Phytoplankton growth regulation by dissolved P and mortality regulation by endogenous cell death over 35 years of P control in a Mountain Lake.

Dynamics of phytoplankton and phosphorus were quantified in Lake Dillon, Colorado, over 35 years of P control. The lake provides an example of early intervention for P enrichment rather than remediation of advanced eutrophication. Phosphorus control began with tertiary treatment of effluent, which caused a phytoplankton decline (8.

Biogeochemistry of beetle-killed forests: explaining a weak nitrate response.

A current pine beetle infestation has caused extensive mortality of lodgepole pine (Pinus contorta) in forests of Colorado and Wyoming; it is part of an unprecedented multispecies beetle outbreak extending from Mexico to Canada. In United States and European watersheds, where atmospheric deposition of inorganic N is moderate to low (<10 kg⋅ha⋅y), disturbance of forests by timber harvest or violent storms causes an increase in stream nitrate concentration that typically is close to 400% of predisturbance concentrations. In contrast, no significant increase in streamwater nitrate concentrations has occurred following extensive tree mortality caused by the mountain pine beetle in Colorado.

Rationale for control of anthropogenic nitrogen and phosphorus to reduce eutrophication of inland waters.

Concentrations of phosphorus and nitrogen in surface waters are being regulated in the United States and European Union. Human activity has raised the concentrations of these nutrients, leading to eutrophication of inland waters, which causes nuisance growth of algae and other aquatic plants. Control of phosphorus often has had the highest priority because of its presumed leading role in limiting development of aquatic plant biomass.

Land use change and nitrogen enrichment of a Rocky Mountain watershed.

Headwater ecosystems may have a limited threshold for retaining and removing nutrients delivered by certain types of land use. Nitrogen enrichment was studied in a Rocky Mountain watershed undergoing rapid expansion of population and residential development. Study sites were located along a 30-km transect from the headwaters of the Blue River to Lake Dillon, a major source of drinking water for Denver, Colorado.

Regulation and stability in fish assemblages of neotropical floodplain lakes.

Neotropical floodplain lakes provide an excellent opportunity to examine the regulation and stability of fish assemblages. At low water, when lakes are separated, fish are concentrated in the lakes and are presumably subject to strong interspecific interactions that can shape assemblage structure. At high water, when the lakes and river channels become broadly interconnected, ample potential exists for alteration of assemblage structure because eggs, larvae, and older fish may undergo spatial reshuffling among waterbodies.

RELATIONSHIPS BETWEEN GENETIC VARIABILITY AND LIFE-HISTORY FEATURES OF BONY FISHES.

Correlations between genetic variation and life-history variables were obtained for 80 species of bony fishes as a means of testing the hypothesis that genetic variation is directly related to 1) opportunity for balancing selection, as indicated by fecundity, and 2) environmental variation, as indicated by capacity for population increase. Genetic data were taken from the literature, and data on longevity, age at maturity, egg size, body size, and lifetime fecundity were taken from the literature where available and were otherwise estimated from other variables. Average heterozygosity does not increase significantly with increasing fecundity.

Ecological energetics of Chaoborus in a tropical lake.

Ecological energetics of Chaoborus brasiliensis from Lake Valencia, Venezuela, were studied between February 1979 and February 1980. Direct measurements were made of the respiration rate, assimilation efficiency, and growth rate of all 4 larval instars and of the pupae. For the larval stages, respiration increased as the 0.

Nonvisual feeding in a visual planktivore, Xenomelaniris venezuelae.

Studies of the diel feeding patterns of the planktivorous fish, Xenomelaniris venezuelae, in Lake Valencia, Venezuela, revealed that, although the fish is primarily a diurnal feeder, it consumes substantial numbers of Chaoborus larvae and pupae at night. A number of fish species are known which feed on plankton at night, but these fish are filter feeders and their diets largely consist of relatively small, nonevasive prey. Chaoborus, however, is large and agile.

Cost and speed of locomotion for rotifers.

The hypothesis that the ciliary locomotion of rotifers is size limited and that it accounts of a significant portion of the energy budget was investigated using the genera Brachionus and Asplanchna. Speed of movement was measured among clones of different size in Brachionus, which shows little size variation through development. The same tests were done among individuals of different size within a clone of Asplanchna, which shows significant postembryonic size increase.

Metabolic responses to temperature change in a tropical freshwater copepod (Mesocyclops brasilianus) and their adaptive significance.

Metabolic rates of Mesocyclops brasilianus from Lake Valencia, Venezuela, were determined at several temperatures spanning the environmental range (22-28° C). The QO's (oxygen consumption per unit weight) of all Mesocyclops stages from Lake Valencia are higher than most but not all QO's from temperate copepod species that have been studied. The QO is essentially static through naupliar development and shows a sudden jump between N6 and CI, which probably results from the major change in morphology and behavior at this point in the life history.