Age and growth,reproduction and diet of a sublittoral population of the rock goby Gobius paganellus (Teleostei,Gobiidae)

Colonisation of extremely acidic waters (pH 3) by aquatic angiosperms occurs widely, but is poorly documented. Unlike acid rain affected and other naturally acidic aquatic ecosystems, waters with pH 3 usually have a high conductivity, with high concentrations of SO₄ ^2- and often high concentrations of Fe³⁺, other heavy metal ions and Al³⁺. Where Fe³⁺ concentration is high, as in many mine waters, it provides a strong buffering system. In such waters, the biogeochemical Fe cycle exerts over water chemistry and the availability of nutrients and carbon for organisms. Biological activity is limited by low concentrations of phosphorus and inorganic carbon (DIC), which in this pH range is essentially all in the form of dissolved CO₂. A number of angiosperms grow in such waters including Phragmites australis, Typha spp. and Juncus bulbosus, though the last is the only one reported to grow totally submerged in waters with pH 3 . J. bulbosus occurs in many lignite mining lakes in Lusatia (north eastern Germany) with pH 3. The characteristics and possible survival strategies for this and other species are discussed.     

Changes in the bacterial community structure in two-stage constructed wetlands with different plants for industrial wastewater treatment

This study focused on the diversity of bacterial communities from two series of two-stage constructed wetlands (CWs) treating tannery wastewater, under different hydraulic conditions. Series were separately planted with Typha latifolia and Phragmites australis in expanded clay aggregates and operated for 31 months. The effect of plant species, hydraulic loading and unit stage on bacterial communities was addressed through bacterial enumeration and denaturating gradient gel electrophoresis (DGGE). Diverse and distinct bacterial communities were found in each system unit, which was related in part to the type of plant and stage position (first or second unit in the series). Numerical analysis of DGGE profiles showed high diversity in each unit with an even distribution of species. No clear relation was established between the sample collection time, hydraulic loading applied and the bacterial diversity.     

Inhibition of <Emphasis Type="Italic">Zizania latifolia</Emphasis> growth by <Emphasis Type="Italic">Phragmites australis</Emphasis>: an experimental study

The influence of Phragmites australis on the growth of Zizania latifolia, and the morphological characteristics of both species, were investigated at two nutrient levels. The experiment was carried out over three growing seasons between May 2003 and December 2005. The experimental plot was longitudinally divided into two equal halves, one of which was planted with Zizania latifolia (Zizania zone) and the other one with Phragmites australis (Phragmites zone). Four weeks after transplantation, the plot was again divided horizontally, perpendicular to the previous division, and subject to low (LN) and high nutrient (HN) treatments. Measured growth indices of the two species were more developed in the HN than in the LN treatments. Both species were observed to invade each other’s zone, but Phragmites latifolia seemed to out-compete Zizania latifolia individuals. This was evident from the decrease in below ground biomass of Zizania latifolia in the third growing season and deterioration in above ground organs with time. It was concluded that Phragmites australis out-competes Zizania latifolia due to better developed root and rhizome system.     

Herbivory in sun versus shade at a natural meadow-woodland ecotone in the Rocky Mountains

We examined herbivore damage in a natural association in order to evaluate the hypothesis that herbivory is generally greater in the shade (Maiorana 1981). Damage was measured in relation to habitat, adult plant distribution, and plant size for 13 species of native herbaceous forbs that cross the natural shade/sun ecotone at the interface of montane meadow and aspen (Populus tremuloides) woodland. Eight of the 13 species had statistically significant differences in leaf area damaged between sun and shade individuals (p<0.05). Only 3 of those were more damaged in shade (Aquilegia coerulea, Epilobium angustifolium, and Galium biflorum), while six were more damaged in the sun (Delphinium nelsoni, Helianthella quinquenervis, Lupinus argenteus, Thalictrum fendleri, and Vicia americana). No pattern was detected for 5: Erigeron speciosus, Fragaria ovalis, Lathyrus leucanthus, Viguiera multiflora, and Viola nuttallii. Levels of herbivory were species-specific rather than habitat-related. Thus, the shade habitat hypothesis must be rejected for our system, and the null hypothesis accepted for this natural assemblage. Herbivory within the shade was generally related to plant and leaf size. Two equally common community level patterns of loss occurred in relation to plant distribution. These were: 1. frequency-related, where herbivory was higher in the habitat of highest adult plant occurrence, and 2. inversely-related, where herbivory was higher in the habitat where plants were less common.     

