Note that a declining number of species doesn't mean fewer living animals.
As the world globalizes, 10 isolated bird species occupying an ecological niche can be replaced by 1 species across the planet, without there being fewer birds total.
As the world globalizes, 10 isolated bird species occupying an ecological niche can be replaced by 1 species across the planet, without there being fewer birds total.
There is nothing unsustainable about this, but I agree that it is quite dull.