Browsing by Author "Van Wilgen, Nicola J."

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    Alien reptiles and amphibians in South Africa : towards a pragmatic management strategy
    (Academy of Science of South Africa -ASSAf, 2008-02) Van Wilgen, Nicola J.; Richardson, David M.; Baard, Ernst H. W.
    Biological invasions are a growing problem in South Africa. Many alien species have been introduced for various reasons and through multiple pathways over the past few centuries. Invasive alien reptiles and amphibians (herpetofauna) are not yet a major problem in the country. However, escalating difficulties with invasive species in these groups worldwide, and changing circumstances in South Africa, suggest a high risk of increased problems in the future. This paper reviews key issues pertaining to invasive alien herpetofauna worldwide and discusses how risk assessment can be used as part of an effective biosecurity strategy for South Africa. Nearly 300 species of alien herpetofauna have already been imported into the country via the pet trade and are being kept in captivity. There is a need to consider the potential threat of these species, and others still to be introduced, in line with practices in other countries where formal risk assessment policies are in place to separate potentially invasive species from those that are unlikely to be problematical. New legislation in South Africa seeks to regulate activities involving alien species, but exactly how this will be done has yet to be finalized. Each province in South Africa currently has its own legislation with different requirements; this causes many problems. Records of permit applications are also poor, complicating attempts to compile accurate inventories and to discern trends in imports and permit allocations. We define a pragmatic framework for dealing with alien reptiles and amphibians in South Africa. The framework identifies key issues facing the country and considers how the situation and advances elsewhere in the world can be used to set priorities. We propose that a risk assessment protocol be implemented for categorizing species as permissible or prohibited for import and trade. Accurate data are needed on the alien species already in South Africa.
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    Assessing the association between pathways of alien plant invaders and their impacts in protected areas
    (Pensoft Publishers, 2019-03-05) Foxcroft, Llewellyn C.; Spear, Dian; Van Wilgen, Nicola J.; McGeoch, Melodie A.
    Protected areas face mounting pressures, including invasion by alien plant species. Scientifically sound information is required to advise invasive species management strategies, where early detection and rapid response is particularly important. One approach to this is to determine: (i) the relative importance of pathways of invasion by which a species is introduced, (ii) the range of likely impacts associated with each species, and (iii) the relationship between pathways and impacts, to assess the relative threats posed by different pathways of alien species introductions. This assessment was performed on 139 alien plants that are invasive across the South African National Parks (19 national parks, covering ~39,000 km2), and based on available literature and expert opinion, known to have negative ecological impacts. For each species the likelihood of being introduced by each of eight pathways, and of having negative impacts in each of 13 identified impact categories, was assessed. The similarity of impact and pathway types between species was assessed using the Jaccard index and cladograms. Differences in the prevalence of impacts and pathways and relationships between these were assessed using a Chi-squared contingency and Generalised Linear Model. Nearly 80% of the species are ornamental plants and about 60% are also dispersed by rivers, highlighting the importance of managing ornamental species and surveillance along rivers in preventing future invasions. As to the impacts, ~95% of the species compete directly with native species and 70% change the physical structure of the environment. The majority of species exert multiple impacts, with 70% of species assessed having five or more impacts. There was a significant positive relationship between the number of pathways via which a species can be introduced into an area and the number of potential impacts they can have. This suggests that species using multiple pathways reach a wider range of suitable habitats, increasing the potential for different kinds of impacts over a wider area.
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    Biological invasions in South African National Parks
    (AOSIS Publishing, 2017) Foxcroft, Llewellyn C.; Van Wilgen, Nicola J.; Baard, Johan A.; Cole, Nicolas S.
    Objectives: A core objective in South African National Parks (SANParks) is biodiversity conservation and the maintenance of functional ecosystems, which is compromised by alien species invasions. The 2016 Alien and Invasive Species Regulations of the National Environmental Management: Biodiversity Act (NEM:BA) requires landowners to develop management plans for alien and invasive species, as well as report on the status and efficacy of control. Method: To compile the species list, we started with the 2011 SANParks alien species list. Name changes were updated and SANParks ecologists and park managers contacted to verify the species lists and add new records. Species reported by external experts were added in the same manner. The management programme costs and species controlled per park per year were extracted from SANParks’ Working for Water programme database. Results: SANParks has listed 869 alien and extra-limital species, including 752 plants and 117 animals, increasing from 781 alien species in 2011. About R 590 million has been spent by the Working for Water/Biodiversity Social Programmes since 2000/2001. Of the species recorded, 263 are listed by NEM:BA, including 12 Category 1a species, 184 Category 1b species, 28 Category 2 species and 39 Category 3 species. Conclusion: While large clearing programmes have been maintained since at least 1998, improving prioritisation is necessary. We provide a short synopsis of (1) what alien species are present in SANParks, (2) the species and parks that management has focused on, (3) the implications of the NEM:BA Invasive Alien Species Regulations and (4) future developments in monitoring.
