Important changes have been observed in recent decades in small pelagic fish (SPF) populations of the NW Mediterranean Sea: declines in biomass and landings of European anchovy and sardine, and a ...geographical expansion of round sardinella. These changes have been linked to environmental factors directly influencing annual recruitment and growth. The role of climate change in affecting the composition of plankton has also been suggested to explain declines in SPF, while other causes could be the recovery of predators, competition with other pelagic organisms that prey on early life phases of SPF (i.e. gelatinous zooplankton), interspecific competition for food, or impacts from fisheries harvest. To test the role of these potential pressures, we developed qualitative mathematical models of a NW Mediterranean pelagic food web. We used analyses of sign directed graphs and Bayesian belief networks to compare alternative hypotheses about how SPF species may have responded to combinations of different pressures. Data documenting changes in SPF populations were used to test predicted directions of change from signed digraph models. An increase in sea surface temperature (SST) that had either a positive impact on round sardinella or on gelatinous zooplankton abundance was the pressure that alone provided the most plausible insights into observed changes. A combination of various pressures, including an increase in SST, an increase of exploitation and changes to zooplankton also delivered results matching current observations. Predators of SPF were identified as the most informative monitoring variable to discern between likely causes of perturbations to populations of SPF.
The crown-of-thorns starfish Acanthaster planci (COTS) has contributed greatly to declines in coral cover on Australia's Great Barrier Reef, and remains one of the major acute disturbances on ...Indo-Pacific coral reefs. Despite uncertainty about the underlying causes of outbreaks and the management responses that might address them, few studies have critically and directly compared competing hypotheses. This study uses qualitative modelling to compare hypotheses relating to outbreak initiation, explicitly considering the potential role of positive feedbacks, elevated nutrients, and removal of starfish predators by fishing. When nutrients and fishing are considered in isolation, the models indicate that a range of alternative hypotheses are capable of explaining outbreak initiation with similar levels of certainty. The models also suggest that outbreaks may be caused by multiple factors operating simultaneously, rather than by single proximal causes. As the complexity and realism of the models increased, the certainty of outcomes decreased, but key areas that require further research to improve the structure of the models were identified. Nutrient additions were likely to result in outbreaks only when COTS larvae alone benefitted from nutrients. Similarly, the effects of fishing on the decline of corals depended on the complexity of interactions among several categories of fishes. Our work suggests that management approaches which seek to be robust to model structure uncertainty should allow for multiple potential causes of outbreaks. Monitoring programs can provide tests of alternative potential causes of outbreaks if they specifically monitor all key taxa at reefs that are exposed to appropriate combinations of potential causal factors.
Models of social-ecological systems (SES) are acknowledged as an important tool to understand human-nature relations. However, many SES models fail to integrate adequate information from both the ...human and ecological subsystems. With an example model of a future Offshore Wind Farm development and its effects on both the ecosystem and local human population, we illustrate a method facilitating a “balanced” SES model, in terms of including information from both subsystems. We use qualitative mathematical modeling, which allows to quickly analyze the structure and dynamics of a system without including quantitative data, and therefore to compare alternative system structures based on different understandings of how the system works. By including similar number of system variables in the two subsystems, we balanced the complexity between them. Our analyses show that this complexity is important in order to predict indirect and sometimes counterintuitive effects. We also highlight some conceptually important questions concerning social compensations during developmental projects in general, and wind farms in particular. Our results suggest that the more project holders get involved in various manner in the local socio-ecological system, the more society will benefit as a whole. Increased involvement through e.g. new projects or job-opportunities around the windfarm has the capacity to offset the negative effects of the windfarm on the local community. These benefits are enhanced when there is an overall acceptance and appropriation of the project. We suggest this method as a tool to support the decision-making process and to facilitate discussions between stakeholders, especially among local communities.
•We explore the potential effects of different social compensatory measures on the local acceptance of an Offshore Wind Farm•We present a balanced Social Ecological System model, in terms of integrating balanced information from both the ecosystem and social subsystems•This contributes to the discussion of the links between compensatory measures and the local acceptance of an OWF, focusing on social compensation.•The paper has relevance for both policy makers, managers, stakeholders, and the like, as well as to researchers
•We propose a method for more comprehensive detection of environmentally driven community change.•We compare spatial observations with model predictions of responses to perturbation.•Observations vs ...predictions agreement indicates community gateways for perturbation.•We thus detect environmental impacts cascading through complex interaction networks.
