Trophic Resource Allocation between Percina sciera and P. ouachitae in the Tombigbee River, Mississippi

Abstract

Aspects of the trophic ecology of Percina sciera and P. ouachitae from a site on the Tombigbee River, Mississippi, were compared to: (1) determine the extent of seasonal, sexual and size class trophic allocation in the two species; (2) describe the feeding habits of the two species and compare these habits to a syntopic group of benthic fishes, and (3) determine whether a relationship exists between predator morphology and prey characteristics. The two species had similar diets which corresponded closely to diets for darters of similar habitats. There were small qualitative differences in diet, and gut content changed seasonally in both species. Percina sciera took larger prey than P. ouachitae in the autumn, and this was related to differences in fish size (standard length). Males and females differed in prey size selectivity and the differences were greatest in the spring. With the exception of standard length, no morphological trait of the two species was highly correlated with prey size. Trophic competition is likely of minor importance between these species. INTRODUCTION One means by which species of similar habits may coexist is by allocation of trophic resources (Schoener, 1974a). The gut contents of sympatric fishes of similar feeding habits may differ in prey kind (e.g., Hartley, 1948; Keast, 1966; Mathur, 1972), actual prey length (e.g., Northcote, 1954; Tyler, 1972; Ross, 1977; Yoshiyama, 1980); and prey may be selected on the basis of prey size (O'Brien et al., 1976) or prey evasiveness (Vinyard, 1980). Trophic resource partitioning may also be effected by ontogenetic use patterns (Ross, 1978; Nakashima and Leggett, 1978; Fahy, 1980). Limiting morphological similarity relating to the trophic function of the species within the community may also be important (Hartman, 1958; Werner, 1974; Montgomery, 1977; Smartt, 1978; Gatz, 1979b; Ricklefs and Travis, 1980). Studies of resource partitioning are best carried out on functional groups of species, or guilds (Root, 1967; Krebs, 1978), which exploit a common resource base in a similar way and in which competition is expected to be greatest. Comparative studies of the trophic ecology among guilds of fishes are common (e.g., Hartley, 1948; Northcote, 1954; Keast and Webb, 1966; Keast, 1966, 1978; Thomerson and Wooldridge, 1970; Tyler, 1972; Ross, 1977; Yoshiyama, 1980). However, even though the feeding habits of benthic stream fishes have been studied (e.g., Scalet, 1972; Page and Smith, 1970; Page, 1974; Schenck and Whiteside, 1977; Burr and Page, 1978), fewer studies are available which directly compare the food habits of closely related darters (Percidae). Cordes and Page (1980) compared aspects of the trophic ecology of Etheostoma zonale and E. microperca in Illinois. Adamson and Wissing (1977) observed the diets of E. careruleum, E. flabellare and E. zonale in an Ohio stream. Daiber (1956) compared the food habits of the darter E. flabellare with Cottus bairdi in New York, and Thomas (1970) examined diets of four species of darters in Illinois. This study describes aspects of the trophic ecology of two ecologically and morphologically similar darters, Percina sciera and P. ouachitae, from the Tombigbee River in Mississippi. I compare diet complement, prey size and volume and the morphology of trophic structures, as well as seasonal, size class and sexual differences in diet. I evaluate one assumption of the ecomorphological model (Gatz, 1979a) by comparing 'Present address: Department of Entomology, Mississippi Entomological Museum, Drawer EM, Mississippi State, Miss. 39762.