Read our COVID-19 research and news.
TECHNICAL COMMENTS
Comment on “Can We Name Earth’s Species Before They Go Extinct?”
Camilo Mora1, Audrey Rollo2, Derek P. Tittensor3,4,5
See all authors and affiliations
Science  19 Jul 2013:
Vol. 341, Issue 6143, pp. 237
DOI: 10.1126/science.1237254
Article
Figures & Data
Info & Metrics
eLetters
PDF
Abstract
Costello et al. (Review, 25 January 2013, p. 413) challenged the common view that many species are disappearing before being described. We suggest that their conclusion is overly optimistic because of a limited selection and interpretation of available evidence that tends to overestimate rates of species description and underestimate the number of species on Earth and their current extinction rate.
SIGN UP FOR THE SCIENCE eTOC
Get the latest issue of Science delivered right to you!
In an attempt to draw attention to the challenge of describing and monitoring Earth’s biodiversity in the face of looming environmental crises, it has been frequently claimed that many species are likely going extinct before being named (15). Costello and colleagues (6) challenged this view and suggested that such a worry “result[s] from overestimates of how many species may exist, beliefs that the expertise to describe species is decreasing, and alarmist estimates of extinction rates.” We suggest that their conclusions are overly optimistic because of a limited selection and interpretation of the available evidence. We consider each strand of evidence individually.
Are there fewer species? Previous estimates of the number of species on Earth have fallen broadly between 3 and 100 million species [see table 1 in (3) and table 1 in (5)]. Costello et al.’s consensus estimate of 5 ± 3 million species falls at the low end of this range primarily because of the inclusion of two very low values as part of a small sample of estimates. We argue that there is little support for a preferential selection of those two estimates and that a broader review of available estimates will give higher consensus values. One of these studies was derived from extrapolating species description rates and provides perhaps the lowest estimate yet of the total number of species on Earth: 2 million (7). The other combined estimates from species description rates, ratios of undescribed species in samples, and expert opinions and put the global number of marine species at 0.7 to 1 million (8). The limitations of these methodologies are well known: Modeling rates of species description underpredict true values when using incomplete data [figure 3, K to O, in (3)]; ratios are highly variable depending on how well the sampled areas have been studied (9); and expert opinions have limited empirical basis and considerable subjectivity (9, 10). In turn, a broader consideration of available estimates would have given values above 8 million species even without including controversial hyperdiverse estimates (6). For example, the estimates compiled by Scheffers et al. (5) yield 7.8 to 8.7 million species of animals, 0.29 to 0.39 million plants, and 0.6 to 1.5 million fungi (excluding hyperdiverse estimates), for a total of 8.7 to 10.6 million species (without including protists and prokaryotes). Costello et al. also suggested that the fact that the number of species per author is decreasing is an indication that the pool of undescribed species on Earth is getting smaller. However, the fact that ~0.5 million species may be in museum jars awaiting description (6) suggests that the downward trend in the number of species per author is unlikely to be due to a shortfall of species to name; another possibility that should also be considered regarding the downward trend in the number of species per author is that there may now be more coauthors per described species.
Is taxonomic effort overestimated? The number of species described each year is a key metric of taxonomic effort for estimating the time it would take to describe the unknown species on Earth. Costello et al. suggest that some 18,000 species are described every year, citing work derived mainly from The International Plant Names Index and The Zoological Record (11). However, these databases are repositories for nominal species (i.e., all species that have received a name regardless of their current status), and thus their use may err on the side of overestimation when quantifying rates of description of valid species. For instance, we cross-checked all 229,309 species names reported since 2000 in the Zoological Record with authoritative databases such as the Catalog of Life and the World Register of Marine Species and found that only 56,397 were recognized as valid species and 47,395 as synonyms, invalid names, and/or duplicates due to either variations in the names of authors or by also being named as subspecies and/or as subgenera. Unfortunately, 125,517 species names in the Zoological Record could not be matched to authoritative databases and should be considered with caution as several other sources of duplication may exist, including basionyms (i.e., valid species that receive new names to control for homonyms and changes to different taxonomic ranks or positions) and typographical errors. For comparison, the combined record of species from all kingdoms of life in the Catalog of Life, the World Register of Marine Species, and the List of Prokaryotic Names with Standing in Nomenclature indicates that on average ~8000 valid species were described annually from 1990 to 2000 (this period was chosen to avoid the time lag it takes to store species names into these databases).
