Influence of Current Velocity on Substratum Selection by Naucoridae (Hemiptera): An Experimental Approach Via Stream Simulation

Abstract

Microhabitat preferences of three sympatric naucorids ( Ambrysus circumcinctus Montandon, Limnocoris lutzi La Rivers, and Cryphocricos hungerfordi Usinger) from the South Llano River of central Texas were evaluated in laboratory experiments. Each species was individually subjected to all paired contrasts produced from three substratum size classes (coarse gravel, small pebble, and small cobble). Within each contrast, three trials were conducted, each involving a different current velocity (slow, 6.6 ± 0.1 cm/s; intermediate, 9.8 ± 0.1 cm/s; and fast, 13.7 ± 0.5 cm/s). The gravel substratum was never preferred; moreover, preference in the pebble versus cobble contrast, when present, was only shown for the cobble substratum. Overall, A. circumcinctus exhibited consistent substratum preferences (cobble> pebble> gravel) independent of current velocity. C. hungerfordi preferred cobble over either gravel or pebble substrata; however, a synergistic effect between current velocity and substratum size was detected in the gravel versus pebble contrast. Finally, L. lutzi exhibited the highest degree of velocity-dependent substratum selection. Laboratory analyses corroborated field investigations and offered insight into the influence of interacting abiotic variables on the microdistribution of Naucoridae.