Browsing by Author "Visser, Vernon"

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    The global distribution of bamboos : assessing correlates of introduction and invasion
    (Oxford University Press on behalf of the Annals of Botany Company, 2016-12-23) Canavan, Susan; Richardson, David M.; Visser, Vernon; Le Roux, Johannes J.; Vorontsova, Maria S.; Wilson, John R. U.
    There is a long history of species being moved around the world by humans. These introduced species can provide substantial benefits, but they can also have undesirable consequences. We explore the importance of human activities on the processes of species dissemination and potential invasions using the Poaceae subfamily Bambusoideae (‘bamboos’), a group that contains taxa that are widely utilised and that are often perceived as weedy. We (1) compiled an inventory of bamboo species and their current distributions; (2) determined which species have been introduced and become invasive outside their native ranges; and (3) explored correlates of introduction and invasion. Distribution data were collated from Kew’s GrassBase, the Global Biodiversity Information Facility and other online herbarium information sources. Our list comprised 1662 species in 121 genera, of which 232 (14 %) have been introduced beyond their native ranges. Twelve (0.7 % of species) were found to be invasive. A non-random selection of bamboos have been introduced and become invasive. Asiatic species in particular have been widely introduced. There was a clear over-representation of introduced species in the genera Bambusa and Phyllostachys which also contain most of the listed invasive species. The introduction of species also correlated with certain traits: taxa with larger culm dimensions were significantly more likely to have been moved to new areas; and those with many cultivars had a higher rate of dissemination and invasion. It is difficult to determine whether the patterns of introduction and invasion are due simply to differences in propagule pressure, or whether humans have deliberately selected inherently invasive taxa. In general, we suggest that human usage is a stronger driver of introductions and invasions in bamboos than in other taxa that have been well studied. It is likely that as bamboos are used more widely, the number and impact of invasions will increase unless environmental risks are carefully managed.
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    Global environmental and socio-economic impacts of selected alien grasses as a basis for ranking threats to South Africa
    (Pensoft Publishers, 2018-12-21) Nkuna, Khensani V.; Visser, Vernon; Wilson, John R. U.; Kumschick, Sabrina
    ENGLISH ABSTRACT: Decisions to allocate management resources should be underpinned by estimates of the impacts of biological invasions that are comparable across species and locations. For the same reason, it is important to assess what type of impacts are likely to occur where, and if such patterns can be generalised. In this paper, we aim to understand factors shaping patterns in the type and magnitude of impacts of a subset of alien grasses. We used the Generic Impact Scoring System (GISS) to review and quantify published impact records of 58 grass species that are alien to South Africa and to at least one other biogeographical realm. Based on the GISS scores, we investigated how impact magnitudes varied across habitats, regions and impact mechanisms using multiple regression. We found impact records for 48 species. Cortaderia selloana had the highest overall impact score, although in contrast to five other species (Glyceria maxima, Nassella trichotoma, Phalaris aquatica, Polypogon monspeliensis, and Sorghum halepense) it did not score the highest possible impact score for any specific impact mechanism. Consistent with other studies, we found that the most frequent environmental impact was through competition with native plant species (with 75% of cases). Socio-economic impacts were recorded more often and tended to be greater in magnitude than environmental impacts, with impacts recorded particularly often on agricultural and animal production (57% and 51% of cases respectively). There was variation across different regions and habitats in impact magnitude, but the differences were not statistically significant. In conclusion, alien grasses present in South Africa have caused a wide range of negative impacts across most habitats and regions of the world. Reviewing impacts from around the world has provided important information for the management of alien grasses in South Africa, and, we believe, is an important component of management prioritisation processes in general.
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    Grasses as invasive plants in South Africa revisited : patterns, pathways and management
    (AOSIS Publishing, 2017) Visser, Vernon; Wilson, John R. U.; Canavan, Kim; Canavan, Susan; Fish, Lyn; Le Maitre, David; Nänni, Ingrid; Mashau, Caroline; O’Connor, Tim; Ivey, Philip; Kumschick, Sabrina; Richardson, David M.
