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BIRD RADIATIONS Ing Islands, Suggesting They May Host Local Lineages of JEFFREY PODOS and DAVID C

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BIRD RADIATIONS Ing Islands, Suggesting They May Host Local Lineages of JEFFREY PODOS and DAVID C by endemic mosquitoes in a human-modifi ed landscape Van Riper, C., S. G. Van Riper, M. L. Goff, and M. Laird. The epi- with relatively few native birds. Its original host remains zoootiology and ecological signifi cance of malaria in Hawaiian land birds. Ecological Monographs : –. unknown, but unlike many islands, New Zealand had Wikelski, M., J. Foufopoulos, H. Vargas, and H. Snell. Galápagos endemic mosquitoes, which could have coevolved with birds and diseases: invasive pathogens as threats for island species. Ecol- viruses. ogy and Society :. http://www.ecologyandsociety.org/vol/iss/art/. Another signifi cant disease because of its pandemic potential is avian infl uenza. The normal hosts are water- fowl, shorebirds, and seabirds. Sampling for infl uenza antibodies in Australian seabirds shows variation between different species (wedge-tailed shearwaters Puffi nus paci- fi cus and black noddies Anous minutus) and local breed- BIRD RADIATIONS ing islands, suggesting they may host local lineages of JEFFREY PODOS AND DAVID C. LAHTI infl uenza. University of Massachusetts, Amherst THE FUTURE Our understanding of the effects of introduced bird dis- Bird radiations provide informative illustrations of eco- eases on island avifauna has begun to lead to protective logical and evolutionary processes, including those that measures such as the removal of alien-host rock doves help to generate biodiversity as ancestral species radiate (Columba livia) in Galapagos and vector mosquitoes into multiple descendent species. Adaptive radiation (Culex quiquefasciatus) on Midway Island in the Pacifi c, involves initial phases of divergence among populations the implementation of quarantine systems of varying or incipient species, accompanied by or followed by the degrees of competence, the sterilization of boots in the evolution of reproductive isolation. In this article, aspects Antarctic, and the institution of bans on importation of these two key processes—divergence and the evolution of high-risk hosts. Despite these efforts, diseases such as of reproductive isolation—are outlined and examined Newcastle disease, West Nile, and avian infl uenza remain with specifi c reference to island bird radiations. ever ready to make an appearance, facilitated by today’s BIRD RADIATIONS ON ISLANDS: ECOLOGICAL rapid forms of transportation and international trade. AND EVOLUTIONARY INSIGHTS The potential for emerging diseases from islands also continues and may even increase as ecotourism brings Island habitats provide biologists valuable if not unique travelers onto ever more remote islands and then rapidly opportunities for the study of ecology, evolution, and back to sophisticated medical facilities where their ail- animal behavior. Relative to continental habitats, islands ments can be diagnosed as something beyond “fever.” tend to express low biological diversity, high abundance of The study of bird diseases on islands remains one of constituent species, streamlined food webs, and environ- the last frontiers for exploratory biology. It is likely to mental fl uctuations that can be both marked and unpre- continue to provide unexpected insights into immunol- dictable. The simplifi ed and dynamic profi le of island ogy, public health, community ecology, and conservation biology has facilitated the study of a wealth of biological biology, as additional islands, their avifaunas, and their patterns and processes, with results gleaned from island diseases are examined. studies often extrapolated to more complex and empiri- cally less accessible habitats such as tropical rain forests. SEE ALSO THE FOLLOWING ARTICLES Birds have taken center stage in many fi eld studies of island ecology and evolution, following a tradition set by Extinction / Honeycreepers, Hawaiian / Inbreeding / Seabirds David Lack in the mid-twentieth century. Bird radiations FURTHER READING have been numerous and varied, featuring outcomes such as fl ightlessness and robust variations in plumage, size, and Clifford, C. M. Tick-borne viruses of seabirds, in Arctic and tropical beak form and function (Table ). This entry provides a arboviruses. E. Kurstak, ed. New York: Academic Press, –. Daszak, P., A. A. Cunningham, and A. D. Hyatt. Anthropogenic brief overview of some ecological and evolutionary processes environmental change and the emergence of infectious diseases in that drive island bird radiations and then discusses recent wildlife. Acta Tropica : –. fi ndings from the authors’ own studies of two island bird Matson, K. D. Are there differences in immune function between continental and insular birds? Proceedings of the Royal Society B : systems: introduced island