Quantification and comparisons of the structure of open-water plankton communities from 25 inland lakes of Ontario, from the Laurentian Great Lakes Superior, Huron, St. Clair, Ontario, and Erie, and from the Central Gyre in the North Pacific Ocean were made on the basis of the normalized biomass size spectrum. Residual variation around the fitted straight lines (corresponding to a theoretical steady state) was least for the large, oligotrophic Lake Superior and the North Pacific Gyre and greatest for eutrophic Saginaw Bay and shallow Lake Erie, suggesting progressive departure from steady-state conditions with increasing system productivity. The slopes of the normalized spectra decrease with increasing eutrophy, indicating that nannoplankton abundances are similar in all communities studied, but that associated zooplankton abundances vary by 2.5 orders of magnitude. Our results suggest that parameterization of particle-size models for prediction of potential fish production must be adjusted according to the size and productivity of the ecosystem, and that routine monitoring of communities by the normalized biomass spectrum could provide early warning of nutrient or toxic stress in aquatic ecosystems.
12Charles Elton introduced the 'pyramid of numbers' in the late 1920s but this remarkable insight 13 into body-size dependent patterns in natural communities lay fallow until the theory of the biomass size 14 spectrum was introduced by aquatic ecologists in the mid-1960s. They noticed that the summed 15 biomass concentration of individual aquatic organisms was roughly constant across equal logarithmic 16 intervals of body size from bacteria to the largest predators. These observations formed the basis for a 17 theory of aquatic ecosystems, based on the body size of individual organisms, that revealed new insights 18 into constraints on the structure of biological communities. In this review we discuss the history of the 19 biomass spectrum and the development of underlying theories. We indicate how to construct biomass 20 spectra from sample data, explain the mathematical relations among them, show empirical examples of 21 their various forms, and give details on how to statistically fit the most robust linear and nonlinear 22 models to biomass spectra. We finish by giving examples of biomass spectrum applications to 23 production and fisheries ecology, and offering recommendations to help standardize use of the biomass 24 spectrum in aquatic ecology. 25 26
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Two distinct communities exist in a series of small subalpine ponds on Galena Mountain, Colorado, at 3,400 m. In the deep ponds, two predators, the culicid larva Chaoborus and the axolotl Ambystoma tigrinum, coexist with two small herbivores, the copepod Diaptomus coloradensis and the cladoceran Daphnia rosea. In the shallow ponds the predatory salamander (Ambystoma tigirinum) coexists with three large herbivores, Daphnia pulex, Diaptomus shoshone (which may be predatory as an adult), and the fairy shrimp, Branchinecta shantzi, as well as the small Diaptomus coloradensis. Despite the proximity of deep and shallow ponds, each community has remained resistant to invasion from the other for at least 5 years. To determine why, I recorded the survival of organisms placed in cages in foreign ponds alone and in combination with the native species. Results revealed that chemical or physical conditions were limiting only for Daphnia pulex, which did not survive well in deep ponds. The large Diaptomus shoshone and Daphnia pulex could not invade deep ponds probably because they were heavily preyed upon by Chaoborus and the axolotl, respectively. This occurred in the presence of small prey, since laboratory experiments showed that predators selected large food items. Branchinecta shantzi was restricted by axolotl predation as well. Light predation pressures in shallow ponds were unimportant. Results suggest that Daphnia rosea could not invade shallow ponds because the larger native cladoceran D. pulex outcompeted it for food. Diaptomus coloradensis survives in shallow ponds because it avoids competition with its larger congenitor D. shoshone. Only the deep ponds are suitable for the aquatic Chaoborus larvae and axolotl since shallow ponds freeze completely each winter and periodically dry up during the summer.
Zooplankton samples, usually together with morphometric, physical, and chemical data, were collected from 696 lakes in glaciated eastern North America between 1969 and 1978. Geographical distributions of the 44 Crustacea and 4 Diptera species suggest six broad categories: 23 species appear to have no barriers to dispersal throughout the area; 7 have restricted ranges, possibly because of either recent evolution or competitive exclusion; 3 may be gradually invading the area from centres to the south or west; 1 is a euryhaline estuarine form with a limited freshwater distribution; 4, possibly 5, are found almost exclusively in areas of former glacial lakes or spillways and may be classified as "glacial opportunists"; 9 species have distributions which appear to be linked in some unspecified way to calcium–magnesium water hardness.
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