The evaluation of individual production and scope for growth in aquatic sow bugs (Asellus aquaticus)

The possibility to assess the instantaneous production of benthic invertebrates in the field avoiding direct measurements of somatic and generative growth is discussed. The scope for growth (SfG) (assimilation minus respiration) and instantaneous individual production (mass increment during growth) for Asellus aquaticus were determined and compared. Results of this study have confirmed the assumption that the difference between SfG and individual production of isopods P is approximately equal to reproductive investment. In juveniles and males these differences should be compensated, in large degree, for the exuviae. As confirmed by the closely identified values of P after summing it with eggs production, excess of SfG in comparison with P may be attributed to the part of energy which is allocated to generative products. So, the predicted coincidence of SfG with P coupled with egg production allows to expect that SfG may be implicated in evaluation of instantaneous population production. To verify this assumption, the data on population production of A. aquaticus previously reported in the literature were drawn. The results have shown a close conformity of compared data, and led to the conclusion that this method should be of more general use, and not limited to the populations exposed to stress, as it is currently treated.     

Secondary production and energetics of the shrimp Caridina nilotica in Lake Victoria, East Africa: model development and application

Measurements of body mass, carbon content, respiration, growth, and egestion are combined in a model of secondary production by the tropical freshwater shrimp Caridina. The model is developed to permit its direct application to empirical data for abundances and size frequency distributions of field populations. Model calculations combined with population data for offshore Lake Victoria over a period of two years indicate that Caridina consume the equivalent of 2.2% of annual lake primary production. Present net annual secondary production by the shrimp is an order of magnitude greater than the present fishery yield of the lake. Detritus-fed experimental organisms evidently had assimilation efficiencies as low as 10% by model calculation.     

Grazing and assimilation rates of natural populations of planktonic cladocerans in a eutrophic lake

The filtering rates of ¹⁴ carbon-labelled Chlamydomonas sp. by 4 dominant species of Cladocera were studied in eutrophic Lake Aydat. The mean individual filtering rates were 364, 399, 403 and 408 µl ind^–1 h^–1 for Bosmina longirostris, Daphnia longispina, Chydorus sphaericus and Ceriodaphnia quadrangula, respectively. Their maximum assimilation efficiencies attained ± 50%. These populations collectively could consume the available food in less than 4 days during August (maximum daily grazing rate = 29%).In eutrophic conditions lake Aydat D. longispina appears to be more efficient in energy utilization than other cladocerans. Some individuals of Daphnia and Chydorus continued to filter in the zone of low oxygen where an important bacterial biomass had developed. Our results support the importance of the cladocerans in the regulation of phytoplankton production.     

The burrowing crab Neohelice granulata affects the root strategies of the cordgrass Spartina densiflora in SW Atlantic salt marshes

Salt marshes are among the most productive systems of the world, with plant primary production limited by soil oxygen deficiency and nutrient availability. Nevertheless, root adaptations to anoxia and nutrient acquisition are different and often incompatible. The SW Atlantic salt marshes are characterized by high densities of the deep (up to 1 m) burrowing crab Neohelice granulata (Dana, 1851) that may change soil physical and chemical characteristics by burrow construction. In this work, we experimentally evaluated the hypothesis that crab burrowing can enhance soil oxygenation, causing changes in Spartina densiflora Brongniart below ground tissues from structures adapted to anoxia to systems adapted for nutrient acquisition. This response, in turn, would enhance plant productivity. Results from field observations show that oxygen availability is higher in zones with high burrow densities. As burrow densities increased, the plant root distribution changed from shallow (associated to low oxygen availability) to deeper and vertically homogeneous, with a positive correlation between burrow density and plant aboveground biomass. Experimental exclusion of crabs shows that they induce changes of root strategies from anoxia toleration to nutrient efficient acquisition, with increasing plant productivity. The invasive success that this plant shows in other parts of the world is likely to be due to their ability to tolerate harsh environmental conditions. Our results suggest that the morphological plasticity of S. densiflora is also important in their native zone given the characteristics of their specific habitat.     

