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Key Highlights
- Bergmann’s Rule states that species and individuals of larger size are found in colder regions, while species of smaller size are found in warmer regions.
- The rule has been applied to female crocodilians, humans living near the poles and salamanders.
- The exception to Bergmann’s Rule is Birds of California.
- The rule specifies the relationship between surface area and volume in living organisms.
- Deep Sea Gigantism states that deep-sea species grow far larger than their shallow-water relatives.
Bergmann’s Rule is an ecogeographic rule stating that the body structure of organisms living at higher altitudes is larger and has a thicker coat than species living at lower altitudes.
- The rule is applicable to species and populations living near the equator.
- It is one of the important theories in the field of biological adaptation and evolution.
- Humans living near the poles, such as the Inuit, Aleut, and Sami, are some common examples of Bergmann’s Rule.
Key Terms: Bergmann’s Rule, Deep Sea Gigantism, Organisms, Species, Bergmann’s Rule Exceptions
What is Bergmann’s Rule?
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Bergmann’s rule is a generalised law derived after observing the patterns of living organisms. It says that organisms living at higher altitudes will have a thicker coat and be larger than those living near the equator.
- The theory was proposed by a German Biologist called Karl Bergmann in the 19th Century.
- His study was proved when it was discovered that turtles and salamanders follow the same rule.
- Bergmann’s rule states that an animal’s total surface area plays an important role in calculating the dissipation of heat.
- Thus indicating a relationship between surface area and volume in living organisms.
- The law assumes when heat is produced, the volume or capacity of the body to hold and produce heat is also considered.
- In higher altitudes or near the poles, the temperature is lower, and there are severe winters.
- Therefore, the larger bodies of the organisms help them have a thicker layer of heat and keep them warm.
- In regions near the equator, the temperature is warm and moderate.
- Therefore, organisms with smaller bodies can manage with less body heat.
- Other common examples of Bergmann’s rule include marine copepods and reptiles.
Bergamann’s Rule
Deep Sea Gigantism
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Deep Sea Gigantism states that animals living in greater depths of the sea are said to have larger body sizes as compared to living organisms living in shallower depths.
- The law is considered similar to Bergmann’s rule.
- Deep Sea Gigantism is also known as abyssal gigantism.
- According to Bergmann’s rule, the size of the creatures increases with a decrease in temperature and as one goes deeper into the sea.
- The explanation for deep Sea gigantism includes colder temperatures, food scarcity, and predation pressure.
- It also depends upon the increased oxygen concentrations in the deep sea.
- In deeper depths, organisms adapt to larger body sizes, while in shallower waters, due to warmer temperatures, there are small-sized organisms.
Deep Sea Gigantism ExampleFor example, the colossal squid is heavy and large because it has to manage its cold climatic conditions, which are 7,200 ft below. It has expanded cells due to its cold temperature, which increases its lifespan for survival. |
Bergmann’s Rule Exceptions
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Although proof and evidence have been found that assures the certainty of Bergmann's rule, there are some bewildering exceptions, too. The birds of California are the exception.
- The common reason suggested for this exception is global warming.
- In fact, it has been noted that the birds continue to decrease in size with the rise in global warming.
- Another strange phenomenon is that birds are getting heavier, and their wingspan has grown by 2-5% in the last four decades.
- Due to the change in the climatic conditions, birds have changed their diets.
- They are storing more fat in their tissues to stay warm.
- However, concrete evidence has yet to be found to prove the point.
Sample Questions
Ques. Is Bergmann’s rule applicable to humans? (2 marks)
Ans. The application of Bergmann’s rule has been widely found and accepted in humans. It has been noted that the people of colder regions have stocky bodies, like those of the Inuit places. The larger size contributes to saving heat while smaller and slender bodies, as seen in the Masai people of Kenya and Tanzania, contribute well in warmer climates.
Ques. What is Bergmann’s rule? (3 marks)
Ans. Bergmann’s rule states that the body size of the organism differs as per climatic conditions. Colder or regions of high altitudes or near the poles stimulate larger-sized organism survival for preventing heat dissipation while near the equator, organisms smaller-size are suitable.
- It means that animals with larger bodies will have larger surface area while animals with smaller bodies will have smaller surface area.
- Thus, the larger the surface area, the less heat will escape from their body and the smaller surface area, the more heat leaves.
- It happens because smaller bodies do not have large volume or high capacity of holding body heat while larger bodies have larger volumes to keep body heat from escaping.
