Snail analysis could help assess and save the 99 percent

According to the International Union for the Conservation of Nature (IUCN) Red List, the most authoritative inventory of the status of the world’s biodiversity, 830 species have gone extinct since 1600. That works out to about 2 species lost per year – which is roughly equivalent to the background rate of extinction in the fossil record, prompting some skeptics to question whether a biodiversity crisis is really underway.

The trouble is, the Red List mostly captures the status of vertebrates, especially birds and mammals. But 99 percent of all animal species are invertebrates, and only a tiny fraction of these have been assessed according to Red List criteria.

Three recent papers set out new approaches to assessing the conservation status of invertebrates, suggesting that invertebrate extinctions have been underestimated in the past, but also that it might be possible to identify species at risk of extinction more cheaply and quickly in the future.

In the first paper, a team of taxonomists, mathematicians, and bioinformatics specialists used a sample of 200 land snail species, selected at random from 17,102 species in a well-known compendium of global snail biodiversity, and applied two independent approaches to estimate recent extinctions [1].

In one analysis, the researchers assembled data from scientific publications, museum collections, and consultations with taxonomic experts to gauge whether a given snail species was likely to still exist or not. The second approach was more quantitative, involving mathematical modeling based on collection records from four major natural history museums.

The results of the model analysis are slightly more pessimistic than those of the expert analysis, but both lead to similarly sober conclusions, the team reported in June in the Proceedings of the National Academy of Sciences. And extrapolating from snails to other, even more poorly known invertebrate groups, the researchers estimate that about 7 percent of known terrestrial animals – as many as 130,000 species – have disappeared in the recent past.

Some members of the team, in collaboration with other snail biologists, have applied a similar methodology to a more detailed assessment of recent extinctions among amastrid snails, which are found only in the Hawaiian archipelago [2].

This analysis draws on collection records from the Bishop Museum in Honolulu, input from various amastrid experts, and 10 years of field data from extensive land snail surveys on the six largest Hawaiian islands.

According to the team’s analysis, there are 282 modern species of amastrid snails. Of these, 88 species are almost certainly extinct, the researchers report July 31 in Conservation Biology. Only 15 species of amastrids turned up in the field surveys and are known to still be alive, albeit critically endangered.

Against these data, the IUCN Red List’s classification of just 33 species of amastrid snails as extinct looks like it seriously underplays the situation. The new analysis suggests that at least 40 percent of amastrid biodiversity, and possibly up to 95 percent, has been lost.

What remains:

But how should we triage still existing species of invertebrates to determine which ones need conservation attention – which, after all, is the primary purpose of the Red List?

4,000 miles to the southwest of Hawaii, a Wildlife Conservation Society researcher has been working on an answer to that question with a study that involves – you guessed it – another species of snail [3].

This study focuses on the Manus green tree snail, a striking creature with a pale ivory body and a shell like a spiral of highly polished jade that is found only on Manus island in Papua New Guinea.

Nathan Whitmore and his team surveyed 400 local people at the island’s main market, asking them to map their observations of the snail’s distribution and abundance in 2013, when the study took place, as well as their recollections from 1998.

The method is based on a concept known as the “Wisdom of Crowds,” which aggregates knowledge from a large number of individuals and integrates their responses into a single estimate that often proves remarkably accurate.

The approach is drawing increasing attention in fields such as politics, economics, computer science, and sociology, but has not yet been applied to conservation biology.

In the case of the Manus green tree snail, the Wisdom of Crowds analysis suggests that the snail is declining in abundance, Whitmore reports in the journal Oryx.

Survey participants identified fewer areas as having a “plentiful” population of snails in 2013 than they did in 1998. The analysis also revealed that snail abundance is linked to forest cover, which is known to have declined on Manus island in recent years due to development.

Based on this analysis, IUCN decided to list the snail as “Near Threatened” in the 2015 Red List. Previously, the organization said that there was not enough information to determine the species’ status.

The approach isn’t a substitute for careful, quantitative ecological field research, Whitmore says. But given that funds simply aren’t available to conduct such research for most invertebrate species, this take on crowdsourcing is a whole lot better than nothing. – Sarah DeWeerdt | 18 August 2015


[1] Regnier C.  et al. “Mass extinction in poorly known taxa.” Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1502350112

[2] Regnier C. et al. “Extinction in a hyperdiverse endemic Hawaiian land snail family and implications for the underestimation of invertebrate extinction.” Conservation Biology DOI: 10.1111/cobi.12565

[3] Whitmore N. “Harnessing local ecological knowledge for conservation decision making via Wisdom of Crowds: the case of the Manus green tree snail Papustyla pulcherrima” Oryx DOI: 10.1017/S0030605315000526

Header image: The Manus green tree snail, subject of the Wisdom of Crowds. Credit: Nathan Whitmore.