About the Author(s)


Susana Clusella-Trullas Email symbol
Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, South Africa

Raquel A. Garcia symbol
Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, South Africa

Citation


Clusella-Trullas, S. & Garcia, R.A., 2017, ‘Impacts of invasive plants on animal diversity in South Africa: A synthesis’, Bothalia 47(2), a2166. https://doi.org/10.4102/abc.v47i2.2166

Note: This paper was initially delivered at the 43rd Annual Research Symposium on the Management of Biological Invasions in South Africa, Goudini Spa, Western Cape, South Africa on 18-20 May 2016.

Original Research

Impacts of invasive plants on animal diversity in South Africa: A synthesis

Susana Clusella-Trullas, Raquel A. Garcia

Received: 01 Sept. 2016; Accepted: 25 Nov. 2016; Published: 31 Mar. 2017

Copyright: © 2017. The Author(s). Licensee: AOSIS.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background: Increasing numbers of invasive alien plant (IAP) species are establishing around the globe and can have negative effects on resident animal species function and diversity. These impacts depend on a variety of factors, including the extent of invasion, the region and the taxonomic group affected. These context dependencies make extrapolations of IAP impacts on resident biota from region to region a substantial challenge.

Objectives: Here, we synthesised data from studies that have examined the effects of IAPs on animal diversity in South Africa. Our focus is on ectothermic organisms (reptiles, amphibians and invertebrates).

Method: We sourced relevant articles using keywords relating to (1) the effects of IAPs on species diversity (abundance, richness and composition), (2) the IAP and (3) the native ectotherm. We extracted the taxonomic and spatial coverage of IAPs and affected native species and assessed the extent of information given on potential mechanisms driving IAP impacts.

Results: Across the 42 studies, IAPs had a decreasing or neutral effect on native animal abundance and richness and significantly changed species composition. This review highlighted the paucity of studies and the research deficits in taxonomic and geographic coverage and in the mechanisms underlying IAP impacts on ectotherms.

Conclusion: By assessing the status of knowledge regarding the impacts of IAPs on resident animal species in South Africa, this study identifies information gaps and research priorities at the country level with a view to informing monitoring and conservation efforts, such as alien plant removal and control programmes, and ensuring that endemic terrestrial animal diversity is maintained.

Introduction

Invasive alien species are considered a major pressure on the current state of biodiversity globally (Butchart et al. 2010). Invasive alien plants (IAPs), in particular, have spread rapidly and extensively in many regions of the world, impacting resident species diversity, ecosystem processes and people’s livelihoods (Levine et al. 2003; Pyšek et al. 2012; Schirmel et al. 2016; Vilà et al. 2011). South Africa is no exception and nearly two million hectares of land have been invaded by alien plants (Van Wilgen et al. 2012), with well-known impacts on hydrology, nutrient cycling and fire regimes (Kraaij, Cowling & Van Wilgen 2011; Le Maitre, Gush & Dzikiti 2015; Richardson & Van Wilgen 2004). This estimate of alien plant coverage includes 27 species, without incorporating arid and transformed land except for Prosopis trees in the arid northwest of the country (Kotzé et al. 2010; Van den Berg, Kotze & Beukes 2013). Alien Acacia species cover most of the dense areas of invasion, followed by Eucalyptus and Pinus trees, Opuntia cacti and Chromolaena odorata shrubs. These invasions extend across the country, with higher concentrations in the southwestern, southern and particularly eastern coastal belts and the adjacent interior (Henderson 2007; Kotzé et al. 2010; Van Wilgen et al. 2012). Overall, there is reasonable knowledge of alien plant occurrence in South Africa, especially at a coarse spatial resolution. Whereas their effects on native plant diversity have been fairly well assessed (e.g. Gaertner et al. 2009; Richardson & Van Wilgen 2004), fewer studies have focused on the impacts of alien plants on native animal communities (Richardson et al. 2011, but see Breytenbach 1986).

Species population and community metrics such as abundance, richness and composition can provide useful baseline data as indicators of animal diversity change between invaded and uninvaded areas. The direction and magnitude of effects of alien plant invasions on animal communities can, however, depend on a variety of factors, including the scale of the plant invasion (extent and density), the stage of invasion, and the region and taxonomic group affected (Kumschick et al. 2015; Ricciardi et al. 2013). These context dependencies make extrapolations of the effects of IAPs on resident biota from region to region a substantial challenge, especially for the development of generalised management frameworks across diverse habitats. The invasion of alien plants into natural or previously uninvaded habitats involves a number of significant changes to the habitat, often negatively affecting resident fauna and sometimes in counterintuitive or non-obvious ways (Figure 1). Alien plants may directly modify the structure and complexity of the physical environment and, thus, restrict the opportunities for the animal to thermoregulate or hydroregulate within its microenvironment or impose barriers to essential functions such as moving, creating nests or finding refuges. Alien plants can also directly or indirectly affect food resources for animal communities (e.g. Groot, Kleijn & Jogan 2007). For example, a change in plant composition will affect herbivores directly by reducing the amount or quality of plant hosts whereas a change in habitat structure, microenvironment and litter or soil properties can indirectly affect prey availability or predator abundance and alter trophic interactions (Figure 1; e.g. Pearson 2009).

FIGURE 1: Potential mechanisms through which invasive alien plants (IAPs) affect ectotherm diversity.

Whereas reports of negative impacts of invasive plant species are pervasive in the literature, positive effects have also been reported, for example, via increases in suitable habitat or net resources to recipient fauna (e.g. Schlaepfer, Sax & Olden 2010). Whether the latter represent rare case studies or whether any general patterns can be drawn from these is presently unclear. Thus, knowledge of the underlying mechanisms should improve the understanding of the consequences of alien plant invasions on native diversity. More importantly, knowledge of proximate and ultimate causes of species declines may enhance our ability to predict responses of animal communities in newly invaded areas of South Africa with similar characteristics to those studied previously, or facing concomitant pressures such as global climate change or habitat transformation (Ricciardi et al. 2013). Together, these are essential elements of the scientific framework that will allow invasion science to robustly predict the impacts of new and developing invasions, and not simply be viewed as a series of unique invasion case studies.

In this study, we aim to synthesise studies that have examined the effects of IAPs on animal diversity in South Africa. We concentrate this review on ectotherms (reptiles, amphibians and invertebrates) for several reasons. Firstly, their energy budgets are more directly influenced by the environment compared with endotherms (Gates 1980). Consequently, environmental factors likely play a major role in determining a suite of physiological and behavioural attributes and, at least partly, influence life history and timing of key phenological events (e.g. mating and reproduction) in the group. Secondly, they typically have smaller dispersal abilities than mammals and birds (Endler 1977), likely reducing their capacity to move away from disturbance or suboptimal conditions. Finally, they make a large contribution to overall animal diversity that is mostly explained by high insect diversity and abundance (Wilson & Peter 1988), playing a central role in food webs and ecosystem function. To present a comprehensive view of the status of knowledge of impacts of IAPs on resident animal species in South Africa and identify information gaps, we ask three key questions: (1) How many studies have addressed the effects of IAPs on terrestrial ectotherm diversity and what general patterns can we draw from these?, (2) What is the taxonomic and spatial coverage of IAPs and affected native species studied so far? and (3) How much is known about the mechanisms underlying these impacts? These questions are central to assess the status of knowledge of alien plant impacts on animal species diversity and inform invasive plant monitoring and control programmes in South Africa (Wilson et al. 2017).