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    Investigating the effects of management practice on mammalian co-occurrence along the West Coast of South Africa
    (2020-01-27) Winterton, Deborah Jean; Van Wilgen, Nicola J.; Venter, Jan A.
    ENGLISH ABSTRACT: The subtle and cascading effects (e.g., altered interspecific interactions) that anthropogenic stressors have on local ecological assemblages often go unnoticed but are concerning given their importance in ecosystem function. For example, elimination of buffalo from the Serengeti National Park is suggested to have driven increased abundance of smaller antelope as a result of release from competition. The perceived low abundance of small antelope in the contractual Postberg section of the West Coast National Park (the park) has been an ongoing management concern which has been anecdotally attributed to predation by a mesopredator (the caracal, Caracal caracal). However, we hypothesized that the historical overstocking, and consequent overgrazing by larger-bodied managed ungulates would influence small antelope abundance. Using camera traps, we investigated species co-occurrence and temporal activity between small antelope, managed ungulates and caracals in Postberg as well as another part of the park (Langebaan) and a farm outside of the park. Results suggest that small antelope and managed ungulates have a high degree of temporal overlap (Delta = 0.74, 0.79 and 0.86 for the farm, Langebaan and Postberg respectively), while temporal partitioning between small antelope and caracal is apparent (Delta = 0.59). Further, small antelope and managed ungulates appear to occur independently of one another (SIF = 0.91-1 across areas). Managed ungulates were detected almost three times more frequently on fallow lands when compared to the more vegetated sites within the park suggesting that segregated food/cover resources allow for independent occurrence. Small antelope had a much higher probability of occurrence outside of the protected area (e.g., psi = 0.192 and 0.486 for steenbok at Postberg, Langebaan compared to 0.841 on the farm), likely due to less variable (more intact) habitat outside of the protected area. There is not sufficient evidence to currently warrant management intervention for predators. The small size of the protected area provides limited scope for spatial replication thus reducing possibilities to infer the cause and effect for complex interactions (which would historically have taken place over much larger areas) with negative implications for adaptive management. We recommend continued monitoring over multiple seasons and a wider area to determine the spatial information requirements to inform management of small protected areas.
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    A taxonomically and geographically constrained information base limits non-native reptile and amphibian risk assessment : a systematic review
    (PeerJ, 2018-11-08) Van Wilgen, Nicola J.; Gillespie, Micaela S.; Richardson, David M.; Measey, John; Roberts, David
    ENGLISH ABSTRACT: For many taxa, new records of non-native introductions globally occur at a near exponential rate. We undertook a systematic review of peer-reviewed publications on non-native herpetofauna, to assess the information base available for assessing risks of future invasions, resulting in 836 relevant papers. The taxonomic and geographic scope of the literature was also compared to a published database of all known invasions globally. We found 1,116 species of herpetofauna, 95% of which were present in fewer than 12 studies. Nearly all literature on the invasion ecology of herpetofauna has appeared since 2000, with a strong focus on frogs (58%), particularly cane toads (Rhinella marina) and their impacts in Australia. While fewer papers have been published on turtles and snakes, proportionately more species from both these groups have been studied than for frogs. Within each herpetofaunal group, there are a handful of well-studied species: R. marina, Lithobates catesbeianus, Xenopus laevis, Trachemys scripta, Boiga irregularis and Anolis sagrei. Most research (416 papers; 50%) has addressed impacts, with far fewer studies on aspects like trade (2%). Besides Australia (213 studies), most countries have little location-specific peer-reviewed literature on non-native herpetofauna (on average 1.1 papers per established species). Other exceptions were Guam, the UK, China, California and France, but even their publication coverage across established species was not even. New methods for assessing and prioritizing invasive species such as the Environmental Impact Classification for Alien Taxa provide useful frameworks for risk assessment, but require robust species-level studies. Global initiatives, similar to the Global Amphibian Assessment, using the species and taxonomic groups identified here, are needed to derive the level of information across broad geographic ranges required to apply these frameworks. Expansive studies on model species can be used to indicate productive research foci for understudied taxa.