A review of the impacts of biological invasions in South Africa

Abstract

Compared to other facets of invasion science, the impacts of biological invasions have been understudied, but many studies have been published in the last decade. This paper reviews the growing body of evidence of impacts of invasions in South Africa. We classified information for individual species into ten ecological and four social categories of impact. We also reviewed studies that upscaled this information to larger spatial scales, as well as progress with assigning invasive species to impact severity categories. We identified 123 studies that documented the impacts of 71 invasive alien species, about 5% of the country's naturalized alien biota. The most frequently reported impact category was species interactions (changes to habitat suitability, pollination networks or seed dispersal mechanisms), followed by direct competition, changes to ecosystem functioning (hydrology or nutrient dynamics), hybridization and predation. Trees and shrubs accounted for more than half of the species studied, but there were examples from most other groups of plants and animals. The social consequences of invasions have been less well studied at the level of individual species. Most studies (72%) considered the impacts of a single species, based on data collected on < 1 ha, and were completed in less than a year. Space-for-time substitution was widely used, but widespread collection of data from numerous small plots allowed for reporting impact over larger spatial scales. We also identified seven studies that either monitored impacts over longer periods (up to 40 years), or repeated surveys in the same area to assess change over time. Prominent landscape-scale impacts included reductions in water resources, the attrition of native biodiversity, reductions in rangeland productivity, predation of marine birds and freshwater fishes, and disease organisms affecting native mammals and trees. Nineteen studies at broader scales estimated substantial impacts on landscape-scale water yield, habitats and biodiversity, rangeland productivity, and the economic value of ecosystem services. Despite considerable progress, our understanding remains fragmentary. Impacts are expected to grow as invasions enter exponential phases of spread and densification and as the duration of invasions increases. A robust understanding needs to be developed to provide justification for management costs.

The Potential of Foraging Chacma Baboons (Papio ursinus) to Disperse Seeds of Alien and Invasive Plant Species in the Amathole Forest in Hogsback in the Eastern Cape Province, South Africa

“…In the absence of the rare and large indigenous fruits preferred by large mammal frugivores [57,[91][92][93][94], the baboons may opt for the large fruit crops of the alien plant species in gardens [35], which deprives the natural vegetation of seed dispersal services. This is concerning, since invasive plant species are known to alter habitat functionality and damage biodiversity [52,53].…”

“…Therefore, the fragmented state of the patches of Amathole indigenous forests in the Eastern Cape Province may increase certain species' vulnerability to extinction [45,51]. In addition, the invasion of alien and invasive plant species is an emerging conservation issue, and needs urgent attention, since invasive plants alter the structure and functionality of the habitat [52,53]. Consequently, understanding the role of baboons in the seed dispersal of alien and invasive plants is important for the conservation of the threatened indigenous Amathole Southern Mistbelt forest fragments in Hogsback in the Eastern Cape Province of South Africa.…”

Collaborative Adaptive Stewardship for Invasive Alien Plants Management in South Africa

“…Invasive Alien Plants (IAPs) have a threat to the natural ecosystem and global biodiversity. Hence, it is considered one of the drivers of biodiversity and alters the ecosystem services and socio-economic conditions of an ecosystem [1][2][3][4]. The actors and information are a diverse and scattered, necessitating collaboration with regard to IAPs management.…”

“…IAPs management is critical on a global scale as invasive species have threatened native biodiversity and adversely impacted water resources and ecosystem services [1,3,4,6,[9][10][11][12]14,[16][17][18][19][20][21]. The Working for Water Programme in South Africa (1995) aimed to manage IAPs in order to achieve environmental (e.g., soil and water conservation, biodiversity conservation) and social (e.g., green job creation, skills and capacity building, and inclusion of marginalised and disadvantaged communities) sustainability goals [7,22,23].…”

Niche expansion by indigenous fish species following the introduction of rainbow trout (Oncorhynchus mykiss) in a subtropical river system, upper Blyde River, South Africa

“…Currently, O. mykiss has established populations in the mountain streams and upland reservoirs in over 80% of the major drainage basins in the country (Weyl et al, 2020). There is, however, limited information on the impacts of O. mykiss invasions in South Africa (Zengeya et al, 2020;Van Wilgen et al, 2022). The few available studies have, however, shown that O. mykiss can cause a decline, and in some cases local extirpation of indigenous invertebrates, frogs, and fishes (Karssing et al, 2012;Rivers-Moore et al, 2013;Shelton et al, 2015a;Jackson et al, 2016;Weyl et al, 2020).…”