Home About us Contact
|
Home About us Contact | ||
|
|
||
Area Density (area + density)
Selected AbstractsNocturnal migration of dragonflies over the Bohai Sea in northern ChinaECOLOGICAL ENTOMOLOGY, Issue 5 2006HONG-QIANG FENG Abstract 1.,A sudden increase and subsequent sharp decrease of catches of dragonflies in a searchlight trap, with Pantala flavescens Fabricius (Odonata: Libellulidae) predominating, observed at Beihuang Island in the centre of the Bohai Gulf, in 2003 and 2004, indicated a seasonal migration of these insects over the sea during the night in China. The movements were associated with the onset of fog. 2.,Simultaneous radar observations indicated that the nocturnally migrating dragonflies generally flew at altitudes of up to 1000 m above sea level, with high density concentrations at about 200,300 or 500 m; these concentrations were coincident with the temperature inversion. 3.,During early summer, the dragonflies oriented in a downwind direction, so that the displacement direction varied between different altitudes. In contrast, during late summer, the dragonflies were able to compensate for wind drift, even headwind drift, so as to orient south-westward no matter how the wind changed, and thus the displacement direction was towards the south-west. 4.,The duration of flight, estimated from the variation of area density derived from radar data and hourly catches in the searchlight trap through the night, was about 9,10 h. The displacement speed detected using radar was ,5,11 m s,1. Therefore, the dragonflies might migrate 150,400 km in a single flight. 5.,The dragonflies were thought to originate in Jiangsu province and they migrated into north-east China to exploit the temporary environment of paddy fields in early summer. Their offspring probably migrated back south during late summer and autumn. [source] Poorly crystalline mineral phases protect organic matter in acid subsoil horizonsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2005M. Kleber Summary Soil minerals are known to influence the biological stability of soil organic matter (SOM). Our study aimed to relate properties of the mineral matrix to its ability to protect organic C against decomposition in acid soils. We used the amount of hydroxyl ions released after exposure to NaF solution to establish a reactivity gradient spanning 12 subsoil horizons collected from 10 different locations. The subsoil horizons represent six soil orders and diverse geological parent materials. Phyllosilicates were characterized by X-ray diffraction and pedogenic oxides by selective dissolution procedures. The organic carbon (C) remaining after chemical removal of an oxidizable fraction of SOM with NaOCl solution was taken to represent a stable organic carbon pool. Stable organic carbon was confirmed as older than bulk organic carbon by a smaller radiocarbon (14C) content after oxidation in all 12 soils. The amount of stable organic C did not depend on clay content or the content of dithionite,citrate-extractable Fe. The combination of oxalate-extractable Fe and Al explained the greatest amount of variation in stable organic C (R2 = 0.78). Our results suggest that in acid soils, organic matter is preferentially protected by interaction with poorly crystalline minerals represented by the oxalate-soluble Fe and Al fraction. This evidence suggests that ligand exchange between mineral surface hydroxyl groups and negatively charged organic functional groups is a quantitatively important mechanism in the stabilization of SOM in acid soils. The results imply a finite stabilization capacity of soil minerals for organic matter, limited by the area density of reactive surface sites. [source] Modelling night-time ecosystem respiration by a constrained source optimization methodGLOBAL CHANGE BIOLOGY, Issue 2 2002Chun-Ta Lai Abstract One of the main challenges to quantifying ecosystem carbon budgets is properly quantifying the magnitude of night-time ecosystem respiration. Inverse Lagrangian dispersion analysis provides a promising approach to addressing such a problem when measured mean CO2 concentration profiles and nocturnal velocity statistics are available. An inverse method, termed ,Constrained Source Optimization' or CSO, which couples a localized near-field theory (LNF) of turbulent dispersion to respiratory sources, is developed to estimate seasonal and annual components of ecosystem respiration. A key advantage to the proposed method is that the effects of variable leaf area density on flow statistics are explicitly resolved via higher-order closure principles. In CSO, the source distribution was computed after optimizing key physiological parameters to recover the measured mean concentration profile in a least-square fashion. The proposed method was field-tested using 1 year of 30-min mean CO2 concentration and CO2 flux measurements collected within a 17-year-old (in 1999) even-aged loblolly pine (Pinus taeda L.) stand in central North Carolina. Eddy-covariance flux measurements conditioned on large friction velocity, leaf-level porometry and forest-floor respiration chamber measurements were used to assess the performance of the CSO model. The CSO approach produced reasonable estimates of ecosystem respiration, which permits estimation of ecosystem gross primary production when combined with daytime net ecosystem exchange (NEE) measurements. We employed the CSO approach in modelling annual respiration of above-ground plant components (c. 214 g C m,2 year,1) and forest floor (c. 989 g C m,2 year,1) for estimating gross primary production (c. 1800 g C m,2 year,1) with a NEE of c. 605 g C m,2 year,1 for this pine forest ecosystem. We conclude that the CSO approach can