1,720,985 research outputs found
Pests and pest controlling organisms across tropical agroecological landscapes in relation to forest and tree-cover
No full textA 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clear effect of complexityon the top-down effect of birds.At the time of the doctoral defence the following papers were unpublished and had a status as follows: Paper 1: Manuscript; Paper 3: Manuscript; Paper 4: Manuscript</p
Pattern of crop raiding by wild large mammals and the resultant impacts vary with distances from forests in southwest Ethiopia
No full textCrop raiding is a major form of human-wildlife interaction mainly in the ecotone areas of human-modified-natural landscapes. The aim of this study was to examine the spatial pattern of crop raiding and the resultant impacts on how farmers perceive forests at different distances from Yayu Coffee Forest Biosphere Reserve which is located in southwest Ethiopia. For this, thirty transects (each 1km long) were laid out at 200m interval parallel to forest edges: ten transects close to forest (1km). Along each transect 2-6 households were randomly selected and interviewed using semi-structured questionnaire. The perception of the respondents on forests at different distances from forest edges was analyzed using Pearson's Chi-square test. The variation in the amount of damage among these three locations was tested using one-way ANOVA. Four wild large mammals including; olive baboon, vervet monkey, bush pigs and crested porcupine were identified as top crop raiders in the area. The frequencies of occurrence of crop raiders decreased with increasing distance from forest edges. Similarly, the amount of damage in maize fields was higher close to forests when compared with that of either at intermediate or far from forest edges (P1km) in similar method used by Lemessa et al. (2013). By walking along each transect in zigzag way turning right and left, the households were randomly selected for questionnaire survey. Accordingly, from each three locations from forest edges (i.e., 48 households close to, 38 intermediate and 38 far away from forest households) or 2-6 households from each thirty transects and in total 124 households were interviewed using semi-structured questionnaire. This household level interview was executed during the crop growing and maturity seasons from February 1st to 30 July 2019.
The major data collected were the type of crop raiders and the frequency of occurrences per year, crop species liable to be raided, extent of crop damage and how the households perceive the about the Yayu Coffee Forest. The scientific names of the large mammals were identified using field guide of large mammals of Africa after their local or common names in Afaan Oromo were collected during the questioner survey ((Stuart, 2006). Moreover, after the maize crop was identified as the most liable to crop raiding, one maize field of each of 22, 21 and 21 households used for questionnaire survey were respectively selected from the three locations close to forest, intermediate and far away from forest edge at random to estimate the extent of crop raiding. Correspondingly, four permanent plots (size: 4´4m each) were randomly established in each of the 64 maize sown fields of the households (0.5ha each on average) in March 2019 and at the maturity stage the number of damaged stems due to crop raiding were recorded in July, 2019. Moreover, the amount of annual yield loss estimated by respondents was compared with the yield loss we computed based on the secondary data of the average annual yield of maize from Yayu District Agricultural Development Office of the study area (YDADO, 2019). Here, the percent of annual yield loss due to crop raiding was calculated in percent from the difference between the amount of annual maize yield from the field survey (actual yield of maize) and average annual yield of maize obtained from YDADO
Crop pests and Natural Enemies in Agricultural Landscapes in Relation to Spatial Heterogeneity of Wild Trees and Forests
No full textThe conversion of natural habitat for human use such as, agricultural intensification and others cause the simplification of landscape and loss of biodiversity. The fragmentation of landscape may influence the ecological functions like trophic cascades or predator-prey-primary producer interactions either directly or indirectly. This paper presents the review of the major theories in population regulation, island biogeography, and general concepts in brief and some reports of research findings in trophic cascades, population dynamics of natural enemies in agricultural landscape in both temperate and tropical contexts. The result of the review indicated that the heterogeneity of agricultural landscape (e.g. from simple crop habitat to complex natural habitat) determines not only the cross-edge spillover but also affects the magnitude (abundance), direction of flow and diversity of natural enemies and crop pests. As a result, the efficiency of natural regulation of crop pests in top-down and bottom-up processes may vary accordingly. Nevertheless, from the literature I have assessed, I would suggest that further empirical research is needed to get a comprehensive understanding concerning the relationship between natural pest regulation functions (top-down and bottom-up mechanisms) and crop pests in agroecosystem both at local and regional scales. This suggestion may be vital mainly in tropical regions context where the high biodiversity is declining rapidly on one hand and where little information is currently available on the other verge
Haulm Forage Value of Lentil Varieties in Central Ethiopia
Get PDFThe major livestock feed next to natural pasture in central highlands of Ethiopia is cereal crop residue; however, supplementation with additional nutritional entities is most often recommended. The present study aims to examine the nutritive value of lentil haulm and how this value varies among the varieties and locations. For this, 80gms of haulm samples of Alemaya, Derash and local lentil varieties were collected with four replications from Bishoftu, Akaki, and Chefe-Donsa from on farm trial sites of Ethiopian institute of agricultural research. To test for the variation in haulm nutritional values among the varieties, two-way ANOVA was employed. The results showed that the interaction of variety and location had significant effect on crude protein (CP), neutral detergent fiber (NDF), metabolizable energy (ME) and in vitro organic matter digestibility (IVOMD) (P<0.05). Here, CP content of lentil haulm was higher for a local variety when compared with the two commercial varieties. The haulm yield (4.38t/ha) and haulm dry matter yield (3.97 t DM/ha) were higher for Derash when compared with that of the local variety (P<0.05). Overall, the present finding denoted that although in some cases the lentil haulm nutritional values and yields vary among varieties and were dependent on growing locations, it can be observed to have optimum feeding values to supplement livestock feed with the cereal crop residues in central Ethiopia
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Birds and arthropod predation on plasticine caterpillars across tropical agricultural landscapes
No full textVariations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The effect of local and landscape level land-use composition on predatory arthropods in a tropical agricultural landscape
No full textIt 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.</p
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