Center for Invasion Biology

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Center for Invasion Biology

South Africa
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Hargrove J.S.,University of Florida | Weyl O.L.F.,South African Institute For Aquatic Biodiversity | Weyl O.L.F.,Center for Invasion Biology | Austin J.D.,University of Florida
Biological Invasions | Year: 2017

The Largemouth Bass (Micropterus salmoides) is a global invader with demonstrated ecological impacts on native fish communities. Introductions of fishes in freshwater ecosystems are often characterized as complex processes, yet an understanding of the nature of the introduction can inform management and conservation actions. Early in the twentieth century, two introductions of Largemouth Bass were made into South Africa for the establishment of a recreational fishery, and subsequent translocations have expanded their distribution to include much of southern Africa. In this study we quantified neutral genetic variation, modeled potential introduction scenarios, and identified potential source regions from within the native range. We documented limited levels of genetic diversity in nuclear microsatellite genotypes across populations (mean allelic richness = 1.80 and mean observed heterozygosity = 0.16) and observed low levels of genetic differentiation among four of the five focal populations (mean pairwise fixation index = 0.09), with a fifth population displaying greater levels of genetic divergence (mean pairwise fixation index = 0.27). A total of three cytochrome b haplotypes were recovered from South Africa samples and the single most common haplotype (93% of individuals) was identical to a haplotype from a population of Largemouth Bass in Maryland, USA. Using limited available stocking data along with outputs from Principal Component Analysis and approximate Bayesian evaluation of competing introduction scenarios we confirm the presence of multiple introductions. Despite evidence for multiple introductions, Largemouth Bass in South African water bodies harbor extremely low neutral genetic diversity, suggesting that even a very limited number of propagules can experience a high likelihood of success in invading nonnative waters. © 2017 Springer International Publishing Switzerland


Woodford D.J.,University of Witwatersrand | Woodford D.J.,South African Institute For Aquatic Biodiversity | Ivey P.,South African National Biodiversity Institute | Jordaan M.S.,South African Institute For Aquatic Biodiversity | And 4 more authors.
Bothalia | Year: 2017

Background: South Africa hosts a large number of non-native freshwater fishes that were introduced for various industries. Many of these species are now listed under the National Environmental Management: Biodiversity Act (NEM:BA) Alien and Invasive Species (A&IS) lists and regulations, though the practical options available to conservation agencies to effectively manage these fishes vary greatly among species and regions. Objectives & methods: We assessed the history and status of national legislation pertaining to invasive freshwater fishes, and the practical implications of the legislation for managing different species with contrasting distributions, impacts and utilisation value. Results: The smallmouth bass, despite being a potential conflict-generating species, is fairly straightforward to manage based on current legislation. Two species of trout, which remain absent from the NEM:BA A&IS lists because of ongoing consultation with stakeholders, continue to be managed in regions like the Western Cape province using existing provincial legislation. To maximise the limited capacity for management within conservation agencies, we proposed a decision-support tool that prioritises invasive fish populations that represent high environmental risk and low potential for conflict with stakeholders. Using three case studies, we demonstrated how the tool can be used to set management goals of 'eradicate', 'manage against impacts and further spread' and 'continue to monitor population' as the most pragmatic solutions given the state of an invasion, its socio-economic impact and the capacity of the responsible agency to act. Conclusion: By choosing a pragmatic management strategy, conservation agencies can maximise the effective deployment of limited resources, while minimising avoidable conflicts with stakeholders. © 2017. The Authors.


