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- ItemBotanical gardens as key resources and hazards for biosecurity(2021) Wondafrash, M.; Wingfield, M.J.; Wilson, J.R.U.; Hurley, B.P.; Slippers, B.; Paap, T.Biodiversity and economic losses resulting from invasive plant pests and pathogens are increasing globally. For these impacts and threats to be managed effectively, appropriate methods of surveillance, detection and identification are required. Botanical gardens provide a unique opportunity for biosecurity as they accommodate diverse collections of exotic and native plant species. These gardens are also often located close to high-risk sites of accidental invasions such as ports and urban areas. This, coupled with routine activities such as the movement of plants and plant material, and visits by millions of people each year, place botanical gardens at risk to the arrival and establishment of pests and pathogens. Consequently, botanical gardens can pose substantial biosecurity risks to the environment, by acting as bridgeheads for pest and pathogen invasions. Here we review the role of botanical gardens in biosecurity on a global scale. The role of botanical gardens has changed over time. Initially, they were established as physic gardens (gardens with medicinal plants), and their links with academic institutions led to their crucial role in the accumulation and dissemination of botanical knowledge. During the second half of the 20th century, botanical gardens developed a strong focus on plant conservation, and in recent years there has been a growing acknowledgement of their value in biosecurity research as sentinel sites to identify pest and pathogen risks (novel pest-host associations); for early detection and eradication of pests and pathogens; and for host range studies. We identify eight specific biosecurity hazards associated with botanical gardens and note potential management interventions and the opportunities these provide for improving biosecurity. We highlight the value of botanical gardens for biosecurity and plant health research in general, and the need for strategic thinking, resources, and capacity development to make them models for best practices in plant health.
- ItemPropagule pressure helps overcome adverse environmental conditions during population establishment(2021) Saccaggi, D.L.; Wilson, J.R.U.; Terblanche, J.S.The establishment success of a population is a function of abiotic and biotic factors and introduction dynamics. Understanding how these factors interact has direct consequences for understanding and managing biological invasions and for applied ecology more generally. Here we use a mesocosm approach to explore how the size of founding populations and the number of introduction events interact with environmental conditions (temperature) to determine the establishment success of laboratory-reared Drosophila melanogaster. We found that temperature played the biggest role in establishment success, eclipsing the role of the other experimental factors when viewed overall. Under optimal temperature conditions propagule pressure was of negligible importance to establishment success. At adverse temperatures, however, establishment success increased with the total founding population size. This effect was considerably stronger at the cold than at the hot extreme. Whether the population was introduced all at once or by increments (changing the number of introduction events) had a negligible global effect. However, once again, a stronger effect of increasing number of introduction events was seen at adverse temperatures, with hot and cold extremes revealing opposite effects: adding flies incrementally decreased their establishment success at the hot extreme, but increased it at the cold extreme. These differing effects at hot and cold thermal extremes implies that different establishment mechanisms are at play at either extreme. These results suggest that the effort required to prevent (or conversely, to facilitate) the establishment of populations varies with the environment in ways that can be complicated but predictable.
- ItemThe status of alien bamboos in South Africa(South African Association of Botanists, 2021) Canavan, Susan; Richardson, David M.; Le Roux, Johannes J.; Kelchner, Scot A.; Wilson, John R. U.The growing interest in commercial cultivation of bamboos (Poaceae subfamily Bambusoideae) has led to the introduction of new alien species into South Africa. The rate at which bamboos are being planted in South Africa is a cause for concern because of the impacts of bamboo invasions in other parts of the world. To understand the risks associated with new introductions and new plantings, we assess the outcomes of past introductions of bamboos into South Africa. To this end we: (1) produce an inventory of alien bamboo taxa; (2) assess the distribution of bamboos; (3) determine the rate of spread of bamboo at a site with a high density of naturalised stands; and (4) evaluate the current regulatory status of alien bamboos in South Africa. We used a combination of expert opinion, literature, historical records of populations, and public participation to produce a species list and locate populations of alien bamboos. We also attempted to confirm species identities using DNA barcoding. We found that 28 currently-accepted species of bamboo have been recorded in South Africa. However, we have little confidence in this estimate, as 20 of the species could not be confirmed or identified as present in the country. Bamboos are an inherently challenging group to identify using vegetative material, and DNA barcoding was inconclusive. The distribution of bamboos across the country varied with the type or lineage (e.g. herbaceous, tropical or temperate) and the source of information (e.g. herbarium records, in-field observation or public contribution). Although alien bamboos are naturalised at several sites, we found no large invasive stands nor evidence of widespread negative environmental impacts. Nonetheless, we recommend caution regarding future introductions of bamboos for commercial cultivation, as the nature of the plantings will likely differ from the historical situation in both the location, configuration, and the scale of cultivation, and as new species are likely to be introduced. We propose several changes to the current listing of bamboo taxa in national legislation pertaining to alien and invasive species.
