Impact of avian frugivores on dispersal and recruitment of the invasive <Emphasis Type="Italic">Prunus serotina</Emphasis> in an agricultural landscape

Although seed dispersal is considered to be a key process determining the spatial structure and spread of non-native plant populations, few studies have explicitly addressed the link between dispersal vector behaviour, seed distribution and seedling recruitment to gain insight into the process of exotic species invasion within a fragmented landscape context. The present study analyses the relationship between avian frugivory and spatial patterns of seed deposition and seedling recruitment for an expanding population of the invasive Prunus serotina in a hedgerow network landscape in Flanders, Belgium. We quantified fruit production, observed frugivores, and determined the spatial distribution of bird droppings and P. serotina seedlings. A relatively diverse assemblage of frugivores visited P. serotina seed trees, with Columba palumbus and Turdus merula being by far the most important dispersers. Landscape structure strongly affected dispersal vector behaviour and the spatial distribution of perching birds, droppings and seedlings. Frugivorous birds non-randomly dispersed seeds to perching sites and an association between perching birds, seed deposition and seedling recruitment was found. Results indicate that landscape structure contributes to non-random seed deposition of P. serotina by common local frugivores. Cutting the larger seed trees is proposed as the most feasible measure to slow down the invasion rate.     

Predicting patterns of invasion by black cherry (Prunus serotina Ehrh.) in Flanders (Belgium) and its impact on the forest understorey community

The design of cost-efficient control strategies for invasive species that are too widespread and abundant for complete eradication, at least in the short term, will benefit from a rigorous analysis of invasion patterns and associated effects on native biodiversity. In this paper, the case of the invasive North American tree Prunus serotina in Flanders (Belgium) is presented. Our main objectives were to determine the susceptibility of forest stands to invasion by P. serotina and the subsequent effects of invasion on the understorey community. We used the large database of the first Flemish Forest Inventory. Multiple logistic regressions indicated that P. serotina occurred more frequently in privately owned, younger forest on coarse-textured, dry soils (podzols), and the combination of these factors allowed us to correctly predict presence/absence of P. serotina in 70% of the validation plots. However, locational variables proved to be important as well, indicating that the invasion process is still ongoing. Prediction of P. serotina densities by means of multiple linear regressions was less successful. Effects on the understorey richness were analysed by comparing the number of species and the mean Ellenberg values between pairs of plots, only differing by the presence of P. serotina in the shrub layer. A reduction of the understorey richness following invasion was only pronounced on the more moist soils, while compositional changes mainly occurred on drier soils. It is concluded that priority for control should be given to landscapes with a low fraction of invaded stands and to forest stands located on more moist soils. However, using its potential to threaten native biodiversity as an argument for control should be done with care as further research is needed whether the observed negative effects are due to a species (i.e. native vs. non-native) or a density effect (high vs. low).     

Parasitoid and inquiline attack in the galls of four alien, cynipid gall wasps: host switches and the effect on parasitoid sex ratios

1. Four alien cynipid gall wasps of the genus Andricus are established and still spreading in the British Isles. The order, according to the northerliness of their distribution boundary, is: A. corruptrix→A. quercuscalicis→A. lignicola→A. kollari. All four aliens have a sexual generation in spring on Quercus cerris (introduced to Britain) and an agamic generation in autumn on native oak species. 2. For 2 years 1994 and 1995, galls of both generations of the four alien species were sampled at eight sites from the south of England to the north of Scotland to determine the parasitoid and inquiline species that attack the new galls. The spring generations of the invading species shared a parasitoid complex of four pteromalid species. Five species of inquilines and 11 species of parasitoids emerged from the autumn galls. 3. Two colonisation events were recorded for A. lignicola and A. corruptrix. On both occasions, the spring generations were found first at the new sites, indicating that the agamic generation provides the colonisers for these invading species. After colonisation, the galls of both species were attacked by parasitoids in their first season. 4. In spring, the invading species were among the most abundant cynipids at all eight sites. By sampling the whole local community of cynipid galls, it was found that the parasitoid species attacking the spring galls of the invaders seemed to have shifted their attack to the new hosts. 5. The secondary sex ratios of the parasitoid species emerging from the sexual galls of A. quercuscalicis (the smallest of the four) showed a strong and significant male bias at all sites and in both years. Parasitoid emergence from the galls of the sexual generations of the other three species (all about equal in size) was between 60 and 70% male, and variable among sites and between years.     

