Answer:
There wouldn't be enough resources for the alligator population to live off of thus decreasing its population number. This decrease affects the other populations because it without alligators, its predators and prey wouldn't gain its nutrition from it and it would overall change its environments' habitation. The gar population would increase because they wouldn't be eaten by the alligators and therefore increasing the diving duck population as well. The crab population would decrease because the gar (their prey) population increased which overcomes the number of crab in the population.
Step-by-step explanation:
Hope this helped :)