The abundance of wild animals is regressing speedily as the number of domesticated animals and persons keeps escalating. Such demographic contrast signals that we urgently need to modify our model of subsistence and our interaction with Mother Nature.
If we had to choose between a biodiverse landscape and one hosting a monoculture of pine trees with ruminating cattle, many would take the first option. Biodiversity has an aesthetic value to humans, and also gives us free services like pollination, climate regulation, freshwater depuration or soil formation (1, 2). That is why the mounting rates of biodiversity loss have propelled a multi-angled debate about whether the Earth is experiencing the sixth mass extinction (3, 4) and how biodiversity should be managed to secure our access to ecosystem services (5, 6).
Think individuals, not species
A different way of approaching the biodiversity crisis consists of examining trends in the number of wild animals, with not so much emphasis on the variety of species. Thus, the Living Planet Report 2020, published by the World Wildlife Fund, has compiled thousands of scientific studies about > 21,000 populations of wild vertebrates studied over time (> 4,000 species represented) and concluded that, on average, the number of individuals per population has diminished by 70% since the 1970s (7).
On the other hand, Yinon Bar-On et al. (8) quantified that the biomass of humans and our domesticated mammals currently multiplies the biomass of wild mammals by a factor of 10, and there are 3 kg of humans and poultry for every kg of wild birds (see video featuring this study).
Not only that, during the last 100,000 years through which anatomically modern humans have thrived from a handful of bands of African hunter-gatherers to complex societies living in metropolis, the cattle industry has ended up quadrupling the global biomass of mammals (8).
The mechanism is straightforward. The human population is growing exponentially and we have been generating meat (and vegetables) to feed ourselves at the same pace. And the most profitable strategy to do so has been to globalise large-scale farming technology and the consumption of a few types of meat.
Almost everyone is familiar with the shelves of his/her favorite supermarket layered with beef steaks, pig sausages and chicken tenderloins. In many places, the homogenisation of the cattle industry is occurring at the expense of alternative practices. Thus, the FAO Second Global Assessment of Animal Genetic Resources chronicled that > 500 local varieties of domesticated mammals are no longer exploited and many more are at risk of extinction (9). And the same pattern of homogeneisation is governing agriculture worldwide (10).
Focus on the obvious
In only half a century, our generation has witnessed the fastest period of wildlife defaunation since we became Homo sapiens (11). The main cause of this process has been habitat destruction and degradation in combination with anthropogenic climate change (12, 13). We need no more science to corroborate such a cause-effect link.
We have also worked out the numbers that the area of forests that we have already cut down for farming is already enough to feed all the people in the world (14). Therefore, from a subsistence viewpoint, we can dispense with further destruction of natural habitats.
Of course, science must continue refining the methods to estimate how many species there are on Earth (15) and how many of those are becoming, or likely to go, extinct (16). However, if we found out that we are are not experiencing a mass extinction (3 of every 4 species disappearing in < 2 million years) like any of the previous five mass-extinction events (17), we might fall in an intellectual trap, let our guard down and believe that nothing must be urgently changed. Far from reality.
The practical question we must ask ourselves is whether the extinction of only tens to hundreds (not millions) of species jeopardises our survival. And the answer is definitely YES. The obvious examples are insect pollinators and plankton. A few species of those little critters (relative to their huge species richness) fertilise our forests, fields and orchards (18), and sustain our fisheries (19).
We can keep playing the role of notaries of further biodiversity losses, but the solution is acting now: reduce green-house emissions, change our model of consumption of natural resources and make agriculture, farming and fisheries sustainable.
Salvador Herrando-Pérez and David R. Vieites
NOTE: a Spanish version of this aritcle has been published in journal Quercus June 2021 issue.
References
- Díaz S et al. (2019) Pervasive human-driven decline of life on Earth points to the need for transformative change. Science 366: eaax3100
- Sandifer PA, Sutton-Grier, AE & Ward, BP (2015) Exploring connections among nature, biodiversity, ecosystem services, and human health and well-being: opportunities to enhance health and biodiversity conservation. Ecosystem Services 12: 1-15
- Briggs JC (2017) Emergence of a sixth mass extinction? Biological Journal of the Linnean Society 122: 243-248
- Ceballos G & Ehrlich, PR (2018) The misunderstood sixth mass extinction. Science 360: 1080-1081
- Ricketts TH et al (2016) Disaggregating the evidence linking biodiversity and ecosystem services. Nature Communications 7: 13106
- Souza BA et al. (2021) Mitigating impacts on ecosystem services requires more than biodiversity offsets. Land Use Policy 105: 105393
- World Wildlife Fund (2020) Living Planet Report 2020 – Bending the curve of biodiversity loss. (Gland, Switzerland).
- Bar-On YM, Phillips, R & Milo, R (2018) The biomass distribution on Earth. Proceedings of the National Academy of Sciences of the USA 115: 6506-6511
- Rischkowsky B & Pilling, D (2016) The state of the world’s animal genetic resources for food and agriculture. Food and Agriculture Organization of the United Nations (FAO)
- Castañeda-Álvarez NP et al. (2016) Global conservation priorities for crop wild relatives. Nature Plants 2: 16022
- Dirzo R et al. (2014) Defaunation in the Anthropocene. Science 345: 401-406
- Stork NE (2010) Re-assessing current extinction rates. Biodiversity and Conservation 19: 357-371
- Travis JMJ (2003) Climate change and habitat destruction: a deadly anthropogenic cocktail. Proceedings of the Royal Society of London B 270: 467-473
- Erb K-H et al. (2016) Exploring the biophysical option space for feeding the world without deforestation. Nature Communications 7: 11382
- Larsen BB et al. (2017) Inordinate fondness multiplied and redistributed: the number of species on Earth and the new pie of life. Quarterly Review of Biology 92: 229-265. https://doi.org/10.1086/693564
- Padian K (2018) Measuring and comparing extinction events: reconsidering diversity crises and concepts. Integrative and Comparative Biology 58: 1191-1203
- Barnosky AD et al. (2011) Has the Earth’s sixth mass extinction already arrived? Nature 471: 51-57
- Rader R et al. (2016) Non-bee insects are important contributors to global crop pollination. Proceedings of the National Academy of Sciences 113: 146-151
- Benoiston A-S et al. (2017) The evolution of diatoms and their biogeochemical functions. Philosophical Transactions of the Royal Society B 372: 20160397
