TOLERANCE
Specific Objectives:
The students should at the end of these lessons be able to:
1. Define tolerance
2. State the importance of tolerance to
conservation of the ecosystem
3. State the Shelford’s Law of Tolerance
and apply it to survival of organisms.
4. Draw a profile to show the various
tolerance zones and concepts in a habitat.
WHAT IS TOLERANCE
Tolerance is the ability of an organism to withstand little unfavourable
changes in the environment which affects their survival. Living organisms
can only be in a particular environment if they can tolerate the ranges of
abiotic factors that operate there. Due to changes in environmental
conditions, some of these factors are unfvourable. Too little or too much
of such factors such as light, heat, cold, acidity, etc may affect the survival
of organisms. In 1840, a German scientist named Justus Liebig highlighted
the importance of single factors in his “LAW OF THE MINIMUM”. The law
state that “the growth of a pant will be limited by whichever requisite factor
is most efficient in a local environment”.
V.E. Shelford in 1913 expanded this law to embrace animals. He recognized
the fact that too much of anything may be as bad as too little. Hence his
law is called The Shelford’s Law of Tolerance. It states that the
distribution of specie will be limited by the environmental factors for which
the organism has the narrowest range of adaptability. Since organisms can
only live within certain minimum and maximum limits for each abiotic
factor. The range between the maximum and minimum limit is known as
tolerance range for that factor. Example, most animals have a minimum
range 0oc and maximum limit of 42oc. The tolerance
range is therefore 0oc – 42oc.
Hence tolerance range is defined as the range between the minimum and maximum
limits to which organisms can tolerate certain changes in their environment so
as to survive.
Beyond the tolerance range, death occurs. 0oc here is the
lower limit/lethal temperature while 42oc is the upper lethal
temperature.
Within the tolerance range is the optimum range where there is maximum survival
rate of organisms. A zone of physiological stress where growth and
reproduction falls (organisms struggle to survive) and an intolerance
where organism are absent.
One factor may affect the tolerance ranges of other factors e.g. when the O2 level
of water is low, lobsters can tolerate temperature up to 29oc, but
at higher oxygen level they can tolerate temperature up to 32oc.
GEOGRAPHICAL RANGE
A space can
only be found in areas that are within their maximum and minimum range of
abiotic factor or tolerance such areas are called Geographical range of that
organism.
Abiotic factors are responsible for the geographical of any organism. The
geographical range of the rain frost is within the equator as a result of high
rainfall and temperature whereas the northern and southern poles have no
tropical rainforest due to absence of rainfall.
The biomes of the world are due to the tolerance ranges of various types of
plant species. Hence the v analion in abiotic factors are
responsible for the geographical range of a specie.
CD
3: SUMMARY/TEST
The teacher
summarizes by saying that the management of our ecosystem is essential for the
maintenance of balance and hence enhance the survival of organisms within their
geographical ranges of survival.
Certain concepts like:
- Tolerance
- Tolerance
Range
- Geographical
Range
- Optimum
Range
- Biological
Associations
- Symbiosis
- Commensalism
- Parasitism
- Eutrophication, etc.
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