| 1. |
- Allan, Eric, et al.
(author)
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Interannual variation in land-use intensity enhances grassland multidiversity
- 2014
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In: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 111:1, s. 308-313
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Journal article (peer-reviewed)abstract
- Although temporal heterogeneity is a well-accepted driver of biodiversity, effects of interannual variation in land-use intensity (LUI) have not been addressed yet. Additionally, responses to land use can differ greatly among different organisms; therefore, overall effects of land-use on total local biodiversity are hardly known. To test for effects of LUI (quantified as the combined intensity of fertilization, grazing, and mowing) and interannual variation in LUI (SD in LUI across time), we introduce a unique measure of whole-ecosystem biodiversity, multidiversity. This synthesizes individual diversity measures across up to 49 taxonomic groups of plants, animals, fungi, and bacteria from 150 grasslands. Multidiversity declined with increasing LUI among grasslands, particularly for rarer species and aboveground organisms, whereas common species and belowground groups were less sensitive. However, a high level of interannual variation in LUI increased overall multidiversity at low LUI and was even more beneficial for rarer species because it slowed the rate at which the multidiversity of rare species declined with increasing LUI. In more intensively managed grasslands, the diversity of rarer species was, on average, 18% of the maximum diversity across all grasslands when LUI was static over time but increased to 31% of the maximum when LUI changed maximally over time. In addition to decreasing overall LUI, we suggest varying LUI across years as a complementary strategy to promote biodiversity conservation.
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| 2. |
- Andersson, Georg, et al.
(author)
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Landscape heterogeneity and farming practice alter the species composition and taxonomic breadth of pollinator communities
- 2013
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In: Basic and Applied Ecology. - : Elsevier BV. - 1618-0089 .- 1439-1791. ; 14:7, s. 540-546
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Journal article (peer-reviewed)abstract
- Effects of landscape heterogeneity and farming practice on species composition are less well known than those on species richness, in spite of the fact that community composition can be at least as important for ecosystem services, such as pollination. Here, we assessed the effect of organic farming and landscape heterogeneity on pollinator communities, focusing on multivariate patterns in species composition and the taxonomic breadth of communities. By relating our results to patterns observed for species richness we show that: (1) species richness generally declines with decreasing landscape heterogeneity, but taxonomic breadth only declines with landscape heterogeneity on conventionally managed farms. We further highlight the importance to provide results of species composition analyses as (2) primarily hoverfly species benefited from organic farming, but three bee species from different families were favoured by conventionally managed farms and (3) two hoverfly species with aphidophagous larvae showed contrasting responses to landscape heterogeneity. These results advance the understanding of how landscape heterogeneity and farming practices alter insect communities and further suggest that diversity patterns need to be analysed beyond species richness to fully uncover consequences of agricultural intensification.
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| 3. |
- Birkhofer, Klaus, et al.
(author)
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Arthropod food webs in organic and conventional wheat farming systems: a stable isotope approach
- 2011
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In: Agricultural and Forest Entomology. - : Wiley. - 1461-9555. ; 13:2, s. 197-204
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Journal article (peer-reviewed)abstract
- 1 Agricultural intensification not only alters the structure of arthropod communities, but also may affect biotic interactions by altering the availability of basal resources. We analyzed variations in stable isotope ratios (15N/14N and 13C/12C) of fertilizers, plants, prey and generalist predators in organic and conventional farming systems in a long-term agricultural experiment [DOK trial (bioDynamic, bioOrganic, Konventionell)]. Two basal resources with pronounced differences in carbon isotope signatures, wheat litter (C3 plant) and maize litter (C4 plant), were used to uncover differences in food web properties between the two farming systems (conventional versus organic). 2 Predators incorporated significantly higher proportions of carbon from wheat sources in organically managed fields, suggesting that they were more closely linked to wheat-consuming prey in this system. The δ15N values of three predaceous species were more than 2‰ greater in summer than in spring. 3 The results obtained suggest that generalist predators consumed higher proportions of herbivore prey in the organic system and that starvation and intraguild predation rates increased in some predator species with time. 4 Because the effects of farming system and sampling date on predators were species-specific, conserving a diverse natural enemy community including species with different phenologies and sensitivities to management practices may, in the long term, be a good strategy for maintaining high pest suppression throughout the growing season.
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| 4. |
- Birkhofer, Klaus, et al.
