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FIGURE 8.11 The percentages of fish from West African rivers that are piscivorous in a given maximum length class. (Reproduced from Allan et al. 2005a, based on analyses by RL Welcomme.)

Maximum length class (cm)

FIGURE 8.11 The percentages of fish from West African rivers that are piscivorous in a given maximum length class. (Reproduced from Allan et al. 2005a, based on analyses by RL Welcomme.)

wide size range, predatory fishes of all body sizes were able to exploit taxa low on the food web, resulting in relatively short, size-structured food chains for individual components of the overall web. However, no relationship was found between body size and trophic position across the range of body sizes for the 31 predaceous species in this system, due to the wide range of body sizes of the primary consumer fish taxa.

In sum, the categorization of fishes into feeding guilds provides useful insights into trophic structure, but requires similar caution as when categorizing invertebrate FFGs. Diet changes with age because of growth in size, and with season because of shifts in availability of habitat and food types. Even a single individual at a particular time and place may fall into more than one feeding category. In practice, guilds are a useful way to summarize the broad similarities in the trophic ecology of taxa that have similar feeding roles, as long as their use does not obscure the individual differences and great flexibility of which fish are capable. Because of differences in resource availability between temperate and tropical regions, their fish guilds also differ, particularly in the greater roles of det-ritivory and ooze feeding in the tropics. Moreover, guild structure appears less uniform from place to place among river-dwelling fishes of tropical rivers, compared to temperate zone studies.

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