Assessing the invasiveness of alien aroids using modelling techniques and ecological assessments.

Doctor of Philosophy in Environmental Sciences. University of KwaZulu-Natal, Durban 2016.Biological invasions represent one of the main drivers of the present decline in biodiversity worldwide and are difficult and costly to control. Consequently, identifying which factors allow a small proportion of species to successfully invade is a key area of research in invasion biology and is essential for effective management. In this thesis, I studied invasion patterns of the Araceae family, explored some of their ecological drivers, and unravelled mechanistic relationships that caused species to become successful. There are several emerging generalizations in invasion biology, but often the factors determining invasiveness are group-specific. Therefore the primary aim of this thesis was to establish whether general patterns of invasion biology also applied to Araceae. At a global scale, I found that, similar to other plant families, species with large native ranges and those that have been widely introduced were more likely to become invasive. What is unique to the family is the great diversity of growth forms, some of which are more likely to become invasive than others. I identified nine lineages in the family that have a greater tendency to invasiveness and recommended a precautionary approach be taken for these clades. At a regional scale, I used Epipremnum aureum as my case study species, because of the detection of the species in the country, as well as knowledge on its invasive cogener. In the KwaZulu-Natal province of South Africa, I found 78 naturalized E. aureum populations and 321 cultivated populations, of which the naturalized populations covered nearly 3 hectares in total. Disturbance played a major role in facilitating invasions and species distribution models indicated that E. aureum has a high probability of expanding its current range. Due to the invasion threat of this species, I recommended that all plants outside cultivation be removed. Lastly, I assessed a unique case where a widely planted species, Monstera deliciosa, has not yet become a global invader. I explored whether introduction history drives invasiveness in the Monsteroideae subfamily. I found that long residence times and high propagule pressure facilitated invasiveness in this subfamily. This was followed by as a local scale approach to identify factors influencing invasion success. The naturalization of Monstera deliciosa was largely driven by anthropogenic effects in Limpopo, South Africa, despite the plants‟ occurence in suitable habitat. Therefore, I concluded that M. deliciosa poses a low invasion risk to South Africa. Overall, this thesis demonstrated the importance of using a taxonomic group to identify the contribution of multiple factors in the success of invasive species, but that species-specific assessments will still be required for effective management

Global costs of plant invasions must not be underestimated

First paragraph: The impacts of biological invasions have become a key focus of researchers in recent decades, leading to a rapid accumulation of evidence on economic losses associated with invasions. In a synthesis paper, Diagne et al. (2021) use a new database, InvaCost (Diagne et al. 2020), to quantify the global economic costs of biological invasions. They demonstrate that the global costs associated with invasive alien species are massive, at least US$ 1.3 trillion between 1970 and 2017, and increasing rapidly. Such high costs emphasize the critical importance of preventing and controlling biological invasions. Their paper thus delivers an important and much needed contribution to invasion science, which can strengthen invasive alien species management and policy globally. However, the costs of plant invasions presented by Diagne et al. (2021) are substantially underestimated compared to those of vertebrate and invertebrate invasions, and with respect to the available literature. While Diagne et al. (2021) state that the reported costs have pronounced geographic and taxonomic gaps, we believe that their significant underestimation of plant costs in comparison with other taxonomic groups needs to be clarified, to correctly demonstrate the severity of plant invasions and guide appropriate prioritization, budgeting, and allocation of limited management resources

A global assessment of a large monocot family highlights the need for group-specific analyses of invasiveness