(author)
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Assessing spatiotemporal predator-prey patterns in heterogeneous habitats
- 2010
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In: Basic and Applied Ecology. - : Elsevier BV. - 1618-0089 .- 1439-1791. ; 11:6, s. 486-494
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Journal article (peer-reviewed)abstract
- Disentangling the contribution of biotic interactions (density-dependent) and environmental heterogeneity (density-independent) to the formation of spatial patterns between predators and prey is crucial for a better understanding of food-web interactions. Most techniques for the analysis of spatial patterns assume that abiotic processes influence the distribution of individuals with similar intensity at all locations of a study area (stationarity). This simplification may result in a spurious description of predator–prey associations in environmentally heterogeneoushabitats. In a spatially explicit way we sampled ground-active linyphiid and lycosid spiders and their Collembola prey along a forest-meadow gradient and analysed the change in spatial relationships with time. We used techniques of point pattern analysis and pair-correlation functions to summarize spatial patterns. To disentangle the contribution of biotic interactions and environmental heterogeneity on pattern formation we compared observed functions with those arising from null models either assuming environmental homogeneity or accounting for habitat heterogeneity. All taxa were aggregated at the three sampling periods if habitat homogeneity was assumed, but only linyphiid spiders were still clustered after accounting for environmental heterogeneity. A similarly contrasting result was present for the spatial relationship between predators and their prey, with association under the assumption of homogeneity, but strong repulsion that intensified with time if accounting for environmental heterogeneity. Results from additional bivariate null models under which either predator or prey locations were fixed, suggest that Collembola showed lower activity density in more suitable, but predator-rich habitats. Biotic interactions were important drivers of the spatial distribution of ground-active predators and their decomposer prey in the analysed forest floor food-web. However, these structuring forces remain hidden when using simple spatial models that ignore environmental heterogeneity. Therefore, for understanding predator–prey interactions in spatially complex habitats, such as grasslands and forests, spatial models considering habitat heterogeneity are indispensible.
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| 5. |
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| 6. |
- Birkhofer, Klaus, et al.
(author)
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Density-dependent and -independent effects on the joint use of space by predators and prey in terrestrial arthropod food-webs
- 2011
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In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 120:11, s. 1705-1711
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Journal article (peer-reviewed)abstract
- The spatial distribution of predators and their prey is affected by their joint use of space. While the formation of such spatial patterns may be driven by density-dependent and -independent factors our knowledge on the contribution of different land-use activities on the formation of spatial patterns between predators and prey remains very limited. Agriculture is one of the most prevailing land-use activities with strong effects on invertebrate densities and structural habitat conditions. Here, we used replicated conventionally and organically managed winter wheat fields to investigate the effects of agricultural land-use on the spatial patterns of generalist predators and decomposer prey. We then identified the explanatory power of density-dependent (prey and predator activity density) and density-independent (vegetation structure) predictors for the observed spatial patterns. Generalist predators were regularly distributed only in conventionally managed fields and this pattern intensified with decreasing Collembola prey availability and increasing spider activity density. Segregation between carabid and spider predators was strongest in fields with lowest wheat plant height, suggesting more intense intraguild interactions in structurally less complex habitats. Collembola were aggregated independent of management and aggregation was strongest in fields with highest Collembola and carabid activity density. Spiders and Collembola prey were associated, but higher aphid densities under conventional management weakened or interrupted this spatial relationship. We conclude that active control of crop plant physiognomy by growth hormones and herbicides in conventionally managed fields promotes predator–predator segregation and that a high availability of aphid prey seems to decouple predator–Collembola prey associations. Our results emphasise the need for a more mechanistic understanding of the effects of land-use on the formation of spatial patterns and species interactions, especially under scenarios of environmental change and an ongoing loss of biodiversity.
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| 7. |
- Birkhofer, Klaus, et al.
(author)
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Effects of extreme climatic events on small-scale spatial patterns: a 20-year study of the distribution of a desert spider.
- 2012
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In: Oecologia. - : Springer Science and Business Media LLC. - 1432-1939 .- 0029-8549. ; 170:3, s. 651-657
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Journal article (peer-reviewed)abstract
- Individuals of most animal species are non-randomly distributed in space. Extreme climatic events are often ignored as potential drivers of distribution patterns, and the role of such events is difficult to assess. Seothyra henscheli (Araneae, Eresidae) is a sedentary spider found in the Namib dunes in Namibia. The spider constructs a sticky-edged silk web on the sand surface, connected to a vertical, silk-lined burrow. Above-ground web structures can be damaged by strong winds or heavy rainfall, and during dispersal spiders are susceptible to environmental extremes. Locations of burrows were mapped in three field sites in 16 out of 20 years from 1987 to 2007, and these grid-based data were used to identify the relationship between spatial patterns, climatic extremes and sampling year. According to Morisita's index, individuals had an aggregated distribution in most years and field sites, and Geary's C suggests clustering up to scales of 2 m. Individuals were more aggregated in years with high maximum wind speed and low annual precipitation. Our results suggest that clustering is a temporally stable property of populations that holds even under fluctuating burrow densities. Climatic extremes, however, affect the intensity of clustering behaviour: individuals seem to be better protected in field sites with many conspecific neighbours. We suggest that burrow-site selection is driven at least partly by conspecific cuing, and this behaviour may protect populations from collapse during extreme climatic events.
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| 8. |
- Birkhofer, Klaus, et al.
(author)
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General Relationships between Abiotic Soil Properties and Soil Biota across Spatial Scales and Different Land-Use Types.
