Islands as individuals

Abstract

In natural history, as in history, there is a tension between the generalization and the individual event. In this book, an example of the general is the equilibrium theory of island biogeography (which Whittaker abbreviates to ETIB), whereas the individual is exemplified by the lighthouse keeper's cat. The feline in question belonged to a lighthouse keeper on Stephens Island in the Cook Strait (New Zealand). The cat discovered the Stephens Island wren, which was duly named Traversia lyallii (after the lighthouse keeper, not the cat). However, the cat was an overenthusiastic collector, which became a problem for the wren. The details of this individual history provide insights into many aspects of island biology – but so too does a general ‘story’ like the ETIB. Going from the specific to the general has the advantage of universality but the disadvantage of simplification, because islands are not homogeneous in age, size, natural disturbance, human disturbance, biota, climate or geology. They are not even homogeneous in what surrounds them, as isolated habitats like the eastern arc mountains of Tanzania are islands in everything but sea.One important factor of the past five years or so that has tended to swing the balance away from general theory towards individual history is the revolution in molecular phylogenetics. When there are enough phylogenies, important new generalizations can emerge or existing generalizations can be supported or refuted, but we are still at the stage where each new phylogeny represents an individual history of colonization, radiation and persistence. Island Biogeography is not a book about phylogenetics (only two cladograms are included), but Whittaker refers readers to Wagner and Funk's compilation1xSee all References1, which is a bold attempt to integrate phylogeny and biogeography in the Hawaiian islands. The great advantage that islands lend to phylogenetics is that the ingroup is present in a confined area and is easily collectable. This is particularly attractive for studies of adaptive radiation, such as the pioneering work of Baldwin and others on the Hawaiian silverswords2xBaldwin, B.G. et al. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 1840–1843Crossref | PubMedSee all References2. However, difficulties remain in tracking down the outgroup taxa, which (particularly with relict taxa) can be widely scattered in continental regions. Both relicts and recent explosive radiation can occur on different islands in the same group, as in Saintpaulia on East African mountains3xMoeller, M. and Cronk, Q.C.B. Proc. R. Soc. London Ser. B. 1997; 264: 1827–1836Crossref | PubMed | Scopus (24)See all References3.Whittaker examines the role that island thinking (particularly the ETIB) has had outside the island domain and poses the question: does conservation biology need island theory? The answer is probably a qualified yes while agreeing that ‘…the abundance of publications on the theory of island biogeography and applications [of it] has misled many scientists and conservationists into believing we now have a ready-to-wear guide to natural area preservation…’4xSee all References4 We don't – both because natural areas are individuals as much as they are a class and also because in the ‘single-large’ or ‘several-small’ debate, many practical conservationists must simply answer: ‘anything-we-can-get’.Even if conservation biology does not need island theory, islands certainly do need conservation biology. According to the recently published IUCN Red List of Threatened Plants5xSee all References5, the British island of St Helena has the most endangered flora in the world. Excluding those plants that have already been allowed to slip into extinction, such as the string tree (Acalypha rubrinervis), numerous plants exist as populations of less that 20 individuals6xSee all References6. These include Trochetiopsis ebenus (St Helena ebony), which has two plants left in the wild but many cultivated individuals, Nesiota elliptica (St Helena olive), which is extinct in the wild and has only two cultivated individuals remaining, and Commidendrum spurium (false gumwood), with six plants in the wild and a few in cultivation. These plants are no longer in equilibrium within their system; they are individual stories waiting for an ending – either extinction or rehabilitation. Because they have completely lost their habitats, habitat restoration is an important issue, in particular the restoration of viable breeding systems (in cases of pollinator extinction) and viable patterns of gene exchange. As Whittaker is at pains to point out, islands all too often exist in a ‘non-equilibrium world’ and he concludes that ‘we should no longer give equilibrium models primacy in island ecology’.This book balances individuality and theory well. A thorough and even-handed account of island theory is given, providing many new insights, and it also provides a mine of stimulating facts about island life. It is sure to emerge as the standard text for university teaching of island issues.