Final answer:
In the given food web, the rabbit is crucial for the survival of both the fox and the hawk as it is preyed upon by both. Therefore, the rabbit is the species necessary for the survival of all other species in this food web.
Step-by-step explanation:
The question pertains to a specific food web in a community near a small lake and asks which species is necessary for the survival of all the other species in the food web. In this food web, the rabbit serves as a prey species for both the fox and the hawk. The fern is not mentioned in the provided food web, but it could be inferred to be a primary producer that the rabbit might consume. The hawk is a top predator and while it plays a role in controlling populations of species below it in the food web, it is not a source of food for other species in the food web provided. The fox is a middle-level predator that consumes the rabbit but does not provide a food source to the hawk within this food web.
In this case, the rabbit (C) would be the species necessary for the survival of both the fox and the hawk, as it is directly preyed upon by both of these predators. If the rabbit population were to disappear, it would affect the fox's ability to survive because it loses a source of food, and subsequently, the hawk might also be affected if the fox is a part of its diet or if the rabbit is a significant part of the hawk's diet.