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The architecture of antagonistic networksNuwagaba, Savannah 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Designing a mechanistic model that can give rise to realistic architecture of ecological
networks is central to the understanding of how species assemble and function in ecosystems.
As species are constantly adjusting their diets in an antagonistic network, we
here incorporate this adaptive behaviour of diet choice into a bipartite network model,
with the effect of antagonistic interactions between species depicted by Holling’s type
II functional response. Predictions of this model fit extremely well with the observed
levels of nestedness, modularity and node-degree distributions for 61 real host-parasitoid
and plant-herbivore networks. We further examined two specific scenarios of our model
(species with identical [neutral] demographic parameters and interactions with identical
[neutral] benefit in the network) and found that the demography-neutral scenario overestimated
observed modularity, whilst the benefit-neutral scenario over-estimate observed
nestedness. Relationships between nestedness, modularity and connectance were found
strong. Moreover, in contrast to the common belief of the high modularity in antagonistic
networks, most real networks (> 80%) are significantly nested, whilst nearly 40% of the
real networks are surprisingly less compartmentalized than random networks generated
from null models. Regardless of the controversy on whether antagonistic networks are
nested or compartmentalized, the proposed model captured the essence of the dynamic
nature of structural emergence in antagonistic networks. Due to its predictive power, this
model was further used to investigate robustness in antagonistic networks. Predictions
showed that the robustness of a network is determined by many factors, such as connectance,
resource degree distribution, resource-consumer ratio, diversity, nestedness and
compartmentalisation. Surprisingly, the manner of network response to species loss was
independent of the sequence followed while removing species from a network. Variations
were only noticed in the intensity of the effect resulting from the removals. In addition,
we also showed that species extinction procedures which ignore the interaction switch
underestimate the effect of any loss of species in these networks. We must therefore value
our knowledge of possible adaptive processes in the ecosystem as they may be important
for resolving the diversity-stability debate. / AFRIKAANSE OPSOMMING: Die ontwerp van ’n meganistiese model wat aanleiding kan gee tot realistiese argitektuur
van ekologiese netwerke is sentraal tot die begrip van hoe spesies bymekaar kom
en funksioneer in ekosisteme. Soos spesies voortdurend hul dieet aanpas in ’n antagonistiese
netwerk, het ons hierdie aanpasbare gedrag van dieet keuse in ’n bipartiet netwerk
model ingewerk, met die effek van antagonistiese interaksies tussen spesies wat uitgebeeld
word deur Holling se tipe II funksionele reaksie. Voorspellings van hierdie model pas
baie goed met die waargenome vlakke van nestedness, modulariteit en node-graad uitkerings
vir 61 ware gasheer-parasiet en plant-herbivoor netwerke. Verder het ons twee
spesifieke gevalle van ons model (spesies met identiese [neutrale] demografiese parameters
en interaksies met identiese [neutrale] voordeel in die netwerk) ondersoek en gevind
dat die demografie-neutrale geval waargenome modulariteit oorskat, terwyl die voordeelneutraal
geval waargenome nestedness oorskat. Verhoudings tussen nestedness, modulariteit
en konnektiwiteit is sterk bevind. Verder, in teenstelling met die algemene verwagting
van hoe modulariteit in antagonistiese netwerke, is oorhoofse werklike netwerke
(> 80%) aansienlik geneste, terwyl byna 40% van die werklike netwerke is verbasend
minder gekompartimenteerd as ewekansige netwerke gegenereer uit null modelle. Ongeag
van die omstredenheid oor of antagonistiese netwerke geneste of gekompartimenteerd is,
die voorgestelde model vang die essensie van die dinamiese aard van die strukturele opkoms
in antagonistiese netwerke. As gevolg van sy voorspellende krag, is hierdie model
verder gebruik om robuustheid te ondersoek in antagonistiese netwerke. Voorspellings
het getoon dat die robuustheid van ’n netwerk word bepaal deur verskeie faktore, soos
konnektiwiteit, hulpbron-graad verspreiding, hulpbron-verbruiker verhouding, diversiteit,
nestedness en kompartementasie. Verrassend, die wyse van die netwerk reaksie op die
verlies van spesies was onafhanklik van die reeks wat gevolg het toe die spesies verwyder
is uit ’n netwerk. Variasies is slegs opgemerk in die intensiteit van die effek van die verskuiwings.
