_extinction.ppt tutorials for students learning

Extinction

2. 99.9999% of all species that have ever lived are extinct
Extinction has always been a major force in
macroevolution.
Species do not last forever…the mean expected lifespan of
a marine bivalve is about 14 million years, and the mean
expected lifespan of a terrestrial mammal might is about a
tenth that.
Climate change, natural disasters, and other phenomena
have always caused extinction.
As some species originate, they inevitably drive other
species extinct.
Extinctions, in turn, pave the way for speciation.
An adaptive radiation is a wave of speciation that occurs as
a new habitat is colonized by a lineage, or in the wake of
the extinciton of another lineage.
An adaptive radiation of mammals followed the extinction
of the dinosaurs.

3. At all times in history, groups of organisms
have a “background extinction rate”…species
go extinct because of normal ecological or
evolutionary processes, and as they
disappear, other species take their places.
◦For instance, on oceanic islands, the arrival of a
predator, such as a monitor lizard or a snake, might
precipitate the extinction of ground-nesting birds.
Any such birds that are endemic to the island (that
is, they live nowhere else) are gone for good.
◦But oceanic islands come and go, as geological
forces shape the Earth’s crust, and such extinctions
are considered to be “normal”.

4. The history of life on Earth has been punctuated by
a series of mass-extinctions.
Extinction rates are much higher than background rates
for a short period of time.
Some are better understood than others, but they have
profoundly influenced the evolution of life on Earth.
Over the last 500 million years, there have been several
major mass extinctions (not counting the current one):
here are some big ones
○1) The Late Devonian
○2) Mid-Ordovician
○3) Permian-Triassic
○4) Late Triassic
○5) Cretaceous-Tertiary.

6. Since the development of agriculture, 10,000
years ago, humans have modified an increasing
proportion of the Earth’s resources for our own
purposes.
Humans impact has caused extinction rates to be
10 to 1000 times greater than any time in the last
100,000 years.
For example-one estimate for the recent
background extinction rate for birds is one
species extinction per 400 years.
◦If only this natural rate of loss affected the number of bird
species, no more than a couple of extinctions should have
occurred in the past 800 years.
We have set in motion a mass extinction, one of
the largest, that will not culminate until thousands
of years from now.

7. Humans have extensively modified the
biosphere
 The human population passed 7 billion in
the year 2011, and is growing at a rate of
almost 3% per year.
○ Each human uses so much energy and so
many resources that our activities influence virtually every
aspect of the biosphere.
In temperate areas, nearly all the land area that is
suitable for agriculture is plowed or fenced.
 Worldwide, more than 35% of all land area is
used for farms or permanent pastures. Much of the
rest is grazed or logged on a regular basis.

8. From 35-45% of Global Net Primary
Productivity now goes to serve human
needs.
In aquatic ecosystems as well, an
increasing amount of productivity is
harvested by humans. Nearly every major
fishery in the Northern Hemisphere has
showed strain from overharvesting, and
many have collapsed.
The Human Mass-
Extinction

9. Habitat destruction and habitat
fragmentation
Habitat Change and Disruption of Ecosystem
Processes
Introduction of Exotics
Overexploitation

10. Essentially, every habitat fragment becomes a
biological "island" (analogous to continental shelf
islands, rather than the oceanic kind).
As in the Mac Arthur Wilson model, the smaller the
island, the smaller the population of any given species it
can support.
Small populations are at much greater risk of extinction
due to random events, such as weather, disasters, and
natural fluctuations in their population and sex ratio.

11. Here is a fragment seen from the air

12. Additionally, smaller populations support less
genetic variation, which could lead to the
fixation of harmful alleles and the ultimate
extinction of the population (for very small
fragments), or simply inhibit their ability to
evolve in response to changing conditions

13. Edge effects fundamentally alter habitat. For certain
species, this can be critical to their ability to survive.
For instance, places where human habitation
borders nature preserves frequently have weedy
plants, fire is controlled, domestic cats and dogs
escape and prey on native wildlife, and human noise
and activity disturb the behavior of certain animals.

14. Surviving areas of natural habitat often
change because humans have
fundamentally altered natural ecosystem
processes.

15. Ladys' Slipper Orchids. There are probably about
25, 000 species of orchids worldwide, and they are
being lost faster than they can be classified.
Orchids are typically tightly coevolved in
mutualistic relationships with other species, and
the loss of any of these relationships can lead to
extinction.
Ladys' slippers are a very diverse group that
occupy a wide variety of habitats in the Northern
Hemisphere. They are in decline even in
protected areas, such as Indiana Dunes.