Alexander M.E.,Stellenbosch University | Dick J.T.A.,Queen's University of Belfast | Weyl O.L.F.,South African Institute For Aquatic Biodiversity | Weyl O.L.F.,Center for Invasion Biology | And 2 more authors.
Biology Letters | Year: 2014

Predicting ecological impacts of invasive species and identifying potentially damaging future invaders are research priorities. Since damage by invaders is characterized by their depletion of resources, comparisons of the 'functional response' (FR; resource uptake rate as a function of resource density) of invaders and natives might predict invader impact. We tested this by comparing FRs of the ecologically damaging 'world's worst' invasive fish, the largemouth bass (Micropterus salmoides), with a native equivalent, the Cape kurper (Sandelia capensis), and an emerging invader, the sharptooth catfish (Clarias gariepinus), with the native river goby (Glossogobius callidus), in South Africa, a global invasion hotspot. Using tadpoles (Hyperolius marmoratus) as prey, we found that the invaders consumed significantly more than natives. Attack rates at lowprey densities within invader/native comparisons reflected similarities in predatory strategies; however, both invasive species displayed significantly higher Type II FRs than the native comparators. This was driven by significantly lower prey handling times by invaders, resulting in significantly higher maximumfeeding rates. The higher FRs of these invaders are thus congruent with, and can predict, their impacts on native communities. Comparative FRs may be a rapid and reliable method for predicting ecological impacts of emerging and future invasive species. © 2014 The Author(s) Published by the Royal Society.


Haussmann N.S.,Stellenbosch University | McGeoch M.A.,Center for Invasion Biology | Boelhouwers J.C.,Uppsala University
Acta Oecologica | Year: 2010

Positive plant interactions, such as those associated with nurse plants, have been suggested to dominate over negative interactions in environments with high abiotic stress. Here we demonstrate that the sub-Antarctic cushion plant species, Azorella selago (Apiaceae), positively affects the distribution of both its own seedlings and those of the perennial grass, Agrostis magellanica (Poaceae). As a result of the light weight and small size of seeds of both species, coupled with strong winds experienced in the study area, we consider it unlikely that these patterns are the result of very localized seed dispersal from the study cushions themselves. Instead, we suggest that both cushions and rocks act as seed traps, trapping seeds dispersed by wind, runoff and/or downslope sediment transport through frost creep. In addition, increased A. selago seedling numbers around cushions, but not around rocks, suggest that cushions provide a biological nurse effect, such as improving soil nutrient status or providing mychorrizae, to seedlings of their own kind. © 2010 Elsevier Masson SAS. All rights reserved.


Hui C.,Stellenbosch University | Veldtman R.,Stellenbosch University | McGeoch M.A.,Center for Invasion Biology
Ecography | Year: 2010

Non-random (aggregated) species distributions arise from habitat heterogeneity and nonlinear biotic processes. A comprehensive understanding of the concept of aggregation, as well as its measurement, is pivotal to our understanding of species distributions and macroecological patterns. Here, using an individual-based model, we analyzed opinions on the concept of aggregation from the public and experts (trained ecologists), in addition to those calculated from a variety of aggregation indices. Three forms of scaling patterns (logarithmic, power-law and lognormal) and four groups of scaling trajectories emerged. The experts showed no significant difference from the public, although with a much lower deviation. The public opinion was partially influenced by the abundance of individuals in the spatial map, which was not found in the experts. With the increase of resolution (decrease of grain), aggregation indices showed a general trend from significantly different to significantly similar to the expert opinion. The over-dispersion index (i.e. the clumping parameter k in the negative binomial distribution) performed, at certain scales, as the closest index to the expert opinion. Examining performance of aggregation measures from different groups of scaling patterns was proposed as a practical way of analyzing spatial structures. The categorization of the scaling patterns of aggregation measures, as well as their overand in-sensitivity towards spatial structures, thus not only provides a potential solution to the modifiable areal unit problem, but also unveils the interrelationship among the concept, measures and perceptions of aggregated species distributions. © 2010 The Author. Journal compilation © 2010 Ecography.


