Browsing by Author "Weyl, Olaf L. F."

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    Confronting the wicked problem of managing biological invasions
    (Pensoft, 2016) Woodford, Darragh J.; Richardson, David M.; MacIsaac, Hugh J.; Mandrak, Nicholas E.; Van Wilgen, Brian W.; Wilson, John R. U.; Weyl, Olaf L. F.
    The Anthropocene Epoch is characterized by novel and increasingly complex dependencies between the environment and human civilization, with many challenges of biodiversity management emerging as wicked problems. Problems arising from the management of biological invasions can be either tame (with simple or obvious solutions) or wicked, where difficulty in appropriately defining the problem can make complete solutions impossible to find. We review four case studies that reflect the main goals in the management of biological invasions – prevention, eradication, and impact reduction – assessing the drivers and extent of wickedness in each. We find that a disconnect between the perception and reality of how wicked a problem is can profoundly influence the likelihood of successful management. For example, managing species introductions can be wicked, but shifting from species-focused to vector-focused risk management can greatly reduce the complexity, making it a tame problem. The scope and scale of the overall management goal will also dictate the wickedness of the problem and the achievability of management solutions (cf. eradication and ecosystem restoration). Finally, managing species that have both positive and negative impacts requires engagement with all stakeholders and scenario-based planning. Effective management of invasions requires either recognizing unavoidable wickedness, or circumventing it by seeking alternative management perspectives.
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    Coordinated approaches to rehabilitating a river ecosystem invaded by alien plants and fish
    (Academy of Science of South Africa, 2013-11-27) Impson, N. Dean; Van Wilgen, Brian W.; Weyl, Olaf L. F.
    Large sums have been spent on controlling invasive alien species in South Africa over the past two decades, but documented accounts of successes are almost non-existent. This brief account describes progress with a coordinated pioneering project to simultaneously clear invasive alien trees and predatory alien fish from a degraded but ecologically important river ecosystem in the Cederberg region of the Western Cape Province, South Africa. Dense infestations of invasive Australian Acacia and Eucalyptus species were cleared over 2 years (2010–2012) from the riparian zone of the lower reaches of the Rondegat River. This clearance was followed by the local eradication of an alien fish, smallmouth bass Micropterus dolomieu, from the lower reaches of the river in February 2012 and March 2013 using the piscicide rotenone, so that native threatened fish species could re-colonise from the upper reaches of the river. Overall costs of the clearance and eradication amounted to nearly R4.5 million, and early indications are that the native riparian vegetation and fish are recovering well. The project illustrates several aspects of good practice: careful planning; close and enthusiastic collaboration between affected state and private landowners; public participation to address concerns; the simultaneous and coordinated application of mechanical, chemical and biological control of alien plants and chemical control of alien fish; and direction by qualified ecologists. Although it is too early to assess the long-term success, the exercise provides useful lessons for such projects elsewhere, and paves the way for the more widespread use of similar approaches in selected areas that are a priority for conservation.
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    Evaluating invasion risk for freshwater fishes in South Africa
    (AOSIS Publishing, 2017) Marr, Sean M.; Ellender, Bruce R.; Woodford, Darragh J.; Alexander, Mhairi E.; Wasserman, Ryan J.; Ivey, Philip; Zengeya, Tsungai; Weyl, Olaf L. F.
    Background: South Africa, as a signatory of the Convention on Biological Diversity, has an obligation to identify, prioritise and manage invasive species and their introduction pathways. However, this requires knowledge of the introduction pathways, factors influencing establishment success, invasive potential, current distributions and ecological impacts. Objectives: To evaluate the Fish Invasiveness Screening Kit (FISK) to predict the invasion risk posed by fish species proposed for introduction into South Africa. Method: FISK assessments were compiled for species whose invasion status in South Africa was known. A Receiver operating characteristic (ROC) analysis was conducted to calibrate the FISK for South Africa. The calibrated FISK was used to evaluate the risk that three species recently proposed for importation for aquaculture could become invasive in South Africa. Results: A FISK score of 14 was identified as the threshold to delineate between species that could become invasive in South Africa and those that are unlikely to become invasive. Of the three species evaluated, Silurus glanis had a high risk of becoming invasive in South Africa, Lates calcarifer was likely to be invasive and Oncorhynchus tshawytscha was unlikely to be invasive in South Africa. Conclusion: FISK was demonstrated to be a useful risk assessment tool to evaluate the invasion risk posed by species proposed for use in aquaculture. For the large number of fish imported for the pet trade, a rapid screening assessment to flag potentially high risk species was recommended prior to a full FISK assessment for flagged species.
