Showing papers by "Helmholtz Centre for Environmental Research - UFZ published in 2004"

Rings, circles, and null-models for point pattern analysis in ecology

Abstract: A large number of methods for the analysis of point pattern data have been developed in a wide range of scientific fields. First-order statistics describe large-scale variation in the intensity of points in a study region, whereas second-order characteristics are summary statistics of all point-to-point distances in a mapped area and offer the potential for detecting both different types and scales of patterns. Second-order analysis based on Ripley's K-function is increasingly used in ecology to characterize spatial patterns and to develop hypothesis on underlying processes; however, the full range of available methods has seldomly been applied by ecologists. The aim of this paper is to provide guidance to ecologists with limited experience in second-order analysis to help in the choice of appropriate methods and to point to practical difficulties and pitfalls. We review (1) methods for analytical and numerical implementation of two complementary second-order statistics, Ripley's K and the O-ring statistic, (2) methods for edge correction, (3) methods to account for first-order effects (i.e. heterogeneity) of univariate patterns, and (4) a variety of useful standard and non-standard null models for univariate and bivariate patterns. For illustrative purpose, we analyze examples that deal with non-homogeneous univariate point patterns. We demonstrate that large-scale heterogeneity of a point-pattern biases Ripley's K-function at smaller scales. This bias is difficult to detect without explicitly testing for homogeneity, but we show that it can be removed when applying methods that account for first-order effects. We synthesize our review in a number of step-by-step recommendations that guide the reader through the selection of appropriate methods and we provide a software program that implements most of the methods reviewed and developed here.

Predictors of species sensitivity to fragmentation

Abstract: We reviewed empirical data and hypotheses derived from demographic, optimal foraging, life-history, community, and biogeographic theory for predicting the sensitivity of species to habitat fragmentation. We found 12 traits or trait groups that have been suggested as predictors of species sensitivity: population size; population fluctuation and storage effect; dispersal power; reproductive potential; annual survival; sociality; body size; trophic position; ecological specialisation, microhabitat and matrix use; disturbance and competition sensitive traits; rarity; and biogeographic position. For each trait we discuss the theoretical justification for its sensitivity to fragmentation and empirical evidence for and against the suitability of the trait as a predictor of fragmentation sensitivity. Where relevant, we also discuss experimental design problems for testing the underlying hypotheses. There is good empirical support for 6 of the 12 traits as sensitivity predictors: population size; population fluctuation and storage effects; traits associated with competitive ability and disturbance sensitivity in plants; microhabitat specialisation and matrix use; rarity in the form of low abundance within a habitat; and relative biogeographic position. Few clear patterns emerge for the remaining traits from empirical studies if examined in isolation. Consequently, interactions of species traits and environmental conditions must be considered if we want to be able to predict species sensitivity to fragmentation. We develop a classification of fragmentation sensitivity based on specific trait combinations and discuss the implications of the results for ecological theory.

The flora of German cities is naturally species rich

Abstract: Previous studies on various scales and for various European regions and North America have shown that cities harbour more plant species than the surrounding landscape. It has been argued that the greater number of plant species is usually caused by a high number of alien plants promoted by human influence. We analysed native and naturalized vascular plant species distribution data from a comprehensive German database comparing city and non-city grid cells of 10 minutes latitude × 6 minutes longitude (c. 130 km 2 ). The number of city grid cells (n = 68) and non-city grid cells (n = 1856) differed by two orders of magnitude and species richness was highly autocorrelated. We therefore used resampling techniques. We resampled the species richness of 68 randomly selected grid cells 9999 times. This showed that not only naturalized alien but also native plant species richness was significantly higher in city grid cells. To relate environmental variables to species richness, we used 10,000 analyses of covariance of 68 city grid cells and 68 randomly selected non-city grid cells. We demonstrated that a large proportion of the higher native plant species richness could be explained by the number of geological types per grid cell (i.e. a measure of natural geological diversity). Additionally, we showed by resampling the number of geological types per grid cell that cities are not randomly distributed but are in fact in areas of high geological diversity. Hence, we conclude that city areas are preferentially located in pre-existing biodiversity hotspots and argue that they are species rich not because of but in spite of urbanization.

