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The ECI species dispersion model

A spatially explicit cellular automata model has been developed which simulates the stochastic dispersal of species through fragmented landscapes. Species dispersal over a specified time step is simulated within the boundaries of the climate and land-cover suitability surfaces generated by the downscaled SPECIES model. This approach enables new climate and land-cover surfaces to be introduced at future time steps, representing a range of climate and/or land use change scenarios.

The model is based on a cellular automata which simulates the stochastic dispersal of species in terms of two main processes: the release of a number of propagules (seeds, spore, insects, etc.) by an existing population and the redistribution of the propagules according to a dispersal function. The number of propagules released by a population is related to its population growth curve. Thus, once populations have become established, they will release a number of propagules proportional to the population density within a cell.

The dispersal function used to redistribute the propagules includes a fat-tailed dispersal kernel. This enables rare, long-distance dispersal events to be simulated, which are thought to be the primary driver of rapid migration events, such as those evident in the palaeo record following the last glacial maximum.

The function is controlled by two parameters: a 'distance' parameter, which controls the mean distance a propagule can travel, and a 'shape' parameter which controls the fatness of the tail. The stochasticity of the model reflects the random nature of many dispersal events and it is therefore necessary to run the simulations many times using a Monte Carlo approach to build up a probability surface showing likely patterns of spread.

The model requires parameterisation for six species-dependent variables. These are maximum and mean dispersal distance, the shape parameter for the dispersal kernel, net reproductive rate, years to reach reproductive maturity and fecundity. A parameter database has been created containing this information for the 11 species modelled in the project based on an extensive search of the ecological literature, supplemented by expert opinion (Campanula glomerata, Helictotrichon pratense, Silene gallica, Papaver dubium, Legousia hybrida, Lepus europaeus, Chorthippus dorsatus dorsatus, Ostrya carpinofolia, Quercus ilex, Pinus pinaster and Pinus halepensis).

Results from the dispersal model indicate the ability of a species to track changing climate and land use space and thus provides a means of assessing the effectiveness of current conservation policy if continued into the future. It will also facilitate the identification of bottlenecks or gaps in the landscape for dispersal and show where further Natura 2000 sites or similar reserves should be located to enable species to adapt to climate change.

More information on the ACCELERATES project can be found at:

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University of Oxford
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OX1 3QY Oxford
United Kingdom
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