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Own Biomass (own + biomass)
Selected AbstractsNutrient cycling efficiency explains the long-term effect of ecosystem engineers on primary productionFUNCTIONAL ECOLOGY, Issue 1 2007SÉBASTIEN BAROT Summary 1Soil organisms, such as earthworms, accelerate mineralization of soil organic matter and are thought to be beneficial for plant growth. This has been shown in short-term microcosm experiments. It is thus legitimate to ask whether these increases in plant growth are due to brief pulses of mineralization or whether these increases are long-lasting. 2This question was addressed using a system of differential equations modelling the effects of decomposers on nutrient cycling via trophic (nutrient assimilation) and nontrophic effects (through their ecosystem engineering activities). 3The analytical study of this model showed that these processes increase primary production in the long term when they recycle nutrients efficiently, allowing a small fraction of the recycled nutrients to be leached out of the ecosystem. 4Mineralization by the ecosystem engineering activities of decomposers seems to deprive them of a resource. However, it was shown that a decomposer may increase its own biomass, through its ecosystem engineering activities, provided the created recycling loop is efficient enough. 5Mechanisms through which earthworms may modify the efficiency of nutrient cycling are discussed. The necessity of measuring the effect of earthworms on the nutrient input,output balance of ecosystems under field conditions is emphasized. [source] A MICRO-LEVEL ,CONSUMER APPROACH' TO SPECIES POPULATION DYNAMICSNATURAL RESOURCE MODELING, Issue 1 2007THOMAS CHRISTIAANS ABSTRACT. In this paper we develop a micro ecosystem model whose basic entities are representative organisms which behave as if maximizing their net offspring under constraints. Net offspring is increasing in prey biomass intake, declining in the loss of own biomass to predators and Allee's law applies. The organism's constraint reflects its perception of how scarce its own biomass and the biomass of its prey is. In the short-run periods prices (scarcity indicators) coordinate and determine all biomass transactions and net offspring which directly translates into population growth functions. We are able to explicitly determine these growth functions for a simple food web when specific parametric net offspring functions are chosen in the micro-level ecosystem model. For the case of a single species our model is shown to yield the well-known Verhulst-Pearl logistic growth function. With two species in predator-prey relationship, we derive differential equations whose dynamics are completely characterized and turn out to be similar to the predator-prey model with Michaelis-Menten type functional response. With two species competing for a single resource we find that coexistence is a knife-edge feature confirming Tschirhart's [2002] result in a different but related model. [source] A MICROFOUNDATION OF PREDATOR-PREY DYNAMICSNATURAL RESOURCE MODELING, Issue 3 2006THOMAS EICHNER ABSTRACT. Predator-prey relationships account for an important part of all interactions betweenspecies. In this paper we provide a microfoundation for such predator-prey relations in afood chain. Basic entities of our analysis are representative organisms of species modeled similar to economic households. With prices as indicators of scarcity, organisms are assumed to behave as if they maximize their net biomass subject to constraints which express the organisms' risk of being preyed upon during predation. Like consumers, organisms face a ,budget constraint' requiring their expenditure on prey biomass not to exceed their revenue from supplying own biomass. Short-run ecosystem equilibria are defined and derived. The net biomass acquired by the representative organism in the short term determines the positive or negative population growth. Moving short-run equilibria constitute the dynamics of the predator-prey relations that are characterized in numerical analysis. The population dynamics derived here turn out to differ significantly from those assumed in the standard Lotka-Volterra model. [source] THE IMPACT OF SCARCITY AND ABUNDANCE IN FOOD CHAINS ON SPECIES POPULATION DYNAMICSNATURAL RESOURCE MODELING, Issue 3 2003THOMAS EICHNER ABSTRACT. The population dynamics in a food chain are derived from a sequence of short-run equilibria of an ecosystem where predator species demand prey biomass, supply own biomass to their predators and are assumed to behave as if they maximize net biomass intake. Introducing prices as scarcity indicators for the biomass of each species enables us to determine a short-run ecosystem equilibrium guided by prices. Equilibrium regimes differ with respect to their mix of zero-priced (= abundant) and positive-priced (= scarce) species. The population dynamics turn out to vary with the prevailing equilibrium regime. Our analysis yields a richer and more complex population dynamics than the traditional predator-prey dynamics of the Lotka-Volterra type. [source] | ||||||||||