What contributes to the combined effect of a complex mixture

Abstract: The effect of a mixture of 10 compounds, which have previously been identified in an effect-directed analysis as potentially relevant for a specific contaminated riverine sediment (Brack et al Arch Environ Contam Toxicol 1999, 37, 164), were investigated for the underlying joint effect Components identified in an organic sediment extract included several PAHs (benzo[ghi]fluoranthene, benz[a]anthracene, fluoranthene, pyrene, 2-phenylnaphthalene, anthracene, and phenanthrene) plus prometryn, N-phenyl-2-naphthylamine, and parathion-methyl Experiments were performed using a one-generation algal bioassay with the unicellular green algae Scenedesmus vacuolatus as well as chlorophyll fluorescence quenching analysis to describe the effects of the components and mixtures thereof Analysis of the mixture effects based on concentration−response modeling of the effect data reveals that indeed effect contributions of several components can be expected although the mixture ratio is not equitoxic and the individu

Fragmented landscapes, road mortality and patch connectivity: modelling influences on the dispersal of Eurasian lynx

Abstract: Summary 1. Although many reintroduction schemes for the Eurasian lynx Lynx lynx in Germany have been discussed, the implications of connectivity between suitable patches have not been assessed. 2. We introduce an individual-based, spatially explicit dispersal model to assess the probability of a dispersing animal reaching another suitable patch in the complex heterogeneous German landscape, with its dense transport system. The dispersal model was calibrated using telemetric data from the Swiss Jura and based on a map of potential lynx dispersal habitat. 3. Most suitable patches could be interconnected by movements of dispersing lynx within 10 years of reintroduction. However, when realistic levels of mortality risks on roads were applied, most patches become isolated except along the German‐Czech border. Consequently, patch connectivity is limited not so much by the distribution of dispersal habitat but by the high mortality of dispersing lynx. Accordingly, rather than solely investing in habitat restoration, management efforts should try to reduce road mortality. 4. Synthesis and applications. Our approach illustrates how spatially explicit dispersal models can guide conservation efforts and reintroduction programmes even where data are scarce. Clear limits imposed by substantial road mortality will affect dispersing lynx as well as other large carnivores, unless offset by careful road-crossing management or by the careful selection of release points in reintroduction programmes.

Insights into Pseudomonas putida KT2440 response to phenol-induced stress by quantitative proteomics

Abstract: To gain insight into the global mechanism underlying phenol toxicity and tolerance in bacteria, we have generated a two-dimensional protein reference map and used it to identify variations in protein expression levels in Pseudomonas putida KT2440 following exposure to sub-lethal inhibitory concentrations of this solvent. Inspection of the two-dimensional gel electrophoresis gels revealed that 1 h following sudden cell exposure to two different concentrations of phenol, leading to the inhibition of exponential growth (600 mg/L) or to growth arrest for, at least, 4 h before inhibited growth resumption (800 mg/L), the amount of 68 proteins was increased while the amount of 13 proteins was reduced. The up-regulated proteins include proteins involved in the: (i) oxidative stress response (AhpC, SodB,Tpx and Dsb); (ii) general stress reponse (UspA, HtpG, GrpE and Tig); (iii) energetic metabolism (AcnB, AtpH, Fpr, AceA, NuoE, and MmsA-1); (iv) fatty acid biosynthesis (FabB, AccC-1 and FabBx1); (v) inhibition of cell division (MinD); (vi) cell envelope biosynthesis (LpxC, VacJ, and MurA); (vii) transcription regulation (OmpR and Fur); and (viii) transport of small molecules (TolC, BraC, AotJ, AapJ, FbpA and OprQ). Among the down-regulated proteins are those involved in nucleotide biosynthesis (PurM, PurL, PyrH and Dcd) and cell motility (FliC). The information emerging from this genome expression profiling and the detailed investigation of the biological role of candidate genes, as targets of phenol toxicity or as determinants of phenol resistance in P. putida KT2440, will allow more rationale strategies for developing bacteria with greater solvent tolerance with impact in bioremediation and whole-cell biotransformations in media with organic solvents.

