Are there any laws/theoretical foundations about how diversity of species relate with total biomass on Earth?

While there is a lot of esoteric sort of talk "humanity dis-balances the live on the Earth", I thought, there are formally seen the following hard facts (correct me if I am wrong):

  • biomass of human species and species we need (plants/cattle etc) is increasing;

  • diversity of species is decreasing

So it looks like some sort of global system change (correct me if I am wrong), but how does biology science discuss them (in case my inquiry can be anyhow scientifically formulated)?

  • $\begingroup$ Biomass includes algae, plants, and insects. Humans are almost certainly negligible. $\endgroup$ – terdon Mar 26 at 17:51

I don't work in ecology, but my first thought is that I would not expect any relationship whatsoever between diversity and biomass. Biomass simply means the combined mass of all life on the planet. If that mass consists of one extremely fat goat the size of the moon, or several trillion different organisms doesn't make a difference, mass is mass.

Now, it is undoubtedly true that loss of diversity is a huge issue. However, the way this works is usually that we replace the local ecosystem with its several, varied species with a monoculture. For example, grasses like wheat and barley are taking over the world. Destroying a forest to plant wheat might easily result in no net change in biomass or even a net positive, but it will certainly be a significant loss in the diversity of the local ecosystem.

Finally, humans are a teeny tiny part of the world's biomass, most of which consists of unicellular life, plants and insects:

breakdown of biomass by life form

Note that the axes in the image above are logarithmic. You can get a clearer image, perhaps, from this:

comparative size of biomass by

(both images taken from Bar-On YM, Phillips R, Milo R., The biomass distribution on Earth, PNAS, 2018 Jun 19;115(25):6506-6511. https://www.pnas.org/content/115/25/6506)

See how all animals, let alone humans, are just a tiny part of the image on the right? That gives you a pretty clear indication of just how irrelevant we are in terms of global biomass. So yes, diversity is indeed decreasing, but there is no reason to think that the accumulated mass of living organisms will decrease, only the diversity of said mass will decrease.

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  • $\begingroup$ thank you! wow did not think there is so much fish as one could think we have "fished out" seas!? $\endgroup$ – J. Doe Mar 26 at 23:31
  • 2
    $\begingroup$ @J.Doe the idea of "fishing out seas" really is a major ecological/economic issue, but not to the point of eliminating life (biomass) from the seas. The concern is that extending beyond a maximum sustainable yield, we can cause an individual species to be extirpated or to go extinct. This presents 2 problems. 1) we rely on that fish species for a reason -- perhaps ease/cost of capture, nutrition, etc.. 2) I invite you to investigate further concepts of food webs, keystone species, and trophic cascades. A short summary: what you do to 1 species can and will impact the rest of the ecosystem... $\endgroup$ – theforestecologist Mar 27 at 5:52

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