Interspecific Interactions and Limiting Factors of Abundance and Distribution in the Red River Pupfish, Cyprinodon rubrofluviatilis

Abstract

The Red River pupfish, Cyprinodon rubrofluviatilis, was positively associated in occurrence with Fundulus zebrinus, Hybognathus, placitus and Notropis bairdi and negatively associated with a large, predominantly fresh-water (salinity 10 ppt) where few other species occurred. An apparent lack of intrinsic limiting factors was demonstrated. The pupfish seems adapted to a ecological niche, creating competition with an array of fresh-water forms that are better adapted to exist in richer faunas. A W to E filter-bridge based on decreasing nurnbers of saline streams seems to be the major factor limiting eastward distribution of the pupfish. Competition and direct behavioral interaction with the pupfish seemed to be major factors depressing F. zebrinus populations in saline waters. A variety of broad adaptations of the pupfish may help to confer a numbers advantage over F. zebrinus, magnifying the effects of behavioral interaction. These effects may also help make the pupfish successful at moderate salinities (10-20 ppt) where there are at least 12 potentially competing species.