populations of African weaver- –. birds, and Darwin’s fi nches of the Galápagos Islands. BIRD RADIATIONS 105 Gillespie08_B.indd 105 4/13/09 2:50:45 PM TABLE 1 Representative Examples of Bird Radiations on Islands Bird Assemblage Islands Distinctive Features of the Radiation Vangas (15–22 species) and Madagascar The vangas’ common ancestor presumably arrived on Madagascar about Malagasy songbirds 25 million years ago and subsequently radiated into a group unusually (9+ species) diverse in both plumage and bill morphology. Another diverse group, Malagasy songbirds (previously placed into three different families of bulbuls, babblers, and warblers), represent a radiation from a single colonizing species 9–17 million years ago. At 587,000 km2, Madagascar is the smallest single island in the world with a prominent bird radiation. Moas (14 species) New Zealand Beginning about 20 million years ago, these herbivorous and fl ightless birds evolved in the absence of predators, radiating mostly within the last 10 million years into a variety of body forms and sizes. Darwin’s fi nches Galápagos and Cocos A grassquit or warbler-like ancestral species colonized the Galápagos about (14–15 species) islands 2–3 million years ago, followed by a pattern of island-hopping and speciation; descendant species eventually redistributed themselves throughout the islands without interbreeding. Bill morphology diverged by adaptation to available seed types, song subsequently diverged as a by-product; female preference for both traits is thought to have promoted reproductive isolation upon secondary contact. Myiarchus fl ycatchers West Indies A single immigration to Jamaica from Central America about 4 million years (fi ve species) ago, led to subsequent island-hopping and divergence. Several island-specifi c forms are designated as subspecies; thus this is apparently a radiation in process. Honeycreepers Hawaiian Islands Beginning about 4–5 million years ago, the descendants of a single colonizing (∼52 species) fi nch species radiated explosively; highly diverse feeding methods and bill types were faciliated by a broad range of vacant feeding niches. Golden whistler Pachycephala Northern Melanesia Called the world’s “greatest speciator” by Mayr and Diamond (2001), this bird pectoralis (66 forms, and New Guinea has diverged greatly in color patterns, but species boundaries are diffi cult to perhaps can be grouped determine. Some forms arose by divergence but others through hybridization into 5 species) (mixing) of existing forms. Chaffi nches Fringilla coelebs North Atlantic islands DNA evidence has indicated the history of chaffinch expansion from an (four forms, designated ancestral stock that ranges across Europe and Africa, to several nearby island as subspecies) groups: a Portuguese chaffi nch population colonized the Azores, birds from the Azores colonized Madeira, and birds from Madeira then colonized the Canary Islands twice. Island Ecology A clear demonstration of competition leading to COMPETITION AND CHARACTER DISPLACEMENT character displacement has been reported by Peter and Any given habitat supports a diversity of species. Species Rosemary Grant, who have been conducting fi eld studies that share habitats are thought to partition limited sets on Galápagos fi nches for over three decades. During an of resources such as space and nutrients. Shorebirds, for initial decade of study, beginning in , the small cen- instance, have evolved to forage in distinct shoreline zones. tral island of Daphne Major was found to support a large Moreover, resource partitioning appears to be adaptive; breeding population of the medium ground fi nch Geospiza sandpipers and plovers, to illustrate, are adept in extract- fortis. This population featured birds of a wide range of ing distinct food sources at particular depths within the beak sizes feeding on a diverse array of seed types, includ- sand or mud, by means of distinct bill lengths and shapes. ing the relatively hard seeds of caltrop Tribulus cistoides . Adaptive partitioning of resources among present-day Observations of feeding fi nches revealed that only the species implies two historical processes: competition for largest-beaked G. fortis were able to crack Tribulus seeds, a limited resources, followed by selection favoring the occu- capability that served these large-beaked birds well during pation of divergent niches (“character displacement”). a severe drought in . With exclusive access to this food These processes are thought to be highly generalized, resource, large-beaked G. fortis were able to survive and explaining, for example, how tropical rainforests can sup- proliferate. In , however, a breeding population of the port a rich biota. However, these processes have proven large ground fi nch (Geospiza magnirostris) began to take notoriously diffi cult to study in fi eld environments. root on Daphne, building slowly and
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