    Background: In many countries around the world, the most damaging invasive plant species are grasses. However, the status of grass invasions in South Africa has not been documented recently. Objectives: To update Sue Milton’s 2004 review of grasses as invasive alien plants in South Africa, provide the first detailed species level inventory of alien grasses in South Africa and assess the invasion dynamics and management of the group. Method: We compiled the most comprehensive inventory of alien grasses in South Africa to date using recorded occurrences of alien grasses in the country from various literature and database sources. Using historical literature, we reviewed past efforts to introduce alien grasses into South Africa. We sourced information on the origins, uses, distributions and minimum residence times to investigate pathways and patterns of spatial extent. We identified alien grasses in South Africa that are having environmental and economic impacts and determined whether management options have been identified, and legislation created, for these species. Results: There are at least 256 alien grass species in the country, 37 of which have become invasive. Alien grass species richness increased most dramatically from the late 1800s to about 1940. Alien grass species that are not naturalised or invasive have much shorter residence times than those that have naturalised or become invasive. Most grasses were probably introduced for forage purposes, and a large number of alien grass species were trialled at pasture research stations. A large number of alien grass species in South Africa are of Eurasian origin, although more recent introductions include species from elsewhere in Africa and from Australasia. Alien grasses are most prevalent in the south-west of the country, and the Fynbos Biome has the most alien grasses and the most widespread species. We identified 11 species that have recorded environmental and economic impacts in the country. Few alien grasses have prescribed or researched management techniques. Moreover, current legislation neither adequately covers invasive species nor reflects the impacts and geographical extent of these species. Conclusion: South Africa has few invasive grass species, but there is much uncertainty regarding the identity, numbers of species, distributions, abundances and impacts of alien grasses. Although introductions of alien grasses have declined in recent decades, South Africa has a potentially large invasion debt. This highlights the need for continued monitoring and much greater investment in alien grass management, research and legislation.
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    Patterns and traits associated with invasions by predatory marine crabs
    (Pensoft Publishers, 2018-08-28) Swart, Cheruscha; Visser, Vernon; Robinson, Tamara B.; Ruiz, G.
    Predatory crabs are considered amongst the most successful marine invasive groups. Nonetheless, most studies of these taxa have been descriptive in nature, biased towards specific species or regions and have seldom considered traits associated with invasiveness. To address this gap in knowledge, this study presents a global review of invasions by this group and applies biological trait analysis to investigate traits associated with invasion success. A total of 56 species belonging to 15 families were identified as having spread outside their native ranges. The family Portunidae supported the highest number of alien species (22). Most crabs had their origin in the North West Pacific IUCN bioregion while the Mediterranean Sea received the most species. No traits associated with successful establishment were identified, but this finding may reflect the paucity of basic biological knowledge held for many species. This lack of foundational knowledge was unexpected as crabs are large and conspicuous and likely to be well studied when compared to many other groups. Addressing this knowledge gap will be the first step towards enabling approaches like biological trait analysis that offer a means to investigate generalities in invasions.
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    The world needs BRICS countries to build capacity in invasion science
    (Public Library of Science, 2019-09-19) Measey, John; Visser, Vernon; Dgebuadze, Yury; Inderjit; Li, Bo; Dechoum, Michele; Ziller, Silvia R.; Richardson, David M.
    Developed countries are producing policies to reduce the flow of invasive species and control or eradicate existing invasions, but most developing countries are under-resourced to tackle either aspect without help. Emerging economies, such as Brazil, Russia, India, China, and South Africa (BRICS), are responsible for donating many of the world’s invasive species that have the potential to reach nearly all terrestrial biomes. Implementing a proactive ‘facilitated network’ model is urgently required to build capacity and stimulate effective appropriate invasion science. We contend that creating a BRICS network of invasion scientists will have the immediate impact required to meet future policy demands.