Showing papers by "Stephen R. Carpenter published in 1987"

Regulation of lake primary productivity by food web structure

Abstract: We performed whole-lake manipulations of fish populations to test the hy- pothesis that higher trophic levels regulate zooplankton and phytoplankton community structure, biomass, and primary productivity. The study involved three lakes and spanned 2 yr. Results demonstrated hierarchical control of primary production by abiotic factors and a trophic cascade involving fish predation. In Paul Lake, the reference lake, productivity varied from year to year, illustrating the effects of climatic factors and the natural dynamics of unmanipulated food web interactions. In Tuesday Lake, piscivore addition and planktivore reduction caused an increase in zooplankton biomass, a compositional shift from a copepod/rotifer assemblage to a cla- doceran assemblage, a reduction in algal biomass, and a continuous reduction in primary productivity. In Peter Lake, piscivore reduction and planktivore addition decreased zoo- planktivory, because potential planktivores remained in littoral refugia to escape from remaining piscivores. Both zooplankton biomass and the dominance of large cladocerans increased. Algal biomass and primary production increased because of increased concen- trations of gelatinous colonial green algae. Food web effects and abiotic factors were equally potent regulators of primary production in these experiments. Some of the unexplained variance in primary productivity of the world's lakes may be attributed to variability in fish populations and its effects on lower trophic levels.

The Temporal Scale of Variance in Limnetic Primary Production

Abstract: Substantial variability in the productivity of the world's lakes cannot be explained by methodology, weather, hydrology, or nutrient supply. A deterministic model shows that variable piscivory, cascading through the food web and causing fluctuations in planktivory, herbivory, and primary production, can bring about variability in primary production comparable in magnitude and time scale to the variability that cannot be explained by physical or chemical factors. The variance of productivity and the correlation between primary production and zooplankton biomass are functions of the time scale over which model results were averaged. The scatter of data around regressions of annual production versus nutrient loading represents internal system dynamics at a host of time scales, some of which may be regulated by fish populations. An important consequence of these dynamics is that variances and covariances of limnological variables are strongly related to sampling scale. Nutrient loading, hydrology, and spring ...

Chaoborus populations: response to food web manipulation and potential effects on zooplankton communities

Abstract: Chaoborus populations were studied in two lakes in which fish predation was experimentally reduced, and in a reference lake. In Tuesday Lake, major reduction of fish predation led to substantial increases in density of Chaoborus punctipennis. Analysis of crop contents and estimates of consumption rates suggested that C. punctipennis caused declines of rotifer and copepod populations following the manipulations. In Peter Lake, lesser changes in fish predation caused no major change in density of Chaoborus flavicans, perhaps because food limitation compensated for effects of reduced predation. In both Peter Lake and the reference lake, Paul Lake, C. flavicans preyed heavily and selectively on Daphnia less than about 1.4 mm in total length. Bioenergetic calculations indicated that up to 46% of the daphnids were consumed daily. At some times of the year, certain zooplankton populations (especially noncolonial rotifers, small copepods, and small cladocerans) were strongly influenced by Chaoborus predation.

Daphnia size structure, vertical migration, and phosphorus redistribution

Abstract: The timing and magnitude of diel migration in two daphnid assemblages were determined from a series of vertical profiles of daphnid size distribution. Animals were collected concurrently for gut fullness determination. Only large daphnids (> 1.4 mm) migrated, but these animals could account for substantial vertical and diel differences in phosphorus excretion rate. Gut fullness measurements and time courses of diel vertical migration suggested that large Daphnia can cause a net downward flux of phosphorus during summer in thermally stratified lakes.