The UN Climate Panel IPCC predicts global warming of 2-4 degrees Celsius over the next one hundred years. Even though the underlying cause of this warming is new, similar and even more violent fluctuations in the climate have occurred several times before in the earth’s history. This type of large scale climate change has had a great impact on the distribution of species.
Through fossil excavations and detailed dating methods we know, for example, that the distribution of several European mammals has changed, expanded and shrunk several times over the past 50,000 years. However, what we know much less about is in what way these changes in distribution occurred. If, for example, the distribution of a certain species changed from a southern geographical region to a more northerly region, this does not automatically imply that the southerly population had migrated northwards. It is just as likely that the southerly population had become extinct, and that the fossils we find in more recent fossil strata further to the north are the result of colonisation from some other region, for example Asia.
Prediction of future migrations
This lack of knowledge as to whether populations can cope with migration from one place to another when the climate changes is today a serious problem for researchers who are engaged on modelling how species are expected to respond to future climate changes. In the models (species distribution models) that are used today it is found that the habitats of many species are expected to move northwards, without any overlap between the present and future distribution. In order to be able to predict how many species may be expected because of climate changes to become extinct in future, two different estimates are therefore usually made, one in which the populations are expected to be able to migrate to the new habitat without any limitations, and another where they are not allowed to migrate at all. It is not surprising that this results in great uncertainty as to how many species are expected to become extinct over the next hundred years.
Even if it is found that by far the most populations can manage to migrate with the climate, which would result in a relatively low degree of extinction, we also know extremely little of what consequences this will have on a genetic level. It is probable that a change in distribution will cause a loss of genetic variation, but it is not clear at present how large these losses will be in the future.
The models are tested backwards
One possible procedure of coping with these issues, instead of modelling for the future, is to project the above species distribution models backwards in time. By combining these models with genetic analyses of fossil bones and teeth found in excavations all over Europe, which originate from different historical periods, we can investigate to what extent populations die out, or migrate, when the climate changes.
In the spring of 2009 an international research project, CLIMIGRATE, will start with the aim of investigating how different species responded to historic climate changes over the past 50,000 years, by combining species distribution models with DNA analysis of fossil material. This is a collaborative project among researchers from three countries, where the Swedish part is led by Love Dalén of the Swedish Museum of Natural History. Other partners are Ian Barnes of Royal Holloway University, London, and Nigel Yoccoz of the University of Tromsö. The species to be investigated include both Arctic species such as arctic fox, lemming and reindeer, and temperate species such as red deer, red fox and water vole. In the final phase of the project the results from the genetic analyses will be used to adjust and improve the species distribution models in use at present. They will then be applied to the model species included in the project, in order to predict how these species will respond to the climate change we are facing in the next one hundred years.
Author
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Love Dalén
is assistant professor at the Molecular systematic laboratory, Museum of Natural History, Stockholm.