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Biodiversity
Biodiversity,
or biological diversity, is generally defined as "the variety of
life and its processes," and can be thought of as the full richness
of life that exists on Earth. The term "biodiversity" can be
applied on several scales. We often talk of the biodiversity of an ecological
or climatic region, such as the biodiversity of the Arctic region, of
tropical rainforests, of coastal regions, or of plains and prairies.
At a smaller
scale, we sometimes talk of genetic biodiversity within a given species,
or even a local population of a species. For example, even before the
current biotechnology upsurge, genetic manipulation of plants by horticulture
significantly decreased biodiversity in the world's corn crops. Species
of corn were selected to be propagated specially for their desirable characteristics,
such as amount of crop yield or low susceptibility to certain pests. Such
"monocultures," however, are then all susceptible to the same
diseases or pests. Monocultures have very little genetic diversity to
ensure resilience of at least some of the species to certain stresses.
This can lead to destruction of large corn crops all at once. Continued
genetic engineering by large agricultural corporations will only exacerbate
the problem.
The
corn example is a good illustration of the fact that a species or ecosystem
can exist on a very large scale but not exhibit biodiversity. Another
similar example is the cultivation of plantations of genetically identical
pine trees that are replacing the forests of the south. E.O. Wilson, a
Pulitzer Prize-winning biologist at Harvard, estimates that a pine plantation
has 90 to 95% fewer species than the natural forest it replaces.1
Species
richness also varies from place to place depending on the energy available
for different species to share and the stability of climate. Solar energy
and water availability are of course the most important factors for biodiversity.
This is why tropical forest have the most species diversity.
A viable
ecosystem therefore must have:
- A source
of energy
- A supply
of raw materials
- Mechanisms
for storing and recycling the necessary materials
- Mechanisms
that allow it to evolve at suitable rates
In general,
biodiversity of a given ecosystem consists of three components: composition,
structure, and function. The composition of an ecosystem includes
the groups of organisms, species and the various organic and inorganic
substances that are inputs and residues of the organisms. An ecosystem
has two primary types of structures: architectural structure, consisting
of spatial organization and patterns; and social structure, which includes
the interdependence and relationships among the parts. Organisms, materials,
and energy of the ecosystem function in relation to one another.
They might interact to influence processes in the ecosystem or the structure
of the ecosystem.
IMPORTANCE
OF BIODIVERSITY
The importance
of biodiversity stems from the fact that ecosystems evolved over thousands,
hundreds of thousands, or even millions of years, and are therefore in
delicate balance, with each species playing a vital role. Appreciation
of biodiversity has come about as a result of an increased understanding
of the interrelatedness of species in a given habitat.
Recognition
of the importance of biodiversity represents a paradigm shift for conservationists.
Within a biologically diverse community, each species -- no matter how
small -- plays an important role in the ecosystem. Historically, humans
have been moved to conserve and protect that which is beautiful and inspiring,
and meets our narrow definition of "importance." To maintain
biodiversity, it is necessary to protect species that we may not find
beautiful, and some that may be barely visible.
There are
varying ideas about how and what biodiversity must be protected or conserved
in nature. As seen above, biodiversity as a whole includes soil fertility,
water quality, and air pollution levels in addition to species diversity.
So these qualities are as important as endangered species in understanding
and maintaining biodiversity. Preserving these is central to the stability
of an ecosystem. The three different types of stability that need to be
preserved are: species stability, structural stability, and process stability.
These three very general factors are in somewhat of a hierarchical relationship.
Process (including inputs and ways to overcome shocks) interacts with
structures to preserve species. But disturbing the species balance will
affect the other two, so that this once again demonstrates the close interdependence
of the components of this system - the ecosystem.
| Exercise: |
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Name any animal populations that have become extinct in your
lifetime. |
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ECOSYSTEM
STABILITY
Ecosystem
stability is not a static property, but a dynamic balance. The two qualities
(or properties) which characterize ecosystem stability are resistance
and resilience. Resistance represents the potential that prevents tree
and animal populations from succumbing to stresses such as drought or
high pollution. Resilience is the capability that comes into play when
organisms are weakened or killed. It is defined as the rate at which population
density in an ecosystem returns to equilibrium after it has been disturbed
away from equilibrium. Alternatively, it could be defined as how large
a range of conditions a system can tolerate and still remain in equilibrium.
