Implications of changes in trophic diversity and food webs on fisheries and the environment

Most of the earth's ecosystems are experiencing slight tocatastrophic losses of biodiversity, caused by habitatdestruction, alien species introduction, climate change andpollution (Wilcove et al., 1998). These human effects haveled to the extinction of native fish species, the collapse of their populations and the loss of ecological integrity and ecosystem functioning (Ogutu-Ohwayo & Hecky, 1991;Witte et al. , 1992a; Mills et al., 1994; Vitousek et al., 1996).Food webs are macro-descriptors of community feedinginteractions that can be used to map the flow of materialsand nutrients in ecosystems (Jepsen & Winemiller, 2002).Comparative food web studies have been used to address theoretical questions such as 'does greater trophic connectivity increase stability?' (Cohen et al., 1990), and 'does the number of trophic levels increase with productivity?' (Briand & Cohen, 1987). Answers to such questions have obvious applications for natural resources management. From a multi-species fisheries standpoint, there is a need to understand consumer-resource dynamics within complex trophic networks.