Island Biogeography: A Perspective from Tasmania

It is a great privilege to have been asked to respond to Lee Durrell’s account of the Durrell Wildlife Conservation Trust’s extraordinary work. Lee has provided a succinct explanation of why islands are so suitable for the study of biodiversity. She has pointed out that islands comprise only 5% of the Earth’s land mass, but contain a quarter of all terrestrial species, with such species more vulnerable to extinction than species on mainlands. ‘Of the 840 known extinctions since 1640’, she has told us, ‘60% were known only from islands’.

The central place of islands in the development of evolutionary science is now a given. Charles Darwin, pondering observations made in the Galapagos, and Alfred Wallace, working in the islands of the Malay Peninsula, simultaneously developed their revolutionary theories from the study of life on islands. Pioneering works of island biogeography, many rising independently from studies in the field, suddenly proliferated. Then, in 1967, with Robert MacArthur and Edward O. Wilson’s The Theory of Island Biogeography, the centrality of islands to evolutionary science and global species distribution was firmly established, though points of contention remain. An explosion of writing on the subject ensued, much of it in hefty tomes that demonstrate the complexity and contentious nature of the principles that explain the life and death of island species. David Quammen’s magisterial The Song of the Dodo: Island Biogeography in an Age of Extinctions (1996), for example, runs to over 700 pages. Much of this writing extended the insights of island biogeography to insular habitats on mainlands, arguing for an ‘island effect’ of profound import; revolutionary in its significance (for example, Diamond 1975; Simberloff 1974).

It would be impossible to rehearse the scientific complexities and points of disputation here. An outline of the key tenets must suffice.