Niche Relationships and Population Ecology of Rainbow (Etheostoma Caeruleum) and Fantail (E. Flabellare) Darters in a Temporally Variable Environment

Abstract

The importance of interspecific competition and fluctuations in stream flow were studied to determine the relative abundance and spatial distribution of E. caeruleum and E. flabellare. The species exhibited considerable overlap in prey size and taxa. The number of prey types utilized by each species increased in summer during periods of reduced resource availability. Fluctuations in prey availability had no effect on overlap in prey utilization. The species exhibited subtle differences in microhabitat use, with E. caeruleum foraging over the top surfaces of substrates and E. flabellare foraging in crevices between rocks. The distribution patterns of the species differed in substrate preference experiments but presence or absence of congeners did not influence substrate use. Microhabitat use appeared to be constrained by morphological characteristics of the species. The spatial distribution of E. caeruleum was more responsive to changes in flow conditions than E. flabellare, exhibiting a greater shift towards deeper habitats during low flows. E. caeruleum also exhibited greater temporal variability in population size than E. flabellare because of greater emigration and/or mortality of age I + individuals during low flow periods in late summer and autumn. In ecological time these species may vary in their distribution and abundance independently of each other. Species specific responses to fluctuations in discharge, related to subtle differences in microhabitat use, appeared to be the critical ecological factor determining the relative abundance and spatial distribution of these species.