Resistance and resilience depend on a variety of factors, each important
on different temporal and spatial scales.
Biodiversity,
the fact that typically there are a variety of species in an ecosystem,
shows that natural evolution results in subtly complex systems that best
preserve local habitats -- systems that can hardly be designed and engineered
by human technologies. Local ecosystem change and undergo modifications
through time. Certain niches became modified in time and space through
small and large disturbances. Some species extinction may even be "natural."
It is the rate at which technology induced change, or anthropogenic change
in general, happens that might disturb an ecosystem beyond its own capacity
to repair.
Interactions
among organisms maintain diversity and in destroying or enhancing one
species in a local ecosystem may destroy the whole system in time. While
grazing elk normally reduce shrub dominance and promote diversity in early
successional forest of the western United States, some of this same region
now has had its biodiversity significantly reduced by overgrazing cattle.
This type of phenomenon, "overgrazing" for example, occurs when
humans intervene to pus the system out of equilibrium.
Keystone
and Indicator Species
There are certain species whose role in maintaining the balance of an
ecosystem is so significant that they are known as the "keystone
species." A keystone is the stone at the summit of an arch that supports
all the other stones and keeps the entire arch from collapsing. Therefore,
the keystone species in an ecosystem is a species that supports many other
species in that ecosystem. The removal of the keystone species would result
in quick and noticeable change or degradation of an ecosystem.
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The sea
otter has been referred to as a keystone species in western Alaskan coastal
ecosystems by the US
Department of the Interior and the US Geological Survey .
Because of a decline in the population of Steller sea lions and harbor
seals in Alaskan waters, killer whales have been feeding on sea otters.
The sea otter is considered keystone because it feeds on sea urchins,
who in turn feed on kelp. Without the sea otter, sea urchin populations
would rise, leading to probable destruction of the kelp forests, disrupting
large portions of that coastal community. Without the otters to keep the
sea urchin population in check, the habitat of the entire community would
be altered significantly.
However,
the designation of keystone species is sometimes controversial. For example,
it could be argued in this case that since it was actually the decline
in population of Steller sea lions and harbor seals that caused killer
whales to feed on sea otters, the sea lions or seals are also a sort of
keystone species. This case demonstrates that large disruptions in ecosystems
can often be traced back even farther than disruptions in populations
of the so-called keystone species, again underscoring the strongly interrelated
nature of ecosystems.
But keystone
species are those that play a role in the ecosystem that is much larger
than their total number or biomass suggests. Their interaction and rate
of consumption determines the tolerance of the system in an important
way. Thus the sea otter is considered the keystone species in this chain
because they consume sea urchins in large enough quantities and at a fast
enough rate so that the relatively slow-growing kelp can keep up with
its consumption by sea urchins.
Indicator
species are species whose changes in behavior -- or more often, population
-- alert us to environmental conditions that threaten ecological niches,
or even the entire global system. These species serve as the "canaries
in the coal mine," warning us that levels of something in the environment
are increasing or decreasing beyond the resilience of the system.
Many scientists
today believe that the hundreds of species of amphibians on the decline
globally are indicator species, warning us of how human impacts on the
climate and air/water quality are having cumulative effects. For more
information on this topic, see Tracking the Vanishing Frogs, by Kathryn
Phillips.
ECOSYSTEM
"MANAGEMENT"
Land management,
including forest management, is often chosen as a way of maintaining biodiversity.
In certain cases, land (including forests) is managed by reducing diversity
to maintain what is required for some economic crop, such as the earlier
mentioned pine plantations of the south for paper and wood. This reduction
of biodiversity eliminates habitat and sets in place a system that requires
continuous maintenance. When laws and forest are managed to preserve natural
diversity, the existing structures and processes have to be studied in
some detail for a significant amount of time. Even then, "managing"
always implies interfering with what would have occurred naturally.
