Transcript Human Impact on Ecosystems

Succession
The non-seasonal, directional (time)
change in community within a habitat
 Unstable r-strategists stable Kstrategists

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.
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.

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
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)
Human Impact on Ecosystems
– Food Production

“The battle to feed humanity is over. In
the course of the 1970’s the world will
experience starvation of tragic
proportions – hundreds of millions of
people
willmore
die.”
Paul
Ehrlich,
We
now have
food– than
ever
before The
Population
time
Bomb,
- Improved
irrigation
and1968.
farming methods
- High yield crops
- Fertilizers & pesticides
What Cost?
Effects of Intensive food ProductionProblems

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
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)
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
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)
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
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
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
Climate change solutions

Change of 0.6°C 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
Global Warming Problems

Coral bleaching
– Loss of photosynthetic algae (zooxanthellae) from
commensal relationship due to 1°C 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
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
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
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
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
Pollution - Biomagnification
If a pollutant is not excreted or
destroyed by an organism, it will
concentrate in the animal’s 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
Correlation between DDE concentrations in the eggs of Alaskan falcons and hawks and
reduction in the thickness of their eggshells (compared with shells collected prior to 1947).
DDE is a metabolite of DDT. Data from T. J. Cade, et. al., Science 172:955, 1971.
Species
Location
Peregrine falcon
Alaskan tundra (north
slope)
Central Alaska
Peregrine falcon
Rough-legged
hawk
Gyrfalcon
Aleutian Islands
Alaskan tundra (north
slope)
Seward Peninsular, Alaska
Peregrine falcon
Average
Concentration
of DDE in Eggs (ppm)
Reduction in
Shell
Thickness
889
-21.7%
673
-16.8%
167
-7.5%
22.5
-3.3%
3.88
0
http://www.ourstolenfuture.org/Basics/chemlist.htm
Tributyl Tin
Anti fouling chemical (now banned)
used to prevent build up on ship’s hulls
 In higher concentrations can lead to
changes in molluscs e.g. dog whelks/
oysters

– Sex ratio changes/ bifurcate penis

“Love Canal”
– housing estate near Niagara falls, built on
chemical dump (dioxin, benzene)
– Low birth weight and growth retardation
– Canal