沈阳市郊秋菜田的景观生态研究Ⅱ．秋菜田斑块五其它相邻景观要素间相互关系

对沈阳市郊区秋菜田斑块与相邻接的其它景观要素的某些相互关系进行了研究 ,得出了在某一时段内通过一秋菜田斑块和一玉米田斑块之间界面移动的节肢动物类群和数量 ,观测到 7个目的昆虫以平均流量 10 .3只·m-1·d-1通过两斑块边界相互流动 ,以及一乡村道路交通扬尘对秋菜田上降尘率大小和范围的影响 ,受道路交通影响较大的范围可达菜田内 14m处 .并以这些观测结果为基础 ,讨论了农业景观中农业生态系统镶嵌的某些原理 .     

Adaptive feeding across environmental gradients and its effect on population dynamics

This paper analyzes a consumer's adaptive feeding response to environmental gradients. We consider a consumer-resource system where resources are distributed among many discrete resource patches. Each consumer exhibits a feeding morphology allowing it to remove resources from a patch down to some threshold density (or level) before having to seek resources elsewhere. Assuming consumers trade off resource extraction with patch access and predation, we show that for a given environment there often exists a single evolutionarily stable feeding threshold and it is an evolutionary attractor. We then investigate how the population dynamics of the resource and the consumer change as the environment changes. Two cases are considered: (i) all consumers exhibit a fixed feeding threshold that is adaptive for an intermediate environment; and (ii) the consumer population adapts and adopts the evolutionarily stable feeding threshold associated with the current environment. In less harsh environments (i.e., environments where consumers experience a lower risk of predation, or environments where resource patches are more abundant) the adaptive consumer population is predicted to evolve so that resources within a patch are depleted to lower densities. We show that the change in consumer density due to environmental change can be rather different depending on whether or not the population can adapt. In some situations we observe that when the consumer's environment becomes harsher, the consumer population may increase in density before a rapid crash to extinction. This result has implications for monitoring and managing a population.     

Increased toxic effect of methylmercury on <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> under high light and cold stress conditions

The toxic effect of methylmercury on the photosynthetic activity of Chlorella vulgaris was shown to increase under high illumination and unfavorable low temperature. Increased toxic action of methylmercury resulted from the decreased capacity of photosystem II (PS II) for reparation. It was proposed that mild stress conditions might be used to enhance the detection limit of toxicants by microalgae used as test objects.     

Establishment of phosphate-solubilizing strains of Azotobacter chroococcum in the rhizosphere and their effect on wheat cultivars under green house conditions

A pot experiment was conducted in the green house to investigate the establishment of phosphate solubilizing strains of Azotobacter chroococcum, including soil isolates and their mutants, in the rhizosphere and their effect on growth parameters and root biomass of three genetically divergent wheat cultivars (Triticum aestivum L.). Five fertilizer treatments were performed: Control, 90 kg N ha^—1, 90 kg N + 60 kg P₂O₅ ha^—1, 120 kg N ha^—1 and 120 kg N + 60 kg P₂O₅ ha^—1. Phosphate solubilizing and phytohormone producing parent soil isolates and mutant strains of A. chroococcum were isolated and selected by an enrichment method. In vitro phosphate solubilization and growth hormone production by mutant strains was increased compared with soil isolates. Seed inoculation of wheat varieties with P solubilizing and phytohormone producing A. chroococcum showed better response compared with controls. Mutant strains of A. chroococcum showed higher increase in grain (12.6%) and straw (11.4%) yield over control and their survival (12—14%) in the rhizosphere as compared to their parent soil isolate (P4). Mutant strain M37 performed better in all three varieties in terms of increase in grain yield (14.0%) and root biomass (11.4%) over control.     

