Spatial and temporal distribution of Empoasca vitis within a vineyard

1 The intra‐plot spatial distribution of the green leafhopper Empoasca vitis (Goethe) (Cicadellidae, Empoascini) was assessed over three successive growing seasons in a Bordeaux vineyard. Weekly measurements of adult trappings and nymphal counts were performed in a 1.7‐ha plot on 130 sampling points. 2 Statistical and geostatistical analyses revealed inconsistent spatial distributions of adults and nymphs in spring, but consistent spatial distributions in summer, which were identical every year. 3 Similarities between spatial distributions of the mobile adults and the sedentary and aggregated nymphs strongly suggest that adults disperse inside the plot to areas preferred for egg deposition. 4 The similarity of summer populations among years suggests that this insects distribution is based on (perennial) differences in plot characteristics.     

Habitat selection and diel distribution of the crustacean zooplankton from a shallow Mediterranean lake during the turbid and clear water phases

1. The fish fauna of many shallow Mediterranean Lakes is dominated by small‐bodied exotic omnivores, with potential implications for fish–zooplankton interactions still largely unknown. Here we studied diel variation in the vertical and horizontal distribution of the crustacean plankton in Lake Vela, a shallow polymictic and eutrophic lake. Diel sampling was carried out on three consecutive days along a horizontal transect, including an open‐water station and a macrophyte (Nymphaea alba) bed. Since transparency is a key determinant of the predation risk posed by fish, the zooplankton sampling campaigns were conducted in both the turbid (autumn) and clear water (spring) phases. 2. In the turbid phase, most taxa were homogeneously distributed along the vertical and horizontal axes in the three consecutive days. The only exception was for copepod nauplii, which showed vertical heterogeneity, possibly as a response to invertebrate predators. 3. In the clear water phase, most zooplankton taxa displayed habitat selection. Vertically, the general response consisted of a daily vertical migration (DVM), despite the limited depth (1.6 m). Horizontally, zooplankters showed an overall preference for the pelagic zone, independent of the time of the day. Such evidence is contrary to the postulated role of macrophytes as an anti‐predator refuge for the zooplankton. 4. These vertical (DVM) and horizontal (macrophyte‐avoidance) patterns were particularly conspicuous for large Daphnia, suggesting that predation risk from size‐selective predators (fish) was the main factor behind the spatial heterogeneity of zooplankton in the spring. Thus, the difference in the zooplankton spatial distribution pattern and habitat selection among seasons (turbid and clear water phases) seems to be mediated the predation risk from fish, which is directly related to water transparency. 5. The zooplankton in Lake Vela have anti‐predator behaviour that minimises predation from fish. We hypothesise that, due to the distinct fish community of shallow Mediterranean lakes, aquatic macrophytes may not provide adequate refuge to zooplankters, as seen in northern temperate lakes.     

Interplay between ecological, behavioural and historical factors in shaping the genetic structure of sympatric walleye populations (Sander vitreus)

Disentangling ecological, behavioural and evolutionary factors responsible for the presence of stable population structure within wild populations has long been challenging to population geneticists. This study primarily aimed at decoding population structure of wild walleye (Sander vitreus) populations of Mistassini Lake (Québec, Canada) in order to define source populations to be used for the study of spatial partitioning using individual-based multilocus assignment methods, and decipher the dynamics of individual dispersal and resulting patterns of spatial resource partitioning and connectivity among populations. A second objective was to elucidate the relationships between biological characteristics (sex, size, age and population of origin) and an individual's probability to migrate and/or disperse. To do so, a total of 780 spawning individuals caught on five distinct spawning sites, and 1165 postspawning individuals, captured over two sampling seasons (2002-2003) were analysed by means of eight microsatellite loci. Four temporally stable walleye populations associated with distinct reproductive grounds were detected. These populations were differentially distributed among lake sectors during their feeding migration and their spatial distribution was stable over the two sampling seasons. Dispersing individuals were identified (n=61); these revealed asymmetrical patterns of dispersal between populations, which was also confirmed by divergent admixture proportions. Regression models underlined population of origin as the only factor explaining differential dispersal of individuals among populations. An analysis of covariance (ancova) indicated that larger individuals tended to migrate from their river of origin further away in the lake relative to smaller fish. In summary, this study underlined the relevance of using individual-based assignment methods for deciphering dynamics of connectivity among wild populations, especially regarding behavioural mechanisms such as differential spatial partitioning and dispersal responsible for the maintenance of genetic population structure.     

Compact housing in built-up areas: spatial patterning of nests in aggregations of a ground-nesting bee

Abstract .1. The spatial patterning of nests in ten aggregations of a ground-nesting bee Halictus rubicundus (Christ) was examined using nearest-neighbour distance analysis.
2. Large scale aggregation was demonstrated and attributed to a preference for nesting in limited areas of the most suitable substrate in conjunction with natal site fidelity of nest-founding females.
3. Within patches of high nest density, there was a fine-scale regularity resulting from competition for sufficient substrate to maintain the structural integrity of the nest.
4. The appropriateness of four statistical tests is discussed with respect to analysing the spatial arrangement of nests in populations with both aggregated and regular components.     

Spatial distribution and environmental risk assessment of heavy metals identified in soil of a decommissioned uranium mining area

Abstract

The spatial distribution of six heavy metals (Cd, As, Zn, Pb, Cr, and Cu) in the soil of a decommissioned uranium mining area was investigated and their potential environmental risk was assessed. Soil samples were collected along the main riversides enclosing the mining area. The heavy metal distribution was determined by geospatial interpolation. Pearson correlation coefficient and principal component analysis were used to locate the sources of pollution which are the mine ore as natural source, and dressing plants and tailing area from human activity. The results indicate that the average concentrations of As and Cd strongly exceed the recommended EQSS (Environmental Quality Standard for Soils of China) limits at all sampling sites, whereas Zn concentrations were found to be slightly over the limit only at sampling sites close to the mining area. The concentrations of Cr, Cu and Pb were all within the recommended limits. Environmental risk was assessed using the toxicity characteristic leaching procedure defining the degree to which extend the metal is released into the solution. High leaching rates were found only for Zn and Cd, suggesting that together with its high concentrations Cd is the most toxic metal around the mining area, followed by As.     

