Extinctions and Ecosystem Stability

Human society\u27s 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 incidental/fortuitous fluctuations as well as climate, migration and, evolution, in a human time-frame ecosystems are relatively stable, upholding certain qualities and functions. Stability of an ecosystem can refer to many different aspects but in general denotes an ability to keep the 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 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 perturbed/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. 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 structures of ecosystems which determine response behaviour to a high degree, important when analysing systems and assessing their vulnerability in an uncertain environment

Stability and complexity of ecosystems - Global interaction constraints, landscape and extinctions

Human society\u27s 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

Spatial heterogeneity enhance robustness of large multi-species ecosystems

Understanding ecosystem stability and functioning is a long-standing goal in theoretical ecology, with one of the main tools being dynamical modelling of species abundances. With the help of spatially unresolved (well-mixed) population models and equilibrium dynamics, limits to stability and regions of various ecosystem robustness have been extensively mapped in terms of diversity (number of species), types of interactions, interaction strengths, varying interaction networks (for example plant-pollinator, food-web) and varying structures of these networks. Although many insights have been gained, the impact of spatial extension is not included in this body of knowledge. Recent studies of spatially explicit modelling on the other hand have shown that stability limits can be crossed and diversity increased for systems with spatial heterogeneity in species interactions and/or chaotic dynamics. Here we show that such crossing and diversity increase can appear under less strict conditions. We find that the mere possibility of varying species abundances at different spatial locations make possible the preservation or increase in diversity across previous boundaries thought to mark catastrophic transitions. In addition, we introduce and make explicit a multitude of different dynamics a spatially extended complex system can use to stabilise. This expanded stabilising repertoire of dynamics is largest at intermediate levels of dispersal. Thus we find that spatially extended systems with intermediate dispersal are more robust, in general have higher diversity and can stabilise beyond previous stability boundaries, in contrast to well-mixed systems

Fatigue : perceived, described and assessed by persons with systemic lupus erythematosus

Fatigue is an individual and subjective sensation interfering with daily living for patients with several chronic conditions. Systemic lupus erythematosus (SLE) is characterized by inflammation in different organs combined with immunological abnormalities. The complexity of the disease SLE has several consequences for daily living, and fatigue is among one of the most burdensome symptoms of SLE. The impact of fatigue in a person’s life is difficult for others to understand. Therefore, to better understand the enigma of fatigue, how fatigue can be measured and patient’s descriptions of how fatigue is experienced are necessary. Aim: The overall aim of this cohort-based project, was to explore patients experiences of symptoms related to SLE with a main focus on fatigue, how it is described and measured. Subjects: 327 patients from the SLE-cohort at Karolinska University Hospital, Solna, and 311 age- and gender- matched control persons contributed to the data. Both qualitative and quantitative data have been used, with interview material from focus group discussions (study I), free-written answers (study II) and self-assessments measures/questionnaires (study II+III+IV). Results: In study I, women (n=33) in seven focus group discussions (FGD) described their experience of SLE-related fatigue; how they perceived the feeling of fatigue, impact on life and strategies developed to manage fatigue in daily living. Transcripts from the FGD were analyzed using content analysis. The results were presented as four themes where the “Nature of fatigue” involved the sensation, occurrence and character of fatigue, “Aspects affected by fatigue” described emotions that arose with fatigue as well as aspects of work, family life, social contacts, and leisure activities that were affected by SLE related fatigue; “Striving towards power and control” described a balance of strategies used to manage daily life and were categorized into mental struggle, structure, restrict, and provide; “Factors influencing the perception of fatigue” described understanding from surrounding persons and the pain as strongly influencing the experience and perception of fatigue. The result from the open questions in study II (n=324), showed that fatigue and pain were reported as most troublesome symptoms of SLE, followed by musculoskeletal symptoms. In study III (n=51) in groups of 6-9 patients patents filled in seven questionnaires about fatigue; Numeric rating scale (NRS), Chalder fatigue scale, Vitality from SF-36, Fatigue Severity Scale, Multi-dimensional Assessment of Fatigue, Multidimensional Fatigue Inventory and Functional Assessment of Chronic Illness Therapy – Fatigue. This followed by a dialogue procedure resulting in 260 contrasting assessment. The minimally clinically important difference for the seven measures of fatigue was calculated using the comparative assessment as anchor. All measures of fatigue used in the study seemed to capture differences as experienced by the group of patients themselves, least favorable was however the one question (NRS) this were strengthen by patients free written comments. In study IV (n=305 patients and 311 controls) three clusters of fatigue were identified. The High fatigue cluster (n = 221) had most symptoms of anxiety/depression, lowest health related quality of life and were dominated by the patients (80%). Participants in the Low fatigue cluster (n = 240, controls 78%) reported more physical exercise and less smoking than the other clusters. Conclusion: Patients description of SLE related fatigue (study I) provide important knowledge that can be used in educational discussions with patients as well as health care workers. The recommended measures of fatigue, evaluated in this thesis, can detect clinically important differences as perceived by the patients (study III). Not all patients with SLE experienced distress from current illness, 10 % reported that they did not perceive any SLE related symptom (study II) and 17% had low levels of fatigue and healthy behavior (physical exercise, non-smoker)(study IV). With special focus on fatigue, this thesis contributes to the understanding of patients’ experience of SLE. Knowledge of the experience of symptoms from the patients’ perspective is pivotal in order to support the patient, facilitate assessment and choice of treatment as well as generate a base for appropriate intervention programs