Vegetation dynamics in the fens of Chautagne (Savoie,France) after the cessation of mowing

The mechanisms controlling secondary succession on eutrophic peat are analyzed on an area of 500 ha marsh near the Lac du Bourget in the Rhône floodplain between Geneva and Lyon. After describing the succession, the authors compare the succession with that described for fens in England.During succession, three categories of phenomena occur:-Predictable phenomena based on the occurrence of well-established relationships between species with a high cover density. When mowing ceases, populations with increasingly higher biomasses reach dominance one by one.-Phenomena which were to be expected although the manner in which they occurred were more difficult to predict, such as the conditions in which woody plants take over.-Phenomena hidden in the framework of a synchronic analysis. The lowering of the water table, for example, can modify the entire community of species occurring in the sequence as well as the competition between species. The pecularities of each type of ecological situation made it difficult to develop general models.     

Resistance in tomato to the greenhouse whitefly: analysis of population dynamics

Life history parameters including longevity, developmental time, and reproduction were determined for whiteflies, Trialeurodes vaporariorum (Westwood), kept in clip-on cages on susceptible parent, Lycopersicon esculentum, resistant parent, L. hirsutum glabratum, and intermediate breeding lines of tomato. Using the Lewontin triangular reproductive function, the intrinsic rate of increase (r_m) was calculated for each genotype. This is an elegant tool for detecting resistance, as it incorporates all salient factors of life history. Comparing r_m to the other parameters measured, selection criteria were chosen. Developmental time is not a suitable selection criterion as it varies very little even between the most susceptible and the most resistant genotypes. Additionally, developmental time of T. vaporariorum offspring was found to be highly significantly correlated to parental age on all tomato genotypes except L. hirsutum glabratum. Total reproduction, truncated population counts, and longevity appear good criteria for selection. This test, focusing on antibiotic factors, shows large differences between the resistant and susceptible parent genotypes, but much smaller differences between the breeding lines and the susceptible parent. Earlier screenings relying on a variety of tests appear to have maintained antixenotic rather than antibiotic properties in the breeding lines.     

Genetic diversity patterns in Phragmites australis at the population,regional and continental scales

Genetic diversity, population structure and interrelationships were investigated in eight populations of the common reed, Phragmites australis, in the Po Plain, Italy, by means of amplified fragments length polymorphisms (AFLPs) and random amplified polymorphic DNAs (RAPDs). Patterns of genetic diversity were analysed in relation to size, age and degree of human impact in the wetlands and compared with that of a distant population in Romania. Genetic distances between Po Plain clones and geographically distant clones were measured to determine the geographical extent of the gene pool.     

Density-dependent population dynamics in larvae of the dragonfly Pachydiplax longipennis: a field experiment

Summary Several features of dragonfly population biology suggest that population regulation occurs in the larval stage. This study was designed to determine if density-dependent interactions among larval odonates can affect survival, growth and emergence. First-instar larvae of the dragonfly Pachydiplax longipennis were raised in outdoor experimental ponds at initial densities of 38, 152, and 608 larvae · m^-2, under two levels of food availability. Food availability was supplemented in half the pools by volumetric addition of zooplankton every other day. Pools in the low food treatment did not receive the zooplankton supplement.There was a strong negative effect of density on the mean growth rate of survivors, which included both emerging tenerals and individuals overwintering in the larval stage. A higher proportion emerged from low density than high density pools. Metamorphs from high density populations were smaller and emerged slightly later than those from low density, but the absolute number of metamorphs did not differ significantly among density treatments. Food supplementation significantly increased the proportion of overwintering larvae. There were no significant food-by-density interactions, indicating that food and density acted independently on larval population dynamics. Density-dependent mechanisms can clearly contribute to odonate population regulation, especially by controlling the number of larvae which emerge and the average age at reproduction. Population-level responses to density may be a result of interference among larvae.     

Microbial population dynamics, especially stress tolerant Bacillus thuringiensis, in partially anaerobic rice field soils during post-harvest period of the Himalayan, island, brackish water and coastal habitats of India

Population ( × 10⁷ c.f.u./g dr. soil) of the aerobic (30.5–154.1) and anaerobic (5.9–91.4) heterotrophic, aerobic (24.0–56.0) and anaerobic (2.4–4.2) spore forming, Gram (-)ve (1.6–2.9), phosphate solubilizing (10–20), asymbiotic N₂-fixing (0.5–0.9), sulfur oxidizing (1.1–2.0), nitrifying (1.0–5.8) and denitrifying (12.1–18.7) bacteria; as well as, the actinomycetes (about 10⁴ c.f.u./g dr. soil) and fungi (about 10⁵ c.f.u./g dr. soil) were variable in the partially anaerobic, saline and drain out flooded rice soils during the post harvest period of the Himalayan, brackish water flooded, island and coastal habitats of India. The aerobic heterotrophic and spore forming bacteria were more than the anaerobic counterparts in the soils. Population (0.51–3.51 × 10⁶ c.f.u./g dr. soil) and crystal morphotype (spherical, bipyramidal and polymorphic) of the Bacillus thuringiensis (Bt) isolates of different soils were variable. Bt index was 0.002 at Mahe but 0.006 in other soils. The Bt isolates tolerated 5–12% NaCl. The osmolytes (mg/g dr. wt.) like the amino acids (0.38–99.45) and proline (0.38–0.80); and the antioxidative enzymes (units (U)/mg protein/min) viz. the catalase (0.17–5.59) and superoxide dismutase (0.35–74.46) were related with intrinsic osmotic stress tolerance of the Bt but they formed spores to overcome anoxic stress. Two Bt isolates were potent tolerant to both osmotic and anoxic stresses.     

