The answers are as follows:
1. Specie B is the predator of specie A.
A predator is an animal that eat other animals while the prey is the animal that is killed and eaten. Both the predators and the preys usually co-exist in the same ecosystem. The relationship between the predator and the prey affect the population of the organisms in all ecosystem; it determines the mortality of preys and the birth of new predators.
2. The vegetation it eats increases and then decreases repeatedly with changing seasons.
Cyclic population change refers to the changes that occur in the ecosystem as a result of fluctuations in one or two of the components of the ecosystem. For instance a decrease in the amount of found that is available for a particular specie in an ecosystem will result in cyclic changes in the population of that specie.
3. The deer population will increase, and will strip the region of the vegetation.
If the animals that are preying on the deer are removed, the deer population will increase significantly because they are not been killed again. And because the deer feed on the vegetation, the deer will strip the ecosystem of all its vegetation.
4. The ecosystem collapses.
The keystone specie of an ecosystem is that particular specie, which have a large influence on the ecosystem and which to a large extent determines what happens in the ecosystem. If a keystone species is removed for its ecosystem, the ecosystem will collapse.