The terrestrial invertebrate fauna of a temporary stream in southern Africa

Abstract

The terrestrial invertebrate fauna of an intermittent stream was examined in the absence of surface flows within the context of the flood pulse concept. Terrestrial invertebrates were collected from three sites on the Kruis River in theWestern Cape Province, South Africa, using pitfall traps within the dry stream bed over summer months (Jan–Feb). 9848 individuals representing 19 different orders were collected. Taxa were separated and biomass determined for aerial and non-aerial  invertebrates. Significantly greater (P < 0.05) numbers of aerial than non-aerial taxa and individuals suggest that most individuals could use flight to escape the onset of surface flows. The absence of significant differences between the biomass (wet weights) of aerial and non-aerial individuals (P>0.05) suggests, however, that a large proportion of the biomass is confined to the main channel. The inability of a large portion of the biomass to escape the onset of flow through the use of flight suggests that periodically inundated areas of the stream channel constitute an ecologically significant component of temporary stream ecosystems. The concept of the flood pulse should be expanded to include aseasonal and secular variations in flow which in temporary streams create lateral movements that provide the driving mechanism for the entrainment of organic material.

Key words: ephemeral, intermittent, flood pulse concept.