Availability and selection of arboreal termitaria as nest-sites by Orange-fronted Parakeets Aratinga canicularis in conserved and modified landscapes in Mexico

Few studies have investigated the use of termitaria by nesting parrots, or how this may be affected by habitat transformation. We determined selection of termitaria by nesting Orange-fronted Parakeets Aratinga canicularis , and evaluated the effect of habitat transformation on the availability of termitaria nest-sites for Parakeets in the tropical dry forest of Western Mexico. Availability of termitaria was quantified in 24 survey plots in a factorial design of six 1-ha plots in each of conserved and modified, deciduous and semi-deciduous forest. Characteristics of termitaria were determined in survey plots, as well as 21 nest-termitaria used by Parakeets, and their nearest adjacent termitarium. There was an overall density of 1.6 termitaria/ha suitable for nesting by Parakeets, which did not differ between habitats, although only 8% of apparently suitable termitaria were occupied by nesting Parakeets. However, termitaria in conserved semi-deciduous forest were significantly higher above the ground, and termitaria in conserved deciduous forest were significantly smaller in volume. In the modified landscape, termitaria were significantly lower and their volume significantly larger than in conserved landscapes. Termitaria used by nesting parrots were at a significantly greater height above the ground than the nearest adjacent termitaria. Termitarium volume did not reliably predict the likelihood of nest-site selection, although Parakeets only used termitaria between 15 and 150 l. Parakeets nesting in modified habitats used termitaria at a significantly lower height than Parakeets nesting in conserved habitat. It is unclear whether this represents a decline in nest-site quality in modified habitats, which could affect reproductive success of Parakeet populations in fragmented landscapes.     

The Phloem of Nelumbo nucifera Gaertn

In common with other aquatic angiosperms, Nelumbo nucifera Gaertn.has a relatively strongly developed phloem tissue. The vascularsystem consists of discrete collateral bundles in which no cambiumdevelops and the phloem and xylem are separated by a narrowlayer of parenchyma cells. The phloem consists of sieve elements,companion cells, and phloem parenchyma cells. The sieve elementshave transverse end walls with simple sieve plates. The cellsattain considerable width in the late phloem (metaphloem). Thecompanion cells are in vertical strands. In the early phloem(protophloem) of large bundles the sieve tubes and companioncells are eventually obliterated. The parenchyma cells alsoform vertical strands which may contain tannin cells. Some parenchymacells and companion cells are binucleate. The sieve elementsshow ultrastructural features common for these cells in dicotyledons.At maturity, they lack nuclei, ribosomes, and tonoplasts, butretain a plasmalemma, mitochondria, and plastids. The latterare poorly differentiated and form starch. The endoplasmic reticulumis in part stacked, in part it forms a network next to the plasmalemma.The P-protein occurs in two forms. One consists of tubules notassembled in any specific type of array. The other, possiblycomposed of much extended tubules, is assembled in crystallineaggregates which are retained as such in mature cells. The sieveplate pores are lined with callose and plasmalemma. The lateralwalls are relatively thin and the nacreous layer varies in degreeof distinctness.     

A Longitudinal Study of Escherichia coli in Cows and Calves with Special Reference to the Distribution of O-antigen Types and Antibiotic Resistance

The faecal excretion of E. coli from 6 adult cows was followed over a period of 105 days. E. coli were excreted in only 23·4% of specimens and the patterns of excretion varied between animals. All isolates of E. coli were antibiotic sensitive and fell into 6 O-antigen types; very few were non-typeable. The O-types excreted by each animal, compared with those from other cows in the same house, were traced with time. A similar but less intense study was undertaken in 8 calves. In contrast E. coli was excreted from all samples and included both antibiotic sensitive and resistant strains; 37 O-types were represented. The persistence of specific O-types within each calf and their spread to other calves in the same house were studied. A comparison of the O-types in the bovine species with those isolated from man has been made.     

