If you’ve ever noticed that some animals seem to be everywhere—like squirrels—while others, like raccoons or foxes, are much harder to find, you’re not alone. Scientists have been puzzled by this pattern for nearly a century.
Now, researchers at the University of Virginia believe they’ve found the answer—and it turns out this rule applies not just to animals, but also to plants, bacteria, and even cars.
In nearly every ecosystem, a few species are very common, while most are rare. This uneven pattern is known as the species-abundance distribution. Scientists have long tried to create a model to explain it.
Now, a team led by biology professor Martin Wu, along with graduate students Yingnan Gao and Ahmed Abdullah, has identified a model called the “powerbend distribution” that works across all forms of life—from towering trees to microscopic bacteria.
Their research, recently published in Nature Communications, analyzed more than 30,000 datasets, including information on trees in U.S. forests and bacteria in the human gut.
For example, in Virginia’s forests—some of the most diverse in the country—just five species, including red maple and loblolly pine, make up almost half of the state’s 10.6 billion trees. The remaining half consists of more than 120 different tree species.
The pattern the team found is similar to the Pareto Principle, also known as the 80/20 rule. Just like how 20% of the population holds 80% of the wealth, a small number of species dominate most ecosystems.
This discovery has big implications. Not only does it help explain patterns in nature, but it can also improve biodiversity conservation.
Scientists can now make educated guesses about how many species are in a sample without counting every single one.
For instance, using DNA sequencing, a researcher can analyze a gram of soil and estimate how many types of bacteria are in it—even if they can’t grow most of them in a lab.
Before 2008, it was extremely hard to study microbes because they couldn’t be seen or grown easily. But new DNA sequencing technology changed everything, leading to a flood of new data. Wu and his team applied their model to this microbial world and confirmed that microbes follow the same abundance rules as plants and animals.
Wu hopes this model can also help people understand broader patterns in the world around them. Whether it’s tree species in a forest, microbes in our gut, or even the most common car brands in your city, the same rule applies: a few types dominate, and many others appear only once in a while.
