Browsing by Subject "multispecies"

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    A critical look at the potential of Ecopath with ecosim to assist in practical fisheries management
    (National Inquiry Services Centre, 2004) Plagányi, Éva E; Butterworth, Doug S
    Ecosystem-orientated thinking is increasingly incorporated into fishery management. Given the complexity of ecosystem processes, there is a need to evaluate the tools used to steer this thinking critically. ECOPATH with ECOSIM (EwE), an aggregate system-modelling package, is currently the most widely employed approach to assess the ecosystem effects of fishing. The basic equations and assumptions, strengths and weaknesses, and the potential of this approach to contribute to practical fisheries management advice are reviewed. Strengths include the structured parameterization framework, the inclusion of a well-balanced level of conceptual realism, a novel representation of predator-prey interaction terms, and the inclusion of a Bayes-like approach (ECORANGER) to take account of the uncertainty associated with values for model inputs. Weaknesses in model structure include the constraining nature of the mass-balance assumption (of ECOPATH) for initiating projections, the questionable handling of life history responses such as compensatory changes in the natural mortality rates of marine mammals, overcompensatory stock-recruit relationships that result from default parameter settings, possible problems in extrapolating from the microscale to the macroscale, as well as some (not too far-reaching) mathematical inconsistencies in the underlying equations. There is a paucity of systematic and stepwise investigations into model behaviour and properties, and users are cautioned against non-critical use of the default settings. An important limitation related to the predominant use of EwE as a "black-box" modelling tool is that some users fail to consider a range of alternative interaction representations. As with all multispecies approaches, the major limitation in applying the EwE approach lies in the quality and quantity of available data. Current EwE applications generally do not adequately address uncertainty in data inputs and model structure. Prudent EwE applications that utilize good data and are based upon rigorous statistical analyses can complement the quantitative predictions of traditional single-species models. They could be particularly useful in some contexts if output in the form of probability distributions encompassing a range of likely ecosystem responses were to be coupled with attempts to extend Operational Management Procedure (OMP) approaches to fisheries management beyond the singlespecies level. In particular, such applications could serve as the operating models of the underlying dynamics that are used for computer simulation testing of OMPs.
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    On Stories of Liveliness: following the Arts of Living on a Damaged Karoo Veld
    (2019) Köster, Terena; Solomon, Nikiwe
    This thesis is concerned with the conditions of generating a livable Karoo landscape and the arts of living on a damaged Karoo veld. It takes place in a context where the anthropogenic influences on land degradation, desertification and biodiversity loss continues to haunt the Karoo in the present. The Karoo is a semi-arid region that spans the interior of South Africa. It is also region that has been subject to ongoing and widespread concern of the impact of overgrazing, threatening the livability of the Karoo landscape. This is a result of human/nonhuman relations that have been grounded in a colonial mastery of the land, whereby the advent of private property regimes, modernist technologies and capitalist extraction has allowed for the land to be cheapened, exhausted and severely degraded in a process of colonial dispossession. This research is a qualitative ethnography interacting with farmers and nonhumans on rangelands in the Great Karoo. This thesis shows how the earlier degradation of the Karoo has demanded farmersto pay attention to the relationalities between ecology and economy, since their economic/ecological survival depends entirely on the ongoing multispecies assemblages of which humans form a part. Infrastructures and technologies have become grounds for new ontological practices of regenerating the Karoo veld. Infrastructures (namely fencing) and sheep are used in ways that mimic the earlier migration of large herds of antelope. Here, the bodies of sheep are curated and moved in order to perform a particular ordering of a Karoo ‘nature’. This movement is believed to instigate multispecies liveliness. Sheep, who were once destroyers of the veld, are now enrolled in practices that are believed to bring back the ‘natural’ vegetation of the Karoo. The thesis problematises the ongoing Western ways of knowing that separate the world into binaries of ‘nature’/’culture’, ‘human’/’non-human’, ‘subject’/object’, ‘domestic’/‘wild’, ’economy’/‘ecology’, ‘life’/‘death’. Rather, it argues that a concern with ontological plurality is a process of paying attention to the mutual ecologies and multiple species that gather in human/nonhuman worlding projects on rangelands in the Karoo.