Reduced competitive ability in an invasive plant

Abstract: One explanation for successful plant invaders is that they evolved to be more competitive. An intuitive prediction of this Evolution of Increased Competitive Ability (EICA) hypothesis never previously tested is that invasive populations should outcompete their native ancestors in a common environment. We tested this idea in a diallel competition experiment with Alliaria petiolata where offspring from native and invasive populations were grown alone or in all pairwise combinations. While without competition, there were no differences between native and invasive populations, native populations outperformed invasive ones when competing against each other. Our results contradict the EICA hypothesis and we conclude that it does not not hold for Alliaria petiolata. Instead, we formulate a new ERCA (Evolutionary Reduced Competitive Ability) hypothesis: if there is less competition in the invasive range and competitive ability involves traits that have a fitness cost, then selection might act against it, thereby reducing intraspecific interactions too.

Mode of delivery and development of atopic disease during the first 2 years of life.

Abstract: It has been hypothesized that cesarean delivery might have an impact on the development of atopic diseases because of its gut flora modulating properties. In the present study, we analysed the association between cesarean delivery and atopic diseases using data of 2500 infants enrolled in the LISA-Study, a German prospective multicenter birth cohort study. Data on symptoms and physician-diagnosed atopic diseases were gathered by questionnaires shortly after birth and at infant's age 6, 12, 18, and 24 months. In addition, sensitization to common food and inhalant allergens was assessed by measuring specific immunoglobulin E (IgE) using the CAP-RAST FEIA method at the age of 2 yr. Confounder-adjusted odds ratios (aOR) with 95% confidence intervals (CI) were calculated by multiple logistic regression. We found a positive association between cesarean delivery and occurrence of at least one episode of wheezing [aOR 1.31 (95% CI 1.02-1.68)] and of recurrent wheezing [1.41 (1.02-1.96)] during the first 2 yr of life. Furthermore, effect estimates for allergic sensitization defined as at least one specific IgE >/=0.70 kU/l against any allergen [1.48 (0.98-2.24)], against food allergens [1.64 (1.03-2.63)], and against inhalant allergens [1.75 (0.98-3.12)] were increased. Symptoms of atopic dermatitis [1.21 (0.92-1.59)], physician-diagnosed atopic dermatitis [1.04 (0.79-1.39)], and symptoms of allergic rhinoconjunctivitis [1.40 (0.80-2.44)] were only marginally increased in children delivered by cesarean section. In conclusion, our results suggest that cesarean delivery may be an additional risk factor for wheezing and allergic sensitization at least to food allergens up to the age of 2 yr. This should be considered when cesarean section is done for other than medical reasons.

Effects of Matrix Heterogeneity on Animal Dispersal: From Individual Behavior to Metapopulation-Level Parameters

Abstract: Mounting theoretical and empirical evidence shows that matrix heterogeneity may have contrasting effects on metapopulation dynamics by contributing to patch isolation in nontrivial ways. We analyze the movement properties during interpatch dispersal in a metapopulation of Iberian lynx (Lynx pardinus). On a daily temporal scale, lynx habitat selection defines two types of matrix habitats where individuals may move: open and dispersal habitats (avoided and used as available, respectively). There was a strong and complex impact of matrix heterogeneity on movement properties at several temporal scales (hourly and daily radiolocations and the entire dispersal event). We use the movement properties on the hourly temporal scale to build a simulation model to reconstruct individual dispersal events. The two most important parameters affecting model predictions at both the individual (daily) and metapopulation scales were related to the movement capacity (number of movement steps per day and autocorrelat...

Microscale and molecular assessment of impacts of nickel, nutrients, and oxygen level on structure and function of river biofilm communities.

