Islands as model systems in ecology and evolution: prospects fifty years after MacArthur‐Wilson

The study of islands as model systems has played an important role in the development of evolutionary and ecological theory. The 50th anniversary of MacArthur and Wilson's (December 1963) article, ‘An equilibrium theory of insular zoogeography’, was a recent milestone for this theme. Since 1963, island systems have provided new insights into the formation of ecological communities. Here, building on such developments, we highlight prospects for research on islands to improve our understanding of the ecology and evolution of communities in general. Throughout, we emphasise how attributes of islands combine to provide unusual research opportunities, the implications of which stretch far beyond islands. Molecular tools and increasing data acquisition now permit re‐assessment of some fundamental issues that interested MacArthur and Wilson. These include the formation of ecological networks, species abundance distributions, and the contribution of evolution to community assembly. We also extend our prospects to other fields of ecology and evolution – understanding ecosystem functioning, speciation and diversification – frequently employing assets of oceanic islands in inferring the geographic area within which evolution has occurred, and potential barriers to gene flow. Although island‐based theory is continually being enriched, incorporating non‐equilibrium dynamics is identified as a major challenge for the future.     

Charles Darwin's theory of evolution: A review of our present understanding

The paper characterizes Darwin's theory, providing a synthesis of recent historical investigations in this area. Darwin's reading of Malthus led him to appreciate the importance of population pressures, and subsequently of natural selection, with the help of the wedge metaphor. But, in itself, natural selection did not furnish an adequate account of the origin of species, for which a principle of divergence was needed. Initially, Darwin attributed this to geographical isolation, but later, following his work on barnacles which underscored the significance of variation, and arising from his work on botanical arithmetic, he supposed that diversity allowed more places to be occupied in a given region. So isolation was not regarded as essential. Large regions with intense competition, and with ample variation spread by blending, would facilitate speciation. The notion of place was different from niche, and it is questioned whether Darwin's views on ecology were as modern as is commonly supposed. Two notions of struggle are found in Darwin's theory; and three notions of variation. Criticisms of his theory led him to emphasize the importance of variation over a range of forms. Hence the theory was populational rather than typological. The theory required a Lamarckian notion of inheritable changes initiated by the environment as a source of variation. Also, Darwin deployed a use/habit theory; and the notion of sexual selection. Selection normally acted at the level of the individual, though kin selection was possible. Group selection was hinted at for man. Darwin's thinking (and also the exposition of his theory) was generally guided by the domestic-organism analogy, which satisfied his methodological requirement of a vera causa principle.     

Four Darwinian themes on the origin,evolution and preservation of island life

Charles Darwin’s observations and insights continue to inspire nearly all scientists who are captivated by both the marvels and the perils of island life. Here I feature four themes inspired by Darwin’s singular insights: themes that may continue to provide valuable lessons for understanding the ecological and evolutionary development of insular biotas, and for conserving the natural character and evolutionary potential of all species restricted to isolated ecosystems (natural or anthropogenic).     

Darwin's changing views on evolution: from centres of origin and teleology to vicariance and incomplete lineage sorting

It is a strange fact that in many ways the first edition of Charles Darwin's Origin of Species is closer to modern neodarwinism than the sixth and last edition. Sometimes this is attributed to a decline in the quality of the argument, but the opposite interpretation is given here. It is suggested that Darwin's early work on evolution is naïve and based on the two creationist principles of centre of origin and teleology (panselectionism). This fusion later became the 'modern synthesis'. However, after the first edition of the Origin , Darwin developed a non-teleological synthesis that integrated natural selection with what he called 'laws of growth'– phylogenetic/morphogenetic trends or tendencies. Discussion of Darwin's later, more sophisticated model of evolution has been suppressed in the teleological modern synthesis, but similar ideas are re-emerging in current work on molecular phylogenetics and biogeography. This indicates that the ancestor of a group can be diverse in its morphology and its ecology, that this diversity can be inherited, and that groups usually originate over a broad region and not at a single point.     

