Spatially explicit analysis of gastropod biodiversity in ancient Lake Ohrid

The quality of spatial analyses of biodiversity is improved by (i) utilizing study areas with well defined physiogeographical boundaries, (ii) limiting the impact of widespread species, and (iii) using taxa with heterogeneous distributions. These conditions are typically met by ecosystems such as oceanic islands or ancient lakes and their biota. While research on ancient lakes has contributed significantly to our understanding of evolutionary processes, statistically sound studies of spatial variation of extant biodiversity have been hampered by the frequently vast size of ancient lakes, their limited accessibility, and the lack of scientific infrastructure. The European ancient Lake Ohrid provides a rare opportunity for such a reliable spatial study. The comprehensive horizontal and vertical sampling of a species-rich taxon, the Gastropoda, presented here, revealed interesting patterns of biodiversity, which, in part, have not been shown before for other ancient lakes. <br><br> In a total of 284 samples from 224 different locations throughout the Ohrid Basin, 68 gastropod species, with 50 of them (= 73.5%) being endemic, could be reported. The spatial distribution of these species shows the following characteristics: (i) within Lake Ohrid, the most frequent species are endemic taxa with a wide depth range, (ii) widespread species (i.e. those occurring throughout the Balkans or beyond) are rare and mainly occur in the upper layer of the lake, (iii) while the total number of species decreases with water depth, the proportion of endemics increases, and (iv) the deeper layers of Lake Ohrid appear to have a higher spatial homogeneity of biodiversity. Moreover, gastropod communities of Lake Ohrid and its feeder springs are both distinct from each other and from the surrounding waters. The analysis also shows that community similarity of Lake Ohrid is mainly driven by niche processes (e.g. environmental factors), but also by neutral processes (e.g. dispersal limitation and evolutionary histories of species). For niche-based mechanisms it is shown that large scale effects such as type of water body or water depth are mainly responsible for the similarity of gastropod communities, whereas small scale effects like environmental gradients affect gastropod compositions only marginally. In fact, neutral processes appear to be more important than the small scale environmental factors, thus emphasizing the importance of dispersal capacities and evolutionary histories of species

Weed species, not mulching, affect web-building spiders and their prey in organic fruit orchards in South Africa

CITATION: Arvidsson, F. et al. 2020. Weed species, not mulching, affect web-building spiders and their prey in organic fruit orchards in South Africa. Ecosphere, 11(3):e03059, doi:10.1002/ecs2.3059.The original publication is available at https://esajournals.onlinelibrary.wiley.comWeed infestation affects economically relevant orchard properties, including tree performance, yield, and fruit quality negatively, and weeds are therefore often controlled by herbicide application in conventional farming. The addition of organic mulch below tree canopies has been proposed as an alternative reliable practice to suppress weeds and preserve soil moisture in organic farming. Mulching, however, may also affect arthropod pest and natural enemy populations, which highlights the need for simultaneously assessing weed, natural enemy, and animal pest communities in mulch experiments. This study addresses the limited knowledge about nonchemical ground cover management strategies for the control of plant and animal pests in orchards as a major constraint for organic growers. Here, we hypothesize that decisions about ground cover management practices in organic temperate fruit orchards affect the composition of web-building spider communities and their functional role as natural enemies of pest arthropods through effects on weed and insect pest communities. We studied weed, prey, and spider communities, as well as spider diet composition, in four temperate fruit types (apricot, peach, plum, and quince) on a single farm in the Western Cape, South Africa. We established experimental plots with and without addition of dead organic mulch under fruit tree canopies. Addition of organic mulch did not significantly affect weed cover under trees or the taxonomic composition of weed or spider communities over the eight-month study period. However, independent of mulching, the taxonomic composition of weed communities was significantly related to the composition of potential prey and spider communities. These relationships indirectly affected the prey composition of web-building spiders. These results suggest that the identity of weed species in the study orchards had a pronounced effect on the diet composition and functional role of web-building spiders. Future research should focus on the value of individual plant species for the promotion of pest control services provided by spiders across larger spatial scales and with higher levels of replication to allow for wider generalizations. The expected results would not only be relevant for weed control but could also be considered during the development of future flower strips in orchards.Publisher's versio