Methods

We searched the ISI Web of Science for relevant studies comparing abundance, richness or composition of terrestrial ectotherms between invaded and uninvaded sites in South Africa. Our search combined terms for (1) invasive plants; (2) native reptiles, amphibians and terrestrial invertebrates; and (3) effects on species abundance, richness or composition (shown in detail in Appendix 1). We included studies comparing sites with native vegetation or cleared of alien vegetation to sites invaded by alien plants or with plantations of alien species. A second search targeted studies addressing only the mechanisms underlying the potential effects on ectotherm species, without necessarily quantifying changes in species diversity. This second search thus replaced the search terms for effects with terms for mechanisms such as altered thermoregulatory behaviour, prey availability or reproductive output (Appendix 1). We retrieved articles, reviews or book chapters for all years available on the Web of Science Core Collection on 10 June 2016. The articles considered relevant for our review were then screened for additional references.

We gathered information from the studies on the location of the field sites and respective biomes (Mucina et al. 2014), and on the native animal and IAP species included. We classified the studies according to the phyla of native animals potentially affected by plant invasions (Arthropoda, Annelida, Chordata and Onychophora). For the IAP species included, we used three classifications. Firstly, we assigned IAP species to six major growth forms: tree, shrub or bush, vine, forb, grass and aquatic plant. Secondly, we used the categories of the Alien and Invasive Species (A&IS) Lists that were published under the National Environmental Management: Biodiversity Act (NEM:BA) in 2014. The NEM:BA A&IS categories include eradication targets (category 1a), widespread invasive species where a national species management programme is required (category 1b) and invasive species that can be kept under managed circumstances (categories 2 and 3). Thirdly, to assess the extent to which the existing studies focus on the invasive plants with the largest potential impacts on ectotherms, we also considered a published classification of the most prominent invasive plant species in South Africa, according to their estimated impacts on native biodiversity (Van Wilgen et al. 2008). For all classifications above, we assigned studies to multiple categories when they presented individual comparisons for more than one biome, native phylum or IAP category.

To assess the impacts of alien plants on native animal diversity, we focused on comparisons of species abundance or richness between sites with native and alien vegetation and classified the effects as positive (i.e. an increase in abundance or richness in sites with alien vegetation), negative (decrease) or neutral effect. Native vegetation sites included sites cleared of alien plants in two studies where authors indicated that sufficient time had elapsed for recovery of native vegetation. We incorporated comparisons based on original data, accumulation and rarefaction curves, and richness estimators (e.g. Chao1 and Chao2) but did not include diversity indices (e.g. Shannon’s or Simpson’s index) as their use was very variable across studies. For composition, comparisons were classified as alien vegetation resulting in a change or not in species composition. These comparisons were typically the result of ordination techniques based on similarity measures or cluster analyses. When studies presented the effects of alien plants on fauna for several functional or taxonomic groups (e.g. herbivores vs. predators and beetles vs. spiders) or for different habitat types (e.g. invaded by Eucalyptus vs. Pinus), we considered each comparison separately in the synthesis unless there were no statistical tests associated with these. Therefore, the number of comparisons was typically higher than the number of studies assessed. If available, we extracted information on the growth form, stand age and spatial coverage of the IAP and on mechanisms driving the impacts such as changes in habitat structure, thermal opportunities, food resources, predators and refuge or nest site availability.

Results

Our first search for studies addressing the effects of invasive plants on ectotherm diversity in South Africa yielded 358 studies. Of these, only 42 were relevant for this review (Appendix 2). Our second search for articles studying the mechanisms underlying the effects of alien plants on ectotherms in South Africa yielded 702 papers. Among these, we only retained six relevant studies (Appendix 2), partly because a large portion of the articles found investigated the viability of biological agents for invasive plant control which was outside the focus of this study.

The 42 papers reviewed were published between 1985 and 2016, with a slight increase in the annual number of publications since 2000 (Figure 2a). The vast majority of studies focused on arthropods (Figure 2b), particularly in the Insecta (mostly Coleoptera, Hymenoptera, Diptera, Lepidoptera and Odonata) and Arachnida (mostly Araneae) classes. A single study included Onychophora and two studies focused on earthworms. Only three studies addressed vertebrate ectotherms, covering amphibians (Order Anura), lizards and snakes (Order Squamata).

FIGURE 2: Distribution of studies (a) per year of publication, (b) per taxonomic group (phylum) of native ectothermic organisms, and (c) per biome and taxonomic group of native ectothermic organisms. The map in (c) shows the distribution of study sites (black dots) in South Africa across seven biomes, with the shades of grey indicating the density of invasive plants.

Most studies compared sites along the coastal belt and adjacent interior in the Western Cape and KwaZulu-Natal provinces (Figure 2c). The majority of studies took place in the Fynbos and Grassland biomes, whereas a few studies covered the Savanna, Indian Ocean Coastal Belt and Albany Thicket biomes (Figure 2c). Native arthropods remained the focal native class across biomes (Figure 2c). Trees, particularly those belonging to the genera Acacia, Eucalyptus and Pinus, were the most common growth form of invasive plants (Figure 3a), followed by shrubs such as Chromolaena odorata, Hakea species, Lantana camara and Solanum mauritianum. These alien trees and shrubs are listed as major invaders in the country (Henderson 2007; Le Maitre, Versfeld, & Chapman 2000; Van Wilgen et al. 2012). Many of them are species that need to be controlled according to the NEM:BA A&IS regulations (category 1b; Figure 3a) and are estimated to have high impacts on native biodiversity (Van Wilgen et al. 2008; Figure 3b).

FIGURE 3: Distribution of studies per growth form of the invasive plant species studied and their classification according to (a) the NEM:BA regulations for control and management of invasive species and (b) their estimated impacts on biodiversity according to a published classification.

