to track preferred environments. Long distance dispersal provides a potential solution to this situation. Identified mechanisms that would promote long distance dispersal would be updrafts, birds, and attachment to the fur of mammals. Currently, there is limited studies available that attempt to understand the effects of long distance dispersal on plant species migration rates, but progress has been made demonstrating phenomenological patterns of effects long distance dispersal can have on migration rates.  Building on this knowledge, researchers developed a simulated model asking questions about how habitat fragmentation may influence the ability of a plant species to undertake large-scale migrations.

Methods:

The modeling approach adopted to simulate plant dispersal was a grid-based Geographic Information System, essentially a map lattice. The model operates in discrete time and space and allows for stochastic dispersal at the landscape scale. The dispersal kernel was designed in such a way to allow for flexibility between short range and long range dispersal events. The dispersal kernel is based on a p.d.f. that describes the seed arrival at a distance x from a parent plant, with direction of the dispersal selected for at random. More specifically, the dispersal pdf includes exponential and Gaussian density functions and can be described as having a ‘fat-tailed’ functions. Within population model assumes that the likelihood of a population releasing propagules increases with population size and that population size increases through time. Each within cell population is modeled through a logistic growth equation. A Monte-Carlo method was used to account for multiple low probability dispersal events.

Results:

SP is assumed to be the survival probability of the plant species. From the figure provided, it is clear to see how long range migration can influence the survival probability of a plant species in an increasingly fragmented landscape. One point to consider in the future is a dynamic landscape, where patches oscillate between suitable and unsuitable. While another point would be how unsuitable habitats might inhibit mechanisms from dispersal.