CITATION: Moodley, D., Proches, S. & Wilson, J. R. U. 2016. A global assessment of a large monocot family highlights the need for group-specific analyses of invasiveness. AoB PLANTS, 8:1-14, doi:10.1093/aobpla/plw009.The original publication is available at http://aobpla.oxfordjournals.org/Significant progress has been made in understanding biological invasions recently, and one of the key findings is that the determinants of naturalization and invasion success vary from group to group. Here, we explore this variation for one of the largest plant families in the world, the Araceae. This group provides an excellent opportunity for identifying determinants of invasiveness in herbaceous plants, since it is one of the families most popular with horticulturalists, with species occupying various habitats and comprising many different life forms. We first developed a checklist of 3494 species of Araceae using online databases and literature sources. We aimed to determine whether invasiveness across the introduction–naturalization–invasion continuum is associated to particular traits within the family, and whether analyses focussed on specific life forms can reveal any mechanistic correlates. Boosted regression tree models were based on species invasion statuses as the response variables, and traits associated with human use, biological characteristics and distribution as the explanatory variables. The models indicate that biological traits such as plant life form and pollinator type are consistently strong correlates of invasiveness. Additionally, large-scale correlates such as the number of native floristic regions and number of introduced regions are also influential at particular stages in the invasion continuum. We used these traits to build a phenogram showing groups defined by the similarity of characters. We identified nine groups that have a greater tendency to invasiveness (including Alocasia , the Lemnoideae and Epipremnum ). From this, we propose a list of species that are not currently invasive for which we would recommend a precautionary approach to be taken. The successful management of plant invasions will depend on understanding such context-dependent effects across taxonomic groups, and across the different stages of the invasion process.https://academic.oup.com/aobpla/article/2609518/A-global-assessment-of-a-large-monocot-familyPublisher's versionAuthors retain copyrigh

Different traits determine introduction, naturalization and invasion success in woody plants : proteaceae as a test case

Publication of this article was funded by the Stellenbosch University Open Access Fund.The original publication is available at http://www.plosone.org/A major aim of invasion ecology is to identify characteristics of successful invaders. However, most plant groups studied in detail (e.g. pines and acacias) have a high percentage of invasive taxa. Here we examine the global introduction history and invasion ecology of Proteaceae—a large plant family with many taxa that have been widely disseminated by humans, but with few known invaders. To do this we compiled a global list of species and used boosted regression tree models to assess which factors are important in determining the status of a species (not introduced, introduced, naturalized or invasive). At least 402 of 1674 known species (24%) have been moved by humans out of their native ranges, 58 species (14%) have become naturalized but not invasive, and 8 species (2%) are invasive. The probability of naturalization was greatest for species with large native ranges, low susceptibility to Phytophthora root-rot fungus, large mammal-dispersed seeds, and with the capacity to resprout. The probability of naturalized species becoming invasive was greatest for species with large native ranges, those used as barrier plants, tall species, species with small seeds, and serotinous species. The traits driving invasiveness of Proteaceae were similar to those for acacias and pines. However, while some traits showed a consistent influence at introduction, naturalization and invasion, others appear to be influential at one stage only, and some have contrasting effects at different stages. Trait-based analyses therefore need to consider different invasion stages separately. On their own, these observations provide little predictive power for risk assessment, but when the causative mechanisms are understood (e.g. Phytophthora susceptibility) they provide valuable insights. As such there is considerable value in seeking the correlates and mechanisms underlying invasions for particular taxonomic or functional groups.Stellenbosch UniversityPublishers' versio

Invasive alien species add to the uncertain future of protected areas

Establishing and managing protected areas (national parks, nature reserves and other sites of conservation value) represent the most common approach to conserving species and ecosystems, but these areas are vulnerable to global environmental change. Recently, Golden Kroner et al. (2019) suggested protected area downgrading, downsizing, and degazettement (PADDD) as one of the main threats to biodiversity conservation. However, there are several other elements, of similar concern, that threaten conservation efforts in protected areas, such as climate change and pollution. Here, in a commentary to the Golden Kroner et al. (2019) paper, we address an additional important element affecting protected area dynamics and robustness that was overlooked by these authors – invasions by alien species. We argue that invasive alien species (IAS) contribute directly to the pressures of biodiversity loss by competing with native species and modifying the characteristics of the invaded ecosystems, and virtually no protected areas are free from these effects. Therefore, excluding IAS from legal instruments and policy frameworks underpinning current conservation approaches in protected areas presents a great risk for nature conservation. Consequently, this aligns poorly with the idea of protected areas being a cornerstone for conservation at local, regional and national levels. For that reason and to paint a more complete picture of the effectiveness of protected areas, we argue that when other factors threatening the existence and functioning of protected areas are discussed, we also need to account for biological invasions. This will ensure that adaptive conservation management strategies protect a wide range of species, ecosystems, and landscapes. Hence, this commentary aims to be of general interest for policymakers, managers and researchers