Abstract: Studies were carried out to assess the influence of nutrients, dissolved oxygen (DO) concentration, and nickel (Ni) on river biofilm development, structure, function, and community composition. Biofilms were cultivated in rotating annular reactors with river water at a DO concentration of 0.5 or 7.5 mg liter(-1), with or without a combination of carbon, nitrogen, and phosphorus (CNP) and with or without Ni at 0.5 mg liter(-1). The effects of Ni were apparent in the elimination of cyanobacterial populations and reduced photosynthetic biomass in the biofilm. Application of lectin-binding analyses indicated changes in exopolymer abundance and a shift in the glycoconjugate makeup of the biofilms, as well as in the response to all treatments. Application of the fluorescent live-dead staining (BacLight Live-Dead staining kit; Molecular Probes, Eugene, Oreg.) indicated an increase in the ratio of live to dead cells under low-oxygen conditions. Nickel treatments had 50 to 75% fewer 'live' cells than their corresponding controls. Nickel at 0.5 mg liter(-1) corresponding to the industrial release rate concentration for nickel resulted in reductions in carbon utilization spectra relative to control and CNP treatments without nickel. In these cases, the presence of nickel eliminated the positive influence of nutrients on the biofilm. Other culture-dependent analyses (plate counts and most probable number) revealed no significant treatment effect on the biofilm communities. In the presence of CNP and at both DO levels, Ni negatively affected denitrification but had no effect on hexadecane mineralization or sulfate reduction. Analysis of total community DNA indicated abundant eubacterial 16S ribosomal DNA (rDNA), whereas Archaea were not detected. Amplification of the alkB gene indicated a positive effect of CNP and a negative effect of Ni. The nirS gene was not detected in samples treated with Ni at 0.5 mg liter(-1), indicating a negative effect on specific populations of bacteria, such as denitrifiers, resulting in a reduction in diversity. Denaturing gradient gel electrophoresis revealed that CNP had a beneficial impact on biofilm bacterial diversity at high DO concentrations, but none at low DO concentrations, and that the negative effect of Ni on diversity was similar at both DO concentrations. Notably, Ni resulted in the appearance of unique bands in 16S rDNA from Ni, DO, and CNP treatments. Sequencing results confirmed that the bands belonged to bacteria originating from freshwater and marine environments or from agricultural soils and industrial effluents. The observations indicate that significant interactions occur between Ni, oxygen, and nutrients and that Ni at 0.5 mg liter(-1) may have significant impacts on river microbial community diversity and function.

Dealing with Uncertainty in Spatially Explicit Population Models

Abstract: It has been argued that spatially explicit population models (SEPMs) cannot provide reliable guidance for conservation biology because of the difficulty of obtaining direct esti- mates for their demographic and dispersal parameters and because of error propagation. We argue that appropriate model calibration procedures can access additional sources of informa- tion, compensating the lack of direct parameter estimates. Our objective is to show how model calibration using population-level data can facilitate the construction of SEPMs that produce reliable predictions for conservation even when direct parameter estimates are inadequate. We constructed a spatially explicit and individual-based population model for the dynamics of brown bears (Ursus arctos) after a reintroduction program in Austria. To calibrate the model we developed a procedure that compared the simulated population dynamics with distinct fea- tures of the known population dynamics (=patterns). This procedure detected model param- eterizations that did not reproduce the known dynamics. Global sensitivity analysis of the uncalibrated model revealed high uncertainty in most model predictions due to large parameter uncertainties (coefficients of variation CV ≈ 0.8). However, the calibrated model yielded pre- dictions with considerably reduced uncertainty (CV ≈ 0.2). A pattern or a combination of various patterns that embed information on the entire model dynamics can reduce the uncer- tainty in model predictions, and the application of different patterns with high information content yields the same model predictions. In contrast, a pattern that does not embed infor- mation on the entire population dynamics (e.g., bear observations taken from sub-areas of the study area) does not reduce uncertainty in model predictions. Because population-level data for defining (multiple) patterns are often available, our approach could be applied widely.

The intrinsic mean time to extinction: a unifying approach to analysing persistence and viability of populations

Abstract: Analysing the persistence and viability of small populations is a key issue in extinction theory and population viability analysis. However, there is still no consensus on how to quantify persistence and viability. We present an approach to evaluate any simulation model concerned with extinction. The approach is devised from general Markov models of stochastic population dynamics. From these models, we distil insights into the general mathematical structure of the risk of extinction by time t, P 0 (t). From this mathematical structure, we devise a simple but effective protocol - the ln(1-P 0 )-plot - which is applicable for situations including environmental noise or catastrophes. This plot delivers two quantities which are fundamental to the assessment of persistence and viability: the intrinsic mean time to extinction, T m , and the probability c 1 of the population reaching the established phase. The established phase is characterized by typical fluctuations of the population's state variable which can be described by quasi-stationary probability distributions. The risk of extinction in the established phase is constant and given by 1/T m . We show that T m is the basic currency for the assessment of persistence and viability because T m is independent of initial conditions and allows the risk of extinction to be calculated for any time horizon. For situations where initial conditions are important, additionally c 1 has to be considered.

