I understand that each animal group has a different weight range and that, if you reduce animal groups to “total weight” metric, you can compare cows with mice on that metric.

I do not agree that this is some kind of meaningful unit, especially in percentage terms, for anything that ecologists might be interested in, like population health, or whatever else.

The fact that ecologists think in terms of biomass while putting on a lab coat and getting a PhD does not make this metric make more sense.

All you've done is asserted it doesn't make sense. You could at least make an argument as to why.

What do we talk about when we talk about human populations? Like say, you want to formulate an opinion on Germanic peoples' population in history. Do you EVER talk about percentage aggregate biomass of Germanic peoples?

No, meaningful numbers are # of individuals, lifespan, sex/age composition, fertility, height, weight, etc. Percentage of aggregate biomass is not among them, for good reason.

Look, I have no problem if scientists are measuring things in an exploratory way. Let's add up the mass, subtract, play around - this fun exploration is good. But if you are doing fun exploration, don't tell me this is to "measure the richness of the mammal kingdom" and throw around a shocking "96%" as if to pretend it is meaningful. It is not.

EDIT/PS: Thought of another example - say you are studying dogs and human interaction in history. You would never think of showing historical aggregate [dog biomass / dog+human biomass] as some kind of meaningful metric. You would show dog count, dogs per human, dog speciation, etc. Not dog biomass percentage.

Oh come on. We do in fact talk about the biomass of human populations, relative to what an ecosystem can sustain.

Broadly speaking, different ecosystems can support different total biomasses, as a function of total energy input into the system (mainly from the sun), and a variety of limiting factors (like availability of water). So a desert--which can be a perfectly healthy ecosystem--sustains, both in theory and practice--far less biomass than, say, a tropical rain forest.

Let's take an example, pulled more or less randomly from Google Scholar, an article titled "Hunting pressure modulates the composition and size structure of terrestrial and arboreal vertebrates in Amazonian forests". Here is the abstract:

>Overhunting is a leading contemporary driver of tropical forest wildlife loss. The absence or extremely low densities of large-bodied vertebrates disrupts plant-animal mutualisms and consequently degrades key ecosystem services. Understanding patterns of defaunation is therefore crucial given that most tropical forests worldwide are now “half-empty”. Here we investigate changes in vertebrate community composition and size structure along a gradient of marked anthropogenic hunting pressure in the Médio Juruá region of western Brazilian Amazonia. Using a novel camera trapping grid design deployed both in the understorey and the forest canopy, we estimated the aggregate biomass of several functional groups of terrestrial and arboreal species at 28 sites along the hunting gradient. Generalized linear models (GLMs) identified hunting pressure as the most important driver of aggregate biomass for game, terrestrial, and arboreal species, as well as nocturnal rodents, frugivores, and granivores. Local hunting pressure affected vertebrate community structure as shown by both GLM and ordination analyses. The size structure of vertebrate fauna changed in heavily hunted areas due to population declines in large-bodied species and apparent compensatory increases in nocturnal rodents. Our study shows markedly altered vertebrate community structure even in remote but heavily settled areas of continuous primary forest. Depletion of frugivore and granivore populations, and concomitant density-compensation by seed predators, likely affect forest regeneration in persistently overhunted tropical forests. These findings contribute to a better understanding of how cascading effects induced by historical defaunation operate, informing wildlife management policy in tropical peri-urban, rural and wilderness areas.

Let's think about this for a bit. You are making observations about lots of different animals. Some animals are common. Some are not. Some animals are small. Some are not. But you aren't interested in, say, just the effect of hunting on some particular species of woodland mouse, but across groups of species (e.g. frugivores, granivores, etc.), and as a whole. So, how are you going to do it. You found a 10,000,000 really healthy ants, and 5000 mice, 100 snakes, 10 weasels and 1 cougar. You can't just add them up. Sure, you could measure the decline in number of individuals from each of those in percentage terms, and then, maybe, what, average that? But aren't you really making a mistake doing that? What if that 1 cougar died, roughly the weight of all those ants put together. Aren't we missing something here? Yes, we are. And that thing is the total mass.

A fact like, humans and our livestock, account for (some huge proportion) of the total biomass in a particular ecosystem, that's actually pretty damn relevant, and meaningful. Less meaningful perhaps than comparing to the theoretical capacity it could achieve, if such numbers could actually be derived, but it still says a lot about the state of ecosystems today.