Spatial relation between xylem and phloem in the stem of Hibiscus cannabinus L. (Malvaceae)

The distribution of the phloem in relation to the xylem was examined in the stem of Hibiscus cannabinus L. with reference to a report in the literature that this species has internal (intraxylary) phloem, a feature not previously observed in the Malvaceae. In the present study, the stem was found to have phloem only outside the xylem (external or extraxylary phloem). In the protophloem, the sieve tubes are obliterated while the internode elongates and the associated cells become fibres with thick secondary walls. Fibres occur in the secondary phloem also. As seen in transections of stems, the secondary xylem forms a continuous ring. The primary xylem extends in the form of arcs into the pith. The tracheary cells of the protoxylem become crushed or completely obliterated in elongating internodes. The associated parenchyma cells either retain thin walls or develop secondary thickenings.     

A study of the source of virus in the Pholem exudate appearing on leaves of Amscinckia infected with the beet curly top virus

Abstract Leaves of Amsinckia douglasiana discharging phloem exudate after infection with the beet curly top virus (BCTV) were studied with the electron microscope. Infected tissue differed from the noninfected in having much hyperplastic phloem characterized by abnormally high proportion of sieve elements, scarcity of companion cells, degenerating parenchyma cells, and some unusually large intercellular spaces. Many spaces contained amorphous debris. Particles resembling BCTV were discernible within the debris. Such particles were encountered also in the debris trapped between stomatal guard cells. Since the phloem exudate excreted from leaves of BCTV-infected plants contains virus particles, and since the virus is found extremely rarely in sieve elements, we suggest (1) that most of BCTV particles apparently released into intercellular spaces are derived from degenerating parenchyma cells in which the virus had multiplied; (2) that the exudate is derived from sieve elements of the hyper-plastic phloem in which the normal functional control by companion cells is lacking; (3) that the exudate leaks from the nontransporting sieve elements through cell walls into intercellular spaces and carries the virus to the outside. Initially, stomata may serve as exits for the infectious exudate, but subsequently ruptures in the epidermis are involved.     

The influence of landscape position on lakes in northern Wisconsin

1. Using data from the North Temperate Lakes Long-Term Ecological Research site in northern Wisconsin, we present a series of examples illustrating how landscape setting can influence the static and dynamic aspects of many physical, chemical and biological properties of lakes. 2. One important landscape attribute is the hydrologic position of a lake within the regional flow regime. Lake position determines the relative importance of groundwater and precipitation input to a lake, with lakes high in the landscape receiving a greater proportion of their input waters from precipitation than lakes lower in the landscape. Landscape position is strongly correlated with the concentration of base cations such as calcium and magnesium. 3. Landscape position also influences how lakes respond to drought conditions. Lakes high in the landscape responded to a 4-year drought with decreases in calcium mass, whereas lakes low in the landscape increased in mass of calcium. During extended dry conditions, these differential responses of lakes suggest that lakes already low in calcium (i.e. in a high position in the flow system) will have further reductions in calcium concentrations. These reductions could decrease the number of lakes offering suitable habitat for organisms such as crayfish and snails whose distributions are limited by calcium. 4. Landscape position also affects silica concentrations in lakes, with lakes low in the landscape having silica concentrations up to three orders of magnitude greater than lakes high in the landscape. Differences in silica concentration affect robustness of freshwater sponge spicules which can potentially alter some aspects of the dynamics of littoral zone food webs. 5. Landscape position can influence the vertical distribution of primary production. Concentrations of dissolved organic carbon are affected by landscape setting and can influence vertical light penetration, thus affecting the depth at which primary production can occur. 6. Lake area and fish species richness are correlated with landscape position: larger, species-rich lakes are low in the landscape, whereas smaller lakes with fewer species tend to be high in the landscape. 7. By taking a landscape-scale view, in addition to the more usual lake-specific view, it is possible to reach a more robust understanding of lake dynamics and avoid some of the problems associated with extrapolating from single lake results.     

