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- ItemClassifying the introduction pathways of alien species: are we moving in the right direction?(2020) Faulkner, K.T.; Hulme, P.E.; Pagad, S.; Wilson, J.R.U.; Robertson, M.P.Alien species are introduced to new regions in many different ways and for different purposes. A number of frameworks have been developed to group such pathways of introduction into discrete categories in order to improve our understanding of biological invasions, provide information for interventions that aim to prevent introductions, enable reporting to national and international organisations and facilitate the prediction of threats. The introduction pathway classification framework proposed by the Convention on Biological Diversity (CBD) as a global standard is comprised of six main categories and 44 sub-categories. However, issues have arisen with its implementation. In this position paper, we outline five desirable properties of an introduction pathway classification framework – it should be compatible (i.e. the level of detail of the categories is similar to that of the available data), actionable (i.e. categories link to specific interventions), general (i.e. categories are applicable across the contexts that are of interest (e.g. taxa, habitats and regions)), equivalent (i.e. categories are equivalent in their level of detail) and distinct (i.e. categories are discrete and easily distinguished) – termed the CAGED properties. The six main categories of the CBD framework have all of the CAGED properties, but the detailed sub-categories have few. Therefore, while the framework has been proposed by the CBD as a global standard and efforts have been made to put it into practice, we argue that there is room for improvement. We conclude by presenting scenarios for how the issues identified could be addressed, noting that a hybrid model might be most appropriate.
- ItemThe Convention on Biological Diversity (CBD)’s Post-2020 target on invasive alien species – what should it include and how should it be monitored?(2020) Essl, F.; Latombe, G.; Lenzner, B.; Pagad, S.; Seebens, H.; Smith, K.; Wilson, J.R.U.; Genovesi, P.The year 2020 and the next few years are critical for the development of the global biodiversity policy agenda until the mid-21st century, with countries agreeing to a Post-2020 Global Biodiversity Framework under the Convention on Biological Diversity (CBD). Reducing the substantial and still rising impacts of invasive alien species (IAS) on biodiversity will be essential if we are to meet the 2050 Vision where biodiversity is valued, conserved, and restored. A tentative target has been developed by the IUCN Invasive Species Specialist Group (ISSG), and formally submitted to the CBD for consideration in the discussion on the Post-2020 targets. Here, we present properties of this proposal that we regard as essential for an effective Post-2020 Framework. The target should explicitly consider the three main components of biological invasions, i.e. (i) pathways, (ii) species, and (iii) sites; the target should also be (iv) quantitative, (v) supplemented by a set of indicators that can be applied to track progress, and (vi) evaluated at medium- (2030) and long-term (2050) time horizons. We also present a proposed set of indicators to track progress. These properties and indicators are based on the increasing scientific understanding of biological invasions and effectiveness of responses. Achieving an ambitious action-oriented target so that the 2050 Vision can be achieved will require substantial effort and resources, and the cooperation of a wide range of stakeholders.
- ItemInterspecific competition in germination of bird-dispersed seeds in a habitat with sparse tree vegetation in South Africa(2021) Mokotjomela, T.M.; Vukeya, L.; Malebo, N.; Oke, S.Avian frugivores provide directed seed dispersal services that contribute in shaping the native plant communities and facilitate population persistence. By transporting and scarifying the seeds during ingestion, avian frugivores reduce the competition with siblings, and may improve the germination which is critical for dispersal effectiveness. However, generally, there is limited knowledge on how deposited seeds interact/compete in the new microsite. Therefore, we investigated 1) whether bird-dispersed seeds benefit from improved germination after their passage through the bird’s gut; and 2) the potential impact of seed density on competition at the microsites by determining whether seed density and species diversity influence germination in the Free State Province, South Africa. Overall, the results partly supported the hypothesis. Germination trials with defecated seeds of five plant species compared with the manually depulped seeds showed that despite prolific seed germination observed in Ziziphus mucronata, only Searsia lancea seeds had significantly high seed germination after passage through the bird gut. Overall, there was a significant correlation between seed size and the germination of bird-ingested seeds except in Olea subsp. africana possibly due to possession of extremely hard protective seed cover. Seeds competition experiments pointed to Z. mucronata and O. subsp. africana having significant germination performance that was positively correlated to seed density and seed size while E. rigida did not germinate at all. Seed species diversity in the germination trays did not have significant impact since only two former plant species consistently displayed significantly higher germination across the competition levels. We conclude that not all bird-defecated seeds have their germination improved, and that further long-term tests for germination physiological responses of the seeds’ samples used in this study are required since poor germination observed in other tree/shrub species cannot be attributed to competition solely.
