Could species threatened by climate change and other stresses avoid extinction through rapid evolution?
Image credit: Norman Lee (St. Olaf College, Northfield, MN).
New Research In
Physical Sciences
Featured Portals
Articles by Topic
Biological Sciences
Featured Portals
Articles by Topic
Edited by James H. Brown, University of New Mexico, Albuquerque, NM, and approved May 5, 2015 (received for review February 7, 2015)
Significance
Many suggest we are approaching a sixth mass extinction event, and yet estimates of how many species exist, and thus how many might become extinct, vary by as much as an order of magnitude. There are few statistically robust methods to estimate global species richness, and here we introduce several new methods, including one that builds on the observation that larger species are often described before smaller species. We combine these, giving equal weight to each, to provide mean global species estimates for the most speciose order, class, and phylum on Earth, beetles, insects, and arthropods (terrestrial). We attempt to aid conservation planning by broadening the range of methods used and bringing greater stability to global estimates for these taxa.
Abstract
It has been suggested that we do not know within an order of magnitude the number of all species on Earth [May RM (1988) Science 241(4872):1441–1449]. Roughly 1.5 million valid species of all organisms have been named and described [Costello MJ, Wilson S, Houlding B (2012) Syst Biol 61(5):871–883]. Given Kingdom Animalia numerically dominates this list and virtually all terrestrial vertebrates have been described, the question of how many terrestrial species exist is all but reduced to one of how many arthropod species there are. With beetles alone accounting for about 40% of all described arthropod species, the truly pertinent question is how many beetle species exist. Here we present four new and independent estimates of beetle species richness, which produce a mean estimate of 1.5 million beetle species. We argue that the surprisingly narrow range (0.9–2.1 million) of these four autonomous estimates—derived from host-specificity relationships, ratios with other taxa, plant:beetle ratios, and a completely novel body-size approach—represents a major advance in honing in on the richness of this most significant taxon, and is thus of considerable importance to the debate on how many species exist. Using analogous approaches, we also produce independent estimates for all insects, mean: 5.5 million species (range 2.6–7.8 million), and for terrestrial arthropods, mean: 6.8 million species (range 5.9–7.8 million), which suggest that estimates for the world’s insects and their relatives are narrowing considerably.
Footnotes
- ↵1To whom correspondence should be addressed. Email: nigel.stork{at}griffith.edu.au.
Author contributions: N.E.S. designed research; N.E.S. and A.J.H. performed research; N.E.S., J.M., C.G., and A.J.H. analyzed data; and N.E.S. and A.J.H. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1502408112/-/DCSupplemental.
Freely available online through the PNAS open access option.
New species estimates for beetles and insects
Sign up for Article Alerts
Jump to section
You May Also be Interested in
Opinion: The proposed change to the definition of “waters of the United States” flouts sound science
The administration’s proposed rule ignores or misrepresents the conclusions of an EPA panel and, if enacted, will damage our nation’s water resources.
Image credit: Shutterstock/Martha Marks.
Since 1972, ice loss from Greenland has contributed to an estimated 13.7 mm rise in global sea level, with the largest contributions coming from northwest, southeast, and central west Greenland, according to a study.
Image courtesy of Eric Rignot.
Global warming has likely increased the economic disparity between the top and bottom population deciles across the world, thereby generating greater economic inequality than would have occurred without global warming, according to a study.
Image courtesy of Noah S. Diffenbaugh and Marshall Burke.
Some species of aphids use a form of social defense to protect colonies from predators, uncovering potential molecular clues to the evolutionary roots of altruistic social defense, according to a study.
Image courtesy of Mayako Kutsukake.