Biochemistry of topoisomerase inhibtion and cellular mechanisms of anthraquinone-amino acid conjugates in vitro

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Spatial coherence and the persistence of high diversity in spatially heterogeneous landscapes

Our planet hosts a variety of highly diverse ecosystems. The persistence of high diversity is generally attributed to factors such as the structure of interactions among species and the dispersal of species in metacommunities. Here, we show that large contiguous landscapes-that are characterized by high dispersal-facilitate high species richness due to the spatial heterogeneity in interspecies interactions. We base our analysis on metacommunities under high dispersal where species densities become equal across habitats (spatially coherent). We find that the spatially coherent metacommunity can be represented by an effective species interaction-web that has a significantly lower complexity than the constituent habitats. Our framework also explains how spatial heterogeneity eliminates differences in the effective interaction-web, providing a basis for deviations from the area-heterogeneity tradeoff. These results highlight the often-overlooked case of high dispersal where spatial coherence provides a novel mechanism for supporting high diversity in large heterogeneous landscapes

Stability of ecosystems enhanced by species-interaction constraints

Ecosystem stability is a central question both in theoretical and applied biology. Dynamical systems theory can be used to analyze how growth rates, carrying capacities, and patterns of species interactions affect the stability of an ecosystem. The response to increasing complexity has been extensively studied and the general conclusion is that there is a limit. While there is a complexity limit to stability at which global destabilisation occurs, the collapse rarely happens suddenly if a system is fully viable (no species is extinct). In fact, when complexity is successively increased, we find that the generic response is to go through multiple single-species extinctions before a global collapse. In this paper we demonstrate this finding via both numerical simulations and elaborations of theoretical predictions. We explore more biological interaction patterns, and, perhaps most importantly, we show that constrained interaction structures-a constant row sum in the interaction matrix-prevent extinctions from occurring. This makes an ecosystem more robust in terms of allowed complexity, but it also means singles-species extinctions do not precede or signal collapse-a drastically different behavior compared to the generic and commonly assumed case. We further argue that this constrained interaction structure-limiting the total interactions for each species-is biologically plausible

Mobility and mobility-related participation outcomes of powered wheelchair and scooter interventions after 4-months and 1-year use.

Purpose: The aim was to investigate outcomes of powered wheelchair and scooter interventions after 4-months and 1-year use regarding need for assistance when moving around, frequency of mobility-related participation, easiness/difficulty in mobility during participation, and number of participation aspects performed in everyday life. Method: The study was a prospective cohort study, using an instrument focusing on mobility-related participation outcomes of mobility device interventions (NOMO 1.0), at baseline, after 4-months and 1-year use. Results: The results show that the outcomes in terms of participation frequency and easiness in mobility occur in a short time perspective, and that the effects remained stable at 1-year follow-up. The frequency of going for a walk increased most prominently (26%). Even though the majority of the participation aspects were not performed, more often they became easier to perform: 56-91% found that shopping, walking and visiting family/friends were easier. Moreover, independence outdoors and indoors increased. Conclusions: This small study provides knowledge about the outcomes of powered wheelchairs and scooters in terms of mobility and mobility-related participation in real-life situations. The study supports results from former studies, but even so, larger studies are required in order to provide evidence for the effectiveness of powered wheelchairs and scooters. [Box: see text]