Ecology is the study of the interactions between organisms and
their environment. In this science, a number of concepts were proposed by
different ecologists to explain simple truths that actually determine the
interaction between organisms and their environment. Here we would like to
share some major concepts that put forward as a result of close observation of
environment and the impact of environment on organisms thriving there.
Allen’s
rule
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In endothermic animals from cold climates tend to have shorter
ears, tail & leg in colder parts than in the warmer parts; thus reducing
their surface: volume ratio.
Bergman’s rule
Effect of temperature on the absolute size of an animal. The birds
& mammals of colder areas are larger in size as compared to their
equivalents in warmer area, again to reduce their surface area: volume ratio.
There is some evidence to support Bergmann's Rule: polar bears, for example, are much larger than spectacled bears, which live
closer to the equator, and a number of animals do develop size variation both
within species and in closely related species which can be correlated to
geographic location.
Bergmann's Rule has also been used to explain the
typically heavier body types of people from Arctic regions when compared to
equatorial peoples.
e.g : 1m long penguin in Antartica & 0.5m long in Galapagos
island
Gause's Hypothesis/ Exclusion Principle
The competitive exclusion principle says that if two
species have almost completely overlapping niches they cannot continue to
coexist. One of the two species will outcompete the other and persist. The
other will go locally extinct. The classic experiments were by Gause using two
species of Paramecium (Fig1). Paramecium caudatum and Paramecium
aurelia.When cultured separately in yeast medium. P aurelia was found to have faster rate of
increase than P caudatum.
When both species were added to the same culture vessel. P aurelia dominated the mixture and eventually P caudatum died out.(Fig:2)
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| Fig1: Paramecium caudatum (1) and Paramecium aurelia (2) |
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| Fig 2: Competitive exclusion of one species of the Paramecium caudatum by another (Paramecium aurelia) |
Gloger’s rule
In warm, humid climates animals bear dark pigmentation than
those found in cool & dry climates.Influence of temperature on the absolute
size of an organism.Formative of narrow wings in colder regions & boarder
wings in warmer regions.
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| The Song Sparrow (Melospiza melodia) generally follows Gloger's rule of ecogeographic variation whereby birds that live in more humid environments tend to be more heavily pigmented |
Gordu’s rule
Influence of temperature on the morphology of animals.
Jordon’s rule
Temperature also influences the morphology of certain fishes and
is found to have some relation with the number of vertebrae. Fishes inhabiting
water of low temperature tend to have more vertebrae than those of warmer
water.
Fish size as well as number of vertebrae increase in colder areas
compared to warmer areas.
Lindeman's Law of Trophic Efficiency
While transferring organic food
from one trophic level to the next about 10% of the organic matter is stored as
flesh, the remaining is lost during transfer or broken down in respiration.
Liebig’s law of minimum (1840)
The growth & reproduction of plants & hence productivity
of soil is limited by an essential nutrient that becomes deficient or
critically minimum in relation to its requirement.
Law of limiting factor (Blackman, 1905)
When a process is conditioned as to its rapidity by a number of separate
factors, the rate of the process is limited by pace of its slowest factor.
Shelford’s Law of tolerance
The abundance & distribution of organisms is controlled by any
of the ecological factor below its critical minimum & above its critical
maximum. Critical minimum &critical maximum values of an environmental
factor influencing organisms are called limits of tolerance.
Rensch’s rule
Narrow & acuminate wings of birds in the colder regions than
broader wings in the warmer regions.
Yoda’s Law / self-thinning rule/ 3/2 power rule
Sessile organisms ,including plants cannot escape
competition by movement, and therefore the losers in the competition battle
die. In a group of plants of the same age, this results in fewer individuals of
larger size surviving.This is known as 'self-thinning'.This
results in a relationship between density and individual plant mass, which
typically has a slope of -3/2 on a log plot.This relationship is known as
Yoda's -3/2 law.
Log w = -3/2 (log N) + log c
( w = mean plant weight, N = plant density, c = constant)
w = cN3/2
Tags:
Allen’s rule
Bergman’s rule
Ecology Notes
Gause's Hypothesis
Gloger’s rule
Gordu’s rule
Jordon’s rule
Rensch’s rule
Rules' in Ecology
Yoda’s Law