Quite an
amount of work has gone into understanding the forces that create and
maintain biodiversity. Any management looks at habitat closely. Trees
and shrubs provide the primarily habitats for animals as well as other
plants and microbes. Biodiversity is also believed to play an important
role in stabilizing an ecosystem against stress, such as climate fluctuations
and pest outbreaks. So even in forest managed for an economic product,
managers are beginning to work to preserve diversity. However, the complexity
and the dependencies are never completely understood, and the disruptions
caused often destabilize the system.
THREATS
TO BIODIVERSITY
Threats
to biodiversity are as numerous and varied as the sum of problems that
face the overall environment. Symptoms of severe stress in ecosystems
have been noted all over the world. Following are several main categories
of threats to biodiversity. It is important to note that, although we've
grouped the threats into several main categories below, almost all threats
facing ecosystems today are the result of human and industrial activity.
As the human
population increases, and we use up more and more land area for residences,
industry, and commercial or recreational activity, habitat loss becomes
a greater threat to biodiversity. Species are forced to live in higher
concentration, or move into habitats to which they are not adapted.
Humans often
also bring with them exotic or invasive species -- species that are not
native to a region or habitat. These invasive species sometimes carry
with them viruses or disease to which the local population is not adapted,
causing a direct harmful effect. The exotic species present competition
for food and habitat, and sometimes "edge out" native species
due to their pervasiveness.
As we mentioned
before, there is a high level of interdependency among species in an ecosystem,
and a reduction of population or loss of one species often leads to population
changes among other species. An ecosystem, once altered, can take years
to return to a state of equilibrium after a disturbance.
Common
environmental problems -- like air pollution, ozone depletion, and global
climate change -- are also often serious dangers to the survival of threatened
species. Tracking the Vanishing
Frogs, by Kathryn Phillips, documents
the research of scientists into the disappearance of many populations
and species of amphibians. Scientists are more and more convinced that
many of these disappearances are related to increased UV exposure (due
to the thinning of the ozone layer) or seemingly slight changes in weather
and precipitation patterns that affect the frogs' reproductive behavior.2
Within the last twenty years, 5100 amphibian species (including 2300 frog
and toad species) have disappeared. As we mentioned earlier, amphibians
are considered by many scientists to be an indicator species for damage
from ozone depletion or global climate change. We say that this is an
indicator of global, rather than local, change because amphibians in totally
unrelated niches are disappearing concurrently!
Damage to
trees from industrial pollution in Germany provide another example of
ecosystem stress due to environmental problems. In 1982, the former West
Germany noted that 8% of its forests showed decline. In 1983 it was 34%
and by 1985, 50%! Dying of forests from pollution has become a sever problem
Acid precipitation, causing an imbalance in soil chemistry, has been identified
as the reason in Germany and in the Great Smokies Nature Park in the U.
S.. Pollution is believed to have stressed the ponderosa pines in the
San Bernardino National Forest of California so that they could not produce
then natural digestive chemicals. This made them susceptible to bark beetles.
Trees can also get overpowered by fungi that cause root rot when they
are stressed.
The causes
of soil degradation are deforestation, over-exploitation, overgrazing,
industrialization, and large-scale agricultural activities maintained
through artificial fertilizers. This leads to loss of natural cycles -
decay of organic matter, nitrogen fixation, etc. - and decline in soil
fertility. Soil fertility in Wyoming, Panama, Thailand and other regions
have been destroyed by clear cutting forests which lead to loss of topsoil
and of soil compaction that preserves nutrients.
LOSS
OF BIODIVERSITY
There are
different types of losses of species as follows:
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Buffalo
from a wildlife refuge in Nebraska being reintroduced to Theodore
Roosevelt National Park in North Dakota. (1956) Photo courtesy
of the NPS.
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Depletion
of a once common species - the population of a species is greatly
reduced, but the habitat still exists and the species could be replaced
though there is still some loss of variety in the gene pool.
Example:
Buffalo on the American plains, whose population faced near extinction
due to large-scale slaughter... Buffalo populations were tremendously
reduced, to near extinction, the end of the 19th century. Buffalo were
slaughtered for reasons of commerce, sport, and even political reasons.
