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  • 1.
    Lemessa, Debissa
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Pests and pest controlling organisms across tropical agroecological landscapes in relation to forest and tree-cover2014Doktoravhandling, med artikler (Annet vitenskapelig)
    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.

  • 2.
    Lemessa, Debissa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Hambäck, Peter A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Hylander, Kristoffer
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    The effect of local and landscape level land-use composition on predatory arthropods in a tropical agricultural landscape2015Inngår i: Landscape Ecology, ISSN 0921-2973, E-ISSN 1572-9761, Vol. 30, nr 1, s. 167-180Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 3.
    Lemessa, Debissa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Hambäck, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Hylander, Kristoffer
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Birds and arthropod predation on plasticine caterpillars across tropical agricultural landscapesManuskript (preprint) (Annet vitenskapelig)
  • 4.
    Lemessa, Debissa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Hylander, Kristoffer
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Hambäck, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Composition of crops and land-use types in relation to crop raiding pattern at different distances from forests2013Inngår i: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 167, s. 71-78Artikkel i tidsskrift (Fagfellevurdert)
    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.

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