Benewens, ons het ook aangetoon dat die prosedures van spesies se uitsterwing
wat die interaksie skakelaar geignoreer het, onderskat die effek van ’n verlies van spesies in
hierdie netwerke. Ons moet dus die waarde van ons kennis van die moontlike aanpassing
prosesse in die ekosisteem in agneem, aangesien dit belangrik kan wees vir die oplossing
van die diversiteit-stabiliteit debat.
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Modelo de simulação dinâmica para valoração ecológica de serviços ecossistêmicos hídricos nas bacias hidrográficas dos rios Piracicaba, Capivari e Jundiaí / Dynamic simulation model to valuate ecological hydrological services at Piracicaba, Capivari e Jundiaí rivers basinOrellana Gonzalez, Alba Maria Guadalupe 16 December 2010 (has links)
O objetivo principal desta pesquisa foi desenvolver um modelo de simulação dinâmica para a valoração ecológica de serviços ecossistêmicos hídricos, baseado em princípios de Dinâmica de Sistemas com o auxílio do software STELLA. A hipótese básica adotada foi que: a valoração ecológica dos serviços ecossistêmicos deve contar com uma ferramenta integradora dos elementos envolvidos na modelagem ecológica como requisito básico para compreensão da dinâmica ecossistêmica que gera fluxos de serviços ecossistêmicos hídricos (SEH). Os SEH são os benefícios gerados a partir das complexas interações, entre os componentes do ciclo hidrológico e que tem a ver com a preservação tanto em quantidade como em qualidade da oferta de água. O modelo foi desenvolvido, através de uma análise sistêmica dos processos ecossistêmicos compreendidos dentro do ciclo hidrológico, foram determinadas as principais variáveis e suas respectivas inter-relações, de acordo com a estrutura desse ciclo. Essa estrutura foi representada no diagrama causal, que serviu de base à elaboração do diagrama de estoque e fluxo, por meio do qual se estabeleceu o modelo matemático que permitiu efetuar a simulação numérica. A escala temporal de aplicação do modelo é diária e foram efetuadas 365 simulações, o que permitiu estimar fluxos anuais de SEH. O modelo foi parametrizado na sub-bacia das Posses, Município de Extrema, Minas Gerais; aqui esta sendo implementado o primeiro projeto piloto, baseado na relação floresta-água, de pagamentos por SEH do Brasil. Foram examinados 36 cenários, com o objetivo de avaliar o impacto que têm variáveis como: textura de solo, altura da vegetação, índice de área foliar e profundidade do lençol freático na geração dos fluxos de SEH em água na superfície, infiltrada e armazenada; porém foi avaliado como estes incidem de forma quantitativa na manutenção da oferta de água disponível. O modelo desenvolvido permitiu aumentar a compreensão dos fluxos de SEH, o que representa uma ferramenta de elevado potencial de aplicação nas fases de definição de âmbito, de avaliação de alternativas e monitoramento de esquemas de pagamentos por SEH no Brasil. / The main objective of this research was to develop a dynamic simulation model to valuate ecological hydrological ecosystem services. The principles of System Dynamics were applied using the software STELLA. A basic hypothesis was adopted: ecological valuation of ecosystem services must use a tool to integer all the elements involved in ecological modeling, as a basic requirement to understand the ecosystem dynamic that generates water fluxes as hydrological ecosystems services (HES). HES are the benefits generated from complex interactions that occur within the hydrologic cycle; those interactions deals with the preservation of available water, in quantity and quality. The model was developed after a systemic analysis of the ecosystem processes involved in the hydrologic cycle; pointing out the main variables and the interrelations that constitute it. Then, the structure of those relations was represented in a causal diagram; becoming the base to built up the stocks and flows diagram. This later diagram established the mathematical model that allowed the numerical simulation. The time step of the model is one day during 365 days, estimating annual water HES. The model was parameterized at Poses sub-watershed, Extrema County, Minas Gerais. In Extrema was established the first payment for HES project in Brazil, based on the relationship between forest land and water availability. Thirty six scenarios were studied considering surface, infiltrated and stored water services fluxes; affecting the availability of water. The objective of those scenarios was to evaluate the impact that variables such as: soil texture, vegetation height, leaf area index and groundwater depth have on water flux generation. The model developed enables to increase the understanding of HES fluxes, becoming a tool with a broad spectrum of applications during the stages of assessing and scoping alternatives for payment of environmental services and to monitor HES programs in Brazil.