McGeoch M.A.,Center for Invasion Biology | Butchart S.H.M.,BirdLife International | Spear D.,Stellenbosch University | Marais E.,Stellenbosch University | And 4 more authors.
Diversity and Distributions | Year: 2010

Aim Invasive alien species (IAS) pose a significant threat to biodiversity. The Convention on Biological Diversity's 2010 Biodiversity Target, and the associated indicator for IAS, has stimulated globally coordinated efforts to quantify patterns in the extent of biological invasion, its impact on biodiversity and policy responses. Here, we report on the outcome of indicators of alien invasion at a global scale. Location Global. Methods We developed four indicators in a pressure-state-response framework, i.e. number of documented IAS (pressure), trends in the impact of IAS on biodiversity (state) and trends in international agreements and national policy adoption relevant to reducing IAS threats to biodiversity (response). These measures were considered best suited to providing globally representative, standardized and sustainable indicators by 2010. Results We show that the number of documented IAS is a significant underestimate, because its value is negatively affected by country development status and positively by research effort and information availability. The Red List Index demonstrates that IAS pressure is driving declines in species diversity, with the overall impact apparently increasing. The policy response trend has nonetheless been positive for the last several decades, although only half of countries that are signatory to the Convention on Biological Diversity (CBD) have IAS-relevant national legislation. Although IAS pressure has apparently driven the policy response, this has clearly not been sufficient and/or adequately implemented to reduce biodiversity impact. Main conclusions For this indicator of threat to biodiversity, the 2010 Biodiversity Target has thus not been achieved. The results nonetheless provide clear direction for bridging the current divide between information available on IAS and that needed for policy and management for the prevention and control of IAS. It further highlights the need for measures to ensure that policy is effectively implemented, such that it translates into reduced IAS pressure and impact on biodiversity beyond 2010. © 2010 Blackwell Publishing Ltd.


van Wilgen B.W.,Center for Invasion Biology | van Wilgen B.W.,South African Council for Scientific and Industrial Research | Forsyth G.G.,South African Council for Scientific and Industrial Research | Prins P.,South African National Parks
Ecology and Society | Year: 2012

The Table Mountain National Park is a 265-km 2 conservation area embedded within a city of 3.5 million people. The highly diverse and unique vegetation of the park is both fire prone and fire adapted, and the use of fire forms an integral part of the ecological management of the park. Because fires are both necessary and dangerous, fire management is characterized by uncertainty and conflict. The response of vegetation to fire is reasonably well understood, but the use of fire for conservation purposes remains controversial because of key gaps in understanding. These gaps include whether or not the vegetation is resilient to increases in fire frequency, how to deal with fire-sensitive forests embedded in fire-prone shrublands, and how to integrate fire and invasive alien plant control. National legislation emphasizes the need to protect communities from dangerous wildfires, and this compels fire managers to adopt a cautious approach to the application of fire. Ecological outcomes are optimized under a fire regime of relatively high-intensity, dry-season fires. Obtaining permission to burn under such conditions is not possible, and so the practice of prescribed burning is constrained, and this results in a fire regime dominated by wildfires. Ecological uncertainties, and the divergent requirements for maintaining healthy ecosystems on the one hand, and ensuring human safety on the other, result in a complex fire management environment. These complexities could be, and in some cases are being, alleviated by raising awareness, increasing fire management capacity, improving ecological monitoring of the effects of fire, and prioritizing areas for integrated fire and invasive alien plant management. © 2012 by the author(s). Published here under license by the Resilience Alliance.


Weyl O.L.F.,South African Institute For Aquatic Biodiversity | Weyl O.L.F.,Center for Invasion Biology | Ellender B.R.,Rhodes University | Woodford D.J.,South African Institute For Aquatic Biodiversity | And 2 more authors.
African Journal of Aquatic Science | Year: 2013

