Extinction

1
Extinction
2
Extinction is a normal process. Can result from
demographic failure or genetic swamping.
Speciation is another. Anagenesis is another.
3
Goal of conservation biology is NOT to abolish
extinction, but to keep it from overpowering the
rate of speciation.
4
Normal extinction and speciation rates have
probably balanced each other over much of
geologic time. Rates differ for different
groups. Marine inverts new species every 2-20
years Birds estimate of extinction rate of one
species every 83.3 years.
5
Extinction rates have not remained constant over
time. Some controversy about the relative
magnitude of these mass extinctions.
Mass Extinctions of the Phanerozoic
6
North America supported a rich megafauna until
about 11,000 years ago. Rivaled modern-day Africa
7
Fauna included 31 general of large mammals. Only
14 genera remain. Some 22 genera of birds also
disappeared.
Bonus Can you name the 14 remaining genera of
large, North American mammals?
8
What the heck happened?
9
Could it have been early humans?
10
Man colonized the Americas from north to south,
and the movement seems to have been coupled with
local extinctions.
11
Martin has hypothesized that, in all areas except
Africa and Asia, man arrived on the scene as a
skilled hunter and encountered a naïve local
fauna, with overkill resulting.
12
Whatever happened, the extinction of many large
mammals had a influence on the local vegetation,
and probably led to the extinction of many plant
species.
13
In the Pacific, the arrival of humans may have
led to rapid extinction of many animals,
particularly birds. Polynesia and Micronesia
were populated by humans between 1500 BC and 400
AD. Reached New Zealand about 800 AD. It looks
like they wiped out many bird species as they
went.
14
Rate has gone up even more recently. Why? Early
on, it was primarily because of hunting and other
exploitation. Now, it has more to do with exotic
species and habitat destruction.
15
Stresses that increase mortality and decrease
fecundity push the population toward extinction.
Killing, habitat destruction, disease, etc. are
such processes. A more detailed study in birds
showed that killing by humans and the effects of
introduced predators have been the major causes
of extinctions since 1650.
16
Man has been responsible for a number of
extinctions through simply killing the species
off.
17
Black rhino
18
Another major cause of extinctions has been
introduced species, whether predators (often rats
or cats) or competitors. The brown tree snake
reached Guam in late 40s or early 50s.
Probably in fruit shipments. It has eliminated
most of the native bird species. Other harmful
introductions kudzu zebra mussels carp
19
Another threat - genetic swamping Has led to the
extinction of 15 or more fish species in North
America. In New Zealand, the native gray duck
has been driven nearly to extinction by
hybridization with mallards.
20
Red wolf
21
Perhaps the biggest threat now is habitat
destruction.
22
ALMOST ALL RECENT EXTINCTIONS ARE ATTRIBUTABLE TO
HUMAN ACTIVITES.
23
Stochastic processes may play a big role in
extinction in small populations.   Demographic
stochasticity chance variation in mortality and
reproduction. Small populations are also subject
to genetic stochasticity. Genetic diversity may
be lost by purely random processes.
Environmental stochasticity may affect small
populations more heavily than large populations.
24
What makes a species vulnerable?   Biggest thing
small population size. Because of this large
species. Migratory species.
25
Especially vulnerable Large species with low
reproductive potential whales, rhinos, great
apes, condors, whooping cranes. Species with high
economic value whales, sea turtles, elephants,
spotted cats, rhinos. Species at the end of long
food chains birds of prey, cats,
reptiles. Species restricted to local, insular
habitas snail darter, Key deer. Highly
specialized species, as for feeding giant
panda, black-footed ferret. Migratory species
monarch butterflies, marine mammals, many birds.
26
GLOBAL EXTINCTION RATES   How do we estimate?
Tough. Usually use species-area curves. Curve
usually steeper for islands than for continental
areas. If we get the equation for a curve, we
can estimate the loss of species if we lose a
certain amount of area. Discuss.
27
Has been used to estimate that a 90 loss of
habitat would lead to a 50 loss of species.