Spatial pattern formation in semi-arid shrubland: a priori predicted versus observed pattern characteristics

Abstract: Ecologists increasingly use spatial statistics to study vegetation patterns. Mostly, however, these techniques are applied in a purely descriptive fashion without a priori statements on the pattern characteristics expected. We formulated such a priori predictions in a study of spatial pattern in a semi-arid Karoo shrubland, South Africa. Both seed dispersal and root competition have been discussed as processes shaping the spatial structure of this community. If either of the two processes dominates pattern formation, patterns within and between shrub functional groups are expected to show distinct deviations from null models. We predicted the type and scale of these deviations and compared predicted to observed pattern characteristics. As predicted by the seed dispersal hypothesis, small-scale co-occurrence within and between groups of colonisers and successors was increased as compared to complete spatially random arrangement of shrubs. The root competition predictions, however, were not met as shrubs of similar rooting depth co-occurred more frequently than expected under random shrub arrangement. Since the distribution of rooting groups to the given shrub locations also failed to match the root competition predictions, there was little evidence for dominance of root competition in pattern formation. Although other processes may contribute to small-scale plant co-occurrence, the sufficient and most parsimonious explanation for the observed pattern is that its formation was dominated by seed dispersal. To characterise point patterns we applied both cumulative (uni- and bivariate K-function) and local (pair- and mark-correlation function) techniques. Based on our results we recommend that future studies of vegetation patterns include local characteristics as they independently describe a pattern at different scales and can be easily related to processes changing with interplant distance in a predictable fashion.

Alien Species and Evolution: The Evolutionary Ecology of Exotic Plants, Animals, Microbes, and Interacting Native Species

Abstract: Review: Alien Species and Evolution: The Evolutionary Ecology of Exotic Plants, Animals, Microbes and Interacting Native Species By G.W.Cox Reviewed by Nana Nehrbass Centre for Environmental Research, Leipzig, Germany George W. Cox. Alien Species and Evolution: The Evolutionary Ecology of Exotic Plants, Animals, Microbes, and Interacting Native Species. Washington D.C.: Island Press, 2004. 377 pp. ISBN: 1-55963-009-4. US$ 75 (paperback). Recycled, acid-free paper. Alien Species and Evolution leads the reader toward an eye penning recognition of the evolutionary potential of alien species. In his extensive work, Cox illustrates that evolution is not just a theoretical controversy about the history of life on earth, but is also occurring here and now. The book starts off with a substantial discussion about invasions and provides the reader with insights on the techniques of genetic analyses. Equipped with this sound background it is easy even for nonspecialists to follow the argumentation in each chapter. The author leads the reader through all aspects of alien invasions, pointing out the significance of evolutionary adaptation in each instance. He raises awareness of the fact that many invasions are sped up and facilitated by human activities; that is, “accelerated evolution” takes place. The book stresses that although ecosystems might be restored through control measures, evolutionary adaptation is usually irreversible. Hence, sustainable means are needed to prevent invasion in the first place if native species are to be preserved. Finally, even the often-neglected subject of the introduction of transgenic organisms and its consequences is treated in detail. The well-chosen examples vividly illustrate the economic and ecological impact of alien invasive species, covering all taxonomic groups from fungi to mammals. Cox is able to show both sides of the story by demonstrating changes in invaders as well as in native organisms and communities. Although the order of the sections, especially in the introductory part, does not follow a clear structure, the work does not lose its readability. Each part of the book has a summarizing introduction and a short bridging passage, leading the argumentation to the next chapter. The book is written in a comprehensive manner, making it easy to read in only a few hours. After the first perusal, the extensive index makes it a valuable reference book for invasion biologists and interested laypersons. Nana Nehrbass , UFZ- Centre for environmental

Why do alien plant species that reproduce in natural habitats occur more frequently

