THE EFFECTS OF DISTURBANCE ON A HERBIVORE-EPILITHON INTERACTION IN ANUPLAND STREAM

Two experiments were performed in an upland stream to determine the ef fects of the frequency of physical disturbance on the relationship bet ween an abundant glossosomatid trichopteran (Agapetus monticolus; Bank s) and the epilithon upon which it feeds. Artificial cobbles with an e stablished epilithic community were tumbled either every 1, 2 or 4 wee ks. The first experiment failed to detect any significant effects of r ock tumbling on the abundance of A. monticolus or the epilithon: a res ult due to several spates. The first experiment did reveal that distur bances may disrupt the ability of A. monticolus to locate patches of a bundant food. The second experiment found that although the abundance of A. monticolus was not affected by the disturbances, periphyton abun dance was significantly reduced. Increasing the frequency of disturban ce did not magnify this effect. Comparisons of these results with othe r studies of disturbance in streams indicate that the effects of distu rbance on herbivory may be highly variable. A variety of factors, such as the relative resistances of the herbivores and the epilithon, need to be examined before the effects of disturbances on lotic herbivorou s interactions can be completely understood.