I'm modelling the distributions of Australian parrots in response to climate change. I have two climate scenarios (present and future), and have used Maximum Entropy modelling to generate maps of future distributions. These distribution maps are binary maps consisting only of 'presence pixels' or 'absence pixels'.
I want to use three different dispersal scenarios in the future projections to limit how far each parrot species can disperse; for example 'no dispersal' and 'unlimited dispersal'. The third scenario is what I am needing help with: contiguous dispersal. I want to create a raster layer that limits the future distribution of a species only to pixels that directly or indirectly touch presence pixels from the current distribution, i.e. limiting the distribution to presence pixels (under the future scenario) that are indirectly contiguous with presence pixels of the current climate scenario.
For example I've included a diagram of one of the species. I have a species that has a relatively small distribution under current conditions (purple pixels), and a much larger projected range under future conditions (yellow pixels), the area of presence overlap between the two scenarios is shown by brown pixel, areas of absence in both scenarios are grey. I want to create a presence-absence raster layer that excludes all yellow pixels that do not form a contiguous surface with a brown or purple pixel - i.e. exclude yellow pixels that are separated from purple/brown pixels (and the yellow pixels that are contiguous with them) by areas of absence.
I'm hoping there is a tool that will allow me to exclude these 'discontinuous' yellow pixels so that the extent of the presence pixels in the presence-absence raster layer is restricted.