Browsing by Author "Rouget, Mathieu"
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- ItemAn assessment of the information content of South African alien species databases(http://www.aosis.co.za/, 2015-05) Faulkner, Katelyn T.; Spear, Dian; Robertson, Mark P.; Rouget, Mathieu; Wilson, John R. U.National alien species databases indicate the state of a country’s biodiversity and provide useful data for research on invasion biology and the management of invasions. In South Africa there are several different published alien species databases, but these databases were created for different purposes and vary in completeness and information content. We assessed the information content of published South African alien species databases in the context of other such databases globally, and evaluated how the information content of South African databases varies across taxonomic groups. Although introduction pathway, date of introduction, region of origin and current broad-scale distribution data are available for most taxonomic groups assessed (60% – 90%), data on invasion status, introduction effort and introduction source are available for few taxonomic groups (5% – 18%). South African alien species databases have lower information content than the detailed databases available in other parts of the world and thus cannot be utilised to the same extent. We conclude with 11 recommendations for improving South African alien species databases. In particular, we highlight the data types that should be incorporated in future databases and argue that existing data should be collated in a single, standardised meta-database to facilitate cross-taxon comparisons, highlight gaps in effort, and inform managers and policy makers concerned with alien species.
- ItemThe balance of trade in alien species between South Africa and the rest of Africa(AOSIS Publishing, 2017) Faulkner, Katelyn T.; Hurley, Brett P.; Robertson, Mark P.; Rouget, Mathieu; Wilson, John R. U.Background: Alien organisms are not only introduced from one biogeographical region to another but also spread within regions. As South Africa shares land borders with six countries, multiple opportunities exist for the transfer of alien species between South Africa and other African countries; however, the direction and importance of intra-regional spread is unclear. Objectives: The aim of this study was to gain a greater understanding of the introduction of alien species into Africa and the spread of species between South Africa and other African countries. Method: We developed scenarios that describe the routes by which alien species are introduced to and spread within Africa and present case studies for each. Using data from literature sources and databases, the relative importance of each scenario for alien birds and insect pests of eucalypts was determined, and the direction and importance of intra-regional spread was assessed. Results: Alien species from many taxonomic groups have, through various routes, been introduced to and spread within Africa. For birds and eucalypt insect pests, the number of species spreading in the region has recently increased, with South Africa being a major recipient of birds (14 species received and 5 donated) and a major donor of eucalypt insect pests (1 species received and 10 donated). For both groups, many introduced species have not yet spread in the region. Conclusion: The intra-regional spread of alien species in Africa represents an important and possibly increasing threat to biosecurity. To address this threat, we propose a framework that details how African countries could cooperate and develop a coordinated response to alien species introductions.
- ItemForestry trial data can be used to evaluate climate-based species distribution models in predicting tree invasions(Pensoft, 2014) Motloung, Rethabile Frangenie; Robertson, Mark Peter; Rouget, Mathieu; Wilson, John Ross U.Climate is frequently used to predict the outcome of species introductions based on the results from species distribution models (SDMs). However, despite the widespread use of SDMs for pre- and post-border risk assessments, data that can be used to validate predictions is often not available until after an invasion has occurred. Here we explore the potential for using historical forestry trials to assess the performance of climate-based SDMs. SDMs were parameterized based on the native range distribution of 36 Australian acacias, and predictions were compared against both the results of 150 years of government forestry trials, and current invasive distribution in southern Africa using true skill statistic, sensitivity and specificity. Classification tree analysis was used to evaluate why some Australian acacias failed in trials while others were successful. Predicted suitability was significantly related to the invaded range (sensitivity = 0.87) and success in forestry trials (sensitivity = 0.80), but forestry trial failures were under-predicted (specificity = 0.35). Notably, for forestry trials, the success in trials was greater for species invasive somewhere in the world. SDM predictions also indicate a considerable invasion potential of eight species that are currently naturalized but not yet widespread. Forestry trial data clearly provides a useful additional source of data to validate and refine SDMs in the context of risk assessment. Our study identified the climatic factors required for successful invasion of acacias, and accentuates the importance of integration of status elsewhere for risk assessment.
- ItemNational-scale strategic approaches for managing introduced plants : insights from Australian acacias in South Africa(Blackwell Publishing, 2011) Van Wilgen, Brian W.; Dyer, Colin; Hoffmann, John H.; Ivey, Philip; Le Maitre, David C.; Moore, Joslin L.; Richardson, David M.; Rouget, Mathieu; Wannenburgh, Andrew; Wilson, John R. U.Aim: A range of approaches and philosophies underpin national-level strategies for managing invasive alien plants. This study presents a strategy for the management of taxa that both have value and do harm. Location: South Africa. Methods: Insights were derived from examining Australian Acacia species in South Africa (c. 70 species introduced, mostly > 150 years ago; some have commercial and other values; 14 species are invasive, causing substantial ecological and economic damage). We consider options for combining available tactics and management practices. We defined (1) categories of species based on invaded area (a surrogate for impact) and the value of benefits generated and (2) management regions based on habitat suitability and degree of invasion. For each category and region, we identified strategic goals and proposed the combinations of management practices to move the system in the desired direction. Results: We identified six strategic goals that in combination would apply to eight species categories. We further identified 14 management practices that could be strategically combined to achieve these goals for each category in five discrete regions. When used in appropriate combinations, the prospect of achieving the strategic goal will be maximized. As the outcomes of management cannot be accurately predicted, management must be adaptive, requiring continuous monitoring and assessment, and realignment of goals if necessary. Main conclusions: Invasive Australian Acacia species in South Africa continue to spread and cause undesirable impacts, despite a considerable investment into management. This is because the various practices have historically been uncoordinated in what can be best described as a strategy of hope. Our proposed strategy offers the best possible chance of achieving goals, and it is thefirst to address invasive alien species that have both positive value and negative impacts.
