Death, detritus, and energy flow in aquatic ecosystems

1. Pelagic trophic structure and energy fluxes are evaluated predominantly on the basis of ingestion of particulate organic matter by living organisms and the effects of consumption on the population dynamics of trophic levels. 2. Population fluxes are not representative of the material and energy fluxes of either the composite pelagic region or the lake ecosystem. Metabolism of particulate and especially dissolved organic detritus from many pelagic and non-pelagic autochthonous and from allochthonous sources dominates both material and energy fluxes. Because of the very large magnitudes and relative chemical recalcitrance of these detrital sources, the large but slow metabolism of detritus provides an inherent ecosystem stability that energetically dampens the ephemeral, volatile fluctuations of higher trophic levels. 3. The annual time period is the only meaningful interval in comparative quantitative analyses of material and energy fluxes at population, community, and ecosystem levels. 4. Non-predatory death and metabolism by prokaryotic and protistian heterotrophs dominate. Continued application of animal-orientated relationships to the integrated, process-driven couplings of the aquatic ecosystems impedes understanding of quantitative ecosystem pathways and control mechanisms.     

N-methyl-N′-nitro-N-nitrosoguanidine and UV induced mutants of the dinoflagellate Crypthecodinium cohnii*

SYNOPSIS. Mutant strains were chemically induced by treatment with N-methyl-N′-nitro-N-nitrosoguanidine (NTG) and UV irradiation. UV and NTG mutation rates were obtained that were both consistent with the organism being haploid. Three types of mutants were produced: (a) strains deficient in both β- and γ-carotene, the only carotenoids found in the wild type; phenotypes include albinos (translucent, dull white, “snow white”) and cream-colored on agar as compared to the yellow-orange color of wild type colonies; (b) strains requiring adenine, guanine or cytosine in addition to the minimal medium for growth; (c) mutants that grow at a rate less than 40% of the wild type in minimal medium.     

Ultrasonic Control of Maternal Behavior: Developmental Implications

Infant rodents of many species emit high frequency vocalizationswhen aroused. These signals, when detected by adult femalesof the same species, elicit increased care-giving. The behaviorof the dam towards her offspring influences the developmentof arousal mechanisms of the offspring and appears to alterturnover of brain dopamine. These effects are quite pervasivesince altered maternal care induced by ultrasonic vocalizationsfrom an initial litter is observable in the behavior of thedam towards a subsequent litter; similar alterations in thedevelopment of arousal mechanisms and brain dopamine turnoverare observable in the subsequent litters; and the effects ofthis altered caregiving during the first three weeks of developmentare observable in laboratory rats (Rattus norgevicus) at oneand two years of age.     

Ontogenetic and Non-Thermal Seasonal Effects on Thermal Preferenda of Fish

Ontogenetic and non-thermal seasonal effects on thermal preferendaof fishes were sought both by a general review of the literatureand by examining those papers in which such effects were evident.The growing list of other non-thermal factors that have beenshown to influence thermal preferenda made this search difficult,since these factors could conceivably obscure subtle ontogeneticand non-thermal seasonal effects. Those few studies, however,in which ontogenetic effects were intentionally studied supportthe hypothesis that young fishes select higher temperaturesthan do older conspecifics; this is consistent with distributionsin nature, in which younger fishes are often found in shallower,warmer waters than the adults. Pronounced non-thermal seasonaleffects have been demonstrated in some species, while in otherslitde or no such influence was evident. In spite of conflictingevidence which precludes generalities, the age of a fish andthe season of the year are among the factors to be consideredor specified in describing the preferred-temperature relationsof species.     

Factors Affecting Clonal Diversity and Coexistence

Recent genetic studies of asexually reproducing fishes in thegenus Poeciliopsis (Poeciliidae) revealed abundant variationin the form of multiple sympatric clones. Recurrent hybridizationsbetween sexual species provides the principal source of clonalvariation. The hybrids are spontaneously endowed with a clonalreproductive mechanism that perpetuates a high level of heterozygosity.Migration within and between river systems, and mutations, alsocontribute to clonal diversity in these fish. Coexistence amongdifferent clones and with the sexual ancestors depends in partupon specializations characteristic of individual clones. Clonalreproduction is an efficient mechanism for freezing a portionof the niche-width variation contained in the gene pool of themore broadly adapted, sexual ancestors. Multiclonal populationsachieve significantly higher densities relative to the sexualforms than do monoclonal populations. This relationship is afunction of the clonal variability upon which natural selectioncan act and upon the capacity of a multiclonal population tobetter exploit a heterogeneous environment through niche diversification.In all-female organisms such as Poeciliopsis, which are dependentupon sexual species for insemination, competitive abilitiesprobably are at a premium in the densely populated pools andarroyos of the Sonoran Desert. Competitive abilities are probablyless important for truly parthenogenetic clones which rely oncolonization abilities to escape from their sexual ancestorsand from other clones.     

An improved hexagon open‐top chamber system for stable diurnal and nocturnal warming and atmospheric carbon dioxide enrichment

The use of solar passive hexagonal open‐top chambers (POTCs) is a viable method for experimentally manipulating daytime air temperatures in low‐stature plant communities at high latitudes. Here we describe a new hexagon POTC‐based system that uses thermal inertia to increase overnight temperatures and variable chamber height to reduce overheating in summer. Field data collected in tall temperate grasslands show that the presence of thermal mass raised minimum and mean nighttime air temperatures by up to 1.5 °C while lowering chamber height, along with thermal mass, limited the development of extreme daytime chamber temperatures in summer. We also demonstrate that, by using a simple, inexpensive twin carbon dioxide (CO₂) injection system regulated by an infrared gas monitor, it is possible to generate targeted and stable atmospheric CO₂ enrichment within these chambers. These innovations significantly improve the conventional hexagon POTC design and represent a low‐cost method for assessing the effects of warming and CO₂ enrichment on low‐stature vegetation in low latitude environments.