Invertebrate colonization of a new, man-made stream in southern Sweden

SUMMARY.

• 1 The invertebrate colonization of a man-made stream, Flugströmmen, in southern Sweden was monitored for 18 months in 1988 and 1989. Benthic samples were taken on twelve occasions from three sites (upstream, middle and downstream) and community structure was compared with that at ten natural, permanent reference sites nearby.
• 2 The number of species colonizing increased rapidly during the first 3 months. The increase was most rapid upstream but levelled off during the second year at this site, while numbers continued to increase downstream.
• 3 Simuliid species were the earliest colonizers and reached high densities at upstream and middle sites during the first year. Ephemeropteran and plecopteran species also occurred early on, whereas Coleoptera, Odonata and Trichoptera were, on average, slower to colonize. Blackfly densities decreased upstream after the first year and hydropsychids became numerically dominant.
• 4 The colonization order of functional feeding groups was as predicted: filter feeders first, grazers/collectors intermediate, predators and shredders last.
• 5 After a year, the community structure in Flugströmmen closely resembled that in lake-outlet streams situated in the area, although communities at the three sites within the stream were most similar to one another.
• 6 The possible role of competitive and predatory processes in determining the observed successional patterns are discussed.

     

Observations of gynoecial structure in Philodendron (Araceae)

MAYO, S. J., 1989. Observations of gynoecial structure in Philodendron (Araceae). The gynoecial morphology and anatomy of 15 species of the genus Philodendron , representing all the subgenera and a majority of the sections, are described and illustrated. The study emphasizes the morphology of the style, compitum and stylar canals; gynoecial vasculature is only superficially treated. Variation of gynoecial morphology in P . subgenus Meconostigma is described and illustrated and a pilot study of gynoecial ontogeny in this subgenus is presented. Ideas on phylogenetic trends in style and stylar canal morphology, ovary locule number, placentation and ovule number are discussed. Gynoecial characters are shown to be taxonomically useful at the subgeneric and sectional level in Philodendron. The following taxonomic and nomenclatural changes are made: P. section Pteromischum is raised to subgeneric rank. In P. subgenus Philodendron sections Polyspermium and Oligospermium are reduced to the synonymy of sections Philodendron and Calostigma respectively, and the following new names and combinations are made at subsectional rank: subsections Canniphyllum, Oligocarpidium, Bulaoanum and Eucardium.     

The non-correlation of bioelectric potentials with ionic gradients

The sartorius muscles of 320 toads have been analyzed for Na⁺ and K⁺. There is a wide variation in the Na⁺ content which when calculated intracellularly varied from 0 m.eq./kg. to 58 m.eq./kg. In particular it was found that the distribution of internal Na⁺ in the intact animal was such that only 17 per cent of the muscles should give from the Nernst equation the observed overshoot of 37 mv. In contrast to this wide variation the K⁺ content is comparatively constant, the range being 71 to 112 m.eq./kg. The mean observed resting potential of 87 mv. agreed well with the potential calculated from the mean intracellular K⁺ by the Nernst equation. Analyses of plasma show that the Na⁺ content is constant at 130 m.eq./liter, and the K⁺ is 3.0 m.eq./liter. The resting and action potentials of 77 muscles have been recorded and then the muscles have been analyzed. The results have shown that there is no correlation between the level of intracellular Na⁺ and the overshoot. Furthermore the apparent correlation between the average K⁺ content and the average resting potential has been shown to be fortuitous, when the correlation in individual muscles is considered. When a muscle is soaked in Ringer solution for several hours there is a gain of Na⁺ and a loss of K⁺. These shifts should result in changes in the respective potentials, but such changes were not found. The above findings have been discussed in the light of the present theories that the resting potential and the action potential are directly related to the ionic ratio across the membrane. Our results very definitely do not support the theory that the overshoot is related to the Na⁺ gradient, and this also applies with respect to the K⁺ gradient and the resting potential.     

Membrane Lipids in Senescing Green Tissues2

At a late stage in sensescence cucumber cotuledons lose freshweight rapidly; at the same time there is an increase in apparentfree space and large quantities of electrolyte leak out whendiscs of cotyledon tissue are floated on water. It is concludedthat tonoplast and plasma membrane become leaky at this time. Phosphatidyl choline, the major phospholipid present, beginsto disappear once the cotyledons reach maximum fresh weight;by the time rapid water loss starts, 56 per cent has gone, andphosphatidyl ethanolamine and inositol start to disappear. Onlyat maturity is there enough of these phospholipids to furnishmore than two complete membranes around each cell; it is suggestedthat the decline in phospholipid level at senescence destroysmembrane integrity and allows leakage. The glyohpids begin to disappear at the same time as chlorophyll,2 weeks before weight loss starts. The minor lipid phosphatidyl glycerol is the first to disappearfrom the cotyledons.     

