Fix for wildlife overspawning

Fixed wildlife overspawning. Kevin's earlier change to population radii was causing wildlife populations to become overly dense. I've allowed them to be a special case and remain at a fixed radius. Also I've removed the dependency on distance from their 'epicenters' in their spawning rate (only for wildlife pops). As it was, being closer to the corner of the map (where wildlife pops are added) was increasing the spawn rate.