Alien plants had a larger decreasing effect on native species abundance compared to species richness (Figure 4a and Table 1). Most studies found that the effects of alien plants were either neutral or decreasing for native animal species richness, but increasing effects of alien plants were rare for both species richness and abundance. Alien plants had a substantial impact on species composition (Figure 4b and Table 1). Among the 15 IAPs listed on NEM:BA, only 3 species (Arundo donax, Chromolaena odorata and Passiflora edulis) showed no negative effects on the arthropod species studied. However, these results refer to a single study conducted for each alien plant, highlighting the data deficiency for these species (Table 1). Acacia mearnsii was the IAP, most commonly studied, with negative or neutral effects on arthropod species found in four studies (Table 1). Although most studies incorporated standard metrics of species abundance and richness, accumulation and rarefaction curves were presented (or mentioned) in only 13 and 7 studies, respectively, and 10 studies provided comparisons of metrics between invaded and uninvaded sites without presenting accompanying statistical analyses.

FIGURE 4: Percentage of comparisons performed in the 42 studies reviewed that found invaded sites to have (a) positive (increased diversity), neutral or negative (decreased diversity) effects on native ectotherm species richness (n = 80 comparisons) and abundance (n = 52), and (b) the same or altered species composition (n = 36) as uninvaded sites.

TABLE 1: Impacts of specific invasive alien plants on abundance, richness and composition of several taxonomic groups of ectotherms.

Seventy percent of the studies investigating differences in species diversity between invaded and uninvaded habitats referred to potential mechanisms underlying the patterns found. These mechanisms included changes in habitat structure (n = 15 of 29 studies), microclimates (n = 13 of 29 studies) and food resources (including host specificity for herbivores, n = 14 of 29 studies), and the degree of species’ ecological breadth (e.g. generalists vs. specialists, n = 3 of 29 studies). In the 6 publications that solely referred to mechanisms (Appendix 2), the authors highlighted habitat structure, microclimate and food resources as mechanisms affecting functional diversity (according to McGill et al. 2006) and animal behaviours such as the ability to create nests, flight dynamics and flower visitation rates. Of a total of 35 studies that addressed mechanisms, 21 studies used an observational (correlative) approach to assess the link between impact and mechanism, 4 studies followed a manipulative experimental approach (including a study that incorporated the clearing history of the invasive plant) and 10 studies speculated on potential mechanisms.

Discussion

IAPs have been recognised as a threat to South Africa’s native biodiversity for more than two decades, with efforts to manage invasions underway through the Working for Water Programme since 1995 (Van Wilgen et al. 2016). Our review underscores the importance of controlling IAPs to reduce their impacts on terrestrial ectotherm diversity in the country. Although not always statistically significant, reductions in abundance and richness of native ectothermic species were found in 56% and 41% of the comparisons presented in the studies reviewed, respectively, and changes in species composition were reported in almost 75% of the comparisons. These findings echo those of global reviews and meta-analyses, which have reported significant decreases in native animal species abundance, diversity and fitness as impacts of plant invasions (Pyšek et al. 2012; Schirmel et al. 2016; Van Hengstum et al. 2014; Vilà et al. 2011). In the following three sections, we discuss key directions for future research, the context-dependent nature of the problem and issues relating to methodologies used to assess impacts.

Research gaps

The studies reviewed in this synthesis covered some of the areas of South Africa most heavily invaded by alien plants such as Acacia, Eucalyptus and Pinus tree species, along a southern and eastern coastal belt (Kotzé et al. 2010; Figure 2c). The extent of this coverage was, however, very small relative to the distribution of invasive plants in the country. Study locations tend to be clumped in particular areas (Figure 2c), likely associated with the accessibility of sites, management prioritisation for particular problematic alien plant species or fields of interest of research institutes and invasion biologists. The arid regions of the country, including the Succulent Karoo, Nama Karoo and Desert biomes, and the arid parts of the Savanna and Grassland biomes have not been assessed. However, these areas are invaded by dense stands of Prosopis spp. (Van den Berg et al. 2013), listed as NEM:BA category 1b and estimated to have high impacts on natural ecosystems. Less attention has also been given to invasive forbs, aquatic plants, vines and grasses (Figure 3). Alien grasses, for example, are recognised as understudied in South Africa (Milton 2004; Richardson & Van Wilgen 2004; Visser et al. 2017), despite their prominence in invasion science in other regions of the world (Hulme et al. 2013; Visser et al. 2016). In South Africa, however, forbs, vines and grasses tend to be less prominent than invasive shrubs and trees, and introduced grasses are not well adapted to local conditions, such as fire regimes (Van Wilgen et al. 2008, 2012; Visser et al. 2016). Overall, the 42 studies assessing alien plant impacts on native ectotherms addressed some of the major IAP species of South Africa in terms of potential impacts and control regulations in place (e.g. Acacia, Eucalyptus and Pinus species; Figure 3 and Table 1) but gave less or no attention to other important alien plants such as Lantana camara in the Savanna Biome and Populus species in the Grassland Biome (Henderson 2007). For each NEM:BA-listed IAP species examined individually, the evidence collated typically comes from a small number of studies and refers to a small number of native taxonomic groups (Table 1).

Our synthesis highlights a serious deficit in the knowledge of impacts of IAPs on terrestrial ectothermic groups other than arthropods, which mostly comprised insects and spiders. South Africa is known for its exceptional reptile and amphibian diversity and its high level of endemism; between 40% and 67% of its indigenous species of amphibians, chelonians, lizards and snakes are unique to the country (Bates et al. 2014; Measey 2011). Invasive alien vegetation has been highlighted as a major threat to reptile and amphibian diversity, both nationally and globally (Gibbons et al. 2000; Martin & Murray 2011; Measey 2011; Mokhatla et al. 2012), but despite this realisation, little focus has been given to the effects of alien vegetation on these organisms in South Africa. The three studies that examined the effects of alien vegetation on squamate and amphibian species found significant reductions in species richness and substantial changes in species composition (Russell & Downs 2012; Schreuder & Clusella-Trullas in press; Trimble & van Aarde 2014). A single study demonstrated that the encroachment of alien vegetation into nesting habitat of the Nile crocodile (Crocodylus niloticus) altered the temperatures in egg chambers, potentially affecting hatchling sex ratios, and clearing of the roots of the alien plant increased the number of females nesting (Leslie & Spotila 2001). To our knowledge, no study has been conducted to assess the impacts of alien vegetation on tortoises, a taxonomic group with high species diversity in South Africa and high endemism in the Cape region (Branch, Benn & Lombard 1995). Some of the life history characteristics of tortoises, such as herbivory, long lifespans and habitat structure needed for shelter, likely increase their vulnerability to alien plant invasions (Gray & Steidl 2015; Stewart, Austin & Bourne 1993). Similarly, only two studies (Russell & Downs 2012; Trimble & van Aarde 2014) considered amphibians, despite their potential vulnerability to the impacts of alien plants on water resources (Le Maitre et al. 2015).

