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Crop-noncrop spillover: arable fields affect trophic interactions on wild plants in surrounding habitats.

Gladbach DJ, Holzschuh A, Scherber C, Thies C, Dormann CF, Tscharntke T - Oecologia (2010)

Bottom Line: Parasitism rates were not related to landscape simplification, but benefited from increasing proportions of OSR.In contrast, rape pollen beetles benefited from simple landscape structures, presumably due to multi-annual population build-ups resulting from long-term OSR planting (as part of the crop rotation).In conclusion, we showed that spillover from cropland affects parasitism rates on related wild plants outside cropland, which has not been shown so far, but can be expected to be a widespread effect shaping noncrop food webs.

View Article: PubMed Central - PubMed

Affiliation: Agroecology, Department of Crop Science, Georg-August University Göttingen, Göttingen, Germany. david.gladbach@web.de

ABSTRACT
Ecosystem processes in agricultural landscapes are often triggered by resource availability in crop and noncrop habitats. We investigated how oilseed rape (OSR; Brassica napus, Brassicaceae) affects noncrop plants in managed systems and semi-natural habitat, using trophic interactions among wild mustard (Sinapis arvensis, Brassicaceae), rape pollen beetles (Meligethes aeneus, Nitidulidae) and their parasitoids (Tersilochus heterocerus, Ichneumonidae). We exposed wild mustard as phytometer plants in two cropland habitat types (wheat field, field margin) and three noncrop habitat types (fallow, grassland, wood margin) across eight landscapes along a gradient from simple to complex (quantified as % arable land). Both landscape and local factors affected the abundance of rape pollen beetles and parasitoids. Rape pollen beetle infestation and parasitism rates on these plants were lower in noncrop habitats and higher in wheat fields and field margins, whereas beetles and parasitoids responded differently to landscape scale parameters. We found the hypothesized spillover from OSR crop onto wild plants in surrounding habitats only for parasitoids, but not for pollen beetles. Parasitism rates were not related to landscape simplification, but benefited from increasing proportions of OSR. In contrast, rape pollen beetles benefited from simple landscape structures, presumably due to multi-annual population build-ups resulting from long-term OSR planting (as part of the crop rotation). In conclusion, we showed that spillover from cropland affects parasitism rates on related wild plants outside cropland, which has not been shown so far, but can be expected to be a widespread effect shaping noncrop food webs.

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Back-transformed data of parasitism rates as a function of percentage of oilseed rape crop area for each of the tested habitats. The lines represent model predictions of parasitism rates in each of the habitats. Parasitism rates were significantly higher in wheat fields and field margins (dashed lines) than in grassland, fallow and wood margins (solid lines). Lines of the same type do not differ significantly from each other. Also significant was the increase with OSR crop area
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Fig2: Back-transformed data of parasitism rates as a function of percentage of oilseed rape crop area for each of the tested habitats. The lines represent model predictions of parasitism rates in each of the habitats. Parasitism rates were significantly higher in wheat fields and field margins (dashed lines) than in grassland, fallow and wood margins (solid lines). Lines of the same type do not differ significantly from each other. Also significant was the increase with OSR crop area

Mentions: At the landscape scale, parasitism rates responded only to % OSR crop area (F1,23 = 13.06, p = 0.002; Figs. 2 and 3; Online Resource 5). Locally, host density, (i.e., larvae per flower; F1,23 = 6.84, p = 0.015) and habitat type (F4,21 = 2.88, p = 0.047) were significant predictors. Since these two factors correlated with each other, we calculated two different models, the design model with % OSR and habitat type (Fig. 2), and the model that included % OSR crop area and larvae per flower (Fig. 3). Parasitism rates increased more strongly with larval density if OSR crop area was high as shown by the interaction between both factors (F1,23 = 6.09, p = 0.022; Fig. 3). In landscapes with a low OSR crop area of 2%, parasitism was not observed, or only at rates below 10%. Parasitism rates by T. heterocerus increased with larvae per flower and increasing proportion of OSR crops (up to a maximum of 50%, Fig. 3).Fig. 2


Crop-noncrop spillover: arable fields affect trophic interactions on wild plants in surrounding habitats.

