A very, very famous example is the Galapagos finches
They all radiated from a common ancestor. With a overcrowding of population and genetic differences, different species of birds radiated from the common ancestor and now eat a variety of foods.
Each finch group now has a unique niche, though the common ancestor diet had a different diet
ANOTHER is Polar Bears
In the past they relied solely on seals and breathing hole in the ice as hunting grounds
With current global warming, many are struggling for survival and turning to other food sources such as human waste; as seals can no longer provide a adequate food source, the ice is melting and the hunting grounds disappearing with the ice.