Context dependencies

It is well recognised that the impacts of alien plants on fauna are context-dependent and are shaped by a variety of factors, including the abundance and distribution of the IAP, the time since its introduction and the invasion history (e.g. rate of spread and lag times), the spatial extent of the study area, the degree of contrast of the alien plant form and function to the native vegetation, the ecosystem type and climatic conditions (e.g. seasonality) and the habitat preference of the animal species assessed (Kumschick et al. 2015; Maron & Marler 2008; Pyšek et al. 2012; Schirmel et al. 2016; Vilà et al. 2011). Little knowledge of these factors and the extent to which they may interact makes the prediction of impacts of invasive alien vegetation on native animal diversity a difficult task. Furthermore, these variables are essential for incorporating moderators in meta-analyses that seek to explore the direction of effects of alien plants on community metrics and avoid spurious results. These difficulties were encountered in our synthesis in various ways. The 42 studies differed in alien vegetation abundance, ranging from mildly invaded sites (e.g. Robertson et al. 2011) to plantations of alien plants (e.g. Pryke & Samways 2009) but, in general, little information was provided about the extent of the invasion, the study site size and its landscape context (e.g. degree of fragmentation and edge effects), and the invasion history, with a few notable exceptions (e.g. Liu, Janion & Chown 2012; Mgobozi, Somers & Dippenaar-Schoeman 2008). In some cases, or regions, the lack of long-term vegetation surveys or a poor knowledge of the alien plant (e.g. site of origin and genetic lineage; Thompson et al. 2014) may explain the lack of such detailed accounts.

Our synthesis also showed that opposite effects of alien plants on the same taxonomic group are found and generally depend on the animal group investigated, the type of IAP and the occurrence of other environmental stresses (cattle and habitat alteration). For example, alien plants can have decreasing (Samways & Grant 2006), neutral (Kinvig & Samways 2000; Samways & Sharratt 2010) or increasing (Kietzka, Pryke & Samways 2015) effects on dragonfly species diversity. Kietzka et al. (2015) suggested that the invasive American bramble (Rubus cuneifolius) provided additional perching sites and protection from predators to dragonflies, but where the alien plant stands were very dense, the negative effects outweighed the positive. The direction of the impact is also influenced by the behaviour and physiological requirements of the species or groups investigated. For example, shade specialists such as some Odonata species can benefit from increased shade (Samways & Grant 2006), whereas basking species are negatively affected by closed canopies that can result from plant invasions. Similarly, herbivore arthropods were generally more affected than detritivores (e.g. van der Colff et al. 2015). Finally, novel or very dissimilar alien plant forms to those of native plants species are likely to impact local communities most (Martin & Murray 2011), and although some comparisons involving alien plants with similar growth form to the native vegetation found no differences in native species abundance or richness (e.g. Olckers & Hulley 1989; van der Colff et al. 2015; van der Merwe, Dippenaar-Schoeman & Scholtz 1996), this was not always the case (Pryke & Samways 2009; Ratsirarson et al. 2002).

Study approaches

This review further revealed that most studies examining the impacts of alien plants on ectothermic animals employed the same methodological approach, comparing invaded and non-invaded sites. A very small proportion of studies included a gradient of alien plant abundance (e.g. Schreuder & Clusella-Trullas in press; Robertson et al. 2011) or incorporated comparisons with restored sites that had been cleared from alien plants (e.g. Maoela et al. 2016) or among sites with different times since invasion (e.g. Mgobozi et al. 2008). Although all of these approaches have their strengths and caveats (Hulme et al. 2013; Kueffer, Pyšek & Richardson 2013), progress in the understanding of impacts of alien plants on animal diversity requires a multifaceted approach (Kumschick et al. 2015). For example, comparisons of invaded and uninvaded plots can be confounded by differences that are inherent to each site (altitude, topography and soil properties) and require increased replication to boost the power of the analyses by incorporating variation originating from each site’s characteristics. It is often particularly difficult to find uninvaded reference sites because baseline data (prior to the invasion) are not available. Despite South Africa having a national-scale government-funded project to clear alien plants, the Working for Water Programme, relatively few studies have incorporated removal of aliens as part of their study design or assessed how rapidly fauna assemblages reflect pre-invasion reference sites.

Species abundance, richness and composition results provided useful data to compare key animal community changes between invaded and uninvaded habitats (albeit with the known problems associated with, e.g., comparison of species richness; Gotelli & Colwell 2001). However, this review also illustrated that in some cases, these metrics were insufficient to obtain an adequate understanding of the change detected or lack thereof. For example, Magoba & Samways (2012) showed that adult dragonfly species richness was not hampered by riparian alien vegetation, but assemblages changed drastically in sites cleared of IAPs. Although some generalist, widespread species (e.g. spiders and hymenopterans) can thrive in invaded areas, rare, endemic or sensitive species often disappear from alien-infested sites (e.g. Stewart & Samways 1998). These findings illustrate that additional metrics such as beta-diversity, species evenness, measures of commonness and rarity and functional richness (e.g. Magurran & McGill 2011) should be incorporated in assessments of impacts of alien vegetation on animal communities in South Africa.

Overall, these metrics alone give little insight into the mechanisms underpinning community changes. Less than 13% of the studies reviewed here incorporated an experimental approach for testing for mechanisms. These are essential for describing processes underpinning patterns, distinguishing direct and indirect effects of alien plants on ecosystems (Hulme et al. 2013) and, ultimately, enabling predictions of invasion outcomes in the context of future distributions of alien plants in South Africa (Rouget et al. 2004) and in the face of other environmental alterations and climate change. The ability to forecast impacts of IAPs and develop management strategies will rest on knowing these mechanisms.

Conclusion

The current state of knowledge of the impacts of IAPs on resident ectothermic animal species in South Africa relies heavily on a few key studies, with distinct biases in geographic locations and taxonomic groups. In cases where detailed information is available, it is nevertheless clear that there are pronounced negative impacts of IAPs on terrestrial animal (ectotherm) species diversity. The mechanisms underlying these impacts are unclear, but here we highlight a few key abiotic and biotic processes that could be examined in future, especially if microenvironments determine key behaviours and life-cycle timing that lead to changes in population abundance. Such an integrated approach to the question of IAPs and their impact on native animal species diversity would be of direct value to monitoring and conservation efforts, such as alien plant removal and control programmes. At present, it is wholly unclear whether the removal of IAPs will be sufficient to allow recovery of native ectotherm biodiversity.

Acknowledgements

S.C.-T. is supported by the Centre for Invasion Biology, Stellenbosch University and the Incentive Funding for Rated Researchers from the South African National Research Foundation. R.A.G. is supported by a post-doctoral fellowship from the Centre for Invasion Biology, Stellenbosch University.

Competing interests

The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this article.

Author(s) contributions

Both S.C.-T. and R.A.G. contributed equally to the article.

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Kietzka, G.J., Pryke, J.S. & Samways, M.J., 2015, ‘Landscape ecological networks are successful in supporting a diverse dragonfly assemblage’, Insect Conservation and Diversity 8(3), 229–237. https://doi.org/10.1111/icad.12099

Kinvig, R.G. & Samways, M.J., 2000, ‘Conserving dragonflies (Odonata) along streams running through commercial forestry’, Odonatologica 29(3), 195–208.

