Knowing when a species should be declared extinct is a long-standing dilemma for biologists. In fact, an international study has concluded that there are more than 500 “lost” species; that is, it is not known for sure if they continue to exist or have become extinct.
Species such as Sir David’s long-beaked echidna (Zaglossus attenboroughi), the ivory-billed woodpecker (Campephilus principalis) and the Baiji or Chinese river dolphin (Lipotes vexillifer) remain in limbo, since it is not certain that they continue to exist, but it has not been possible to confirm that they are extinct either.
The formal definition of “Extinct” on the International Union for Conservation of Nature (IUCN) Red List is: “When there is no reasonable doubt that the last individual of a species has died“, which in many cases is difficult to verify.
A taxon is presumed extinct when comprehensive studies in known and/or expected habitat, at appropriate times (diurnal, seasonal, annual), throughout their historical range they have failed to record any individuals.
Several decades ago, it was proposed to classify a species as extinct if it was not observed for 50 years. But this proposal was not widely accepted due to its simplistic natureand conservation agencies now adopt a more cautious approach before the declarations of extinction.
There are many cases where species declared ‘extinct’ have been rediscovered decades or even centuries later.. For example, two species of coelacanth, (Latimeria chalumnae) Y (Latimeria menadoensis), Miles’ Thief Frog (Craugastor milesi) or a bird, the black-browed babbler (Malacocincla perspicillata), declared extinct and ‘rediscovered’. And in the case of the latter, an endemic songbird from Borneo, it was observed again two years ago, 172 years after being considered extinct.
The problem of ‘false alarms’
These cases – and many others – undermine the validity and reliability of a rigid ’50 years’ criterion. But also, the premature declaration of extinction of a species can have harmful consequences for conservationbecause a fundamental habitat for the species in question may no longer be protected.
Likewise, Continued ‘false alarms’ could undermine public empathy and undermine confidence in the accuracy and severity of extinction as a label, the study authors note.
The researchers reviewed information on 32,802 species on the IUCN Red List of Threatened Species and identified 562 lost species. His findings have just been published in the journal ‘Animal Conservation’.
According to Simon Fraser University (SFU) biodiversity professor and study co-author Arne Mooers, the Red List classifies 75 of these 562 lost species as “possibly extinct.” And he adds that the existence of many species with an uncertain conservation status may become increasingly problematic as the extinction crisis worsens.
Initially, the authors of the research identified 1,674 disappeared species with a date of last observation of more than 10 years. But they found that 57 of them had been recently rediscoveredwhich left a total of 1,617 species missing (602 amphibians, 584 reptiles, 102 birds and 329 mammals).
The next step was to eliminate all species with a date of last observation less than 50 years, leaving a final central sample with the aforementioned 562 lost species (137 amphibians, 257 reptiles, 38 birds and 130 mammals).
Tropical countries, the most affected
Given that a total of 311 species of terrestrial vertebrates have been declared extinct since the year 1500, it turns out that 80 percent more species are considered lost than declared extinct. Many of these lost animals were last seen in countries such as Indonesia (69 species), Mexico (33) and Brazil (29).
Although not surprising, this concentration in a few countries is important, according to the researchers. “The fact that most of the lost species are in megadiverse tropical countries is worrying, given that they are expected to experience the highest number of extinctions in the coming decades“says the study’s lead author, Tom Martin, of the UK’s Paignton Zoo.
Gareth Bennett, an undergraduate at SFU who did much of the data matching, hopes this simple study will help make missing species “a focus of future searches.”
The authors suggest that future study efforts focus on the “critical points“identified as those where the existence of many particular species remains in doubt.
They note that more funding would be needed to support such fieldwork directed at hotspots to rediscover lost species or to remove reasonable doubt that a particular lost species does, in fact, still exist.
Reference study: https://zslpublications.onlinelibrary.wiley.com/doi/10.1111/acv.12788
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