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8/13/2019 Ecosystems and Extinctions
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Ecosystems and Extinc-
tions
jonathan tomkin, ph.D.
University of Illinois.
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Dodo
Now that weve looked at
fisheries, lets take a general
example of a more general ToC
threat: ecosystems and extinctions.Well discuss why humanity derives
advantages from intact ecosystems
later. ToC mechanisms explain manyof the pressures the natural world
faces...
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Land-use change
Introduced speciesDeforestation
Climate change
Frank Vassen
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Pre-Hum
Before we look at hum
we should put things in
has never been a safe p
ity of species have alrea
natural causes. There ar
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Extinction Events
Episodes in Earths
extinctions than w
aged such as: astero
volcanoes.
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Five Mass Extinctions 1/2
T
here were five previous mass extinc-
tions. In this example, the vertical axis
shows the percentage extinction ofgenera, while the horizontal axis shows time in
millions of years.
Genus is broader than species. So, for example,
the canisgenus includes domestic dogs, wolves,
dingos, jackals and coyotes.
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Five Mass Extinctions 2/2
Paleontologists characterizemass extinc-
tions as times when the Earth loses more than
three-quarters of its species in a geologicallyshort interval. This has happened only five
times in the past 540 million years or so.
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Prehistory Extinctions
E
xtinct
moder
have b
came into exi
Every time a m
colonized by h
tem was altere
extinct. Our te
Not just mode
nology such as
fire, agricultur
On the left, is
animals from giant birds, w
a marsupial li
However, som
change that w
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Arrival of Homo Sapiens is bad for the locals
As people migrated out of Africa, the
fossil record suggests that native animals
suffered especially large mammals. Look
at Australia for example. Shortly after
humankind arrived on the continent, most of
the large mammals became extinct around
90% were wiped out.
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The Thylacine or
extinct in 1936.
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Hunters
What about people? This was all caused far
before humans evolved. Of course, modern
humans have caused extinctions too. So where
are we now? Are we in a 6th extinction?
Its very difficult to tell. Creatures natu-
rally go extinct, and we dont know exactly
how many different species there are on
the planet. Nonetheless, we have a pretty
good handle on mammals though, so can
use that as an example. Mammals, have an
average species lifespan from origination
to extinction of about 1 million years. .
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Deforestation 1/2
When an individual clears forest
or other habitat for agriculture or
human needs, there is a private ben-
efit. But the loss of collective ecosystems effects
everyone. So development can lead to extinction
it is too much for any individual to stop.
Its been happening for a long time...
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Deforestation 2/2
Brazil, 2011
...and we havent made as much
progress as you might hope.
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Current world fo
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Forest Trends
Forests are growing back,but as
this graph shows, not in the tropics.
Between 1990 and 2005 the loss of
forests was highest in the tropics, where
just under half of the worlds forests are
located. Net losses in this region averaged
6.9 million hectares per year between 1990
and 2005.
Net loss, in which losses of forest cover arepartially offset by afforestation or natural
expansion, totaled 72.9 million hectares.
Well look at why functioning natural eco-
systems are good for humans in a later
week.
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Back
This brings us back to the dodo. It
was a good bird to eat, so sailors had
an incentive not to destroy the species.
But for individual ships, the personal
gain of taking as much meat as possible
outweighed the help for other, future
sailors let alone the dodo itself.
So what about cl
herald the 6th e
see habitat chan
world look like i
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