Bergmann’s Rule

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What is Bergmann’s Rule?

Bergmann’s rule states that organisms at higher altitudes should be larger and thicker than those present near the equator. For eg., the population of white-tailed deer is larger in Canada than in Florida. This principle was named after a German Biologist, Karl Bergmann in the nineteenth century. Recent research has indicated that turtles and salamanders also follow Bergmann’s rule.

Bergmann assumed that the surface area of an animal determines the rate of heat dissipation, and the heat production is determined by the volume. Larger animals have a smaller surface area to volume ratio than the smaller animals and therefore they radiate less heat. Thus, they are able to keep themselves warm in a colder climate. The small insects and tapeworms do not require lungs due to their larger surface-to-volume ratio. Larger animals require certain systems to carry food and oxygen from the surface to the interiors.

Also read: Adaptation

Deep Sea Gigantism

The organisms that are present deeper in the sea are larger in size than those present in shallow water. The abnormal increase in the size of the deep-sea dwellers can be explained with the help of Bergmann’s rule. According to Bergmann’s rule, the size of the sea creatures increases with the decrease in temperature. The larger sea animals are found in colder areas than the smaller animals. The low temperatures lead to an increase in the size of their cell and their lifespan. For eg., colossal squid lives 7,200 feet below the sea. At such a depth, it is able to increase in weight and height incredibly.

Bergmann’s Rule Exceptions

The birds in California are an exception to Bergmann’s rule. The increasing size of birds contradicts Bergmann’s rule which states that larger animals survive in colder regions or higher altitudes. The birds of the same genus are found smaller in size in warmer climates. So, the birds in California must be getting smaller in size as a result of global warming. However, according to recent research, birds in California have increased in weight and wingspan from 2-5 per cent over the last 40 years.

It was believed that the birds are storing more fat in their tissues to protect themselves from cold. Thus, the larger birds are being naturally selected by the environment, thereby, increasing their number. Also, the diet of the birds has changed due to changes in the climate. They would not find the same insects they fed on when in the warmer climate. This might have increased the body weight of the birds. However, scientists are still not clear about the concept of “increase in size”

Also read: Human Evolution

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Frequently Asked Questions

What do you understand by Bergmann’s rule?

Bergmann’s rule is an ecogeographical rule which states that organisms with larger sizes are found in colder altitudes while those with smaller sizes are found in warmer regions.

Does Bergmann’s rule apply to humans?

It is widely accepted that humans fit Bergmann’s rule. The rule states that the size of the body decreases with the increase in temperature. Thus, we can say that humans follow Bergmann’s rule only when there are differences in temperature and latitude.

What is Allen’s rule?

Allen’s rule is an ecogeographical rule which states that the limbs, ears and other appendages of animals living in colder climates are shorter than the animals of the same species living in warmer regions.

How are the animals with a large size adapted to a colder climate?

Large animals have a smaller surface area to volume ratio that helps to reduce heat loss. This keeps their body warm and helps them to survive in colder regions.

How is a smaller body size advantage to the animals in warmer regions?

Smaller animals have a higher surface area to volume ratio that helps them to lose heat quickly and cools down the body faster. This enables them to adapt to warmer regions.

What is deep sea gigantism?

The organism present deep in the seas is larger than the animals found in shallow water. This is according to Bergmann’s rule which states that the size of the animals increases with the decrease in temperature. The temperature in the deep sea is lower than the shallow water.

 

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