Where is Black an Advantage? | Geography of Melanistic Animals

Black Jaguars, black Leopards, black squirrels, black Adders, black Garter snakes. Melanism in the animal kingdom is stunning to say the least, but it's not evenly distributed across our planet. In some places, you're a lot more likely to run into the melanistic morph of a species than in other places. The black morph of the common Grey squirrel, for instance, is naturally found most often around the Great Lakes. Why is this? Why are the black morphs more common in some regions, than others?

Image sources:
Benny Mazur: https://www.flickr.com/photos/benimoto/
Brian Brettschneider (@Climatologist49 on twitter): http://us-climate.blogspot.com
Ignacio Yufera: http://www.iyufera.com/about/
Wikipedia commons

Sources:
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Polymorphic Clay Models of Thamnophis sirtalis Suggest Patterns of Avian Predation. Tonya D. Bittner , Department of Biological Sciences, Northern Illinois University

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