Wild mammals make up only a few percent of the world’s mammals
Livestock make up 62% of the world’s mammal biomass; humans account for 34%; and wild mammals are just 4%.
Humans have transformed the mammal kingdom.
A diverse range of mammals once roamed the planet. This changed quickly and dramatically with the arrival of humans. Since then, wild land mammal biomass has declined by an estimated 85%.
Humans are now the dominant species.
We see this when we look at the distribution of mammals across the world today.
There are various ways that we could look at mammal species: we could compare them based on the number of individuals: their abundance. This tends to favor very small animals with large populations and doesn’t necessarily give us an idea of how dominant different species are.
Instead, ecologists often look at a different metric: biomass. This not only takes into account the number of animals but also factors in their size. 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’: these rely on well-functioning bases below them.
Let’s then look at the breakdown of the global mammal kingdom in 2015. This data is sourced from the study by Yinon Bar-On, Rob Phillips, and Ron Milo.2
Each icon is equivalent to around one million tonnes of carbon. This includes both land and marine wild mammals.
Wild mammals make up just 4% of the mammal kingdom.
The dominance of humans is clear. Alone, we account for around one-third of mammal biomass. Almost ten times greater than wild mammals.
Our livestock then accounts for almost two-thirds. Cattle weigh almost ten times as much as all wild mammals combined. The biomass of all of the world’s wild mammals is about a third of our pigs alone.
Global poultry weighs more than twice that of wild birds
When I show people the chart above, one question always comes up: what about chickens? Of course, chickens are not mammals. But we can do a similar comparison between poultry and wild birds.
For birds the distribution is similar: poultry biomass is more than twice that of wild birds. We see this in the chart.
Wild mammals have declined, but the total amount of mammal biomass has increased a lot
The charts above give us a snapshot of how the mammal kingdom looks in the modern day. But both the distribution and amount of mammal biomass have changed dramatically over time.
In the visualization we can see the total biomass of mammals at four points in time: 100,000 years ago; 10,000 years ago, in the year 1900, and the 2015 snapshot we looked at previously.3
In the last 100,000 years, as the human population increased, wild mammal biomass has declined by 85%.4 I looked at this history in a related article.
The decline of wild mammals is not the only change. At the same time, humans and our livestock have grown significantly – from millions to billions.
What’s interesting is that, while the diversity of the mammal kingdom has decreased, its total size has expanded a lot. Terrestrial mammals weighed in at an estimated 20 million tonnes of carbon 10,000 years ago. This is now around nine times larger.5
Within centuries, humans have increased the size of the mammal kingdom almost ten-fold.
Acknowledgments
Many thanks to Max Roser for providing feedback and suggestions on this article and its visualizations.
Keep reading at Our World in Data
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Endnotes
To calculate the biomass of a taxonomic group, the researchers multiplied the carbon stock for a single organism by the number of individuals in that group. In humans, for example, they calculate the average carbon quantity of a person and multiply by the human population. If you want to quickly estimate your carbon biomass: calculate 15% of your weight.
Bar-On, Y. M., Phillips, R., & Milo, R. (2018). The biomass distribution on Earth. Proceedings of the National Academy of Sciences, 115(25), 6506-6511.
These estimates were constructed from three key sources: long historical figures come from the work of Anthony Barnosky (2008); figures for the year 1900 figures from Vaclav Smil (2011); and 2015 figures from Yinon Bar-On, Rob Phillips and Ron Milo (2018).{ref} Barnosky, A. D. (2008). Megafauna biomass tradeoff as a driver of Quaternary and future extinctions. Proceedings of the National Academy of Sciences, 105(Supplement 1), 11543-11548.
Smil, V. (2011). Harvesting the biosphere: What we have taken from nature. MIT Press.
Bar-On, Y. M., Phillips, R., & Milo, R. (2018). The biomass distribution on Earth. Proceedings of the National Academy of Sciences, 115(25), 6506-6511.
This was first driven by hunting: a global population of less than 5 million early humans hunted more than 100 of the largest mammals to extinction. Since the agricultural revolution, the decline in wild mammals has been driven by a mix of hunting but also habitat loss from the expansion of agricultural land.
With the rise and spread of farming, humans started to change the balance of carbon across ecosystems. We cut down forests, releasing carbon, and replaced them with farmlands. We also became much more skilled at balancing other nutrients that are essential for agriculture: until the early 1900s, we slowly improved our ability to balance nitrogen within our soils. This reached a whole new level in the 1920s with the invention of synthetic fertilizers from the Haber-Bosch process.
Around half of the humans alive today owe their existence to synthetic fertilizers.
We were no longer trying to move nitrogen around the biosphere. We were taking nitrogen from the atmosphere and pulling it into the soils and crops where we could use it for food production, and the raising of livestock.
The Industrial Revolution lay at the heart of this change. To grow, we needed energy. Again, we were not just moving carbon around the biosphere. We were adding to it.
Erisman, J. W., Sutton, M. A., Galloway, J., Klimont, Z., & Winiwarter, W. (2008). How a century of ammonia synthesis changed the world. Nature Geoscience, 1(10), 636-639.
Smil, V. (2004). Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production. MIT Press. ISBN: 9780262194495.
Stewart, W. M., Dibb, D. W., Johnston, A. E., & Smyth, T. J. (2005). The contribution of commercial fertilizer nutrients to food production. Agronomy Journal, 97(1), 1-6.
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Hannah Ritchie (2022) - “Wild mammals make up only a few percent of the world’s mammals” Published online at OurWorldInData.org. Retrieved from: 'https://ourworldindata.org/wild-mammals-birds-biomass' [Online Resource]BibTeX citation
@article{owid-wild-mammals-birds-biomass,
author = {Hannah Ritchie},
title = {Wild mammals make up only a few percent of the world’s mammals},
journal = {Our World in Data},
year = {2022},
note = {https://ourworldindata.org/wild-mammals-birds-biomass}
}
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