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Ecosystems: Change and Challenge
The Structure of Ecosystems

Ecosystem: a dynamic, stable system characterised by the interaction of plants and animals with each other and with the
non-living components of the environment

The components of an ecosystem are categorised as either biotic and abiotic

Biotic means the living…

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The movement of energy up the trophic levels shows the food chain as each trophic level occupies a different position.
However food chains, in reality, are often more complicated than this. Some species can occupy more than one position in every
food web ­ may be prey to…

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There are two basic types of succession:

1. Primary succession-occurs on surfaces that have had no previous vegetation

There are two main types of primary succession:

Xeroseres are formed on dry land, this group can be divided into lithoseres on bare rock and psammoseres on sand

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A hydrosere develops as follows:

i). In a freshwater environment, submerged aquatics are the first plants to develop, they help to trap sediment which
enables other species to move in

ii). The next seral stage is the growth of reed beds and swamp conditions

iii). Colonisation by…

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Arresting factors

Plant successions can be stopped from reaching climatic climax or deflected to a different climax, by human interference

The resulting vegetation is called a plagioclimax, this can be caused by:

deforestation or afforestation
animal grazing or trampling
fire clearance

A secondary succession is one that develops…

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Humidity is high throughout the year, continuous evapotranspiration adds water vapour to the air

On the forest floor there is little breeze as the trade winds converge here


Underlying soil will have developed naturally over a long period of time and be in balance with its environment,…

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Climatic climax vegetation has been destroyed, this has resulted in both secondary succession and plagioclimax
The vegetation that replaces the original rainforest tends to be smaller in height and less diverse, with a reduction
in the general biomass

Causes of deforestation

Demand for hardwood, e.g. teak, its demand…

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Deep red lateric soils
Influenced by climate
Silica is leached downwards in the wet season
Crust formed in the dry season


Greater towards the equator
Acacia, Baobab, Umbrella Thorn, Elephant Grass
Great animal migrations occur meaning that biodiversity drops at certain times
40% of the land…

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Northern Ghana characteristics:

lengthy period of moisture deficit
Short period of moisture surplus
Total annual potential evapotranspiration greater than total potential precipitation

Adaptations by vegetation

Vegetation in wetter areas consist of tall coarse grasses, with many deciduous trees- Tree savanna
Shorter tussock grass becomes dominant in desert margins,…

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Winds blow in from the ocean with very moist air and heavy rainfall during May-October, the rest of the year
the air is drier

Ecological responses

Soil moisture budgets

Precipitation is much higher than potential evapotranspiration during the wet season
High rainfall totals result in saturation of the…


Mr A Gibson


These notes are great. Use them as your notes, build on them from the case studies you use yourself and then use them to create revision cards from. Everything is here - definitions, examples and so on.

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