Thank you for the thoughtful response. Your explanation makes sense, but it makes me modify my objection two-fold:

1) humans+livestock should not factor into these biomass calculations.

Humans+Livestock are not meaningfully competing against other animals, in desert, in bush, or in the rainforest, because we modify the environment and make it far more calorie-rich: we farm. Even the densest rainforest wouldn't come close in # of mammal-consumable calories per acre to what humans can produce in farms. And the energy to farm is enabled mostly from fossil fuels, ore mining, etc - another thing that only humans do - we are not using solar energy to make or operate tractors, so not really meaningfully taking sunshine resources from other animals.

In other words, you can't lump human+livestock biomass, as if it's a passive consumer of ecological biomass resources, because we increase those resources.

Then, the only meaningful thing to compare is wild natural area displacement (like in miles squared) through settlements and farms. To the extent that other mammal populations shrink or go extinct, it will be simply due to smaller square miles we squeeze them into.

2) for the remaining animals, biomass is still not a good number.

> Sure, you could measure the decline in number of individuals from each of those in percentage terms, and then, maybe, what, average that?

Those intra-species population changes would be far more meaningful, yes. Averaging - no. I still do not accept this idea that if you kill a cougar, then the ecology will support cougars-weight more ants in that area. That is a major unsubstantiated hidden assumption. Only animals that consume the same resources at the same rates are fungible like that. When a cougar dies, no more ant-compatible food sources pop up. Need to show species level individual count. Biomass implies fungibility.

re (1)

In terrestrial ecosystems, the sun's energy is captured by primary producers (plants). That energy is used for plant metabolism, reproduction, and growth (building tissues, storing energy, etc.). Net primary productivity (NPP) of an ecosystem is the the difference between what energy primary producers capture from the sun and onvert into sugars during photosynthesis, and the energy loss to maintenance and metabolism. It is principally measured as the accumulated biomass. Importantly, NPP is an upper bound, since the primary, if not only way, for all other organisms to obtain their energy is to consume plants (herbivores), or consume those who consume plants (carnivores).

NPP is different between terrestrial ecosystems. Deserts have the lowest. Tropical rainforests the highest (excluding marshes, etc.). Temperate forests are quite high, and much higher than grasslands or farmlands.

e.g. 9000 kilocalories/square meter/year for rain forests, 6000 for temperate forests, about 2000 for farmland.

Now what most modern farming does do, is bring in energy from elsehwere. For example, cattle might be fed corn brought it from elsewhere. Not to mention the energy inputs from fossil fuels (fertilizers, tractors, etc.)

(2) You are right that comparisons in terms of biomass imply fungibility and it is not always appropriate. But it is also true that individual species often simply fill niches that arise as a property of the system (the system of energy inputs and limiting factors). How else would you compare, say, a forest in Washington with a forest in northern Europe? different species, and all that. But the niches are largely the same.

> Now what most modern farming does do, is bring in energy from elsehwere. For example, cattle might be fed corn brought it from elsewhere. Not to mention the energy inputs from fossil fuels (fertilizers, tractors, etc.)

Yes! Minus the corn, which is another farmland, fossil fuels, Haber Bosch fertilizers are things that only humans do.

Are you saying that with all the technologies of modern farming, it still produces less than 0.25x mammal-consumable calories per square mile (9000 for rainforest vs 2000 for farmland)?

That is unbelievable on its face, frankly, but also of couse farmland is not generally replacing lucious rainforests, but other bushland or something. So, humans and their farmland has to be enormously increasing the mammal-consumable calories per plot of farmland compared to wildland, otherwise farming wouldn’t make sense.

The point is, there is only 1 animal (human) that drastically increases calories per square meter wherever it goes, so we (and livestock we choose to feed with farming) can not be lumped into any biomass calculations.

2) I would compare the species within themselves, and the “niches” between forests. Ultimately, I think biomass confuses more than it elucidates. Talk about ant colonies of Antium Washingtonicum to Antium Europium, don’t plop them into the same metric as Cougarium Washingtonium, in my opinion this is will lead to maybe nice-looking graphs with “findings” that are nonsensical.