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

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916 M. Heads where the taxa do not range to the top of the latter, could be partly explained by differential uplift ± the mountains are lower in Milne Bay, for example, because there has been less uplift there and for the same reason the altitudinal vegetation bands have remained telescoped together. The more or less constant wet-season mists also lie much lower on these isolated mountains than in the central Highlands, where they usually only descend to about 2700 m (pers. obser., around Goroka). This may explain the survival of moss forest communities at low altitudes on the isolated mountains, but perhaps not their origin. It is often thought that mountains are uplifted and then invaded by a new ¯ora and fauna from elsewhere. However, before the land was uplifted it was not an ecological vacuum. There would have been a diverse array of plants and animals present, some of which would have been able to survive uplift by pre-adaptation (or adaptation), while many other populations would die out. This would allow pre-adapted taxa to attain a very wide altitudinal range, and many such taxa are known in New Guinea. Like the family Paradisaeidae, the most diverse bird genera in New Guinea, Ptilinopus Swainson (fourteen species) and Pachycephala (®fteen species), range from mangrove forest to 3400 and 3650 m, respectively, and at species rank trees like Schuurmansia henningsii range widely from sea-level to 3000 m (Kanis, 1978). Whether the `montane' elements occur at low altitude through downwarping of terranes bearing these populations, or because there has been relatively little uplift there compared with the main central mountains, it seems unrealistic to discuss the altitudinal range of communities and taxa without reference to the geological changes of altitude by orogenic and epeirogenic uplift, sedimentation, downwarping and erosion. Ophiolite endemism It is suggested here that the distributions of the birds of paradise mainly re¯ect geological change, and are generally much older than was thought. Unlike chance dispersal and chance extinction this tectonic hypothesis seems to account for some of the standard aspects of the distribution patterns and leads to interesting, testable correlations. An example of biogeographical and tectonic correlation is that of endemism on ultrama®c terranes. Rocks with less than 45% silica are rare and are termed ultrabasic or ultrama®c (that is, high in magnesium and iron). They usually occur as part of ophiolitic igneous suites, or ophiolites, which comprise pillow basalts, massive gabbros, and serpentinized ultrama®cs. The presence of ultrama®cs on the earth's surface is of great tectonic signi®cance as they are sections of oceanic crust and upper mantle that have been uplifted and obducted onto land (rather than subducted below it). This has occurred at plate margins during island-arc collision, and accreted arc terranes and orogenic belts frequently include ophiolites. In the Western Papuan Islands, Waigeo, Batanta and nearby Ko®au (but not Salawati) comprise an ophiolite complex, the Waigeo terrane (Pigram & Davies, 1987). Waigeo and Batanta are also distinguished by the presence of local endemics such as Cicinnurus respublica (Bonaparte) and Paradisaea rubra (Fig. 27). Similarly, Melidora Lesson (Alcedinidae) is widespread in New Guinea west to Waigeo and Batanta, but is not on Salawati. The straits between Salawati and Batanta Islands are less than two miles wide, but `have prevented the crossing' of seventeen species of Salawati birds to Batanta and ®ve from Batanta to Salawati (Mayr, 1940). It seems more likely that this striking faunistic difference is due to different tectonic and evolutionary histories, rather than to a 2-mile wide sea-barrier. The New Guinea orogen is characterized by abundant outcrops of ultrama®c rocks. The largest of these, the Papuan Ultrama®c Belt (Bowutu terrane) covers an area 400 ´ 40 km and is one of the world's most spectacular ophiolites. It forms a series of subsidiary mountain ranges north of the main ranges of the Papuan Peninsula and its emplacement must have been a major tectonic event. Botanists have long recognized that these northern New Guinea ultrama®cs were strong foci of endemism (e.g. Kairothamnus Airy Shaw ± Airy Shaw, 1980; Calophyllum streimannii Stevens ± Stevens, 1974a), but it was felt that much of this endemism was the result of edaphic rather than historical factors. Polhemus (1996) pointed out that although many animals (e.g. Parotia lawesii helenae) show similar patterns, zoologists have been slow to realize that this correlation greatly weakens the edaphic hypothesis. Instead, Polhemus (1996) regarded the ophiolites as biogeographically signi®cant because they are arc terrane markers. The most mature phase of arc collision is seen in old arc fragments now deeply embedded in modern mainlands, such as New Guinea and the Philippines. The remnants of these Mesozoic arc systems have been crushed between even older arcs or continents but have left a biological signature in the disjunct distributions of living taxa. Survival of taxa in situ At ®rst it seemed unlikely that bird taxa would maintain their distributions over geological time as precisely as indicated here. However, results from another ®eld ± ecological studies of current populations ± also show that New Guinea rainforests and their bird fauna have a great capacity to survive more or less in situ, despite high levels of disturbance by volcanic activity, movement on faults, landslides, rivers changing course, storms, human activity, and as seen dramatically in 1997, drought and ®re. Life is `stickier' and less easily `eroded' away than biologists often assume. Comparatively few New Guinea rainforest trees regenerate in full shade and the long-held idea of tropical rainforest as fragile and undisturbed has more recently been rejected by ecologists (Johns, 1986). So it is not surprising that while all birds of paradise are generally found in closed rainforest, the vast majority are also occasionally seen in at least one of the following: forest edge, secondary or broken forest, selectively logged forest, disturbed forest near villages, abandoned gardens, and even open agricultural land with scattered shrubs. Parotia se®lata is most abundant in wellestablished secondary forest, Lophorina superba (Pennant) is Ó Blackwell Science Ltd 2001, Journal of Biogeography, 28, 893±925