- ItemNative range size and growth form in Cactaceae predict invasiveness and impact(Pensoft, 2016) Novoa, Ana; Kumschick, Sabrina; Richardson, David M.; Rouget, Mathieu; Wilson, John R. U.Many recent studies in invasion science have identified species traits that determine either invasiveness or impact. Such analyses underpin risk assessments and attempts to prioritise management actions. However, the factors that mediate the capacity of an introduced species to establish and spread (i.e. its invasiveness) can differ from those that affect the nature and severity of impacts. Here we compare those traits correlated with invasiveness with those correlated with impact for Cactaceae (“cacti”) in South Africa. To assess impact magnitude, we scored 70 cacti (35 invasive and 35 non-invasive species) using the Generic Impact Scoring System (GISS) and identified traits correlated with impact using a decision tree approach. We then compared the traits correlated with impact with those identified in a recent study as correlated with invasiveness (i.e. native range size and growth form). We found that there is a significant correlation between native range size and both invasiveness and impact. Cacti with larger native ranges were more likely to become invasive (p=0.001) and cause substantial impacts (p=0.01). These results are important for prioritising efforts on the management of cactus species. Understanding when and why impact and invasiveness are correlated (as they appear to be for Cactaceae) is likely to be an important area of future research in risk assessment.
- ItemPrioritising surveillance for alien organisms transported as stowaways on ships travelling to South Africa(Public Library of Science, 2017-04-05) Faulkner, Katelyn T.; Robertson, Mark P.; Rouget, Mathieu; Wilson, John R. U.The global shipping network facilitates the transportation and introduction of marine and terrestrial organisms to regions where they are not native, and some of these organisms become invasive. South Africa was used as a case study to evaluate the potential for shipping to contribute to the introduction and establishment of marine and terrestrial alien species (i.e. establishment debt) and to assess how this varies across shipping routes and seasons. As a proxy for the number of species introduced (i.e. ‘colonisation pressure’) shipping movement data were used to determine, for each season, the number of ships that visited South African ports from foreign ports and the number of days travelled between ports. Seasonal marine and terrestrial environmental similarity between South African and foreign ports was then used to estimate the likelihood that introduced species would establish. These data were used to determine the seasonal relative contribution of shipping routes to South Africa’s marine and terrestrial establishment debt. Additionally, distribution data were used to identify marine and terrestrial species that are known to be invasive elsewhere and which might be introduced to each South African port through shipping routes that have a high relative contribution to establishment debt. Shipping routes from Asian ports, especially Singapore, have a particularly high relative contribution to South Africa’s establishment debt, while among South African ports, Durban has the highest risk of being invaded. There was seasonal variation in the shipping routes that have a high relative contribution to the establishment debt of the South African ports. The presented method provides a simple way to prioritise surveillance effort and our results indicate that, for South Africa, port-specific prevention strategies should be developed, a large portion of the available resources should be allocated to Durban, and seasonal variations and their consequences for prevention strategies should be explored further.
- ItemTourists' perceptions and willingness to pay for the control of Opuntia stricta invasion in protected areas : a case study from South Africa(AOSIS, 2014-07-15) Nikodinoska, Natasha; Foxcroft, Llewellyn C.; Rouget, Mathieu; Paletto, Alessandro; Notaro, SandraInvasive alien plants have a long history of establishment in the national parks of South Africa. In particular, Opuntia stricta (sour prickly pear) has invaded several protected areas in the country, threatening the biodiversity conservation mandate of these conservation areas. This article focuses on the economic estimation of O. stricta’s negative impacts in protected areas by using Contingent Valuation surveys conducted amongst a sample of tourists in the Pilanesberg National Park (North West Parks and Tourism Board, South Africa). Tourists’ familiarity and awareness of selected invasive alien plants and their willingness to pay for the implementation of a control programme for O. stricta were assessed. The results show that many tourists are familiar with invasive alien plants and their (positive and negative) impacts and, in particular, perceived the presence of O. stricta to be negative, due to the impacts on aesthetics and recreation. Socio-demographic characteristics, as well as individual attitudes and biocentric beliefs, have an influence on the willingness to contribute financially to a control programme for O. stricta. The individual willingness to pay assessment found that the majority of respondents (78%) were willing to pay a higher entrance fee (an additional R57.30 or $7.00 per day) for a hypothetical programme to control the invasion of O. stricta in the Pilanesberg National Park. Conservation implications: The willingness of tourists to pay for O. stricta management provides useful insights in the decision-making process of park management. The results are encouraging, since, in general, tourists are aware of the problem and are in support of providing additional economic input for preventing future alien plant invasions.