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Silent declines: recognising unlisted ‘endangered’ species

Only 5% of the world’s plants, and 1% of invertebrates have been assessed under IUCN guidelines. Tim√

Silent declines: recognising unlisted ‘endangered’ species

Only 5% of the world’s plants, and 1% of invertebrates have been assessed under IUCN guidelines. Tim√

If an entire forest falls and its occupants approach extinction, does anybody hear it?

Since for the vast majority of species, the answer is most likely no, we decided to be proactive and recently published a study about a poorly-studied island in the western Pacific, Palau. Along with archaeologist Jolie Liston, we used the island as a model for developing a new method for rapidly assessing the extinction threat to multiple species at the same time. Why did we do this? Well, read on.

Today we use the term “endangered species” to highlight organisms with a perilous survival trajectory, and to heighten our senses to the potential of their extinction.

But the conservation of “endangered” species is a tricky business. To start with, the term “endangered” generally applies to a species that is at risk of extinction – but in practise it has several definitions.

The International Union for Conservation of Nature (IUCN) lists species as “endangered” only if they qualify for a specific set of criteria.

Both Australia and New Zealand have national legislation based on the IUCN system but other countries, such as the United States, have a completely different process for defining an “endangered” species.

The endangered Cyanea superba, Hawaii. US Army Environmental Command

Other systems, such as NatureServe, use different terminology (“imperiled” instead of “endangered”) to avoid confusion with the specific criteria and political connotations of the former systems.

Although this may seem like a nit-picking technicality, it’s well known that the majority of the world’s species are found in tropical or developing countries, many of which do not have legally-binding systems for listing and protecting “endangered” species.

Recent studies – our own included – have shown that the system used to classify threat has a very big influence on which species make it to the endangered species list. Indeed, concerns have been raised that the most widely adopted and promoted system in such countries, the IUCN Red List, does not treat all species as equal.


To date, only 5% of the world’s plants, and 1% of invertebrates have been assessed under IUCN guidelines, compared to 100% of mammals, 100% of birds and 94% of the world’s amphibians.

These are alarming figures considering a recent study that indicated one out of every five plants is at risk of extinction.

Euhadra peliomphala. Takahashi

Thus the specific classification system utilised is likely to have a huge impact on the ultimate conservation efforts dedicated towards specific species.

Many people, when they hear the word “endangered species”, may think of iconic animals such as the tiger, rhino, or panda. But what about other, less charismatic, creatures, such as endemic snails, insects, or rare trees and plants in the rainforest? How do they get noticed and protected?

Beyond the flagships

One of the leading NGOs working on threatened species, the World Wildlife Fund (WWF), focuses its efforts on flagship species. The logic is that the protection of habitat for elephants, for example, would simultaneously protect a large area of habitat for other species too.

Certainly this is a reasonable approach in many areas but what does this mean for other less well-known species under equal or more severe threat, or for places such as oceanic islands that don’t have large mammals or iconic species?


Nearly everyone has heard of the island extinction of the dodo bird, but did you know that in Hawaii 900 of the 1,263 species (71%) of land snails and approximately 97 (8%) of land plants are believed to have gone extinct since humans colonised the islands?

Or that the largest palm tree to have ever existed, the Rapa Nui Palm, was driven to extinction along with the elimination of all other native trees by humans on Easter Island?

The majority of extinctions that take place seem to go unnoticed. But we can do better at sensing impending species extinctions even for those that are small, poorly known and/or unpopular.


For our study in Palau with Jolie Liston our goal was to create an efficient method for assessing the extinction threat to multiple species at the same time, even when no population data was available (required for IUCN listing).

Palau is circled in green. Wikimedia Commons

Our method was identical to the IUCN system, but with one primary modification – it included information on habitat destruction extending beyond 100 years.

Although for most tropical regions, population data for species is very sparse, Palau, as with many other locations, has ample evidence of historic deforestation from the archaeological record.

The evidence compiled by Liston showed that more than 30% of the original forest on the islands had been cut down since the arrival of humans.

A minimum of 30% for habitat decline is used by IUCN for eligibility for a species to qualify as “vulnerable”. Thus if a species is endemic to that forest type then it should qualify – but this 30% decline must occur over three generations or within 100 years to be considered by IUCN.

There is a fundamental problem with this criterion. In most tropical regions, forest recovery after removal can be extremely slow, and in this case much of the forest had been converted to savanna or grassland habitats.

Oceanic islands and tropical areas are unique in that they commonly harbour endemic species, occurring nowhere else in the world, with very small natural distributions.

The view from Palau. T.Chan

It may not sound like much, but a decline of 30% for a small oceanic island is a lot, especially if the island is rich in endemic species. When you think about it, 100 years in the life of a species that evolved over millions of years is nothing.

If a 30-50% decline in the total population size of such a species occurred over the course of a few hundred years at the hands of humans this should be more than enough to justify global recognition of threatened status.

But currently, the leading system in place for recognising endangered species, that of the IUCN, does not [accept this logic, notwithstanding numerous published scientific case studies calling for modifications to the IUCN’s system.

Less rigid but equally creditable approaches, such as the US Endangered Species Act, which allows for any form of evidence proving threat, are urgently needed for areas where the population data required to meet IUCN standards are difficult to obtain.

Concerns over the method of threat recognition may seem only remotely relevant to conversation to most people. But if it means thousands of endangered species remain unnoticed and unlisted in some of the most species-rich parts of the globe it’s clearly a problem.

Developing countries often rely on international grant schemes some of which only fund conservation activities targeted towards IUCN-listed species.

Thus anyone genuinely interested in the conservation of threatened species should be actively concerned about the process of determining how a species is classified as “endangered”.

Without a recognised threat status countless additional species may meet a similar fate as the 900 land snails species that disappeared silently in the forests of Hawaii.