H. Charles J. Godfray is inspired by the scientific memoir of late island ecologist Ilkka Hanski.
Messages from Islands: A Global Biodiversity Tour
By Ilkka Hanski
Combining 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.
Åland, of course, is the basis of a chapter. We learn how Hanski drew on the deep knowledge of Finnish butterflies and moths that he gained as a keen teenage naturalist in his search for a suitable model system. As elsewhere in the book, he explores much broader questions in population biology — for example, how agriculture, deforestion and other types of habitat change have shattered what would once have been contiguous habitats. Many more species live in metapopulations today than in the past, so understanding them can help in the design of protected areas, increasing the chance that a threatened species will persist.
Hanski's passionate concern for biodiversity is evident throughout the book. The chapter on Madagascar discusses the island's community of nearly 300 species of dung beetle (the subject of Hanski's doctorate and an abiding passion throughout his life). Madagascar has experienced extensive deforestation in the past century, making it likely that some of the dung-beetle species known from nineteenth-century collections are now extinct. More positively, Hanski and his students have documented how some species have evolved to utilize the dung of introduced livestock such as cattle.
This leads to a more general discussion of how biodiversity is generated, for example drawing lessons from Darwin's finches and pollinating bees about when natural selection favours specialization or being a jack-of-all-trades. That, in turn, leads back to the Glanville fritillary, in which Hanski has demonstrated genetic differences in the colonization ability of butterflies from the core and periphery of the metapopulation.
Haminanluoto is the smallest island discussed in the book. This 2-hectare islet is on the south coast of Finland near the village of Hanski, named after a seventeenth-century ancestor of the ecologist. At the age of 14, Hanski counted 15 species of bird on the island. Repeat counts in 2003 and 2013 found about the same number of species, although some of the original species had gone and new ones had colonized the island. Hanski muses on how human activities have affected the natural dynamics of species turnover. This leads to thinking about the future potential impacts of climate change.
Here again, Hanski's own experiences are illuminating. As a doctoral student he took part in an expedition to the virgin forests of Gunung Mulu in Sarawak, on the north coast of Borneo. He studied the dung-beetle communities living at different altitudes and found that species composition changed as you moved up the mountain. Thirty-five years later, he returned and repeated the exercise. He found the same sequence of species along the transect, but the whole distribution had shifted upwards, probably owing to global warming. Hanski laments another difference: Gunung Mulu is itself now an island in a sea of oil palm, no longer part of a much more extensive forest.
Hanski wrote Messages from Islands after being diagnosed with cancer. His book does not shy away from the challenges that face humanity or the threats to biodiversity. Yet it is an uplifting read, revealing the author's humanity and deep love of the natural world. I cannot think of a better book to give to a general reader who wants an insight into modern ecology and how ecologists go about their trade.