The shifting roles of dispersal and vicariance in biogeography

Abstract

Dispersal and vicariance are often contrasted as competing processes primarily responsible for spatial and temporal patterns of biotic diversity. Recent methods of biogeographical reconstruction recognize the potential of both processes, and the emerging question is about discovering their relative frequencies. Relatively few empirical studies, especially those employing molecular phylogenies that allow a temporal perspective, have attempted to estimate the relative roles of dispersal and vicariance. In this study, the frequencies of vicariance and dispersal were estimated in six lineages of birds that occur mostly in the aridlands of North America. Phylogenetic trees derived from mitochondrial DNA sequence data were compared for towhees (genus Pipilo), gnatcatchers (genus Polioptila), quail (genus Callipepla), warblers (genus Vermivora) and two groups of thrashers (genus Toxostoma). Di¡erent area cladograms were obtained depending on how widespread and missing taxa were coded. Nonetheless, no cladogram was obtained for which all lineages were congruent. Although vicariance was the dominant mode of evolution in these birds, approximately 25% of speciation events could have been derived from dispersal across a preexisting barrier. An expanded database is now needed to estimate the relative roles of each process. Applying a molecular clock calibration, nearly all speciation events are of the order of a million or more years old, much older than typically presumed.

Population genetics of dwarf eelgrass Zostera noltii throughout its biogeographic range

“…In making these comparisons, it is widely accepted that the founding populations colonizing new areas of suitable habitat should represent subsets of the source populations, with fewer alleles and increased levels of homozygosity (=lower genetic diversity) (Hewitt 1996, 2000, Johnson et al 2000, Zink et al 2000. The expectation of decreased genetic diversity in colonizing populations, however, may be too simplistic and a recent study has demonstrated that genetic diversity in founding populations can be either higher or lower depending on the estimator (Comps et al 2001).…”

Molecular phylogeny and plumage signal evolution in a trans Andean and circum Amazonian avian species complex

“…In contrast, the mtDNA reconstructions presented here suggest that the Phaeothlypis complex is comprised of six well-differentiated, geographically structured mtDNA lineages and that five of these lineages originated nearly simultaneously in the mid-Pliocene. The magnitude of mtDNA differentiation separating the six Phaeothlypis populations exceeds that between a number of pairs of other parulid warbler taxa that are widely considered valid species (e.g., Zink et al, 2000). From a phylogenetic species perspective, the Phaeothlypis complex would likely be subdivided into six species-level taxa.…”

Biogeography of Camphorosmeae (Chenopodiaceae): tracking the Tertiary history of Australian aridification

“…Since vicariance is the default mode of speciation recognised by the program, optimisation was conducted with the maximum number of ancestral areas set to two to favour dispersal rather than vicariance (Donoghue et al 2001;Ronquist 1996Ronquist , 1997Zink et al 2000). This mode of analysis also helps to identify the possible geographical distribution of the ancestors of the group (Zink et al 2000).…”