a. A population's success might be positively influenced if, within a given forest island, competitors and predators are excluded. Success would be negatively influenced if the island is so small or non-diverse that there are insufficient resources for a species to survive. Also, of course, if the island is too small too support a viable breeding population, success would be negatively impacted.
b. Large animals with long generation periods and few offspring need large stable territories to support a population large enough to maintain genetic variation. As the forest fragments the larger mammals find their populations less able to meet for genetic recombination so inbreeding depression becomes a problem. Fragmentation and disturbances produce smaller foraging territories with small populations with little variation within each gene pool. Large mammals like moose a K strategists in their life cycle.. K-strategists are niche resource specialists meaning they are usually highly adapted rather than generalists. They are resource partition adapters rather than emigraters able to move on to another area with slightly different resources. Many endangered species are K-strategists. Moose in fragmented forest would be endangered along with other K strategists. Worms are small, with a short life span but reproduce in large numbers as r strategists. While they can readily disperse at the edges of the habitat they will be much more likely to actually speciate with forest fragmentation but each fragment will be large enough to support a genetically diverse population of worms.