This massive study, led by Dr. John J. Wiens, a University of Arizona professor and Dr. Daniel Moen, an assistant professor at the University of California Riverside, is the first of its kind. Their research provides some new context for the longstanding question of how species diversity develops. Their detailed analysis provides greater insight into how species richness and diversification rates are allocated across various clades. In particular, they found that most described species are concentrated in a small subset of groups that underwent lightning-fast explosive diversification. This study covered nearly 17,000 kingdoms and 2,545 families, totaling more than two million species.
Their massive computation tackled 10 phyla, 140 orders and 678 families of the land plant tree of life. Combined, these groups account for over 300,000 described species. The resulting data set involves 31 unique orders and 870 families of insects, which account for well over one million known species. It includes 12 classes of vertebrates, representing over 66,000 species. The team explored 28 phyla and 1,710 families of terrestrial animals, which encompass more than 1.5 million described species. The researchers identified about 10,000 previously known species of bacteria. According to estimates, that number may be in the millions or possibly trillions.
Rapid Radiations Explained
Overall, the study reinforces the idea that protective rad explosions of species are most common when new slots in the ecological hierarchy are opened up. Though perfect examples of rapid radiations are rare, Dr. Wiens noted that well-documented cases provide powerful evidence. He highlighted the diversification of Darwin’s finches and the origin of bats 50 million years ago as key examples.
“Here we show for the first time that most living species do indeed belong to a limited number of rapid radiations: that is, they form groups with many species which evolved in a relatively short period of time,” Dr. Wiens stated.
The full report’s findings paint a dismal picture where key groups overwhelm the biodiversity landscape. Beetles now universally dominate the insect world, constituting more than 40% of all described species of living organisms. At the same time, passerines make up 60% of avian diversity and angiosperms—flowering plants—over 85% of plant diversity.
Implications for Understanding Biodiversity
Dr. Wiens and Dr. Moen’s research suggests that more than 80% of known species belong to a minority of groups exhibiting exceptionally high rates of species diversification. “It seems that the majority of the diversity of life can be accounted for by these kinds of relatively fast radiations,” said Dr. Wiens. The researchers suggest a few key traits help explain why these rapid diversifications happened in such dramatic fashion in many kingdoms of life.
Key multicellular traits recognized multicellularity in plants, animals, fungi. At the same time, arthropods transitioned to a terrestrial lifestyle and became herbivorous, and angiosperms evolved with flowers and insect pollination. These characteristics offer a much clearer picture of how some of the aforementioned groups have been able to attain such incredible strides toward diversity.
Caution on Bacterial Diversity
The research provides important new evidence towards understanding how life on earth has diversified. It further emphasizes the complex, cryptic reality of bacterial diversity. “If actual bacterial richness really is much higher than described richness for other groups, then a clade with low diversification rates [namely bacteria] would contain the majority of species across life,” Wiens and Moen cautioned. This would be a huge contrast to our findings. As such, we warn that our findings are still only relevant to described species diversity.
The researchers’ findings challenge existing assumptions about the distribution of biodiversity and suggest that understanding the mechanisms behind rapid radiations could illuminate the evolutionary processes that shape life on Earth.