Variation in fish community composition along an Iberian river basin from low to high discharge: relative contributions of environmental and temporalvariables

Factors associated with the spatial and temporal variation of the lower Gua diana basin (southern Iberia) fish community were determined using data fro m 20 sites sampled during the summer of 1994 (dry year following a period o f low discharge, total discharge from 1992 to 1994=1.45x10(9) m(3)) and aga in during the summer of 1996 (wet year following a period of higher dischar ge, total discharge from January 1995 to August 1996=6.18x10(9) m3). From t he 17 explanatory variables initially considered six were retained for anal ysis by a forward selection procedure: maximum depth, altitude, channel wid th, substrate coarseness, SALT (a dummy variable identifying sampling locat ions belonging to tributaries that discharge to the brackish Guadiana) and YEAR (a dummy variable identifying the sampling year). Further, we partitio ned the total variability in the Guadiana fish community into that accounte d uniquely by selected environmental variables (34.9%), uniquely by samplin g year (4.1%), by both sampling year and environmental variables (0.3%), an d unexplained (60.7%).