Restrictions in empirical research of biological communities have limited our understanding of the combined influence of environmental variability and system structure on community composition. Spatial patterns of community composition in less accessible systems, such as marine benthos, can often not be explained by many factors beyond the direct impact of the environment on community members. We present a method that combines commonly collected data of community composition with analyses of qualitative mathematical models, to assess not only direct impacts of environmental variability, but also the propagation of impacts through complex interaction networks. Transformed spatial data of community composition describe the community members’ observed similarity of response to an external input. The output of qualitative mathematical models describes the community members’ predicted similarity of response to input entering the system through any of its variables. A statistically significant agreement between the observed and any of the predicted response similarities indicates the respective system variable as a likely gateway for environmental variability into the system. The method is applied to benthic macroinvertebrate communities in the Rance estuary (Brittany, France). Organisms identified as likely gateways have traits that agree with their predicted response to documented spatially and temporally structured environmental variability. We suggest use of this novel framework for more comprehensive identification of environmental drivers of community change, including gateway community members and cascades of environmentally driven change through community structure.
1. Invaded ecosystems present complex management issues. This problem is exacerbated in many situations by a lack of knowledge about the ecosystem. However, delaying conservation action to collect ...further data and so reduce such uncertainty is often either impractical or inadvisable. 2. The Macquarie Island Pest Eradication Project, currently underway, is attempting to eradicate rabbits, rats, and mice from the island. We undertook qualitative modelling of this project, examining a range of likely outcomes and their possible ecological consequences. The results were aggregated across a large number of possible models, in order to account for uncertainty concerning interactions within the ecosystem. 3. The results strongly support the current actions of simultaneous eradication of all three pest species, as simulated eradications of only one or two generally led to continued impacts on the island's native biota. The results also provided support for the anticipated positive outcomes of the project, with predicted recoveries of tall tussock vegetation, and burrow- and surface-nesting seabirds. 4. However, the model predictions also highlighted potential risks: the eradication of mice from the island may not succeed, due in part to the structural position of this species within the ecosystem. Successful eradication of all three target species could potentially release the self-introduced, non-native redpolls and starlings, allowing expansion of their populations, with possible impacts on macro-invertebrates and vegetation. 5. Synthesis and applications. These results demonstrate that qualitative modelling approaches can in some cases deliver consistent results, despite high levels of uncertainty regarding interactions within the underlying ecosystem. Such outcomes can provide assistance in the development of strategic contingency plans and ongoing future management action.
As the number of marine protected areas (MPAs) increases globally, so does the need to assess if MPAs are meeting their management goals. Integral to this assessment is usually a long-term biological ...monitoring program, which can be difficult to develop for large and remote areas that have little available fine-scale habitat and biological data. This is the situation for many MPAs within the newly declared Australian Commonwealth Marine Reserve (CMR) network which covers approximately 3.1 million km2 of continental shelf, slope, and abyssal habitat, much of which is remote and difficult to access. A detailed inventory of the species, types of assemblages present and their spatial distribution within individual MPAs is required prior to developing monitoring programs to measure the impact of management strategies. Here we use a spatially-balanced survey design and non-extractive baited video observations to quantitatively document the fish assemblages within the continental shelf area (a multiple use zone, IUCN VI) of the Flinders Marine Reserve, within the Southeast marine region. We identified distinct demersal fish assemblages, quantified assemblage relationships with environmental gradients (primarily depth and habitat type), and described their spatial distribution across a variety of reef and sediment habitats. Baited videos recorded a range of species from multiple trophic levels, including species of commercial and recreational interest. The majority of species, whilst found commonly along the southern or south-eastern coasts of Australia, are endemic to Australia, highlighting the global significance of this region. Species richness was greater on habitats containing some reef and declined with increasing depth. The trophic breath of species in assemblages was also greater in shallow waters. We discuss the utility of our approach for establishing inventories when little prior knowledge is available and how such an approach may inform future monitoring efforts within the CMR network.
As part of the energy transition, the French government is planning the construction of Offshore Wind Farms (OWFs) in Normandy. These OWFs will be integrated into an ecosystem already facing multiple ...anthropogenic disturbances. A holistic view of cumulated impacts (OWF construction, global warming and fisheries) were developed on the Courseulles-sur-Mer’ ecosystem through the use of a qualitative mathematical modelling approach. This modelling approach provides the mean to consider alternative hypotheses about how the ecosystem structure and function affects its dynamics. Alternative models were constructed to address the different hypotheses regarding the behaviour of top predator (whether the top predators will be scared away by the OWF or attracted by the reef effect), impacts of global warming and changes in fisheries activities. Key findings from these analyses are that the OWF construction could lead to an increase in benthos species and fish benthos feeders whatever the perturbation scenario, while the predicted response of top predators was ambiguous across all perturbation scenario. Qualitative modelling results can play a vital role in decision making by improving long term planning for the marine environment but also as a tool for communication with the public and so contribute to a better acceptability of the Marine Renewable Energy (MRE) project.
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•Holistic view of cumulated impacts on the Bay of Seine.•Qualitative modelling approach of an offshore wind farm impacts.•Links between trophic web models and management policy.
