[imtringued]

What is economics? Physical capital? Financial capital? Land? The human sphere of influence?

If you are generous and argue that humans help plants grow, then e.g. harvesting plants is beneficial for plants and humans and physical capital is not zero sum despite the fact that humans are intentionally killing plants and depriving them of their body.

Financial capital is zero sum, when you borrow money, you create money and debt simultaneously. Pay off all debt and you end up with zero money. Money is zero sum.

Land is zero sum. If one person owns all the land on the planet, everyone else must rent from that person or be homeless.

The human sphere of influence? I would argue that this is zero sum because a hypothetical tribe of neanderthals wouldn't be welcome in this modern world, we would never let them take over the planet, hence our domination over the planet comes at the expense of other species.