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Pests and pest controlling organisms across tropical agroecological landscapes in relation to forest and tree-cover
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
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 [en]
activity abundance, crop raiding, exclosure experiment, homegarden, leaf damage, predation, spatial scales, structural complexity
National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-102849ISBN: 978-91-7447-881-5 (print)OAI: oai:DiVA.org:su-102849DiVA: diva2:713678
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
List of papers
1. Birds and arthropod predation on plasticine caterpillars across tropical agricultural landscapes
Open this publication in new window or tab >>Birds and arthropod predation on plasticine caterpillars across tropical agricultural landscapes
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-102863 (URN)
Available from: 2014-04-23 Created: 2014-04-23 Last updated: 2014-04-24
2. Composition of crops and land-use types in relation to crop raiding pattern at different distances from forests
Open this publication in new window or tab >>Composition of crops and land-use types in relation to crop raiding pattern at different distances from forests
2013 (English)In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 167, 71-78 p.Article in journal (Refereed) Published
Abstract [en]

Among the issues that farmers need to account for when planning their land-use and crop choice is yield loss from wild animals. The aim of this study was to examine both the distribution of land-use types and crops (in fields and homegardens) in relation to distance from forest edges and the possible impact of crop raiding mammals. Thirty transects of 1 km in length were laid out in a pair-wise design - 15 close to (<= 0.3 km) and 15 far from (1-3.5 km) forest edges. We measured the cover of the land-use types and field crops in each transect and assessed crop species composition in 4-6 homegardens along each transect. We also conducted a questionnaire survey for the occurrence of baboons and bush pigs in maize fields and in homegardens. Our results indicated that the distribution of land-use types and field crops was not significantly different between sites close to and far from forest edges. Similarly, the distributions of field and homegarden crop species composition were also similar between these locations. The occurrence pattern of baboons and bush pigs coming to the fields and homegardens was however strongly inclined toward transects close to forest edges according to the answers from the farmers. Although crops, such as maize, sorghum, tuber and root crops are frequently attacked by either baboons or pigs or both, farmers apparently did not stop growing these crops. The major reasons for this lack of response in growing practices between sites close to and far from forests could either be a perceived lack of alternative less susceptible crops or that farmers have adapted different protection mechanisms for the problem to be manageable. Both ecological and socio-economic studies are needed in order to understand the variation (and sometimes lack of variation) of ecosystem properties and corresponding management practices across landscapes.

Keyword
Afromontane forest, Ecotone, Homegarden, Pest, Primate, Species composition
National Category
Agricultural Sciences Ecology Environmental Sciences
Identifiers
urn:nbn:se:su:diva-90007 (URN)10.1016/j.agee.2012.12.014 (DOI)000317326700009 ()
Funder
Sida - Swedish International Development Cooperation Agency, SWE-2009-134Formas, 229-2009-991
Note

AuthorCount:3;

Available from: 2013-05-20 Created: 2013-05-20 Last updated: 2017-12-06Bibliographically approved
3. The effect of local and landscape level land-use composition on predatory arthropods in a tropical agricultural landscape
Open this publication in new window or tab >>The effect of local and landscape level land-use composition on predatory arthropods in a tropical agricultural landscape
2015 (English)In: Landscape Ecology, ISSN 0921-2973, E-ISSN 1572-9761, Vol. 30, no 1, 167-180 p.Article in journal (Refereed) Published
Abstract [en]

It has been suggested that the composition of different non-crop land-use types along with tree density regulate local biodiversity in agricultural landscapes. However, specific data is limited, not least from tropical regions. We examined how different land-use types and forest cover at different scales influenced the abundance and species composition of predatory arthropods in 40 homegardens of southwest Ethiopia. We collected specimens using pitfall traps during two separate months and related sample composition to land-use in the vicinity (1 ha plot, local scale, field data) and tree cover within 200 and 500 m radius zones (landscape scale, satellite data). Spiders, beetles and ants were most common. A high abundance of ants was found in tree-rich homegardens while the variation in abundance of spiders was best explained by the interaction between tree cover at the local and landscape scales. The highest spider abundances were found when either the homegarden or the surroundings had high tree-cover and was lower in both the most tree-rich and tree-poor landscape-garden combinations. In addition, open non-crop cover (mostly grasslands) and ensete (a banana-like perennial crop) favored spiders. This pattern demonstrates that different land-use types at different scales can interact to create variations in biodiversity across an agricultural landscape. To enhance numbers of predatory arthropods in homegardens, which may be beneficial for natural pest control, our results suggest that different strategies are needed depending on the target group or species. Grasslands, ensete fields and tree-rich habitats seem to play important roles.

Keyword
Ant, Activity abundance, Beetle, Species composition, Spider, Tropics
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-113699 (URN)10.1007/s10980-014-0115-y (DOI)000347284600013 ()
Note

AuthorCount:3;

Available from: 2015-03-18 Created: 2015-02-09 Last updated: 2017-12-04Bibliographically approved
4. Tree cover mediates the effect on rapeseed leaf damage of excluding predatory arthropods, but in an unexpected way
Open this publication in new window or tab >>Tree cover mediates the effect on rapeseed leaf damage of excluding predatory arthropods, but in an unexpected way
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.

Keyword
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:nbn:se:su:diva-122232 (URN)10.1016/j.agee.2015.05.009 (DOI)000362049800008 ()
Available from: 2015-11-03 Created: 2015-10-28 Last updated: 2017-12-01Bibliographically approved

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