Transcript What is resilience?

Ecosysytem stability and
resilience .
LECTURE 2.
SABIHA SULTANA
Ecosysytem stability
• Stability is commonly defined as a state in
which changes does not occur. But stable
ecosystem change constantly; for example,
population levels increase and decrease from
day to day, season to season &year to year.
Only fully development or mature ecosystem
are stable. They are considered stable because
their structure and function remain more or
less the same over long periods.
• Thet are in a state of dynamic equilibrium
(steady state) in which things change but
remail more ar less the same.For example- if
we examined a mature ecosysytem each
spring for an extended period-say, 20 years-we
would find that
• (1)the total number of species was fairly
constant from year to year.
• (2) the same species were present each year.
• (3) the population size of each species was
approximately the same from year to year.
• As a tightrope walker moves along the high
wire, tilting right, the left but always staying
on the wire, So a mature ecosystem
undergoes small-scale fluctuations as it
remain on its main course.
Stability is also the ability of a disturbed
ecosysytem to return its original condition.
What is resilience?
Why is it important?
• In ecology, resilience is the capacity of an
ecosystem to respond to a disturbance by
resisting damage and recovering quickly. Such
perturbations and disturbances can include
stochastic events such as fires, flooding,
windstorms, insect population explosions, and
human activities such as deforestation and the
introduction of exotic plant or animal species.
• The concept of resilience in ecological systems
was first introduced by the Canadian ecologist
C.S. Holling
. Resilience has been defined in following
ecological literature:
• “Ability of a living system to restore itself to
original condition after being exposed to an
outside disturbance that is not too drastic”.
• So,Ecosystem resilience describes the
capacity of an ecosystem to cope with
disturbances, such as fire, pollution,
flooding, windstorms, insect population
explosions, and human activities such as
deforestation and the introduction of exotic
plant or animal species without shifting into
a qualitatively different state
A resilient ecosystem has the capacity to
withstand shocks and surprises and, if
damaged, to rebuild itself.
• In a resilient ecosystem, the
process of rebuilding after
disturbance promotes renewal and
innovation. Without resilience,
ecosystems become vulnerable to
the effects of disturbance that
previously could be absorbed.
• Clear lakes can suddenly turn into
murky, oxygen-depleted pools,
grasslands into shrub-deserts,
and coral reefs into algae covered
rubble. The new state may not
only be biologically and
economically impoverished, but
also irreversible.
Human impacts on resilience
• As resilience refers to ecosystem's stability and
capability of tolerating disturbance and restoring
itself so, If the disturbance is of sufficient
magnitude or duration, a threshold may be reached
where the ecosystem changes state, possibly
permanently.
• However, the elements which influence ecosystem
resilience are complicated. For example various
elements such as the water cycle, fertility,
biodiversity, plant diversity and climate, interact
fiercely and effect different systems.
• There are many areas where human activity
impacts upon and is also dependent upon the
resilience of terrestrial, aquatic and marine
ecosystems. These include agriculture,
deforestation, pollution, mining, recreation,
overfishing, dumping of waste into the sea
and climate change.
Gradual loss of resilience can lead
to unexpected collapse
• There is increasing evidence that ecosystems
seldom respond to gradual change in a
gradual way.
• Studies of forests and oceans also show that
human-induced loss of resilience can make
an ecosystem vulnerable to random events
like storms or fire that the system could
earlier cope with
• An ecosystem with low resilience can often
seem to be unaffected and continue to
generate resources and ecosystem services
until a disturbance causes it to exceed a
critical threshold. Even a minor disturbance
can cause a shift to a less desirable state that
is difficult, expensive, or even impossible to
reverse.
After minor changes induced by nature or
human causes a stable ecosystem can ‘bounce
back’ to its previous condition. Stabilty is also
a property of an ecosystem that causes it to
resist being changed by natural events or by
human interference (inertia).
What keeps Ecosystems stable?
• Population growth& environmental resistance.
• The forces that affect an ecosystem stability
are the factors that control the size of its
populations. There forces can be broken down
Into two group.
• 1.Growth factor +Reduction factors
=Ecosystem Balance.
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Growth factors
BioticReproductive rate.
Ability to adapt to environmental change.
Ability to migrate to new habitat.
Ability to compete, hide, defend to find food.
Adequet food supply.