Crop diversity benefits carabid and pollinator communities in landscapes with semi-natural habitats

In agricultural landscapes, arthropods provide essential ecosystem services such as biological pest control and pollination. Intensified crop management practices and homogenization of landscapes have led to declines among such organisms. Semi-natural habitats, associated with high numbers of these organisms, are increasingly lost from agricultural landscapes but diversification by increasing crop diversity has been proposed as a way to reverse observed arthropod declines and thus restore ecosystem services. However, whether or not an increase in the diversity of crop types within a landscape promotes diversity and abundances of pollinating and predaceous arthropods, and how semi-natural habitats might modify this relationship, are not well understood. To test how crop diversity and the proportion of semi-natural habitats within a landscape are related to the diversity and abundance of beneficial arthropod communities, we collected primary data from seven studies focusing on natural enemies (carabids and spiders) and pollinators (bees and hoverflies) from 154 crop fields in Southern Sweden between 2007 and 2017. Crop diversity within a 1-km radius around each field was positively related to the Shannon diversity index of carabid and pollinator communities in landscapes rich in semi-natural habitats. Abundances were mainly affected by the proportion of semi-natural habitats in the landscape, with decreasing carabid and increasing pollinator numbers as the proportion of this habitat type increased. Spiders showed no response to either crop diversity or the proportion of semi-natural habitats. Synthesis and applications. We show that the joint effort of preserving semi-natural habitats and promoting crop diversity in agricultural landscapes is necessary to enhance communities of natural enemies and pollinators. Our results suggest that increasing the diversity of crop types can contribute to the conservation of service-providing arthropod communities, particularly if the diversification of crops targets complex landscapes with a high proportion of semi-natural habitats

The DOK long-term experiment - lessons learned from 40 years of interdisciplinary research

The world’s growing population calls for sustainable food production within the limits of planetary boundaries. With respect to nitrogen and phosphorus cycling, the loss of biodiversity, land use change and the emission of greenhouse gases, four of these boundaries have been crossed already. Although fragmented knowledge of effects of different cropping systems on these focal planetary boundaries exists, there is a lack of comprehensive data from comparative cropping system experiments over the long run. Four decades back, farmers and researchers co-designed a system comparison experiment, located in Therwil (Basel-Land) Switzerland, comprising a seven-year ley crop rotation. Two conventional (with and without manure), and two organic systems (biodynamic and bioorganic) are compared. This experiment has served as a platform for national and international interdisciplinary research teams in the field of agronomy, soil quality, biodiversity, plant nutrition, food quality, sustainability assessment and modelling. Results of the 40years old DOK experiment show that organic systems, receiving distinctly less external inputs (chemical N, P, K and pesticides), maintained a higher biodiversity and produced lower greenhouse gas emissions. Yield averages over 40 years were 20% lower in organic systems across all crops. A nitrogen balance, including biological nitrogen fixation and stock changes of soil nitrogen, revealed a surplus for all manured systems, whereas the conventional system with sole mineral fertiliser was well balanced. Soil nitrogen stocks only increased slightly in the biodynamic system receiving composted manure. The biodynamic soil showed also increased soil organic carbon stocks, while the conventional soil receiving only mineral fertilizer acted as source for atmospheric CO2. A climate impact analyses encountering nitrous oxide, methane and soil organic matter changes resulted in lower CO2eq emissions in organic compared to the conventional systems, both area and yield scaled. Biodiversity and especially biomass of invertebrate fauna and plant seeds was enhanced in the organically managed systems. Our results demonstrate that organic cropping systems can contribute to a more sustainable production with respect to key planetary boundaries. To further improve system performance, yield gaps between organic and conventional systems need to be reduced by adapted cultivars, more effective organic plant protection and by closing urban and rural nutrient cycles

