Are rats getting smaller, is it related to climate change and urbanization?

BEIJING, June 5 ( Xinhua) — According tomedia reports, according to a well-documented but controversial principle, Bergmann’s Law, species in cold climates will be larger and larger, but in warmer climates will be smaller and smaller, due to modern human activities caused by global warming, will it lead to mammals becoming smaller and smaller?

A new study published recently in the journal Scientific Reports analyzes the survival records of North American deer rats, one of the most common mammals in the United States, and the most detailed and complete rodent in the collection and survey of north American museum samples.

Surprisingly, the researchers found that the deer population has gradually smaller over time over time, but the trend may not be related to changes in climate or population density, an important indicator of urbanization. Another surprising finding suggests that in recent years, larger species of deer and rat have become smaller, while smaller species of deer and mouse have become larger and larger.

“The most exciting thing about this study is that it’s still a mystery – deer rats seem to be getting smaller and smaller over time, but it doesn’t seem to be directly linked to climate change and urbanization, and do other mammals do it?” said study co-author Robert Guralnick, curator of bioinformation at the Florida Museum of Natural History. “

Are rats getting smaller, is it related to climate change and urbanization?

The researchers combined museum data with historical observations from the Neon National Ecological Observation Network to obtain a comprehensive and detailed data set.

Why study animal body size trends? Body size is a particularly important physiological feature for warm-blooded animals because it helps maintain proper body temperature and ensures biological functions such as metabolism and heat transfer.

Study co-author Bryan McLean, an assistant professor at the University of North Carolina at Greensboro, said: “Even small mammals like deer mice have a significant impact on the optimization of their fitness balance. “

Relative to body size, larger animals release less heat than small animals, so they are more adaptable to cold climates than smaller animals, which is the thermodynamic basis of Bergman’s law, because body size affects body temperature regulation, so changes in body size can affect the animal’s ability to adapt to climate change.

To study the relationship between deer and mouse size and space, time, climate and population density, Guralnik and colleagues obtained data resources from three institutions: museum samples, the North American Census library for small mammals, and the Neon National Ecological Observation Network. Based on this information, they used thousands of researchers in the United States to analyze data on the size and quality of deer rats measured over the past 70 years. They call the data a “time machine” for insight into the history of deer rats in recent years, and the detailed data provide insight into many of the changes that have taken place in deer mice, and the first study of mammalian body size trends combined with published survey data and museum-collected data.

“I don’t think anyone can combine museum data with historical observations from the Neon National Ecological Observation Network like we do, and we now have a comprehensive and detailed data set, which is a very novel and exotic way to see how size changes over time and space,” Guralnik said. “

The results showed that deer rats living in cold climates tended to have longer bodies and larger surface areas, which is consistent with Bergman’s law. As ambient temperatures change, the deer mice gradually lose weight, which is also in line with the researchers’ guesses that as rainfall increases, the deer mice gain weight because the increase in rainfall increases the foraging resources, but they lose weight.

Are rats getting smaller, is it related to climate change and urbanization?

The researchers analyzed the size records of deer rats from 1945 to 2015 and marked them with colored dots for 10 years.

Studies have shown that deer rats living in urban environments are more complex: urban areas are significantly warmer than rural suburbs, a phenomenon known as the urban heat island effect. According to Bergman’s law, deer and mice living in cities should be smaller in size, thus acting as a summer escape. But because human food and garbage are abundant in cities, deer rats can grow larger by taking advantage of this constant supply of food.

The data suggest that as population density increases, deer-mouse populations tend to be constant in weight and smaller, which may mean that the urban heat island effect outweighs the benefits of the city’s abundant food resources, or simply that deer rats with smaller sizes are more likely to avoid humans.

To the researchers’ bewilderment, if the weight of mice were separated from these factors, they would notice that their general weight loss over time meant that the role of climate and urbanization in affecting the size of deer mice may be more complex.

“Initially, this is a very interesting experiment, but so far we still don’t know what causes the deer mice to lose weight, and the next step the team turned its attention to analyzing the body size of all mammals,” Guralnik said. How will the size of the Earth’s mammals change in the future? The best way for us to see this is to look at historical data. Data from museums and other institutions provide us with a comprehensive and detailed understanding of deer rats, and body size is a very important variable, with millions of historical specimens directly reflecting the changes in this data. (Ye Ding Cheng)

Are rats getting smaller, is it related to climate change and urbanization?