101 research outputs found
Effects of habitat isolation and predation pressure on an arboreal food-web
No full textHabitat isolation is expected to reduce population densities of animals via reduced immigration. However, altered trophic interactions in isolated habitats may modify these effects, especially since the strength of isolation effects is expected to increase with trophic rank. Here, we studied effects of habitat isolation on a food-web module consisting of herbivorous beetles, predatory spiders, spider-preying wasps and arthropod-feeding birds. We compare two systems that were studied in subsequent years: a study on 29 mature apple orchards that varied in the degree of isolation from forest, and a study on 20 groups of newly planted cherry trees that showed similar variation in their degree of habitat isolation. No birds were observed on the young fruit trees. Wasps and spiders showed the expected lower abundances in isolated habitats. On mature trees, birds were present and showed lower abundances in isolated habitats. Wasps were reduced to a similar degree by habitat isolation as on the young trees. Surprisingly, spider densities on the mature trees were higher in isolated than in connected habitat. This contrasting response of spiders to habitat isolation is likely to be due to release from bird predation in isolated mature orchards. In both study systems, beetles showed no significant effect of habitat isolation. Our results confirm that the sensitivity to fragmentation increases with trophic rank, and suggest that trophic interactions should receive more attention in fragmentation studies.Swiss National Science foundation [3100A0-114058
Positive effects of local and landscape features on predatory flies in European agricultural landscapes
No full textProvisioning of suitable habitats for predatory insects in agricultural landscapes can improve natural pest control and hence the sustainability of agriculture. Apart from Syrphidae, the spatial ecology of predatory flies remains little studied. We investigated the response of Dolichopodidae, Empididae and Syrphidae to local features of seminatural habitats and to the composition of the surrounding landscape. We sampled adult predatory flies with pan traps in 183 field-bordering seminatural habitats along gradients of landscape composition in Italy, Germany and Switzerland. Local habitat type, the composition of the surrounding landscape and proximity to watercourses affected the abundance of predatory flies. Across countries, Empididae and Syrphidae were more abundant in woody (i.e. forests and in particular hedgerows) than in herbaceous habitats, whereas Dolichopodidae had lowest abundance in forests. The abundance of Dolichopodidae in Italy and Empididae in Germany were furthermore enhanced by the proximity of watercourses. Abundance of Dolichopodidae increased with the proportion of seminatural habitats in 1 km radius. Empididae were more abundant in landscapes with higher proportion of forests. We identified hedgerows as favorable habitats for predatory flies in agricultural landscapes. Moreover, our study reveals the importance of proximity to watercourses, which has rarely been considered when studying natural enemies of pests in agroecosystems. The varying responses indicate that preserving or restoring habitat-diverse, heterogeneous landscapes guarantees high numbers of predatory flies across families
Structure, function and management of semi-natural habitats for conservation biological control : A review of European studies
No full textDifferent semi-natural habitats occur on farmland, and it is the vegetation's traits and structure that subsequently determine their ability to support natural enemies and their associated contribution to conservation biocontrol. New habitats can be created and existing ones improved with agri-environment scheme funding in all EU member states. Understanding the contribution of each habitat type can aid the development of conservation control strategies. Here we review the extent to which the predominant habitat types in Europe support natural enemies, whether this results in enhanced natural enemy densities in the adjacent crop and whether this leads to reduced pest densities. Considerable variation exists in the available information for the different habitat types and trophic levels. Natural enemies within each habitat were the most studied, with less information on whether they were enhanced in adjacent fields, while their impact on pests was rarely investigated. Most information was available for woody and herbaceous linear habitats, yet not for woodland which can be the most common semi-natural habitat in many regions. While the management and design of habitats offer potential to stimulate conservation biocontrol, we also identified knowledge gaps. A better understanding of the relationship between resource availability and arthropod communities across habitat types, the spatiotemporal distribution of resources in the landscape and interactions with other factors that play a role in pest regulation could contribute to an informed management of semi-natural habitats for biocontrol.</p
Species richness-environment relationships of European arthropods at two spatial grains: habitats and countries
No full textWe study how species richness of arthropods relates to theories concerning net primary productivity, ambient energy, water-energy dynamics and spatial environmental heterogeneity. We use two datasets of arthropod richness with similar spatial extents (Scandinavia to Mediterranean), but contrasting spatial grain (local habitat and country). Samples of ground-dwelling spiders, beetles, bugs and ants were collected from 32 paired habitats at 16 locations across Europe. Species richness of these taxonomic groups was also determined for 25 European countries based on the Fauna Europaea database. We tested effects of net primary productivity (NPP), annual mean temperature (T), annual rainfall (R) and potential evapotranspiration of the coldest month (PETmin) on species richness and turnover. Spatial environmental heterogeneity within countries was considered by including the ranges of NPP, T, R and PETmin. At the local habitat grain, relationships between species richness and environmental variables differed strongly between taxa and trophic groups. However, species turnover across locations was strongly correlated with differences in T. At the country grain, species richness was significantly correlated with environmental variables from all four theories. In particular, species richness within countries increased strongly with spatial heterogeneity in T. The importance of spatial heterogeneity in T for both species turnover across locations and for species richness within countries suggests that the temperature niche is an important determinant of arthropod diversity. We suggest that, unless climatic heterogeneity is constant across sampling units, coarse-grained studies should always account for environmental heterogeneity as a predictor of arthropod species richness, just as studies with variable area of sampling units routinely consider area
