Why Are There So Many Beetles? They're Extinction-Resistant

The rich diversity seen in modern-day beetles could have more to do with extinction resistance than a high rate of new species originations / Photo courtesy of D. Smith via CU-Boulder
Janet Fang 20 Mar 2015, 18:56

There are about 380,000 species of beetles that we know of—and that’s a whole lot. Now researchers studying the fossil record may have figured out why beetles are the most species-rich group of animals in the world: historically low extinction rates. The findings are published in Proceedings of the Royal Society B this week. 

For there to be so many species today, one of two (or both) things likely happened: Older species keep chugging along or new species keep popping up. “Much of the work to understand why beetles are diverse has really focused on what promotes speciation,” Dena Smith from the University of Colorado-Boulder says in a news release

To see if it really is all about high species emergence rates, Smith and Jonathan Marcot from the University of Illinois at Urbana-Champaign compiled a database of fossil beetle occurrences using open access catalogues and papers written in the 1800s through 2014. The duo ended up constructing a database with 5,553 beetle occurrences from 221 unique fossil locations older than the Pliocene (or about 5 million years). Some beetles go as far back as the Permian period, 284 million years ago. 

All four suborders living today, as well as the majority of all beetle families, they found, are preserved in the fossil record: 69 percent of all beetle families ever known and 63 percent of beetle families still alive today.

Compared to the fossil record of other groups ranging from clams and corals to vertebrates, beetles have some of the lowest family-level extinction rates ever measured. It's almost negligible. Furthermore, not a single family in the largest beetle subgroup—Polyphaga, which includes weevils, scarab beetles, and lady bugs—have gone extinct in their entire evolutionary history. They maintained a family-level extinction rate of zero even during major mass extinction events like the dino-dooming one that occurred at the K-Pg (formerly K-T) boundary 65 million years ago.

“By looking at the fossil history of the group, we can see that extinction, or rather lack of extinction may be just as important, if not more important, than origination,” Smith says. “Perhaps we should be focusing more on why beetles are so resistant to extinction.” 

She adds: “There are several things about beetles that make them extremely flexible and able to adapt to changing situations.” Members of Polyphaga, for example, enjoy a wide diet of algae, plants, and other animals. And the ability of beetles (along with many other insects) to metamorphose from soft-bodied larvae to winged, armored adults means they can take advantage of varying types of habitats during different life stages. 

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