Does it matter if the rate of extinction has increased?

Extinctions

It is estimated that approximately 1.82 million species that live or have lived on Earth have been named, but we only know a small fraction of the species that exist or have existed. Some of the more extinct species include the dinosaurs and the dodo. In recent decades, most extinctions have occurred because of over-exploitation (for example hunting of the passenger pigeon in the USA), habitat damage (e.g. deforestation) or bioinvasion (e.g. the introduction of rats onto islands, where they eat bird's eggs. Islands have been particularly vulnerable, as the native species may have relatively few numbers to start with, may have no way of escaping from hunters (e.g. flightless birds), or may have never seen man before and not try to escape hunters. Species may also die if their food becomes extinct - this would probably happen to Giant Pandas if their bamboo were to become extinct, for example. Species that are known to be in danger of extinction are listed in the International Union for Conservation of Nature and Natural Resources (IUCN) 'Red List'. There are currently over 11,000 species on the list, but we know so little about many species that we do not know if they are facing extinction.

To know whether current rates of extinction are unusual, we need to know what extinction rates have been over the ages. Fossil records, though useful, give a very incomplete picture as many kinds of species do not leave fossil remains, particularly if the species did not have a hard skeleton or tended to be eaten by predators or scavengers or only existed in a small area. Fossils also tend to be predominately of longer-lived species. All statistics concerning numbers and extinctions of species tend therefore to be rough estimates, and scientists differ in their estimates. Fossils have been found for around a quarter of a million species - perhaps 1% of all the species that have ever lived. We also need to know how many new species have arisen. It is believed that up to 99% of species that ever lived are now extinct, but that the number of species alive at any given time has increased over the past 600 million years. The average lifespan of species is estimated to be 4 Ma.

It is believed that the background extinction rate has fluctuated over time, but averages about 25% of species per million years. The background extinctions are believed to account for about 96% of all extinctions, with the remaining 4% being due to 5 mass extinction periods, during one of which the dinosaurs died out.

Estimates for the background extinction rate of mammals (of which there are about 4,000 currently) vary from 1 every 10 years to 1 every 100 years; for birds from 1 every 50 years to 1 every 5 years. About 100 birds have gone extinct since 1800; or around 1 every 2 years. Bird Life International estimates that only 50% of 182 bird species on its list are likely to survive for the next 10 years, or 9 per year. Estimates like these, plus the sight of large areas of land given over to monoculture or new desert, give the impression that we have had a noticeable impact on extinction rates in recent centuries.

One reason for caring if species become extinct is that we have derived many food plants and animals and our medicines from wild species. There are probably many more to be found. Another is that a single species is more vulnerable to being wiped out by disease if individuals are very similar and concentrated together, as happens with our field of single crops. Insects and diseases are less likely to reach epidemic proportions if the plants and animals they live off of are well mixed with other species.

Woodpecker Thought Extinct Rediscovered, Long Search for 'Extinct' Woodpecker Pays Off, Ivory Billed Woodpecker, Feared Extinct, Isn't

A woodpecker last seen in 1944 and thought to have been extinct has been rediscovered by researchers hunting for it. A single blurry video clip was filmed of a male ivory-billed woodpecker in eastern Arkansas. Protecting it will be a challenge, as much of its habitat has been destroyed, though there has been some reforestation.

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