Desert water bugs on the move: the effects of distance from potential source populations on colonization of novel habitats

Authors: Michael T. Bogan, Kate S. Boersma

Year: 2009 (xli)

Abstract

Streams in arid western North America are experiencing extreme droughts and increased anthropogenic water withdrawals. As a result, many streams are transitioning from perennial to ephemeral flow. Understanding dispersal and colonization potential of aquatic organisms is essential in order to predict changes in local community structure as a result of this increased aridity. We examined aquatic invertebrate colonization dynamics over a 6-week period at one perennial and one ephemeral stream, using replicate mesocosms placed at three distances from the stream corridor: 5m, 75m, and 250m. Over 50 species of aquatic invertebrates colonized the mesocosms during the study period. Contrary to our predictions, we found that distance from the stream channel affected colonist species richness at the ephemeral site, but not at the perennial site. At both sites, rainfall was strongly associated with large pulses in colonization, though many new colonists left the mesocosms within a week of the rainfall event. We identified at least five types of colonizers: (1) widespread opportunistic, (2) range-restricted opportunistic, (3) cue-limited opportunistic, (4) widespread haphazard, and (5) infrequent. These results suggest that overland dispersal of aquatic invertebrates is frequent in arid-land streams, but that species exhibit greatly varying abilities and strategies for colonization. Additionally, despite the lack of surface water, ephemeral stream channels may be important dispersal corridors for aquatic invertebrates. Given the wide variety of species-specific colonization potential demonstrated in our experiment, we expect that increased spatial and temporal rarity of perennial habitat will greatly alter community structure in arid-land streams.