- ItemBiological Invasions in South Africa: an overview(2020 2020) van Wilgen, B.W.; Measey, J.; Richardson, D.M.; Wilson, J.R.; Zengeya, T.A.South Africa has much to offer as a location for the study of biological invasions. It is an ecologically diverse country comprised of nine distinct terrestrial biomes, four recognised marine ecoregions, and two sub-Antarctic Islands. The country has a rich and chequered socio-political history, and a similarly varied history of species introductions. There has been a long tradition of large-scale conservation in the country, and efforts to manage and regulate invasions began in the nineteenth century, with some notable successes, but many setbacks. With the advent of democracy in the early 1990s, South Africa established large alien species control programmes to meet the dual demands of poverty alleviation and conservation, and has since pioneered regulatory approaches to address invasions. In terms of research, South Africa has played an important role in the development of invasion science globally. It continues to have one of the most active communities anywhere in the world, with strengths in theoretical and applied invasion science, and world-leading expertise in specific sub-disciplines (e.g. the classical biological control of invasive plants). In this introductory chapter to the book “Biological Invasions in South Africa”, we highlight key events that have affected biological invasions, their management, and the research conducted over the past two centuries. In so doing, we build on earlier reviews—from a national situational review of the state of knowledge in 1986, culminating most recently with a comprehensive report on the status of biological invasions and their management at a national level in 2018. Our book comprises 31 chapters (including this one), divided into seven parts that examine where we have come from, where we are, how we got here, why the issue is important, what we are doing about it, what we have learnt, and where we may be headed. The book lists over 1400 alien species that have established outside of captivity or cultivation. These species cost the country at least US$1 billion per year (~ZAR 15 billion), and threaten South Africa’s unique biodiversity. The introduction and spread of alien species, the impacts that they have had, the benefits that they have brought, and the attempts to manage them have provided many opportunities for research. Documenting what we have learned from this unplanned experiment is a primary goal of this book. We hope this book will allow readers to better understand biological invasions in South Africa, and thereby assist them in responding to the challenge of addressing the problem.
- ItemPotential Futures of Biological Invasions in South Africa(2020) Wilson, J.R.; Measey, J.; Richardson, D.M.; van Wilgen, B.W.; Zengeya, T.A.Biological invasions are having a moderately negative impact on human livelihoods and the environment in South Africa, but the situation is worsening. Predicting future trends is fraught with many assumptions, so this chapter takes an outcome-orientated approach. We start by envisaging four scenarios for how biological invasions might look like 200–2000 years from now: (1) “Collapse of Civilisation, but no return to Eden”, there is no advanced human civilisation left on Earth and current biological invasions play out in full; (2) “New Pangea”, a combination of the unregulated and rapid movement of species around the world and other global change drivers leads to the biotic homogenisation of areas that were previously distinct biogeographic regions such that the concept of biological invasions no longer has meaning; (3) “Preserve or Use”, while parts of the Earth continue to be utilised, some areas are actively managed and native biodiversity and biogeographic distributions are maintained; and (4) “Conservation Earth”, a highly advanced civilisation restores the Earth to a state prior to the human-mediated movement of organisms (i.e. biological invasions are reversed). Based on various horizon-scanning exercises and our own deliberations, we discuss how technological, socio-political, trade, global change, and ecological-evolutionary processes in South Africa might affect biological invasions by 2070 (i.e. when people born today will be the key decision-makers). Finally, we explore how planning, regulation, funding, public support, and research might affect invasions by 2025 (i.e. over the next planning/management/political cycle). There are many things we can neither predict nor influence, but, in part based on the insights from this book, we highlight some actions that could enable the next generation to decide what they want their future to be. A greater focus on appropriate and innovative training opportunities would increase the efficacy and responsiveness of the management of biological invasions. A shift in regulatory approach from “identify and direct” to a variety of flexible, inclusive, and sophisticated approaches underpinned by evidence might provide more societally acceptable means of addressing the multitude of competing interests. Greater co-operation on biosecurity and implementation with neighbouring countries would assist prevention measures. Finally, monitoring and research aimed at documenting, tracking, and predicting invasions and their impacts would assist with efforts to identify priorities and help us to understand the consequence of different management and policy decisions. While this was a sobering exercise, it was also empowering. If South Africans can agree on a long-term trajectory for how they want to deal with biological invasions, the potential consequences of decision-making over the short-term will become much clearer.