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    The ghost of introduction past : spatial and temporal variability in the genetic diversity of invasive smallmouth bass
    (Wiley Open Access, 2018) Diedericks, Genevieve; Henriques, Romina; Von der Heyden, Sophie; Weyl, Olaf L. F.; Hui, Cang
    Understanding the demographic history of introduced populations is essential for unravelling their invasive potential and adaptability to a novel environment. To this end, levels of genetic diversity within the native and invasive range of a species are often compared. Most studies, however, focus solely on contemporary samples, relying heavily on the premise that the historic population structure within the native range has been maintained over time. Here, we assess this assumption by conducting a three-way comparison of the genetic diversity of native (historic and contemporary) and invasive (contemporary) smallmouth bass (Micropterus dolomieu) populations. Analyses of a total of 572 M. dolomieu samples, representing the contemporary invasive South African range, contemporary and historical native USA range (dating back to the 1930s when these fish were first introduced into South Africa), revealed that the historical native range had higher genetic diversity levels when compared to both contemporary native and invasive ranges. These results suggest that both contemporary populations experienced a recent genetic bottleneck. Furthermore, the invasive range displayed significant population structure, whereas both historical and contemporary native US populations revealed higher levels of admixture. Comparison of contemporary and historical samples showed both a historic introduction of M. dolomieu and a more recent introduction, thereby demonstrating that undocumented introductions of this species have occurred. Although multiple introductions might have contributed to the high levels of genetic diversity in the invaded range, we discuss alternative factors that may have been responsible for the elevated levels of genetic diversity and highlight the importance of incorporating historic specimens into demographic analyses.
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    Monitoring the silver carp invasion in Africa : a case study using environmental DNA (eDNA) in dangerous watersheds
    (Pensoft Publishers, 2020-04-29) Crookes, Steven; Heer, Tej; Castaieda, Rowshyra A.; Mandrak, Nicholas E.; Heath, Daniel D.; Weyl, Olaf L. F.; MacIsaac, Hugh J.; Foxcroft, Llewellyn C.
    Biodiverse habitats are increasingly subject to an intensification of anthropogenic stressors that may severely diminish species richness. Invasive species pose a dominant threat to biodiversity and biosecurity, particularly in biodiversity hotspots like Kruger National Park, South Africa. The invasive silver carp, Hypophthalmichthys molitrix, was introduced into the Olifants River and may experience range spread owing to favorable environmental conditions. Intensive monitoring protocols are necessary to effectively manage invasions of species like silver carp. Unfortunately, tropical and sub-tropical aquatic systems are difficult to monitor using conventional methods (e.g., netting, electrofishing and snorkeling) owing to a range of factors including the presence of dangerous megafauna. Conservation of such systems may be advanced by the adoption of novel methods, including environmental DNA (eDNA) detection. Here, we explore the utility of environmental DNA (eDNA) to conduct safe, reliable and repeatable surveys in dangerous watersheds using silver carp as a case study. We conducted eDNA surveys at 12 sites in two neighbouring watersheds, and determined that the species has expanded its range within the Olifants River and to the south in the Sabie River. Expansion in the former is consistent with the presence of suitable spawning conditions. We discuss the implications of this survey for biodiversity monitoring in similar aquatic systems in the tropics and advocate an integrative approach to biomonitoring in these ecosystems.