Birds of paradise, biogeography and ecology in New Guinea: a review
Birds of paradise, biogeography and ecology in New Guinea: a review
Birds of paradise, biogeography and ecology in New Guinea: a review
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918 M. Heads<br />
<strong>and</strong> are usually gregarious. He concluded: `One might<br />
suppose that such birds would be exempt from the st<strong>and</strong>ard<br />
zoogeographical patterns, but this is not borne out by an<br />
exam<strong>in</strong>ation <strong>of</strong> their breed<strong>in</strong>g distribution. In fact, st<strong>and</strong>ard<br />
zoogeographical patterns emerge¼' One such pattern is the<br />
curious poverty <strong>of</strong> forms on Madagascar <strong>and</strong> Australasia,<br />
also seen <strong>in</strong> woodpeckers <strong>and</strong> many other groups.<br />
Frith & Beehler (1998) suggested that `both Manucodia<br />
<strong>and</strong> Paradisaea have dispersed across deep-water barriers¼<br />
over water differentiation follows chance dispersal across a<br />
permanent water barrier. Although this is evidently a rare<br />
event <strong>in</strong> the birds <strong>of</strong> <strong>paradise</strong>, it has produced six <strong>in</strong>sular<br />
species¼ Apparently over-water dispersal is a highly effective<br />
pathway to speciation <strong>in</strong> birds <strong>of</strong> <strong>paradise</strong>'.<br />
However, this begs the question: why has over-water<br />
dispersal not been effective <strong>in</strong> gett<strong>in</strong>g the birds to the nearby<br />
isl<strong>and</strong>s fr<strong>in</strong>g<strong>in</strong>g northern PNG?<br />
A related problem with long-distance dispersal is not<br />
concerned with how it could occur <strong>in</strong> the ®rst place ± that<br />
seems obvious <strong>in</strong> birds, mammals, ferns, orchids, etc., all<br />
with their ord<strong>in</strong>ary means <strong>of</strong> survival ± but how <strong>and</strong> why the<br />
`<strong>in</strong>vasion' would be occurr<strong>in</strong>g at one period <strong>in</strong> time <strong>and</strong> then,<br />
for no apparent reason, cease, <strong>and</strong> such a cessation is<br />
necessary for allopatric evolution. To expla<strong>in</strong> this without<br />
<strong>in</strong>vok<strong>in</strong>g geological change biologists have <strong>of</strong>ten employed a<br />
concept <strong>of</strong> `chance dispersal' which can `expla<strong>in</strong>' any pattern<br />
at all, but is ad hoc <strong>and</strong> untestable.<br />
In 1605 Clusius already knew that Paradisaea apoda lives<br />
on the Aru Isl<strong>and</strong>s, while P. m<strong>in</strong>or is on the western Papuan<br />
Isl<strong>and</strong>s (Gilliard, 1969). S<strong>in</strong>ce that time vicariance (that is,<br />
geographical replacement or representation) has been discovered<br />
<strong>in</strong> many birds <strong>and</strong> s<strong>in</strong>ce the 1890s the use <strong>of</strong><br />
tr<strong>in</strong>omials <strong>in</strong> ornithology <strong>and</strong> mammalogy has been based<br />
on the ubiquitous phenomenon. The impression on read<strong>in</strong>g<br />
through a list <strong>of</strong> world birds <strong>and</strong> their ranges is not one <strong>of</strong><br />
active range expansion, but one <strong>of</strong> each bird's localized<br />
distribution <strong>in</strong>terlock<strong>in</strong>g <strong>in</strong> a vicariant way with that <strong>of</strong> its<br />
relatives, form<strong>in</strong>g just one tile <strong>in</strong> a global mosaic. Perhaps<br />
the normally observed powers <strong>of</strong> physical movement <strong>in</strong> birds<br />
that are crucial for survival (feed<strong>in</strong>g, avoid<strong>in</strong>g predation,<br />
reproduction, etc.) are <strong>of</strong> little signi®cance <strong>in</strong> establish<strong>in</strong>g the<br />
geographical range <strong>of</strong> taxa.<br />
Dur<strong>in</strong>g periods <strong>of</strong> major tectonic <strong>and</strong> physiographical<br />
change, such as rift<strong>in</strong>g <strong>and</strong> terrane accretion, whole faunas<br />
may well exp<strong>and</strong> their range, for example along new shore<br />
l<strong>in</strong>es, but <strong>in</strong> birds such as the Paradisaeidae there is no<br />
evidence for recent, long-distance dispersal over modern<br />
geography. In fact most birds <strong>of</strong> <strong>paradise</strong> appear to be<br />
sedentary forest dwellers with relatively small home ranges<br />
(Frith & Beehler, 1998) <strong>and</strong> rather than their <strong>biogeography</strong><br />
be<strong>in</strong>g determ<strong>in</strong>ed by their <strong>ecology</strong>, the <strong>ecology</strong> <strong>of</strong> the birds<br />
(for example, their altitude) may be determ<strong>in</strong>ed by their<br />
prior <strong>biogeography</strong> <strong>and</strong> subsequent tectonic developments.<br />
The age <strong>of</strong> birds<br />
Evidence is mount<strong>in</strong>g that most groups <strong>of</strong> birds are considerably<br />
