On a planet filled with millions of species, is it ethically defensible to consider these matters from the perspective of just one?

The other millions of species don't have an ethical perspective. But okay, lets grant their perspective of wanting to survive and reproduce, behave in the way they evolved to. Fine, but how do you balance the perspectives of those millions? We still need to plow and harvest large fields even if we all go vegan. We still have to deal with pests in our homes.

Should we kill a bunch of cows to make way for native species? Was it okay when the feral goats in the Galapagos were machine gunned down from the air so they would stop eating all the vegetation the native tortoises relied on? Should we kill off all the feral cats, or just let them continue killing birds and small mammals? Is it okay to spray for mosquitos and ticks, or do we let them carry disease and infect us and other animals?

There's a million different tradeoffs, thousands of which we have to decide no matter what.

> We still need to plow and harvest large fields even if we all go vegan

We would need just 25% of those fields. The rest can be returned to the nature. [0]

> Should we kill a bunch of cows to make way for native species

But we're killing them already, at astonishing quantities. It's enough to not make new ones, the problem will solve itself.

> okay when the feral goats in the Galapagos were machine gunned down

Maybe don't introduce farm animals where they don't belong?

> kill off all the feral cats, or just let them continue killing birds and small mammals

Give the birds & mammals a chance to live and procreate, by giving them enough habitat to live in. In time nature will solve the feral cats problems - when bigger predators appear.

> Is it okay to spray for mosquitos and ticks

No, because you're spraying poisons and killing other species as well, and reducing the human health. That's not practical. But you know, biodiversity is the solution [1].

When you kill predators (owls, foxes, coyottes ...), mice proliferate. More mice, more ticks. Let the mice eating predators return and ticks numbers goes down.

Mosquitos? Don't spray poisons and let number of amphibians/fish go up. The problem solved.

[0] If the world adopted a plant-based diet we would reduce global agricultural land use from 4 to 1 billion hectares - https://ourworldindata.org/land-use-diets

[1] The biggest little farm - https://www.imdb.com/title/tt8969332/ - not a scientific resource, but pretty illustrative

Yes.

In a global civilization composed of countless groups of humans, is it ethically defensible to consider the perspective of just one?