Impact assessment of seven alien invasive bird species already introduced to South Africa

Invasive alien plant species have been identified as a major threat to biodiversity and the relationship with native avian dispersers may increase their invasion potential. The impact of invasive plant species needs to be quantified using comparable assessment tools across different habitats and species to allocate limited resources to high-priority species. Here, we used the Generic Impact Scoring System (GISS) to assess the impacts of 16 fleshy-fruited alien invasive plant species in South Africa generally dispersed by native avian species. The results showed that fleshy-fruited invasive species have both environmental and socio-economic impacts. The cumulated impact scores for lantana (Lantana camara) and the tree of heaven (Ailanthus altissima) were the highest, with scores of 42 and 32, respectively. Some species, such as white mulberry (Morus alba), camphor tree (Cinnamomum camphora), American bramble (Rubus cuneifolius) and Brazilian pepper tree (Schinus terebinthifolius), had low overall impact scores of 8, 18, 14 and 16, respectively, but scored the maximum impact of 5 for certain mechanisms. Environmental impacts of fleshy-fruited invasive plant species had a high impact magnitude through effects on the ecosystem and vegetation. Socio-economic impacts were mainly through effects on forest production, agriculture and human health. Species with large crop sizes, small seeds and fruit sizes had higher environmental and socio-economic impact magnitude. The information generated in this study is important for guiding resource allocation and preventing the uncontrolled introduction of invasive species in South Africa. The impact of the fleshy-fruited invasive species transcended sectors and, therefore, effective management of invasive species will require the collaboration of multiple and inter-sectoral stakeholders in South Africa.

Nest-site competition between invasive and native cavity nesting birds and its implication for conservation

Avian frugivores play a key role in seed dispersal of many plant species, including invasive alien plants. We assessed the effect of gut passage on the germination of selected invasive alien plant species in South Africa. Fruits of four fleshly-fruited invasive alien plant species: Solanum mauritianum, Cinnamomum camphora, Psidium guajava, and Morus alba, were fed to two species of indigenous turacos, Knysna (Tauraco corythaix) and purple-crested (Gallirex porphyreolophus) turacos, and to invasive rose-ringed parakeets (Psittacula krameri). Seed retention time was determined as this can influence both seed dispersal and germination success. Germination success of ingested seeds was compared with that of manually de-pulped seeds, as well as to seeds in whole fruit. The germination success of seeds of all the invasive plant species increased significantly after ingestion by both turaco species compared with seeds from whole fruits. Germination success of manually de-pulped seeds did not differ significantly from that of turaco ingested seeds. In contrast, seed passage through the digestive tract of rose-ringed parakeets significantly reduced germination success and viability of ingested invasive plant species. Our results suggest that Knysna and purple-crested turacos are legitimate seed dispersers of fleshy-fruited invasive plants, while rose-ringed parakeets are mainly seed predators. Although seed predation by rose-ringed parakeets negatively affects the reproductive success of these plants, it is unlikely that this will suppress the spread of these invasive alien plants in South Africa as they are already well established. Furthermore, they can facilitate dispersal by seed regurgitation and dropping uneaten fruits away from the parent plant. Similar trends could be expected for indigenous seeds that rose-ringed parakeets feed on and therefore these birds remain a negative influence within invaded ecosystems.

