What is Bergmann’s Rule?
The Bergmann’s rule states that the organisms at higher altitude should be larger and thicker than those present near the equator. For eg., the population of white-tailed deer is larger in Canada than Florida. This principle was named after a German Biologist, Karl Bergmann in the nineteenth century. Recent researches have indicated that turtles and salamanders also follow the 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 larger 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 to increase their surface area. 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 incredible.
Bergmann’s Rule Exceptions
The birds in California are an exception to Bergmann’s rule. The increasing population of birds contradicts the 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 change 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 with the concept “increase in size”
Also read: Human Evolution
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