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Role of dispersal in the invasion of an exotic tree in an East African submontane forest

Published online by Cambridge University Press:  07 July 2004

Norbert J. Cordeiro
Affiliation:
Department of Biological Sciences (m/c 066), University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607, USA Tanzania Wildlife Research Institute, P.O. Box 661, Arusha, Tanzania
David A. G. Patrick
Affiliation:
Durrell Institute of Conservation and Ecology, The University of Kent, Canterbury, Kent CT2 7NZ, UK
Billy Munisi
Affiliation:
P.O. Box 1, Amani, Tanzania
Vipul Gupta
Affiliation:
Department of Biological Sciences (m/c 066), University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607, USA

Abstract

Early successional tree species typically attract numerous generalist frugivores, many of which serve as seed dispersers. This study evaluated whether several such dispersers facilitated the invasion of an exotic, early successional tree species, Maesopsis eminii (Rhamnaceae), in submontane forests of the East Usambara Mountains, Tanzania. The primary seed dispersers and their dispersal effectiveness were determined through focal watches at eight trees. Only 3 of 13 frugivores that consumed Maesopsis fruits functioned as seed dispersers (silvery-cheeked hornbill Ceratogymna brevis, Fischer's turaco Tauraco fischeri and blue monkey Cercopithecus mitis). On average, hornbills dispersed >26 times more seeds than monkeys, and >3 times as many seeds as turacos per visit and were thus considered the most important disperser. Seed germination was not affected by gut passage through hornbills. Germination in four microhabitats was experimentally evaluated to determine whether microhabitat influences germination success. Large gaps and forest edges had significantly higher germination rates compared with understorey locations; the germination rate in small gaps was not significantly different from that in the understorey. Expansive Maesopsis invasion in the East Usambaras was likely enhanced in both rapidity and scale by the presence of an extremely effective dispersal agent, the silvery-cheeked hornbill.

Type
Research Article
Copyright
2004 Cambridge University Press

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