Physical Factors Within Drainages as Related to Fish Assemblages

Abstract

Local fish assemblages are influenced by physical or ecosystem factors within individual drainages (lake basins, rivers, small streams) or local sites (stream reaches, parts of a lake). This chapter examines the structure of fish assemblages relative to (1) drainage area, (2) local-site dimensions (e.g., width, habitat volume, discharge, depth, and pool development), (3) habitat heterogeneity, (4) physical structure, (5) biotic productivity, (6) zonation in lakes or longitudinal patterns in streams, and (7) the landscape in or surrounding the water. This is a mixed array of factors sharing in common that all (1) characterize external environments of fishes on a scale at which an individual fish, in its daily or seasonal activities, could “sample” the variable and (2) are mostly abiotic or “noninteractive” variables (which the fish generally do not control, in contrast to biological-interactive variables dependent on or involving the fishes). However (Chapter 11), some fishes strongly influence their own external environment or that of others (e.g., if algivorous fishes alter the physical structure of the environment for other fishes (Power et al., 1985, 1988; Gelwick and Matthews, 1992; Gelwick, 1995; Flecker, 1996), so strict categorization of factors as “extrinsic” is difficult.