Correction: Approaches to identify the value of seminatural habitats for conservation biological control
No full textWe would like to change the authors’ names and email addresses on page 195 of paper [1] from: John M. Holland 1,*, Philippe Jeanneret 2, Anna-Camilla Moonen 3, Wopke van der Werf 4, Walter A.H. Rossing 5, Daniele Antichi 6, Martin H. Entling 7, Brice Giffard 8, Herman Helsen 9, Mark Szalai 10, Carlo Rega 11, Caroline Gibert 12 and Eve Veromann 13 1 Farmland Ecology Unit, Game and Wildlife Conservation Trust, Fordingbridge SP6 1EF, UK 2 Agroecology and Environment, Agroscope, CH-8046 Zurich, Switzerland; [email protected] 3 Scuola Superiore Sant’Anna, Agroecology Group, Institute of Life Sciences, Via Santa Cecilia 3, 56127 Pisa, Italy; [email protected] 4 Wageningen University & Research, Crop Systems Analysis, Droevendaalsesteeg 1, 6708PBWageningen, The Netherlands; [email protected]
Disentangling multiple drivers of pollination in a landscape-scale experiment
No full textAnimal pollination is essential for the reproductive success of many wild and crop plants. Loss and isolation of (semi-)natural habitats in agricultural landscapes can cause declines of plants and pollinators and endanger pollination services.We investigated the independent effects of these drivers on pollination of young cherry trees in a landscape-scale experiment. We included (i) isolation of study trees from other cherry trees (up to 350 m), (ii) the amount of cherry trees in the landscape, (iii) the isolation from other woody habitats (up to 200 m) and (iv) the amount of woody habitats providing nesting and floral resources for pollinators. At the local scale, we considered effects of (v) cherry flower density and (vi) heterospecific flower density. Pollinators visited flowers more often in landscapes with high amount of woody habitat and at sites with lower isolation from the next cherry tree. Fruit set was reduced by isolation from the next cherry tree and by a high local density of heterospecific flowers but did not directly depend on pollinator visitation. These results reveal the importance of considering the plant’s need for con-specific pollen and its pollen competition with co-flowering species rather than focusing only on pollinators’ habitat requirements and flower visita-tion. It proved to be important to disentangle habitat isolation from habitat loss, local from landscape-scale effects, and direct effects of pollen availability on fruit set from indirect effects via pollinator visitation to understand the delivery of an agriculturally important ecosystem service
Moderate pollination limitation in some entomophilous crops of Europe (article)
No full textThis is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordThe dataset associated with this article is available in ORE at: https://doi.org/10.24378/exe.2463Pollination services to crops may be worsening because of declines in farmland pollinators, but the consequences for yields have been uncertain. We therefore investigated pollination limitation in four entomophilous crops (oilseed rape, sunflower, pears and pumpkin) by quantifying the difference in harvestable mass between open-pollinated and saturation-pollinated (hand-pollinated) flowers. We also examined whether pollination limitation in the four crops was associated with the number of flower visits by insects. Across 105 commercial fields in six European countries, the average decrease in harvestable mass due to pollination limitation was 2.8 % (SE = 1.15). Among crops, the highest decreases were in sunflowers (8%) and in one of three oilseed rape production regions (6%). We observed substantial variation among crops in the numbers of insect visits received by flowers, but it did not significantly correspond with the levels of pollination limitation. Our results suggest that yields in these crops were not severely pollination-limited in the regions studied and that other factors besides visitation by pollinators influenced the degree of pollination limitation.European Union FP
Bees increase seed set of wild plants while the proportion of arable land has a variable effect on pollination in European agricultural landscapes
No full textBackground and aims – Agricultural intensification and loss of farmland heterogeneity have contributed to population declines of wild bees and other pollinators, which may have caused subsequent declines in insect-pollinated wild plants. Material and methods – Using data from 37 studies on 22 pollinator-dependent wild plant species across Europe, we investigated whether flower visitation and seed set of insect-pollinated plants decline with an increasing proportion of arable land within 1 km. Key results – Seed set increased with increasing flower visitation by bees, most of which were wild bees, but not with increasing flower visitation by other insects. Increasing proportion of arable land had a strongly variable effect on seed set and flower visitation by bees across studies. Conclusion – Factors such as landscape configuration, local habitat quality, and temporally changing resource availability (e.g. due to mass-flowering crops or honey bee hives) could have modified the effect of arable land on pollination. While our results highlight that the persistence of wild bees is crucial to maintain plant diversity, we also show that pollen limitation due to declining bee populations in homogenized agricultural landscapes is not a universal driver causing parallel losses of bees and insect-pollinated plants.Background and aims – Agricultural intensification and loss of farmland heterogeneity have contributed to population declines of wild bees and other pollinators, which may have caused subsequent declines in insect-pollinated wild plants. Material and methods – Using data from 37 studies on 22 pollinator-dependent wild plant species across Europe, we investigated whether flower visitation and seed set of insect-pollinated plants decline with an increasing proportion of arable land within 1 km. Key results – Seed set increased with increasing flower visitation by bees, most of which were wild bees, but not with increasing flower visitation by other insects. Increasing proportion of arable land had a strongly variable effect on seed set and flower visitation by bees across studies. Conclusion – Factors such as landscape configuration, local habitat quality, and temporally changing resource availability (e.g. due to mass-flowering crops or honey bee hives) could have modified the effect of arable land on pollination. While our results highlight that the persistence of wild bees is crucial to maintain plant diversity, we also show that pollen limitation due to declining bee populations in homogenized agricultural landscapes is not a universal driver causing parallel losses of bees and insect-pollinated plants
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