Winged insights

H. Charles J. Godfray in Nature:

WingedCombining a personal memoir with serious discussion of a scientific subject is a difficult literary trick. The Finnish biologist Ilkka Hanski succeeded with aplomb in his last book, Messages from Islands, in which each chapter begins with insights from an island that moulded his thinking about ecology, evolution and conservation. Hanski, one of the foremost ecologists of his generation, died in May (A.-L. Laine Nature 534, 180; 2016). Finland is a land of lakes and islands, so perhaps it is not surprising that Finnish ecologists are drawn to investigating how populations and communities persist in fragmented habitats. Hanski is most celebrated for developing the ecological concept of a metapopulation — a population of populations connected by dispersal — and its applications to conservation. There are several types, but a classical metapopulation is sometimes likened to a collection of “blinking lights”, with individual short-lived populations winking in and out of existence while the whole ensemble persists.

Hanski explored the concept through his 25-year, and ongoing, study of the Glanville fritillary (Melitaea cinxia) in the Åland Archipelago between Finland and Sweden. This checkerspot butterfly has exacting habitat requirements: it occupies a fluctuating number of the small woodland meadows that constitute a habitat archipelago within the geographical archipelago. The meadows are so tiny that they support only a small butterfly population; each has a high risk of extinction every year. Hanski, his colleagues and an ever-changing army of students surveyed all 4,000 or so meadows, which support 400–800 populations each year. Through this and many experiments, such as quantifying rates of dispersal between patches, they constructed a model of the butterfly's metapopulation — the most detailed and satisfying description of such a population structure currently available, by some distance.

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