A major decline in the catch of the banana prawn shrimp,
Penaeus
(
Fenneropenaeus
)
merguiensis
, occurred over a six-year period in the Weipa region of the northeastern Gulf of Carpentaria, ...Australia. Three main hypotheses have been developed to explain this decline: (1) prawn recruitment collapsed due to overfishing; (2) recruitment collapsed due to a change in the prawn's environment; and (3) adult banana prawns were still present, but fishers could no longer effectively find or catch them. Qualitative mathematical models were used to link population biology, environmental factors, and fishery dynamics to evaluate the alternative hypotheses. This modeling approach provides the means to rapidly integrate knowledge across disciplines and consider alternative hypotheses about how the structure and function of an ecosystem affects its dynamics. Alternative models were constructed to address the different hypotheses and also to encompass a diversity of opinion about the underlying dynamics of the system. Key findings from these analyses are that: instability in the system can arise when discarded fishery bycatch supports relatively high predation pressure; system stability can be enhanced by management of fishing effort or stock catchability; catch per unit effort is not necessarily a reliable indicator of stock abundance; a change in early-season rainfall should affect all stages in the banana prawn's life cycle; and a reduced catch in the Weipa region can create and reinforce a shift in fishing effort away from Weipa. Results from the models informed an approach to test the hypotheses (i.e., an experimental fishing program), and promoted understanding of the system among researchers, management agencies, and industry. The analytical tools developed in this work to address stages of a prawn life cycle and fishery dynamics are generally applicable to any exploited natural resource.
Animals exposed to high levels of predation risk may exhibit a variety of changes in life history, behaviour, physiology and morphology that can affect survival. Under predation threat, prey ...individuals may increase their aerobic metabolism to allocate energy toward escaping behaviours (e.g. ‘fight or flight’), although the associated energetic cost of such behaviour remains largely unknown. Lobsters display different anti-predatory responses, such as sheltering and/or escaping, but the underlying energetic cost of such responses has not been examined. Here, we tested the aerobic metabolic response of southern rock lobsters Jasus edwardsii in the presence of predator (Maori octopus Octopus maorum) olfactory cues (kairomones) using open-flow respirometry. We examined the routine metabolic rate of lobsters in response to predator kairomones during the active phase of their diurnal cycle (at night) to investigate the physiological anti-predator response when lobsters are most vulnerable. Our findings revealed that lobsters strongly reduced their routine metabolism for 3 h by 31.4% when exposed to kairomones in comparison to controls. Our findings suggest that under laboratory conditions, lobsters exposed to predation risk during the night reduce their activity to avoid predators, i.e. the anti-predator mechanism is to be immobile or inactive rather than showing a fight-or-flight response. Lobster immobility may be an energetically advantageous anti-predator response in the short term; however, prolonged or regular predator exposure could have significant consequences on foraging time and foraging area, with an overall impact on lobster performance, particularly in environments with high predator presence such as fishing grounds.
Ecological Risk Assessments (ERAs) are important tools for supporting evidence-based decision making. However, most ERA frameworks rarely consider complex ecological feedbacks, which limit their ...capacity to evaluate risks at community and ecosystem levels of organisation.
We used qualitative mathematical modelling to add additional perspectives to previously conducted ERAs for the rehabilitation of the Ranger uranium mine (Northern Territory, Australia) and support an assessment of the cumulative risks from the mine site. Using expert elicitation workshops, separate qualitative models and scenarios were developed for aquatic and terrestrial systems. The models developed in the workshops were used to construct Bayes Nets that predicted whole-of-ecosystem outcomes after components were perturbed.
The terrestrial model considered the effect of fire and weeds on established native vegetation that will be important for the successful rehabilitation of Ranger. It predicted that a combined intervention that suppresses both weeds and fire intensity gave similar response predictions as for weed control alone, except for lower levels of certainty to tall grasses and fire intensity in models with immature trees or tall grasses. However, this had ambiguous predictions for short grasses and forbs, and tall grasses in models representing mature vegetation. The aquatic model considered the effects of magnesium (Mg), a key solute in current and predicted mine runoff and groundwater egress, which is known to adversely affect many aquatic species. The aquatic models provided support that attached algae and phytoplankton assemblages are the key trophic base for food webs. It predicted that shifts in phytoplankton abundance arising from increase in Mg to receiving waters, may result in cascading effects through the food-chain.
The qualitative modelling approach was flexible and capable of modelling both gradual (i.e. decadal) processes in the mine-site restoration and the comparatively more rapid (seasonal) processes of the aquatic ecosystem. The modelling also provides a useful decision tool for identifying important ecosystem sub-systems for further research efforts.
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•Experts constructed signed diagraphs for the ERA of a large mine-site rehabilitation.•Weeds and fires affected the success of terrestrial ecosystem rehabilitation.•Key aquatic taxonomic groups supporting higher trophic levels were highlighted.•Feedback loops, cumulative risks and whole of ecosystem effects could be visualised.•Qualitative modelling added value to other risk assessment approaches.
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