Gladbach DJ, Holzschuh A, Scherber C, Thies C, Dormann CF, Tscharntke T - Oecologia (2010)

Back-transformed data of parasitism rates as a function of percentage of oilseed rape crop area for each of the tested habitats. The lines represent model predictions of parasitism rates in each of the habitats. Parasitism rates were significantly higher in wheat fields and field margins (dashed lines) than in grassland, fallow and wood margins (solid lines). Lines of the same type do not differ significantly from each other. Also significant was the increase with OSR crop area
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3094532&req=5

Fig2: Back-transformed data of parasitism rates as a function of percentage of oilseed rape crop area for each of the tested habitats. The lines represent model predictions of parasitism rates in each of the habitats. Parasitism rates were significantly higher in wheat fields and field margins (dashed lines) than in grassland, fallow and wood margins (solid lines). Lines of the same type do not differ significantly from each other. Also significant was the increase with OSR crop area
Mentions: At the landscape scale, parasitism rates responded only to % OSR crop area (F1,23 = 13.06, p = 0.002; Figs. 2 and 3; Online Resource 5). Locally, host density, (i.e., larvae per flower; F1,23 = 6.84, p = 0.015) and habitat type (F4,21 = 2.88, p = 0.047) were significant predictors. Since these two factors correlated with each other, we calculated two different models, the design model with % OSR and habitat type (Fig. 2), and the model that included % OSR crop area and larvae per flower (Fig. 3). Parasitism rates increased more strongly with larval density if OSR crop area was high as shown by the interaction between both factors (F1,23 = 6.09, p = 0.022; Fig. 3). In landscapes with a low OSR crop area of 2%, parasitism was not observed, or only at rates below 10%. Parasitism rates by T. heterocerus increased with larvae per flower and increasing proportion of OSR crops (up to a maximum of 50%, Fig. 3).Fig. 2

Bottom Line: Parasitism rates were not related to landscape simplification, but benefited from increasing proportions of OSR.In contrast, rape pollen beetles benefited from simple landscape structures, presumably due to multi-annual population build-ups resulting from long-term OSR planting (as part of the crop rotation).In conclusion, we showed that spillover from cropland affects parasitism rates on related wild plants outside cropland, which has not been shown so far, but can be expected to be a widespread effect shaping noncrop food webs.

View Article: PubMed Central - PubMed

Affiliation: Agroecology, Department of Crop Science, Georg-August University Göttingen, Göttingen, Germany. david.gladbach@web.de

ABSTRACT
Ecosystem processes in agricultural landscapes are often triggered by resource availability in crop and noncrop habitats. We investigated how oilseed rape (OSR; Brassica napus, Brassicaceae) affects noncrop plants in managed systems and semi-natural habitat, using trophic interactions among wild mustard (Sinapis arvensis, Brassicaceae), rape pollen beetles (Meligethes aeneus, Nitidulidae) and their parasitoids (Tersilochus heterocerus, Ichneumonidae). We exposed wild mustard as phytometer plants in two cropland habitat types (wheat field, field margin) and three noncrop habitat types (fallow, grassland, wood margin) across eight landscapes along a gradient from simple to complex (quantified as % arable land). Both landscape and local factors affected the abundance of rape pollen beetles and parasitoids. Rape pollen beetle infestation and parasitism rates on these plants were lower in noncrop habitats and higher in wheat fields and field margins, whereas beetles and parasitoids responded differently to landscape scale parameters. We found the hypothesized spillover from OSR crop onto wild plants in surrounding habitats only for parasitoids, but not for pollen beetles. Parasitism rates were not related to landscape simplification, but benefited from increasing proportions of OSR. In contrast, rape pollen beetles benefited from simple landscape structures, presumably due to multi-annual population build-ups resulting from long-term OSR planting (as part of the crop rotation). In conclusion, we showed that spillover from cropland affects parasitism rates on related wild plants outside cropland, which has not been shown so far, but can be expected to be a widespread effect shaping noncrop food webs.

Show MeSH
Related in: MedlinePlus