Stable isotopes and gut contents indicate differential resource use by coexisting asp (Leuciscus aspius) and pikeperch (Sander lucioperca)

Differential use of habitat and prey resources is an important mechanism that may allow coexistence of sympatric species. Unlike interactions between smaller cyprinid and percid fishes, the resource use by coexisting predatory asp (Leuciscus aspius) and pikeperch (Sander lucioperca) is relatively unknown. Here, gut content and stable isotope analyses were used to study ontogenetic dietary shifts and interspecific trophic niche overlap between asp and pikeperch coexisting in two reservoirs. The hypothesis that both species show an ontogenetic dietary shift from small invertebrates to large fish prey, but at the same time use different prey resources to reduce potential competitive interactions, was validated. The isotopic niches of the two predators showed no, or only a moderate, degree of overlap (0%–65%). The ontogenetic changes in the degree of interspecific isotopic niche overlap were different in the two reservoirs, suggesting that trophic segregation can be dynamic and variable among systems. Gut contents revealed that small (<100 mm standard length) asp consumed mostly terrestrial invertebrates and emerged aquatic insects, whereas small pikeperch foraged on zooplankton, larval and pupal stages of aquatic insects and fish. Larger individuals (>100 mm) of both species were predominantly piscivorous, with asp consuming more cyprinid prey and pikeperch more percid prey. Coexisting asp and pikeperch populations are able to utilise different prey resources, thereby reducing potential negative competitive interactions.     

BMC ecology image competition 2017: the winning images

For the fifth year, BMC Ecology is proud to present the winning images from our annual image competition. The 2017 edition received entries by talented shutterbug-ecologists from across the world, showcasing research that is increasing our understanding of ecosystems worldwide and the beauty and diversity of life on our planet. In this editorial we showcase the winning images, as chosen by our Editorial Board and guest judge Chris Darimont, as well as our selection of highly commended images. Enjoy!     

Effect of thinning on anatomical adaptations of Norway spruce needles

Conifers and other trees are constantly adapting to changes in light conditions, water/nutrient supply and temperatures by physiological and morphological modifications of their foliage. However, the relationship between physiological processes and anatomical characteristics of foliage has been little explored in trees. In this study we evaluated needle structure and function in Norway spruce families exposed to different light conditions and transpiration regimes. We compared needle characteristics of sun-exposed and shaded current-year needles in a control plot and a thinned plot with 50% reduction in stand density. Whole-tree transpiration rates remained similar across plots, but increased transpiration of lower branches after thinning implies that sun-exposed needles in the thinned plot were subjected to higher water stress than sun-exposed needles in the control plot. In general, morphological and anatomical needle parameters increased with increasing tree height and light intensity. Needle width, needle cross-section area, needle stele area and needle flatness (the ratio of needle thickness to needle width) differed most between the upper and lower canopy. The parameters that were most sensitive to the altered needle water status of the upper canopy after thinning were needle thickness, needle flatness and percentage of stele area in needle area. These results show that studies comparing needle structure or function between tree species should consider not only tree height and light gradients, but also needle water status. Unaccounted for differences in needle water status may have contributed to the variable relationship between needle structure and irradiance that has been observed among conifers.     

Economic potential of agroforestry for public recreational parks

The availability of public recreational facilities is being threatened by growing demands, limited supplies, and declining government funding. In response to these pressures, the economic potential of agroforestry for supplementing operating budgets of public recreational parks is examined in a case study park consisting of 324 hectares. Agroforestry enterprises native to the area were selected for development on 70 hectares of the site. Linear programming was used to determine the optimum combinations of 23 agroforestry regimes composed of the following activities: 1) conventional forestry planting, tree density of 1682 trees/hectare, 2) the selected agroforestry planting with hay, tree density of 1495 trees/hectare, 3) the selected agroforestry planting with grazing, 4) hay production, and 5) rental of pasture for grazing. The objective function of the study was to maximize the net present value of the study site subject to land, labor, capital, and minimum annual income constraints. The preferred optimal regime generated $1782 per hectare from an agroforestry planting configuration of 1495 trees/hectare with 75 percent hay, 25 percent grazing, and no annual income requirements. Minimum annual income requirements of $2400 and $4800 were feasible but suboptimal from a net present value criteria. The study found that agroforestry could be used to privatize selective activities of public recreational parks and thus enable public agencies to provide these facilities more effectively.     

