Human Impact on Ecosystems

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Succession

• The non-seasonal, directional (time) change in
  community within a habitat
• Unstable r-strategists ?stable K-strategists

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Primary succession is the series of community
changes which occur on an entirely new habitat
which has never been colonized before. Examples
of such habitats would include newly exposed or
deposited surfaces, such as landslips, volcanic
lava and debris, elevated sand banks and dunes,
quarried rock faces. A number of stages (seres)
will take place in which an initial or 'pioneer'
community will gradually develop through a number
of different seres, into a 'climax' community,
which is the final stage.
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• Secondary succession is the series of community
  changes which take place on a previously
  colonized, but disturbed or damaged habitat.
  Examples include areas which have been cleared of
  existing vegetation (such as after tree-felling
  in a woodland) and destructive events such as
  fires.
• Secondary succession is usually much quicker than
  primary succession for the following reasons
• There is already an existing seed bank of
  suitable plants in the soil.
• Root systems undisturbed in the soil, stumps and
  other plant parts from previously existing plants
  can rapidly regenerate.
• The fertility and structure of the soil has also
  already been substantially modified by previous
  organisms to make it more suitable for growth and
  colonization.

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• As a result of Succession
• Stability increases (r ? K)
• Diversity increases
• 2 types
• Primary - from bare rock (Xerarch)
• Secondary from a disturbed habitat e.g. water
  course silting (Hydrarch)
• 2 mechanisms
• Autogenic changes are caused by the organisms
  themselves e.g. lichen
• Allogenic - change is elicited by external
  agency e.g. climatic event, landslide, human
  intervention

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Human Impact on Ecosystems

• Man impacts environments for a number of reasons
• Food production agriculture and wild harvest
• Energy production
• Pollution
• Together these activities stress ecosystems
• Stress leads to a reduction in species diversity
• Populations sizes may increase (lack of
  interspecific competition)

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Human Impact on Ecosystems Food Production

• The battle to feed humanity is over. In the
  course of the 1970s the world will experience
  starvation of tragic proportions hundreds of
  millions of people will die. Paul Ehrlich, The
  Population time Bomb, 1968.

We now have more food than ever before -
Improved irrigation and farming methods - High
yield crops - Fertilizers pesticides What
Cost?
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Effects of Intensive food Production-Problems

• Monoculture
• growing a single species over a large area
  trees/ food crops
• Loss of habitat including increase in field size
  for efficiency
• Reduces species diversity
• Loss of nutrients leaching due to soil erosion
• Invasion of opportunistic weeds
• Intensification of disease/ predation problems
• Loss of soil structure due to inorganic
  fertilisers leads to topsoil erosion

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Effects of Intensive food Production - Solutions

• CHEMICALS
• Herbicides (weedkillers, natural/ synthetic)
• Pesticides (insecticides fungicides
  natural/synthetic)
• Fertilisers (NPK organic)
• DIFFICULTIES
• Toxicity (to consumer non target species)
• Bioaccumulation through food chain (leading to
  toxicity)
• Resistance requiring stronger chemicals
• Persistence
• Pollution (leaching/ runoff)

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Examples - Fertilisers

• Fertilisers (organic or NPK)
• Eutrophication excessive nutrients into water
  (deoxygenation)
• Nitrate in water blue baby syndrome due to
  nitrite oxidation of haemoglobin
• Cancer not certain

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Examples - Pesticides

• Pesticides can be toxic to man and other species
• DDT/DDE synthetic oestrogen
• thin egg shell - birds of prey
• altered sex ratio (small penis, testicles
• RATS, alligators, fish
• Link to breast cancer
• Fall in sperm counts (controversial - sex more
  often)
• Organic farmers better sperm quality (Denmark)

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Examples - Herbicides

• Kill indiscriminately
• Good bad weeds killed
• Loss of food/ habitat for variety of animals
• Loss of food web diversity unstable
• Loss of useful insect etc. species
• Loss of soil improving microbes/ animals
• Possibly toxic

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Increasing Energy Needs

• Energy requirements have increased
• Principally they have been met by polluting
  fossil fuels
• This has lead to carbon dioxide emissions
  increasing substantially

Carbon dioxide causes GLOBAL WARMING
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Global Warming

• Principally due to carbon dioxide (60)
• Other gases include
• Methane (20)
• CFCs (14)
• Nitrogen Oxides (6)
• Ozone (upper atmosphere) (8)
• Carbon dioxide has increased by 31 during
  industrial revolution
• Increase due to combustion, deforestation

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Climate change solutions

• Change of 0.6C over last century
• Projected rise 1.5 -4.5 C
• Not all due to Carbon Dioxide, sunspot activity
• Solutions
• Reduce fossil fuel combustion
• Switch to alternative fuel sources (renewable)

Conserve forests Add iron to sea
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Global Warming Problems

• Coral bleaching
• Loss of photosynthetic algae (zooxanthellae) from
  commensal relationship due to 1C increase in sea
  temperature
• Disease spread
• Malaria possible in south britain
• Loss of species niches
• e.g. arctic species on cairngorms

http//www.metoffice.gov.uk/research/hadleycentre/
models/modeldata.html
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• Food production needs to double to meet the needs
  of an additional 3 billion people in the next 30
  years

Climate change is projected to decrease
agricultural productivity in the tropics and
sub-tropics for almost any amount of warming
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Other Pollution from combustion of fossil fuels

• Acid rain (SO2, Nox)
• Other pollutants
• PM 10s - Asthma
• Ozone layer
• CFCs activated by high energy photons
• Chlorine free radicals react with ozone in upper
  atmosphere

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Pollution

• Heavy metals
• Interfere with enzyme action/ biochemical
  processes
• Result of industrial activity, common at foundry
  sites/ gas works
• Can be removed by expensive soil cleaning
• Reeds may be able to concentrate and so remove
  them in their tissues

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Pollution - biotransformation

• Biotransformation is when organisms metabolise
  chemicals into different chemicals. Typically
  this is a detoxification process.
• Sometimes less toxic chemicals are changed into
  more toxic chemicals
• e.g. metallic mercury to very toxic methyl
  mercury
• Minamata bay, Japan

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Pollution - Biomagnification

• If a pollutant is not excreted or destroyed by an
  organism, it will concentrate in the animals
  body.
• If that animal is subsequently consumed, all of
  the toxin will pass to the consumer
• Consequently, the consumer will have a higher
  concentration of toxin in their body.
• HCB hexachlorbenzene

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http//www.ourstolenfuture.org/Basics/chemlist.htm
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Tributyl Tin

• Anti fouling chemical (now banned) used to
  prevent build up on ships hulls
• In higher concentrations can lead to changes in
  molluscs e.g. dog whelks/ oysters
• Sex ratio changes/ bifurcate penis

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• Love Canal
• housing estate near Niagara falls, built on
  chemical dump (dioxin, benzene)
• Low birth weight and growth retardation
• Canal