Vertebrates in Lotic Food Webs

Although all vertebrate classes have representatives in running waters, fishes are the principal vertebrate component of most riverine food webs. In small headwater streams, salamanders and snakes may be important top predators; there are many species of fish-eating birds and some that consume aquatic invertebrates; a few mammals feed primarily or exclusively on aquatic prey, and a surprising diversity of mammals do so at least occasionally.

8.3.1 Fishes

A number of attempts have been made to construct feeding categories for stream fishes. In North America, most stream fishes are inverti-vores, some become piscivorous for much of their life cycle, and a few are herbivores (Allen 1969). Just as was true for early efforts to categorize invertebrates (most were herbivore-detriti-vores, some were predators), so simple a scheme is of limited value. Additional detail on where and how feeding occurs allows greater resolution of fish trophic categories (Table 8.3), and some of these categories can be subdivided further. Herbivorous fish with scraping mouthparts such as the stone roller Campostoma anoma-lum clearly have little in common with ooze feeders such as the bluntnose minnow Pime-phales notatus. Some benthic invertebrate feeders utilize prey primarily from soft bottoms (the suckermouth minnow Phenacobius mirabilis), and others from stony bottoms (the greenside darter Etheostoma blennioides). Table 8.3 gives the percentage of fish species in each category from Horwitz' (1978) study of 15 river systems in the United States. All but one

TABLE 8.3 Trophic guilds of stream fishes, for temperate North America (modified from Horwitz 1978) and tropical South America (modified from Welcomme 1979).

Guild Description for temperate Occurrencea Comments for tropical streams by species (%) streams

TABLE 8.3 Trophic guilds of stream fishes, for temperate North America (modified from Horwitz 1978) and tropical South America (modified from Welcomme 1979).

Guild Description for temperate Occurrencea Comments for tropical streams by species (%) streams

Piscivore

Consumes primarily fish and/or large invertebrates, but includes smaller invertebrates

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