Effects of potassium levels over the range occurring in host plants on the growth of an insect herbivore (Manduca sexta)

Third instar tobacco hornworms (Manduca sexta L.: Sphingidae) on low dietary potassium had a lower relative growth rate than individuals on diets with potassium concentrations reflecting those in host-plants, due to decreased consumption rate, lower efficiencies of conversion of ingested and digested food (ECI and ECD), and a prolonged growth/feeding phase. Furthermore, these larvae, when placed on a diet with a moderate potassium concentration through the fourth stadium, ended up being smaller due to lower ECI and less biomass gained, and had a prolonged growth phase, which suggest an irreversible cost of the previous low potassium diet. Third instar hornworms on high potassium diets had lower ECI and ECD, and they had a prolonged growth phase. These individuals, when placed on a moderate potassium diet in the fourth stadium, gained less biomass, than those previously offered hostplant-like-potassium diets. Body potassium concentrations (% dw) at the end of the third stadium were similar among treatment groups. With increasing potassium concentrations in the diet, utilization efficiencies of potassium decreased and potassium concentrations in the frass increased. Correspondingly, water content (% fw) of the newly-molted fourth instar larvae declined with increasing potassium, indicating a passive loss of water during potassium excretion. Low and high dietary potassium reduced survivorship of third instar larvae; fourth instar caterpillars previously fed the low potassium diet also had poor survivorship. We conclude that, within the normal range of potassium concentrations in the hostplants, caterpillar performance is largely unaffected by potassium concentration, but that potassium-poor and potassium-rich diets, such as those hornworms may sometimes experience, can reduce growth and survivorship.     

Worldwide distribution of commercial resources of seaweeds including Gelidium

The commercial exploitation of seaweeds for use as food and for the production of agar, alginate and carrageenan is outlined. The quantities of seaweed harvested for each purpose are tabulated and discussed. Seaweeds for food are derived chiefly from China, Japan and Korea, with almost 94% obtained by cultivation. Alginophytes are collected in 15 countries but six of these account for more than 80% of the total harvest; all are from natural stocks except for a large quantity of Laminaria cultivated in China. Natural carrageenophytes, from 12 countries, now account for only 20% of the total harvest; the remainder is cultivated Eucheuma species, 99% of which is produced in only two countries, the Philippines and Indonesia. Of the four categories of commercial resources of seaweeds considered, agarophytes are spread more evenly over a greater number of countries; they come from 20 countries and only five of these are minor contributors to the total. Gelidium species are particularly important because of the high quality agar they yield; their distribution and location are discussed.     

Mechanisms of food selection in Daphnia

A conceptual behavioural and mechanistic Holling-type model of food selection in Daphnia pulicaria is derived from SEM observations with animals feeding on mixtures of spherical-cylindrical diatoms, oblongate green algae, and filamentous cyanobacteria, as well as ultrafine particles. The algae used were Stephanodiscus hantzschii (<- 6 µm length), Monoraphidium setiforme ( 20 µm), and Oscillatoria aghardii (strands, >- 80 µm). Cell (strand) selection can occur at any or all of three stages: (i) interception from the feeding currents, (ii) collection and channeling to the food groove, and (iii) compaction and transport to the mouth. During each stage, given equal initial cell densities, elongate cells are more likely to escape collection than spherical cells and are more likely to be rejected. In addition, filaments require increased handling time at stages (ii) and (iii) and promote entanglement with limb 5 and the postabdominal claw. Food is collected primarily with the aid of limbs 3 (and 4), but limbs 1 and 2 also intervene. Neither the leaky sieve hypothesis alone nor any other single-process hypothesis explains the observations on examined in corpore positions, morphology, and derived movements of the feeding limbs. Attachment and mucus appear to be important for the ingestion of bacteria and ultrafine particles.The model is consistent with many experimental results of differential feeding by Daphnia pulicaria on mixtures of variously shaped algae and other observations on Daphnia feeding behaviour. The paradigm of invariate, nonselective feeding by Daphnia is rejected.     

The diet of two species of Isoperla (Plecoptera: Perlodidae) in relation to season,site, and sympatry

The seasonal change in gut contents of nymphs of Isoperla grammatica and I. difformis from six streams in southern Sweden was analysed. Both species had ingested a variety of benthic prey and vegetable matter, predominantly diatoms. Some seasonality was evident with high percentages of diatoms in spring in I. grammatica, and in autumn in I. difformis. The scope of food was larger in the latter species which contained about equal proportions of vegetable matter, chironomids, mayfly, stonefly, and black fly larvae. In I. grammatica plant matter and chironomids dominated strongly, comprising > 50% of the gut contents on an annual basis, > 90 % in spring. While small nymphs of I. difformis contained a low proportion of animal matter, only gradually increasing with size, the nymphs of I. grammatica were carnivorous from very early instars. Both species switched to a temporarily strong utilization of algae in spring. This differed among sites, and appeared to reflect differences in insolation and thus the availability of algae. There was a significant negative relationship between the mean densities of Isoperla nymphs and the proportion of animal material found in the guts of I. grammatica (R ² = 0.86). Considering the density of I. grammatica alone, the relationship was weaker (R ² = 0.56). A positive correlation between predator and prey size was observed. With chironomid prey the size range increased with predator size. With simuliid prey, however, prey size increased with predator size in such a way that it suggests selection rather than just an expanding prey size range. Correlations were stronger and regression coefficients significantly higher for I. grammatica than for I. difformis. We suggest that I. grammatica, which ingests a much wider size range of prey might choose prey of optimal sizes more readily than the more synchronously developing I. difformis. Although the life cycles of the two species are staggered, overlap in size distribution indicates that competition for food could be important in spring. However, observed differences in diet should facilitate coexistence. Gut content differences might in turn be accomplished through microhabitat segregation.     

