Why are urban animals getting bigger?

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Why are urban animals getting bigger?
Why are urban animals getting bigger?
Anonim

Scientists will never be able to accurately answer how many cities there are on our planet. The fact is that "city" is a rather abstract concept and different numbers are indicated in each source. But what scientists know for sure is that large settlements strongly influence flora and fauna. Usually the air temperature in cities is much higher than in the wild. This is due to the dense arrangement of buildings, heating of asphalt and houses, as well as a host of other factors. Previously, it was believed that animals living in warm cities are much smaller in size than their wild relatives. But recently, scientists from the American state of Florida found that urban animals, on the contrary, are much larger than wild animals. And they have a very logical explanation for this.

What is Bergman's Rule?

In 1847, the German biologist Karl Bergman described a very interesting scientific observation. He noticed that animals living in warm regions of our planet are always smaller in size than their counterparts from cold regions. This phenomenon is due to the fact that small body size allows animals to cool faster in case of heat, and large animals keep warm longer in the cold.

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Brown bears are always smaller than polar bears

The so-called Bergman rule is indeed very often observed in nature. For example, the Amur tigers living in rather cold regions are always larger than the thermophilic Sumatran tigers. Also, nature lovers probably know that the wolves living in the North are larger in size than their southern counterparts. Finally, remember the hummingbirds - the smallest birds in the world. This rule is also quite applicable to them, because the dimensions of their bodies fluctuate within only 5-22 centimeters, which provides them with the best heat transfer. But they live in very warm places: South, Central and North America.

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Amur tiger

But with all this, Bergman's rule was often questioned. For example, some skeptics draw attention to the fact that many other factors often affect the size of animals. In addition, evolution does not always adjust animals to ambient temperature by decreasing or increasing body size. Most often, changes concern internal organs - usually nature increases the size of the heart and lungs. Scientists recently discovered another factor that affects the size of animals.

How does evolution help animals?

Florida researchers conducted a study and published the results in the scientific journal Communications Biology. As part of the scientific work, scientists have studied information about the length and body weight of 140,500 animals, which has been collected over the past 80 years. It was found that despite the high temperature, urban animals often grow larger than their wild counterparts. Scientists explained this phenomenon by the fact that urban animals have access to more food than animals living in forests. Feeding on leftovers from garbage cans, they quickly gain weight and eventually become very large creatures.

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It is really easier for animals to get food in the city. I recently talked about how parrots steal food from garbage cans.

But at the same time, the authors of the scientific work noted that some animals in warm cities still decrease in mass. This is especially noticeable in animals that hibernate in winter. Scientists did not give specific examples, but hedgehogs, which occasionally still appear in urban areas, in particular, in various parks, can be attributed to such animals. Before winter, they actively accumulate subcutaneous fat, and then hibernate inside abandoned burrows or between tree roots. Some hedgehogs sleep for six months, starting from the first frost and ending in April. Perhaps during hibernation, they become more sensitive to changes in air temperature and decrease in size, because the fat warms them so well.

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