Why is surface area to volume ratio bigger in smaller animals and vice versa?

In surface area to volume ratio (SA:Vol) we are comparing the outside surface area of an object to its internal volume. So imagine 3 rubber balls, one's small, one's medium, one's large. The smallest ball has little internal content (volume) compared to it's outside surface area. Therefore it has a big surface area compared to it's volume, so a high SA:Vol. In the medium ball, compared to the smaller ball, the Surface area hasn't increased hugely, but the internal content (volume) will be much much greater, this means that surface area to volume ratio is reduced. In the biggest ball again, the surface area covering the ball hasn't increased significantly but the internal contents have increased greatly bringing the surface area to volume ratio down (making it smaller) because the internal volume is far greater than the outside surface area. If we apply that to animals, things like polar bears which have a great deal of central mass and very few appendages (eg. they don't have large ears)- these animals will have small surface area to volume ratio because their internal volume is much greater than their outside surface area. Animals such as the fennec fox have very large ears, and are very lean (not fat), the big ears increase the surface area and the leanness reduces the volume of the animal, increasing the surface area to volume ratio. In general, remember: Small things have big SA:Vol. Big things have small SA:Vol.