Matrix quality and habitat configuration interactively determine functional connectivity in a widespread bush cricket at a small spatial scale

Unlike rare or specialised species, widespread abundant species have often been neglected when studying effects of habitat fragmentation. However, recently, it was shown that in the widespread abundant bush cricket Pholidoptera griseoaptera gene flow becomes restricted when the share of suitable habitat dropped below a threshold of 20% at the landscape scale. Here, using the same highly fragmented landscape, we studied the impact of habitat configuration and matrix quality on genetic variation and population differentiation of P. griseoaptera at a small spatial scale. We investigated four clusters of three populations that were either disconnected or connected and had either low quality (arable land) or high quality (grassland) matrix. The number of alleles was significantly lower in disconnected than in connected clusters, irrespective of matrix quality. Genetic differentiation was equally high in the two disconnected clusters and in the connected cluster with low quality matrix (G _ST ≥ 0.030; D ≥ 0.082), whereas it was significantly reduced when connected habitats were embedded in a high quality grassland matrix (G _ST = 0.004; D = 0.011). Analyses of least-cost paths showed that grassy landscape elements in fact represent high quality matrix, but that linear grassy margins are costly for dispersal. The effect of habitat configuration on genetic diversity may be explained by lower effective population sizes in disconnected habitats. The fact that only the connected populations in high quality matrix were not differentiated indicates that landscape management should simultaneously consider habitat configuration and matrix quality to effectively promote small and dispersal-limited species, also at small spatial scales.     

Biodiversity and functioning of ecological communities — why is diversity important in some cases and unimportant in others?

The paper gives an overview of ecological theories and hypotheses that have been raised in order to predict diversity‐function relationships. In particular, those reasons are discussed that may explain the discrepancy between the theoretical expectation for widespread effects of diversity on functioning and the ambiguous empirical evidence for such effects. Structural differences in the ecology of plants, invertebrates, and micro‐organisms are considered which lead to differences in diversity‐function relationships among these groups of organisms. Four criteria are derived that determine diversity‐function relationships: (1) motility of the organisms under consideration, (2) decoupling of population persistence and functional activity in these organisms, (3) species richness of the organisms' community, and (4) equilibrium stability of the considered ecological process. From these criteria the authors predict that measurable effects of diversity on functioning are (a) likely to be found in plants and in micro‐organisms while they are (b) unlikely to be found in the soil fauna. They predict that diversity is (c) likely to affect primary production, soil energy turnover, and nutrient losses from the system, while it is (d) unlikely to durably influence litter decomposition rate. It is shown that these predictions are largely corroborated by empirical evidence compiled from the literature. The issue of spatial and temporal scale is briefly discussed.     

Apparent digestibility of macro‐nutrients and phosphorus in plant‐derived ingredients for Atlantic salmon,Salmo salar and Arctic charr,Salvelinus alpinus

Alternative protein sources for aquafeeds need to be indentified in order to increase the efficiency of production. Many studies have examined terrestrial plant meals/protein concentrates as alternatives. Recently the focus has turned to aquatic protists and plants as well as by‐products from other industries, such as breweries. Atlantic salmon, Salmo salar, and Arctic charr, Salvelinus alpinus, were fed diets containing canola meal, soybean meal, corn gluten meal, soy protein concentrate, barley protein concentrate, and solar dried algae included at 30% of the test diet. Barley protein concentrate had the highest apparent protein digestibility values for both species (96.3% for Atlantic salmon and 85.1% for Arctic charr), followed by corn gluten meal. Algae had the highest organic matter digestibility value for arctic charr (80.1%) while corn gluten meal had the highest organic matter digestibility value for Atlantic salmon (88.4%). Algae had a high energy apparent digestibility coefficient (82.4 salmon, 82.7 charr) along with corn gluten meal (78.5 salmon, 82.7 charr) for both species. In general, Atlantic salmon had higher apparent digestibility coefficients compared to Arctic charr for most of the tested ingredients. Both corn gluten and barley protein concentrate appear good candidates as alternative protein sources with both species.     

