Birds of paradise, biogeography and ecology in New Guinea: a review

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918 M. Heads and are usually gregarious. He concluded: Òne might suppose that such birds would be exempt from the standard zoogeographical patterns, but this is not borne out by an examination of their breeding distribution. In fact, standard zoogeographical patterns emerge¼' One such pattern is the curious poverty of forms on Madagascar and Australasia, also seen in woodpeckers and many other groups. Frith & Beehler (1998) suggested that `both Manucodia and Paradisaea have dispersed across deep-water barriers¼ over water differentiation follows chance dispersal across a permanent water barrier. Although this is evidently a rare event in the birds of paradise, it has produced six insular species¼ Apparently over-water dispersal is a highly effective pathway to speciation in birds of paradise'. However, this begs the question: why has over-water dispersal not been effective in getting the birds to the nearby islands fringing northern PNG? A related problem with long-distance dispersal is not concerned with how it could occur in the ®rst place ± that seems obvious in birds, mammals, ferns, orchids, etc., all with their ordinary means of survival ± but how and why the ìnvasion' would be occurring at one period in time and then, for no apparent reason, cease, and such a cessation is necessary for allopatric evolution. To explain this without invoking geological change biologists have often employed a concept of `chance dispersal' which can èxplain' any pattern at all, but is ad hoc and untestable. In 1605 Clusius already knew that Paradisaea apoda lives on the Aru Islands, while P. minor is on the western Papuan Islands (Gilliard, 1969). Since that time vicariance (that is, geographical replacement or representation) has been discovered in many birds and since the 1890s the use of trinomials in ornithology and mammalogy has been based on the ubiquitous phenomenon. The impression on reading through a list of world birds and their ranges is not one of active range expansion, but one of each bird's localized distribution interlocking in a vicariant way with that of its relatives, forming just one tile in a global mosaic. Perhaps the normally observed powers of physical movement in birds that are crucial for survival (feeding, avoiding predation, reproduction, etc.) are of little signi®cance in establishing the geographical range of taxa. During periods of major tectonic and physiographical change, such as rifting and terrane accretion, whole faunas may well expand their range, for example along new shore lines, but in birds such as the Paradisaeidae there is no evidence for recent, long-distance dispersal over modern geography. In fact most birds of paradise appear to be sedentary forest dwellers with relatively small home ranges (Frith & Beehler, 1998) and rather than their biogeography being determined by their ecology, the ecology of the birds (for example, their altitude) may be determined by their prior biogeography and subsequent tectonic developments. The age of birds Evidence is mounting that most groups of birds are considerably older than was thought. Ever since Matthew's (1915) very in¯uential text on vertebrate palaeontology, a literal reading of the fossil record is the technique which has featured in most work on the chronology of evolution. This would suggest, for example, a Tertiary radiation of the mammal and bird orders. The fact that no bird of paradise fossils are known would be taken as evidence for a very young age of the group. However, new palaeontological and molecular evidence (e.g. Hedges et al., 1996) indicates an earlier, Cretaceous diversi®cation of modern mammal and bird lineages, and emphasizes the major gaps in the fossil record. Nearly complete specimens from north-eastern China show that modern birds as a subclass (Ornithurae) have existed since at least the Late Jurassic (Hou et al., 1996). Similarly, recent studies in palaeontology (Chatterjee, 1998; Forster et al., 1998; Stidham, 1998) and molecular sequencing (Cooper & Penny, 1997) indicate that bird diversity is much older than previously thought, with most or all of the major modern orders present in the Cretaceous. For nearly a century the orthodox school of evolutionary chronology has been devoted to a virtual cult of the oldest fossil of a taxon which is inferred, often implicitly, to have originated with it. But in recent times gene sequencing has been undermining this approach, despite the fact that the gene trees are often calibrated using fossils to give minimum ages. These molecular studies indicate that the fossil record is severely ¯awed and that a literal reading of evolutionary detail in it is an unrealistic approach. Coupled with the traditional chronological paradigm was the Pleistocene refugium model, an idea proposed in the 1970 and 1980s to explain tropical diversity. In applying the idea to New Guinea, it was suggested that during the Pleistocene ice ages populations of forest birds were fragmented on a large scale and only occurred in a relatively small number of forest refugia. There are many problems with this scenario. For example, a long pollen record from the Amazon rainforest, the area for which the theory was developed, indicated that there has been continuous rainforest there for 40,000 years ± it was not fragmented during the glacial maxima (Colinvaux et al., 1996). Likewise DNA differences between sister species of North American birds indicate a speciation history over the last 5 Myr, implying a history ten times longer than that predicted by the Late Pleistocene origins model (Klicka & Zink, 1997). Similarly, in the Pseudomyrmex viduus (F. Smith) group of ants, centred in the Amazon basin, the geographical ranges of most species do not coincide with the proposed Pleistocene forest refugia. Instead, phylogeny, biogeography and host plant speci®city indicate that much of the diversi®cation took place in the Tertiary (Ward, 1999). Cracraft & Prum (1988) criticized the refugium theory, and instead proposed a vicariance event (the rising of the Andes) to explain birds with western Colombian ± upper Amazonian disjunctions, supporting earlier ideas of Chapman (1917) and Croizat (1958). Recent evidence con®rms that the lineage of many Andean birds and mammals differentiated well before the Pleistocene, and probably even before the uplift of the Andes. Many botanists and zoologists previously thought that Ó Blackwell Science Ltd 2001, Journal of Biogeography, 28, 893±925