Introduced species may pose one of the biggest threats to biodiversity conservation. Today, monitoring their status, distribution and abundance constitutes an important part of ecological and conservation studies throughout the world. In the Afrotropical Region (sub-Saharan Africa), avian introductions have attracted the attention of many researchers, but there is a lack of a comprehensive review of this subject on a continental scale. The presented paper constitutes an attempt to overview the status, distribution, threats and control measures of birds introduced to sub-Saharan Africa in the last 200 years. This review lists 146 bird species introduced to sub-Saharan Africa. Only 49 (33.6%) of them have developed viable populations and only 7 (4.8%) became invasive species, namely Passer domesticus, Sturnus vulgaris, Acridotheres tristis, Corvus splendens, Columba livia var. domestica, Psittacula krameri and Pycnonotus jocosus. Data on distribution of most introduced species are provided, together with information on the place and year of their first introductions. For Passer domesticus and Columba livia var. domestica, data on population densities are also provided from several southern African towns. The most speciose groups of introduced species were parrots (Psittaciformes), comprising 33.6% (including Psittacidae: 13.7%; and Psittaculidae: 15.1%); Anatidae: 12.3%; Phasianidae: 11.0%; and Passeriformes: 30.1%. Most avian introductions in sub-Saharan Africa took place in Southern Africa (mainly the Cape Town, Durban and Johannesburg areas) and in Madagascar and the surrounding islands (mostly Mauritius, Reunion and Seychelles). Most introduced species which have developed viable populations originate from the Afrotropical, Oriental and Palearctic regions (altogether 78%), with only 2% from the New World. The proportions among the introduced species which have not established viable populations are quite different: 29% from the New World and only 60% from the Afrotropical, Oriental and Palearctic regions. The main factors affecting successful avian introductions and introduction pathways have been identified. A review of the control measures undertaken in sub-Saharan Africa (mainly in small oceanic islands) is outlined for the following species: Passer domesticus, Acridotheres tristis, Corvus splendens, Pycnonotus jocosus, Foudia madagascariensis, Psittacula krameri and Agapornis roseicollis.

Cardiospermum grandiflorum

A recent global assessment of terrestrial alien true ferns (Polypodiophyta; hereafter alien ferns) showed that alien ferns have a high probability of becoming naturalised or invasive once introduced. We provide the first systematic assessment, based on field surveys, of the invasion status of this large taxon in South Africa. Thirteen species of alien ferns were recorded outside of cultivation and subsequently identified as invasive in South Africa. Surveys were focused in known hotspots of alien and native ferns, with invasion density peaking along the eastern coastal belt of South Africa. Within the surveyed areas, alien ferns commonly occurred with other invaders, closer to water and often in indigenous forests. The species considered in this study generally occurred in similar habitat types across their native and globally introduced ranges (including South Africa). The potential spread of alien ferns in South Africa appears limited when compared to other major invaders, however, their common occurrence in indigenous forests highlights a concern for native, co-habiting fern species (in terms of competition). Our study provided regulatory insight for 12 previously unregulated alien fern species in South Africa. We propose that eradication remains feasible for Diplazium esculentum, Doodia caudata, Lygodium japonicum, Phlebodium aureum and Platycerium bifurcatum. A risk analysis for Sphaeropteris cooperi classified the species as high risk and comprised the first quantification of risk for any alien fern species (inclusive of aquatics) in South Africa. The information put forward in this study can be used to inform risk analyses for the remaining species in South Africa, as well as countries with similar habitats and climates. Furthermore, widely traded species need to be identified as candidates for future risk assessment since horticulture is an important introduction pathway for alien ferns globally.

Seed banks of invasive Australian Acacia species in South Africa: Role in invasiveness and options for management

Community science initiatives are revolutionising our ability to detect and respond to biological invasions. Non‐native trees and shrubs are among the world's most damaging invasive species and community science data can be used to inform protocols for managing these invasions. This study explores the utility of iNaturalist in informing management practices for the widely cultivated and naturalised genus Melaleuca L. (Myrtaceae; here including the genus Callistemon ) in South Africa. We applied data from iNaturalist to assess the distribution and invasion ecology of Melaleuca species in South Africa. Melaleucas, first recorded in South Africa in 1882, have been widely used as garden ornamentals and street trees in the country for over 50 years. Naturalisation of melaleucas in South Africa was first reported in 1998 and the first records of naturalisation/invasiveness for other species are accumulating rapidly. Data on all Melaleuca species in South Africa were downloaded from iNaturalist and analysed using Geographic Information System software. In September 2023, iNaturalist had 3221 records of melaleucas across the country. After checking and filtering, and applying criteria to increase reliability, 2815 records remained, with confirmed identifications of 26 species. These species were recorded in a total of 138 quarter‐degree cells (QDCs) in South Africa (7% of the country); Research Grade (RG, wild‐growing) records occurred in 21 QDCs, records of cultivated plants in 75 QDCs, and 42 QDCs had records of both cultivated and wild‐growing plants. An Invasiveness Index was calculated for each species in the country, provinces, and municipalities, to show which species are already invasive or have substantial invasion debt. Thirty‐two percent of the filtered records were RG (naturalised). The municipality with the highest number of records is the City of Cape Town, with 43% RG records. iNaturalist provided useful information on the occurrence of five Melaleuca species for which no information was available before this study was undertaken. Case studies of invaded habitats highlight that melaleucas have the potential to alter ecosystems incurring substantial control costs. Practical implications : Our study highlights the value of community science data in the detection, monitoring, and management of invasive plant species.

