Demise and rise : the biogeography and taxonomy of the Odonata of tropical Africa

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Demise and rise : the biogeography and taxonomy of the Odonata of tropical Africa

Type: Doctoral thesis
Title: Demise and rise : the biogeography and taxonomy of the Odonata of tropical Africa
Author: Dijkstra, Klaas-Douwe Benediktus
Publisher: Department of Biology, Faculty of Mathematics and Natural Sciences, Leiden University
Issue Date: 2007-05-16
Keywords: Odonata
Abstract: Africa has a large and almost uninterrupted land surface that is isolated from surrounding continents. In the last 20 million years Africa had a variable and increasingly dry climate. As a result the Afrotropics have only half as many odonate species as tropical America or Asia. ‘Relict’ families are scarce and concentrated in five isolated, climatically stable areas: (1) the Cameroon highlands, (2) locally in East Africa, (3) the Cape region, (4) the granitic Seychelles, and especially (5) Madagascar. Most African odonate species, about two-fifths, are restricted to the Central and West African forests. The remainder is found, in three fairly equal parts, in (1) the highlands from Arabia to the Cape, (2) Madagascar and surrounding archipelagos, and (3) open habitats throughout the region. Most mainland species appear related to the relatively diverse fauna of tropical Asia, but have few relatives on Madagascar, suggesting that the modern continental fauna mostly diversified after the arrival of Asian ancestors. Being best adapted to change, Coenagrionidae and Libellulidae are the largest odonate families on Earth. Only in temperate regions, impacted strongly by the ice ages, is their dominance comparable to that in changeable Africa. The climatic influence is further seen in forest species ‘stranded’ in highlands by forest reduction, savanna species ‘trapped’ by forest expansion, and overseas colonisation of East Africa by island species. Traditional theory is that speciation took place in habitat fragments created by climatic change, especially in forest refuges, but such refuges seem to conserve old species rather than generate new ones. Abrupt habitat gradients in heterogeneous landscapes may be more important in speciation, especially close to areas where potential ancestors are conserved. The habitat mosaic on the Congo-Zambezi watershed is the best modern example of such an area. Phylogenetic research of various African plants and animals indicate that environmental and dispersal barriers are easily straddled, with savanna species radiating from a forest ancestors and vice versa. Species were eliminated with climatic change, but new ecological space was also constantly created. Such processes must also have lead to the ‘demise’ of most of Africa’s old odonate diversity and the ‘rise’ of a rich new fauna.
Description: Promotor: E. Gittenberger, Co-promotor: V. Clausnitzer
With Summary in Dutch
Faculty: Faculteit der Wiskunde en Natuurwetenschappen
Citation: Dijkstra, K.D.B., 2007, Doctoral Thesis, Leiden University

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