Kotzé, J.D.F., Beukes, H., van der Beg, E. & Newby, T., 2010, National Invasive Alien Plant Survey – Dataset, Agricultural Research Council: Institute for Soil, Climate and Water, Pretoria.

Kraaij, T., Cowling, R.M. & Van Wilgen, B.W., 2011, ‘Past approaches and future challenges to the management of fire and invasive alien plants in the new Garden Route National Park’, South African Journal of Science 107(9–10), 16–26.

Kueffer, C., Pyšek, P. & Richardson, D.M., 2013, ‘Integrative invasion science: Model systems, multi-site studies, focused meta-analysis and invasion syndromes’, New Phytologist 200, 615–633. https://doi.org/10.1111/nph.12415

Kumschick, S., Gaertner, M., Vilà, M., Essl, F., Jeschke, J.M., Pyšek, P. et al., 2015, ‘Ecological impacts of alien species: Quantification, scope, caveats, and recommendations’, Bioscience 65(1), 55–63. https://doi.org/10.1093/biosci/biu193

Le Maitre, D.C., Gush, M.B. & Dzikiti, S., 2015, ‘Impacts of invading alien plant species on water flows at stand and catchment scales’, AoB Plants 7, plv043. https://doi.org/10.1093/aobpla/plv043

Le Maitre, D.C., Versfeld, D.B. & Chapman, R.A., 2000, ‘The impact of invading alien plants on surface water resources in South Africa: A preliminary assessment’, Water SA 26(3) 397–408. https://doi.org/10.1093/aobpla/plv043

Leslie, A.J. & Spotila, J.R., 2001, ‘Alien plant threatens Nile crocodile (Crocodylus niloticus) breeding in Lake St. Lucia, South Africa’, Biological Conservation 98, 347–355. https://doi.org/10.1016/S0006-3207(00)00177-4

Levine, J.M., Vila, M., Antonio, C.M., Dukes, J.S., Grigulis, K. & Lavorel, S., 2003, ‘Mechanisms underlying the impacts of exotic plant invasions’, Proceedings of the Royal Society of London B: Biological Sciences 270(1517), 775–781. https://doi.org/10.1098/rspb.2003.2327

Liu, W.P.A., Janion, C. & Chown, S.L., 2012, ‘Collembola diversity in the critically endangered Cape Flats Sand Fynbos and adjacent pine plantations’, Pedobiologia – International Journal of Soil Biology 55, 203–209.

Maoela, M.A., Roets, F., Jacobs, S.M. & Esler, K.J., 2016, ‘Restoration of invaded Cape Floristic Region riparian systems leads to a recovery in foliage-active arthropod alpha- and beta-diversity’, Journal of Insect Conservation 20(1), 85–97. https://doi.org/10.1007/s10841-015-9842-x

Maron, J.L. & Marler, M., 2008, ‘Effects of native species diversity and resource additions on invader impact’, The American Naturalist 172(suppl. 1), S18–S33. https://doi.org/10.1086/588303

Martin, L.J. & Murray, B.R., 2011, ‘A predictive framework and review of the ecological impacts of exotic plant invasions on reptiles and amphibians’, Biological Reviews 86(2), 407–419. https://doi.org/10.1111/j.1469-185X.2010.00152.x

McGill, B.J., Enquist, B., Weiher, E. & Westoby, M., 2006, ‘Rebuilding community ecology from functional traits’, Trends in Ecology & Evolution 21(4), 178–185. https://doi.org/10.1016/j.tree.2006.02.002

Magoba, R.N. & Samways, M.J., 2012, ‘Comparative footprint of alien, agricultural and restored vegetation on surface-active arthropods’, Biological Invasions 14(1), 165–177. https://doi.org/10.1007/s10530-011-9994-x

Magurran, A.E. & McGill, B.J. 2011, Biological diversity: Frontiers in measurement and assessment, Oxford University Press, Oxford, xvii + 345 p.

Measey, G.J., 2011, Ensuring a future for South Africa’s frogs: A strategy for conservation research. SANBI Biodiversity Series 19. South African National Biodiversity Institute, Pretoria.

Mgobozi, M.P., Somers, M.J. & Dippenaar-Schoeman, A.S., 2008, ‘Spider responses to alien plant invasion: The effect of short- and long-term Chromolaena odorata invasion and management’, Journal of Applied Ecology 45(4), 1189–1197. https://doi.org/10.1111/j.1365-2664.2008.01486.x

Milton, S.J., 2004, ‘Grasses as invasive alien plants in South Africa’, South African Journal of Science 100(1/2), 69–75.

Mokhatla, M.M, Measey, G.J., Chimimba, C.T. & van Rensburg, B.J., 2012, ‘A biogeographical assessment of anthropogenic threats to areas where different frog breeding groups occur in South Africa: Implications for anuran conservation’, Diversity and Distributions 18, 470–480. https://doi.org/10.1111/j.1472-4642.2011.00870.x

Mucina, L., Rutherford, M.C., Powrie, L.W., van Niekerk, A. & van der Merwe, J.H., 2014, Vegetation Field Atlas of Continental South Africa, Lesotho and Swaziland. In Strelitzia 33. South African National Biodiversity Institute, Pretoria.

Olckers, T. & Hulley, P.E., 1989, ‘Insect herbivore diversity on the exotic weed Solanum mauritianum Scop. and three other Solanum species in the eastern Cape Province’, Journal of the Entomological Society of Southern Africa 52(1), 81–93.

Padayachi, Y., Proches, S. & Ramsay, L.F., 2014, ‘Beetle assemblages of indigenous and alien decomposing fruit in subtropical Durban, South Africa’, Arthropod-Plant Interactions 8, 135–142.

Pearson, D.E., 2009, ‘Invasive plant architecture alters trophic interactions by changing predator abundance and behavior’, Oecologia 159, 549–558. https://doi.org/10.1007/s00442-008-1241-5

Pryke, J.S. & Samways, M.J., 2009, ‘Recovery of invertebrate diversity in a rehabilitated city landscape mosaic in the heart of a biodiversity hotspot’, Landscape and Urban Planning 93(1), 54–62. https://doi.org/10.1016/j.landurbplan.2009.06.003

Pryke, J.S. & Samways, M.J., 2012, ‘Conservation management of complex natural forest and plantation edge effects’, Landscape Ecology 27(1), 73–85. https://doi.org/10.1007/s10980-011-9668-1

Pyšek, P., Jarošík, V., Hulme, P.E., Pergl, J., Hejda, M., Schaffner, U. et al., 2012, ‘A global assessment of invasive plant impacts on resident species, communities and ecosystems: The interaction of impact measures, invading species’ traits and environment’, Global Change Biology 18(5), 1725–1737. https://doi.org/10.1111/j.1365-2486.2011.02636.x

Ratsirarson, H., Robertson, H.G., Picker, M.D. & van Noort, S., 2002, ‘Indigenous forests versus exotic eucalypt and pine plantations: A comparison of leaf-litter invertebrate communities’, African Entomology 10(1), 93–99.

