Geography Reference
In-Depth Information
The analysis revealed a distinct biogeographic pattern, with one major clade
restricted to the east of Wallace's line and another to the west. In order to interpret
it, Brown et al. (2006) offered two alternative hypotheses. Hypothesis 1 considers
Vireya
as an old group, with ancestors present in Gondwana before India rifted
north in the Cretaceous. As the islands of Malesia formed and moved to their
present positions, species of
Vireya
dispersed farther into Malesia. Similar scen-
arios have been suggested for the establishment of other angiosperms in tropic-
al Asia-Australasia. Hypothesis 2 considers
Vireya
as a young group, which dis-
persed eastward from India to Australia and the Solomon Islands because the is-
lands of Malesia were in, or close to, their present-day positions. Two main radi-
ation-dispersal events into Malesia are likely to have occurred, representing the
main two lineages resolved in the phylogeny. There was only one eastward ra-
diation into New Guinea, Australia, and the Solomon Islands, followed by mass
speciation leading to the present-day diversification, possibly related to orogenic
events in New Guinea. A similar hypothesis has been put forward for genera of
Dipterocarpaceae. On the basis of the presence of taxa in relictual rain forests that
include ancient angiosperms and fossil minimal ages, the authors preferred hypo-
thesis 1. It may be that deep divergences within the taxa analyzed have an old
history, but diversification within clade is more recent.
References
Brown, G. K., G. Nelson, and P. Y. Ladiges. 2006. Historical biogeography of
Rhodo-
dendron
section
Vireya
and the Malesian Archipelago.
Journal of Biogeography
33:1929-1944.
Farris, J. S. 1988.
Hennig86 reference.
Version 1.5. Port Jefferson, N.Y.: Author.
Proposed by Ronquist (1997a), based on the ideas developed by Ronquist
and Nylin (1990) to analyze host-parasite relationships, this method re-
constructs ancestral distributions from one given phylogenetic hypothesis,
without assuming a particular process a priori, taking into account vicari-
ance, dispersal, and extinction (Miranda Esquivel et al. 2003). It recon-
structs the biogeographic history of individual taxa, but it can also be used
to find the general relationships of an area, especially when these relation-
ships do not conform to a hierarchical pattern, that is, when there are retic-
ulate relationships due to biogeographic convergence.
The biogeographic reconstruction is based on a cost matrix, which is
constructed according to the following premises (Crisci et al. 2000):