Biogeography of birds of paradise 917 well-known around gardens and on houses, and Cicinnurus magni®cus (Pennant) and Ptiloris victoriae have been recorded breeding in secondary growth and gardens (Frith & Beehler, 1998). Of the ®ve birds of paradise recorded only from `forest', Paradigalla carunculata Lesson, Astrapia nigra and A. rothschildi are very poorly known in the ®eld, and Manucodia jobiensis Salvadori and Paradisaea apoda are also rather poorly known. The latter at least probably occurs in disturbed vegetation as do all the other Paradisaea species; P. raggiana is considerably more numerous in ecologically disturbed areas than in the forest interior (Diamond, 1972) and in some sites P. rudolphi is easily observed in gardens and at forest edge (Beehler et al., 1986) although it will not tolerate intensive gardening (cf. Diamond, 1972). Mangroves form a succession on shifting intertidal mud banks. It was mentioned above that at least ®ve out of fourteen genera of Paradisaeinae (35%) are found in mangrove and associated vegetation. Similarly, in the Sapindaceae, an important family of rainforest trees, nine of the forty-two Malesian genera (21%) occur in or around mangrove and eleven others (26%) are known from coastal cliffs and sands (data from Adema et al., 1994). In New Guinea Euphorbiaceae eleven out of fourty-seven genera (25%) are recorded in or around mangroves (Airy Shaw, 1980). In these and other birds and trees the New Guinea mangrove shows clear af®nities with dry-land rainforest, and there is also an obvious link between mangrove and the more or less freshwater swamp forests found along the central depression in New Guinea. In many birds there are direct ecophyletic links among taxa of mangrove, back-mangrove and secondary, disturbed vegetation. For example, Geopelia humeralis (Temminck) is particularly associated with mangrove swamps and disturbed places in and around human habitation (Rand & Gilliard, 1967). Finally, more broken, lower mangrove often provides an impenetrable tangle of woody vegetation similar to that of subalpine forest, and Manucodia comrii frequents both. Because of these factors, populations of what are currently mountain birds may not necessarily need mountains to survive; as Mayr (1953) noted, birds often show remarkable independence from habitat restrictions. The unmistakeable ribbon-tailed Astrapia mayeri Stonor, with the longest tail for its body of any bird, is possibly another example of survival more or less in place, despite massive local disturbance. It is only found in the Karius Range (SW of Tari), the nearby Doma Peaks, mountains by Laiagam, Mount Giluwe and Mount Hagen, and so is largely restricted to Quaternary volcanoes. Similarly, the striking bowerbird Archboldia papuensis sanfordi Mayr & Gilliard is only known from Mounts Giluwe and Hagen which are also major centres of endemism for plants. Can prior, Tertiary endemics survive such extensive volcanic activity? It would usually be inferred that a vast area has been biologically sterilized and must have been repopulated by long distance dispersal. Naturally life cannot survive literally in situ on molten lava, but individual lava ¯ows are often rather narrow. Many very recent ones on the volcanic islands north of New Guinea resemble straight, sealed roads running through the rainforest, and make for easy walking. The forest is obviously eliminated along the path of the ¯ow, but regenerates quickly. Lava ¯ows do not cover an entire island such as Manam or Karkar all at once, but over thousands or millions of years, eruption by eruption. This allows the biota to survive, more or less in situ, by constantly colonizing younger ¯ows from older ones until the entire island may eventually be covered by younger strata and the older living communities which have `¯oated' on them (cf. Craw et al., 1999, Figs 2±5). Many plants of active margins are surprisingly tolerant of volcanic activity, and the ash is often highly fertile. After eruptions on the volcanic islands north of New Guinea mainland, palm nuts germinate in the steaming ash following the ®rst rain, and plants such as Thymelaeaceae, Symplocaceae, Ericaceae and Epacridaceae often thrive in active craters around the Asia-Paci®c region (Pers. obser.). Means of dispersal or means of survival? Many ornithologists have questioned the apparent signi®cance of birds' means of dispersal in establishing their distributions, as the following quotations indicate: Birds offer us one of the best means of determining the law of distribution; for though at ®rst sight it would appear that the watery boundaries which keep out the land quadrupeds could be easily passed over by birds, yet practically it is not so¼ (Wallace, 1962 [1869]). To the person who is impressed by the bird's potential mobility, the occurrence of the same or representative species at widely separated localities is simply a matter of ¯ight from one station to the other¼ But the avian geographer is not so easily answered. He knows that most birds are closely con®ned to their own ranges¼ (Chapman, 1926). Most species of birds, especially on tropical islands, are extraordinarily sedentary (Mayr, 1940). That birds can ¯y across barriers is one of those apparently simple facts that are not simple. (Darlington, 1957). One of the ®rst facts that strikes the student of bird distribution is that most birds, in spite of the very great mobility resulting from the power of ¯ight, have sharply demarked distribution (Van Tyne & Berger, 1959). Despite powers of dispersal through the air, we have the paradox that ornithologists constantly stress the value of birds as objects of distributional and dispersal studies derived from the fact that known cases of such dispersal are so rare (Deignan, 1963). It has been shown many times that the apparent `means of dispersal' proposed as an explanation of distribution do not correlate with actual distributions. For example, studying the eighty-three species of swifts (Apodidae) Brooke (1970) observed that these are among the strongest-¯ying land-birds 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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