What is Bergmann’s Rule: If we notice carefully we will find that shape, size and other morphological features of different animals greatly vary with the effect of environmental conditions. Ecogeographical rules are formulated by different scientists which say that ecological distribution, size, shape, color are greatly depending on the geographical regions where they live.
Bergmann’s rule is also an ecogeographical rule which says that the size of animals are influenced by the environmental temperature and the body size decreases which increases in temperature while with decrease in temperature the body size increases.
So according to bergmann’s rule the size of a member will be larger at polar cold region while in equator region where the temperature is much higher than the temperature of polar regions will have smaller size of the same species animals.
So only temperature controls the size of animals of the same species in different geographical regions and it is regulated by the ecogeographical rule Bergmann’s rule which explains why animals of the same species vary in size with different geographical regions.
For example, as in case of turtles, salamanders are much larger in cold regions while their size is much smaller in high temperature regions and this pattern was first observed by German biologist Karl Bergmann so this pattern is known as Bergmann’s rule and is also applicable to other animals as well as humans.
Now if we want to know the scientific logic behind this rule why the size increases with decreasing temperature then we have to know about basic thermodynamics in living organisms. Animals who can keep their body temperature constant in varying external temperatures have the main factors: surface area of their body and volume of their body.
Now the animals take food and some energy they get from the food is used to produce heat to maintain their body temperature so more the size of animals more is the tissues volume so more heat production. But the surface area determines the heat radiation from their body to the environment and the more the surface area the more the loss of heat through their body surface.
In colder region heat production must be higher as compared to heat loss so their surface area to volume ratio should be adapted for conservation of body temperature which occurs in case of larger body size in colder region while in warmer region the smaller size ensure such surface area to volume ratio so that head radiation occurs more than heat production.
Explanation of Deep Sea Gigantism:
The animals that live in the deep sea show gigantism where the sunlight is not able to reach so the temperature is very low so it is due to conservation of heat energy because according to Bergmann’s rule size of the body is much larger in colder regions.
If we notice carefully the fish present in deep sea have very large body size as compared to the fishes present in shallow water where the temperature is much higher than deep sea is also an example of Bergmann’s rule.
Bergmann’s rule is also applicable for human beings where the human in colder regions show larger body structure while size decreases with the increase in temperature as in the case of equator the size of human is much smaller so we can explain the gigantism in colder region by Bergmann’s rule.
Exception of Bergmann’s Rule:
Birds in California are an exception to Bergmann’s rule because they show an increase in their size and body weight with increasing temperature due to global warming which is against Bergmann’s rule but the reason is unknown to scientists why the size increases in the case of California birds with increasing temperature.
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