Assessment of somaclonal variability in hop (Humulus lupulus L.) in vitro meristem cultures and clones by molecular methods

In vitro meristem tissue cultures are used for production of virus-free rootstocks of hop (Humulus lupulus L.). Because use of plant tissue cultures is associated with occurrence of somaclonal variability, we assessed somaclonal variability in hop meristem in vitro cultures before and after thermotherapy by different molecular methods (RFLP, RAPD, STS, ISSR and AFLP) and compared it with existing clonal variability of Osvald's clones 31, 72 and 114. No molecular differences were observed between mother plants and in vitro mericlones by RFLP and STS analyses. Amplified molecular differences were found in RAPD and ISSR products of one from five in vitromericlones cvs. Eroica (E5) and Southern Brewer (SB2), respectively. Similarities with mother plants were 0.965 and 0.913 (JSC), respectively. Specific amplified polymorphic products were found for every mericlone and mother plant in AFLP reactions and variability of DNA sequence ranged from 0.824 to 0.993 (JSC). This variability was very similar to determined intra-clonal variability within Osvald's clones 31, 72 and 114 by AFLP analysis. Inter-clonal variability of DNA sequence was exactly higher than intra-clonal variability of DNA sequence in these clones. The molecular differences between Osvald's clone 72 normal and meristem derived were not verifiable. Thermotherapy increased frequency of molecular changes, since amplified differences were found in 14 from 20 in vitro mericlones of cv. Eroica, in 6 from 11 in vitro mericlones of cv. Yeoman and in 15 from 23 in vitro mericlones of cv. Southern Brewer by RAPD and ISSR analyses.     

Influence of mycotoxin producing fungi (Fusarium, Aspergillus, Penicillium) on gluten proteins during suboptimal storage of wheat after harvest and competitive interactions between field and storage fungi

Cereals contaminated by Aspergillus spp., Penicillium spp., and Fusarium spp. and their mycotoxins, for example, ochratoxin A (OTA) and deoxynivalenol (DON), are not only a risk to human and animal health but can also show poor technological properties and baking quality. The influence of these genera on the sulfur speciation of low molecular weight (LMW) subunits of glutenin was characterized by investigating suboptimally stored wheat samples in situ by X-ray absorption near edge structure (XANES) spectroscopy and baking tests. Field fungi of the genus Fusarium have hardly any influence on both the sulfur speciation of wheat gluten proteins and the baking properties, whereas storage fungi of the genera Aspergillus and Penicillium have a direct influence. An increased amount of sulfur in sulfonic acid state was found, which is not available for thiol/disulfide exchange reactions in the gluten network, and thus leads to a considerably reduced baking volume. From changes of the composition of the mould flora during suboptimal storage of wheat and from the mycotoxin contents, it can be concluded that microbial competitive interactions play an important role in the development of the mould flora and the mycotoxin concentrations during (suboptimal) storage of wheat.     

Occurrence of Polycyclic Musks in Sewage Sludge and their Behaviour in Soils and Plants. Part 1: Behaviour of Polycyclic Musks in Sewage Sludge of Different Treatment Plants in Summer and Winter (5 pp)

