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Michael Heads
Heads, Michael (Science Faculty, University of Goroka, PO Box 1078, Goroka, Papua
New Guinea. Current address: Biology Department, University of the South Pacific, P.O.
Box 1168, Suva, Fiji. Email:[email protected]) 2003. Ericaceae in Malesia: vicariance
biogeography, terrane tectonics and ecology.
Telopea 10(1): 311–449. The Ericaceae are cosmopolitan but the main clades have wellmarked centres of diversity and endemism in different parts of the world. Erica and its
relatives, the heaths, are mainly in South Africa, while their sister group, Rhododendron
and relatives, has centres of diversity in N Burma/SW China and New Guinea, giving an
Indian Ocean affinity. The Vaccinioideae are largely Pacific-based, and epacrids are
mainly in Australasia. The different centres, and trans-Indian, trans-Pacific and transAtlantic Ocean disjunctions all indicate origin by vicariance. The different main massings
are reflected in the different distributions of the subfamilies within Malesia. With respect
to plant architecture, in Rhododendron inflorescence bracts and leaves are very different.
Erica and relatives with the ‘ericoid’ habit have similar leaves and bracts, and the
individual plants may be homologous with inflorescences of Rhododendron.
Furthermore, in the ericoids the ‘inflorescence-plant’ has also been largely sterilised,
leaving shoots with mainly just bracts, and flowers restricted to distal parts of the shoot.
The epacrids are also ‘inflorescence-plants’ with foliage comprised of ‘bracts’, but their
sister group, the Vaccinioideae, have dimorphic foliage (leaves and bracts). In Malesian
Ericaceae, the four large genera and the family as a whole have most species in the 1500–
2000 m altitudinal belt, lower than is often thought and within the range of sweet potato
cultivation. The same belt is also most diverse for ferns, birds-of-paradise and
bowerbirds. Distribution maps of Malesian Ericaceae are presented, with related species
indicated. Concentric patterns of distribution are frequent and could be attributable to
evolution around shrinking seas. In New Guinea the main axial range is a composite
structure, with the southern part formed by the old Australian craton and the northern and
eastern parts formed from 32 tectonostratigraphic terranes or microplates. These formed
independently and then docked with each other and the craton. The tectonic boundary
between the craton and the accreted terranes is also an important biogeographic
boundary. Many taxa have distributions linking different accreted terranes but are not on
the craton. Movement and integration of island arcs and more substantial terranes has led
to complex patterns of disjunction throughout Malesia, but there is an underlying
parallel-arc structure, seen clearly in New Guinea. The tectonic provinces in Borneo are
also reflected in the two main biogeographic tracks: Kuching—Kinabalu and Kutei
Mts./Mt. Kemul–Kinabalu, the Lupar River boundary and the Meratus Mts. centre. The
islands of the Riouw Pocket (Corner 1978a) are notably surrounded by many groups
which are absent there, including mangrove and Ericaceae species. However, other
mangrove and coastal taxa occur along a CW Sumatra – Riouw Pocket – SW Borneo
track. In Malesia, Rhododendron and Vaccinium mangrove and coastal species are
mainly restricted to the west, in Sumatra–Borneo and often the Riouw Pocket; and are
represented in New Guinea by related montane taxa. Van Steenis (1963, 1984) drew
attention to mangroves uplifted by tectonics and the Malesian Ericaceae in general could
be largely derived from mangrove forms.
Rhododendron species occur as epiphytes in mangrove, and many Ericaceae occur in
calcareous and saline sites. The very rapid rates of tectonic uplift occurring in New
Guinea would raise a mangrove community or a coastal ‘padang’ to the upper montane
zone in just one million years.