The original population of salamanders migrated southward from the north of California. They avoided the Central Valley because it was too dry and hot for them to live there. As they moved south, the eastern and western salamander populations evolved and by the time they got together again in Southern California, they could no longer interbreed and had become two new species of salamanders.

the two answers are a, the population of birds with large beaks will increase on the island, and c, the trait for large beaks will be passed on to future generations through natural selection. the reason for that is because if the birds that have beaks developed for eating small seeds lose all of their food, they will go hungry and eventually starve because they physically cannot eat the large seeds, therefore making the population of large beaked birds higher. also, if the trait of large beaks are dominant on the island over small beaks, then over time the large beaked birds will reproduce more and more, while the smaller beaked birds will reproduce less and less because they can't survive with the food provided. that leads to the trait of small beaks disappearing and the trait of large beaks taking over the island.