In this ecosystem, the animal whose absence would have the greatest negative effect would be the wolf.
Here’s the reasoning:
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Wolves are the top predators in this ecosystem and control the populations of both foxes and deer. If wolves were to disappear, the populations of foxes would likely increase significantly, potentially leading to over-predation of rabbits. Additionally, without wolves, deer populations could also grow unchecked, which might result in overgrazing and subsequent degradation of vegetation.
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Foxes primarily prey on rabbits, but they are also preyed upon by wolves. If foxes were removed, rabbit populations might increase, but this could lead to imbalances as well.
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Rabbits serve as a food source for foxes and wolves. If rabbits were removed, it would primarily affect fox populations and could lead to their decline, but wolves would still have deer as a food source.
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Deer are preyed upon by wolves, and while their absence might affect the wolves, the wolves could still sustain themselves on foxes and rabbits.
In summary, the absence of wolves would destabilize the entire ecosystem, affecting multiple levels of the food web. Therefore, the wolf would have the greatest negative impact if absent. However, since "wolf" is not an option in your responses, based on what's available, the next best answer would be fox.