中华鳖（Trionyx sinensis）幼体能量转换的初步研究

在突验室内,对中华鳖幼体的能量转换进行了初步研究。结果表明：１）温度结中华鳖幼体对食物的同化效率无显著影响,但影响总转化效率和生长效率。二者在２２℃左右最高,２６—３２℃温度范围内各温度组之间元显著差异,３５℃则显著下降。２）体重与同化效率的关系为：ＡＥ＝９４．１８６＋２．７６０ｌｇＷ,而生长效率和总转化效率在各体重组间无显著变化;３）中华鳖幼体能量收支方程为：１００Ａ＝７４Ｒ＋２６Ｇ,并认力中华鳖将较多能量（７４％）投入代谢,而将较少能量（２６％）投入生长是适应其生态习性的缘故。     

Food utilization by insects: Interpretation of observed differences between dry weight and energy efficiencies

Over 80% of the values of approximate digestibility (AD), efficiency of conversion of assimilated food to biomass (ECD) and efficiency of conversion of ingested food (ECI) calculated using energy terms are greater than the corresponding dry weight (DW) values, based on data for over 65 species (38 studies; number of comparative values: AD=139, ECD=128 and ECI=169). Largest positive differences (energy > DW values) are 30 (AD, ECD) and 24 (ECI) percentage points and largest negative differences (energy < DW values) are 9 (AD), 11 (ECD) and 8 (ECI) percentage points. These differences generally are least for ECI (71% of the differences fall between 0 and +5 percentage points), and AD (68%), followed by ECD (only 47% fall between 0 and +5), and they may vary with temperature, food and other factors. The differences tend to increase (esp. for ECD and ECI) when comparing later with earlier instars. Energy > DW efficiency values are commonly expected for AD because of the generally greater energy content of food than feces, and for ECD and ECI because of the generally greater energy content of insect biomass than ingested and assimilated food. Deviations from predicted differences in surveyed literature data are discussed in terms of possible methodological sources of error.

---

Résumé Plus de 80% des valeurs de la digestibilité approchée (AD), de l'efficacité de la conversion de la nourriture assimilée en biomasse (ECD) et de l'efficacité de la conversion de l'aliment ingéré (ECI), calculées en termes énergétiques, et obtenus à partir de données sur 65 espèces, sont supérieures aux valeurs des poids secs correspondants (DW): 38 études; valeurs comparatives: AD=139, ECD=128, ECI=169. Les plus importantes différences positive (énergie>valuers DW) sont de 30 (AD, ECD) et de 24 (ECI) centièmes (les différences négatives les plus fortes = 9 (AD), 11 (ECD) et 8 (ECI); ces différences sont moindres pour ECI (71% des différences tombent à 0 et +5 centièmes), et AD (68%), suivi de ECD (seulement 47% tombent entre 0 et +5). Ces différences peuvent varier avec la température, l'alimentation et d'autres facteurs; les différences tendent à croître (particulièrement pour ECD et ECI) quant on les compare plus tard avec des stades plus précoces. Energie > aux valeurs d'efficacité DW sont généralement attendues pour AD par suite du contenu énergétique supérieur de l'aliment à celui des excréments, et pour ECD et ECI par suite du contenu énergétique généralement plus élevé pour la biomasse de l'insecte que pour l'aliment ingéré et assimilé. Les écarts par rapport aux différences prédites dans les données de la littérature examinée sont analysées en considérant les sources possibles d'erreurs méthodologiques.

     

Application of 13C NMR to investigate the transformations and biodegradation of organic materials by wood- and soil-feeding termites, and a coprophagous litter-dwelling dipteran larva

Solid-state 13C nuclear magnetic resonance spectroscopy has been used to characterize the C in samples of the food (wood), gut contents and faeces from the wood-feeding termite, Microcerotermes parvus; soil in the guts and mound material from the soil-feeding termite, Thoracotermes macrothorax; and the food and faeces from the litter-feeding, coprophagous larvae of the dipteran fly, Bibio marci. Spectra from the wood-feeding termite indicated preferential loss of polysaccharide and accumulation of lignin with some modification to the O-aromatic-C and methoxyl-C (O-methyl-C) components during passage through the gut. Spectra for the soil-feeding termite indicated little change in the distribution of 13C between resonances following passage through the gut, except for some evidence of preferential polysaccharide loss. Interpretation of the spectra from these organisms was restricted by the relatively low C content of the soils and mound material, and by the large contribution to the NMR spectra from the gut tissue rather than the gut contents. Spectra for the litter-feeding dipteran larvae indicated preferential feeding on the polysaccharide-rich component of the litter and then overall loss of polysaccharide-C and accumulation of both aromatic-C and methoxyl-C in the gut. These changes were greater for the second passage than for the first passage through the gut, suggesting that principally mechanical and physical changes occurred initially and that chemical digestion was prevalent during the second passage.     

