Resilience in marine ecosystems: the effects of environmental and ecological context on ecosystem multistability
In recent times, disturbances in ecosystems due to anthropogenic and natural drivers have become increasingly prevalent. Many previous studies have tried to understand and quantify how these disturbances influence food web dynamics and ecosystem functioning and ultimately how this affects overall ecosystem stability. The aims of this thesis are to enhance such studies by investigating: 1) The mechanisms that determine multiple forms of ecological stability by manipulating key components of a food web that are thought theoretically to drive stability, i.e. food web connectance, predator-prey interaction strengths and species richness; 2) The effects of multiple stressors or press perturbations on the susceptibility of food webs to episodic shocks or pulse perturbations, i.e. systems were stressed with press perturbations including nutrient enhancement and biodiversity loss and then subject to a pulse perturbation (biomass loss) to investigate whether systems subject to stress were less able to absorb, recover and adapt to episodic shocks; and 3) How multiple measures of ecosystem stability vary in response to similar disturbances compared between similarly structured intertidal communities across geographically different areas. Three main forms of stability, i.e. variability, resistance and recovery, were analysed in each data chapter for their changes in response to perturbations using large scale mesocosm experiments. By analysing these three stability metrics simultaneously, an investigation of how the factors in each study influenced ecosystem multistability is presented. The work of this thesis highlights 4 main points for consideration: 1) the necessity of future studies to consider multiple forms of stability simultaneously as analysis of single stabilities alone can present misleading descriptions of ecosystem responses to disturbance; 2) the requirement of future research to consider the effects on ecosystem properties across multiple stability metrics simultaneously to achieve a more comprehensive understanding of overall ecosystem stability; 3) the importance of considering effects from multiple stressors simultaneously when attempting to unravel contributions of food web properties to ecosystem multistability; and 4) the necessity of considering the effects of far-reaching and similarly occurring perturbations on ecosystems across different biogeographical areas.
Ecology, ecosystem, food webs, ecosystem stability, marine
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