Estimating number of species and relative abundances in stream-fish communities: effects of sampling effort and discontinuous spatial distributions

Abstract

The authors sampled fishes and measured microhabitat in series of contiguous habitat units (riffles, runs, pools) in three Virginia streams. Monte Carlo simulations were used to construct hypothetical series of habitat units. Proportions of all species and microhabitats represented were relatively low and variable at low sampling effort, but increased asymptotically and became less variable with greater effort. Negative exponential curves indicated that 90% of the species present were usually found by sampling 5-14 habitat units (stream length of 22-67 stream widths). Estimates of species relative abundances required less sampling effort for a given accuracy than estimates of number of species. Rates of species accumulation (with effort) varied among streams and reflected discontinuity in species distributions among habitat units. Most discontinuity seemed to be due to low population density rather than to habitat selectivity. Greater sampling effort is needed to characterize fish community structure in more homogeneous stream reaches. -from Authors