elephant herd in the Okavango Delta, Botswana

The reason for biodiversity loss

There is one reason for biodiversity loss currently making up the sixth mass extinction, and it is beyond time that it was owned. Here are the basics from an unusual angle.

Human actions are the reason for biodiversity loss. It is true, we are to blame for the sixth mass extinction. And this should not be a surprise given there are now 8 billion of us alive at the same time—put another way, 7% of all the Homo sapiens that have ever lived are living right now.

When conservationists lament the loss of habitat and the species that live in it, they are angry and sad. Emotions are triggered and often result in railing at the system that cleared the habitat, polluted the rivers and oceans and hunted the wildlife.

It is much harder to focus on the real reason for biodiversity loss.

Here it is.

Estimates suggest that 97% of the land mammal biomass on earth today—that’s the weight of the mammals that we can see with our eyes—is made up of livestock, the animals that human beings manage for our benefit. 

I’ll just say that number again… ninety-seven per cent

Almost all the land mammal biomass comprises cattle, sheep, pigs, goats, horses, companion animals, and the occasional alpaca.

Here is what that looks like—the green squares represent the biomass of wild mammals.

The current biomass of Earth’s land mammals. Source: image from The Overpopulation Project, data from Smith et al. 2015 – Megafauna in the Earth system; based on Vaclav Smil: “The Earth’s Biosphere – Evolution, Dynamics, and Change”

I will say it again, 97%

That means just 3% of the biomass of all land mammals is available to distribute among the mammal species not used as human livestock, and there are at least 5,488 mammal species. 

In 2008, the International Union for Conservation of Nature (IUCN) completed a five-year Global Mammal Assessment for its IUCN Red List that counted 5,488 mammal species.

Recall that biomass is the physicality of the organism. The mass of an object is a measure of the object’s inertial property or the amount of matter it contains and a measure of the force exerted on the object by gravity. So of all of the available mass in land mammals, only 3% is available to be distributed among thousands of wild mammal species. 

Not much.

Feeding all the livestock

Some basic ecology is needed here. 

Animals respire. That means they use energy from their environment in the form of other organisms to survive, grow, and reproduce. The energy conversion rate isn’t great, and mammals with warm bodies need to eat a lot, especially plant eaters.

And it’s the herbivores that humans use. We are not fond of carnivores; anyway, there are relatively few of them due to that energy conversion problem.

At least 50% of the habitable land area of the planet is used for agriculture, and 77% of that, some 40 million km2, is for the rearing of livestock. In other words, humans have converted vast amounts of land to either graze or grow feed for our livestock. 

It’s not just the land mammal biomass but the land needed to support them that has impacted the biodiversity of not just the other mammal species but the plants and invertebrate animals too.

large herd of beef cattle in Australia to illustrate the reason for biodiversity loss

Photo by Alloporus

Another way to see the reason for biodiversity loss

Here is another way to look at the reason for biodiversity loss.

The sun shines and delivers energy to the Earth.

Some of that energy is captured by plants and converted into biomass that animals utilize. The microbes and fungi are around too to help with the nutrient transfers, and the whole ecosystem has a maximum amount of energy transfer determined by the location, the season and the climate.

There is maximum biomass that the planet can deliver, and what’s happened is that humans have appropriated, directly or indirectly through the animals that they consume, a large proportion of that biomass. 

Agriculture and, in particular, livestock husbandry has resulted in a huge proportion of primary production going into that 97%. 

Whichever way you look at it, humans have gone from less than 3% of the mammal biomass in pre-industrial revolution days to being responsible for 97% of it today.

Many mammal species will inevitably be under great pressure to survive. As will so many other species deprived of their energy source. 

Somehow I don’t understand what is hard about this basic logic. 

We can’t have our steak and eat it in this case. You can’t appropriate all the biomass and still expect to keep all the other animals you like. 

As an ecologist, this logic is so basic and ingrained that it’s kind of a no-brainer. 

We shouldn’t be surprised about any of the biodiversity loss that we see around the world. That appropriation of energy and biomass is sufficient to make it happen. 

Add habitat change, climate issues, and the altering of habitats through pollution and other externalities that businesses are so keen on delivering to the world, then it just makes biodiversity loss inevitable—the reason for biodiversity loss is that humans have to eat. 

a small herd of zebra in Hwange National Park Zimbabwe

Photo by Alloporus

Farming our only planet

It’s also hard to dispute the numbers. Whether it’s 97% or 79%, is not the issue. 

Load Google Earth and pan across any of the continents at a height of around 1,000m (you can see that number in the bottom right-hand corner of the screen), maybe start at your home town. What you will see is a landscape has been altered by human activity. There will be a mosaic of fields, maybe some forests or grasslands but the evidence of humans altering the landscape for food is everywhere. There are very few countries with more than 10 or 15 per cent of their land area that’s in anything other than agricultural production. 

A few reserves here and there, a few patches of vegetation here and there, but essentially the landscape has been converted into one massive farm for the benefit of humanity. 

There will always be a dispute over the numbers, dare we say denial, but the imagery is there to be seen and if you don’t believe the satellite imagery just drive through the countryside. When driving just look beyond the fringing vegetation on the roadside and into the fields. And you’ll see that they go for miles. We have converted the landscape, there’s no question about it.

That is our current legacy. 

What sustainably FED suggests

A legacy of global land use change to accommodate crops and livestock—the real reason for biodiversity loss—is a hard one to take. 

The reality and the magnitude of this change to the planet, our only planet, isolated in this tiny corner of the universe. The only place that we have, the only place we’ll ever have, is being ripped from underneath us by our actions. 

That is what it is. 

The only hope is that we are smart. Having figured out all these ways to appropriate resources, maybe we’re smart enough to realise what we’re doing and turn it around. There’s a small window of opportunity over the next 50 to 100 years, but we have to start now. 

Or that window will shut.

Some better conservation questions 

  • Should we focus on the 3% or the 97%?
  • What will happen if the 97% becomes 100%?
  • Will some land mammal species be saved by the law of diminishing returns?
  • Will remote and inaccessible habitats be the only saviour for some species?
  • Can national parks and wildlife reserves save land mammal species?

Feel free to send us some answers or ask us for answers to more of these pointed questions about the reason for biodiversity loss.

Just in case you needed more.

On 11 March 2020, WHO declared the outbreak of COVID-19 a pandemic. Two months later the first version of this post was written. As I write these edits it is 6 June 2023 the time lapsed is 1,182 days, a little over three years.

In the period of time lapsed, there are now 235,948,000 more people to feed, clothe and house than there were because, even without lockdowns, the human population is growing at a net rate of roughly 8,000 humans an hour.

When these new people become adults, they will go about their business, just as all the rest of us are doing. And we can estimate the consequence of that activity in greenhouse gas emissions.

At the average global rate of emissions per capita in 2021—4.7 tCO2e per annum—these people will emit roughly 1,109 million tCO2e every year throughout their adult lives. The same as the total emissions in 2016 of the UK, Italy and France combined.

Think about the reason for biodiversity loss.

image of earth from space
Photo by NASA on Unsplash

Hero image modified from a photo by Alloporus


Mark is an ecology nerd who was cursed with an entrepreneurial gene and a big picture view making him a rare beast, uncomfortable in the ivory towers and the disconnected silos of the public service. Despite this he has made it through a 40+ year career as a scientist and for some unknown reason still likes to read scientific papers.

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