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Tree cover mediates the effect on rapeseed leaf damage of excluding predatory arthropods, but in an unexpected way
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Number of Authors: 4
2015 (English)In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 211, 57-64 p.Article in journal (Refereed) Published
Abstract [en]

Birds and predatory arthropods are often implicated in pest control, but their relative impact and how this is mediated by variation in tree cover requires elucidation. We excluded birds and ground predatory arthropods from rapeseed plants in 2.5 x 1 m plots in 26 homegardens in Ethiopia, leaving the same sized control plots. From six groups of plants in bird exclosure and control plots, respectively, three groups were excluded from ground predatory arthropods. Data on leaf damage were surveyed four times at weekly intervals. The tree cover and land-use composition within 100 x 100 m surrounding each plots were recorded in the field and from a satellite image within 200 and 500 m buffer zones. The results show that the mean leaf damage was higher on rapeseed plants from which predatory arthropods were excluded than on control plants. However, excluding birds had no or only a weak impact on leaf damage. The mean leaf damage within predatory arthropod exclosures decreased with increasing tree, forest and perennial cover but increased with increasing grazing land cover and annual crop cover, while on control plants it was low across the tree cover variation. This pattern may indicate the presence of a higher density of herbivores on rapeseed plants and also more predatory arthropods (i.e., to control them) in tree-poor homegardens compared to tree-rich homegardens. Hence, tree-poor homegardens in this landscape have sufficient habitat heterogeneity to support natural enemies to deliver significant pest control on rapeseed. Our results show that there was variation in the dynamics of pests and predatory arthropods across the tree cover variation, suggesting changes in landscape composition could affect the pest control services and the outcomes for local farmers.

Place, publisher, year, edition, pages
2015. Vol. 211, 57-64 p.
Keyword [en]
Agroecology, Exclosure experiment, Leaf damage, Spatial scales, Tree cover, Tropics
National Category
Agricultural Science, Forestry and Fisheries Biological Sciences Earth and Related Environmental Sciences
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-122232DOI: 10.1016/j.agee.2015.05.009ISI: 000362049800008OAI: oai:DiVA.org:su-122232DiVA: diva2:866633
Available from: 2015-11-03 Created: 2015-10-28 Last updated: 2017-12-01Bibliographically approved
In thesis
1. Pests and pest controlling organisms across tropical agroecological landscapes in relation to forest and tree-cover
Open this publication in new window or tab >>Pests and pest controlling organisms across tropical agroecological landscapes in relation to forest and tree-cover
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A major challenge in agroecosystems is how to manage the systems so that it reduces crop pests and enhances natural pest control. This thesis investigates patterns of crop pests and top-down effects of birds and arthropod predators in relation to land-use composition across spatial scales. In paper (I) I examined the crop distribution and land-use types in relation to the crop raiding patterns in 15 transectsin sites close to and far from forests along with a questionnaire survey at household level. I found severe crop raiding close to forests, but it had no impact on crop composition growing between the two sites. In paper (II) I examined the effect of forest and tree cover, at local and landscape scales, on the abundance of arthropod predators by collecting specimens from 40 home gardens. My result showed higher abundance of arthropod predators when either the home garden or the surroundings had a high tree-cover, compared to when tree-cover at both scales was similarly either high or low. In paper (III) I investigated the effect of excluding birds and arthropod predators on leaf damage on rape seed in 26 home gardens. I found stronger top-down impacts from arthropod predators on crop pests in tree-poor gardens than in tree-rich gardens. There was no effect of birds. In paper (IV) I explored the effect of landscape complexity on bird and arthropod predation using plasticine caterpillars in 36 home gardens across landscapes. The rate of arthropod predation on caterpillars was higher in simple than in complex landscapes. The rate of bird predation did not vary between complex and simple landscapes. In simple landscapes, arthropod predation was higher than that of birds. The overall results suggest that simplified gardens/landscapes still have enough habitat heterogeneity to support arthropod predators for the significant top-down controlling effect on crop pests. However, I did not find clear effect of complexityon the top-down effect of birds.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2014. 38 p.
Keyword
activity abundance, crop raiding, exclosure experiment, homegarden, leaf damage, predation, spatial scales, structural complexity
National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-102849 (URN)978-91-7447-881-5 (ISBN)
Public defence
2014-06-05, Lecture Hall, Lilla Frescativägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Sida - Swedish International Development Cooperation Agency, SWE-2009-134Swedish Research Council Formas, 229-2009-991
Note

At the time of the doctoral defence the following papers were unpublished and had a status as follows: Paper 1: Manuscript; Paper 3: Manuscript; Paper 4: Manuscript

Available from: 2014-05-14 Created: 2014-04-23 Last updated: 2016-02-03Bibliographically approved

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