Darwin's biogeography

The year 2009 marks the 150th anniversary of the publication of Charles Darwin’s Origin of Species. This book was so influential that it is often considered to be the most important scientific work ever written. Many volumes have been published about the Origin and its lasting effects on religion and society, but few have examined its influence on biogeography. However, it was Darwin’s initial interest in comparing the natural history of different regions during the voyage of the Beagle that led him to propose natural selection as an evolutionary force. He had visited the Cape Verde Islands and saw the similarity of their biota to that of Africa, and then noted the South American relationships of the Galapagos fauna and flora. But the island plants and animals were different from their mainland relatives, and, in the Galapagos, each island appeared to have its own endemic forms. It was these biogeographical observations that were critical to Darwin’s formulation of a theory to account for them. His subsequent conclusions on the evolutionary importance of centres of origin and dispersal were generally well accepted for the next 100 years, until the advent of vicarianism, which began in the early 1970s. That vicarianist movement received an impetus from two sources: (1) the works of Leon Croizat, who did not believe that living organisms could disperse overseas by themselves; and (2) the development of plate tectonics and its causation of continental drift. Vicarianists believed that primitive species were originally widespread over the Earth’s surface but were rafted to different parts of the world by continental fractionation and movement. However, continental drift in the Mesozoic could not have involved contemporary species or genera as many vicarianists claimed. The development of phylogeography, beginning in the 1980s, and improved knowledge of the fossil record soon demonstrated that multitudes of living species, and even many genera and families, underwent long‐distance dispersal during the Cenozoic. This resulted in a decline of vicarianism and a vindication of Darwin’s conclusions on centres of origin and dispersal.     

Ogasawaracris gloriosus, a new genus and species of possibly extinct grasshopper (Orthoptera: Acrididae) from the Ogasawara Islands

A new grasshopper genus and species of the subfamily Eyprepocnemidinae, Ogasawaracris gloriosus, is described from the Ogasawara Islands, oceanic islands south of Japan. This species has unique characteristics, such as an extraordinarily large body, rugose and very coarse punctation on the lateral surface of the pronotum, and very strong pronotal lateral carinae. Specimens of this new species have rarely been collected and they are known only from the Ogasawara Islands. The species may already be extinct.     

The Role of Small Islands in Marine Subsistence Strategies: Case Studies from the Caribbean

Caribbean archaeologists have tended to focus exclusively on the prehistory of the largest islands, perhaps because large islands are believed to provide the landmass necessary to support long-term population growth and cultural development. Yet, as research here and elsewhere, e.g., the Pacific, is showing, small islands provided access to resources and landscapes that were not always readily available on the larger islands. Small islands often have superior terrestrial and, especially, marine resources; isolated ritual spaces; and more easily defended locations; although they are susceptible to more rapid overexploitation. This paper examines in detail human needs with regard to island size, demonstrating that small islands were crucial in the development of pre-Columbian Caribbean societies. Four case studies are presented to illustrate that small islands often were preferred over large islands throughout the Caribbean archipelagoes. Finally, these studies show that the prehistoric exploitation and overexploitation of small islands can provide significant insights for establishing baselines that can be used for modern management and conservation efforts.

Darwin's sexual selection: Understanding his ideas in context

Darwin's writings need to be seen in their fullness, as opposed to quote-mining individual sentences without the context of his passages. Sometimes Darwin wrote at length, apparently favorably, about ideas that he subsequently undermined, replacing them with a more integrative view that reflected his own broad compass. Darwin understood that nature is not simple, that not all members of a group may have evolved under the same selective regime, and that variation of all kinds is fundamental to selection in its several forms. Sexual selection requires sexual dimorphism; it is not centred on variation within sexes but on selection for the ability to acquire mates. “Mutual sexual selection” was rejected by Darwin for every species except humans. Mating success is not a matter of mere numbers but of the transmission of the most attractive features to the opposite sex. The term “sexual selection” should only be used when one sex uses a feature not present in the other sex to attract mates or repel rivals for mates.     

Adaptations: Using Darwin's Origin to teach biology and writing

Charles Darwin's On the Origin of Species is at once familiar and unfamiliar. Everyone knows that the Origin introduced the world to the idea of evolution by natural selection, but few of us have actually read it. We suggest that it is worth taking the time not only to read what Darwin had to say, but also to use the Origin to teach both biology and writing. It provides scientific lessons in areas beyond evolutionary biology, such as ecology and biogeography. In addition, it provides valuable rhetorical lessons—how to construct an argument, write persuasively, make use of evidence, know your audience, and anticipate counterarguments. We have been using the Origin in various classes for several years, introducing new generations to Darwin, in his own words.     

