Kerry Edwards... You need to read "The Beak of the Finch"
Great book on specialization of species based on scarce or abundant resources. Basically, they did an intense survey of the Galapagos islands and the available food for a period of like 10 years. They fed the data into a computer model and started with a generic finch and asked the computer to predict how the species would evolve. To their surprise the computer came up with 3 different paths/species. Surprisingly, these three computer species matched up well with the existing finch species on the island. Smaller species did well in times of scarcity while the larger excelled during plenty. The mid tier did the middle thing (memory not holding up here).

Great book on species and how they occur. My abstract doesn't do it justice.