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

920 M. Heads
throughout, say, Melanesia and Australasia might be the
result of a recent range expansion. However, two endemic
genera, each found through the New Guinea mountains,
but one comprising different species and the other not, may
well be the result of the same phase of, for example, early
Tertiary evolution. Taxonomic diversity or distinctiveness
is proportional neither to the age of, nor the time involved
in, the group's origin.
The second factor Frith & Beehler cited in explaining why
some widespread birds of paradise are diverse is the dispersal
ability of local populations, although no examples are given.
The difference between groups that do speciate and those that
do not probably has more to do with the different genetic
potentials of the ancestral populations. To be expressed, this
potential may need to be exposed to a phase of geological
change and physiographic and ecological dynamism, for
example a period of orogeny or terrane accretion.
If the concept of dispersal/migration is de®ned broadly as
`any and all changes of position', it is clear that evolution
should be included as a key component of dispersal, as the
evolution of a form can by itself bring about the distribution
of the form. In periods of allopatric evolution dispersal as
physical movement can be replaced with a concept of
dispersal as evolution. In this view, evolution is not seen as a
morphogenetic and biogeographical radiation from a monophyletic
point centre of origin, and from a single, monomorphic,
ancestral species (or even a parent pair). Rather, it
is a process working on broad geographical and phylogenetic
fronts by phases of modernization (cf. Kerr, 1997) of already
widespread ancestral complexes. (Mayr, 1982; while not yet
accepting this Croizatian idea, regarded it as a `completely
legitimate hypothesis'.) This view implies that evolution
operates mainly by parallel development of characters,
which is clearly seen in the Paradisaeidae ± recombination
of characters in the genera has been referred to in Semioptera
and Seleucidis. In another case, Frith & Beehler (1998)
referred to the `remarkable phenomenon' of geographically
and morphologically parallel variation in the adult females
of Lophorina superba and Parotia carolae, with the western
populations of the two species being `extremely similar'
(Beehler et al., 1986). Parallel evolution of taxa (which may
be cladistically monophyletic, with `uniquely' derived characters)
means that descendant taxa can have the same range
as an ancestral taxon. The range of Paradisaeidae, for
example, could have been inherited more or less directly
from a preparadisaeid ancestral complex.
Naturally a degree of range expansion and contraction is
constantly occurring, and in certain periods many taxa enter
a phase of mobilism. This may have been the case in New
Guinea and New Zealand during the Oligocene marine
transgressions in downwarped basins where many new,
shifting coastlines became available for colonization. However,
there is no evidence of this being important for most
birds in geologically recent times. On the contrary, the
current distributions of the vast majority of New Guinea
birds, and all the birds of paradise and bowerbirds, seem to
be the result of a phase of modernization mainly involving
vicariant phylogenesis.
It is suggested that populations of birds of paradise,
sedentary forest dwellers with small home ranges but
tolerant of disturbance, have been caught in the dramatic
geological uplift and downwarping of different parts of the
New Guinea orogen, leading to speciation, distributional
breaks and disjunctions, and altitudinal anomalies. The
ancestral complex of Paradisaeidae, Ptilonorhynchidae and
other Corvinae may have included birds of the mangrove
and associated vegetation (back-mangrove, swamp forest,
drier secondary vegetation) some of which have been
stranded in central Australia following marine transgressions
(Ptilonorhynchidae) and others uplifted in New Guinea
during Tertiary orogeny (Ptilonorhynchidae and Paradisaeidae).
The entire sequence: mangrove ± subalpine forest is
occupied by Manucodia comrii.
Populations currently juxtaposed on very narrow terranes
or sets of terranes may not always have been so close
together, as the individual terranes may have travelled
hundreds or even thousands of kilometres before docking.
Furthermore, in New Zealand and New Guinea several
accreted terranes have been substantially narrowed by
subduction, faulting and erosion subsequent to their formation,
some to just slivers, and Landis & Blake (1987)
suggested that terranes hundreds of kilometres wide may
have disappeared from within the New Zealand region.
These vanished terranes would have supported living communities,
some of which would have transferred to
encroaching terranes and given rise to modern plants and
animals. The slight differentiation between Paradisaea r.
rudolphi and P. r. margaritae (Fig. 30), for example, may
indicate a deeper structure, a biological and geological faultline
where populations of the birds of one terrane have been
grafted onto the birds and landscapes of another.
Simply because a bird is widespread through New Guinea
on many terranes does not mean this is the result of dispersal
from one terrane to another after terrane suturing. The
taxon might have been widespread before the terranes came
together, as even if the terranes were hundreds of kilometres
apart they probably already shared some taxa. There are
many questions concerning the biogeographical relationships
among populations and taxa of terranes such as the
Jimi, Finisterre and Owen Stanley terranes, or between areas
on the craton such as the Mimika/Setekwa Rivers, and the
areas north of the craton.
Biogeographical analysis is not concerned primarily with
the terranes as strata, even less as centres of origin, but
rather as tectonic indicators. For example, the lithological
differences between the shelf sediments of the craton and the
deeper water sediments of the Aure Trough probably have
little direct effect on the vegetation, but the distinct tectonic
histories of the two regions as revealed by lithology and
structure are of great signi®cance.
Similarly, the currently exposed strata of intrusive and
metamorphic terranes were obviously not colonized by
plants and animals as they formed, as this happened beneath
the earth's surface. However, these rocks indicate phases of
revolutionary physiographical change during which plants
and animals had ample opportunity for evolution. Later, the
Ó Blackwell Science Ltd 2001, Journal of Biogeography, 28, 893±925