Impacts of organic and conventional crop management on diversity and activity of free-living nitrogen fixing bacteria and total bacteria are subsidiary to temporal effects

A three year field study (2007-2009) of the diversity and numbers of the total and metabolically active free-living diazotophic bacteria and total bacterial communities in organic and conventionally managed agricultural soil was conducted at the Nafferton Factorial Systems Comparison (NFSC) study, in northeast England. The result demonstrated that there was no consistent effect of either organic or conventional soil management across the three years on the diversity or quantity of either diazotrophic or total bacterial communities. However, ordination analyses carried out on data from each individual year showed that factors associated with the different fertility management measures including availability of nitrogen species, organic carbon and pH, did exert significant effects on the structure of both diazotrophic and total bacterial communities. It appeared that the dominant drivers of qualitative and quantitative changes in both communities were annual and seasonal effects. Moreover, regression analyses showed activity of both communities was significantly affected by soil temperature and climatic conditions. The diazotrophic community showed no significant change in diversity across the three years, however, the total bacterial community significantly increased in diversity year on year. Diversity was always greatest during March for both diazotrophic and total bacterial communities. Quantitative analyses using qPCR of each community indicated that metabolically active diazotrophs were highest in year 1 but the population significantly declined in year 2 before recovering somewhat in the final year. The total bacterial population in contrast increased significantly each year. Seasonal effects were less consistent in this quantitative study

Effects of farming system and simulated drought on biodiversity, food webs and ecosystem functions in the DOK trial

Organic agriculture promotes overall biodiversity in arable fields, with well-documented positive effects on plant and pollinator diversity and abundance. Responses of soil-living decomposers, aboveground herbivores and predators to organic farming are less uniform and not equally well understood. The DOK trial offers ideal conditions to assess the long-term effects of organic compared to conventional farming practices on these above- and belowground invertebrate communities. Organic treatments in the DOK trial have a pronounced effect on abundances, diversity and species composition across taxonomic borders. Application of farmyard manure promotes nematode and earthworm numbers, whereas mineral fertilizers detrimentally affected potworm and fly larvae numbers. Aboveground predators are more abundant under organic agriculture and herbivores show an opposite response. However, effects go beyond simple numeric responses as organic agriculture alters the species composition of local communities significantly

Land‐use intensity and biodiversity effects on infiltration capacity and hydraulic conductivity of grassland soils in southern Germany

Evidence from experimental and established grasslands indicates that plant biodiversity can modify the water cycle. One suspected mechanism behind this is a higher infiltration capacity (ν$_{B}$) and hydraulic conductivity (K) of the soil on species-rich grasslands. However, in established and agriculturally managed grasslands, biodiversity effects cannot be studied independent of land-use effects. Therefore, we investigated in established grassland systems how land-use intensity and associated biodiversity of plants and soil animals affect νB and K at and close to saturation. On 50 grassland plots along a land-use intensity gradient in the Biodiversity Exploratory Schwäbische Alb, Germany, we measured νB with a hood infiltrometer at several matrix potentials and calculated the saturated and unsaturated K. We statistically analysed the relationship between ν$_{B}$ or K and land-use information (e.g., fertilising intensity), abiotic (e.g., soil texture) and biotic data (e.g., plant species richness, earthworm abundance). Land-use intensity decreased and plant species richness increased ν$_{B}$ and K, while the direction of the effects of soil animals was inconsistent. The effect of land-use intensity on ν$_{B}$ and K was mainly attributable to its negative effect on plant species richness. Our results demonstrate that plant species richness was a better predictor of ν$_{B}$ and K at and close to saturation than land-use intensity or soil physical properties in the established grassland systems of the Schwäbische Alb