utilise routine CO2 concentration profile measurements to corroborate forest carbon balance estimates from eddy-covariance NEE and chamber-based component flux measurements. [source] Effects of habitat disturbance and food supply on population densities of three primate species in the Kakamega Forest, KenyaAFRICAN JOURNAL OF ECOLOGY, Issue 1 2009Christos Mammides Abstract While habitat disturbance and food availability are major factors thought to determine the abundance of primates, evidence for their importance is uneven. We assessed the effects of these factors on three monkey species, guerezas (Colobus guereza), blue monkeys (Cercopithecus mitis) and redtails (Cercopithecus ascanius), in four areas of the Kakamega Forest, Kenya. Group densities of guerezas and blue monkeys were higher in areas where disturbance levels were also higher. Food availability measured as basal area density of food trees did not correlate significantly with the group densities of any of the three monkeys. The diversity of food trees, another potential measure of food abundance did, however, correlate with group densities of guerezas and blue monkeys suggesting that food availability may positively influence monkey density, and may sometimes increase with disturbance. Group densities of redtails did not correlate with any habitat variable examined, suggesting that factors other than those we considered may have influenced the abundance of this species particularly. Résumé Alors qu'on pense que ce sont les perturbations de l'habitat et la disponibilité de la nourriture qui déterminent l'abondance des primates, les preuves de cette importance sont mitigées. Nous avons étudié les effets de ces facteurs sur trois espèces de singes, le colobe guereza (Colobus guereza), le cercopithèque à diadème (Cercopithecus mitis) et le cercopithèque ascagne (Cercopithecus ascanius), dans quatre zones de la forêt de Kakamega, au Kenya. La densité des troupes de guerezas et de cercopithèques à diadème était plus forte dans les zones où le niveau de perturbation était plus élevé. La disponibilité de la nourriture, mesurée par la densité d'arbres alimentaires par unité de surface, ne montrait pas de corrélation positive avec la densité des troupes d'aucune des trois espèces de singes. La diversité des arbres alimentaires, autre mesure potentielle de l'abondance de nourriture, montrait une corrélation avec les troupes de guerezas et de mitis, suggérant que la disponibilité de la nourriture pourrait influencer positivement la densité des singes, et qu'elle peut parfois augmenter avec les perturbations. La densité des troupes d'ascanius ne montrait de corrélation avec aucune des variables de l'habitat étudiée, ce qui suggère que d'autres facteurs que ceux que nous avons étudiés pourraient avoir influencé particulièrement l'abondance de cette espèce. [source] Preventing crown collisions increases the crown cover and leaf area of maturing lodgepole pineJOURNAL OF ECOLOGY, Issue 3 2006SHAWN X. MENG Summary 1Crown collisions induced by tree sway are hypothesized to reduce crown closure and leaf area in maturing cold temperate forests. These declines are thought to lead to the decline in productivity when a stand ages. 2We tethered groups of lodgepole pine (Pinus contorta Dougl. Ex Loud. Var. latifolia Engelm.) trees in a web pattern at 10 m height, in four 15-m tall stands in western Alberta, Canada, to determine whether preventing crown collisions would increase crown cover and leaf area. 3The stands all had less than 65% crown closure at the beginning of study. Photographs of the canopy were taken in each control and webbed plot in 1998 and at the same point in 2004. Six years after webbing, crown cover had increased by 14.4%, compared to a 2.1% increase for the control plots. 4Webbing also resulted in significant increases in mean branch length, leaf area per branch and foliage density of individual branches from top and middle sections of the crown. Polishing of branches, caused by chronic contact with adjacent trees, was three times as common on control trees compared to webbed trees. The mean leaf area per tree was larger for the webbed trees. 5Crowns of webbed trees were more symmetrical than those of control trees. Trees from webbed plots, however, had a decline in leaf area density. The branches of control trees were typically curved upward with twigs pointed inward, making the crowns more compact compared to the outwardly expanding crowns of trees from the webbed plots. 6The fact that crowns expanded laterally after webbing, despite little change in light regime, provides strong evidence against the hypothesis that loss of crown closure in maturing stands is caused by a lack of light. 7The study indicates that the decline in crown closure and leaf area in maturing and tall stands is at least partly related to wind-induced sway of trees abrading the edges of crowns. [source] Stereology of the myocardium in Leontopithecus (Lesson, 1840) callitrichidae , primatesJOURNAL OF MEDICAL PRIMATOLOGY, Issue 3 2003A. Pissinatti Abstract: Rare morphological features of the Leontopithecus cardiovascular system have been reported in the literature. The samples analyzed in this study came from 33 specimens of Leontopithecus from the collection of the Center of Primatology of Rio de Janeiro-FEEMA (CPRJ-FEEMA). Morphometry and stereological data were obtained from all animals. Adult body weights of L. rosalia were the lowest, the greatest being those of L. chrysopygus caissara; body weights of L. chrysomelas and L. c. chrysopygus were similar and in between those of the two former species. Cardiomyocytes (left ventricular myocardium) were bigger in adults than in infants. The myocardium