甲壳动物的生殖量与环境关系：Ⅱ.桡足类

本文是《甲壳动物的生殖量与环境关系》系列论文的第二篇,专述桡足类。它和枝角类一样,是一类小型低等甲壳动物,也是浮游生物群落的一个重要组成部分。种类多、数量大、分布广是它的生态特点。由于生活习性不     

Biology of epiphytic Chironomidae (Diptera:Nematocera) in chalk streams

Submerged macrophytes are a conspicuous feature of chalk stream ecosystems, supporting large populations of diatoms and invertebrates, including larvae of the nematocerous family Chironomidae. Close temporal and spatial association is evident between chironomid larvae and diatoms, and diatoms are frequently a major component of the food of midge larvae. Larvae provided with food that is rich in diatoms survive better and grow and develop more quickly than larvae that are supplied with food that is predominantly fine organic detritus. First instar larvae selectively feed on diatoms but it is likely that selection is on the basis of particle size, rather than for diatoms per se. Three species of epiphytic larvae (2 Cricotopus spp. and Eukiefferiella ilkleyensis) transfer to a diet that is predominantly of fresh plant material (Ranunculus calcareus leaves) in the third and fourth instar. The life cycle strategies of many species of Orthocladiinae equip them to exploit temporarily favourable environmental conditions very rapidly and effectively. This fact helps to explain the coexistence of species with similar strategies of resource utilization, as part of the normal epiphytic fauna of chalk streams.     

A NEW SPECIES OF BEAKED WHALE MESOPLODON PERUVIANUS SP. N. (CETACEA: ZIPHIIDAE) FROM PERU

Mesoplodon peruvianus , a new species of beaked whale, is described on the basis of ten specimens which have either stranded or been captured between 11°12'S and 15°19'S latitude along the coasts of the provinces of Lima and Ica, south central Peru. This is the thirteenth living species of Mesoplodon recognized in the world's oceans. The animals that were examined were uniformly gray above, shading to lighter gray below. This whale is the smallest species of Mesoplodon (maximum body length 3.72 m) and is characterized by its teeth, which are small (31 to 65 mm long), ovate in cross section, and positioned 2.5% to 8.4% of the mandibular length from the anterior extremity, and posterior to the mandibular symphysis.     

Introduction into the ecosystem of the North Sea: Hydrography,biota, and food web relationships

The North Sea, one of the most productive of the earth's seas and oceans, is also surrounded by some of earth's most densely populated and heavily industrialized regions. A growing number of signals are being received which indicate that this valuable ecosystem is increasingly under stress. This has generated a corresponding increase in concern over the steps to be taken to protect the North Sea. While there are divergent views on what constitutes an ‘ideal’ North Sea, there is a general recognition that any decisions that are made should be based on a good understanding of this ecosystem. The intention of this paper is to give an overview of what is presently known, and to identify areas where more studies are needed. A brief summary of the hydrography and the biota of the North Sea is given. Biotic and abiotic structure justify partitioning the North Sea into three ecologically different regions: southern, central, and northern. For the most part, neither the top predators,e.g. marine birds and mammals, nor the macroalgae and sea grasses are included in this overview.     

Neuroethology of olfactory preference development

Young mammals come to approach the odor of their mother, a response that facilitates their survival during early life. Young rats induce a cascade of events in their mother to induce the emission of her odor. The pups increase circulating prolactin levels, which increases food intake and the emission of large quantities of cecotrophe containing the maternal odor. This odor is synthesized by the action of cecal microorganisms and changes with maternal diet. The diet-dependence of the odor requires the pups to acquire their attraction to the odor postnatally. The acquisition of this preference occurs when an odor is paired with the tactile stimulation that pups receive during maternal care. The action of the tactile stimulation appears to be mediated by noradrenaline. The development of this type of olfactory attraction is accompanied by changes in the regions of the olfactory bulb that are responsive to the attractive odor. Metabolic, anatomical, and neurophysiological changes in response to the attractive odor emerge in such regions of the bulb after early olfactory preference training. © 1992 John Wiley & Sons, Inc.     

On predatory tendencies in the feeding ecology of the fairy shrimp Streptocephalus proboscideus (Frauenfeld, 1873) (Crustacea: Anostraca)

The feeding habits of the filter-feeding fairy shrimp Streptocephalus proboscideus are documented experimentally by offering them ciliates, Volvox, rotifers, nematodes and small crustaceans as prey. Escape capabilities (e.g. swimming speed) rather than size or shape were found to determine these animals' vulnerability to predation by the fairy shrimp. Ingestion rates for Volvox increased hyperbolically with size and, at the high temperatures in which they live, fairy shrimps may daily remove the equivalent of their body weight from the environment.