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. This species is a top predator in arid headwater streams and thus its distribution strongly influences the characteristics of the entire aquatic community. Here we present results of a study on the effects of intraspecies interactions on giant water bug distributions in drying stream pools and experimental tanks and discuss potential implications for aquatic community structure.

Results/Conclusions

Isolated giant water bug juveniles preferentially distributed themselves at the air-water interface at the edges of experimental tanks, 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 life stage and pool characteristics. Adults were found in pools with high surface areas and maximum depths, while juveniles were more evenly distributed throughout the reach. Interestingly, adult males that were brooding eggs were an exception to this pattern, and distributed themselves in shallow pools. The use of shallow, peripheral habitats by juveniles and deep, perennial habitats by adults suggests that an ontogenetic niche shift occurs during development, and the return of brooding males to the shallows supports this observation. As anthropogenic water use in arid lands increases, it is important to determine how biotic interactions change throughout the dry season and how organisms respond to stream drying in order to create effective conservation plans for these ecosystems.