Influence of annual flooding on terrestrial arthropod assemblages of a Rio Grande riparian forest

Terrestrial arthropod communities remain poorly described for riparian ecosystems of the arid southwestern United States, and the effects of extensive river regulation and habitat alteration on these potentially important invertebrates are largely unknown. Beginning in 1991, surface-active arthropods were trapped at two riparian sites along the Rio Grande, in central New Mexico, for 2 years. One site was then experimentally flooded from mid-May to mid-June for each of the next 3 years to simulate historic, low intensity flooding, after which arthropod collections were continued. These primary sites. located outside the riverside levee, and isolated from flooding for about 50 years prior to the experiment, were compared with a naturally flooded site and a second non-flooded reference. Experimental flooding and observations of the naturally flooded site indicated that flooding did not affect total taxonomic richness, nor richness of spiders, beetles or ante. However, flooding may have slightly increased the number of carabid beetle taxa present. Flooding altered the overall composition for all taxa, insects, beetles and carabid beetles. Spider taxa composition may be insensitive to flooding, while ant responses were not clear. Abundance of terrestrial isopods and spiders decreased after flooding, while overall beetle abundance did not change. Abundance of crickets and carabid beetles increased, but the response was delayed until after the second flood. Changes in taxa composition and abundance after experimental flooding were generally consistent with arthropod community structure observed at a nearby naturally flooded site. This similarity suggests that reorganization of the terrestrial arthropod community may follow restoration of flooding to this riparian ecosystem. Copyright (C) 2001 John Wiley & Sons, Ltd.