Search

We assessed the relative importance of environmental variation, interspecific competition for space, and predator abundance on assemblage structure and microhabitat use in a stream fish assemblage inhabiting Coweeta Creek, North Carolina, USA. Our study encompassed a 10–yr time span (1983–1992) and included some of the highest and lowest flows in the last 58 years. We collected 16 seasonal samples which included data on: (1) habitat availability (total and microhabitat) and microhabitat diversity, (2) assemblage structure (i.e., the number and abundances of species comprising a subset of the community), and (3) microhabitat use and overlap. We classified habitat availability data on the basis of year, season, and hydrologic period. Hydrologic period (i.e., pre–drought [PR], drought [D], and post–drought [PO]) represented the temporal location of a sample with respect to a four–year drought that occurred during the study. Hydrologic period explained a greater amount of variance in habitat availability data...

The present study establishes the effectiveness of natural drug delivery mechanisms and investigates the interactions between drug and its natural carrier. The binding between the isoflavone diadzein (DZN) and the natural carrier hemoglobin (HbA) was studied using optical spectroscopy and molecular dynamics simulations. The inherent fluorescence emission characteristics of DZN along with that of tryptophan (Trp) residues of the protein HbA were exploited to elucidate the binding location and other relevant parameters of the drug inside its delivery vehicle HbA. Stern-Volmer studies at different temperatures indicate that static along with collisional quenching mechanisms are responsible for the quenching of protein fluorescence by the drug. Molecular dynamics and docking studies supported the hydrophobic interactions between ligand and protein, as was observed from spectroscopy. DZN binds between the subunits of HbA, ∼15 A away from the closest heme group of chain α1, emphasizing the fact that the drug does not interfere with oxygen binding site of HbA.

We quantified the stability of nine stream fish assemblages by calculating coefficients of variation of population size for assemblage members. Coefficients of variation were high and averaged over 96%; indicating that most assemblages were quite variable. Coefficient of variation (CV) estimates were not significantly affected by: (1) years of study, (2) mean abundance, (3) familial classification, or (4) mean interval between collections. We also detected minor regional differences in CVs. The high variability exhibited by many stream fish assemblages suggests that it may be difficult to detect the effects of anthropogenic disturbances using population data alone. Consequently, we urge managers to exercise caution in the evaluation of the effects of these disturbances. More long-term studies of the ecological characteristics of undisturbed stream fish assemblages are needed to provide a benchmark against which disturbed systems can be compared.

In Coweeta Creek, North Carolina, mottled sculpin (Cottus bairdi) co-occurred seasonally with a potential predator, rock bass (Ambloplites rupestris). We conducted experiments to determine whether rock bass affected microhabitat use by sculpin in an artificial stream. The general behavior and microhabitat use of both species in the artificial stream resembled those observed in Coweeta Creek. When all microhabitat observations were pooled, there was little evidence of predator-induced shifts by sculpin. However, at night in trials without predators, sculpin generally occurred farther from shelter, over greater amounts of gravel and lower quantities of erosional substrata. When we added predators, however, this response was obviated. Nonetheless, the lack of strong responses by sculpin to rock bass, coupled with their co-occurrence only during seasons of low metabolic activity, lead us to suspect that rock bass do not produce strong shifts in microhabitat use by most sculpin in the Coweeta drainage.

We monitored fish populations at three sites in a southern Appalachian stream system during a 40-mo study. Assemblages at two sites, consisting of four and five resident species, were persistent in terms of relative species abundances and production. This persistence was related to low variation in abundance of the two numerically dominant fishes, mottled sculpins (Cottus bairdi) and longnose dace (Rhinichthys cataractae). Less abundant residents, rosyside dace (Clinostomus funduloides), rainbow trout (Salmo gairdneri), and greenside darters (Etheostoma blennioides), displayed lower levels of persistence. We also observed pronounced annual variation in either young-of-the-year recruitment and/or subsequent year-class strength of four resident species, possibly resulting from a severe drought during the third year of study. Abundance and production of rosyside dace and trout were greatly affected by fluctuations in recruitment and year-class strength, suggesting that environmental variability strongly influenced these populations. Density-dependent mechanisms may have regulated sculpin and longnose dace populations. The three-species asssemblage at a third site also was persistent as a result of relatively stable sculpin and longnose dace populations, whereas the rainbow trout population fluctuated among years. We observed significant intersite differences in relative year-class strength in a given year and in population structures of sculpins and longnose dace, suggesting that spatial variation in habitat characteristics affected assemblage dynamics and responses to environmental fluctuations.