Stability and complexity of ecosystems - Global interaction constraints, landscape and extinctions
Doktorsavhandling, 2023
Human society's expansion and demand for both biotic and abiotic natural resources exert a large pressure on ecosystems around the globe. Ecosystems are complex networks of species interacting with each other and their physical surroundings. Although they are in constant change due to fortuitous fluctuations as well as migration, climate, and evolution, in a human time-frame ecosystems are relatively stable. Stability of an ecosystem can refer to many different aspects but in general denotes an ability to uphold perceived qualities and functions in the face of external disturbances.
This thesis builds on the long heritage of trying to understand stability of ecosystems, and the more recent use of dynamical modelling and specifically General Lotka-Volterra equations for this purpose. A contested issue in ecosystem research is the role of complexity in facilitating stability. Complexity being an intuitive but not strictly defined concept including among others number of species, amount of interactions, and structure of interactions. Irrespective of the role of complexity for ecosystem stability there is general agreement that there are limits to stability, in terms of some property, at which point an ecosystem if pressured beyond it will transition to a qualitative different state.
This thesis shows that, contrary to previous conception, there are more limits of stability than one. The new limits revise the important transition points of an ecosystem and differentiate between different types of stability, which in turn have differing responses to disturbances of equal magnitude. Species extinctions are found as a mechanism to prevent collapse of an entire community and collapse is found to be divided into two types. Further, these stability aspects are found to hold when spatial extension is modelled explicitly. With spatial extension homogeneous landscapes are shown to enhance robustness by a larger spectrum of dynamics and in the limit of high dispersal heterogeneous landscapes can facilitate much higher complexity. The thesis also exposes certain types of constraints on the structures of interactions among species that have a large influence on the stability limits. Together these results give indication of important local and global features of ecosystems which determine response behaviour and stabilising dynamics to a high degree, important when analysing systems and assessing their vulnerability in face of environmental pressures.
This thesis builds on the long heritage of trying to understand stability of ecosystems, and the more recent use of dynamical modelling and specifically General Lotka-Volterra equations for this purpose. A contested issue in ecosystem research is the role of complexity in facilitating stability. Complexity being an intuitive but not strictly defined concept including among others number of species, amount of interactions, and structure of interactions. Irrespective of the role of complexity for ecosystem stability there is general agreement that there are limits to stability, in terms of some property, at which point an ecosystem if pressured beyond it will transition to a qualitative different state.
This thesis shows that, contrary to previous conception, there are more limits of stability than one. The new limits revise the important transition points of an ecosystem and differentiate between different types of stability, which in turn have differing responses to disturbances of equal magnitude. Species extinctions are found as a mechanism to prevent collapse of an entire community and collapse is found to be divided into two types. Further, these stability aspects are found to hold when spatial extension is modelled explicitly. With spatial extension homogeneous landscapes are shown to enhance robustness by a larger spectrum of dynamics and in the limit of high dispersal heterogeneous landscapes can facilitate much higher complexity. The thesis also exposes certain types of constraints on the structures of interactions among species that have a large influence on the stability limits. Together these results give indication of important local and global features of ecosystems which determine response behaviour and stabilising dynamics to a high degree, important when analysing systems and assessing their vulnerability in face of environmental pressures.
Complexity
Collapse
Stability
Ecosystems
Extinctions
Population dynamics
spatial heterogeneity
Dynamical systems
dispersal
Författare
Susanne Pettersson
Chalmers, Rymd-, geo- och miljövetenskap, Fysisk resursteori
Dagens ekosystem utsätts för enorma påfrestningar på grund av människans utbredning. Vi kräver både levande och materiella resurser samtidigt som vi förändrar ekosystemens förutsättningar genom klimatpåverkan, kemiska föroreningar, markförstöring och landomvandling. För vår överlevnad och våra medvarelsers måste vi hitta sätt att nyttja resurser som inte medför oåterkallelig skada till systemen som upprätthåller allt levande.
Ett av de viktigaste verktygen för att uppnå detta är en förståelse för hur ekosystem fungerar och hur de påverkas av förändringar. Ekosystem är komplexa system bestående av många olika arter som interagerar på en ofantlig mängd olika sätt. Interaktionerna mellan arter bildar ett nätverk där i någon mån alla är beroende av alla. Genom att förstå hur dessa nätverk av interaktioner påverkar stabiliteten i ekosystemet, kan vi bättre förutse när och hur det finns risk för kollaps.
I den här avhandlingen undersöker vi vilka egenskaper som gör ekosystem stabila, när arter riskerar att utrotas vid förändringar och när ekosystemet är på väg mot kollaps. Tillsammans med all kunskap om enskilda arter och förutsättningar för ekosystemfunktioner, kan männskligheten utveckla strategier för att både skydda ekosystemen med alla dess varelser och möjliggöra en hållbar mänsklig utveckling.
Ett av de viktigaste verktygen för att uppnå detta är en förståelse för hur ekosystem fungerar och hur de påverkas av förändringar. Ekosystem är komplexa system bestående av många olika arter som interagerar på en ofantlig mängd olika sätt. Interaktionerna mellan arter bildar ett nätverk där i någon mån alla är beroende av alla. Genom att förstå hur dessa nätverk av interaktioner påverkar stabiliteten i ekosystemet, kan vi bättre förutse när och hur det finns risk för kollaps.
I den här avhandlingen undersöker vi vilka egenskaper som gör ekosystem stabila, när arter riskerar att utrotas vid förändringar och när ekosystemet är på väg mot kollaps. Tillsammans med all kunskap om enskilda arter och förutsättningar för ekosystemfunktioner, kan männskligheten utveckla strategier för att både skydda ekosystemen med alla dess varelser och möjliggöra en hållbar mänsklig utveckling.
Human expansion and development are putting an immence pressure on today's ecosystems. We rely on both living and material resources, at the same time our actions, such as climate change, pollution, and land development, are altering the conditions of ecosystems. In order to sustain both ourselves and other living beings, we must find ways to use resources without causing irreversible damage to the systems that support all life.
To achieve this goal, we need to understand how ecosystems respond to change and when they are at risk of collapse. This is the focus of the research discussed in this text. The complexity of ecosystems makes them difficult to predict, as species interact in a variety of ways forming a network of interactions in which, to some extent, all are dependent on all. This research aims to identify the characteristics of the network of interactions that affect stability, to determine when change can lead to species extinctions and when the entire ecosystem is in danger of collapse. By gaining this knowledge, togehter with knowledge of species traits and ecosystem functions we can develop strategies that balance the needs of ecosystems and human civilization.
To achieve this goal, we need to understand how ecosystems respond to change and when they are at risk of collapse. This is the focus of the research discussed in this text. The complexity of ecosystems makes them difficult to predict, as species interact in a variety of ways forming a network of interactions in which, to some extent, all are dependent on all. This research aims to identify the characteristics of the network of interactions that affect stability, to determine when change can lead to species extinctions and when the entire ecosystem is in danger of collapse. By gaining this knowledge, togehter with knowledge of species traits and ecosystem functions we can develop strategies that balance the needs of ecosystems and human civilization.
Ämneskategorier
Matematik
Biologiska vetenskaper
Annan naturvetenskap
Fundament
Grundläggande vetenskaper
ISBN
978-91-7905-795-4
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5261
Utgivare
Chalmers