Are current extinction rates overestimated? Costello et al. considered that “realistic” extinction rates likely range between ~0.001% and ~0.1% per year (6), which is equivalent to ~50 to ~5000 species going extinct annually, assuming 5 million species on Earth. Although there remains great uncertainty about current extinction rates (12, 13), an assessment of available evidence supports a higher rate. For instance, analysis of the estimates compiled by Stork (13), which included estimates derived from species-area relationships (i.e., extinctions induced by deforestation and climate change), Red List category changes, and co-extinctions, showed that the average rate of species extinction was 0.72% per year (~36,000 species a year if there are 5 million species). Only two out of the 15 case studies were as low as the highest “realistic” rate proposed by Costello et al. Removing all rates derived from species-area relationships, which are currently debated [(12), but see (14)], still yields a mean extinction rate of ~0.22% or ~11,000 species a year if there are 5 million species. Although it is true that our current record of extinct species is very low [~800 recorded extinctions by the IUCN [​www.iucnredlist.org/about/summary-statistics#Tables_3_4 (15)], this number needs to be considered within the context that only ~65,000 species have been assessed to determine their current extinction vulnerability (​www.iucnredlist.org/documents/summarystatistics/2012_2_ RL_Stats_Table_1.pdf​) and that of those only ~55% have assessments based on complete information [​www.iucnredlist.org/about/red-list-overview#expanding_coverage (15)]. This lack of information also accentuates the reluctance to declare species prematurely extinct [due to the skepticism generated when declared-extinct species are rediscovered (16)]; thus, for many species it can take years before being declared extinct (15, 16).
Unfortunately, Costello’s overarching question—can we name Earth’s species before they go extinct?—is very sensitive to changes in the estimates discussed above. For instance, although neither taxonomic effort nor extinction rates will remain constant over time, using the same approach as Costello et al. and assuming 8 million species, 8000 species described per year, and a yearly extinction rate of 0.72%—all intermediate values—we estimate that by the year 2164 all extant species will be described, at which point ~5 million species will become extinct (solid black arrow in Fig. 1). If extinction rates are set to 0.22% a year (i.e., the rate after excluding those derived by species-area), by 2327 all extant species would be discovered and ~4 million would be extinct (dashed black arrow in Fig. 1). These values are far less comforting than those of Costello et al. (6).
Download high-res image
Open in new tab
Download Powerpoint
Fig. 1 Contemporary rates and extrapolations of species description (blue lines) and extinction (red lines).
Although neither description nor extinction rates will remain constant over time, Costello et al.’s (6) approach is useful at indicating when all extant species will be described by identifying the year when the trend of described species (on average, 8000 species a year, blue line) intercepts with the trend of extinct species (on average, 0.72% a year, solid red line; dotted red line indicates the average rate after removing extinction rates yielded by species-area relationships: 0.22% a year). Individual rates analyzed here are shown in light colors. As reference, the extinction level in the five previous mass extinction events (MEE, >75% of all species going extinct) is indicated with the horizontal gray line.
Although we agree with Costello et al. that alarmist overestimates of biodiversity loss are unhelpful, we also contend that underestimating the task ahead and overestimating our capacity to address it could lead to a false sense of confidence. Clearly, multiple sources of uncertainty remain in our knowledge of biodiversity and its rate of loss on Earth; however, the magnitude of the challenge ahead is considerable and should not be underestimated, because the unique diversity of life on our planet and the services it provides to humankind are at stake.
