The finches variations in the founders finches beaks allowed them adapted to the different niche in their environment. Natural selection allowed those with long, pointy beaks to be able to utilize them to feed on insects. Those with shorter, more powerful beaks were able to feed off of nuts. Over time, the selection forces allowed these traits to become predominant in small groups eventually resulting in speciation. Also, behavioral changes (sleep/wake cycles, nesting patterns, the island the lived on, etc.) contributed to the various species of finches.