Population Studies on different agricultural and other bird species were carried out at Students farm, College farm, Agri biodiversity park, and Agricultural Research Institute farm areas of Professor Jayashankar Telangana State Agricultural University (PJTSAU) Campus in semiarid region of Telangana state covering an area of about 36 Sq.km. for a period of eleven years (2012 to 2023). Population diversity of 92 species of different birds, and their distribution within the university campus farm areas were recorded. Important among them are 9 species namely: Blue rock pigeon (Columba livia), Spotted dove (Streptopelia chinensis), Rose ringed parakeet (Psittacula krameri),Common myna (Acridotheres tristis), House crow (Corvus splendens), House sparrow (Passer domesticus), Baya weaver bird (Ploceus philippinus), White throated munia (Lonchura malabarica), and Peafowl (Pavo cristatus) which depredate experimental field crops among them only few birds such as: Rose ringed parakeets, House crows, House sparrows, Pigeons, Baya weavers, Peafowls and Munias were serious bird pests to major agricultural and horticultural crops. The University farm areas were found to be the most preferred habitat for many of these birds, it could be due to availability of food, breeding, roosting and resting sites in abundance because of more agricultural croplands and agro forestry trees.

Submerged aquatic invasive plant species are increasingly being recognised as a major threat to South African water ways. Pet stores, aquarists and the internet-mediated trade were investigated as pathways for submerged invasive macrophyte introductions into South Africa. Online and manually distributed surveys were used to determine the extent of movement of invasive as well as indigenous submerged plant species in South Africa. Sixty-four stores and twenty-three aquarists were surveyed. Four areas of risk were identified in this study. Firstly, and most importantly, a variety of invasive and/or prohibited plants are sold by pet stores. Secondly, there is a lack of knowledge regarding identification as well as regulation of submerged species, which may then result in the unintentional trade of potentially invasive species. It seems that, in many cases, the pet stores are ignorant or misinformed of the potential dangers, rather than intentionally attempting to breach the legislation. Thirdly, aquarists own, trade and move plants in and around the country, which makes it very difficult to monitor which species are being moved around South Africa and to what extent. Finally, the internet is a pathway of potential concern, but it is difficult to quantify its contribution to the trade of invasive species in South Africa.

The common myna (Acridotheres tristis) is one of the most invasive bird species in the world, yet its colonisation history is only partly understood. We identified the introduction history and population structure, and quantified the genetic diversity of myna populations from the native range in India and introduced populations in New Zealand, Australia, Fiji, Hawaii, and South Africa, based on thousands of single nucleotide polymorphism markers in 814 individuals. We were able to identify the source population of mynas in several invasive locations: mynas from Fiji and Melbourne, Australia, were likely founded by individuals from a subpopulation in Maharashtra, India, while mynas in Hawaii and South Africa were likely independently founded by individuals from other localities in India. Our findings suggest that New Zealand mynas were founded by individuals from Melbourne, which, in turn, were founded by individuals from Maharashtra. We identified two genetic clusters among New Zealand mynas, divided by New Zealand’s North Island’s axial mountain ranges, confirming previous observations that mountains and thick forests may form barriers to myna dispersal. Our study provides a foundation for other population and invasion genomic studies and provides useful information for the management of this invasive species.

