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Distribution & Abundance
In any habitat a species occupies a specific niche determined by the environmental conditions (biotic and abiotic factors) and the way that the
species used the habitat (food, shelter etc.). The distribution and abundance are determined by these conditions. Changes in these
conditions therefore lead to changes in distribution and abundance.
The abundance of different species can be described by the niche concept 2 species occupying the similar niches will compete so fewer
individuals of both species will be able to survive in the area.
The distribution of different species can be explained by the niche concept organisms can only exist in habitats where all the conditions
that make up their role exist.
The conditions in which species compete for survival are defined by the ecological factors in their habitat; these factors can be classified into
2 groups which have a complex interaction:
ABIOTIC FACTORS (non-living or physical factors)
Solar energy input which is affected by latitude, season, cloud cover, and changes in the Earth's orbit. Light is vital for plants (due to
photosynthesis) and also has a role in initiating flowering. In many animals, light affects behaviour.
Climate e.g. rainfall, wind exposure and temperature
Topography including altitude (affecting climate) slope, aspect and drainage.
Oxygen availability important in aquatic systems.
Edaphic factors connected with the soil (soil pH, soil texture and mineral salt availability). The underlying geology of an area can have
a significant impact on plant distribution.
Pollution e.g. air, water or land pollution.
Catastrophes infrequent events that disturb conditions e.g. floods, earthquakes, fires etc.
BIOTIC FACTORS (`living' factors)
Competition for resources e.g. food, light, water and space which can be interspecific (between species) or intraspecific (within
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Grazing, predation and parasitism are all relationships between two organisms where one benefits at the other's expense.
Biotic factors are usually density dependent: the effects are related to the size of the population relative to the area available e.g. the
larger the population density, the greater the competition for food etc.
ANTHROPOGENIC FACTORS (human activity) can be abiotic or biotic. Our ecological footprints are far greater than that of any other species.…read more