It was the policy of the U.S. Military (in practice, if not officially)
to kill as many buffalo as possible. "In 1874, Secretary of the
Interior Delano testified before Congress, 'The buffalo are disappearing
rapidly, but not faster than I desire. I regard the destruction of such
game as Indians subsist upon as facilitating the policy of the Government,
of destroying their hunting habits, coercing them on reservations, and
compelling them to begin to adopt the habits of civilization.'"3
- Local
or global species extinction -
the species is gone (either from its habitat or from the Earth) forever
and all current and potential adaptations are lost. Species extinction
has regularly occurred since the beginning of life on Earth. Historically,
losses occurred at a slow enough rate that ecosystems to adapt; however,
losses due to human activity are happening at a much higher rate,
causing concern among scientists and conservationists.
Example:
Deforestation...The
rate of extinction due to deforestation is now 10,000 times that before
human civilization.
<<LIST
FROM STUDENTS OF SPECIES LOST SINCE 1980'S>>
| Exercise: |
| List
two animals from your state on the endangered species list. |
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- Ecosystem
disruption - this is the most serious of the three because it is
not just the loss of several species, but of an entire ecosystem.
Example: Three Gorges Dam... ecosystem loss
that will result from the construction of the Three Gorges Dam in China.
This is a project whose goal is to build the world's largest hydroelectric
dam on the Yangtze River, creating a 400-mile long reservoir and displacing
up to 1.9 million people -- threatening the entire ecosystem.4
POLICY
Ideally all of our environmental regulations and policies protect ecology
by preventing pollutants from degrading the habitats of species. However,
in the USA there is one federal regulation that specifically discusses
species protection: the Endangered Species Act (ESA).
Endangered
Species Act
The ESAwas
enacted in 1973 to place the highest priority on the protection of endangered
species.
It is administered by the US Fish and Wildlife Service, the National Marine
Fisheries Service.
The ESA
prohibits government agencies from authorizing, funding, or carrying out
any activities that might harm an endangered species, or its habitat,
and prohibits individuals from taking an endangered species (taking can
be broadly defined as causing any harm) without regard to economic consequences.
The ESA,
in conjunction with the National Environmental Policy Act (NEPA), is the
main law that can prevent large civil infrastructures from being built
when ecosystems or species are threatened. NEPA was enacted in 1969 with
the goal of ensuring public input regarding actions that affect their
local environment. NEPA requires all agencies to complete an environmental
impact statement (EIS) analyzing the effects of any major project that
it plans to implement.
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CLASSIC
CASE: Tennessee Valley Authority vs. Hill, 1978 court decision.
A federal agency wanted to build the Tellico Dam on a segment of
the Little Tennessee River. A citizens' group wanted to block the
project and tried to do so under NEPA. NEPA required the agency
to do an assessment of the environmental impacts caused by the proposed
dam. In 1973, a small endangered fish known as the snail darter
was found in the Little Tennessee River. The citizens' group filed
a lawsuit claiming that the dam would destroy the fish's habitat.
The court agreed and after many appeals, the 1978 Court of Appeals
stopped the project.
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The ESA
works as follows:
The ESA
works as follows:
- Listing:
The Secretary of the Interior maintains a list of endangered species,
and a list of threatened species (likely endangered in the future).
A species is listed if any of these conditions applies:
a) present or threatened destruction, modification, or curtailment of
its habitat,
b) over utilization for commercial, recreational, scientific, or educational
purposes,
c) disease or predation impacts,
d) inadequacy of existing regulatory mechanisms, and
e) other natural or anthropogenic factors affect the existence.
There is no economic consideration at this stage.
- Critical
habitat: The relevant agencies define a geographical area with physical
and biological features that are essential to species survival. At this
stage the agencies can consider economic impacts to limit the area,
therefore the area is not necessarily equal to the entire habitat.
- Recovery
Plans: These are developed to include specific steps that must be taken
to help the species populations to increase in size.
- God Squad:
overruling authority was added to help negotiate conflicts.
[1]
Williams, Ted. "False Forests," Mother Jones (Magazine).
May/June 2000.
[2]
Phillips, Kathryn. Tracking the Vanishing Frogs,
[3]
Wooster, Robert. The Military and United States Indian Policy 1865-1903
, Yale University Press, 1988.
[4]
Source: International Rivers Network, http://www.irn.org.
OTHER SOURCES:
- Measures of Ecosystem Well Being (Bork)
- http://www.iucn.org/
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