Alien fishes are considered the most serious threat to native headwater stream fishes in South Africa. A 4 km reach of the Rondegat River is the first section of a South African river to be rehabilitated through the attempted removal of alien fish by using the piscicide rotenone. The objectives of the current study were to establish the distribution and relative abundance of native and alien fish prior to treatment, and to assess the immediate impact of the treatment on the fish population. Forty-three sites were sampled using backpack electrofishing, snorkel transects and underwater video analysis. In the invaded lower reaches, native Labeobarbus capensis was detected only at very low densities, while three other native fish species were not detected. Alien fish were not detected above a barrier waterfall 5 km upstream of the river's confluence with a reservoir. The fish density of 97 fish per 100 m2 in non-invaded reaches was more than an order of magnitude higher than that of 7 fish per 100 m2 in the invaded reach. A total of 470 Micropterus dolomieu and 139 L. capensis were removed from a 4 km treatment zone during the rotenone operation. No fish were detected in this area after the rotenone treatment. © 2013 Copyright NISC (Pty) Ltd.


The Table Mountain National Park is a 265 km2 protected area embedded within a city of 3.5 million people. The park contains an extremely diverse flora with many endemic species, and has been granted World Heritage Site status in recognition of this unique biodiversity. Invasive alien plants are arguably the most significant threat to the conservation of this biodiversity, and the past decade has seen the implementation of aggressive programs aimed at the removal of invasions by these plants. These invasive alien plants include several species of trees, notably pines (Pinus species) and eucalypts (Eucalyptus species), which historically have been grown in plantations, and which are utilized for recreation by the city's residents. In addition, many citizens regard the trees as attractive and ecologically beneficial, and for these reasons the alien plant control programs have been controversial. I briefly outline the legal obligations to deal with invasive alien plants, the history of control operations and the scientific rationale for their implementation, and the concerns that have been raised about the operations. Evidence in support of control includes the aggressive invasive nature of many species, and the fact that they displace native biodiversity (often irreversibly) and have negative impacts on hydrology, fire intensity, and soil stability. Those against control cite aesthetic concerns, the value of pine plantations for recreation, the (perceived) unattractive nature of the treeless natural vegetation, and the (incorrect) belief that trees bring additional rainfall. The debate has been conducted through the press, and examples of perceptions and official responses are given. Despite opposition, the policy promoting alien plant removal has remained in place, and considerable progress has been made towards clearing pine plantations and invasive populations. This conservation success story owes much to political support, arising largely from job creation, and a strong body of scientific evidence that could be cited in support of the program. © 2012 by the author(s).


Ellender B.R.,Rhodes University | Ellender B.R.,South African Institute For Aquatic Biodiversity | Ellender B.R.,Center for Invasion Biology | Weyl O.L.F.,South African Institute For Aquatic Biodiversity | Weyl O.L.F.,Center for Invasion Biology
Aquatic Invasions | Year: 2014

The introduction and spread of non-native species is one of the least reversible human-induced global changes. In South Africa, non-native fish introductions have occurred over the last two and a half centuries. Resultant invasions have been cited as a primary threat to imperilled South African fishes and other aquatic fauna. Addressing a problem of this magnitude requires an organised approach. The aim of this paper is to summarise the current knowledge, risk and ecological impacts associated with non-native freshwater fish introductions in South Africa. A total of 55 fishes have been introduced into novel environments in South Africa. Of these, 27 were alien and 28 were extralimital introductions. Only 11 introduced species failed to establish and of the 44 species that have established, 37% are considered fully invasive. Introductions for angling were responsible for the highest proportion (55%) of fully invasive species with the remainder linked to inter-basin water transfers (15%), bio-control (15%), ornamental fish trade (10%) and aquaculture (5%). There was a general paucity of published literature on the introduction, establishment and spread of non-native fishes, and recent research has largely focused on impacts on native biota. While documented impacts spanned multiple levels of biological organisation, most papers focused on individual and population level impacts. Large taxonomic biases were also observed, and invasive impacts were estimated for less than 50% of fully invasive fishes. There is also an extensive knowledge gap on the impacts of associated parasites and diseases introduced with non-native fishes. These knowledge gaps constrain effective management of non-native fishes in South Africa and research at all invasion stages (introduction, establishment, spread and impact) is necessary to guide conservation practitioners and managers with information to manage current invasions and curb future introductions. © 2014 The Author(s).

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