Scales and frequencies of disturbances: Rock size, bed packing and variation among upland streams

Abstract

1. Disturbance is an important source of variability in species composition and diversity, but application of disturbance models is contingent upon a very good understanding of the spatial scales and frequencies of disturbance. Such information is particularly lacking from streams. In this study, we measured the disturbance levels of rocks (defined here as the proportion of the original sample disturbed after 6 months) of differing sizes and positions within the stream bed and looked at the variation between and within three upland streams. 2. Rocks were blazed with distinctive marks in situ and mapped using simple trigonometry and permanently marked points on the banks. Forty rocks were sel..