Abstract: The invasion process can be divided into several phases. We consider invasion patterns related to two aspects of the invasion process: the spread of a species in Germany as counted by the number of occupied grid cells, and the degree of naturalization in Germany (i.e. whether a plant species is exclusively naturalized in human-made habitats or also in (semi-)natural habitats). Although in Germany the area of natural habitats is smaller than that of human-made habitats, the area of occupancy of the respective alien plant species is the opposite. We tested whether both patterns could be explained by niche-breadth variables, namely the number of inhabited habitat types, and vegetation formations, the range of human impact levels, the number of inhabited continents, the number of inhabited floristic zones (climatic zones), and the amplitude of oceanity. Tests were conducted across species and across phylogenetically-independent contrasts, using generalized linear models, in particular, hierarchical partitioning. The number of occupied grid cells could be explained by niche-breadth variables, especially by number of habitats, number of formations, and amplitude of oceanity. Contrary to our expectations, none of these variables could explain the degree of naturalization in cross-species analyses, and amplitude of oceanity is the only stably significant variable that explains the degree of naturalization when analysing phylogenetically-independent contrasts. We conclude that the degree of naturalization is probably independent from niche breadth, and that properties of a larger area of occupancy, i.e. sample size (or propagule pressure), could be responsible for this pattern.

Palatability and tolerance to simulated herbivory in native and introduced populations of Alliaria petiolata (Brassicaceae).

Abstract: The European herb garlic mustard (Alliaria petiolata) is a serious invader of North American deciduous forests. One explanation for its success could be that in the absence of specialized herbivores, selection has favored less defended but more vigorous genotypes. This idea was addressed by comparing offspring from several native and introduced Alliaria populations with respect to their palatability to insect herbivores and their tolerance to simulated herbivory. Feeding rates of a specialist weevil from the native range were significantly greater on American plants, suggesting a loss of resistance in the introduced range. In contrast, there was significant population variation but no continent effect in the feeding rates of a generalist caterpillar. After simulated herbivory, A. petiolata showed a substantial regrowth capacity that involved changes in plant growth, architecture, and allocation. Removal of 75% leaf area or of all bolting stems reduced plant fitness to 81% and 58%, respectively, of the fitness of controls. There was no indication of a difference in tolerance between native and introduced Alliaria populations or of a trade-off between tolerance and resistance.

Secondary succession is influenced by belowground insect herbivory on a productive site

Abstract: We investigated the effects of insect herbivory on a plant community of a productive old-field community by applying foliar and soil insecticides in a full factorial design. During the first 3 years of succession, insecticide treatments had only minor effects on total cover abundance and species richness. However, species ranking within the plant community was strongly affected by soil insecticide but not by foliar insecticide. Creeping thistle, Cirsium arvense , dominated the experimental plots with reduced root herbivory, while square-stemmed willow-herb, Epilobium adnatum , dominated the control and the plots with foliar insecticide. When soil insecticide was applied, cover abundance of monocarpic forbs increased and cover abundance of polycarpic herbs decreased compared to the control. However, this effect was due to a few abundant plant species and is not based on a consistent difference between life history groups. Instead, application of soil insecticide promoted persistence of species that established at the start of succession, and suppressed species that established in the following years. We conclude that below-ground herbivory reduces competitive ability of resident species and, thus, facilitates colonization by late-successional species. Hence, soil insects can exert strong top-down effects on the vegetation of productive sites by affecting dominant plant species and altering competitive balances.

Expansion of brown bears (Ursus arctos) into the eastern Alps: a spatially explicit population model

