Climate Change 2. - Biological Invasions Seminar Summary

First off, I'm going to apologise for the crazy amount of posts this week. I just wanted to post this whilst everything was still fresh in my mind. Secondly, this isn't 100% related to birds, as you'll see, but I thought it might interest those studying Geog3057.

On Wednesday I attended a small seminar given at UCL by Franck Courchamp, a specialist in population dynamics and conservation biology from Université Paris Sud. The talk was on 'Interactions between Climate Change and Biological Invasions' and here I'm giving a quick summary of what was said.

Myrmica rubra; the European Fire Ant (aka. Common Red Ant) - by Tim Keppens on Flickr.

Biological invasions are the second greatest threat to biodiversity; they also impact upon the economy and society. Will climate change effect biological invasions? Will it make them more, or less, of an issue in the future?

Courchamp's research can be roughly divided into two sections; the effect that climate change will have on invasive ant species, and the effect it will have upon the IUCN's 100 of the World's Worst Invasive Alien Species.

Climate Change and Invasive Ant Species

• Over 200 of the ~1200 described species of ant (family; Formidae) are found outside of their native range. Some of these species can be classed as 'exotic' (i.e. not native, but not invasive). 19 of these species, however, are classed as highly invasive; 5 of them are present of the '100 of the World's Worst-' list.
• Ant invasions have important consequences for biodiversity; they may remove native species and other arthropods. They also effect mammals, birds, and other animals, and can impact seed dispersal and pollination by doing so. They also affect us; Red Imported Fire Ant (Solenopsis invicta) causes a total economic loss of around $1 billion per year, as well as roughly 100 deaths from anaphylaxis (severe allergic reaction).

Using climatic models, will invasive ant species increase their range and 'invasive-ness'?

• Some ants (5 species) will benefit from climate change, and will become more able to invade new regions. Amongst these are the Asian Needle Ant (Pachycondyla chinensis), Singapore Ant (Monomorium destructor) and European Fire Ant (Myrmica rubra).
• HOWEVER, many species are projected to freeze or decrease in their invasiveness (7 decreases and 3 remain 'stable'). 3 of the decreasing species are amongst the 'World's Worst'. 
• So, overall, the general global trend seems to be that future climate change will decrease the invasiveness of ants. 
• But don't start the party just yet! When we look at and compare the regions that these invasions are decreasing and increasing in, we get a more grim picture. Though the global trend in the future is to decrease, two-thirds of species show a strong increase in the world's Biodiversity Hotspots which, though they only cover 2.3% of the Earth's land area, contain high numbers of endemic species. 

Climate Change and the 100 of the World's Worst...
Having looked at invasive ants, Courchamp and his PhD students repeated the models, but this time did so for all of the '100 of the World's Worst-'. Would the results be worse, or better?

•  Aquatic and terrestrial invertebrates, as well as terrestrial plants, amongst others, showed an increase in their invasive range. Europe and South America in particular showed a greater risk of being invaded with future climate change.
• Amphibians and birds, amongst others, showed a decrease in their invasive range with climate change. As with the ants, their was a general global decrease in invasiveness. 
• However, as it had been with ants, the picture was different when Biodiversity Hotpsots were focused upon. With climate change, these hotspots were more likely to be invaded in hue he future, and some are more susceptible than others. Polynesia, for example, is at risk from 35 of the 'World's Worst'. 

In the words of Franck Courchamp, the overall pattern is "a lot of invasions everywhere". Even though some species show a decrease in their distribution, as most are predicated to increase their distribution in the places that are most at risk we can be fairly confident in saying that climate change will not suppress biological invasions. 

Journals referenced in the talk:

• Increase in Quantity and Quality of Suitable Areas for Invasive Species
• Impacts of Climate Change on the Future of Biodiversity
• Will Climate Change Promote Future Invasions?

Bird Extinction: The Pre-Industrial Picture

Extinction as a result of anthropogenic activities is not something that can be confined to the last century or two; as humans have expanded their reach across the globe, they have been contributing to a loss of biodiversity on Earth for at least 50,000 years (Braje & Erlandson, 2013). Human induced animal extinction rates are believe to be up to a thousand times higher than the natural background rate, and are associated with the loss of around 8500 species of bird since 1600 AD alone (Braje & Erlandson, 2013).

