Why animals in cold place is bigger than in warm place?

Animals in colder climates need to be bigger so they can last longer without food, as there would not be a constant source, and the general blubber and fat helps keep them warm, because they don't have coats like humans. It is a similar concept to a dog growing a thicker coat in winter, and malting in summer, but with fat instead of fur.

Hope this was useful :)