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

Abstract

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.