MICROHABITAT SEGREGATION OF THE THREATENED SPOTTED DARTER (ETHEOSTOMA-MACULATUM) AND CLOSELY-RELATED ORANGEFIN-DARTER (E BELLUM)

We examined differences in microhabitat use in sympatric populations o f the closely related spotted darter (Etheostoma maculatum) and orange fin darter (E. bellum) (subgenus Nothonotus). Sample plots and underwa ter observations were employed to assess patterns of microhabitat use by both species. Quantitative sampling using a prepositioned electrofi shing sampler demonstrated that species segregated by microhabitats. E theostoma maculatum occupied areas of greater depth and larger, more d iverse substrate sizes than E. bellum in July and October of 1991. Und erwater observations also revealed species-specific differences in sub strate use. Etheostoma maculatum was observed mostly under rocks where as E. bellum was more general in substrate use. The narrow range of mi crohabitat use by E. maculatum may contribute to its status as a threa tened species in Kentucky. During July 1991, an unusually high dischar ge month that year, males of both species occupied microhabitats of si gnificantly higher velocities and larger substrate sizes than females. Our data suggest that opportunities for coexistence between these clo sely related darters are enhanced by microhabitat partitioning which i s linked to behavioral and morphological differences.