Ecosystems and Extinctions

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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Ecosystems and Extinctions