Whilst a loss of species diversity can be seen across the globe, some of the most prominent examples are on the many islands of the South Pacific, where Polynesian expansion across the pacific led to the extinction of many animal species (Pimm et al, 2006). Island populations are especially vulnerable to extinction, as their populations are often small, and may be confined to a minimal area of land. Their isolation also often results in the loss of adaptability to pathogens, predators and competitors that may be introduced, and to the rapid environment change often brought about by humans (Grayson, 2001).

The extinction of endemic flightless birds alongside plants and mammals in Australia coincides with the arrival of humans (Braje & Erlandson, 2013), which may have been visiting the country as early as 22,000 years ago (Flannery & Roberts, 1999), as suggest by a rise in charcoal and a change in tree pollen in the sedimentary record. This has been contributed to anthropogenic deforestation through fire, and not down to climate change (Flannery & Roberts, 1999).

The same applies to New Zealand, which wasn't colonised until much later in the 13th Century (Irwin & Walrond, 2012). Prior to humans living in New Zealand, it was home to many species of endemic birds that are now extinct. 21 species of small landbird are no longer with us today, and alongside them were 11 species of Moas (Braje & Erlandson, 2013) (Grayson, 2001). The only birds known to be totally wingless, the enormous Moa were a family of herbivorous flightless birds. The two largest species, Dinornis robustus and Dinornis novaezelandiae weighed over 200kg, and could reach a height of 3.6m (12ft) if they stood with their neck outstretched (Wikipedia, 2013).

Published in 1879; a photograph of Richard Owen, the director of London's Natural History Museum, standing beside a reconstructed skeleton of Dinornis novaezelandiae - Image via Wikipedia Commons

The only natural predator of the Moa was the Haast's Eagle which was also driven to extinction when the Moa were wiped out completely in just over a century since the Maori populated the islands. Their extinction is believed to be a result of multiple factors, but all are attributed to human activities (BBC, 2009) (Grayson, 2001). Before the arrival of our species it is estimated that up to 90% of New Zealand was covered in forested, yet within a few hundred years almost all of the lowland forest had been destroyed, and with it vanished the habitats of the Moa and other animals (Grayson, 2001). Human predation, evidence of which has been gained from many archaeological sites, was another large factor in the Moas disappearance (Holdaway & Jacomb, 2000). Lastly, the unintentional introduction of Polynesian rats (Rattus exulans) is believed to have played a large role in the extinction of birds not only in New Zealand, but across the whole of the South Pacific (Pimm et al, 2006). Whilst it's doubted by many archaeologists that there was direct predation of Moa eggs by the rats, the rodents are likely to have caused competition for food and impacted the vegetation on which the Moa and other landbirds depended (Grayson, 2001).

Madagascar suffered similar losses following human colonisation roughly 2300 years ago; it too was home to two genera of large flightless bird (Mullerornis and Aepyornis) that are often referred to as Elephant Birds which went extinct between 1600 and 1700 AD (Braje & Erlandson, 2013). Aepyornis was the larger of two, and is believed to have reached weights of up 400kg and a height of 3m (10ft). The causes of extinction are less clear, but signs of butchery from archaeological sites suggest humans played a primary role (Burney & Flannery, 2005).

The birds of other remote islands didn't fare much better. Grayson (2001) suggests that, alongside anthropogenic predation, predation by invasive dogs, pigs and Polynesian rats brought to the islands by humans may have been largely responsible for the disappearance of endemic Hawaiian species. Of 17 species of landbird known from archaeological deposits, only four remain on Hawaii today (Braje & Erlandson, 2013). Rats are also believed to be partly responsible for the loss of 6 species of landbird and several seabird colonies, alongside much of the vegetation (through eating nuts and seeds and thus impairing the ability of the plants to reproduce) on Easter island, which in turn contributed to the breakdown of human society on the island (BBC, 2009)(Braje & Erlandson, 2013).

Grayson (2001) raises the possibility that anthropogenic activities may have, in some instances, created habitats for some subsets of bird species which would not be present were it not for such changes. Despite this, the general consensus is that the increased colonisation of Oceania by humans correlates with an increase in avian extinctions. The past extinction of island fauna paints a grim picture; it shows how easy it is for anthropogenic activities to lead to a loss of biodiversity. Unless we try to minimise our impacts and attempt to preserve and conserve the species that have so far survived, many more species of bird may join the mighty Moa. 

New Zealand by Steve Taylor, on Flickr

Cited:

• Extinctions in Near Time: Causes, Contexts and Consequences - Chapter 10: Late Quaternary Extinctions in Australia (T.F. Flannery & R.G. Roberts, 1999)