Effectiveness of vegetation‐based biodiversity offset metrics as surrogates for ants

Biodiversity offset schemes are globally popular policy tools for balancing the competing demands of conservation and development. Trading currencies for losses and gains in biodiversity value at development and credit sites are usually based on several vegetation attributes combined to yield a simple score (multimetric), but the score is rarely validated prior to implementation. Inaccurate biodiversity trading currencies are likely to accelerate global biodiversity loss through unrepresentative trades of losses and gains. We tested a model vegetation multimetric (i.e., vegetation structural and compositional attributes) typical of offset trading currencies to determine whether it represented measurable components of compositional and functional biodiversity. Study sites were located in remnant patches of a critically endangered ecological community in western Sydney, Australia, an area representative of global conflicts between conservation and expanding urban development. We sampled ant fauna composition with pitfall traps and enumerated removal by ants of native plant seeds from artificial seed containers (seed depots). Ants are an excellent model taxon because they are strongly associated with habitat complexity, respond rapidly to environmental change, and are functionally important at many trophic levels. The vegetation multimetric did not predict differences in ant community composition or seed removal, despite underlying assumptions that biodiversity trading currencies used in offset schemes represent all components of a site's biodiversity value. This suggests that vegetation multimetrics are inadequate surrogates for total biodiversity value. These findings highlight the urgent need to refine existing offsetting multimetrics to ensure they meet underlying assumptions of surrogacy. Despite the best intentions, offset schemes will never achieve their goal of no net loss of biodiversity values if trades are based on metrics unrepresentative of total biodiversity.     

Responses of a bacterial pathogen to phosphorus limitation of its aquatic invertebrate host

Host nutrition is thought to affect the establishment, persistence, and severity of pathogenic infections. Nutrient-deficient foods possibly benefit pathogens by constraining host immune function or benefit hosts by limiting parasite growth and reproduction. However, the effects of poor elemental food quality on a host's susceptibility to infection and disease have received little study. Here we show that the bacterial microparasite Pasteuria ramosa is affected by the elemental nutrition of its aquatic invertebrate host, Daphnia magna. We found that high food carbon:phosphorus (C:P) ratios significantly reduced infection rates of Pasteuria in Daphnia and led to lower within-host pathogen multiplication. In addition, greater virulent effects of bacterial infection on host reproduction were found in Daphnia-consuming P-deficient food. Poor Daphnia elemental nutrition thus reduced the growth and reproduction of its bacterial parasite, Pasteuria. The effects of poor host nutrition on the pathogen were further evidenced by Pasteuria's greater inhibition of reproduction in P-limited Daphnia. Our results provide strong evidence that elemental food quality can significantly influence the incidence and intensity of infectious disease in invertebrate hosts.     

An experimental study on the causal relationships between (ecto-)parasites, testosterone and sexual signalling

Bird song is considered to have evolved via sexual selection and should as such honestly signal aspects of the quality of its bearer. To ensure honesty, the immunocompetence handicap hypothesis proposed a dual role of testosterone, having positive effects on sexual signalling but suppressive effects on immune function. However, recent studies showed that it is rather an immune activation that suppresses the androgen production. This reversed chain of causation may significantly alter the pathways, which translate the effects of parasites and pathogens into changes in the expression of male sexual traits. We infested male canaries with Ixodes ricinus tick nymphs to investigate the causal relationships between (ecto-)parasites, testosterone and sexual signalling, here singing behaviour. We focused on flexible song traits, which may quickly reflect changes in the infestation status, and tested whether these effects relate to changes in the plasma testosterone levels or health state. The experimental tick infestation altered the males’ song performance by reducing song consistency, a trait that had previously been identified to reflect male quality. The tick infestation lowered the plasma testosterone levels and had a negative effect on the health status in terms of a reduced hematocrit. Our pathway analysis then revealed that it is the parasite-induced reduction of the plasma testosterone levels but not of the health state that caused the changes in song consistency. Thus, our study supports the view that it is the effect of parasites and immune activation on plasma testosterone levels that generates the trade-off between immunocompetence and sexual signalling.     

