Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
2003
Abstract
An individual-based agent model is presented which resembles aspects of natural evolution in ecosystems under selective pressure due to limited resources. The environmental conditions are determined by spatial and temporal variability of resource abundances.The agents have to choose between three different types of resources; the one consumed most during lifetime solely counts for the fitness of the individual agent. Simulation runs show that populations specialized in different resource types are mutually influencing each other under temporal variation of a single resource type.Mobility of agents in a locally heterogenous world enables recolonization after a population has starved to death. Wavelet analysis of the population time series reveals that some observed population dynamics show phenomena such as localized periodicities which cannot be explained by linear dependencies on the resource input dynamics.
Abstract
Modern information technology allows the investigation of the characteristic properties of living systems from a new perspective. Which of the ecosystem features are necessary conditions resulting from their constraints, which are accidental, constituting contingent facts of their respective histories?As long as we know of a single phylogenetic tree in nature, the difference is hard to tell, rendering the reconstruction and realisation of artificial ecologies a major challenge. It has been taken up by the high technology of the time since decades; since two decades, IT is leading in this respect.Are there life forms that can be created in contemporary computers, and which ones? Successes and failures of a number of virtualizations are forming de facto constraints for theoretical ecosystem research. Artificial Life (AL) research appears to be not just another attempt towards realistic models for ecological systems, but undermines the basic assumptions of most of conventional modeling in this area: in AL, behavior is in general irreducible to internal mechanisms; behavior results rather from interactive and intentional usage of the simulation.We try to elucidate and demonstrate the crucial role of interaction in these simulations, drawing from current developments in theoretical computer science as well as a number of examples. We propose a new classification of ecosystem models according to its degree of interactivity.
Authors
Anne Kjersti Bakken Ragnar Eltun Trond Haraldsen Tor Arvid Breland Trygve S. Aamlid Tore SveistrupAbstract
The three organic cropping systems Landvik (in Grimstad), Voll (at Ås) and Kvithamar (in Stjørdal) were established in 1993 on previously conventionally farmed soils of marine origin. The six-year crop rotation at Landvik was designed for an organic stockless farm producing cash crops. These crops were fertilized with composted organic household waste from the nearby community (maximum 100 kg N ha-1) and composted waste from the system itself. The rotation at Voll was designed for an arable farm withbeef production from suckling cows (0.9 animal units ha-1), and the rotation at Kvithamar was designed for a dairy cattle farm (1.0 animal unit ha-1). During the first six years of organic farming, the soil reserves of K were slightly depleted. The nutrient balance was –250 kg K ha-1 at Voll and –420 kg K ha-1 at Landvik, and the content of easily soluble K in the plough layer decreased at these sites. At Kvithamar, however, where the K balance for six years was –380 kg ha-1, no changes in soil content of K were recorded. For P, the six-year balance was positive at Landvik, where altogether 120 kg P ha-1 was supplied from composted household waste. The P balance was negative (-40 kg ha-1) at Voll and Kvithamar, and at Voll the content of easily soluble P in the plough layer was lower in 1999 than in 1993. In the study period, the yields were variable both within and between the systems. We have not identified any trends or variations in yields that might have been directly caused by changesin soil nutrient status or other soil quality components. At Voll and Kvithamar, however, the number of earthworm and the soil macroporosity increased from 1993 to 1999, with a concurrent slight increase in the yields of leys (Voll) and grain crops and swedes (Kvithamar). In the system at Landvik the yields of potatos and carrots were higher the first two than the last four years. At this site the soil structure was good, and the porosity and earthworm activity high, during the whole study period.
2002
Authors
Mehreteab TesfaiAbstract
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