Site-specific conditions influence plant naturalization : the case of alien Proteaceae in South Africa

CITATION: Moodley, D. et al. 2014. Site-specific conditions influence plant naturalization: The case of alien Proteaceae in South Africa. Acta Oecologica, 59:62-71. doi:10.1016/j.actao.2014.05.005The original publication is available at https://www.sciencedirect.com/science/article/pii/S1146609X14000630?via%3DihubThe outcome of plant introductions is often considered in binary terms (invasive or non-invasive). However, most species experience a time lag before naturalization occurs, and many species become naturalized at some sites but not at others. It is therefore important to understand the site-specific mechanisms underlying naturalization. Proteaceae is an interesting case as some species are widespread invaders, while others, despite a long history of cultivation, show no signs of naturalization. At least 26 non-native Proteaceae species have been introduced to, and are cultivated in, South Africa. We mapped populations and examined differences between naturalized and non-naturalized populations (e.g. propagule pressure, land use and bioclimatic suitability). Of the 15 species surveyed, 6 were naturalized at one or more sites. Of these, Hakea salicifolia is most widely cultivated, but is only naturalizing in some areas (32 naturalized populations out of 62 populations that were surveyed). We found propagule pressure to be the most important determinant of naturalization for H. salicifolia. However, in suboptimal climatic conditions, naturalization only occurred if micro-site conditions were suitable, i.e. there was some disturbance and water available. For the other naturalized species there were few sites to compare, but we came to similar conclusions - Banksia integrifolia only naturalized at the site where it was planted the longest; Banksia serrata only naturalized at a site influenced by fire regimes; while Banksia formosa naturalized at sites with high propagule pressure, absence of fires and where there is no active clearing of the plants. Naturalization of Proteaceae in South Africa appears to be strongly mediated by site-specific anthropogenic activities (e.g. many planted individuals and water availability). More broadly, we argue that invasion biology needs to focus more closely on the mechanisms by which species and pathways interact to determine the likelihood and consequence of an invasion.Publisher's versio

Factors associated with introduction, naturalization, and invasion in Australian Proteaceae species.

<p>A) native range size; B) the number of susceptible and resistant species to <i>Phytophthora</i>; C) use as barrier plants; and D) plant height (m). Different letters indicate groups that differed significantly at <i>p</i><0.05. For barrier plants and susceptibility to <i>Phytophthora</i>, Fisher's exact test for count data was used. Only factors that explained at least 15% of either model are shown.</p

Taxonomic distribution of Proteaceae genera worldwide.

<p>Patterns depict A) introduced, B) naturalized and C) invasive species. Each point represents a genus (to avoid clutter only selected genus names are included) with lines indicating expectations from a hypergeometric distribution (median and 95% confidence intervals). Genera falling between the lines are not significantly over- or underrepresented. Genera above or below the intervals are significantly over- or underrepresented respectively. To assess how invasiveness differs across the genera of Proteaceae.</p

The number of Proteaceae species that are introduced, naturalized or invasive.

<p>Out of the 1674 species in the family at least 402 species have been introduced worldwide. Out of the 402 species, 336 species have not yet naturalized, 58 species are naturalized but not recorded as invasive and 8 species are invasive. In the same manner, out of the 1121 Australian species at least 206 species have been introduced, of which 147 have not yet naturalized, 51 are naturalized but not invasive and 8 are invasive. Numbers of genera in each category are shown in parentheses.</p

Summary of the boosted regression tree models of factors associated with naturalization (a) and invasion (b) in Proteaceae species.

<p>Only traits contributing at least 5% to the models are shown; traits that explained at least 15% of either model are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0075078#pone-0075078-g003" target="_blank">Figure 3</a> and Table S6. Data range includes the minimum and maximum values from the fitted functions and is representative of effect size.</p