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'Rules' in Ecology- Allen’s rule, Bergman’s rule, Gause's Hypothesis, Gloger’s rule, Jordon’s rule, Gordu’s rule, Rensch’s rule, and Yoda’s Law

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

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)

Fig1: Paramecium caudatum (1) and Paramecium aurelia (2)
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.
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

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