Aggregation of numbers, size and taxa of benthic animals at four levels of spatial scale
Aggregations of individuals, taxa and size in a benthic community were analyzed at four levels of spatial scale in a littoral zone of a mesotrophic, dimictic lake. Distribution of plant roots and sediment types was also determined to demonstrate the impact of the major influencing environmental factors. Two field studies were conducted. The first focused on random sampling in three 9m2 plots. The second tested distribution inside and outside of the macrophyte root zone at three sites within a lake. The aggregation patterns varied with both taxonomical groups and levels of spatial scale. Chironomids were aggregated in level of samples, particularly when 1m2 plots were compared but they were randomly distributed at higher spatial levels. Oligochaetes were randomly distributed at lower levels but aggregated among sites. Red chironomids were aggregated at lower levels and randomly distributed among sites. Predatory chironomids were almost uniformly distributed, especially at lower densities. A triangular model was suggested for relating the aggregation patterns to major influencing factors in the community. Taxonomic composition, animal size and number were considered the basic characteristics of a benthic community, and the three relationships among them were suggested to determine the aggregation pattern. According to the model, chironomids were dominated by interspecific competition at lower levels and by environment at higher levels of the spatial scale Oligochaetes were always influenced by environment. Predatory chironomids were determined by intraspecific competition. Red chironomids shifted from relationship dominated by intraspecific competition the lower levels to one dominated by environment at the higher levels.