Scientists have revealed a consistent pattern of how many species are common and how many are rare on Earth, using over a billion observations of biodiversity. The study, published in Nature Ecology and Evolution, sheds light on one of the most fundamental questions in ecology and evolution: why some species are more abundant than others.
The Global Species Abundance Distribution
The global species abundance distribution (gSAD) is a concept that describes how many species have a certain level of commonness or rarity across the planet. For example, a gSAD could show that most species are moderately common, while only a few are very rare or very abundant. Understanding the gSAD can help scientists explain the patterns and processes of biodiversity, such as how species adapt to different environments, how they interact with each other, and how they respond to human impacts.
However, the true shape of the gSAD has been elusive for over a century, since Charles Darwin first posed the question of why some species are more numerous and widespread than others in his book “The Origin of Species”. Different models have been proposed to explain the gSAD, but they often rely on assumptions or limited data that may not reflect the reality of nature.
A Massive Data Analysis
To solve this problem, an international team of researchers led by the German Centre for Integrative Biodiversity Research (iDiv), the Martin Luther University Halle-Wittenberg (MLU), and the University of Florida (UF) used data from the Global Biodiversity Information Facility (GBIF), which collects and shares biodiversity data from professional and citizen scientists all over the world. The researchers downloaded over a billion records of species observations in nature from 1900 to 2019, covering more than 31,000 species from 14 major groups, such as birds, mammals, insects, plants, and fungi.
The researchers then analyzed the data using a novel statistical approach that accounts for various sources of uncertainty and bias, such as sampling effort, geographic coverage, taxonomic resolution, and data quality. They also compared the results with two competing models of the gSAD: the log-series model, which predicts that most species are very rare and only a few are common; and the log-normal model, which predicts that most species have some intermediate level of commonness and only a few are very rare or very abundant.
A Consistent Pattern Across Species Groups
The results showed that for some well-monitored groups, such as birds and mammals, the gSAD follows a log-normal shape, meaning that most species are neither very rare nor very common. For other groups, such as insects and plants, the gSAD is more uncertain, but still suggests that most species are not extremely rare. The researchers also found that the shape of the gSAD varies depending on the spatial scale and taxonomic level of analysis, but it remains consistent across different regions and time periods.
The study demonstrates that the gSAD is a robust and universal pattern of biodiversity that can be revealed by large-scale data analysis. It also highlights the importance of biodiversity monitoring and data sharing for understanding the distribution and dynamics of life on Earth. The researchers hope that their findings will inspire further research on the causes and consequences of species abundance, as well as inform conservation strategies for rare and threatened species.