Ricciardi, A., Hoopes, M.F., Marchetti, M.P. & Lockwood, J.L., 2013, ‘Progress towards understanding the ecological impacts of nonnative species’, Ecological Monographs 83(3), 263–282. https://doi.org/10.1890/13-0183.1

Richardson, D.M. & van Wilgen, B.W., 2004, ‘Invasive alien plants in South Africa: How well do we understand the ecological impacts?’, South African Journal of Science 100, 45–52.

Richardson, D.M., Wilson, J.R.U., Weyl, O.L.F. & Griffiths, C.L., 2011, ‘South Africa: Invasions’, in D. Simberloff & M. Rejmánek (eds.), Encyclopedia of biological invasions, pp. 643–651, University of California Press, Berkeley, CA.

Robertson, M.P., Harris, K.R., Coetzee, J.A., Foxcroft, L.C., Dippenaar-Schoeman, A.S. & van Rensburg, B.J., 2011, ‘Assessing local scale impacts of Opuntia stricta (Cactaceae) invasion on beetle and spider diversity in Kruger National Park, South Africa’, African Zoology 46(2), 205–223. https://doi.org/10.3377/004.046.0202

Roets, F. & Pryke, J.S., 2012, ‘The rehabilitation value of a small culturally significant island based on the arthropod natural capital’, Journal of Insect Conservation 17(1), 53–65. https://doi.org/10.1007/s10841-012-9485-0

Rouget, M., Richardson, D.M., Nel, J.L., Le Maitre, D.C., Egoh, B. & Mgidi, T., 2004, ‘Mapping the potential ranges of major plant invaders in South Africa, Lesotho and Swaziland using climatic suitability’, Diversity and Distributions 10(5–6), 475–484. https://doi.org/10.1111/j.1366-9516.2004.00118.x

Russell, C. & Downs, C.T., 2012, ‘Effect of land use on anuran species composition in north-eastern KwaZulu-Natal, South Africa’, Applied Geography 35(1–2), 247–256. https://doi.org/10.1016/j.apgeog.2012.07.003

Samways, M.J. & Grant, P.B.C., 2006, ‘Regional response of Odonata to river systems impacted by and cleared of invasive alien trees’, Odonatologica 35(3), 297–303.

Samways, M.J. & Sharratt, N.J., 2010, ‘Recovery of endemic dragonflies after removal of invasive alien trees’, Conservation Biology 24(1), 267–277. https://doi.org/10.1111/j.1523-1739.2009.01427.x

Schlaepfer, M.A., Sax, D.F. & Olden, J.D., 2010, ‘The potential conservation value of non-native species’, Conservation Biology 25(3), 428–437. https://doi.org/10.1111/j.1523-1739.2010.01646.x

Schirmel, J., Bundschuh, M., Entling, M.H., Kowarik, I. & Buchholz, S., 2016, ‘Impacts of invasive plants on resident animals across ecosystems, taxa, and feeding types: A global assessment’, Global Change Biology 22(2), 594–603. https://doi.org/10.1111/gcb.13093

Schreuder, E. & Clusella-Trullas, S., (in press), ‘Exotic trees modify the thermal landscape and food resources for lizard communities’, Oecologia 182(4), 1213–1225. https://doi.org/10.1007/s00442-016-3726-y

Steenkamp, H.E. & Chown, S.L., 1996, ‘Influence of dense stands of an exotic tree, Prosopis glandulosa Benson, on a savanna dung beetle (Coleoptera: Scarabaeinae) assemblage in southern Africa’, Biological Conservation 78(3), 305–311. https://doi.org/10.1016/S0006-3207(96)00047-X

Stewart, M.C., Austin, D.F. & Bourne, G.R., 1993, ‘Habitat structure and the dispersion of gopher tortoises on a nature preserve’, Florida Scientist 56, 70–81.

Stewart, D.A.B. & Samways, M.J., 1998, ‘Conserving dragonfly (Odonata) assemblages relative to river dynamics in an African savanna game reserve’, Conservation Biology 12(3), 683–692. https://doi.org/10.1111/j.1523-1739.1998.96465.x

Thompson, G.D., Bellstedt, D.U., Richardson, D.M., Wilson, J.R.U. & Le Roux, J.J., 2014, ‘A tree well travelled: Global genetic structure of the invasive tree Acacia saligna’, Journal of Biogeography 42(2), 305–314. https://doi.org/10.1111/jbi.1243

Trimble, M.J. & van Aarde, R.J., 2014, ‘Amphibian and reptile communities and functional groups over a land-use gradient in a coastal tropical forest landscape of high richness and endemicity’, Animal Conservation 17(5), 441–453. https://doi.org/10.1111/acv.12111

Van den Berg, E., Kotze, I. & Beukes, H., 2013, ‘Detection, quantification and monitoring of Prosopis in the Northern Cape Province of South Africa using Remote Sensing and GIS’, South African Journal of Geomatics 2(2), 68–81.

van der Colff, D., Dreyer, L.L., Valentine, A., & Roets, F., 2015, ‘Invasive plant species may serve as a biological corridor for the invertebrate fauna of naturally isolated hosts’, Journal of Insect Conservation 19(5), 863–875. https://doi.org/10.1007/s10841-015-9804-3

van der Merwe, M., Dippenaar-Schoeman, A.S. & Scholtz, C.H., 1996, ‘Diversity of ground-living spiders at Ngome State Forest, Kwazulu/Natal: A comparative survey in indigenous forest and pine plantations’, African Journal of Ecology 34(4), 342–350. https://doi.org/10.1111/j.1365-2028.1996.tb00630.x

van Hengstum, T., Hooftman, D.A.P., Oostermeijer, J.G.B. & van Tienderen, P.H., 2014, ‘Impact of plant invasions on local arthropod communities: A meta-analysis’, Journal of Ecology 102, 4–11. https://doi.org/10.1111/1365-2745.12176

Van Wilgen, B.W., Carruthers, J., Cowling, R.M., Esler, K.J., Forsyth, A.T., Gaertner, M. et al., 2016, ‘Ecological research and conservation management in the Cape Floristic Region between 1945 and 2015: History, current understanding and future challenges’, Transactions of the Royal Society of South Africa 71(3), 207–303. https://doi.org/10.1080/0035919X.2016.1225607

van Wilgen, B.W., Forsyth, G.G., Le Maitre, D.C., Wannenburgh, A., Kotzé, J.D.F. van der Berg, E. et al. 2012, ‘An assessment of the effectiveness of a large, national-scale invasive alien plant control strategy in South Africa’, Biological Conservation 148(1), 28–38. https://doi.org/10.1016/j.biocon.2011.12.035

van Wilgen, B.W., Reyers, B., Le Maitre, D.C., Richardson, D.M. & Schonegevel, L., 2008, ‘A biome-scale assessment of the impact of invasive alien plants on ecosystem services in South Africa’, Journal of Environmental Management 89(4), 336–349. https://doi.org/10.1016/j.jenvman.2007.06.015

