An opinion article by Chris Thomas, biologist at the University of York, UK. The article is adapted from a review in Trends in Ecology and Evolution (vol 26, p 216). He writes: “Some places are ideal havens for species threatened by climate change. One is Britain, and it should throw open its doors.”
VISIT an estuary or wetland in the lowlands of Britain and chances are you will see a slender white bird called the little egret. Although widespread, the species is a recent arrival from more southerly latitudes: the first breeding population established itself in 1996.
The little egret isn’t the only one. As the climate warms, species all over the world are relocating to higher latitudes at an average rate of 17 kilometres per decade.
However, some species are unable to relocate – those restricted to the summits of single mountain ranges, for example. Many are projected to become extinct.
What are the options for such species? One possibility is “assisted colonisation“, which means deliberately introducing them into areas where the climate is more suitable. Assisted colonisation divides opinion among conservationists. I would argue it is now the only realistic way to maintain wild populations of some species.
To some extent, assisted colonisation is already part of established practice, as subspecies are sometimes introduced to areas outside their native ranges. The Swedish subspecies of the large blue butterfly, for example, was introduced to Britain after the native one became extinct.
In some cases, extinct species are being replaced with ecologically equivalent ones. On Mauritius’s Round Island, giant tortoises from Madagascar and the Seychelles are being experimentally introduced to replace the native ones driven to extinction in the 19th century.
Why stop there? Introductions could be even more desirable if the introduced species were themselves endangered.
This, too, is not unheard of. In New Zealand, Brothers Island tuataras have been moved to predator-free Titi Island without anyone knowing for sure whether they ever lived there. Similar attempts are under way to establish the Bermuda petrel on Bermuda’s Nonsuch Island, where hurricanes and sea-level rise pose less of a risk than in its native breeding areas.
In these cases, it is accepted that the benefits outweigh any negative consequences. It is surely better to maintain such species somewhere in the wild than condemn them to captivity or extinction.
There are, of course, arguments against assisted colonisation. One is that relocated species could displace native species from their new homes. That is a real danger, but the risks are low in some situations.
It is true that about 40 per cent of extinctions with a known cause have been associated with invasive species. But almost all these extinctions either occurred in environments with high concentrations of “endemic” species that occur nowhere else, or involved moving species between continents. These are not the types of movement I advocate.
Another fear is the creation of “unnatural” communities, but this is not particularly relevant in today’s world. A philosophy of conserving communities as they are, or restoring them to some specified or imagined historical state, is no longer credible. The transport of species has already altered biological communities permanently. Whatever we do, species will continue to be moved for agriculture, horticulture, forestry, the pet trade, medicine – and by accident.
Climate change adds to the melting pot. Everywhere we have looked, it has already altered the composition of biological communities. Why should they not also contain species that would otherwise be endangered?
At present we don’t know how many climate-threatened species with narrow distributions could thrive if they were transported elsewhere, but further research should reveal this.
Another key question is, where should we move species to? Given that invasive species hardly ever cause extinctions in places with few endemics, we should be looking for places dominated by non-endemic species. One such place is Britain.
To the best of my knowledge, no native species has gone extinct here as a result of the arrival of non-native species (other than humans). Britain is already home to around 2000 introduced species which have increased biodiversity while causing few, if any, major problems. True, there have been ecological changes, and we spend a lot of money trying to get rid of aliens, but Britain appears virtually immune to extinctions from introduced species. It therefore represents an ideal destination for endangered species from elsewhere in Europe.
One is the Iberian lynx, the most endangered cat in the world. Establishing it in Britain would represent a great contribution to global conservation. Another is the Spanish imperial eagle; a third possibility is the Pyrenean desman, a semi-aquatic mammal restricted to streams in north-west Iberia.
Various butterflies and water beetles might also find a suitable home in Britain. In fact, the vast majority of species endangered by climate change are likely to be plants and insects that would be relatively easy to accommodate.
Virtually all of Britain’s land is heavily modified by humans, and its extensive tracts of largely artificial habitat – conifer plantations, for example – could be enhanced by translocated species. I think it is time for gardeners, landowners and conservation organisations to get involved in identifying species we might be able to save and places where we could move them.
Conservation is now about managing change. Retaining or restoring the past is no longer feasible. We should avoid the unproductive question “how can we keep things as they are?” and instead ask “how can we maximise our contributions to global conservation?” One way will be to open our doors to endangered aliens.
Source: NewScientist, November 2011