New Scientist - USA (2021-02-20)

Biodiversity: A status report

EXTINCTIONS

If we are to begin to rebalance our relationship with nature, we must first establish

how out of kilter things are. But ecosystems are complex and no single measure

can capture all the changes human activities have caused.

Nevertheless, there are various ways of auditing biodiversity and humanity’s impact

on it, from extinctions and species richness to land use and how much of the planet

is set aside for nature. Almost all of them paint a worrying picture

Perhaps the most eye-catching

metric of humanity’s impact is in our

acceleration of the rate of extinctions.

The background or natural rate is

0.1 to 2 extinctions per million species

per year. Data from the International

Union for Conservation of Nature’s Red

List of Threatened Species suggests

a rate of 34 extinctions per million

species per year now. It documents

at least 680 extinctions and a further

750 possible extinctions among

112,400 species in the past 500

years, with mammals and amphibians

hardest hit among vertebrates.

In recent years, warming, acidifying

oceans have caused a drop in coral

species. Looking at how many

species are considered vulnerable

or endangered, the group under

the most pressure is the cycads,

a group of tropical palm-like plants.

Two other plant groups, dicots and

conifers, are also up there.

The Red List covers fewer than

5 per cent of the world’s known

species. The Intergovernmental

Science-Policy Platform on Biodiversity

and Ecosystem Services (IPBES) says

that a further half a million terrestrial

species of animals and plants may

already be doomed to extinction.

There are many taxonomic groups

for which no firm conclusions can be

drawn due to insufficient data. One

is insects. A recent review concluded

that, “Although a flurry of reports

has drawn attention to declines in

insect abundance, biomass, species

richness, and range sizes, whether

the rates of declines for insects are

on par with or exceed those for other

groups remains unknown.”

Total number of

assessed species

Percentage of species in each category

Current global extinction risk in different species groups

2300

633

10,966

1520

972

1026

1500

5593

2872

1091

845

607

1781

6576

307

Dragonflies

Ferns

Monocots

Reptiles

Birds

Sharks and rays

Amphibians

Corals

Cycads

Conifers

Mammals

Bony fishes

Gastropods

Crustaceans

Dicots

Estimate of percentage threatened

0 20 40 60 80 100

Deficient data

Least concern

Key

Near threatened

Vulnerable

Endangered

Critically

endangered

Extinct in

the wild

SOURCE: IPBES GLOBAL ASSESSMENT REPORT

ON BIODIVERSITY AND ECOSYSTEM SERVICES SOURCE: IUCN AND BIRDLIFE INTERNATIONAL

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Amphibians

Birds

Reptiles

Fishes

Mammals

Extinctions since 1500

15001600 1700 18001900 2018

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0.5

1.0

1.5

2.0

2.5

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Amphibians

Cycads

Corals

Mammals

Sharks and rays

Conifers

Crustaceans

Monocots

Dragonflies

Bony fishesCone snails

Legumes

Reptiles

Declines in species survival

since 1970

1970 1980 1990 2000 2010 2020

0.5

0.6

0.7

0.8

0.9

1.0

Birds

* An index of 1 indicates all species in the group are classified as ”least concern“; an index of 0 indicates all species are extinct

SOURCE: IPBES GLOBAL ASSESSMENT REPORT ON BIODIVERSITY AND ECOSYSTEM SERVICES