Background, Aim and Scope   Part 1: Behaviour of Polycyclic Musks in Sewage Sludge of Different Treatment Plants in Summer and Winter Part 2: Investigation of Polycyclic Musks in Soils and Plants -  Preamble. In Part 1 of the study, screening tests were performed to investigate the occurrence of PCMs in sewage sludges. For a preliminary risk assessment, further information is needed about their behaviour in the terrestrial environment. Hence, Part 2 examined the adsorption of PCMs to soil, their dissipation and leaching in soil and their uptake by plants. Background, Aim and Scope   Polycyclic Musks (PCMs) enter the environment via the waste water system. Because of their persistence, they can accumulate in different matrices like sewage sludge or biota. By the use of sewage sludge as a fertilizer, PCMs are transferred to agricultural soils. Therefore, in Part 1 of the study, screening tests were performed to investigate the occurrence of PCMs in sewage sludge. For a preliminary risk assessment, further information is needed about their behaviour in the terrestrial environment. Hence, Part 2 of the study examined the adsorption of PCMs to soil, their dissipation and leaching in soil, and their uptake by plants. Materials and Methods: In the screening study, samples of activated sewage sludge were taken both in summer and in winter at 21 treatment plants. In order to get an overview of the contamination situation, sampling covered different types of treatment plants (in rural, urban, industrial areas). Analytical methods for the determination of HHCB, AHTN, ADBI, ATTN, AHDI and ATII in the sludge samples were developed and applied. Results: The analytical screening of PCMs showed their presence in activated and dried sewage sludge samples. HHCB and AHTN represented about 95% of the PCMs investigated. Their concentrations in the activated sludge samples varied between 2.9 and 10.4 mg/kg dry mass (dm) and 1.1 to 4.2 mg/kg dm, respectively. Although different types of sewage treatment plants were investigated, similar PCM levels were found, showing the widespread input of these compounds into domestic waste water. Discussion: PCM concentrations in activated sludge varied widely. The variation drops substantially when concentrations are related to the varying dry mass. In dehydrated sludge, PCM concentrations were up to 24 mg/kg dm for HHCB and up to 6.9 mg/kg dm for AHTN. These high values are comparable to those obtained in other investigations analysing PCMs. If the degradation of organic mass during anaerobic decomposition is included in the evaluation, the figures obtained are comparable to those for activated sludge. Elimination in sewage sludge was higher in summer than in winter. Therefore, the contamination of the sludges in winter reached higher levels compared to the summer. Conclusions: The results show that PCMs are widespread contaminants in sewage sludge. Recommendations and Perspectives: PCM should be considered in a risk assessment as potential contaminants of sewage sludge destined for agricultural use. Due to the high PCM levels in sewage sludge, further investigations into the degradation and elimination behaviour in sewage sludge have to be carried out, including that involving PCM metabolites such as lactone derivatives.     

Ein Vergleich deutscher und schweizerischer Regensimulatoren nach Regenstruktur und kinetischer Energie

Comparison of German and Swiss Rainfall Simulators - Rain Structure and Kinetic Energy The drop size distributions of the investigated rain are significantly different. The rainfall simulators Swanson, Bonn, Basel and Trier culminate in the 2 - 3 mm drop diameter class (～40%) and thus simulate best the drop size distribution of natural heavy rainfall. The structure and the kinetic energy of the rains of eight rainfall simulators have been investigated. The data are compared to those registered during a thunder-shower at the research station of Mertesdorf near Trier/FRG. The results are summarized as follows:

• The impact velocity of artificial raindrops depends on the water pressure within the rainfall simulator, the initial velocity of the raindrops and the fall height. A correction factor to match the kinetic energy of natural rainfall, which is based on the percentage of deviation from the terminal velocity, can be applied only to some extend.
• With respect to various fall velocities of the artificial raindrops all tested rainfall simulators except one yield a rainfall energy between 19 and 27 J/m² per mm of rainfall.
• The actual amount of precipitation measured at the end of the rainfall experiments sometimes differs significantly from the aimed value of 60 mm/h. Due to this variation, the total rainfall energy during the experiments accumulated to 9 - 15 MJ/ha.
• This high variability depends on the used rainfall simulator. But it also demonstrates the importance of precipitation measurements on the plot during simulations in order to exactly calculate the rainfall energy.

     

Microbiological characterization of the structures built by earthworms and ants in an agricultural field

The genesis and architecture of the structures built by ants and earthworms differ markedly, suggesting that—in addition to having different physical and chemical properties—the resident microbial community should also have unique properties. We characterized the inorganic N, biomass C, C mineralization rate, and functional diversity of the microbial communities of earthworm casts, earthworm burrow soil, ant mounds, and bulk soil from an agricultural field. Mound soil was most enriched in inorganic N and had the lowest pH, moisture content, and C mineralization rate. Functional diversity was evaluated by determining the ability of microorganisms to grow on 31 substrates using Biolog^®EcoPlates in combination with a most probable number (MPN) approach. Casts had MPNs that were one to two orders of magnitude higher than burrow, mound and bulk soil for most substrates. Casts also had the highest MPNs for particular substrate guilds relative to bulk soil, followed by mound and burrow soil. Indices of substrate diversity and evenness were highest for casts, followed by burrow, mound, and bulk soil. Differences in the type of habitat provided by the structures built by ants and earthworms result in the differential distribution of nutrients, microbial activity, and metabolic diversity of soils within an agricultural field that affect soil fertility and quality.