Possibly areas on a species fringe could lead to higher densities because on the fringe less of the habitat is suitable for providing the species with all that it needs. Proper microhabitat and resource availability could be limited on the fringe. Even species who have wide distribution maps do not use all habitats encompassed in the man made shaded area of the map because it does not provide everything they need to survive. Suitable den sites could be one of the limiting resource which causes this to be the species fringe area. Maybe areas that people would think would be good den sites dont provide what the snake needs farther north to survive the winter? So with less suitable sites to den these fringe zone dens have to be used by more snakes because there are less quality dens on the fringe available than there are in the middle of the species distribution. Just my guess. Take care.

Chip

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