Any herbivores would have thrived if left alive. same with the smaller predators like foxes or owls. populations shoot up. increase in inbreeding if the islands are isolated and eventually disease catches up with them
The effect differs. It could produce a different amino acid in the sequence because the corresponding codon has changed. It could also prevent the production of the originally intended sequence by changing one of the amino acids of a "start" codon (aka AUG) or extend the protein's sequence by modifying a "stop" codon (UAA, UAG, UGA or UGG), producing a new protein that might be useless or have different effects on the cell.
I’m assuming it’s all of the above
