By Hannah Ritchie, Fiona Spooner and Max Roser
There has been a large decline across tens of thousands of wildlife populations since 1970.
Let’s look at that in more detail. One of the most widely-quoted, but misunderstood, metrics on biodiversity is the Living Planet Index.
The Living Planet Index tries to summarize the average change in population size of tens of thousands of studied animal populations. It distills this change into a single number.
It’s important to note that this data is not globally representative: some regions have much more data available than others. Biodiversity data is much more limited in the tropics, for example.
What it reports is the average decline in animal population sizes since 1970. This does not tell us the:
- Number of species lost;
- Number of populations or individuals that have been lost;
- Number or percentage of species or populations that are declining;
- Number of extinctions.
Since 1970, then, the size of animal populations for which data is available have declined by 69%, on average. The decline for some populations is much larger; for some, it’s much smaller. And, in fact, many populations have been increasing in size.
Not all animal populations are in decline; around half have increasing numbers
The Living Planet Index reports that there has been a large average decline across more than 30,000 animal populations.
But, reducing the state of global biodiversity into a single figure is a problem. It hides a huge diversity of changes in animal populations within the dataset.
The Living Planet Project also shows us what percentage of studied populations have increased, decreased, and remained stable since 1970.
Almost half of these animal populations have increased.
Understanding the broad range of changes in populations is crucial if we’re to stop biodiversity loss – we need to know that not all animal populations are declining. We need to also know which populations are doing well and why they’re doing well.
Wild mammals have declined by 85% since the rise of humans
A diverse range of mammals once roamed the planet. This changed quickly and dramatically with the rising number of humans over the course of the last 100,000 years.
Over this period, wild terrestrial mammal biomass has declined by an estimated 85%.
This looks at the change in wild mammals on the basis of biomass. This means that each animal is measured in tonnes of carbon that it holds. This is a function of its body mass.
In an extended period between 50,000 to 10,000 years ago, hundreds of the world’s largest mammals were wiped out. This is called the Quaternary Megafauna Extinction event.
Humans were the main driver of this, killing off species through overhunting and changes to their habitats. What’s staggering is how few humans were alive at this time: fewer than 5 million people across the world.
Since then, wild mammals have continued to decline. A lot of this has been driven by the expansion of human agriculture into wild habitats.
But, the future can be very different. We have the opportunity to restore wild mammals by reducing hunting and poaching, and cutting the amount of land that we use for farming.
Wild mammals make up only a few percent of the world’s mammals
Wild mammals make up just 4% of global mammal biomass. This includes marine and land-based mammals.
The other 96% is humans and our livestock.
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 the same as our sheep.
Poultry is not included here. But for birds, the distribution is similar: poultry biomass is more than twice that of wild birds.
Article written by Hannah Ritchie, Fiona Spooner and Max Roser for Our World in Data and shared under the Creative Commons Licence.