Vilà, M., Espinar, J.L., Hejda, M., Hulme, P.E., Jarošík, V., Maron, J.L. et al. 2011, ‘Ecological impacts of invasive alien plants: A meta-analysis of their effects on species, communities and ecosystems’, Ecology Letters 14(7), 702–708. https://doi.org/10.1111/j.1461-0248.2011.01628.x

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Appendix 1

Literature review search terms

TABLE 1-A1: Search terms used in the literature review on the ISI Web of Science.
Search 1: Effect on diversity (358 records)

TOPIC = “South Africa*” AND (((invas* OR alien* OR non$nativ* OR exotic* OR introduced OR non$indigenous OR naturali?ed OR plantation*) AND (plant* OR vegetat* OR tree* OR shrub* OR grass* OR forest* OR forb* OR herb* OR vine* OR *weed*)) OR (invaded AND (habitat* OR site* OR plot*))) AND ((reptil* OR squamata OR snake* OR python* OR boa* OR cobra* OR mamba* OR viper* OR adder* OR colubrid* OR elapid* OR lizard* OR gecko* OR skink* OR chameleon * OR agama* OR monitor* OR lacertid* OR amphisbaenid* OR cordylid* OR testudine* OR chenolian* OR turtle* OR tortoise* OR terrapin* OR crocodylia OR crocodil*) OR (amphibian* OR frog* OR anura* OR tadpole*) OR (invertebrate* OR platyhelminthe* OR *worm* OR nematod* OR nematomorph* OR nemertea* OR acanthocephalan* OR annelid* OR oligochaet* OR leech* OR mollus* OR gastropod* OR snail* OR slug* OR tardigrad* OR onychophora* OR arthropod* OR crustacea* OR *lice OR “terrestrial crab*” OR amphipod* OR isopod* OR myriapod* OR centipede* OR millipede* OR chilopod* OR diplopod* OR chelicerat* OR Araneae OR arachnid* OR spider* OR Acari OR acarin* OR mite* OR tick* OR opiliones OR harvestm?n OR scorpion* OR hexapod* OR insect* OR apterygot* OR odonat* OR dragonfl* OR damselfl* OR orthoptera* OR grasshopper* OR cricket* OR isoptera* OR termite* OR mantodea* OR mantis* OR mantid* OR blattodea* OR cockroach* OR embioptera* OR webspinner* OR phasmid* OR phasmatodea* OR hemiptera* OR *bug* OR cicada* OR aphid* OR *hopper* OR thysanoptera* OR thrip* OR psocoptera* OR coleoptera* OR beetle* OR lepidoptera* OR butterfl* OR moth* OR diptera* OR *flies OR *fly OR mosquito* OR flea* OR hymenoptera* OR wasp* OR ant OR ants OR bee OR bees OR neuroptera* OR lacewing* OR antilon* OR pollinat*)) AND (((population* OR communit* OR assemblage* OR species) AND (abundan* OR richness OR diversity OR composition OR evenness OR dominance OR equitability OR structure OR poor* OR impoverish*)) OR ((functional OR *genetic) AND diversity))

Refined by: DOCUMENT TYPES: (ARTICLE OR REVIEW OR BOOK CHAPTER)

Timespan: All years.

Search 2: Effect mechanisms (702 records)

TOPIC = “South Africa*” AND (((invas* OR alien* OR non$nativ* OR exotic* OR introduced OR non$indigenous OR naturali?ed OR plantation*) AND (plant* OR vegetat* OR tree* OR shrub* OR grass* OR forest* OR forb* OR herb* OR vine* OR *weed*)) OR (invaded AND (habitat* OR site* OR plot*))) AND ((reptil* OR squamata OR snake* OR python* OR boa* OR cobra* OR mamba* OR viper* OR adder* OR colubrid* OR elapid* OR lizard* OR gecko* OR skink* OR chameleon * OR agama* OR monitor* OR lacertid* OR amphisbaenid* OR cordylid* OR testudine* OR chenolian* OR turtle* OR tortoise* OR terrapin* OR crocodylia OR crocodil*) OR (amphibian* OR frog* OR anura* OR tadpole*) OR (invertebrate* OR platyhelminthe* OR *worm* OR nematod* OR nematomorph* OR nemertea* OR acanthocephalan* OR annelid* OR oligochaet* OR leech* OR mollus* OR gastropod* OR snail* OR slug* OR tardigrad* OR onychophora* OR arthropod* OR crustacea* OR *lice OR “terrestrial crab*” OR amphipod* OR isopod* OR myriapod* OR centipede* OR millipede* OR chilopod* OR diplopod* OR chelicerat* OR Araneae OR arachnid* OR spider* OR Acari OR acarin* OR mite* OR tick* OR opiliones OR harvestm?n OR scorpion* OR hexapod* OR insect* OR apterygot* OR odonat* OR dragonfl* OR damselfl* OR orthoptera* OR grasshopper* OR cricket* OR isoptera* OR termite* OR mantodea* OR mantis* OR mantid* OR blattodea* OR cockroach* OR embioptera* OR webspinner* OR phasmid* OR phasmatodea* OR hemiptera* OR *bug* OR cicada* OR aphid* OR *hopper* OR thysanoptera* OR thrip* OR psocoptera* OR coleoptera* OR beetle* OR lepidoptera* OR butterfl* OR moth* OR diptera* OR *flies OR *fly OR mosquito* OR flea* OR hymenoptera* OR wasp* OR ant OR ants OR bee OR bees OR neuroptera* OR lacewing* OR antilon* OR pollinat*)) AND ((habitat* NEAR/3 (quality OR structure OR heterogeneity)) OR shad* OR thermal* OR hydrolog* OR micro$site* OR micro$climate* OsR micro$habitat* OR refuge* OR prey* OR activity OR thermo$regulat* OR behavio$r* OR bask* OR predat* OR competit* OR herbivo$r* OR resource* OR nutrient* OR fire* OR soil* OR sediment* OR locomoti* OR host* OR reproducti* OR toxic* OR poison* OR hybrid* OR disease* OR parasit*)

Refined by: DOCUMENT TYPES: (ARTICLE OR REVIEW OR BOOK CHAPTER)

Timespan: All years.

