control & regulation regulation & monitoring of populations m r g d a v i d s o n
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Control & Regulation
Regulation & Monitoring of Populations
Mr G D
avidson
Mr G D
avidson
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Populations
A population is a group of individuals of the same species which makes up part of an ecosystem.
The number of individuals of the same species in a unit area/volume of habitat is called the population density.
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Population Stability
When an environment is colonised by a species, the population grows to the highest level supportable by the environment.
The limit is known as the carrying capacity.
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Population Stability
The population level is now relatively stable save short-term oscillations from generation to generation.
It is said to be in a state of dynamic equilibrium.
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Factors influencing change
Every species has a large reproductive potential, but population increase is restricted by environmental resistance, which consists of factors such as:– Food - Water – Space - Oxygen– Light - Shelter– Predation - Disease– Climate
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Factors influencing change
A density independent factor is one which affects population growth regardless of density, e.g. weather extremes, forest fire, flood, etc.
A density dependent factor is one which affects a population once it has grown to a certain size and density.
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Factors influencing change
Once a population reaches this level, it is inevitably affected by one such factor, e.g.– competition starvation– build up of population’s toxic wastes– disease– predation
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Factors influencing change
Predator and prey populations are linked and balanced.
If conditions favour prey, their numbers will increase.
As a result, there will be more food for predators, whose numbers will also rise.
An increase in predator numbers will increase predation and therefore prey numbers will fall.
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Factors influencing change
Increased competition following this reduction in food will cause predator numbers to drop as some die of starvation.
This brings the population back to its original state.
Since there tends to be less predators than prey, population graphs of predator and prey numbers are usually very similar:
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Factors influencing change
Time
Nu
mb
ers
of P
op
ula
tion
Prey
Predator
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Monitoring Populations
Many species of wild plants and animals are surveyed closely by scientists to monitor population numbers and affecting factors.
This data is needed for:– management of species which provide food or
raw materials– pest control– pollution assessment– protection and conservation of endangered
species
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Food Species
The maximum sustainable yield of a population is a measure of the maximum rate at which individuals can be removed without affecting the population’s future productivity.
This keeps populations in check, e.g.– fish – prevent over-fishing by quotas.– keep down red deer populations with
cullings.
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Pests
Pests are species which threaten mankind’s health or economy.
They can include insects, fungi and vermin which spread disease and ruin crops.
Noted examples are:– green fly - pathogenic fungi– locusts - mosquitoes– brown rats
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Indicator Species
Environmental health can be assessed by examining certain indicator species.
Fresh water indicator species include mayfly and stonefly, which show that pollution is low.
Birds of prey are affected by over-use of pesticide sprays as toxic chemicals move up the food chain and accumulate in the bird’s diet.
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Indicator Species
If, however, water is polluted, it can be shown by the presence of rat-tailed maggots and sludgeworms.
On land, air pollution levels can be shown by lichens.
The presence of lichens indicates low air pollution.
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Indicator Species
Phytoplankton, microscopic, oceanic plants acts as the first link in the marine food chains.
They convert much CO2 into O2 during photosynthesis and could possibly make a big difference to the greenhouse effect.
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Endangered Species
Rare species may have values ranging from medicinal to aesthetical.
To prevent extinction, the areas in which some endangered species live in are converted into nature reserves.
Over-hunting, poaching, picking and harvesting are controlled or restricted to maintain species numbers.
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