SvS Biology 2000 - Limits of the Web
Abiotic Factors
All habitats are characterized by a specific combination of factors such as the amount of precipitation, temperature variation, amount of sunlight, humidity levels, aspect, inclination, soil pH, soil salinity and the availability of elements such as oxygen, carbon, phosphorus and nitrogen. These are known as the abiotic, or non-living, factors of an ecosystem. All organisms operate within a fairly specific range of tolerance among these aboitic factors. For example, fish generally tolerate a very narrow range of water temperature and pH, and a large variation could threaten their survival.
Biotic Factors
Biotic factors are those which represent all LIVING organisms within the environment. These establish relationships in the ecosystem that are described as beneficial, neutral or detrimental. For example, the relationship between two organisms may be symbiotic (mutualistic or commensalist), predatory or parasitic.
Limiting Factors
In all ecosystems there are factors - usually abiotic - that limit the continued growth of an organism. This is called the limiting factor, because it outweighs all others in most directly affecting the survival of an organism. During a prolonged drought, for example, moisture becomes the limiting factor for the ecosystem, whereas at a different time, a severe cold snap with very low temperatures becomes the limiting factor. The limiting factor is analogous to the weakest link in the chain, although at a given time one link may be the weakest and at another time in the life of the ecosystem, a different link can become the limiting factor.
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S. van Strien