Lets take in mind that there is a problem to compare two groups when one group is much easier to measure than the other. The error interval in the mammal biomass should be much higher. The actual real values are probably not so extreme.
... I see, is just megafauna. The most competitive groups (rodents and bats) are deliberately excluded. The title is incorrect then.
Is this true? This source (https://www.pnas.org/doi/10.1073/pnas.1711842115) gives a very similar percentage (95.8% of all wild mammals) and doesn't mention anything about excluding rodents or bats from the categorization of wild mammals. Is it in a footnote somewhere that I'm missing?
Certainly the article might not be credible, but can you cite the relevant text from the article, so that the rest of us can quickly verify your claim? I'm not seeing where in the article this is stated.
I think it is an unclear and bizarre term. “The energy contained in one group” - what energy? Is a lean cheetah “less-energy” than an elephant? Why? Or do you literally mean energy like calories (which, IIRC means “how much heat if burned”).
What a bizarre metric, nobody thinks like this, I don’t even think “ecologists” understand why they should think in terms of mass. I, too, can have a metric: number of decibels of sound you can produce; maybe humans make up a SHOCKING 3% on that- doesn’t mean it’s a sensible metric.
> “The energy contained in one group” - what energy?
The chemical energy contained in the links of the molecules
> Is a lean cheetah “less-energy” than an elephant?
Yes, of course. One cheetah, has less biomass than one elephant. But -the- rats, have more biomass than -the- elephants. Is the beauty of the ecology.
> What a bizarre metric, nobody thinks like this, I don’t even think “ecologists” understand why they should think in terms of mass.
Well, this sounds a little arrogant. The professionals that use it, obviously, know their job. They aren't stupid.
Would be like claiming that programmers don't understand why they use an if loop. Biomass is a measure as widespread in ecology as Megabytes is in computers.
And there is not need to use quotes around the word ecologists, in the same way as you wouldn't wrote: the "engineers" or the "programmers".
> I, too, can have a metric: number of decibels of sound you can produce; maybe humans make up a SHOCKING 3% on that- doesn’t mean it’s a sensible metric.
Well, the difference is that nobody uses your metric.
> The professionals that use it, obviously, know their job. They aren't stupid.
I will not defer to authority. I want an explanation for why the percentage of aggregate “chemical energy contained in the links of molecules” is considered a meaningful metric for anything other than “how much percentage heat would I produce if i threw them into a fire”, let alone mammal population health or diversity.
> Well, the difference is that nobody uses your metric.
Correct, because it is not meaningful, and neither is biomass.
I'm not sure why you're so hostile toward this idea...
I know basically nothing about ecology, but it seems relatively straightforward to think of reasons to study biomass. Think about food chains. Food is energy is biomass (as you mention). At a basic level: if you know that a certain ratio of biomass is needed (or expected) between two stages in a chain, then you can keep tabs on one of those stages, and when you see biomass decreasing, it's a signal that the food chain might be soon disrupted. In a food chain, the number of animals seems mostly irrelevant (except in cases of near-extinction), but the total energy is highly relevant.
"To understand how the richness of the mammal kingdom has changed we need a metric that captures a range of different animals and is comparable over time. We could look at their abundance – the number of individuals we have – but this is not ideal. We would be counting every species equally, from a mouse to an elephant and this metric would therefore an ecosystem taken over by the smallest mammals look much richer than one in which bigger mammals roam: if the world’s mouse populations multiplied and multiplied – maybe even to the detriment of other animals – then this abundance metric might suggest that these ecosystems were thriving.
Instead, ecologists often use the metric biomass. This means that each animal is measured in tonnes of carbon, the fundamental building block of life.1 Biomass gives us a measure of the total biological productivity of an ecosystem. It also gives more weight to larger animals at higher levels of the ecological ‘pyramid’"
PERCENTAGE biomass in NO WAY reflects “the richness of the mammal kingdom”. It is a synthetic metric that scientists can futz around with enough to produce some shocking metric and get funding/press.
ABSOLUTE “biomass” is meaningful, simply because mammals have relatively tight weight ranges and you can estimate the individual counts from the biomass- but let’s be real: it is most likely that they start with estimates of number of individuals and multiply that by the average weight to get biomass. So- ditch the biomass and show absolute numbers of individuals over time. That is meaningful.
> Also, “biomass” is a strange term. Is that literally an estimate of mass?
It is indeed. The idea being that individuals vary greatly (it doesn't make sense to compare individual counts of humans with individual counts of ants for example), and that mass at least roughly accounts for the size of individuals.
But, especially in mammals, it is the individual animal that is the fundamental unit. A cheetah and an elephant are unique individuated specimens; it doesn’t make sense to compare their mass. In ants/bees it’s maybe something like “number of colonies/hives” that is the meaningful unit. Why would anyone compare across species by mass- that is a reductive number, you can’t infer anything meaningful out of it. Also, certainly not by percentage - have to look at absolute numbers of meaningful units over time.
You can call me a heretic for questioning His Majesty The Ecologist, but the emperor wears no clothes and percentage of aggregate biomass is the most meaningless metric I've ever heard to study mammals.
Biomass is probably exactly the right measure, when we are talking ecology. A lot of mice to weigh up to one cow, it is true, but then, you could feed a lot of mice on the grain with which you feed your cow.
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.
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.
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.
... I see, is just megafauna. The most competitive groups (rodents and bats) are deliberately excluded. The title is incorrect then.