So, lately I've been nosing through the IUCN Red List of Threatened Species and I've noticed that a fair number of the species listed under "Critically Endangered", are listed not because there has been an observed decrease in the population of those species, but because of how tiny the known population is. For example, on the island of New Caledonia (which is in Oceania, near New Zealand) there are three different species of birds, which are only known from a couple of individuals, the New Caledonian Rail, the New Caledonian Lorikeet and the New Caledonian Owlet-Night Jar. In particular, there hasn't been a definite record made of the New Caledonian Lorikeet since 1913, though there have been local reports through out the 1950s and 1970s. However, when specific searches were made in 1998 the Lorikeet couldn't be found, but the IUCN records say that the Lorikeet is unobtrusive and nomadic, so it seems that there will be continued surveys in the future.
This information is both encouraging and discouraging when considering the maintenance of biodiversity. For one, it shows that some species are simply difficult to detect, so it is impossible to make an accurate judgement concerning the numbers of existing individuals for certain species. It also seems to suggest the, obvious, possibility that there are undiscovered species which are still flying under the radar, so to speak. In this way, it seems possible that there is a sort of hidden biodiversity that just hasn't been detected yet.
However, it is also possible that this information suggests that species are becoming endangered without even being detected. Which leads me to wonder if we, as humans, have caused the extinction of a species without having known of its existence. It seems to be likely, especially considering that some species have relatively small or isolated populations, even in natural conditions due to the specificity of their diet or habitat.
Another endangered species, which demonstrates the previous last point, is the Queen Alexandra Butterfly. The Queen Alexandra butterfly is the world's largest butterfly and is also referred to as a bird-winged butterfly since the wingspan of the female can reach 31 cm. More to the point, the Queen Alexandra Butterfly is restricted to ~100 square kilometres of coastal rainforest in Papua New Guinea and is considered endangered by the IUCN Red List. The population is restricted to old growth rain forests since before pupating the species feeds on the pipe vines of the genus Paraistolochia. Because of the specificity of the Queen Alexandra's Bird-wing Butterfly, habitat destruction (mainly in the forming of spreading palm oil plantations) is a serious threat for the population. However, in this case, the destruction of the Queen Alexandra's habitat cannot be blamed solely on humans as a volcanic explosion destroyed a fair portion it in the 1950s.
So, it seems a rather self-evident that more specific a species' habitat and food or the smaller the original population, the more likely it is that a population will be (or soon become) endangered, sadly.
1. Ornithoptera alexandrae (Rothschild, 1907) Robert Nash, Curator of entomology, Ulster Museum. January 2007. Robert Nash
1. Gimenez Dixon, M. 1996. Ornithoptera alexandrae. In: IUCN 2007. 2007 IUCN Red List of Threatened Species.
2. BirdLife International 2004. Charmosyna diadema. In: IUCN 2007. 2007 IUCN Red List of Threatened Species.
3. BirdLife International 2004. Aegotheles savesi. In: IUCN 2007. 2007 IUCN Red List of Threatened Species.
4. BirdLife International 2004. Gallirallus lafresnayanus. In: IUCN 2007. 2007 IUCN Red List of Threatened Species.
5. Queen Alexandra's Birdwing. (2007, December 7). In Wikipedia, The Free Encyclopedia. Retrieved 08:04, December 15, 2007, from http://en.wikipedia.org/w/index.php? title=Queen_Alexandra%27s_Birdwing&oldid=176424621