Appendix 2

Studies reviewed
Search 1: Effects on diversity

Botzat, A., Fischer, L. & Farwig, N., 2013, ‘Forest-fragment quality rather than matrix habitat shapes herbivory on tree recruits in South Africa’, Journal of Tropical Ecology, 29(02), 111–122. https://doi.org/10.1017/S0266467413000102

Canavan, K., Paterson, I. & Hill, M.P., 2014, ‘The Herbivorous Arthropods Associated with the Invasive Alien Plant, Arundo donax, and the Native Analogous Plant, Phragmites australis, in the Free State Province, South Africa’, African Entomology, 22(2), 454–459. https://doi.org/10.4001/003.022.0204

Coetzee, B.W.T., van Rensburg, B.J. & Robertson, M.P., 2007, ‘Invasion of grasslands by silver wattle, Acacia dealbata (Mimosaceae), alters beetle (Coleoptera) assemblage structure’, African Entomology, 15(2), 328–339. https://doi.org/10.4001/1021-3589-15.2.328

Dlamini, T.C. & Haynes, R.J., 2004, ‘Influence of agricultural land use on the size and composition of earthworm communities in northern KwaZulu-Natal, South Africa’, Applied Soil Ecology, 27(1). https://doi.org/77–88.10.1016/j.apsoil.2004.02.003

Donnelly, D. & Giliomee, J., 1985, ‘Community structure of epigaeic ants in a pine plantation in newly burnt fynbos’, Journal of the Entomological Society of Southern Africa, 48(2), 259–265.

Esterhuizen, J., Green, K.K., Marcotty, T. & van den Bossche, P., 2005, ‘Abundance and distribution of the tsetse flies, Glossina austeni and G. brevipalpis, in different habitats in South Africa’, Medical and Veterinary Entomology, 19(4), 367–371. https://doi.org/10.1111/j.1365-2915.2005.00582.x

French, K. & Major, R.E., 2001, ‘Effect of an exotic Acacia (Fabaceae) on ant assemblages in South African fynbos’, Austral Ecology, 26(4), 303–310. https://doi.org/10.1046/j.1442-9993.2001.01115.x

Grass, I., Berens, D.G., Peter, F. & Farwig, N., 2013, ‘Additive effects of exotic plant abundance and land-use intensity on plant-pollinator interactions’, Oecologia, 173(3), 913–923. https://doi.org/10.1007/s00442-013-2688-6

Haynes, R.J., Dominy, C.S. & Graham, M.H., 2003, ‘Effect of agricultural land use on soil organic matter status and the composition of earthworm communities in KwaZulu-Natal, South Africa’, Agriculture, Ecosystems & Environment, 95(2–3), 453–464. https://doi.org/10.1111/j.1747-0765.2006.00084.x

Kietzka, G.J., Pryke, J.S. & Samways, M.J., 2015, ‘Landscape ecological networks are successful in supporting a diverse dragonfly assemblage’, Insect Conservation and Diversity, 8(3), 229–237. https://doi.org/10.1111/icad.12099

Kinvig, R.G. & Samways, M.J., 2000, ‘Conserving dragonflies (Odonata) along streams running through commercial forestry’, Odonatologica, 29(3), 195–208.

Lawrence, J.M. & Samways, M.J., 2002, ‘Influence of hilltop vegetation type on an African butterfly assemblage and its conservation’, Biodiversity and Conservation, 11(7), 1163–1171. https://doi.org/10.1023/A:1016017114473

Liu, S.S. & Samways, M.J., 2002, ‘Conservation management recommendations for the Karkloof blue butterfly, Orachrysops ariadne (Lepidoptera: Lycaenidae)’, African Entomology, 10(1), 149–159.

Magoba, R.N. & Samways, M.J., 2012, ‘Comparative footprint of alien, agricultural and restored vegetation on surface-active arthropods’, Biological Invasions, 14(1), 165–177. https://doi.org/10.1007/s10530-011-9994-x

Magoba, R.N. & Samways, M.J., 2010, ‘Recovery of benthic macroinvertebrate and adult dragonfly assemblages in response to large scale removal of riparian invasive alien trees’, Journal of Insect Conservation, 14(6), 627–636. https://doi.org/10.1007/s10841-010-9291-5

Maoela, M.A., Roets, F., Jacobs, S.M. & Esler, K.J., 2016, ‘Restoration of invaded Cape Floristic Region riparian systems leads to a recovery in foliage-active arthropod alpha- and beta-diversity’, Journal of Insect Conservation, 20(1), 85–97. https://doi.org/10.1007/s10841-015-9842-x

Mgobozi, M.P., Somers, M.J. & Dippenaar-Schoeman, A.S., 2008, ‘Spider responses to alien plant invasion: the effect of short- and long-term Chromolaena odorata invasion and management’, Journal of Applied Ecology, 45(4), 1189–1197. https://doi.org/10.1111/j.1365-2664.2008.01486.x

Olckers, T. & Hulley, P.E., 1991, ‘Impoverished insect herbivore faunas on the exotic bugweed Solanum mauritianum Scop. relative to indigenous Solanum species in Natal/KwaZulu and the Transkei’, Journal of the Entomological Society of Southern Africa, 54(1), 39–50.

Olckers, T. & Hulley, P.E., 1989, ‘Insect herbivore diversity on the exotic weed Solanum mauritianum Scop. and three other Solanum species in the eastern Cape Province’, Journal of the Entomological Society of Southern Africa, 52(1), 81–93.

Padayachi, Y., Proches, S. & Ramsay, L.F., 2014, ‘Beetle assemblages of indigenous and alien decomposing fruit in subtropical Durban, South Africa’, Arthropod-Plant Interactions, 8, 135–142.

Proches, S., Wilson, J.R.U., Richardson, D.M. & Chown, S.L., 2008, ‘Herbivores, but not other insects, are scarce on alien plants’, Austral Ecology, 33, 691–700. https://doi.org/10.1111/j.1442-9993.2008.01836.x

Pryke, J.S., Roets, F. & Samways, M.J., 2013, ‘Importance of habitat heterogeneity in remnant patches for conserving dung beetles’, Biodiversity and Conservation, 22(12), 2857–2873. https://doi.org/10.1007/s10531-013-0559-4

Pryke, J.S. & Samways, M.J., 2012, ‘Conservation management of complex natural forest and plantation edge effects’, Landscape Ecology, 27(1), 73–85. https://doi.org/10.1007/s10980-011-9668-1

Pryke, J.S. & Samways, M.J., 2009, ‘Recovery of invertebrate diversity in a rehabilitated city landscape mosaic in the heart of a biodiversity hotspot’, Landscape and Urban Planning, 93(1), 54–62. https://doi.org/10.1016/j.landurbplan.2009.06.003

Pryke, S.R. & Samways, M.J., 2003, ‘Quality of remnant indigenous grassland linkages for adult butterflies (Lepidoptera) in an afforested African landscape’, Biodiversity and Conservation, 12(10), 1985–2004. https://doi.org/10.1023/A:1024103527611

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Search 2: Effect mechanisms

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