Ques. What is Allen’s Rule? (2 marks)
Ans. The rule states that the length of the limbs of an organism also corresponds to the latitudinal conditions the organism resides in as well as the environmental temperature. It says that the animals living in the colder regions or in higher latitudes tend to have shorter limbs while the animals living in warmer regions near the equator have longer limbs.
Ques. What do you understand about Deep-sea gigantism? (2 marks)
Ans. The animals living in greater depths of the sea are said to have larger body size as compared to the living organisms on shallower depths. The deeper you go in the sea, the lower the temperature gets. Low temperature again gives rise to colder climate conditions. And now, the organism has to manage the dissipation of heat so as to stay warm.
Ques. Why do large-sized animals adapt well in colder regions? (2 marks)
Ans. In higher altitudes or near the poles, the temperature is less and there are severe winters. Therefore, the larger bodies of the organism will help them to have a thicker layer of heat and keep them warm.
Ques. How do the smaller size of an organism help them to survive near the equator? (2 marks)
Ans. In regions near the equator, the temperature is warm and moderate. Therefore, organisms with smaller bodies can manage with less body heat as their small bodies do not have the capacity of holding large amounts of heat.
Ques. Choose the correct option: (4 marks)
| A | B |
|---|---|
| I. Skin pigmentation |
| II. Metabolic rate |
| III. Size of extremities of body parts |
| IV. No. of Vertebrae of Codfish |
- 1-V, 2-III, 3-I, 4-IV
- 1-II, 2-III, 3-V, 4-I
- 1-I, 2-II, 3-III, 4-IV
- 1-IV, 2-V, 3-II, 4-III
Ans. The correction option is (A).
Explanation: The explanation is as follows:
- Bergmann’s rule states that the body size of the organism differs as per climatic conditions. Colder or regions of high altitudes or near the poles stimulate larger-sized organism survival for preventing heat dissipation while near the equator, organisms will smaller-size are suitable
- Allen’s rule states that the size of limbs or appendages also differs according to region and temperature drop. It says that the animals living in the colder regions or in higher latitudes tend to have shorter limbs while the animals living in warmer regions near the equator have longer limbs.
- Gloger’s rule states that the variation in the color of an animal is the result of its correlation to the broad-scale climatic gradient changes.
- Jordan’s rule states that as per the latitudinal conditions, the number of vertebrae differs (also known as Law of Vertebrae). Colder conditions call for a higher number of vertebrae as compared to fishes living in warmer conditions.
Ques. Does Bergmann’s rule apply to reptiles? (2 marks)
Ans: Bergmann’s rule does not completely align with reptiles. In reptiles like crocodiles, the resemblance of the rule has been found. However, the same cannot be concluded for lizards, turtles and snakes. The several studies conducted suggest that additional factors might be required to induce the law in them.
Ques. What is the difference between Bergmann’s rule and Allen’s rule? (3 marks)
Ans. The difference between Bergmann’s rule and Allen’s rule are as follows:
| Bergmann’s rule | Allen’s rule |
|---|---|
| Bergmann’s rule focuses on body size with respect to climate. | Allen’s rule delves into how the shape of specific body parts adapt to climate. |
| It addresses overall body size as a thermoregulatory adaptation. | It focuses on how specific body part shapes contribute to this process. |
| Within a species, larger individuals tend to inhabit colder environments. | It says that the animals living in the colder regions or in higher latitudes tend to have shorter limbs. |
Ques. What are the limitations of Bergmann's rule? (3 marks)
Ans. The limitations of Bergmann's rule are as follows:
- The rule primarily applies to terrestrial endotherms (warm-blooded animals) and may not hold true for all species or environments.
- Bergmann's rule is often best observed within a single species across a broad geographic range with significant temperature variations.
- Factors like developmental constraints or resource limitations during an animal's growth phase can influence body size, complicating the direct relationship with temperature.
- Applying Bergmann's rule to the fossil record can be challenging as reconstructing body size from fossils can be imprecise.
Ques. How does Bergmann's rule is related to energy efficiency in animals? (3 marks)
Ans. Bergmann's rule suggests that larger individuals are found in colder climates. This larger body size translates to a lower surface area-to-volume ratio. Larger animals conserve energy in colder climates by minimizing heat loss through a smaller surface area relative to their volume. This saved energy can be used for other vital functions like foraging for food, reproduction, or escaping predators. Polar bears have a much lower surface area-to-volume ratio, which makes them able to retain heat efficiently in the frigid Arctic environment.
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