Go to way of the dodo

This week my friends and I have done what I'm sure every group of twenty-somethings do regularly - we went on trips to two different zoos. It doesn't help our case that neither trip involved taking children for a day out, but when you are interested in conservation, who needs an excuse? 

Although I managed to see my first elephants and white rhinos, which were both stunning, I was shocked by how many of the species I saw are under threat at our own hand.

Throughout Man vs Earth we have already examined the loss of megafauna approximately 40,000 years ago, the cause of these extinctions, and the idea we are entering a 6th mass extinction. However we have not yet looked into localised extinctions happening in recent years.

As we have seen, humans have played a part in altering the climate on Earth, which is having knock on effects on the rest of the planet's ecology. On a more local scale, many other human interactions with biodiversity can lead to extinctions. Let's take a look at just a few of the many examples of species that have been threatened to the point of extinction by human influences:

White Rhino's are a well-known example as a species that were hunted widely for their horns for both medical and decorative purposes across Asia and North Africa. Now there are only 6 Northern white rhino individuals left in the wild. 

As the phrase 'to go the way of the dodo' suggests, dodos were a species that were famously over-hunted by humans to the point of extinction, originally an endemic species of Mauritius.

Threats to biodiversity aren't always direct, in 2007 the Yangtze River dolphin, the baiji, was found to be extinct due to over-fishing and construction of the Three Gorges Dam. 

Although the dodo and baiji were localised species, even far-spread successful species can fall at the hand of humans. The passenger pigeon fell from 3 billion to extinction due to over-hunting. The last individual died just over 100 years ago in the Cincinnati zoo. You can read more about each of these extinctions in The Scientific American.

Human-influenced climate change is another anthropogenic factor contributing to the decline of many species. In some cases climate has a direct influence on the survival of a species. In 2012, the International Union for Conservation of Nature (IUCN) considered 20 species to have undergone extinction due to direct impacts of climate change. These include factors such as change in ground, water and air temperature, as well as precipitation. One example is the Aldabra banded snail whose decline correlated to increased dry periods on the Aldabra atoll (Justin Gerlach, 2007). Although originally assumed extinct, the Aldabra banded snail which was found to still exist this year, demonstrating that whilst climate change is capable of causing direct declines in species number, it is not the driving mechanism of extinction.

Indirect influences of climate change can cause extinctions through species interaction; either negative implications affect the focal species through the loss of food source, or positive impacts on pathogens or competitors which thrive under increased temperatures, are detrimental to the focal species. It is concluded by Abigail E. Cahill et al, 2012, that these climate-influenced species interactions are the major cause of species extinction.

The IUCNs red list is the most extensive list of globally threatened species and therefore plays an important role in influencing conservation practices. The 2014 assessment recognizes 5,103 near threatened species, 10,838 vulnerable species, 6,940 endangered species and 4,635 critically endangered species. However, as I mentioned in Man vs Earth on 17th November in 'Is this a mass extinction?', limitations to understanding the threat to species are realised as very few modern animal clades have been sufficiently assessed. Currently, the Global Species Program run by the IUCN has data for 73,000 species, of the 1.8 million species recognised globally (Michael Begon, 2006), and of the estimated 8.8 million species that could inhabit Earth (Camilo Moro et al, 2011).

The groups better represented by IUCN assessment include mammals and birds. A group poorly represented are the amphibians, thought to be analogous to the 'canary in the mine' as an indicator of climate change impacts on biodiversity. Simon N. Stuart et al, 2004, explain that amphibians are more at risk, and therefore declining more rapidly, than birds and mammals. Poor understanding of the threat to these species only exacerbates the potential for widespread amphibian extinctions. 

Percentages of threatened species of vertebrates, invertebrates and plants from IUCN 2002 data. M, mammals; B, birds; R, reptiles; A, amphibians; F, fish. I, insects; M, mollusks; C, crustaceans; O, others. M, mosses; G, gynosperms; D, dycotyledons; Mo, monocotyledons. Taken from Global State of Biodiversity and Loss (Rodolfo Dirzo and Peter H. Razen, 2003).

Rodolfo Dirzo and Peter H Razen estimated that approximately 20% could have been threatened in 2002. The real figure could be much higher but only a small proportion of the species have been assessed. They also estimate that threatened plants were seriously underrepresented.

To protect the future of biodiversity we need to act faster to identify more of the world's unknown species or we will lose them before we even find them.