Darwin's biogeography

The year 2009 marks the 150th anniversary of the publication of Charles Darwin’s Origin of Species. This book was so influential that it is often considered to be the most important scientific work ever written. Many volumes have been published about the Origin and its lasting effects on religion and society, but few have examined its influence on biogeography. However, it was Darwin’s initial interest in comparing the natural history of different regions during the voyage of the Beagle that led him to propose natural selection as an evolutionary force. He had visited the Cape Verde Islands and saw the similarity of their biota to that of Africa, and then noted the South American relationships of the Galapagos fauna and flora. But the island plants and animals were different from their mainland relatives, and, in the Galapagos, each island appeared to have its own endemic forms. It was these biogeographical observations that were critical to Darwin’s formulation of a theory to account for them. His subsequent conclusions on the evolutionary importance of centres of origin and dispersal were generally well accepted for the next 100 years, until the advent of vicarianism, which began in the early 1970s. That vicarianist movement received an impetus from two sources: (1) the works of Leon Croizat, who did not believe that living organisms could disperse overseas by themselves; and (2) the development of plate tectonics and its causation of continental drift. Vicarianists believed that primitive species were originally widespread over the Earth’s surface but were rafted to different parts of the world by continental fractionation and movement. However, continental drift in the Mesozoic could not have involved contemporary species or genera as many vicarianists claimed. The development of phylogeography, beginning in the 1980s, and improved knowledge of the fossil record soon demonstrated that multitudes of living species, and even many genera and families, underwent long‐distance dispersal during the Cenozoic. This resulted in a decline of vicarianism and a vindication of Darwin’s conclusions on centres of origin and dispersal.     

Urban biogeography

Summary Species richness and abundance of Diptera and Coleoptera were assessed in nine city parks in Cincinnati, Ohio, USA. Species richness for each park was related to the area of the park in a manner predicted by island biogeography theory. The z values for the Diptera and Coleoptera were 0.235 and 0.222 respectively. These values are somewhat higher than expected for continental islands and suggest that the Diptera and Coleoptera in these parks are as isolated as many species which occur on true oceanic islands.A stepwise multiple regression was conducted, regressing species richness against several aspects of habitat diversity in the parks. It was found that area alone was the best predictor of species richness. This result, coupled with data on population sizes, suggests that increased area acts primarily to reduce extinction rates rather than to provide new habitats for specialized species.     

3. Biodiversity, biogeography and conservation of diatoms

Recent morphometric and breeding studies of diatoms show that the present species classification is too coarse and hides significant diversity. Many species are subdivided into phenodemes, which often differ in cell size, shape, stria density and pattern, but may also have different ultrastructural features. In raphid diatoms these can include the form of the raphe endings, details of the pore occlusions, and the structure of the girdle, while chloroplast structure can also vary. The phenodemes can be sympatric or allopatric. In Sellaphora pupula and other species, sympatric phenodemes are reproductively isolated. It is recommended that such demes are recognized as separate species; the total number of diatom species worldwide may thus be at least 2 × 10⁵. Use of a fine-grained classification reveals that many diatom species may be endemics, some restricted to a single lake or catchment, others to wider areas. Environmental impact assessments and conservation strategies must begin to take account of endemism and rarity among microscopic algae and protists.     

The biogeography of Gunnera L.: vicariance and dispersal

Aim The genus Gunnera is distributed in South America, Africa and the Australasian region, a few species reaching Hawaii and southern Mexico in the North. A cladogram was used to (1) discuss the biogeography of Gunnera and (2) subsequently compare this biogeographical pattern with the geological history of continents and the patterns reported for other Southern Hemisphere organisms. Location Africa, northern South America, southern South America, Tasmania, New Zealand, New Guinea/Malaya, Hawaii, North America, Antarctica. Methods A phylogenetic analysis of twenty‐six species of Gunnera combining morphological characters and new as well as published sequences of the ITS region, rbcL and the rps16 intron, was used to interpret the biogeographical patterns in Gunnera. Vicariance was applied in the first place and dispersal was only assumed as a second best explanation. Results The Uruguayan/Brazilian Gunnera herteri Osten (subgenus Ostenigunnera Mattfeld) is sister to the rest of the genus, followed sequentially upwards by the African G. perpensa L. (subgenus Gunnera), in turn sister to all other, American and Australasian, species. These are divided into two clades, one containing American/Hawaiian species, the other containing all Australasian species. Within the Australasian clade, G. macrophylla Blume (subgenus Pseudogunnera Schindler), occurring in New Guinea and Malaya, is sister to a clade including the species from New Zealand and Tasmania (subgenus Milligania Schindler). The southern South American subgenus Misandra Schindler is sister to a clade containing the remaining American, as well as the Hawaiian species (subgenus Panke Schindler). Within subgenus Panke, G. mexicana Brandegee, the only North American species in the genus, is sister to a clade wherein the Hawaiian species are basal to all south and central American taxa. Main conclusions According to the cladogram, South America appears in two places, suggesting an historical explanation for northern South America to be separate from southern South America. Following a well‐known biogeographical pattern of vicariance, Africa is the sister area to the combined southern South America/Australasian clade. Within the Australasian clade, New Zealand is more closely related to New Guinea/Malaya than to southern South America, a pattern found in other plant cladograms, contradictory to some of the patterns supported by animal clades and by the geological hypothesis, respectively. The position of the Tasmanian G. cordifolia, nested within the New Zealand clade indicates dispersal of this species to Tasmania. The position of G. mexicana, the only North American species, as sister to the remaining species of subgenus Panke together with the subsequent sister relation between Hawaii and southern South America, may reflect a North American origin of Panke and a recolonization of South America from the north. This is in agreement with the early North American fossil record of Gunnera and the apparent young age of the South American clade.     

Phylogeny and biogeography ofOrobanchaceae

Orobanchaceae, as it is currently defined, includes all levels of parasitic ability ranging from nonparasitic (Lindenbergia) to facultative and obligate hemiparasites to obligate holoparasites. Several genera are of economic importance as crop weeds and have been studied by scientists interested in developing methods of control, but most genera have not been studied in a comparative framework. In this study we have used ITS sequence data to build a phylogenetic framework with which to examine previous systematic hypotheses of relationships among genera, and biogeographic hypotheses of either a Cretaceous, Gondwanan or mid-Tertiary, Laurasian origin of the family. A single-most parsimonious ITS tree was produced from a combined data set of nucleotides and gap characters. Our results support the current classification ofOrobanchaceae and a hypothesis of a mid-Tertiary, Laurasian origin of the family.     

Trophic theory of island biogeography

MacArthur and Wilson's Theory of Island Biogeography (TIB) is among the most well-known process-based explanations for the distribution of species richness. It helps understand the species-area relationship, a fundamental pattern in ecology and an essential tool for conservation. The classic TIB does not, however, account for the complex structure of ecological systems. We extend the TIB to take into account trophic interactions and derive a species-specific model for occurrence probability. We find that the properties of the regional food web influence the species-area relationship, and that, in return, immigration and extinction dynamics affect local food web properties. We compare the accuracy of the classic TIB to our trophic TIB to predict community composition of real food webs and find strong support for our trophic extension of the TIB. Our approach provides a parsimonious explanation to species distributions and open new perspectives to integrate the complexity of ecological interactions into simple species distribution models.