| 1. |
- Riggi, Laura, et al.
(författare)
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Early-season mass-flowering crop cover dilutes wild bee abundance and species richness in temperate regions : A quantitative synthesis
- 2024
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Ingår i: Journal of Applied Ecology. - 0021-8901 .- 1365-2664. ; 61:3, s. 452-464
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Tidskriftsartikel (refereegranskat)abstract
- Pollinators benefit from increasing floral resources in agricultural landscapes, which could be an underexplored co-benefit of mass-flowering crop cultivation. However, the impacts of mass-flowering crops on pollinator communities are complex and appear to be context-dependent, mediated by factors such as crop flowering time and the availability of other flower resources in the landscape. A synthesis of research is needed to develop management recommendations for effective pollinator conservation in agroecosystems. By combining 22 datasets from 13 publications conducted in nine temperate countries (20 European, 2 North American), we investigated if mass-flowering crop flowering time (early or late season), bloom state (during or after crop flowering) and extent of non-crop habitat cover in the landscape moderated the effect of mass-flowering crop cover on wild pollinator abundance and species richness in mass-flowering crop and non-crop habitats. During bloom, wild bee abundance and richness are negatively related to mass-flowering crop cover. Dilution effects were predominant in crop habitats and early in the season, except for bumblebees, which declined with mass-flowering crop cover irrespective of habitat or season. Late in the season and in non-crop habitats, several of these negative relationships were either absent or reversed. Late-season mass-flowering crop cover is positively related to honeybee abundance in crop habitats and to other bee abundance in non-crop habitats. These results indicate that crop-adapted species, like honeybees, move to forage and concentrate on late-season mass-flowering crops at a time when flower availability in the landscape is limited, potentially alleviating competition for flower resources in non-crop habitats. We found no evidence of pollinators moving from mass-flowering crop to non-crop habitats after crop bloom. Synthesis and applications: Our results confirm that increasing early-season mass-flowering crop cover dilutes wild pollinators in crop habitats during bloom. We find that dilution effects were absent late in the season. While mass-flowering crop cultivation alone is unlikely to be sufficient for maintaining pollinators, as part of carefully designed diverse crop rotations or mixtures combined with the preservation of permanent non-crop habitats, it might provide valuable supplementary food resources for pollinators in temperate agroecosystems, particularly later in the season when alternative flower resources are scarce.
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| 2. |
- Aguilera Nuñez, Guillermo, et al.
(författare)
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Organic fertilisation enhances generalist predators and suppresses aphid growth in the absence of specialist predators
- 2021
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Ingår i: Journal of Applied Ecology. - : Wiley. - 0021-8901 .- 1365-2664. ; 58, s. 1455-1465
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Tidskriftsartikel (refereegranskat)abstract
- Biological control by natural enemies is a valuable ecosystem service. The predator community in a crop field is a combination of predators dwelling in the field and those moving into it from the surrounding landscape. The former is mainly affected by field management, the latter more by the composition of the surrounding landscape. Yet, separate and combined effects of local and landscape management on pest suppression have seldom been investigated.We set-up mesocosms within an existing long-term agricultural field experiment to investigate the effects of local management of organic manure or inorganic mineral fertilisation, and simulated the spillover from the surrounding landscape of different predator types: no predators, generalist predators (wolf spiders) and specialist predators (ladybirds). We examined whether aphid density was driven by top-down or bottom-up processes under different fertilisation treatments, and how the magnitude of pest suppression was affected by predator community composition.We found positive synergistic effects between manure fertilisation and predator spillover on the suppression of aphid growth. Top-down suppression of aphids was more effective under manure fertilisation and in presence of specialist predators (ladybirds). Bottom-up effects on the plant biomass growth dominated in inorganically fertilised plots.Organic and inorganic fertilisation gave the same yield, but through different mechanisms. The abundance of locally emerging predators in the manure treatment increased top-down pest suppression yielding plant biomass levels comparable with inorganically fertilised plants, being the latter driven by bottom-up effects.Synthesis and applications. Organic fertilisation enhanced local emergence of predators increasing top-down pest suppression. In contrast, local predator communities were unable to suppress aphid populations in inorganic and no fertilisation treatments. Here, predator inflow from outside the crop field was essential for lowering aphid population growth. Managing landscapes to promote mobile predators emerges as particularly important for crop fields without manure amendments. We advise the active promotion of both local predators in the crop field and mobile predators in the landscape to secure the conservation of biological insect pest suppression.
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| 3. |
- Riggi, Laura, et al.
(författare)
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Subsidy type and quality determine direction and strength of trophic cascades in arthropod food webs in agroecosystems
- 2019
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Ingår i: Journal of Applied Ecology. - : Wiley. - 0021-8901 .- 1365-2664. ; 56, s. 1982-1991
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Tidskriftsartikel (refereegranskat)abstract
- The subsidy hypothesis states that communities receiving nutrient subsidies will demonstrate top-down trophic cascades where predators indirectly increase plant biomass. This has been both confirmed and refuted, which might depend on whether the subsidy has mainly targeted the plant or the detrital food web compartment, and on the subsidy quality. This is particularly poorly understood for terrestrial communities such as heavily subsidized agroecosystems. Using cages covering 4 m(2) of ground in a long-term agricultural fertilization experiment, we tested whether subsidies targeting the detrital soil mesofauna compartment with organic fertilizers, or the plants with mineral fertilizer, impacted the direction and strength of trophic cascades in an arthropod-plant food web. We expected top-down controls of generalist arthropod predators (spiders, ground and rove beetles) on aphid densities to be stronger in organically fertilized plots due to enhanced alternative prey availability in the soil. Bottom-up control from barley quality on aphids was anticipated to be stronger in the mineral treatments. We examined how the quality (decomposability) of the organic subsidy governed the cascades by comparing treatments with labile (manure) and recalcitrant (hay) organic matter. Top-down forces dominated in food webs receiving organic subsidies, while bottom-up forces dominated under mineral fertilization. A high-quality, easily degradable organic subsidy propagated faster through the food chain, leading to a top-down trophic cascade with generalist predators having a positive effect on plant biomass in the labile but not in the recalcitrant organic treatment. Synthesis and applications. Management of agricultural soils that bolster the soil mesofauna, for example adding organic fertilizers, has potential to increase top-down biological control by naturally occurring generalist arthropod predators. Our research demonstrates how barley biomass can be enhanced in manure treatment in the presence of arthropod predators to a level comparable to that of mineral fertilizer.
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