Pollinator dispersal in an agricultural matrix: opposing responses of wild bees and hoverflies to landscape structure and distance from main habitat

Semi-natural habitats provide essential resources for pollinators within agricultural landscapes and may help maintain pollination services in agroecosystems. Yet, whether or not pollinators disperse from semi-natural habitat elements into the adjacent agricultural matrix may to a large extent depend on the quality of this matrix and the corresponding pollinator-specific life history traits. To investigate the effects of matrix quality on the distance decay of wild bees and hoverflies, six transects along vegetated field tracks originating at a large semi-natural main habitat and leading into the adjacent agricultural matrix were established in the Wetterau Region, central Hesse, Germany. Species richness of wild bees did not change with distance from the main habitat in landscapes with sufficient grassland cover in the surrounding landscape, but significantly declined when semi-natural grasslands where scarce and isolated in the adjacent agricultural matrix. Abundance of wild bees declined with distance regardless of matrix quality. Species richness of hoverflies did not decline with increasing distance in any landscape. Abundance even increased with distance to the main habitat independently of matrix quality. Thus, our data show that taxa of the pollinator guild may perceive landscapes quite differently. Because of their differing dispersal modes and resource requirements as compared to wild bees, hoverflies may play an important role in maintaining pollination services in agricultural landscapes unsuitable for bee species. Our results highlight the need for considering these taxon-specific differences when predicting the effect of landscape structure on pollinators. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Nematoda response to forest conversion

This study investigates the response of the Nematoda community to forest conversion from pure coniferous stands into semi-natural montane forests in the southern Black Forest (Germany). The investigation was carried out by comparing existing stands that represent the four major stages of the envisaged conversion process. Major results are: (i) the number of Nematoda genera was highest at the species enrichment stage pointing to a positive influence of a rich ground vegetation on the diversity of Nematoda, (ii) predaceous species reached a particularly high, and omnivorous species having a particularly low, density at the species enrichment stage, and (iii) root-hair feeding Nematoda profited from qualitative changes of fine roots during the conversion process and gradually increased in abundance from the even-aged pure spruce stands to the diverse continuous cover forests. Altogether the comprehensive investigation of the Nematoda of the four conversion stages indicates that forest conversion only weakly alters the structure of the Nematoda community. Neither an overall change nor a clear trend in Nematoda richness and abundance could be established. However, due to the specific responses of the different Nematoda feeding groups to the conditions of the individual conversion stages it seems to be ecological useful to maintain special qualities of each conversion stage (e.g. forest gaps in the species enrichment stage) during forest conversion protecting the structure and diversity of the Nematoda communities.     

Belowground Tritrophic Food Chain Modulates Soil Respiration in Grasslands

Edaphic biota significantly affects several essential ecological functions such as C-storage, nutrient turnover, and productivity. However, it is not completely understood how belowground animal contribution to these functions changes in grasslands subject to different land use types. A microcosm experiment was carried out to test the effect of a tritrophic food chain on CO₂ release from grassland soils. Soil was collected from three differently managed grassland systems (meadow, pasture, and mown pasture) located in three distinct German regions that cover a north-south gradient of approximately 500 km. The tritrophic food chain comprised natural edaphic microflora, nematodes, and predatory gamasid mites. The experimental design involved a full factorial combination of the presence and absence of nematodes and gamasid mites. Nematodes significantly increased the CO₂ emissions in most treatments, but the extent of this effect varied with land use type. The fact that grazing by nematodes stimulated the metabolic activity of the edaphic microflora over a wide range of grassland soils highlighted the critical impact of the microfauna on ecosystem services associated with soil organic matter dynamics. Gamasids slightly amplified the effect of nematodes on microbial metabolic activity, but only in the pastures. This effect was most probably due to the control of nematode abundance. The fact that gamasid addition also augmented the impact of environmental conditions on nematode-induced modulation of soil respiration highlighted the need for including land use differences while evaluating soil fauna contribution to soil processes. To conclude, the differential response of the investigated tritrophic food chain to different grassland management systems suggests that adverse effects of land use intensification on important soil processes such as atmospheric C-release could potentially be reduced by using management methods that preserve essential features of the belowground food web.     