Darwin's legacy: the forms,function and sexual diversity of flowers

Charles Darwin studied floral biology for over 40 years and wrote three major books on plant reproduction. These works have provided the conceptual foundation for understanding floral adaptations that promote cross-fertilization and the mechanisms responsible for evolutionary transitions in reproductive systems. Many of Darwin''s insights, gained from careful observations and experiments on diverse angiosperm species, remain remarkably durable today and have stimulated much current research on floral function and the evolution of mating systems. Here I review Darwin''s seminal contributions to reproductive biology and provide an overview of the current status of research on several of the main topics to which he devoted considerable effort, including the consequences to fitness of cross- versus self-fertilization, the evolution and function of stylar polymorphisms, the adaptive significance of heteranthery, the origins of dioecy and related gender polymorphisms, and the transition from animal pollination to wind pollination. Post-Darwinian perspectives on floral function now recognize the importance of pollen dispersal and male outcrossed siring success in shaping floral adaptation. This has helped to link work on pollination biology and mating systems, two subfields of reproductive biology that remained largely isolated during much of the twentieth century despite Darwin''s efforts towards integration.     

Islands as biological substrates: Continental

Aim

Describe the main geo‐physical features of the various sorts of marine islands that are associated with the continents and consider how the ontogenetic pathways of each landmass type might have shaped the hosted biotas.

Location

Global.

Methods

Review of the literature that underpins understanding of the “continental” marine islands, particularly those publications with biological, geological, geophysical, oceanographical and palaeoceanographical foci.

Results

Based on their geo‐physical settings, islands with continental basements/close connections to the continents can be assigned to one of nine categories: shelf, shelf volcano, orogenic margin, continental arc, continental fore‐arc, rifted arc‐raft, isolated raft atoll, isolated block and micro‐continental terrane. As each functions in a distinctive manner, this must have strongly imprinted the native biotas.

Main conclusions

“Continental” marine islands can be allocated to one of nine groups based on their respective geo‐physical locations. When geological time is considered, then the unique histories of each insular landmass type will have played a critical role in moulding the land‐locked faunal assemblages that have amassed and evolved atop them. Researchers investigating insular biotas, particularly those exploring biodiversity growth, may wish to accommodate these insights.     

Origin and evolution of endemic plants of the Bonin (Ogasawara) Islands

The Bonin Islands are typical oceanic islands, located at the western part of the North Pacific Ocean and approximately 1,000 km south of mainland Japan. This archipelago consists of about 20 small islands. Although floristic diversity is low due to the small area and limited environmental diversity, the Bonin Islands harbor unique endemic flora as in other well-known oceanic islands. This paper presents a brief summary of the results obtained from recent studies on the endemic flora of the Bonin Islands. The results are reviewed in relation to the four stages of the evolution of endemic flora in the oceanic islands; migration, establishment, enlargement and diversification. The ancestors of the flora originated mostly from tropical and subtropical Southeast Asia or mainland Japan by rare events of long distance dispersal. The proportion of bird-dispersed species is relatively high as for other oceanic islands. Genetic data sets obtained from allozyme variation in some endemic species suggest that migration occurred several million years ago and genetic diversity is correlated with current population size. At the time of establishment, self-compatible plants are expected to have an advantage. However, the percentage of dioecious plants is relatively high. This is partly due to evolutionary changes from hermaphroditic ancestors to dioecy which occurred in two genera in the Bonin Islands. In addition, there are some examples of evolutionary changes from herbaceous ancestors to woody endemics. Adaptive radiation is found in some genera, although the number of congeneric endemic species is less than five. Studies of allozyme variation inPittosporum, Symplocos andCrepidiastrum showed that genetic identity is generally very high between congeneric species in spite of their distinct morphologies. This result suggests that divergence of these species occurred rather recently and distinct morphological differences are based on a limited number of genetic changes.