The dispersal–vicariance pendulum and butterfly biogeography
Sammanfattning: The relative importance of dispersal and vicariance in speciation is a subject of long standing debate. The earliest historical biogeographers invoked dispersal to explain disjunct distributions. With the advent of phylogenetic systematics and the acceptance of plate-tectonic theory, vicariance gained prominence and dispersalist explanations were increasingly rejected in favour of the former. This led to a new paradigm termed ‘vicariance biogeography’. The quintessence of vicariance biogeography is the consideration of vicariance as the null hypothesis in explanations of disjunct distributions. The notion of vicariance being the predominant force in allopatric speciation started gaining increasing acceptance in the biogeographic community. This also came to be reflected in analytical methods, many of which are biased towards vicariant inferences. However, the recent past has seen this vicariance-dominated view being confronted by a suite of studies demonstrating that dispersal has played a vital role in speciation and is equally important, if not more. In this thesis, I have studied the historical biogeography of nymphalid butterflies (Family Nymphalidae) in the genus Junonia and two subtribes - Coenonymphina and Mycalesina. Junonia is found in all major zoogeographic regions apart from the Palaearctic. Coenonymphina is found in the Holarctic, Neotropical and Australasian regions. Mycalesina is found all over the Old World tropics. The results in the thesis indicate that dispersal has played a crucial role in the diversification of these groups, while there is little evidence for vicariance in any group. I also critique Dispersal-Vicariance analysis, the widely used analytical method in historical biogeography that is based on the principle of parsimony. I use simulated data to highlight various sources of error when using the method, and suggest ways that may help increase the realism of biogeographic inferences.
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