Biological invasions are a major environmental concern due to their negative impacts on biodiversity and economics. We determined the population sizes and habitat-abundance relationships of the three most successful invasive bird species in Singapore: the house crow Corvus splendens, white-vented myna Acridotheres javanicus and common myna A. tristis. Estimated population sizes of the three species between February 2000 and February 2001 were between 106 000-176 000, 122 000-155 000 and 20 000-29 000, respectively. Population size of the house crow grew dramatically (>30-fold) in the last 15-16 y while that of the white-vented and common myna declined. Habitat-abundance relationships suggest that house crows are highly dependent on anthropogenic food. Their abundance was also positively related to proximity to coast. The common myna associated closely with agricultural areas while the white-vented myna probably preferred urban greenery among residential buildings. Our study shows that the three invasive bird species associated with different aspects of human-modified environment.

This research provides the first detailed assessment of Cistus ladanifer, a woody, perennial shrub native to the Mediterranean, as an invasive species in South Africa. Three small naturalising populations (all less than 0.1 ha) of this species were discovered in 2012 in native heathland vegetation (“Fynbos”) of the Western Cape Province of South Africa. Prior to this discovery, C. ladanifer had not previously been recorded or recognised as an invasive species in South Africa. It poses a significant threat to the local endemic vegetation, largely due to its pre-adaptation to similar environmental conditions, and, if left unmanaged, it has the potential to invade further. However, given the small size of currently known populations and its ease of management, we propose that eradication of C. ladanifer is feasible in South Africa. Here we provide insights into options for the management of C. ladanifer, in particular its eradication from South Africa. Based on the weed risk assessment presented here, we recommend that C. ladanifer be listed as an invasive species under national legislation, thus requiring compulsory management. The results of this study provide detailed information on the extent of the invasion by C. ladanifer and the aspects of its biology pertinent to management (e.g. its reproductive ability, soil-stored seed banks). We show that complete removal of C. ladanifer populations is feasible and results in a steady decline in population size over time. Local extirpation of populations of C. ladanifer can be enhanced through fire-stimulation of the seed bank, but this may not be feasible in an urban setting. Our study emphasises the importance of scientific research in the development and evaluation of species-based management plans for invasive species.

Invasive birds can have serious impacts on native biodiversity, native ecosystems and humans. However, there is a dearth of literature on the status and effects of invasive birds in Southeast Asia. We review the current available information on the invasive bird species in Southeast Asia, first by discussing characteristics that likely make invasive bird species successful and second by reviewing the impacts of the invasive bird species on Southeast Asian economy and biodiversity. We end by discussing the strengths and weaknesses, as well as the applicability of different management options.

Understanding the status and extent of spread of alien plants is crucial for effective management. We explore this issue using Australian Acacia species (wattles) in South Africa (a global hotspot for wattle introductions and tree invasions). The last detailed inventory of wattles in South Africa was based on data collated forty years ago. This paper aimed to determine: 1) how many Australian Acacia species have been introduced to South Africa; 2) which species are still present; and 3) the status of naturalised taxa that might be viable targets for eradication. All herbaria in South Africa with specimens of introduced Australian Acacia species were visited and locality records were compared with records from literature sources, various databases, and expert knowledge. For taxa not already known to be widespread invaders, field surveys were conducted to determine whether plants are still present, and detailed surveys were undertaken of all naturalised populations. To confirm the putative identities of the naturalised taxa, we also sequenced one nuclear and one chloroplast gene. We found evidence that 141 Australian Acacia species have been introduced to South Africa (approximately double the estimate from previous work), but we could only confirm the current presence of 33 species. Fifteen wattle species are invasive (13 are in category E and two in category D2 in the Unified Framework for Biological Invasions); five have naturalised (C3); and 13 are present but there was no evidence that they had produced reproductive offspring (B2 or C1). DNA barcoding provided strong support for only 23 taxa (including two species not previously recorded from South Africa), the current name ascribed was not supported for three species and, for a further three species, there was no voucher specimen on GenBank against which their identity could be checked. Given the omissions and errors found during this systematic re-evaluation of historical records, it is clear that analyses of the type conducted here are crucial if the status of even well-studied groups of alien taxa is to be accurately determined.