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Biology Unit 4
Topic 5: On the wild side
12. Explain how the concept of niche accounts for
distribution and abundance of organisms in a habitat.
The ecological niche of an organism is difficult to define. It can best be described as the role of the
organism in the community, its way of life. It can be broken down into specific elements, for example
the food niche or the habitat niche. Several organisms can share the same habitat, occupying
Eg. The food niche occupied by a fox in woodland is the top predator, squirrels occupy the large
tree-dwelling herbivore niche and rabbits fill the large ground and borrow-living herbivore niche.
Density dependent and density independent factors
The factors that affect the number of organisms occupying a particular niche whether biotic or
abiotic may be density dependent or density independent:
The effect of density-independent factors is the same regardless of population size.
These factors tend to limit the distribution of individuals and therefore of species
E.g. extremes of temperature affects all individuals regardless of their population size
The impact of a density-dependent factor will depend upon how many organisms there are
in a specific area.
They are important in limiting the abundance of species
E.g. disease and parasitism. The more individuals there are in a given area, the more
likely it is that the disease or parasite can be transmitted between individuals.
Breeding success in territorial animals and birds as individuals without territories are
unlikely to breed.
Many factors can be both. E.g. the amount of water present in an area where there are relatively
few plants is completely independent of the number of living things. It is affected by the amount of
rainfall, sunshine and the type of soil. However in a densely overgrown area, the amount of water
taken up by plants in transpiration will have a big impact on the water available in the soil and
therefore it may be a density dependent resource.
Text Book: p. 18, 31-33
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Biology Unit 4
Intraspecific competition is competition for a limited resource between members of the
same population or species.
E.g. Meerkats defend their territory against other groups of meerkats wanting to
As a result of intraspecific competition, some individuals may not survive or may not
reproduce and so population growth slows
Interspecific competition occurs when different species within a community compete for
the same resources.
Competition will reduce the abundance of the competing species.…read more