References and Notes
  1. A. Balmford, R. E. Green, M. Jenkins, Measuring the changing state of nature. Trends Ecol. Evol. 18, 326–330 (​2003​).​doi:​10.1016/S0169-5347(03)00067-3​CrossRef​Web of ScienceGoogle Scholar
  2. R. Dirzo, P. H. Raven, Global state of biodiversity and loss. Annu. Rev. Environ. Resour. 28, 137–167 (​2003​).​doi:​10.1146/annurev.energy.28.050302.105532​CrossRef​Web of ScienceGoogle Scholar
  3. C. Mora, D. P. Tittensor, S. Adl, A. G. B.Simpson, B. Worm, How many species are there on Earth and in the ocean? PLoS Biol. 9, e1001127 (​2011​).​doi:​10.1371/journal.pbio.1001127 pmid:​21886479​CrossRef​PubMed​Google Scholar
  4. S. Bacher, Still not enough taxonomists: Reply to Joppa et al. Trends Ecol. Evol. 27, 65–66, author reply 66 (2012). doi:​10.1016/j.tree.2011.11.003​pmid:​22138045​CrossRef​PubMed​Web of ScienceGoogle Scholar
  5. B. R. Scheffers, L. N. Joppa, S. L. Pimm, W. F.Laurance, What we know and don’t know about Earth’s missing biodiversity. Trends Ecol. Evol. 27, 501–510 (2012). doi:​10.1016/j.tree.2012.05.008​pmid:​22784409​CrossRef​PubMed​Web of ScienceGoogle Scholar
  6. M. J. Costello, R. M. May, N. E. Stork, Can we name Earth’s species before they go extinct?Science 339, 413–416 (​2013​).​doi:​10.1126/science.1230318 pmid:​23349283​Abstract​/​FREE Full TextGoogle Scholar
  7. M. J. Costello, S. P. Wilson, B. Houlding, Predicting total global species richness using rates of species description and estimates of taxonomic effort. Syst. Biol. 61, 871–883 (​2012​).​doi:​10.1093/sysbio/syr080 pmid:​21856630​Abstract​/​FREE Full TextGoogle Scholar
  8. W. Appeltans, S. T. Ahyong, G. Anderson, M. V.Angel, T. Artois, N. Bailly, R. Bamber, A. Barber, I.Bartsch, A. Berta, M. Błażewicz-Paszkowycz, P.Bock, G. Boxshall, C. B. Boyko, S. N. Brandão, R. A. Bray, N. L. Bruce, S. D. Cairns, T. Y. Chan, L.Cheng, A. G. Collins, T. Cribb, M. Curini-Galletti, F.Dahdouh-Guebas, P. J. Davie, M. N. Dawson, O.De Clerck, W. Decock, S. De Grave, N. J. de Voogd, D. P. Domning, C. C. Emig, C. Erséus, W.Eschmeyer, K. Fauchald, D. G. Fautin, S. W. Feist, C. H. Fransen, H. Furuya, O. Garcia-Alvarez, S.Gerken, D. Gibson, A. Gittenberger, S. Gofas, L.Gómez-Daglio, D. P. Gordon, M. D. Guiry, F.Hernandez, B. W. Hoeksema, R. R. Hopcroft, D.Jaume, P. Kirk, N. Koedam, S. Koenemann, J. B.Kolb, R. M. Kristensen, A. Kroh, G. Lambert, D. B.Lazarus, R. Lemaitre, M. Longshaw, J. Lowry, E.Macpherson, L. P. Madin, C. Mah, G. Mapstone, P. A. McLaughlin, J. Mees, K. Meland, C. G. Messing, C. E. Mills, T. N. Molodtsova, R. Mooi, B. Neuhaus, P. K. Ng, C. Nielsen, J. Norenburg, D. M. Opresko, M. Osawa, G. Paulay, W. Perrin, J. F. Pilger, G. C.Poore, P. Pugh, G. B. Read, J. D. Reimer, M. Rius, R. M. Rocha, J. I. Saiz-Salinas, V. Scarabino, B.Schierwater, A. Schmidt-Rhaesa, K. E. Schnabel, M. Schotte, P. Schuchert, E. Schwabe, H. Segers, C. Self-Sullivan, N. Shenkar, V. Siegel, W. Sterrer, S. Stöhr, B. Swalla, M. L. Tasker, E. V. Thuesen, T.Timm, M. A. Todaro, X. Turon, S. Tyler, P. Uetz, J.van der Land, B. Vanhoorne, L. P. van Ofwegen, R. W. van Soest, J. Vanaverbeke, G. Walker-Smith, T. C. Walter, A. Warren, G. C. Williams, S. P. Wilson, M. J. Costello, The magnitude of global marine species diversity. Curr. Biol. 22, 2189–2202 (2012). doi:​10.1016/j.cub.2012.09.036​pmid:​23159596​CrossRef​PubMed​Google Scholar
  9. P. Bouchet, in The Exploration of Marine Biodiversity: Scientific and Technological Challenges, C. M. Duarte, Ed. (Fundación BBVA, Madrid, 2006), pp. 31–62.