Effectiveness of Some Insecticides on Wheat Blossom Midges in Winter Wheat

Orange wheat blossom midge damage can impart serious loss of quantity and quality of winter wheat. Wheat midges were evaluated in large scale field in winter wheat in Bad Lausick (Leipzig, Saxsony) central Germany. The present study aimed at studying the activity of wheat blossom midges WBM, Sitodiplosis mosellana (Géhin) and Contarinia tritici (Kirby) using pheromone, sticky traps and two types of water traps. Management of midges with different treatments was studied; Karate (pyrethroid), Biscaya (neonicotinoid) and NeemAzal T/S (botanical insecticide) were sprayed on wheat at heading stage (GS 55). Monitoring was conducted before the treatment and continued for 4 weeks after the treatment. Pheromone traps were used for forecasting midge adult population and determine the control date. Water traps were used to assess midge larvae, while midge adults were surveyed using sticky traps. A strong correlation between midge catches and weather conditions was obtained; as well a coincidence between pheromone catches and wheat midge infestation in the susceptible growth stages (GS 47–65) was recorded. Insecticide applications to fields of midge-infested winter wheat significantly reduced the wheat midge damage. There were significant differences in wheat midge numbers between treated and untreated; wheat midge numbers were lower in the treated than in control. The results proved that both Karate and Biscaya caused more mortality to wheat midges than NeemAzal T/S.     

Assessment of wheat ear insects in winter wheat varieties in central Germany

Population densities of wheat ear insects infesting different winter wheat varieties (n = 50) were estimated during 2008 and 2009 seasons near Halle, central Germany. The research was aimed at identifying wheat varieties most resistant to wheat ear insect pests. Two methods were used to evaluate the degree of insect infestations in different wheat ear varieties. Wheat ears were dissected when kernels were in Zadoks stage 73 and examined using a binocular microscope to count the number of spikelets and infested kernels, and to identify the insect pests present. In addition, white water traps were placed on the soil underneath each variety to collect mature larvae of wheat blossom midges (WBMs) as an indicator of potential crop risk for the next year. There were significant differences in the number of thrips and WBM infesting wheat ears among varieties in both years. Thrips numbers were the highest in Akratos, Limes and Ritmo varieties in 2008 and in Michigan Amber, Elegant and Kontrast in 2009. Thrips were the lowest in Thuareg in 2008 and Robigus varieties in 2009. The results showed that the highest WBM infestation level was observed in Michigan Amber in both years. The lowest WBM infestations were found in Türkis, Cubus, Capo, Welford and Robigus in both years. The number of infested kernels was positively correlated with WBM among varieties. In the water traps, the highest numbers of WBM larvae were recorded in Saladin and Bussard in 2008 and Orlando, Julius and Glasgow varieties in 2009. The lowest values were recorded in Victo, Enorm, Robigus and Welford varieties in both years. The results provide a guide for selecting winter wheat varieties with resistance to these wheat ear pests.     

Responses of oribatid mite communities to summer drought: The influence of litter type and quality

A litterbag experiment was used to study the impact of extended periods of summer drought on the structure of oribatid mite communities (Acari, Oribatida) developing in two litter types (beech, spruce) of two qualities (fresh, pre-incubated). Within each litter type, litter quality determined species composition and densities and, in turn, this determined the impact of drought upon the oribatid mite communities. In both litter types, drought had a greater impact on community development in the pre-incubated compared to the fresh litter. In the short-term perspective of the present study, oribatid mite communities in beech litter were less sensitive to summer drought than those in spruce litter. This was partly due to the presence of site-specific, drought-tolerant species but seemed also strongly related to differences in the decomposition patterns between the litter types. Marked changes in densities and composition of oribatid communities after only one period of summer-drought suggest that there is a potential for a significant alteration of oribatid community structure in both litter types if climatic changes persist.     

Influence of drought and litter age on Collembola communities

A field experiment was carried out to study the impact of drought and litter quality on the structure and performance of collembolan communities. The hypothesis was tested that changes in substrate humidity and resource quality significantly influence decomposition processes via alterations in soil faunal community structure. Litterbags (1000 μm mesh size) containing either freshly fallen or aged spruce litter were placed on the floor of a German spruce forest for one year. The bags were exposed to either ambient conditions (control) or drought (covered with roofs). Drought-induced changes in biological parameters were associated with a strong reduction in decomposition rates. Moreover, drought stress decreased Collembola abundance and species richness. The influence of drought on some microbiological parameters strongly depended on the litter age. A comparison of the two litter treatments revealed major effects of litter age on microbiological and physico-chemical parameters, but no effects on Collembola abundance and species richness. A detailed analysis of the collembolan community structure showed that certain species are highly adapted to specific characteristics of the substrate and thus rapidly respond to changes in microhabitat conditions.