Intraspecies interactions in giant water bug populations in drying intermittent streams

Authors: Kate S. Boersma, David A. Lytle

Year: 2008 (xl)

Abstract

The intermediate disturbance hypothesis predicts that abiotic processes are more important than biotic processes at structuring natural communities in frequently disturbed systems, such as high relief drought-prone desert streams. However, there is evidence that populations of the giant water bug, Abedus herberti, in the intermittent streams of southeastern Arizona are subject to intense biotic interactions throughout the dry season as their prey base dwindles and cannibalism becomes prevalent. I present results of a study on intraspecies interactions in drying stream pools and experimental tanks. Isolated juveniles preferentially distributed themselves at the air-water interface at the edges of experimental pools, however this preference disappeared when more than one bug was present, suggesting strong effects of the presence of conspecifics, possibly resulting from cannibalism. Field studies confirmed a relationship between bug distribution and depth. Adults were found in pools with high surface areas and maximum depths, while juveniles were more evenly distributed throughout the reach. The selection of shallow, peripheral habitats by juveniles and deep, perennial habitats by adults suggests that an ontogenetic niche shift must occur, but the details of this transition remain unknown. As anthropogenic water use in arid lands increases, it is important to determine organism responses to intermittent streams during the drying season in order to create effective conservation plans for these ecosystems.