- ItemMAcroecological Framework for Invasive Aliens (MAFIA): disentangling large-scale context dependence in biological invasions(2020) Pyšek, P.; Bacher, S.; Kühn, I.; Novoa, A.; Catford, J.A.; Hulme, P.E.; Pergl, J.; Richardson, D.M.; Wilson, J.R.U.; Blackburn, T.M.Macroecology is the study of patterns, and the processes that determine those patterns, in the distribution and abundance of organisms at large scales, whether they be spatial (from hundreds of kilometres to global), temporal (from decades to centuries), and organismal (numbers of species or higher taxa). In the context of invasion ecology, macroecological studies include, for example, analyses of the richness, diversity, distribution, and abundance of alien species in regional floras and faunas, spatio-temporal dynamics of alien species across regions, and cross-taxonomic analyses of species traits among comparable native and alien species pools. However, macroecological studies aiming to explain and predict plant and animal naturalisations and invasions, and the resulting impacts, have, to date, rarely considered the joint effects of species traits, environment, and socioeconomic characteristics. To address this, we present the MAcroecological Framework for Invasive Aliens (MAFIA). The MAFIA explains the invasion phenomenon using three interacting classes of factors – alien species traits, location characteristics, and factors related to introduction events – and explicitly maps these interactions onto the invasion sequence from transport to naturalisation to invasion. The framework therefore helps both to identify how anthropogenic effects interact with species traits and environmental characteristics to determine observed patterns in alien distribution, abundance, and richness; and to clarify why neglecting anthropogenic effects can generate spurious conclusions. Event-related factors include propagule pressure, colonisation pressure, and residence time that are important for mediating the outcome of invasion processes. However, because of context dependence, they can bias analyses, for example those that seek to elucidate the role of alien species traits. In the same vein, failure to recognise and explicitly incorporate interactions among the main factors impedes our understanding of which macroecological invasion patterns are shaped by the environment, and of the importance of interactions between the species and their environment. The MAFIA is based largely on insights from studies of plants and birds, but we believe it can be applied to all taxa, and hope that it will stimulate comparative research on other groups and environments. By making the biases in macroecological analyses of biological invasions explicit, the MAFIA offers an opportunity to guide assessments of the context dependence of invasions at broad geographical scales.
- ItemNiche complementarity between an alien predator and native omnivorous fish in the Wilge River, South Africa(Springer, 2018) Lombard, R.J.; Chimimba, C.T.; Zengeya, T.A.A major challenge in biological invasions is to predict community susceptibility to invasion. This study investigated trophic interrelationships between an alien predator, largemouth bass (Micropterus salmoides), and native omnivores, sharptooth catfish (Clarias gariepinus) and largescale yellowfish (Labeobarbus marequensis), in an invaded aquatic system to elucidate factors that might have aided their successful establishment. It tested the hypothesis that M. salmoides is able to co-exist with the two native omnivores by either utilising a previously vacant food niche or through niche complementarity. Gut content and stable isotope analyses were used to determine trophic interactions. There was no evidence that M. salmoides was utilising a previously vacant food niche but instead it occupied a restricted and specialised niche within a broad niche space utilised by the native omnivores. Differences in niche space and size have resulted in minimal niche overlaps that imply niche complementarity. The introduction of M. salmoides raises concerns about increases in predation pressure in the system. This, however, is difficult to ascertain because of complexities in measuring long-term trends in predator demands, abundance and community compensation mechanisms. There is a need for long-term monitoring of community structure, especially small-sized prey species that are vulnerable to increased predation pressure.
- ItemNon-native small mammal species in the South African pet trade(2021) Shivambu, N.; Shivambu, T.C.; Downs, C.T.Non-native small mammals are amongst the most popular species traded as pets around the world. Some of these mammals have become invasive through various pet trade releases and escapees in most countries. In South Africa, several nonnative small mammals have been introduced for pet trade purposes. We assessed the sale of non-native small mammals in South Africa from September 2018 to 2019 to determine their abundance and degree of trade online and in pet shops. A total of seven websites were recorded selling 2,681 individuals representing 24 species belonging to seven taxonomic orders. For physical pet shops, 19,391 individuals representing 16 species and seven orders were recorded from 122 pet shops. Rodents and primates were the most dominant groups in both online and pet shops. The most common small mammal species traded were the Norwegian rat Rattus norvegicus, the guinea pig Cavia porcellus, the European rabbit Oryctolagus cuniculus and the house mouse Mus musculus. Prices ranged from ZAR9.00 to ZAR12,000.00, with rodents offered at relatively low prices. The most abundant species traded were relatively cheap when compared with the least abundant species and CITES species were more expensive than non-CITES species. Species with high abundances traded at low prices and have a history of invasion through pet trade releases and escapes pose an invasion risk in South Africa. Therefore, their trade should be strictly regulated.
- ItemPredatory impact of non-native rainbow trout on endemic fish populations in headwater streams in the Cape Floristic Regian of South Africa(Springer, 2015) Shelton, J.M.; Samways, M.J.; Day, J.A.Non-native rainbow trout Oncorhynchus mykiss have been widely introduced in the Cape Floristic Region (CFR) at the south-western tip of Africa and may pose a serious threat to endemic freshwater fishes in the region. Quantitative information about trout impacts in the CFR is scarce but is urgently needed to guide legislation and management efforts. We used a combination of comparative and experimental approaches to evaluate impacts of introduced trout on native fish populations in headwater streams draining the upper Breede River catchment in the CFR. Fish populations were surveyed, and 19 environmental variables measured, in 24 minimally disturbed streams, half of which had been invaded by trout. The mean densities of native Breede River redfin Pseudobarbus burchelli, Cape kurper Sandelia capensis and Cape galaxias Galaxias zebratus, were 89–97 % lower in invaded streams than in streams without trout. Furthermore, while native fish were present at all 12 sites without trout, they were not recorded at seven of the 12 invaded sites. None of the measured environmental variables differed significantly between sites with and without trout, and distance-based linear models identified trout density as the best predictor of redfin and kurper density, while galaxias density was best predicted by other environmental variables (riparian vegetation, canopy cover, substrate length, site slope). Native fish B40 mm in length were largely absent from invaded streams, but generally abundant in streams without trout, and a field experiment confirmed that trout selectively consume small redfin. Taken together, these findings constitute evidence that trout have depleted the abundance of CFR-endemic fishes through size-selective predation. It is recommended that managers aim to prevent new trout introductions and consider eradicating trout populations where they pose a threat to highly threatened native species.