Effects of diet and heavy metals on growth rate and fertility in the deposit-feeding snail Potamopyrgus jenkinsi (Smith) (Gastropoda: Hydrobiidae)

Evidence for the influence of food type and heavy metals on shell growth and fertility is presented for a freshwater population of the snail P. jenkinsi. When fed an excess of lettuce or lamb heart (protein source), growth rates were higher for lettuce. Highest growth rates occurred at a diet of lettuce plus lamb heart. Fertility was favoured by a diet of lamb heart. When fed an excess of lettuce, the EC₅₀ growth values were 16 µg Cd l^–1, 13 µg Cu l^–1, and 103 µg Zn l^–1 in lake water; snail fertility was inhibited at 25 µg Cd l^–1 and 30 µg Cu l^–1. A diet of lake detritus spiked with Cd or Cu resulted in a decrease of approximately 50% in growth rates, when compared with growth on non-spiked detritus. Spiked detritus lost metals into lake water. Food type positively interacted with metal stress, both for growth rate and fertility. The assessment of inhibitory effects of detritus contaminated either in the field or, notably, by spiking, and serving as food source for deposit feeders is hampered by sampling problems in the field and by redistribution processes of pollutants between particles and water in laboratory-scale experiments.     

Effect of nitrogen application on growth and photosynthetic nitrogen use efficiency in two ecotypes of wild strawberry, Fragaria chiloensis

The relationships between increasing nitrogen fertilization and growth, maximum CO₂ assimilation and the initial slope of the CO₂ response curve were studied in 2 ecotypes of wild strawberry, Fragaria chiloensis (L.) Duchn. Nitrogen accumulation of CA11, an ecotype from a low-nutrient dune site, was greater at all nitrogen concentrations than that of RCP37, an ecotype from a higher-nutrient strand site. Maximum CO₂ assimilation, total Rubisco activity, dry weight, and initiation of leaves and crowns were higher in CAI1 than RCP37 as nitrogen treatment was increased from 0 to 200 mg ^l-1, whereas these parameters were lower in CAl1 when fertilized at 300 mg T¹, but not in RCP37. The mean leaf area of CA11 was greater than RCP37 when grown with no supplemental nitrogen, but mean leaf area of the 2 lines was similar under nitrogen fertilization. Maximum CO₂ assimilation and carboxylation efficiency increased with increasing leaf nitrogen in both clones. At equivalent concentrations of leaf nitrogen, RCP37 had higher CO₂ assimilation and carboxylation efficiency than CA11 and the difference between the 2 clones increased as ieaf nitrogen increased. Thus, RCP37 had a higher photosynthetic nitrogen use efficiency than CA11. However, at a given applied nitrogen level, CA11 allocated more nitrogen to a unit of leaf area so that photosynthetic rates were higher than RCP37, except at the highest application of 300 mg ^l-1. The high nitrogen accumulation capacity and resource allocation to fruiting structures (crowns) in CA11 leads us to suggest that this clone may possess genes that could increase fruit yield in cultivated strawberry.     

Sediment processing by gizzard shad, Dorosoma cepedianum (Lesueur), in Acton Lake, Ohio, U.S.A.

Gizzard shad are primarily detritivorous in Acton Lake, a 253-ha impoundment in southwestern Ohio, U.S.A. To determine the magnitude of sediment utilization by the gizzard shad population in Acton Lake. I used data on population density and age structure, daily ration, and feeding selectivity in estimating the mass of sediments processed by shad daily from April through November. At densities of 4595–10 645 fish ha⁻¹(wet weight biomass = 90–121 kgha ¹), gizzard shad could process 3.8–23.0 kg of dry sediments ha⁻¹ day ¹. On average throughout the growing season, gizzard shad could process a dry mass of sediments each day equivalent to 13% of shad wet weight biomass. Because of the high rate of sedimentation (> 700 kg dry sediment ha⁻¹ day⁻¹) in Acton Lake, gizzard shad can process < 4% of the freshly deposited sediments each day, and therefore are likely to have little effect on benthic community dynamics in the system.     

Effects of dietary zinc on the assimilation efficiency of carp (Cyprinus cavpio L.)

Adding zinc to the diet of carp lowered assimilation efficiency (AE) proportionately. AE values were higher (and higher proportions of zinc were absorbed) when zinc proteinate replaced zinc sulphate.