Relative importance of factors controlling the success of Oxalis acetosella: an example of linear modelling in ecological research

An ecological hypothesis concerning the relative importance of factors governing the success of Oxalis acetosella on mesic upland forest sites in southern Finland was formulated and tested statistically by means of a multivariate linear model. The data consisted of a stratified random sample of 40 plots with biological measurements and associated observations on environmental variables. The covariance matrix between the incorporated variables was computed and the model parameters were estimated using the method of maximum likelihood provided by the computer programme LISREL V. The results supported the hypothesis based on previous observations and experiments: Oxalis acetosella benefits from a high nutrient level of the soil, but is decisively dependent on the shelter provided by the tree stand. When both spruce stands and well-lit pine stands on mesic and relatively rich forest sites were considered simultaneously, only a weak correlation was found between light availability and site fertility. Accordingly, the presumed value of Oxalis acetosella as an indicator of site fertility appears to be questionable. The adequacy of linear modelling in an ecological context is discussed. The kind of models applied in this study have only a limited application range in non-experimental ecological research. However, linear modelling may contribute to solving particular ecological problems in cases where short environmental gradients are considered so that nonlinearity is not a dominant feature.     

Observations with a different approach to morphological colour variation in an isopod population (Crustacea: Isopoda)

Morphological colour variation in Idotea baltica basteri Audouin, 1827 (Isopoda: Crustacea) is reported for the first time on populations from a brackish water lake (Kucukcekmece Lagoon) in Turkey. According to pigmentation characteristics, the isopods were described and sorted to ten different colour morphs which are named as maculata, maculata-lineata, uniformis, uniformis-lineata, immaculatum, immaculatum-lineata, nigrum, nigrum-lineata, albafusca, and albafusca-fasciatum. The similarity of the morphs was compared by defining digit codes to some of the visual pigmentation characteristics and calculating the Bray-Curtis similarity index of the colour morphs. The albafusca and albafusca-fasciatum forms were found to be the most similar to each other (similarity 96%), whereas immaculatum forms were considered the most different from maculata-lineata (similarity 50%). The morphs named maculata and maculata-lineata, having the highest abundance with 70%, belong to the most successful forms which may achieve crypsis by background matching in their living habitat in Kucukcekmece Lagoon which has sandy and rocky bottom surface area.     

Microbial pathogens of the coconut pest Oryctes rhinoceros: influence of weather factors on their infectivity and study of their coincidental ecology in Kerala,India

The rhinoceros beetle, Oryctes rhinoceros L., is an economically important pest of the coconut palm. Management of this pest has been accomplished using microbial agents viz., Oryctes virus (OrV) and an entomofungal pathogen Metarhizium anisopliae. Recently an opportunistic bacterial pathogen Pseudomonas alcaligenes has also been noticed to cause septicaemia in the grubs when under stress. To unravel the influence of abiotic weather factors and the interactions amongst these microbial pathogens, a 3 year study was conducted from September 1996 to August 1999 in three of the southern districts of Kerala, India. Of the 6627 grubs and 307 adults collected from various breeding sites of the pest, 5% of the grubs and 22% of the adults had natural virus infection, 3% larvae died of M. anisopliae mycosis and 20% larvae succumbed to bacterial septicaemia. Oryctes virus infection in grubs and adults was negatively correlated to minimum temperature (correlation co-efficient, r = –0.4, and –0.6 respectively, sample size, n = 0). Increase in relative humidity increased the fungal activity (r = 0.8) whereas, maximum temperature had a negative impact (r = –0.7). Occurrence of virus infection in grubs and adults was positively correlated (r = 0.6), supporting the contention of active transmission of the virus pathogen between these two stages. The bacterial septicaemia in the grubs was marginally correlated with virus infection and P. alcaligenes undermined the efficiency of the virus pathogen.     

