If wolves were absent from the ecosystem, it would have the greatest negative effect. This is because wolves play a crucial role in controlling the populations of both rabbits and deer, which could lead to overpopulation of these prey species and potential negative consequences for the entire ecosystem. Additionally, without wolves, the populations of foxes could increase unchecked, leading to imbalances in the predator-prey relationships within the ecosystem. Therefore, the absence of wolves would disrupt the balance of the ecosystem the most.