Biogeography of birds of paradise 919 species in the Andes evolved at most a few million years ago, but DNA evidence from Thraupidae, Formicariidae, Emberizidae and others shows lineages dating back 4±10 Myr, again an order of magnitude older than previous estimates (conference papers presented by J. Bates, J. Lundberg and S. Hackett, reported in Moffat, 1996). Roy et al. (1997) also concluded that the Pleistocene refuge theory cannot account for speciation patterns in South American and African lowland bird faunas, and that most of the speciation in tropical lowland biotas occurred before the Quaternary. Until recently the oldest fossil passerines known were from the upper Oligocene (25 Ma), younger than the oldest fossils of other extant bird orders, and so passerines have usually been assumed to actually be a younger group. However, molecular studies (Mindell et al., 1997) indicated that passerines are basal to the other neognaths ± an ùnexpected' result. As a consequence, Mindell et al. noted the possible signi®cance of recently discovered passerine fossils from the Australian Eocene (54 Ma) (Boles, 1995, 1997), still rather young compared with Cooper & Penny's (1997) estimate of a Cretaceous origin for the order. These data are compatible with the terrane tectonics explanation given here for the Paradisaeidae. Based on DNA hybridization, Sibley & Ahlquist (1985) calculated a date of 18±20 Ma for the split between Manucodia and the other members of subfam. Paradisaeinae, which is compatible with Mayr's (1953) proposal that the family was isolated in the New Guinea region in the early Tertiary. Hybridism Hybridism, past and/or present, is especially signi®cant in the birds of paradise, which probably have more interspeci®c and intergeneric wild hybrids than any other bird family except Anatidae. Perhaps the whole family represents an ancient hybrid swarm formed when New Guinea was still a vast series of archipelagos and later becoming more or less `®xed' geographically with the consolidation of the mainland. The reproductive barriers among the populations have remained poorly developed and are disturbed relatively easily. Recombination of characters, in addition to the development of strict synapomorphies, has been an important mode of differentiation among the birds of paradise. For example, Frith & Beehler (1998) wrote that adult males of Seleucidis combine characters of more bird of paradise genera than any other, with `plumes of Paradisaea, pectoral fan-like plume feathers of Epimachus, bill form and plush chest `cushion' feathers like Ptiloris and Paradisaea, iridescent purple and green of Astrapia and Ptiloris, a buff tail and ventral barring like Epimachus and Drepanornis (in immatures), black head in female plumage as in Parotia and Lophorina, and a red iris as in Epimachus. If this species were today known from only one or two adult male skins it would probably be considered a hybrid!'. Many traded skins of birds of paradise described early on as new species were relegated in the 1930s to `hybrid' status. However, Iredale (1950), Gilliard (1969) and Fuller (1995) have argued that at least some of the `hybrids' are indeed distinct species which still await discovery in the wild. At least one appears to have a coherent range distinct from that of the putative parents: the twenty-®ve specimens usually identi®ed as Cicinnurus magni®cus ´ C. regius are `predominantly from north coastal of New Guinea' (Frith & Beehler, 1998), and a distribution map would be very useful. Utilization and conservation The people of New Guinea have always used the plumes of birds of paradise for decorating themselves at ceremonial shows and there was also a thriving international trade in skins for the millinery business of the Western world until this was stopped in the 1920s. Because of its beauty and inaccessibility the blue bird of paradise, Paradisaea rudolphi, was the most valuable species with one skin fetching 40 pounds (Gilliard, 1969). 80,000 adult males (mainly P. raggiana, P. apoda and P. minor) were killed and exported a year. The younger adult males do not have the ornamental plumage and so are not hunted but they are reproductively fertile, and this meant that the trade had little if any effect on the population. However, there is currently another, more serious threat to the birds as many of the lower montane forests they inhabit are under pressure from mining, logging and agricultural development. The staple crop in montane New Guinea, sweet potato (Ipomoea batatas (L.) Lamarck) is intensively cultivated and will grow up to about 2400 m, above the upper limit of most birds of paradise. Although it was emphasized that birds of paradise are surprisingly tolerant of some disturbance in the forest, they will not survive its total removal. A list of the twelve `rarest and most threatened birds' in PNG (Beehler, 1993) included two birds of paradise (Epimachus fastuosus and Paradisaea rudolphi) and two bowerbirds [Archboldia papuensis Rand and Sericulus bakeri (Chapin)]. In their list of globally threatened bird species, Collar et al. (2000) cited Epimachus fastuosus, Parotia wahnesi and Paradisaa rudolphi as Vulnerable, and eight other birds of paradise as Near Threatened. Several races are also possibly threatened, such as the bowerbird Chlamydera l. lauterbachi Reichenow, which along with endemic plants such as Lauterbachia Perkins (Philipson, 1986) is known only from the mid-Ramu Valley, near the site of a proposed large-scale nickel mine. CONCLUDING DISCUSSION: CONCEPTS OF DISPERSAL, AND TECTONICS Concepts of dispersal are central to interpretations of evolution. Frith & Beehler (1998) speculated as to why some widespread populations of birds of paradise have differentiated into a series of regional forms, whereas others have not. They assumed this to be at least partly related to the age of the group. It is true that regional vicariants are almost certainly of geological age, whereas the distribution of a widespread form quite undifferentiated Ó Blackwell Science Ltd 2001, Journal of Biogeography, 28, 893±925
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Birds of paradise, biogeography and ecology in New Guinea: a review

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