Australia: The Land Where Time Began
Biogeography of Australia
Distribution – In and Around Australia
Allodapine bees suggest Australia is not a unit
Current geographic entities are assumed in many biogeographic analyses to also be natural biogeographic regions. Though Australia is a geographic unit in terms of its biogeography parts of it are often related more closely to external areas than to the rest of Australia. The Allodapine bees (Apidae: Allodapini) comprise the 3 main clades (Chenoweth & Schwarz, 2011) are an example:
Africa and Madagascar (Macrogalea).
Africa, Madagascar, Middle East, southern and Southeast Asia, northern Australia.
The first break has occurred in Africa/Madagascar, as with many widespread Indian Ocean groups, and subsequent overlap has occurred there. The second break occurred somewhere between northern and southern Australia, this break coinciding with the marine transgression of the Jurassic and Cretaceous. A single colonisation event from Africa to Australia has been suggested (Chenoweth & Schwarz, 2011) to have occurred at about 34 Ma, which is too late for the Gondwana vicariance models, though as this was a minimum (fossil-calibrated) age for the group, therefore it is still possible that the only time the Allodapine clades dispersed was within Africa/Madagascar.
It is shown by the Allodapine bees that their distribution within Australia is closely related with distribution outside Australia, therefore both must be considered together, and particularly that Australia cannot be assumed to be a simple biogeographic unit, as it is indicated by the bees that differentiation and complexity occurred in the region prior to Australia becoming a discrete geographic entity.
Affinities – in and around Australia
It is indicated by Australian groups that they have trans-Tasman affinities and intercontinental connections across the Indian, Tethys and Pacific Oceans, that have been discussed in connection with Australasia in general. An example is Australian Diptera (Bickel, 2009), there being:
· Many Tethyan groups have connections with the northwest of the continent.
· Disjunct trans-Indian Ocean groups (Heteropsilopus, a dolichopodid: Australia and India; Niminidae: Australia, New Guinea, Madagascar and South Africa).
· Disjunct Tasman Sea groups (e.g., Australiamyzidae: southern Australia, Macquarie Island and New Zealand).
· Disjunct trans-Pacific groups (Brachystomatidae: Australia/Tasmania, New Zealand and South America; Perissommatidae: Australia and South America).
With respect to the trans-Tasman affinities it has been written (Bickel, 2009: 239) that the distribution of some plants and animals on the southern continents and islands is explained better by dispersal that occurred relatively recently than ancient Gondwana vicariance, though there are as yet no well-established examples of Diptera. Heads1 claims that if dispersal is important it would be strange if trans-Tasman flight was not indicated by flies, though this is what was proposed by Bickel (2009). It is implied by this that different connections that were trans-ocean-basin of Australian groups could have resulted from tectonic activity. Other Australian groups show similar external patterns, such as Australian members of Alismataceae, a water plant family (Chen et al., 2012) have trans-Indian Ocean affinities:
· Africa, Madagascar, India (Wiesneria), + Africa, Madagascar, India, Peninsular Malaysia (Limnophyton), + northeast Australia (Astonia).
· Tropical Africa, India, Indochina and Java, New Guinea and northern Australia (Butomopsis).
And the Tethyan affinities:
· Eastern and southwestern Australia, northeast India, Mediterranean region and North America (Damasonium).
Australian flora – an early Australian vicariance model
It has been observed that many groups, e.g., Melastomataceae, are rich in tropical Asia and Africa, though they are rare or absent in Australia (Hooker, 1860). The family Myrtaceae, which is related to Melastomataceae, is diverse in Australia, though poorly represented in Africa. It was noted (Hooker, 1860) in other examples of allopatry at higher levels that Campanulaceae (Asterales) are diverse in South Africa, while related families Goodeniaceae and Stylidiaceae are diverse in Australia, and Ericoideae, a subfamily of Ericaceae, of South Africa is represented by Ericaceae subfam. Styphelioideae (formerly Epacridaceae) in Australia. In light of these these and similar patterns (Hooker, 1860: liv) accepted a vicariance model and wrote that the Australian flora: ‘… though manifestly more allied to the Indian than to any other, differs from it so organically, that it is impossible to look upon one as derived from the other, though both may have had a common parentage’. The trans-Tasman relationship between Australia and New Zealand was interpreted by Hooker in a similar way.
Heads, Michael, 2014, Biogeography of Australasia: A Molecular Analysis, Cambridge University Press
|Author: M.H.Monroe Email: email@example.com Sources & Further reading|