FOOD RESOURCE PARTITIONING BY 9 SYMPATRIC DARTER SPECIES

We compared the diets among members of the diverse darter community of French Creek, Pennsylvania, in relation to seasonal prey availability , feeding ontogeny, and sex. Prey taxa and size attributes were charac terized for nine syntopic darter species; taxon, size, and availabilit y of macroinvertebrate prey were also analyzed from Surber samples. In general, darters fed opportunistically on immature insects; few taxa were consumed in greater proportions than they were found in the envir onment. Some variation in diet composition was expressed, however, amo ng different life stages and species. Juvenile darters consumed smalle r prey and more chironomids than did adults. Etheostoma blennioides an d E. zonale consumed the fewest taxa (2-3), whereas E. maculatum, E. v ariatum, and Percina evides had the most diverse diets (7-10 taxa). Et heostoma maculatum, E. flabellare, E. variatum, and P. evides consumed larger prey (1-13 mm in standard length), whereas E. blennioides, E. caeruleum, E. camurum, E. tippecanoe, and E. zonale rarely consumed pr ey longer than 6 mm. Percina evides fed on larger prey, fewer chironom ids, and more fish eggs than Etheostoma species. Females consumed more prey than males and overlapped less in diet composition with males du ring the spawning season than afterwards. Fish diets did not seem rela ted to habitat use. Greater trophic partitioning was observed in April , when prey resources were scarce, than in July, when prey were abunda nt. Darter species fed opportunistically when prey were dense, whereas they partitioned food resources mainly through the prey size dimensio n when prey were less abundant. The divergence of darter diets during a period of low food availability may be attributed to interspecific c ompetition. Alternatively, the greater abundance of large prey in Apri l may have facilitated better prey size selectivity, resulting in less overlap among darter species.