Ecology of North American Freshwater Fishes by Ross Stephen T.;

Author:Ross, Stephen T.;
Language: eng
Format: epub
Publisher: University of California Press

TROPHIC GUILDS

A useful approach for understanding the trophic organization of fishes is to recognize functionally defined trophic guilds. The term guild was formally proposed as “a group of species that exploit the same class of environmental resources in a similar way” (Root 1967). Defined in this way, the guild concept encompasses both the food resource and the way it is obtained (e.g., piscivory could be achieved by actively chasing prey or by ambush; see also Chapter 8). Importantly, although groups of species with highly similar functional roles within a community would belong to the same guild, say planktivore, in a different community the same guild might comprise different species. The placement of fishes into feeding guilds is necessarily approximate. Given that fishes are often opportunistic feeders, their diets may change spatially and temporally, and most fishes show strong ontogenetic changes in food habitats with growth (Poff and Allan 1995). Feeding guilds, as well as other guild categories, are widely used in the determination of aquatic system health via the Index of Biotic Integrity (Karr 1981; Bramblett and Fausch 1991). Feeding guilds are also important for understanding functional responses of different communities to hydrological or geomorphic changes, as well as temporal changes within a single community (Grossman et al. 1982; Poff and Allan 1995). To enhance the utility of feeding and other guilds (e.g., habitat), it is sometimes desirable to recognize two kinds of guilds related to food habits—a feeding guild as defined by the foraging habitat (i.e., benthic, water column, or surface) and a trophic guild as defined by the nature of the prey (i.e., detritivore, herbivore, or insectivore), as an alternative to combining prey and feeding habitat (Noble et al. 2007). However, most trophic guilds involving fishes combine food and feeding location characteristics, often because the information required for designating two separate guilds is simply inadequate. Species that form a specific guild would have similar trophic positions (see also Chapter 11), but depending on how narrowly a guild is defined, fishes that feed at the same trophic level may still differ in both the kinds of food and their feeding locations, and thereby be placed into different guilds (following Root 1967). For instance, the fishes that consume herbivorous aquatic insects could potentially be separated into two feeding guilds, one characterized by feeding over a soft substratum versus the other feeding over a rocky substratum (see Chapter 11; Figure 11.8).

Although assignments of fishes to feeding guilds are usually based on the dominant prey items from gut contents (usually restricted to large juveniles and adults), other approaches also include multivariate analysis of gut contents and stable isotope studies (Vander Zanden et al. 1997; Olden et al. 2006; Gido and Franssen 2007; Noble et al. 2007).

Based on data from nine faunal studies that are representative of different regions of North America, I have assigned 224 species in 28 families to nine commonly recognized feeding guilds (Table 12.1). If more data were available, most of these categories could be further broken down into subcategories (Goldstein and Simon 1999).

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