Abiotic and Biotic Factors

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Abiotic and Biotic Factors

Abiotic Factors

Abiotic factors are the non-living factors that affect living organisms, and so affect communities.  These factors do not work in isolation - they combine to produce unique environments which support distinct types of animals and plants.

Abiotic factors include:

Light intensity: limited light will limit photosynthesis.  This will affect the distribution of plants, and therefore the distribution of animals that eat plants. Some plants adapt to low light, usually by developing bigger leaves to optimse photosynthesis.

Temperature: temperature is a limiting factor for photosynthesis - and low temperature therefore limits growth of plants.  In cold climates, the number of plants is usually low - which limits the number of herbivores that can live there.

Moisture levels: life needs water!  Plants and animals are rare in deserts.

Soil pH and mineral content: plants need mineral ions like nitrates to grow.  Where they are limited in the soil, plants struggle to grow - unless they get them by trapping animals and digesting the minerals from their decaying bodies.  Low pH in soil slows down the rate of decay, and therefore slows down the relase of mineral ions back into the soil. This inhibits new plant growth.

Wind intensity and direction: the shape and height of plants is severly affected in areas of high wind - and the rate of transpiration is also increased in high winds.

Availability of oxygen in aquatic animals: oxygen is needed for life above and below water.  Some water has very low levels of absorbed oxygen - so life struggles there.  By contrast, air has reasonably constant proportion of oxygen.

Availability of carbon dioxide: plants need carbon dioxide for photsynthesis - so low levels of carbon dioxide inhibit plant growth.

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Biotic Factors

Biotic factors are the non-living factors that affect organisms - and therefore affect communities.

Biotic factors include:

Availability of food: when food is in short supply, animal struggle to survive.  They are therefore less likely to breed.

New pathogens and parasites: organisms have no resistance to new pathogens.  This can reduce the healthiness, or even wipe out communities.

New predators arriving: as with parasites and pathogens, organisms may have no defense against new predators, and may be wiped out by them.

Interspecific communities (competition between species): competiton may result in the numbers of one species getting so low that they are unable to breed successfully.

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