Introduction
When an organism adapts its physical and behavioral characteristics as per its surrounding environment in order to survive better is known as ‘adaptation’. Living organisms always try to adapt to their habitat as they have special features, which arise as a result of evolution. Evolution is a slow process that brings inheritable changes in the population and aids in survival and reproduction. It results due to gene mutation. One example of such adaptation is named ‘Bergmann’s Rule’, which was given by a German biologist ‘Karl Bergman’ in the 19th century.
What is Bergmann's Rule?
Bergmann's rule tells us that the animals or organisms residing at a higher altitude should be larger and have a thicker coat than those that are living at lower altitudes and found close to the equator. Let's say, for example, in Canada, you will find a lot more white-tailed deer than you will find in Florida, this is because of its altitude and climate. This rule that was proposed is known as Bergmann's law in the 19th century because of Karl Bergmann, a German Biologist. The latest study also reports that turtles and salamanders also live by Bergmann's rule.
Bergmann Rule Ecology
Bergmann said that the total surface area of an animal's body plays a major role in the dissipation of heat, and in producing heat, the volume is considered The animals which are large usually have a larger surface area than compared to the smaller animals who obviously have a smaller surface area. This larger surface area prevents the larger animals from emitting a lot of heat into the environment and out of its body and, therefore, does a good job in keeping them warm and cozy during the winters. There are some species like insects and tapeworms who do not require lungs to expand their surface area. Whereas, the larger animals need specific body functions to transport food and oxygen from the exterior to the insides.
Deep-Sea Gigantism
According to deep-sea gigantism, the animals and organisms found residing in the depths of the sea are larger in size when compared to the ones found in the surface water. This increment found in the sizes of the organisms residing in the deep seas can be elucidated with the help of Bergmann's rule. As per Bergmann's rule, as there is a drop in the temperature, there is an increment in the size of the animals. The cold climatic conditions give rise to the expanded cells that make them up and also their lifespan. Let's take, for example, the colossal squid. It resides 7,200 below the sea. Due to the depth of the sea, the squid is capable of being large in weight and height.
Bergmann's Rule Exceptions
The birds residing in California are excluded from Bergmann's rule. The large population of birds found in California is quite the opposite of what Bergmann's rule states and contradicts it. The rule states that animals found in colder climates and higher altitudes are larger in size and have a large surface area; however, these birds are small. The birds in California, therefore, must be assumed are decreasing in size due to the increasing global warming. However, studies show us that the birds found in California are expanding in weight and have an increased wingspan from 2% to 5% in the time span of 40 years.
It was also claimed that these birds, to protect themselves from the cold weather, are now storing more fat in their tissues. Naturally, larger birds suited best for the climatic conditions and the cold environment are being chosen and are, therefore, is found in larger numbers now. Due to the variations in the climatic conditions, these birds have started to change their diets. No longer do they feed on the same insects and worms that they would once feed on. These birds change their feeding habits according to how warm or cold the climate is. Therefore, the birds residing in the colder climatic regions would not feed on the same insects as the birds in the warmer climatic regions. This could have resulted in a significant increase in the mass of the bird's body. However, the concept pertaining to the increase in sizes in birds is still not clear even amongst scientists.
Conclusion
Bergmann’s rule is one of the popular generalizations in zoology, which states that size of animals tend to increase with increase in latitude and decrease in temperature. We discuss examples of animals that follow this rule and some of the exceptions as well.
FAQs on Bergmann's Rule - Ecology and Exceptions
1. Describe the Most Important Facts about Bergmann's Rule
Some of the important facts about Bergmann’s Rule are-
In 1973, German zoologist and ecologist Richard Hesse stated an addition to Bergman's rule. This rule by Hesse is known as the heart-weight rule. This states that those animals who are residing in the colder climates have bigger hearts as compared with their body weight than animals belonging to the same species residing in the lower altitudes and warmer climates.
In 1986, Valerius Geist stated that Bergmann's rule was incorrectly proposed and the correlation with temperature is absolutely incorrect. He stated that body size is directly proportional to the time period of the annual productivity pulse, or the availability of food for an animal during the season.
On the other hand, there are many species that contradict the Bergmann's rule, the largest vascular plants, for example, as well as the largest individuals of many invertebrate species, are found to be residing in lower altitudes and locations with a warm climate and regions that are closer to the equator (that is, tropical regions).
2. Does Bergmann's Rule Apply to Humans as Well as Reptiles?
There is a wide acceptance that present-day human species conforms to Bergmann's rule that describes that with a decrease in temperature, the size of the body in endothermic species will increase. It is usually seen that people residing close to the poles like the Inuit region, Aleut and Sami population, are usually heavier than the human population residing in the lower altitudes. Especially the Native Americans are found to be in sync with Bergmann's rule. But when it comes to reptiles, Bergmann's rule seems to be in sync with reptiles like crocodiles. However, the same case has not been found in lizards and turtles.
3. What is meant by ‘deep-sea gigantism’?
It means that the organisms found in greater depths are larger than those found on the surface. This is according to Bergmann's rule because temperature tends to decrease with increase in depth. And as Bergmann’s rule says that size of the organism increases with decrease in temperature, deep-sea gigantism completely follows the rule.