- 2012
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In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:8
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Journal article (peer-reviewed)abstract
- Very few principles have been unraveled that explain the relationship between soil properties and soil biota across large spatial scales and different land-use types. Here, we seek these general relationships using data from 52 differently managed grassland and forest soils in three study regions spanning a latitudinal gradient in Germany. We hypothesize that, after extraction of variation that is explained by location and land-use type, soil properties still explain significant proportions of variation in the abundance and diversity of soil biota. If the relationships between predictors and soil organisms were analyzed individually for each predictor group, soil properties explained the highest amount of variation in soil biota abundance and diversity, followed by land-use type and sampling location. After extraction of variation that originated from location or land-use, abiotic soil properties explained significant amounts of variation in fungal, meso- and macrofauna, but not in yeast or bacterial biomass or diversity. Nitrate or nitrogen concentration and fungal biomass were positively related, but nitrate concentration was negatively related to the abundances of Collembola and mites and to the myriapod species richness across a range of forest and grassland soils. The species richness of earthworms was positively correlated with clay content of soils independent of sample location and land-use type. Our study indicates that after accounting for heterogeneity resulting from large scale differences among sampling locations and land-use types, soil properties still explain significant proportions of variation in fungal and soil fauna abundance or diversity. However, soil biota was also related to processes that act at larger spatial scales and bacteria or soil yeasts only showed weak relationships to soil properties. We therefore argue that more general relationships between soil properties and soil biota can only be derived from future studies that consider larger spatial scales and different land-use types.
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| 9. |
- Birkhofer, Klaus, et al.
(author)
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Grassy margins along organically managed cereal fields foster trait diversity and taxonomic distinctness of arthropod communities
- 2014
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In: Insect Conservation and Diversity. - : Wiley. - 1752-4598 .- 1752-458X. ; 7:3, s. 274-287
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Journal article (peer-reviewed)abstract
- It is not known if grassy margins contribute to the conservation of biodiversity if situated along organically managed cereal fields as the contrast in environmental conditions between fields and margins may be too small in absence of pesticide applications. Communities of spiders, ground beetles, true bugs and aphids were sampled in 2years along transects from the centre of organically managed cereal fields into adjacent grassy margins. Based on species richness, abundances, ecological and body size traits of species and taxonomic distinctness between species, communities were compared between organically managed cereal fields and their grassy margins. The species richness, abundance and variation in taxonomic distinctness of true bugs were significantly higher in grassy margins. For spiders and ground beetles, these metrics were either higher in cereal fields or did not differ significantly. At the species level, spiders living under stones or in soil crevices, as well as phytophagous ground beetles and true bugs that overwinter as eggs benefited from grassy margins. True bug communities in cereal fields were dominated by a few abundant species, whereas communities in margins were rather dominated by a few large species. Our comprehensive analyses highlight the importance of accounting for species identities and biology in biodiversity studies. The traits that characterised arthropod species that benefited from margins are not characteristic for pest species. Grassy margins along organic fields therefore represent an important agri-environmental scheme for the conservation of several arthropod taxa and margins should not be removed to increase the crop production area in organically managed cereal fields.
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| 10. |
- Birkhofer, Klaus, et al.
(author)
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Soil fauna feeding activity in temperate grassland soils increases with legume and grass species richness
- 2011
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In: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 43:10, s. 2200-2207
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Journal article (peer-reviewed)abstract
- Edaphic fauna contributes to important ecosystem functions in grassland soils such as decomposition and nutrient mineralization. Since this functional role is likely to be altered by global change and associated shifts in plant communities, a thorough understanding of large scale drivers on below-ground processes independent of regional differences in soil type or climate is essential. We investigated the relationship between abiotic (soil properties, management practices) and biotic (plant functional group composition, vegetation characteristics, soil fauna abundance) predictors and feeding activity of soil fauna after accounting for sample year and study region. Our study was carried out over a period of two consecutive years in 92 agricultural grasslands in three regions of Germany, spanning a latitudinal gradient of more than 500 km. A structural equation model suggests that feeding activity of soil fauna as measured by the bait-lamina test was positively related to legume and grass species richness in both years. Most probably, a diverse vegetation promotes feeding activity of soil fauna via alterations of both microclimate and resource availability. Feeding activity of soil fauna also increased with earthworm biomass via a pathway over Collembola abundance. The effect of earthworms on the feeding activity in soil may be attributed to their important role as ecosystem engineers. As no additional effects of agricultural management such as fertilization, livestock density or number of cuts on bait consumption were observed, our results suggest that the positive effect of legume and grass species richness on the feeding activity in soil fauna is a general one that will not be overruled by regional differences in management or environmental conditions. We thus suggest that agri-environment schemes aiming at the protection of belowground activity and associated ecosystem functions in temperate grasslands may generally focus on maintaining plant diversity, especially with regard to the potential effects of climate change on future vegetation structure.
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