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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen




ECOSYSTEMS AND SUSTAINABILITY REVISION NOTES
2.3.1 What is an ecosystem?
Ecosystem=group of living organisms and non-living things occurring together, and the
interrelationships between them.

Components of an ecosystem:

Habitat-place where an organism lives
Population-all of the organisms of one species, who live in the same…

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen




Primary consumers=feed on plants & are eaten by carnivorous secondary consumers

Secondary consumers=feed on primary consumers & eaten by tertiary consumers

Tertiary consumers=feed on secondary consumers

Decomposers=feed on waste material/dead organisms

2.3.2 Energy Transfer
A food chain shows how energy is transferred from one living…

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen




Net productivity =amount of energy that is available to the next tropic level.




Productivity
Even pyramids of energy have limitations:

Only take a snapshot of an ecosystem at one moment in time-because population sizes can
fluctuate over time, this may provide a distorted idea of…

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen




Secondary succession-happens on land that's been cleared of all plants, but where soil remains eg.
After a forest fire or when a forest has been cut down by humans

Seral stages-how succession occurs:

Primary succession starts when species colonise a new land surface, seeds &…

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen




Succession on sand dunes
Sand dunes show all stages of succession in the same place at the same time:

Pioneer plants, like sea rocket and prickly sandwort colonise the sand just above the high
water mark, these can tolerate salt water spray, lack of fresh…

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen




support them-the climax community would be the grassy field-this isn't a natural seral
stage-there should be things like small flowering plants-so succession has been deflected.

Climax communities
Climax community = an ecological community in which populations of plants or animals remain
stable and exist in…

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen




1. Nitrogen fixation-Nitrogen gas makes up 79% of the earth's atmosphere but = very unreactive.
This means it is impossible for plants to use it directly despite its abundance. Instead, they need a
supply of `fixed' nitrogen eg ammonium ions or nitrate ions, nitrogen fixation…

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen




Parts of the nitrogen cycle can be carried out artificially on an industrial scale-the Haber process
produces ammonia from atmospheric nitrogen-used to make fertilisers.

2.3.7 What affects population size?
In some circumstances a species' population size may stay fairly stable over time; however,
population size…

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen




colonise a disturbed habitat before k-strategists, dispersing into other habitats once limiting factors
start to have an effect.

R-strategists = good at colonising disturbed habitats because they usually have a very fast rate of
reproduction-much faster than k-strategists

K-strategists=more likely to be members of a…

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen




INTERSPECIFIC ­ happens between individuals of different species and can affect both the
population size of a species and the distribution of species in an ecosystem.

Gause-did experiments with two species of bacteria, he concluded that overlap between two
species' niche would result in more…

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