Ecosystem vulnerability and resilience

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Ecosystem vulnerability and resilience

• Syllabus
• Vulnerability and resilience of ecosystems
• -impacts due to natural stress
• -impacts due to human modifications to energy
  flows, nutrient cycling and relationships
  between biophysical components

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Definition of vulnerability

• Vulnerability is the ecosystems sensitivity to
  stresses that ca upset the ecological dynamic
  equilibrium.
• These may be natural or human induced stresses.
• All ecosystems are vulnerable but they do vary in
  their sensitivity to change.

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Question

• What types of natural stress could be in an
  intertidal wetland?

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Natural stress

• In intertidal wetlands the majority of natural
  stress comes from salinity and tidal movements.
• The intertidal wetlands must be able to survive
  extreme conditions of mainly salt water at high
  tide, fresh water at low tide and times of flood
  and brackish water at other times.
• The saline water is a very difficult condition
  for plants to survive in.

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Natural stress

• Changes to tidal movements through increased
  run-off or altered drainage can cause the roots
  of mangroves to be inundated for longer than
  normal periods affecting their pneumatophones.
• It can also be pushed past its threshold level if
  water quality is changed. Thus even healthy
  ecosystems are vulnerable to change.

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Natural stress

• Some species such as oysters and molluscs have
  been used as indicator species, with any decline
  in their numbers indicating the ecosystem is
  under stress.
• A decline in nutrient levels will also affect
  primary productivity and thus bring about change.

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Natural stress

• The grey mangrove accomplishes this by excluding
  salt in the root system, salt glands in the leaf,
  and waxy leaves to minimize water loss.
• However it is vulnerable to changes in salinity
  levels.

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Natural stress

• Today's cheetahs are almost carbon copies of each
  other.
• Low genetic variability is a factor that
  increases the vulnerability of the world's
  cheetah populations to a wide variety of diseases
  and physiological defects.
• A population genetic survey of over 200
  structural loci previously revealed that the
  South African cheetah (Acinonyx jubatus jubatus)
  has very little crossing over of chromosomes when
  fertilisation takes place.

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Natural stress

• The apparent consequences of such genetic
  uniformity to the species include
• (i) great difficulty in captive breeding,
• (ii) a high degree of juvenile mortality in
  captivity and in the wild, and
• (iii) a high frequency of spermatozoal
  abnormalities.

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Natural stress

• Cheetahs are often persecuted by other predators,
  who steal their food, eat their cubs, and even
  attack the adults.  For these reasons, cheetahs
  life span in the wild is about 4 to 5 years, but
  they have been to known to live up to 15 years in
  zoos. 
• The cheetah is considered the most endangered big
  cat today. 
• Human excess is probably the major factor pushing
  the cheetah toward extinction - robbing them of
  living space, limiting their food supply, 
  illegal hunting.

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Natural stress

• Some scientists believe that the cheetah
  population was nearly destroyed 10,000 years ago
  by a catastrophic event such as a disease or
  natural disaster that left only 1,000 or so
  surviving . 
• In 1900 - approx 100,000 cheetah worldwide. 
• Present estimates place their number at 10-15
  thousand with about 1/10 of those living in
  captivity. 

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Natural stress

• Volcanoes can exert enormous natural stress on
  ecosystems in the short to medium term.
• The ecosystem can eventually begin to recover as
  the volcanic material can provide nutrients for
  regrowth.

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Natural stress

• As of February 1996, the current eruption has
  destroyed 181 homes.
• Buildings, structures, roads, trails, and
  facilities have been destroyed in Hawaii
  Volcanoes National Park and in Harry K. Brown
  county park. Numerous archaeological sites have
  been buried.
• Total losses exceed 61 million, making this
  eruption the most costly ever in Hawaii.
• More than 500 acres (200 hectometers) of new land
  has been added to the island.
• 1.7 billion cubic yards (1.3 billion cubic m) of
  lava has been erupted.

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Question

• How would cane toads modify energy flows in an
  ecosystem?

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Human modifications to energy flows

• Cane toads were deliberately introduced from
  Hawaii to Australia in 1935, to control scarab
  beetles that were pests of sugar cane.
• In 2002, Cane Toads occur throughout the eastern
  and northern half of Queensland and have extended
  their range to the river catchments surrounding
  Kakadu National Park in the Northern Territory.

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Human modifications to nutrient cycling

• Nutrient cycling would be altered by climate
  change in ways that could exacerbate existing
  water quality problems such as eutrophication.
• Eutrophication of lakes results when nutrient
  inputs from catchments and recycling from bottom
  sediments are large.
• The result is excessive production of blue-green
  algae which reduces water quality.

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Human modifications to nutrient cycling

• In a warmer climate, the longer period of summer
  conditions would increase the solubility of
  phosphates in sediment and increase nutrient
  recycling.

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Relationships between biophysical components

• Lebanon's tourist and fishing industries remain
  battered by what has been described as the
  country's worst environmental catastrophe, which
  erupted when Israeli warplanes struck the Jiyeh
  power plant in mid-July, spilling up to 110,000
  barrels of fuel oil into the clear Mediterranean
  waters.
• Fewer than 3,500 barrels have been cleaned up.
  Lebanon couldn't start any offshore operation for
  weeks, waiting for Israel to lift its naval and
  air blockade on Sept. 8.

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Relationships between biophysical components

• The timing is quite essential with an oil spill.
  The more you wait, the more it spreads.
• It is marine life that could suffer the worst
  consequences, because in the Mediterranean,
  currents don't come in often enough to sweep away
  pollutants.
• Lebanese waters are known as a passage for
  migrating fish, particularly tuna. The oil, which
  sank to the bottom of the sea, where it threatens
  plants and fish that live on the sea floor, could
  resurface unless treated and contaminate the
  coast for years to come.

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Relationships between biophysical components

• It could take up to 10 years for the ecosystem
  of the eastern Mediterranean to recover fully.
• Several countries including France, Spain and
  Italy have sent teams to help the Lebanese navy
  with the cleanup, which could cost 100 million.
• Lebanon, meanwhile, plans to sue Israel for
  damages, though it has not said how much it will
  claim.

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Definition of Resilience

• Resilience relates to the continuity of
  ecosystems and their ability to endure changes
  and disturbances while maintaining the same level
  of productivity and the same relations among
  populations.
• Resilience means that when a population is
  drastically reduced, it still has capacity to
  recover thanks to its regenerating potential and
  the balanced distribution of forest types and age
  classes.

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Examples of resilience?
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Resilience

• Biological diversity appears to enhance the
  resilience of desirable ecosystem states, which
  is required to secure the production of essential
  ecosystem services.
• The diversity of responses to environmental
  change among species contributing to the same
  ecosystem function, which we call response
  diversity, is critical to resilience.
• Response diversity is particularly important for
  ecosystem renewal and reorganisation following
  change.

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Question

• Why might the Antarctic food web lack resilience?

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