Ilkka Hanski has carried out extensive work on how species survive in fragmented habitats, and his results and models have been used by Atte Moilanen to develop a program to determine which areas need to be protected the most against encroachment or destruction.
The title of Professor Ilkka Hanski’s book, The Shrinking World, refers not to phenomena such as the global village and globalisation, but rather to the increasing fragmentation of the world’s natural environment and to the shrinking habitats that many species are faced with as a result.
Hanski has studied the impact of fragmentation on the natural world for more than 20 years, beginning with a study of shrews inhabiting the small islands of a lake in northeast Finland. Studying these small mammals, he outlined the first version of his metapopulation model, a model that has since been refined and adopted by ecologists around the world to look at how species survive in an increasingly disconnected natural world.
|The work done by Professor Hanski’s team on the Glanville fritillary butterfly has been among the most extensive anywhere. Laboratory studies are combined with fieldwork, genetic analyses, and mathematical modelling to advance researchers’ understanding of the underlying factors at work.
Generating truly useful data
Hanski’s research team combines empirical work on individual species, such as the Glanville fritillary butterfly, with mathematical modelling work, to overcome what he says is one of the bottlenecks in population biology studies: the fact that too little research has been done on a sufficiently large spatial scale to address many important phenomena. Seventeen years of work on thousands of Glanville fritillary populations in a network of 4,000 meadows has generated a very rich body of data.
While many habitats are naturally fragmented, many more are becoming dramatically fragmented as a result of growing human impact. Environments rich in terms of natural biodiversity are being destroyed at an alarming rate, including coniferous forests in Europe, rainforest in the Amazon basin, and coral reefs in the Pacific. The areas that are left are becoming ‘island sanctuaries’ for the species that survive.
The parameters of survival
Hanski’s metapopulation model is based in part on the theory of island biogeography first developed in the 1960s and focused on how migration from mainland communities to islands affects the dynamics of the latter.
The same approach can be used with networks of islands or island-like habitat fragments without any mainland. In this case, a species is not ‘rescued’ by migration from the mainland, it either survives or not among the set of habitat fragments alone.
|A simplified map generated by the Zonation program of priority areas in southern and central Finland that would benefit the most from increased protection.
Click here to enlarge picture
When less than 10% of the surface area of a particular landscape remains following habitat destruction and fragmentation, the animal and plant populations that survive tend to be small and unstable. If the bonds between individual populations break down too much, an entire species is liable to disappear. Survival calls for the presence of sufficient amounts of suitable habitat in sufficiently large areas and sufficiently close to each other to maintain the overall metapopulation of a species.
Where to draw the line?
With this in mind, it is relatively easy to see from maps of old-growth forest in Finland why so many species indigenous to these habitats are under threat. Old-growth forest has been reduced to increasingly small ‘islands’ in many places, separated by clear-cut areas and young stands of saplings, as well as roads, fields, and other developments.
While many would agree that more land under threat should be protected, deciding which areas are most at risk is normally not so easy to agree on. Conservationists have their own views and agendas, and others their own. Which is why Atte Moilanen, the deputy head of the unit led by Professor Hanski, decided to develop a more objective tool – in the shape of a high-resolution optimisation program capable of working with large amounts of data from satellite and other remote-sensing sources to identify areas most at risk.
The result was Zonation 1.0, which is now in its second iteration, with version 3 in the pipeline. A free Internet download, the program can provide a map of areas that need to be protected the most, based on the habitat needs of the species concerned and the spatial structure and habitat composition of the landscape. Issues such as land value and the cost of maintaining protected areas can also be included in these calculations.
As with metapopulation models, the Zonation program also calls for data on the biology of species that need to be protected, to take account of the fact that habitats and the links between them can ‘look’ very different, depending on whether you are a frog or a bird, for example.
Zonation has proved useful for a wide variety of users, ranging from scientists to municipalities, regions, and entire countries. In Finland, for example, the program is now used to help plan extensions to areas of old-growth forest that are currently protected. Users can already be found as far afield as Madagascar, Australia, Britain, New Zealand, and the US. Given the increasingly acute need for help in selecting and protecting endangered habitats and species, Zonation is likely to have even more to offer in the future.
For more information on the program, see