The Role of Substratum in Benthic Macroinvertebrate Microdistribution and Litter Decomposition in a Woodland Stream
1980
Reice, Seth R.
This experiment tested the effect of substratum particle size, in the absence of velocity variation, on the determination of macroinvertebrate microdistribution and decomposition in woodland streams. Replicate baskets of three different substrata were placed in a single riffle of New Hope Creek, North Carolina, USA. The substrata were fine gravel (°1 cm diameter), pebbles (°2.5 cm diameter), and large cobbles (°8.5 cm diameter). Half the baskets had leaf packs attached to their upper surfaces. Replicate samples were removed on five dates at 2—wk intervals and analyzed for macroinvertebrates and leaf pack biomass. Colonization and distribution patterns of individual taxa were used to assess substratum preferences, which were correlated with physical properties of the sediments and the presence or absence of the leaf covering. Overall, litter decomposition did not vary among substrata. The fraction of animal populations in leaf packs was proportional to the biomass remaining. Animals showed substratum preferences even when velocity difference were eliminated. Preferences of common taxa were unaffected by the presence or absence of leaf packs on the substratum. Common taxa showed strong preferences for either leaves or substrata. Abundance data (the number of individuals per basket) strongly contradict the density data (number per square metre of substratum surface). The latter measure offers more biological insight. These results emphasize the importance of substratum size as a prime determinant of the structure of lotic macroinvertebrate communities.
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