Changes of cytoplasmic free Ca2+ in the green alga Mougeotia scalaris as monitored with indo-1, and their effect on the velocity of chloroplast movements

The fluorescent calcium-sensitive dye 1-[2-amino-5-(6-carboxyindol-2-yl)-phenoxy]-2-(2-amino-5-methylphenoxy)-ethane-N,N,N,N-tetraacetic acid (indo-1) was loaded by a transplasmalemma pH gradient into filamentous cells and protoplasts of Mougeotia scalaris, such that most of the indo-1 fluorescence originated from the cytoplasm. Incubation of M. scalaris filaments in ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid (EGTA)-buffered media (-log [Ca²⁺] (=pCa) 8 versus pCa 3) caused a consistent and significant decrease in the cytoplasmic free [Ca²⁺]. Pulses of the fluorescence excitation light (UV-A 365 nm, 0.7 s) caused an increase in cytoplasmic free [Ca²⁺] in M. scalaris that was nearly independent of the external [Ca²⁺] and of chloroplast dislocation by centrifugation. This calcium flux, highest in UV-A light, compared with blue or red light, probably resulted from a release of Ca²⁺ from intracellular stores. Increased cytoplasmic [Ca²⁺] may affect the velocity of chloroplast rotation since UV-A-light-mediated chloroplast movement was faster than in blue or red light. Consistently, the calcium ionophore A23187 and the calcium-channel agonist Bay-K8644 both increased the velocity of the red-light-mediated chloroplast rotation. Based on these and other observations, a Ca²⁺-induced decrease in cytoplasmic viscosity in Mougeotia is presumed to occur.Abbreviations EGTA ethylene glycol-bis-(-aminoethyl ether)N,N,N,N-tetraacetic acid - indo-1 1-[2-amino-5-(6-carboxyindol-2-yl)-phenoxy]-2-(2-amino-5-methylphenoxy)-ethane-N,N,N,Ntetraacetic acid - pCa log [Ca²⁺] - P_fr far-red-absorbing form of phytochrome - P_r red-absorbing form of phytochrome - x_G geometric mean Dedicated to Professor Wolfgang Haupt on the occasion of his 70th birthdayThis paper is part of the Ph.D. thesis of U. Russ at the Justus-Liebig-Universitat Giessen (FRG). Part of this work has been presented at a meeting on Calcium and intracellular signalling in plants in Plymouth, UK, Dec. 1990We are indebted to Dr. G. Seibold and Dipl. Phys. H. Weintraut for their advice on the technique of microspectrofluorometry and for allowing access to the microspectrophotometric facilities in the Strahlenzentrum der Justus-Liebig-Universität, Giessen, FRG. We thank Mrs. A. Quanz for reliable culture of the algae and evaluation of the videotapes. Bay-K8644 was a generous gift of Bayer AG, Wuppertal, FRG. U. russ was supported by a scholarship according to the Hessisches Graduierten Förderungsgesetz. This work was supported by the Deutsche Forschungsgemeinschaft.     

Notes on predators and their effect on the survivorship of the endangered giant water bug, <Emphasis Type="Italic">Kirkaldyia (</Emphasis>= <Emphasis Type="Italic">Lethocerus) deyrolli</Emphasis> (Heteroptera,Belostomatidae), in Japanese rice fields

A field research was carried out in Hyogo Prefecture, Japan in order to establish the role of the water-scorpion, Laccotrephes japonensis Scott as predator of nymphs of the endangered giant water bug, Kirkaldyia (= Lethocerus) deyrolli. To assess the impact of this predator, a field experiment was set up with (Control) and without L. japonensis (Removed). The survival rate of K. deyrolli in Removed treatment was higher than in the Control. Our experimental results showed that L. japonensis is an important predator for K. deyrolli nymphs in the field. Handling editor: S. Wellekens