The argument
"If animals deserve respect, and animals are part of nature, then all of nature deserves respect." This argument is used against the idea of helping wild animals that suffer from natural processes, like disease and hunger.
The mistake: the part and the whole
The argument assumes that if a part of something deserves consideration, the whole does too. But that's not true.
Think of an example. You're part of a team, a city, and a country. You deserve respect. That doesn't mean the city itself feels anything, or that the country can be "hurt" the way you can.
Why we consider sentient beings
We consider sentient beings because they can be affected for better and worse: they feel good and bad things. Nature as a whole doesn't feel anything. It's the place where the beings who feel live.
Mixing up "nature" and "animals"
It's false that if we support changing nature to help animals, we're allowing animals to be harmed because they're part of it. It's exactly the opposite: we change nature to help animals.
This mix-up also makes it seem that views that support "preserving nature as a whole" necessarily care about animals. And often they don't.
In short
- A part deserving respect doesn't mean the whole does.
- Animals feel; nature as a whole doesn't.
- Changing nature can be a way of helping animals.