Transcript Extinction and Conservation

Extinction and Conservation
Reading-Freeman, Chapter 55
• Humans have extensively modified
the biosphere
•
The human population passed 6
billion in the year 2000, and is growing
at a rate of almost 2% 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.
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.
Major sources of
anthropogenic extinction
• Habitat destruction and habitat
fragmentation
• Habitat Change and Disruption of
Ecosystem Processes
• Introduction of Exotics
• Overexploitation
Habitat destruction and
habitat fragmentation
• Most of the grasslands and forests of the Northern
Hemisphere were destroyed by the end of the
nineteenth century, the grasslands of the southern
hemisphere are now vanishing, and tropical forests
are disappearing at a rate of about 2% per year.
This type of destruction has become the norm for
most biological communities, as the human
population expands our economic needs require
resources from more and more land. The remaining
habitat is often broken into many small fragments,
which are separated by large areas of land under
cultivation or other human uses, effectively reducing
a single "continent" into many "islands".
Fragmented Habitats Support
Smaller Populations
• 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.
This part of Canada used to be a continuous swath of natural
communities.
Here is a fragment seen from the air
• 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
Fragmented Habitats Frequently
Lack Critical Ecosystem
Processes
• 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.
• The edge habitats have different effects on
different species.
– Some large mammals, such as coyotes and
raccoons, reach much higher densities in edge
habitats because they are able to take advantage of
human resources (garbage), and return to the
safety of the preserve.
• Taking this a step farther,raccoons in the US, and red
foxes in England, have even penetrated urban areas to
become part of the city, reaching high densities.
– Other mammal species cannot tolerate edge
environments, wolves and mountain lions do not
like humans and cannot live on the edge (in cases
where they try, very bad things might happen.
This is a natural area in Massachusetts.
• Example: The brown headed cowbird is
a native to the United States. It is a
brood parasite, evicting the eggs of
other species to replace them with its
own. Cowbirds prefer edge habitats.
Now that forests are fragmented, there
are few safe areas from cowbirds, and
forest interior species such as bluebirds
are suffering a major loss of fitness in
some areas.
Habitat Change and
Disruption of Ecosystem
Processes
–Surviving areas of natural habitat often
change because humans have
fundamentally altered natural ecosystem
processes.
Examples
– 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.
» Human activities have altered their
ecosystems. Ladys' slippers need a
mutualistic fungus to germinate and
grow for the first few years. Airborne
nitrogen compounds (mostly from
automobiles) effectively "fertilize" vast
areas of ground and may put the
mutualistic fungi at an ecological
disadvantage.
» Also, the widespread application of
pesticides, the human tendency to
groom and "clean up" areas of open
sand and fallen wood, and the
introduction of the honeybee to North
America have caused the Andreneaid
bees that would normally pollinate these
plants to disappear from many areas.
– 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.
Introduction of Exotics
• 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.
Zebra Mussels
• 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.
» They have since spread throughout the Great Lakes
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region and throughout the Mississippi and Ohio River valleys.
It forms dense clusters of individuals, and can clog the water
intakes of electrical power stations, water stations, and other
industrial facilities.
Zebra mussels are incredibly effective filter feeders. Zebra
mussels actually make the water much clearer, but alter
native communities of organisms in the process. In the
Hudson River, phytoplankton biomass decreased 85% after
zebra mussels invaded, zooplankton decreased 70% as a
result.
The zebra mussel is a very effective competitor. Extinction of
native bivalves will almost certainly result from this
introduction.
You may have noticed that Chicago water tastes weird during
the summer, that is because the water is now clean enough to
allow the growth of cyanobacteria deep enough in the lake to
be pulled into the water intakes. The residue of cyanobacteria
toxins has an off taste.
Honey Bees
• 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.
• 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.
– The Snake that Ate Guam.
Boiga irregularis, the brown tree
snake, is an arboreal snake native
to New Guinea, Australia, and the
Solomon Islands. It is a small,
nocturnal, rear-fanged snake.
– Boiga irregularis was introduced to
Guam in the late 1940s, probably
by hitching a ride in the wheel well
of a plane. Since that time, it has
literally eaten most of the endemic
birds of Guam to extinction. Since
there are no other native snakes
in Guam (other than a blind,
burrowing species), the bird fauna
there evolved no natural defenses.
• Thus, is an incredibly effective
predator of birds and their nests.
– In Australia, competition and predation
keep it in check, but the simpler ecosystem
of Guam has allowed it to increase in
numbers to up to 20 individuals per square
acre of jungle (among the highest ever
recorded for a snake).
– It also causes other problems in Guam,
including numerous power outages
resulting from large numbers of snakes
resting on power lines.
Garlic Mustard, Purple
Loostrife, Multiflora
Rose
– 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.
Overexpolitation
• 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
What Makes A Species
Vulnerable to extinction?
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Endemism
Rarity
Small Population Size
Ecological Specialization
Beauty/Usefulness to humans/Competitor
with Humans
• Endemism- Species that are restricted
to a particular, small area, are more
vulnerable to extinction
• 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.
• 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.
• 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.
• 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.
• Economic Considerations
•
Any conservation plan that does not take human
economics into account is prone to failure. It is very difficult
to set aside a habitat and protect it from all human activity.
The closest we have ever come are on military bases and
nuclear test sites (the conservation effect was unintentional
at first), and some private organizations (Nature
Conservancy) buy natural land and simply fence it off.
Even these exceptional preserves have neighbors, and are
occasionally eyed by developers and government
reclassification.
•
The vast majority of preserves must balance the needs
of human ecotourists, indigenous peoples, neighbors, and
government budget considerations against conservation
goals.
The Future of Our Own Species
– 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.