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Modelo de simulação dinâmica para valoração ecológica de serviços ecossistêmicos hídricos nas bacias hidrográficas dos rios Piracicaba, Capivari e Jundiaí / Dynamic simulation model to valuate ecological hydrological services at Piracicaba, Capivari e Jundiaí rivers basinAlba Maria Guadalupe Orellana Gonzalez 16 December 2010 (has links)
O objetivo principal desta pesquisa foi desenvolver um modelo de simulação dinâmica para a valoração ecológica de serviços ecossistêmicos hídricos, baseado em princípios de Dinâmica de Sistemas com o auxílio do software STELLA. A hipótese básica adotada foi que: a valoração ecológica dos serviços ecossistêmicos deve contar com uma ferramenta integradora dos elementos envolvidos na modelagem ecológica como requisito básico para compreensão da dinâmica ecossistêmica que gera fluxos de serviços ecossistêmicos hídricos (SEH). Os SEH são os benefícios gerados a partir das complexas interações, entre os componentes do ciclo hidrológico e que tem a ver com a preservação tanto em quantidade como em qualidade da oferta de água. O modelo foi desenvolvido, através de uma análise sistêmica dos processos ecossistêmicos compreendidos dentro do ciclo hidrológico, foram determinadas as principais variáveis e suas respectivas inter-relações, de acordo com a estrutura desse ciclo. Essa estrutura foi representada no diagrama causal, que serviu de base à elaboração do diagrama de estoque e fluxo, por meio do qual se estabeleceu o modelo matemático que permitiu efetuar a simulação numérica. A escala temporal de aplicação do modelo é diária e foram efetuadas 365 simulações, o que permitiu estimar fluxos anuais de SEH. O modelo foi parametrizado na sub-bacia das Posses, Município de Extrema, Minas Gerais; aqui esta sendo implementado o primeiro projeto piloto, baseado na relação floresta-água, de pagamentos por SEH do Brasil. Foram examinados 36 cenários, com o objetivo de avaliar o impacto que têm variáveis como: textura de solo, altura da vegetação, índice de área foliar e profundidade do lençol freático na geração dos fluxos de SEH em água na superfície, infiltrada e armazenada; porém foi avaliado como estes incidem de forma quantitativa na manutenção da oferta de água disponível. O modelo desenvolvido permitiu aumentar a compreensão dos fluxos de SEH, o que representa uma ferramenta de elevado potencial de aplicação nas fases de definição de âmbito, de avaliação de alternativas e monitoramento de esquemas de pagamentos por SEH no Brasil. / The main objective of this research was to develop a dynamic simulation model to valuate ecological hydrological ecosystem services. The principles of System Dynamics were applied using the software STELLA. A basic hypothesis was adopted: ecological valuation of ecosystem services must use a tool to integer all the elements involved in ecological modeling, as a basic requirement to understand the ecosystem dynamic that generates water fluxes as hydrological ecosystems services (HES). HES are the benefits generated from complex interactions that occur within the hydrologic cycle; those interactions deals with the preservation of available water, in quantity and quality. The model was developed after a systemic analysis of the ecosystem processes involved in the hydrologic cycle; pointing out the main variables and the interrelations that constitute it. Then, the structure of those relations was represented in a causal diagram; becoming the base to built up the stocks and flows diagram. This later diagram established the mathematical model that allowed the numerical simulation. The time step of the model is one day during 365 days, estimating annual water HES. The model was parameterized at Poses sub-watershed, Extrema County, Minas Gerais. In Extrema was established the first payment for HES project in Brazil, based on the relationship between forest land and water availability. Thirty six scenarios were studied considering surface, infiltrated and stored water services fluxes; affecting the availability of water. The objective of those scenarios was to evaluate the impact that variables such as: soil texture, vegetation height, leaf area index and groundwater depth have on water flux generation. The model developed enables to increase the understanding of HES fluxes, becoming a tool with a broad spectrum of applications during the stages of assessing and scoping alternatives for payment of environmental services and to monitor HES programs in Brazil.
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