  10. T. L. Erwin, How many species are there?: Revisited Conserv. Biol. 5, 330 (​1991​).​doi:​10.1111/j.1523-1739.1991.tb00145.x​CrossRef​Web of ScienceGoogle Scholar
  11. Q. D. Wheeler, S. Pennak, State of Observed Species (International Institute for Species Exploration, 2011).
  12. F. He, S. P. Hubbell, He and Hubbell reply. Nature 482, E5–E6 (​2012​).​doi:​10.1038/nature10859​CrossRef​Web of ScienceGoogle Scholar
  13. N. E. Stork, Re-assessing current extinction rates. Biodivers. Conserv. 19, 357–371 (​2010​).​doi:​10.1007/s10531-009-9761-9​CrossRef​Web of ScienceGoogle Scholar
  14. J. Rybicki, I. Hanski, Species-area relationships and extinctions caused by habitat loss and fragmentation. Ecol. Lett. 16 (suppl. 1), 27–38 (2013). doi:10.1111/ele.12065 pmid:​23452159​CrossRef​PubMed​Google Scholar
  15. C. Mora, F. A. Zapata, The Balance of Nature and Human Impact, K. Krohde, Ed. (Cambridge Univ. Press, Cambridge, 2013).
  16. S. Pimm, P. Raven, A. Peterson, Ç. H.Şekercioğlu, P. R. Ehrlich, Human impacts on the rates of recent, present, and future bird extinctions. Proc. Natl. Acad. Sci. U.S.A. 103, 10941–10946 (2006). doi:​10.1073/pnas.0604181103​pmid:​16829570​Abstract​/​FREE Full TextGoogle Scholar
  17. Acknowledgments: We thank the Catalog of Life (www.species2000.org), the World Register of Marine Species (​www.marinespecies.org​), the List of Prokaryotic Names with Standing in Nomenclature (www.bacterio.net), the Thomson Reuters Zoological Record (​www.organismnames.com​), The International Plant Names Index (www.ipni.org), and The International Union for Conservation of Nature Red List of Threatened Species (www.iucnredlist.org) for making their data available. We thank M. Costello, N. Stork, K. Gaston, B. Worm, and L. Joppa for comments on the manuscript.
Science
Vol 341, Issue 6143
19 July 2013
ARTICLE TOOLS
Email
Download Powerpoint
Print
Request Permissions
Alerts
Citation tools
Share
MY SAVED FOLDERS
Save to my folders
STAY CONNECTED TO SCIENCE
RELATED CONTENT
Technical Comments
Response to Comments on “Can We Name Earth’s Species Before They Go Extinct?”
Review
Can We Name Earth's Species Before They Go Extinct?
SIMILAR ARTICLES IN:
CITING ARTICLES IN:
Web of Science (23)
NAVIGATE THIS ARTICLE
Read the Latest Issue of Science
23 July 2021
Vol 373, Issue 6553
Table of Contents
FEATURE
A troubled calculus
RESOURCE POLICY
Global implications of the EU battery regulation
PSYCHOLOGY
The elusive quest to make consistent calls
SCI COMMUN
News at a glance
PLANETARY SCIENCE
The interior of Mars revealed
WORKING LIFE
For those we've lost
Get Our E-Alerts
Receive emails from ScienceSee full list
Science Table of Contents
Science Daily News
Weekly News Roundup
Science Editor's Choice
First Release Notification
Science Careers Job Seeker

I also wish to receive emails from AAAS/Science
and Science advertisers, including information on
products, services, and special offers which may
include but are not limited to news, career
information, & upcoming events.

Required fields are indicated by an asterisk (*)
About Us
Journals
News from Science
Leadership
Team Members
Work at AAAS
For Advertisers
Advertising Kits
Awards and Prizes
Custom Publishing
Webinars
For Authors
Submit
Information for Authors
Editorial Policies
For Librarians
Manage Your Institutional Subscription
Information for Librarians
Request a Quote
FAQs
Related Sites
AAAS.org
EurekAlert!
Science in the Classroom
Science Magazine Japanese
Help
Access and Subscriptions
Order a Single Issue
Reprints and Permissions
Contact Us
Accessibility
© 2021 American Association for the Advancement of Science. All rights reserved. AAAS is a partner of HINARIAGORA, OARE, CHORUSCLOCKSSCrossRef and COUNTER.
Science ISSN 1095-9203.
Terms of Service
Privacy Policy
Contact AAAS
ContentsCurrent IssueArchiveCustom PublishingNewsLatest NewsScienceInsiderCareersArticlesEmployer ProfilesFind JobsGraduate ProgramsJournalsScienceScience AdvancesScience ImmunologyScience RoboticsScience SignalingScience Translational MedicineScience Partner Journals