Zum Stichprobenfehler im Human-Biomonitoring

Goal and Scope

Human biomonitoring determines the concentration of xenobiotics in populations by means of smaller samples, thus necessarily arising sampling errors. These are determined.

Methods

For a fictitious population of 200,000 persons, differently broad xenobiotic concentration distributions were simulated. Samples of varying size were randomly drawn and the sampling error, defined as the proportional difference between the geometric means of sample and population, was determined.

Results and Conclusions

The sampling error depends on the sample size and the width of the concentration distribution; its estimation is possible for any xenobiotic, given it has lognormal distribution, and the sample size is between 10 and 50,000. For its estimation an equation was derived.

Outlook

When presenting and interpreting results of human biomonitoring, the sampling error must be considered, together with the uncertainty of the measurement.     

Mineralölkohlenwasserstoffe im Boden bei der Sanierung von Altlasten

Various analyses and evaluative procedures are used to provide evidence of success using remediation procedures. Because of the lack of standardized procedures for soil assessment, general practice has unfortunately propagated the use of DIN standards for determining the level of similar parameters in water as well as for other heterogeneous matrices (e.g. in soil). A precise auditing of quality, however, has not been possible with this method, this procedure has even put the success of such a remediation into question. This article describes the problems of determining mineral hydrocarbon concentrations on soil as well as portraying the remediation of oil damages which has occurred on a site of a former waste oil redestillation facility [1, 2]. This procedure has been proved in practice and serves as a model because an adequately defined, standardized method (DIN standard) is lacking.     

Plants as transmission channels for insect vibrational songs

Summary The vibrational songs of several species of cydnid bugs and small cicadas (leafhoppers and planthoppers) living on various types of plants are recorded by means of laser vibrometry. The recorded vibrational songs are analysed with respect to amplitude, frequency spectrum and structure in the time domain (Figs. 2–5).The emission of vibrational songs from singing insects on plants is simulated. A small magnet is glued to the surface of the plant and moved by means of an electromagnet about one cm away (Fig. 1). The vibrations are recorded by means of laser vibrometry. The propagation velocity of the vibrations increases with the square root of frequency, i.e. in the way expected for bending waves.The mechanical properties of plants ranging from soft bean plants to stiff reeds and maples are measured. The results are used for calculating the theoretical propagation velocities of bending waves. The measured and the calculated values are rather close (Table 1). Although the mechanical properties of the plants studied vary widely, the propagation velocities at a certain frequency are of the same order of magnitude (Table 1).In all the plants studied, only little vibrational energy is lost by friction at frequencies below some kHz. Communication by means of bending waves is possible over distances of some meters. The bending waves are reflected with little loss of energy both from the root and from the top of the plant. The vibration signals may therefore travel up and down the plant several times before decaying completely (Fig. 7). The vibration at a certain spot on the plant depends not only on the distance to and nature of the emitter, but also on the modes of vibration of the plant. The amplitude of vibration does not decrease monotonically with distance from the emitter (Fig. 6).These filtering properties of the plants mean that it is essentially impossible to predict which frequencies in the signals will be amplified or attenuated in the plant at the location of the receiving animal. The vibrational signals recorded from the animals cover wide frequency bandwidths. The signals are therefore well adapted to the filtering properties of the plants, but the signals of the species studied here do not appear to be particularly adapted to specific properties of the host plants.The muscular power needed for communication by means of various types of vibrational signals is calculated. The result of this calculation supports the conclusion that the signals recorded here are carried by means of bending waves.The communication strategies open to small insects are considered. Vibrational signals appear to be an efficient means of communication, but only certain types of signals are suited, because the plants cause a considerable distortion of the signals. One kind of distortion, the dispersive property, may — in theory — be used by the listening animals to obtain information about the direction and distance to the singing animals.Dedicated to Dr. F. ossiannilsson, whose pioneering studies led to the suggestion that small insects may use plants as transmission channels for their songs