Paper: Wan, X., Jiang, G., Yan, C., He, F., Wen, R., Gu, J., … & Zhang, Z. (2019). Historical records reveal the distinctive associations of human disturbance and extreme climate change with local extinction of mammals. Proceedings of the National Academy of Sciences, 116(38), 19001-19008. https://doi.org/10.1073/pnas.1818019116
Above: Giant pandas in China. Source: Wikipedia.
You’re an animal.
Every single one of you reading this, all of you are animals.
Though it’s become a common insult, it’s actually scientific fact (and at least here, certainly not meant to be rude).
We – Homo sapiens, human beings, people – are animals. We’re like other animals in many ways, but very different in significant ways. One of the major differences is how we interact with, use, and change the natural environment around us. Many of these processes are seemingly beneficial, at least for our species (or specific type) of animal. An example of this is farming, which provides mankind with a relatively stable supply of nutritious food. Another example is industrialization, which has lifted millions of people out of poverty, yielded countless improvements in technology and living standards, and has basically led to the world of today – and is taking us to the world of tomorrow.
For all their benefits to mankind, farming and industrialization have also irreversibly altered the natural world. Climate change (a result of industrialization and related pollution) and increased farming have contributed to drastic changes in animal habitats, populations, and ecosystems in today’s world.
But is this a recent phenomenon?
Apparently not. Recent research shows that it has been going on for at least three thousand years.
In a paper recently published in the Proceedings of the National Academy of Sciences (PNAS), researchers from China looked at historical accounts of animal populations from 905 BC to the present day to estimate extinction probabilities of 11 species of mammals found in China.
The researchers used multiple historical sources including a compendium of populations of animal species throughout the last three thousand years. They also looked at historical temperature data along with information on human population densities and cropland usage in the areas for which animal population data was available.
The results shown below, are striking.
In Figure 1 above, each colored line represents one of the 11 animal species in the study (top right), in all the areas in China for which that species’ population data was available. Graph A shows the survival rate for each of these species from about 1000 BC to 2006, and the inset is zoomed in on the time period from 1644 to 2006. The survival rate dropped drastically for all species, especially from 1644 to 2006. In other words, fewer and fewer of each species of animal survived, overall.
Graph B shows the percentage of cropland (areas in which humans were farming) around each species’ total areas of population increased, as did human population density (Graph C). As cropland increased and population density increased in the animal species’ habitat areas, animal extinction increased.
Figure 3 from the article (below) shows these trends more clearly. The graphs to the left (Figures A and C) focus on the time period from 1644 to 1911 (the premodern period of China), and the graphs to the right (Figures B and D) focus on the period from 1911 to 2006 (the modern period).
In both periods, as human population density increased, animal extinction probabilities increased also. However, the premodern period saw a long period of cooling temperatures. As shown in Figure C, the cooling temperatures coincided with lower animal extinction probabilities. In the modern era, temperatures rose (Figure D), and animal extinction probabilities increased drastically.
The lone exception was the panda, which was and remains the focus of extensive and continuing government-funded conservation programs.
Takeaways: With three thousand years of data at hand, researchers were able to show the effects of increased human population density, increased cropland areas, and temperature fluctuations over a long period of time in the same given areas. Lower temperatures led correlated with lower animal extinction, while increased human population density, increased cropland and rising temperatures correlated with higher animal extinction. Unfortunately, all three of these factors are on a steady rise in the current era, and if the patters seen here hold true, animal extinctions will also mirror that rise.