Browsing by Subject "Agrarwissenschaft"

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Agent-based modeling of climate change adaptation in agriculture : a case study in the Central Swabian Jura
(2014) Troost, Christian; Berger, Thomas
Using the MPMAS multi-agent software, the present thesis implements an agro-economic agent-based model to analyze climate change adaptation of agricultural production in the Central Swabian Jura. It contributes to the DFG PAK 346 FOR 1695 research projects dedicated to improve the understanding of processes that shape structure and functions of agricultural landscapes in the context of climate change at regional scale. In the context of this example, this thesis discusses, develops and tests novel approaches to deal with four notorious challenges that have so far hampered the empirical use of agent-based models for applied economic analysis: data availability, process uncertainty, model validity and computational requirements. The model is used to examine climatic effects on agriculture, changes in agricultural price responses and biogas support and agri-environmental policies illustrating the applicability of the model to adaptation analysis. The first part of the thesis is dedicated to a methodological discussion of the use of mathematical programming-based multi-agent systems, such as MPMAS, for the analysis of agricultural adaptation to climate change. It synthesizes knowledge about the potential impacts of climate change and processes of farmer adaptation and reviews existing agent-based models for their potential contribution to adaptation analysis. The major focus of the first part is a discussion of available approaches to model validation, calibration and uncertainty analysis and their suitability for the use with mathematical programming-based agent-based models. This discussion is based on four principles required to ensure the validity of conclusions drawn from modeling studies: (i) a transparent model documentation, (ii) that the invariant elements of the model can really be expected to be invariant between scenarios assessed, (iii) that empirical calibration of the model is limited to the extent warranted by available observation and knowledge about the expected error distribution, and (iv) that the effect of process uncertainty on the conclusions is evaluated and communicated. Based on these conclusions, generic extensions of the MPMAS toolbox are developed to allow the application of suitable approaches for validation and uncertainty analysis. The second part of the thesis describes the application of the newly developed methodology in the construction and use of the Central Swabian Jura model. The model focuses on an endogenous representation of heterogeneity in agent behavior, an empirical parameterization of the model, and an incorporation of climate effects on possible crop rotations and suitable days for field work besides the expected effects on yields. It extends the demographic, investment and land market components of MPMAS to improve the simulation of structural change over time. The model was used to analyze potential effects of climate change adaptation on agricultural production and land use in the study area. The results show that besides effects on yields also other climate change-induced effects on the conditions of agricultural production may have important impacts on land use decisions of farmers and deserve more attention in climate change impact analysis. Potential impacts of changes in the time slots suitable for field work and an additional rotation option are predicted to be comparable to the impact of the changes in yields predicted by a crop growth model. Results point to an expansion of wheat and silage maize areas at the expense of barley areas. The partial crowding out of summer barley by wheat area held for current price relations and is less strong at higher relative prices for summer barley. Price response analysis indicated that winter wheat production enters into a substitutive relationship with summer barley production under climate change conditions, while competition with winter barley area diminishes. This leads also to a higher elasticity of the wheat area with respect to relative summer barley prices. The model was then used to analyze biogas support through the Renewable Energy Act (EEG) and the support for grassland extensification and crop rotation diversification through the MEKA scheme. Especially simulated participation in crop rotation diversification is strongly reduced in the climate change scenarios, while the investments in biogas plants are slightly increased. The conditions established by the latest EEG revision imply that further development of biogas capacity will crucially depend on the existence of demand for excess process heat, because the alternative option of using high manure shares seems to be rather unattractive for farmers in the area according to the simulation results.
Selection methods for local breeds with historical introgression
(2018) Wang, Yu; Bennewitz, Jörn
For the management of local breeds with historical introgression, both genetic gain and the long-term evolution of genetic variability have to be taken into consideration. Traditional optimum contribution selection (traditional OCS) aims at maximizing genetic gain while controlling the rate of inbreeding by optimizing the genetic contribution of each selection candidate to the next generation. It is also a promising approach to maintain genetic diversity since the average kinship of selection candidates is restricted. However, for the breeds with historical introgression, this diversity may be caused by introducing genetic material from other breeds, which can be a risk of the conservation of small local populations. Therefore, the breeding objectives should not only focus on increasing genetic gain but also on maintaining the diversity of native alleles. The main aim of this project was to resolve the existing conflicts in the current breeding program of local breeds with historical introgression. Chapter 1 gave a brief introduction and background of the topic and formulated the objective of the thesis. In chapter 2, the current inbreeding status of German Angler cattle was evaluated based on both pedigree (F_PED) and genomic information. The genomic inbreeding coefficients of 182 Angler cattle were estimated via analyzing the genome proportion of run of homozygosity (F_ROH) and using the genomic relationship matrix (F_GRM). On average, the inbreeding level of Angler is relatively low compared to the other breeds ((F_PED ) ̅:0.013;(F_GRM ) ̅:-0.015; (F_(ROH>1Mb) ) ̅:0.031). Moderate to strong correlations (0.607–0.702) were found between F_PED and F_ROH based on different length categories of ROH segments. Moreover, it proved that F_ROH is a robust estimating method owing to its ability to capture both ancient and recent inbreeding. Although traditional OCS may achieve higher genetic gain with the restriction of the defined rate of inbreeding, in this case, inbreeding is not the main problem in the current breeding program and the advantage of OCS may be limited since the level of inbreeding may be lower than the threshold. In chapter 3, we developed the advanced optimum contribution selection strategy by considering migrant contribution and conditional kinship at native alleles in the OCS procedure. Different scenarios were compared for both functions of production and conservation based on pedigree information. It has been proved that the advanced OCS approach can effectively maintain the diversity of native alleles and genetic originality while ensuring genetic improvement with appropriate settings of constraint values. The availability of high-density single-nucleotide polymorphism (SNP) markers provides a solution for achieving accurate estimates of both coancestry and breed composition. In chapter 4 and chapter 5, we evaluated the long-term performance of advanced OCS strategies in both production and conservation function via simulating several subsequent generations based on genomic information. In chapter 4, we found that traditional OCS procedure has slight advantages in increasing genetic gain whilst controlling relatedness compared to truncation selection. However, the introgression of foreign genetic material by traditional OCS is not desirable in the local breed conservation. In the long run, constraining migrant contribution and kinship at native alleles in the OCS procedure is a promising approach to increase genetic gain whilst maintaining genetic uniqueness and diversity. Chapter 5 mimics a conservation program which aims at increasing the value of a breed for conservation by removing exogenous genetic material, maintaining within-breed genetic diversity, and increasing the genetic diversity among breeds. Simply minimizing the exogenous genetic contribution leads to the loss of both within and between population diversity. Moreover, the recovery process ended at a plateau after several generations. The best scenario was able to increase the native contribution from 0.317 to 0.706 before a segment-based kinship level of 0.10 was reached. This scenario maximized the native contribution, constrained the increase in kinship, and the increase in kinship at native alleles. Moreover, it constrained the mean kinship in a multi-breed core set to the current level, which is desirable for the conservation program. This thesis ends with a general discussion.