Researchers have reported a staggering decline in wildlife. Here’s how to understand it

It is clear that wildlife suffers greatly on our planet, but scientists do not know exactly how much. It is very difficult to determine a comprehensive number. Counting wild animals – on land and at sea, from mosquitoes to whales – is no small feat. Most countries lack national monitoring systems.

One of the most ambitious efforts to fill this void is published every two years. Known as the Living Planet Index, it is a collaboration between two major conservation organizations: the World Wide Fund for Nature and the Zoological Society of London. But the report has repeatedly led to inaccurate headlines when journalists have misinterpreted or overestimated its findings.

The latest assessment figure, released on Wednesday by 89 authors from around the world, is the most alarming yet: From 1970 to 2018, the number of vertebrates observed fell by an average of 69%. That’s more than two-thirds in just 48 years. It’s a staggering number with serious ramifications, especially as countries prepare to meet in Montreal in December to try to agree on a new global plan to protect biodiversity. But does that mean what you think?

What does the data mean and what it doesn’t?

Remember that this figure relates only to vertebrates: mammals, birds, reptiles, amphibians and fish. Absent are creatures without spines, although they make up the vast majority of animal species (scientists have less data about them).

So have land vertebrate populations fallen 69% since 1970?

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The study tracks selected groups of 5,320 species, and all existing relevant published research disappears, adding more each year when new data allows. They include, for example, a group of whale sharks in the Gulf of Mexico counted from small planes flying low over the water and birds counted by the number of nests on the cliffs. Depending on the species, tools such as camera traps and clues such as trail droppings help scientists estimate the population in a particular location.

This year’s update includes approximately 32,000 of this population.

There is a temptation to believe that an average decrease of 69% in these groups means that this is the share of monitored wildlife that has been eliminated. But this is not true. An addendum to the report provides an example of why.

Imagine, as the authors wrote, that we start with three groups: birds, bears, and sharks. The number of birds decreased to 5 from 25, a decrease of 80%. Bears drop to 45 animals from 50, or 10%. And sharks drop to 8 from 20 or 60%.

This gives us an average drop of 50%. But the total number of animals fell to 92 from 150, a drop of about 39%.

The indicator is designed in this way because it seeks to understand how the population has changed over time. It does not measure the number of individuals present.

“The Living Planet Index is truly a contemporary view on population health that underpins the work of nature across the planet,” said Rebecca Shaw, chief scientist at the WWF and author of the report.

Another important factor is the way the controlled population ends up in the index. They do not represent a large random sample. Instead, it reflects the available data. So there is a very potential bias in determining which species is being tracked.

One argument over whether a small number of the population is in a state of drastic decline has called into question the overall results. Two years ago, a study in Nature found that only 3% of the population were driving a sharp decline. When they were removed, the global trend turned to increase.

The paper sparked a flurry of responses in Nature as well as an additional explanation and stress test for this year’s update. On the bright side, the authors note that about half of the population in the Living Planet Index is stable or increasing. However, when they tried to exclude the population with the most drastic changes in both directions, down and up, the average proportions remained steep.

“Even after removing 10% of the full data set, we still saw a 65% decrease,” said Robin Freeman, head of the Indicators and Evaluations unit at the Zoological Society of London and author of the report.

Is it still bad?

yes. Some scientists believe the report actually underestimates the global biodiversity crisis, in part because devastating declines in amphibians may be underrepresented in the data.

Over time, the trend does not change.

“Year after year, we cannot begin to improve the situation, despite major policies,” said Henrique M. Pereira, professor of conservation biology at the German Center for Integrative Biodiversity Research who was not involved in this year’s report. “At most, we were able to slow the decline somewhat.”

Latin America and the Caribbean experienced the worst regional decline, down 94% from 1970. The pattern was most pronounced in freshwater fish, reptiles, and amphibians. Africa came in second with 66%. The Asia Pacific region saw 55%. The region defined as Europe and Central Asia experienced a lower decline of 18%, as did North America of 20%. Scientists have confirmed that the most severe biodiversity losses in these two regions likely occurred well before 1970 and are not reflected in these data.

Scientists know the cause of biodiversity loss. On land, the main driver is agriculture as people turn forests and other ecosystems into farmland for livestock or oil palm. At sea, it’s fishing. There are ways to do both more sustainably.

If climate change is not limited to 2 degrees Celsius, preferably 1.5 degrees, its consequences are expected to become the main cause of biodiversity loss in the coming decades, the report said.

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