Patterns of community assembly in a fourth order stream
published: Apr 14, 2000
ArtNo. ESP141014802010, Price: 29.00 €
Spatial patterns in community structure were studied for one year along a fourth order stream in NW Spain, the Tea Stream. Differences were observed for most biological variables examined between upper-middle lotic reaches and downstream reaches in autumn, a season characterised by the occurrence of high and frequent spates. Diversity and richness values were high at the upper stream reaches throughout the year, even when discharge was high. Downstream sites were inhabited by species-poor communities during autumn and winter. In spring and summer, however, richness and diversity values increased, and invertebrate abundance was higher at these sites than at the upper reaches. Observed spatial patterns in community structure were mainly correlated with physical variables, such as a combination of morphological channel features, dissolved salts and oxygen concentration, and surface water velocities. The spatio-temporal differences in community structure observed in this study are greater than expected for a fourth-order stream. The greatest discontinuity in community composition occurred between high and low gradient sites during periods of high flow. The flow conditions during autumn-winter seemed to exert a strong abiotic influence on communities inhabiting downstream reaches, when species richness and abundances remained low. The upper-middle reaches of the Tea supported high richness throughout the year, with more resilience to high flows than downstream communities.