Effect of native natural enemies on the population dynamics of the grape mealybug,Pseudococcus maritimus (Hom.: Pseudococcidae), in apple and pear orchards

The impact of native natural enemies on populations of the grape mealybug,Pseudococcus maritimus (Ehrhorn) in apple and pear orchards was assessed using a combination of techniques, including exclusion cages, limb-banding, and visual inspection of shoots and fruits. The complex of native natural enemies (which included two encyrtid parasitoids, (Pseudaphycus websteri Timberlake andMayridia species), a coccinellid beetle (Hyperaspis lateralis Mulsant), and a chamaemyiid fly (Leucopis verticalis Malloch), provided reasonably good control in orchards that had not been treated with insecticides for one to two years. However, surveys indicated that most of these species were absent from orchards regularly sprayed with pesticides.     

The population dynamics of Cheilosia fasciata (Diptera,Syrphidae): significance of environmental factors and behavioural adaptations in a phytophagous insect

Summary A population of Cheilosia fasciata Schin. & Egg., 1853 was studied in a beech forest (Melico-Fagetum allietosum) near Göttingen (FRG). This syrphid species is closely associated with ramson (Allium ursinum L.), as the larvae mine the plant's leaves. Adult abundance was determined using emergence traps (1981–1986); egg and larval abundance was determined by examining ramson leaves: puparia were extracted from soil samples (1984 and 1986). Cheilosia fasciata is a univoltine species; the imagines emerge in late April/early May. Larval development took five (1986) to six (1984) weeks. In late June/early July the larvae enter the soil for pupariation. A linear relationship was found between the area of the mines and larval biomass (dry wt.). It was concluded that one larva had to mine 51.90 cm² of leaf area in order to gain the mean maximum dry weight (11.15 mg). Furthermore, it was shown that ovipositing females, laying just one egg per leaf, tended to select large leaves providing this minimum amount of food. It is hypothesized that females probably follow straight-lined routes on their oviposition flights, rather than ovipositing on leaves chosen at random. By applying such a strategy, females can almost completely avoid competition for food among their own offspring. Furthermore, competition among the progeny of the whole population is also reduced, particularly in years when adult abundance is very low. The significance of certain factors influencing the population dynamics of Cheilosia fasciata was evaluated by applying a rank correlation analysis. It was shown that high precipitation rates in April reduced the time available for mating and oviposition resulting in low emergence abundance in the next spring. Larval survivorship was enhanced by high precipitation rates in May and June, indicating that drought may be unfavourable to larvae and reduce food availability. Predation by a parasitoid Phygadeuon ursini Horstmann, 1986 (Hymenoptera, Ichneumonidae), appears to be just an imperfect (Milne 1984) density-dependent control mechanism; in fact, it was shown that food limitation is the only significant mechanism of density-dependent population control.     

Use of the egg parasiteEdovum puttleri [Hym.: Eulophidae] in an IPM system developed for Colorado potato beetle [Col.: Chrysomelidae] control on potatoes,Beltsville, Maryland

Edovum puttleri Grissell in conjunction with the fungal pathogenBeauveria bassiana (Balsamo) Vuillimen, a β-exotoxin ofBacillus thuringiensis varthuringiensis Berliner, and the insect growth regulator triflumuron (Alsystin 4F) were evaluated in a pest management system to control Colorado potato beetle,Leptinotarsa decemlineata (Say). Soil treatments ofB. bassiana had no significant impact on emerging Colorado potato beetle adults. Foliar applications of the β-exotoxin and triflumuron significantly reduced 1 ^st larval generation. Releases ofE. puttleri resulted in 56 % egg mass parasitization, significant reduction of 2 ^nd generation larvae, and significantly higher potato yields.Leptinotarsa texana (Schaeffer) was successfully used as an alternate host for production ofE. puttleri.      

The effects of mullein plants (Verbascum thapsus) on the population dynamics of Dicyphus hesperus (Heteroptera: Miridae) in tomato greenhouses

The response of Dicyphus hesperus Knight (Heteroptera: Miridae) to whitefly populations in tomato greenhouses was measured in the presence and absence of mullein (Verbascum thapsus L.) as an alternative host plant. The dynamics of the D. hesperus population on tomato (Lycopersicon esculentum Mill.) and on mullein plants were followed through an entire growing season. In houses with mullein plants, more predators occurred on mullein when whitefly density was low on tomato. A mark-release-recapture experiment where rabbit IgG was used as an external marker showed that D. hesperus adults moved from mullein plants to tomato plants. D. hesperus was always more abundant in houses with mullein than in the houses with tomato plants alone. Movements between tomato and mullein plants are discussed as a strategy to optimize predator foraging. The use of mullein as an alternative host plant may contribute to the establishment of D. hesperus and help to preserve the predator population when prey on tomato crops is scarce.