older than was thought. Ever s<strong>in</strong>ce Matthew's (1915)<br />
very <strong>in</strong>¯uential text on vertebrate palaeontology, a literal<br />
read<strong>in</strong>g <strong>of</strong> the fossil record is the technique which has featured<br />
<strong>in</strong> most work on the chronology <strong>of</strong> evolution. This would<br />
suggest, for example, a Tertiary radiation <strong>of</strong> the mammal <strong>and</strong><br />
bird orders. The fact that no bird <strong>of</strong> <strong>paradise</strong> fossils are<br />
known would be taken as evidence for a very young age <strong>of</strong> the<br />
group. However, new palaeontological <strong>and</strong> molecular evidence<br />
(e.g. Hedges et al., 1996) <strong>in</strong>dicates an earlier, Cretaceous<br />
diversi®cation <strong>of</strong> modern mammal <strong>and</strong> bird l<strong>in</strong>eages,<br />
<strong>and</strong> emphasizes the major gaps <strong>in</strong> the fossil record.<br />
Nearly complete specimens from north-eastern Ch<strong>in</strong>a<br />
show that modern birds as a subclass (Ornithurae) have<br />
existed s<strong>in</strong>ce at least the Late Jurassic (Hou et al., 1996).<br />
Similarly, recent studies <strong>in</strong> palaeontology (Chatterjee, 1998;<br />
Forster et al., 1998; Stidham, 1998) <strong>and</strong> molecular sequenc<strong>in</strong>g<br />
(Cooper & Penny, 1997) <strong>in</strong>dicate that bird diversity is<br />
much older than previously thought, with most or all <strong>of</strong> the<br />
major modern orders present <strong>in</strong> the Cretaceous. For nearly a<br />
century the orthodox school <strong>of</strong> evolutionary chronology has<br />
been devoted to a virtual cult <strong>of</strong> the oldest fossil <strong>of</strong> a taxon<br />
which is <strong>in</strong>ferred, <strong>of</strong>ten implicitly, to have orig<strong>in</strong>ated with it.<br />
But <strong>in</strong> recent times gene sequenc<strong>in</strong>g has been underm<strong>in</strong><strong>in</strong>g<br />
this approach, despite the fact that the gene trees are <strong>of</strong>ten<br />
calibrated us<strong>in</strong>g fossils to give m<strong>in</strong>imum ages. These<br />
molecular studies <strong>in</strong>dicate that the fossil record is severely<br />
¯awed <strong>and</strong> that a literal read<strong>in</strong>g <strong>of</strong> evolutionary detail <strong>in</strong> it is<br />
an unrealistic approach.<br />
Coupled with the traditional chronological paradigm was<br />
the Pleistocene refugium model, an idea proposed <strong>in</strong> the<br />
1970 <strong>and</strong> 1980s to expla<strong>in</strong> tropical diversity. In apply<strong>in</strong>g<br />
the idea to <strong>New</strong> Gu<strong>in</strong>ea, it was suggested that dur<strong>in</strong>g the<br />
Pleistocene ice ages populations <strong>of</strong> forest birds were<br />
fragmented on a large scale <strong>and</strong> only occurred <strong>in</strong> a relatively<br />
small number <strong>of</strong> forest refugia. There are many problems<br />
with this scenario. For example, a long pollen record from<br />
the Amazon ra<strong>in</strong>forest, the area for which the theory was<br />
developed, <strong>in</strong>dicated that there has been cont<strong>in</strong>uous ra<strong>in</strong>forest<br />
there for 40,000 years ± it was not fragmented dur<strong>in</strong>g<br />
the glacial maxima (Col<strong>in</strong>vaux et al., 1996). Likewise DNA<br />
differences between sister species <strong>of</strong> North American birds<br />
<strong>in</strong>dicate a speciation history over the last 5 Myr, imply<strong>in</strong>g a<br />
history ten times longer than that predicted by the Late<br />
Pleistocene orig<strong>in</strong>s model (Klicka & Z<strong>in</strong>k, 1997). Similarly,<br />
<strong>in</strong> the Pseudomyrmex viduus (F. Smith) group <strong>of</strong> ants,<br />
centred <strong>in</strong> the Amazon bas<strong>in</strong>, the geographical ranges <strong>of</strong><br />
most species do not co<strong>in</strong>cide with the proposed Pleistocene<br />
forest refugia. Instead, phylogeny, <strong>biogeography</strong> <strong>and</strong> host<br />
plant speci®city <strong>in</strong>dicate that much <strong>of</strong> the diversi®cation<br />
took place <strong>in</strong> the Tertiary (Ward, 1999).<br />
Cracraft & Prum (1988) criticized the refugium theory,<br />
<strong>and</strong> <strong>in</strong>stead proposed a vicariance event (the ris<strong>in</strong>g <strong>of</strong> the<br />
Andes) to expla<strong>in</strong> birds with western Colombian ± upper<br />
Amazonian disjunctions, support<strong>in</strong>g earlier ideas <strong>of</strong> Chapman<br />
(1917) <strong>and</strong> Croizat (1958).<br />
Recent evidence con®rms that the l<strong>in</strong>eage <strong>of</strong> many Andean<br />
birds <strong>and</strong> mammals differentiated well before the Pleistocene,<br />
<strong>and</strong> probably even before the uplift <strong>of</strong> the Andes.<br />
Many botanists <strong>and</strong> zoologists previously thought that<br />
Ó Blackwell Science Ltd 2001, Journal <strong>of</strong> Biogeography, 28, 893±925