Extracellular Calcium Concentration Affects Infectivity of Ichthyophthirius (Ciliophora) Theronts

Tomonts and their theront offspring of the hymenostomatid fish parasite Ichthyophthirius multifiliis were exposed to calcium levels from 0 to 0.8 mM Ca^2+. The survival and reproductive rates of tomonts in the absence of extracellular calcium were not significantly different from rates of tomonts provided calcium. Theronts that developed in the absence of calcium, however, were not infective for Ictalurus punctatus even when the extracellular magnesium concentration was doubled. Theronts that developed in 0.10 mM Ca²⁺ were infective (0.77 trophonts/mm² of pectoral fin) to essentially the same extent as theronts provided 0.33 mM Ca^2+. Infectivity of those provided 0.8 mM Ca²⁺ was 1.79 trophonts/mm² of fin, similar to that of theront controls. Theronts deprived of extracellular calcium as they developed contained significantly fewer secretory mucocysts than did theronts provided 0.1 to 0.8 mM Ca²⁺ although no significant differences among groups occurred with respect to abundance of crystalline or differentiating mucocysts. Theronts deprived of extracellular calcium also had swollen or enlarged mitochondria and abnormal crystalline mucocysts.     

Ascogregarina saraviae N. Sp. (Apicomplexa: Lecudinidae) in Lutzomyia lichyi (Diptera: Psychodidae)

Ascogregarina saraviae n. sp. (Apicomplexa: Lecudinidae) is described from wild-caught Lutzomyia lichyi (Diptera: Psychodidae) females. Gametocysts adhered to the hemocoel side of the genital accessory gland walls and oocysts were injected into their lumina. Sporulated oocysts were ellipsoidal, 12.4 × 5.8 (11.6–13.1 × 5.6–5.9) micrometers, contained eight sporozoites and a refractile residuum. The elongate form of A. saraviae n. sp. oocysts, and their more delicate walls, clearly distinguish them from oocysts of A. chagasi (Adler & Mayrink, 1961).     

THE INFLUENCE OF HIGH CONCENTRATIONS OF AMMONIUM AND SODIUM MOLYBDATES ON FLAX, SOYBEAN AND PEAS GROWN IN NUTRIENT SOLUTIONS CONTAINING DEFICIENT OR EXCESS IRON

Ammonium molybdate supplying 20 or 40 p.p.m. Mo prevented chlorosis caused by low iron supply in young flax plants, but sodium molybdate was effective only at the higher concentration. Temporary darkening of the green colour of the shoots was also produced by 40 p.p.m. Mo in iron-deficient soybean and pea plants, but was soon followed by more severe chlorosis. Symptoms of molybdenum toxicity always developed when 40 p.p.m. Mo were given, whether or not the intensity of chlorosis was reduced. With an increase in iron supply, a reduction in molybdenum toxicity symptoms was confirmed in soybean and peas. In flax the higher level of iron eventually proved excessive unless it was combined with 40 p.p.m. Mo. High molybdenum thus seemed able to counteract both iron deficiency and toxicity in this plant.
High iron reduced the molybdenum content (p.p.m./d.m.) of both shoot and root in soybean, peas and also in flax provided the iron was not excessive. High molybdenum usually reduced the iron content of the shoot, but markedly increased it in the root. Molybdenum-induced chlorosis could thus be partly attributed to inhibition in iron translocation, but the beneficial effect of high molybdenum or high iron on colour was not obviously correlated with the analytical data.     

Linking flux network measurements to continental scale simulations: ecosystem carbon dioxide exchange capacity under non-water-stressed conditions

This paper examines long‐term eddy covariance data from 18 European and 17 North American and Asian forest, wetland, tundra, grassland, and cropland sites under non‐water‐stressed conditions with an empirical rectangular hyperbolic light response model and a single layer two light‐class carboxylase‐based model. Relationships according to ecosystem functional type are demonstrated between empirical and physiological parameters, suggesting linkages between easily estimated parameters and those with greater potential for process interpretation. Relatively sparse documentation of leaf area index dynamics at flux tower sites is found to be a major difficulty in model inversion and flux interpretation. Therefore, a simplification of the physiological model is carried out for a subset of European network sites with extensive ancillary data. The results from these selected sites are used to derive a new parameter and means for comparing empirical and physiologically based methods across all sites, regardless of ancillary data. The results from the European analysis are then compared with results from the other Northern Hemisphere sites and similar relationships for the simplified process‐based parameter were found to hold for European, North American, and Asian temperate and boreal climate zones. This parameter is useful for bridging between flux network observations and continental scale spatial simulations of vegetation/atmosphere carbon dioxide exchange.