Aggregation in cooked maize starch

This paper focuses on the aggregation of starch granules. The starch was cooked in a limiting amount of water and dispersed in different solvents. The size of the resulting aggregates was measured using light scattering. The solvents employed in this study (water, glycerol, ethanol, and 2-propanol) dispersed the aggregates to different degrees and resulted in different size distributions for the starch aggregates. It was observed that the size distribution of the cooked starch dispersed in the less polar solvents showed a higher representation of larger aggregates. Higher cooking temperatures resulted in larger aggregates. The methodology here presented proved to be a reproducible and practical way to study aggregation of starch.     

Controlling ‘bois noir’ disease on grapevine: does the timing of herbicide application affect vector emergence?

Bois noir is an important grapevine yellows disease that can cause serious economical losses in European grapevine production. Hyalesthes obsoletus Signoret (Hemiptera, Cixiidae) is the principal vector of bois noir in Switzerland and stinging nettle (Urtica dioica) is its favourite host plant species in vineyards. As bois noir disease can hardly be cured and direct control measures against H. obsoletus are ineffective, viticultural control practices target stinging nettle, the actual reservoir and source of both the pathogen and its vector. Currently, it is recommended to apply herbicides against stinging nettle at the end of the season to kill developing H. obsoletus nymphs. To verify if this late period of herbicide application is justified, stinging nettle patches were treated with glyphosate in the autumn, in the spring or were left untreated as a control. Herbicide applications at both dates controlled the growth of stinging nettle very well in the subsequent summer, although the autumnal treatment was slightly more efficient. To study glyphosate’s direct impact on the development of H. obsoletus nymphs, emergence traps were placed directly in the centre of treated and untreated stinging nettle patches. There was no significant difference among the three treatments in the total number of adults emerging. Thus, an aerial application of glyphosate in either spring or autumn did not inhibit the nymphs’ development on the roots of stinging nettle in the soil. Our results challenge current recommendations of applying herbicides against stinging nettle at the end of the season and suggest that stinging nettle could also be controlled in spring, alike other viticultural weeds.     

Top-down control in a patchy environment: revisiting the stabilizing role of food-dependent predator dispersal

In this paper, we revisit the stabilizing role that predator dispersal and aggregation have in the top-down regulation of predator-prey systems in a heterogeneous environment. We consider an environment consisting of sites interconnected by dispersal, and propose a novel mechanism of stabilization for the case with a non-sigmoid functional response of predators. We assume that the carrying capacity of the prey is infinitely large in each site, and show that successful top-down regulation of this otherwise globally unstable system is made possible through an interplay between the unevenness of prey fitness across the sites and the rapid food-dependent migration of predators. We argue that this mechanism of stabilization is different from those previously reported in the literature: in particular, it requires a high degree of synchronicity in local oscillations of species densities across the sites. Prey outbreaks take place synchronously, but the unevenness of prey growth rates across the sites results in a pronounced difference in the species densities, and so the predator quickly disperses to the sites with the highest prey abundances. For this reason, the consumption of prey mostly takes place in the sites with high densities of prey, which assures an efficient suppression of outbreaks. Furthermore, when the total size of prey population is low, the distribution of both species among the sites becomes more even, and this prevents overconsumption of the prey by the predator. Finally, we put forward the hypothesis that this mechanism, when considered in a tri-trophic plankton community in the water column, can explain the stability of the nutrient-rich low-chlorophyll open ocean regions.     

子午岭油松林灌木层主要树种的空间分布格局和种间关联性研究

对子午岭油松林的主要物种进行实地调查,并根据林下灌木层各物种的重要值确定主要树种,然后用聚集强度指数、x2值和关联度指数对林下灌木层主要树种的空间分布格局和种间关联性进行分析.结果显示:(1)13个主要树种中除辽东栎的K值和CA值小于0外,其余种群皆表现为K>0,C>1,CA>0,I>0,m*/m>0;(2)x2检验显示,大多数树种种间关联性不显著;(3)种间关联度分析显示,树种呈正联结的共计36对,呈负联结的也有36对,有6对是关联强度低的种对.结果表明,在子午岭油松林中辽东栎与其它树种相比,具有广泛均匀分布的倾向,与其它树种之间存在强烈的竞争关系,辽东栎树种具有一定的种间竞争扩张优势.     

Truncated power laws: a tool for understanding aggregation patterns in animals?

Statistical distributions like the negative binomial distribution are commonly used to describe aggregation patterns in animals. However, recently it has been suggested that truncated power laws (TPLs) may also be used for this kind of analysis. A TPL consists of two power functions separated by a cut-off size ( C *). The cut-off size and the slope of power function one (β₁) for the smallest group sizes have been suggested to have a biological explanatory value.
We applied TPLs to aggregation data of tephritid seed predators on a composite plant, aphids on willows and grey seals on a haulout site. β₁ varied between 0.60 and and −0.72, which is higher than predicted. In addition, resource distribution and animal density influenced β₁ and C *. This indicates that environmental dimensionality suggested to affect β₁ is masked by ecological factors. We conclude that TPLs are useful due to their simplicity and, in comparison with traditional methods, provide additional biologically relevant information. Truncated power laws can therefore prove to be useful in studies of animal behaviour and population dynamics.