Updating rDNA Restriction Enzyme Maps of Tetrahymena Reveals Four New Intron-Containing Species1

The extrachromosomal rDNA molecules from a number of Tetrahymena strains wered racterized by restriction enzyme mapping using three different restriction enzymes combined with gel blotting and hybridization analysis. Strains from four out of six recently described species were found to contain an intron in the 26s rRNA coding region. The evolutionary relationship among the species of the T. pyriformis complex was examined on the basis of the rDNA maps with emphasis on similarities between two of the new species and the widely studied T. thermophila and T. pigmentosa. Examination of a large number of T. pigmentosa strains showed this species to exhibit an unusual polymorphism with respect to its rDNA. It is suggested that recombinational cross-over events play a role in the formation of new rDNA alleles in this species.     

Differences in insect species richness and faunal composition of birch seedlings, saplings and trees: the importance of plant architecture

Abstract. 1. Data are presented on the species richness and faunal composition of herbivorous insects on birch seedlings, saplings and trees at one site in Northern England.
2. Species richness of insect herbivores in equal-sized samples from birch seedlings and trees was similar through most of the season.
3. Effects of plant architecture were confined to the first sampling date, when seedling faunas were species poor compared with trees – possibly due to safe overwintering sites on the extensive bark, twigs and buds of trees.
4. The faunal composition of birch seedlings, saplings and trees was also similar. Out of a total of 112 recorded species of herbivores, only one aphid species was confined to seedlings.
5. Similarly, no evidence for clear-cut vertical stratification of insects within trees was found.
6. Species turnover as host plants mature ('horizontal' stratification) and vertical stratification within trees add little to the high overall species richness of birch-feeding insects in Britain, contrary to the predictions of Lawton (1983).     

An Inhibitor of Mitochondrial Oxidations in Extracts Prepared from Senescing Leaves

Aqueous extracts were prepared from leaves of Ricinus Communis,L. by centrifuging homogenates at 18000 g for 20 min. Extractsprepared from yellow or brown leaves inhibited the oxidationof succinate by mitochondria prepared from Ricinus endosperm.Extracts became less inhibitory when dialysed or treated withbovine serum albumen. The inhibitory properties of the extractsare attributed to their fatty acid content.     

Preferences and apparent digestibilities of sugars by fruit damaging birds in Japan

Gray starlings Sturnus cineraceus, azure-winged magpies Cyanopica cyana and brown-eared bulbuls Hypsipetes amaurotis are among the main bird pests in commercial fruit orchards in central Japan. Recently Brugger & Nelms (1991) suggested that developing high-sucrose fruit cultivars could reduce crop damage, because some pest birds lack the enzyme sucrase and can develop an aversion to sucrose. Preferences for, and digestibilities of, the monosaccharides glucose and fructose and the disaccharide sucrose by these pests species were therefore studied to assess whether this idea would be applicable in central Japan. Gray starlings and brown-eared bulbuls were able to detect glucose, fructose, a mixture of glucose and fructose, and sucrose at a concentration of 12% w/v. Azure-winged magpies also detected glucose and fructose, but failed to detect sucrose at the same concentration. In pairwise preference trials gray starlings and azure-winged magpies selected the monosaccharides over sucrose, but brown-eared bulbuls did not. To estimate the digestibility of the sugars the apparent assimilated mass coefficient, AMC*, was calculated for each species eating each sugar by measuring intake and faecal output. Monosaccharides had mean AMC*s of 0.77, 0.96 and 0.92 when consumed by gray starlings, azure-winged magpies and brown-earned bulbuls respectively. AMC* values for sucrose were 0.82 and 0.49 for brown-eared bulbuls and azure-winged magpies respectively, but gray starlings were shown to be unable to digest sucrose. As AMC* values varied from 0.75 to 0.97, consumption rates of sugars increased as digestibility decreased. Although increasing sucrose contents of commercial fruits may deter sucrase-deficient birds such as gray starlings from depredating fruits, it may also lead to increased crop damage by species such as the azure-winged magpie and brown-eared bulbul which may have to consume more of the less digestible fruit in order to meet their energy requirements.     

Buzzards Buteo buteo and Ravens Corvus corax in the uplands of Britain: limits to distribution and abundance

The current breeding ranges of Buzzards Buteo buteo and Ravens Corvus corax in Britain are restricted to the west, and both are relics of former widespread but not necessarily even distributions. Moore (1957) attributed the Buzzard's contraction in range to persecution by gamekeepers, his evidence being the complementary nature of the Buzzard's distribution with those of gamekeepers in the lowlands and grouse moors in the uplands; others have attributed the Raven's decline to the same cause. Is Moore correct and, if so, are these species' ranges still limited by persecution? Here we adopt an approach similar to Moore's, whereby we compare the current geographical patterns of abundance of Buzzards and Ravens in the British uplands with that of an index of grouse moor density. Unlike Moore, however, we take into account climate, land cover, topography and sheep stocking density, as well as grouse moor distribution, using multiple logistic regression modelling. We show that in the uplands the distribution of grouse moors strongly limits that of Buzzards and Ravens but are unable to conclude that this is a result of persecution because there are several competing hypotheses (moor management, food and nest-site availability) between which we are unable to distinguish.