Terrestrial arthropod communities r

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 ants. 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.