Abstract: We present a spatially explicit population model for analysing the expansion of brown bears (Ursus arctos) after the reintroduction program in central Austria. The model is based on field investigations into brown bears in Austria and Slovenia and on current knowledge of brown bears. The landscape of the eastern Alps is represented by a GIS-derived raster map defining local habitat suitability and five major spatial barriers to dispersal. The population model follows the fate of individual bears and simulates reproduction, dispersal, home range establishment, and mortality in annual time steps. We indirectly adjust unknown or uncertain model parameters with 10-year data on the number of females with cubs in central Austria and determine key variables of population dynamics, such as population sizes and growth rates within different population nuclei, dispersal distances, or mortality rates, for model parameterisations that reproduce the data on females with cubs. We estimated a current (1996-2000) growth rate of the population in Austria and adjacent parts of Italy of some 14%; a high proportion of this growth was due to immigration from Slovenia. Consequently, the growth rate of the subpopulation in central Austria, which probably is isolated functionally (i.e., no exchange of females) from the nuclei along the Austrian-Slovenian border, yielded some 7%. This subpopulation may comprise seven residents, and we estimated for females a 33% risk of extinction during the 1992-2000 period. Validation and confirmation of our model results with data on bear densities that were not used for model construction and parameterisation supported our findings. The high female mortality rates, together with the vulnerability of the small population to chance events (i.e., demographic stochasticity), are the most pressing threat for the population in the eastern Alps. Our approach could be widely applied for analysing dynamics of rare and endangered species in which the paucity of data precludes an appraisal of the state of the population using standard methods.

Membrane-assisted solvent extraction of triazines, organochlorine, and organophosphorus compounds in complex samples combined with large-volume injection-gas chromatography/mass spectrometric detection.

Abstract: The performance of the fully automated membrane-assisted solvent extraction was investigated for 47 environmental contaminants (among them 30 organochlorine compounds, 9 organophosphorus compounds, and 7 triazines). The extraction took place in a 20-mL headspace vial filled with the aqueous sample and containing a polypropylene membrane bag with 1 mL of cyclohexane as extractant. This device was handled by a multipurpose sampler, which enabled the sample to be mixed at a defined temperature with subsequent large-volume injection of the organic extract taken out of the membrane bag. After optimization of extraction parameters, the method was validated for the three compound classes, triazines and organochlorine and organophosphorus compounds, using spiked distilled water. Then, the extraction yield of these analytes from several complex samples such as a natural and a synthetic wastewater, a bacterial culture, and orange juice was determined and compared to a conventional liquid-liquid extraction. Furthermore, the possibility of reducing matrix interference by adding salt, methanol, or detergent during membrane-assisted solvent extraction was investigated.

Cuticular hydrocarbons and aggression in the termite Macrotermes subhyalinus.

Abstract: Cuticular hydrocarbons are among the prime candidates for nestmate recognition in social insects. We analyzed the variation of cuticular hydrocarbons in the termite species M. subhyalinus in West Africa (Comoe National Park) on a small spatial scale (<1 km). We found considerable variation in the composition of cuticular hydrocarbons among colonies, with four distinct chemical phenotypes. Different phenotypes occurred within each of the four habitats. The difference between these phenotypes is primarily due to unsaturated compounds. A clear correlation between the difference of the hydrocarbon composition and the aggression between colonies was found. This correlation also holds in a multivariate analysis of genetic similarity (measured by AFLPs), morphometric distances (measured by Mahalanobis-distances), as well as geographic distances between colonies. In a more detailed analysis of the correlation between the composition of cuticular hydrocarbons and aggression, we found that no single compound is sufficient to explain variation in aggression between pairings of colonies. Thus, termites seem to use a bouquet of compounds. Multiple regression analysis suggested that many of these compounds are unsaturated hydrocarbons and, thus, may play a key role in colony recognition.

Age-related decline in forest production: modelling the effects of growth limitation, neighbourhood competition and self-thinning

Abstract: 1 In growing forest stands, above-ground net primary production peaks early in stand development and then declines. The causes for this decline are not yet well understood, but hypotheses include physiological and ecophysiological effects, as well as changes in stand structure due to local competition among neighbouring trees. 2 The majority of existing studies address mono-causal explanations of this decline. Here we study the combined effects of intrinsic growth limitation of individual trees, growth limitation due to neighbourhood competition, and self-thinning. 3 We use an individual-based model to analyse forest wood production of a mangrove species described by a sigmoidal growth function, and two hypothetical species with exponential or linear growth. The model reproduces a decline for all species investigated, even when individual growth rates did not become limited. 4 We conclude that individual, sigmoidal growth curves are sufficient but not necessary to explain the production decline in natural forests where neighbourhood competition is appreciably active. 5 We show that the causes for production decline change during forest development. Whereas growth reduction through neighbourhood competition is the main process at the beginning, imbalanced wood loss dominates the later stage of the decline