16. Pacific Salmon are very important
ecologically and economically off the West
Coast of North America.
Salmon species have experienced dramatic
declines over the past few decades due to a
variety of factors, many of which result from
human habitat modification.
Hydroelectric dams have resulted in
increased juvenile mortality and made
many habitats inaccessible to migrating
salmon.
Additionally, human logging and agriculture
has silted and modified many of their
upstream habitats, causing a drop in
recruitment.

17. Human activities are creating the worldwide
equivalent of the "Great American Faunal
Interchange". This is an uncontrolled
experiment in community ecology, with the
potential result of a massive loss of gamma
diversity worldwide caused by the loss of
endemic species.

18. In 1998, the zebra mussel was
discovered in Lake St. Claire near
Detroit. It was introduced to the
Great Lakes from the Caspian Sea,
probably in the ballast water from
a cargo ship, sometime around
1985. This mode of dispersal is
very common, in 1982 the comb
jelly (a ctenophore) was
introduced to the Black Sea in a
similar manner. Comb jellies
increased in number until they
amounted to an estimated 90% of
animal biomass in the Caspian.

19. Honey bees are native to Europe and Asia.
Apis mellifera, is a European species that is
widely cultivated for honey, beeswax, and as
a pollinator. European immigrants probably
introduced the honeybee to North America in
the nineteenth century (Native Americans
called it "white man's fly".) It is a very
effective competitor, and displaces native bee
species.

20. Recently, honeybees themselves have taken a
hit, when the varolla mite was introduced in the
1980's. The overuse of insecticides, and
widespread destruction of habitat, have
decimated North American bee populations,
both native and non-native.

21. These are three more cases of an
introduced species being too good at
what they do. All three plants were
introduced intentionally in the
nineteenth century. Each of the three
has become so common that it is likely
to displace other species. For example,
in some East Coast marshes, purple
loosestrife amounts to 90% of the
vegetation, displacing native sedges
and other plants.

22. Stellar's Sea Cow-this huge
sirenian mammal lived in the
reached a length of 26 feet
and could way seven
thousand pounds or more. It
existed on a diet of kelp, and
could not dive or swim
quickly.
It was delicious, and was
hunted to extinction by sailors
within 30 years of its
discovery

23. Endemism
Rarity
Small Population Size
Ecological Specialization
Beauty/Usefulness to humans/Competitor
with Humans

24. Endemism- Species that are restricted to a
particular, small area, are more vulnerable to
extinction

25. Rarity-Rarity is not the same thing as endeminsm,
endemics can be very common in the restricted area
where they do occur. "Naturally rare" species have
low population densities, but may be widely
distributed and have respectable population sizes.
We do not completely understand the ecological
factors that make some species "naturally rare", but
when a common species gradually becomes rare, it is
often a prelude to extinction. "Naturally rare" species
can be a challenge to conservation, because they are
difficult to monitor and it is very difficult to ensure
that sufficient habitat is set aside for them.

26. Small Population Size-Small population
sizes render a species very vulnerable to
extinction, through reduced genetic
variation via genetic drift, the potential for
inbreeding depression, demographic
stochasticity caused by random ecological
disasters and, for sexual species, the small
chance that every individual in the
population might be born the same sex.

27. Ecological Specialization-Ecological specialists are
more prone to extinction because there are only a
few ways they can 'fit themselves into" an ecosystem.
They must have certain interspecific relationships in
order to feed, obtain mates, have places to live, or
maintain competitive superiority. The loss of other
species in the community, or habitat change due to
human activity, can change these factors, and render
a formerly successful species vulnerable to
extinction.

28. Useful to Humans or A Competitor of Humans-
Humans have a way of killing all the pretty things,
harvesting all the useful things, and hunting to
extinction everything that could be perceived as a
competitor. For instance, fishermen in San
Francisco are prone to despising the California Sea
Otter, despite its important place in the ecosystem
of the California Coast, because of its status as a
competitor. They are protected now, however, they
were nearly hunted to extinction for their pelts.
Species that cross the paths of humans sometimes
suffer for it.

29. ◦It is one of the strange ironies of our existence that,
though the actions of our species modify the biosphere
to an extent unprecedented in the history of the earth, as
individuals, we do not necessarily feel any collective
responsibility for our actions.
◦The future of our own species will depend, to a very large
extent, upon decisions we make as individuals, regarding
our priorities. It is quite possible for our species to
survive for many thousands of years more, but this is
likely only if this generation takes additional steps to
ensure that the planet will remain habitable to our own
species.