Dietary Specialization by the Speckled Darter, Etheostoma stigmaeum, on Chironomid Larvae in a Mississippi Stream

ABSTRACT

We determined the foraging mode of the speckled darter (Etheostoma stigmaeum) in a small blackwater stream in Mississippi at two levels of prey classification and identified speckled darter prey that were selected or were not selected. Chironomids dominated speckled darter diets (relative abundance 33.0–92.3%, seasonally), and they also dominated the resource base (relative abundance 46.3–74.9%, seasonally). High proportional similarity (PS) and low niche breadth (NB) values suggested that the speckled darter fed opportunistically on a small range of available prey, (PS>0.58 and NB<0.27, seasonally). When chironomids were identified to genus/species, PS and NB values were low (PS<0.37 and NB<0.23, seasonally), suggesting the darter fed selectively on a small number of invertebrate taxa. At this finer level of classification, the speckled darter fed like a classic specialist, selecting only one to three taxa seasonally. The speckled darter selected the chironomids Polypedlium convictum gr., Stelechomyia perpulchra, Xylotopus par, Nilotanypus sp., Psetrocladius elatus, and Psetrocladius sp. (Manly's α>0.111).