Ecology …………………………………………………………. Lecture (9-10)
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ECOLOGY
Lecture (9-10).
Limiting factor
In biology, a limiting factor is a resource or environmental condition
that limits the growth, abundance, or distribution of an organism or a
population of organisms in an ecosystem.
Low of Limiting factor
1. Liebig's Law of minimum: states that growth is controlled not by the
total amount of resources available, but by the scarcest resource.
2. law of tolerance by EV.E.Shelford in 191: Not only may too little of
something be a limiting factor, as proposed by liebig but also too much
as in the case of such factors as heat light and water.
Some principles to the law of tolerance may be stated as follows:
1. organisms may have a wide range of tolerance for one factor and a
narrow range for another.
2. organisms with wide ranges of tolerance for all factors are likely to
be most widely distributed.
3. when conditions are not optimum for a species with respect to one
ecological factor the limits of tolerance may be reduced for other
ecological factor the limits of tolerance may be reduced for other
ecological factor, for example when soil nitrogen is limiting the
resistance of grass to drought is reduced.in other words more water
was required to prevent nitrogen levels than at high levels.
4. organisms in nature are not actually living at the optimum range of
particular physical factor.
5. the limits of tolerance for reproductive individuals seeds eggs
embryos seedlings and larvae are usually narrower than for non-
reproducing adult plants or animals.
For the relative degree of tolerance a series of terms have come in to
general use in ecology that use of the prefixes STENO , meaning narrow
EURY , meaning wide.
Light, temperature and water(rainfall) are ecological factors on land.
Light, temperature ,and salinity are the important ones in the sea and
oxygen may be major importance in fresh water.
Physical factors
1. light and light penetration
Photic zone: depth to which light is penetrates zone of
photosynthesis and primary production.