of L. rosalia showed focal fibrosis, fatty vacuoles, and hyalinization. In L. chrysomelas the myocardium showed areas of fibrosis and presence of mononuclear cells. Fibrosis and areas of congestion were observed in L. c. chrysopygus; areas of disorganization and vascular congestion were found in L. c. caissara. In L. rosalia infants, a greater density of vessels per myocardial area and a greater length density of vessels were observed as compared with those of L. chrysomelas. In adults, L. chrysomelas showed greater density of connective tissue in the myocardium than L. c. chrysopygus and L. c. caissara did. In L. rosalia, cardiomyocyte nuclei had a greater area density than those of the other forms of Leontopithecus. These characteristics may explain the faster development of L. rosalia infants as compared with that of L. chrysomelas and L. c. chrysopygus kept under the same handling conditions at the CPRJ-FEEMA. [source] Structural acclimation and radiation regime of silver fir (Abies alba Mill.) shoots along a light gradientPLANT CELL & ENVIRONMENT, Issue 3 2003A. CESCATTI ABSTRACT Shoot architecture has been investigated using the ratio of mean shoot silhouette area to total needle area ( ) as a structural index of needle clumping in shoot space, and as the effective extinction coefficient of needle area. Although can be used effectively for the prediction of canopy gap fraction, it does not provide information about the within-shoot radiative regime. For this purpose, the estimation of three architectural properties of the shoots is required: needle area density, angular distribution and spatial aggregation. To estimate these features, we developed a method based on the inversion of a Markov three-dimensional interception model. This approach is based on the turbid medium approximation for needle area in the shoot volume, and assumes an ellipsoidal angular distribution of the normals to the needle area. Observed shoot dimensions and silhouette areas for different vertical and azimuth angles (AS) are used as model inputs. The shape coefficient of the ellipsoidal distribution (c) and the Markov clumping index (,0) are estimated by a least square procedure, in order to minimize the differences between model prediction and measurements of AS. This methodology was applied to silver fir (Abies alba Mill.) shoots collected in a mixed fir,beech,spruce forest in the Italian Alps. The model worked effectively over the entire range of shoot morphologies: c ranged from 1 to 8 and ,0 from 0·3 to 1 moving from the top to the base of the canopy. Finally, the shoot model was applied to reconstruct the within-shoot light regime, and the potential of this technique in upscaling photosynthesis to the canopy level is discussed. [source] RATP: a model for simulating the spatial distribution of radiation absorption, transpiration and photosynthesis within canopies: application to an isolated tree crownPLANT CELL & ENVIRONMENT, Issue 4 2001H. Sinoquet ABSTRACT The model RATP (radiation absorption, transpiration and photosynthesis) is presented. The model was designed to simulate the spatial distribution of radiation and leaf-gas exchanges within vegetation canopies as a function of canopy structure, canopy microclimate within the canopy and physical and physiological leaf properties. The model uses a three-dimensional (3D) representation of the canopy (i.e. an array of 3D cells, each characterized by a leaf area density). Radiation transfer is computed by a turbid medium analogy, transpiration by the leaf energy budget approach, and photosynthesis by the Farquhar model, each applied for sunlit and shaded leaves at the individual 3D cell-scale. The model typically operates at a 20,30 min time step. The RATP model was applied to an isolated, 20-year-old walnut tree grown in the field. The spatial distribution of wind speed, stomatal response to environmental variables, and light acclimation of leaf photosynthetic properties were taken into account. Model outputs were compared with data acquired in the field. The model was shown to simulate satisfactorily the intracrown distribution of radiation regime, transpiration and photosynthetic rates, at shoot or branch scales. [source] Abundance and distribution of endangered Franciscana dolphins in Argentine waters and conservation implicationsMARINE MAMMAL SCIENCE, Issue 1 2010Enrique A. Crespo Abstract This is the first study in Argentine waters on the abundance of the threatened Franciscana dolphin, Pontoporia blainvillei. During 2003,2004 we carried out 17 aerial surveys using line transect sampling methodology. We observed 101 Franciscanas in 71 sightings. In northern areas density was estimated at 0.106 individual/km2. Density was lower in southern areas (0.055/km2) and declined with depth beyond 30-m isobaths (0.05/km2). A correction factor for submerged dolphins was applied to density and then extrapolated to the strip between the coastline and the 30-m isobath. Abundance in the northern area was estimated at 8,279 (4,904,13,960) individuals, while in the southern area it was estimated at 5,896 (1,928,17,999) individuals. Considering an annual mortality of about 500,800 individuals, about 3.5%,5.6% of the stock may be removed each year by the fishery and over the 2% recommended by the International Whaling Commission (IWC) and may not be sustainable by the population. Higher densities in coastal areas make Franciscanas more vulnerable to coastal fishing camps, which increased mortality in recent years. A remarkable finding was that while density decreases to the south, values of catch per unit effort (CPUE) increases, indicating different catchability of dolphins between areas. [source] | ||||||||||