[Biology Class Notes] on Bergmann’s Rule Pdf

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.