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In
May, a United Nations report warned that 1 million species are threatened by
extinction. More recently, 571 plant species were declared extinct.
But
extinctions have occurred for as long as life has existed on Earth. The
important question is, has the rate of extinction increased?
Our
research, published today in Current Biology, found some plants have been going
extinct up to 350 times faster than the historical average—with devastating
consequences for unique species.
Madagascar is home to around 12,000 plant species, of which 80% are endemic
(found nowhere else). This includes the baobab
Measuring the rate of extinction
'How
many species are going extinct' is not an easy question to answer. To start,
accurate data on contemporary extinctions are lacking from most parts of the
world.
And
species are not evenly distributed—for example, Madagascar is home to around
12,000 plant species, of which 80% are endemic (found nowhere else). England,
meanwhile, is home to only 1,859 species, of which 75 (just 4%) are endemic.
Areas
like Madagascar, which have exceptional rates of biodiversity at severe risk
from human destruction, are called 'hotspots'.
Based
purely on numbers, biodiversity hotspots are expected to lose more species to
extinction than coldspots such as England.
But
that doesn't mean coldspots aren't worth conserving—they tend to contain
completely unique plants.
We
are part of an international team that recently examined 291 modern plant
extinctions between biodiversity hot- and coldspots.
We
looked at the underlying causes of extinction, when they happened, and how
unique the species were. Armed with this information, we asked how extinctions
differ between biodiversity hot- and coldspots.
Unsurprisingly, we found hotspots to lose more species, faster, than coldspots.
Agriculture and urbanisation were important drivers of plant extinctions in both
hot- and coldspots, confirming the general belief that habitat destruction is
the primary cause of most extinctions.
Overall, herbaceous perennials such as grasses are particularly vulnerable to
extinction.
However, coldspots stand to lose more uniqueness than hotspots. For example,
seven coldspot extinctions led to the disappearance of seven genera, and in one
instance, even a whole plant family.
So
clearly, coldspots also represent important reservoirs of unique biodiversity
that need conservation.
We
also show that recent extinction rates, at their peak, were 350 times higher
than historical background extinction rates.
Scientists have previously speculated that modern plant extinctions will surpass
background rates by several thousand times over the next 80 years.
So
why are our estimates of plant extinction so low?
First, a lack of comprehensive data restricts inferences that can be made about
modern extinctions.
Second, plants are unique in—some of them live for an extraordinarily long time,
and many can persist in low densities due to unique adaptations, such as being
able to reproduce in the absence of partners.
Let's
consider a hypothetical situation where we only have five living individuals of
Grandidier's baobab (Adansonia grandidieri) left in the wild. These iconic trees
of Madagascar are one of only nine living species of their genus and can live
for hundreds of years.
Therefore, a few individual trees may be able to 'hang in there' (a situation
commonly referred to as 'extinction debt') but will inevitably become extinct in
the future.
Finally, declaring a plant extinct is challenging, simply because they're often
very difficult to spot, and we can't be sure we've found the last living
individuals.
Indeed, a recent report found 431 plant species previously thought to be extinct
have been rediscovered.
So,
real plant extinction rates and future extinctions are likely to far exceed
current estimates.
There
is no doubt that biodiversity loss, together with climate change, are some of
the biggest challenges faced by humanity.
Along
with human-driven habitat destruction, the effects of climate change are
expected to be particularly severe on plant biodiversity.
Current estimates of plant extinctions are, without a doubt, gross
underestimates.
However, the signs are crystal clear. If we were to condense the Earth's
4.5-billion-year-old history into one calendar year, then life evolved somewhere
in June, dinosaurs appeared somewhere around Christmas, and the Anthropocene
starts within the last millisecond of New Year's Eve.
Modern plant extinction rates that exceed historical rates by hundreds of times
over such a brief period will spell disaster for our planet's future.
WHAT
DO EXPERTS PREDICT FOR THE FATE OF THE PLANET'S PLANTS AND ANIMALS?
Nature is in more trouble now than at any time in human history with extinction
looming over one million species of plants and animals, experts say.
That's the key finding of the United Nations' (UN) first comprehensive report on
biodiversity - the variety of plant and animal life in the world or in a
particular habitat.
The
report - published on May 6, 2019 - says species are being lost at a rate tens
or hundreds of times faster than in the past.
Many
of the worst effects can be prevented by changing the way we grow food, produce
energy, deal with climate change and dispose of waste, the report said.
The
report's 39-page summary highlighted five ways people are reducing biodiversity:
-
Turning forests, grasslands and other areas into farms, cities and other
developments. The habitat loss leaves plants and animals homeless. About
three-quarters of Earth's land, two-thirds of its oceans and 85% of crucial
wetlands have been severely altered or lost, making it harder for species to
survive, the report said.
-
Overfishing the world's oceans. A third of the world's fish stocks are
overfished.
-
Permitting climate change from the burning of fossil fuels to make it too hot,
wet or dry for some species to survive. Almost half of the world's land mammals
- not including bats - and nearly a quarter of the birds have already had their
habitats hit hard by global warming.
-
Polluting land and water. Every year, 300 to 400 million tons of heavy metals,
solvents and toxic sludge are dumped into the world's waters.
-
Allowing invasive species to crowd out native plants and animals. The number of
invasive alien species per country has risen 70 per cent since 1970, with one
species of bacteria threatening nearly 400 amphibian species.
Via Daily Mail