Cities as hotspots for invasions: the case of the eThekwini Municipality.

Abstract

Increased anthropogenic activities (trade and travel) have caused an increase in the introduction of biological organisms outside of their native range. Biological invasions result in serious negative ecological, economic and social impacts in their invaded range and are responsible for a decline in native biodiversity. These negative impacts become more prominent in highly transformed environments, such as those found in cities which are often the first points of introduction for alien species. Durban (eThekwini) is situated on the east coast of South Africa and is one of the largest port cities on the African continent, making it an important economic centre for the country. It is the third most populated city in South Africa and is a major contributor towards tourism. Additionally, Durban is located in the Maputaland-Pondoland Albany, one of thirty-four global hotspots of biodiversity. This study focuses on the patterns, processes and drivers of biological invasions in Durban. I investigated three important aspects of alien species responses in urban environments: 1) precaution through the prevention of alien species introduction; 2) prioritisation through using a combination of early warning systems and techniques to identify potentially high-risk alien species; and 3) preparedness and response for a potential incursion event of Solenopsis invicta in Durban. I investigated the importance of preventing alien species introductions by identifying the pathways which facilitate the highest number of introductions for prioritisation for prevention efforts. Furthermore, I identified vectors responsible for secondary spread of alien species in cities. The majority of alien species were either released into nature or escaped from captivity and spread within cities through unaided dispersal. It is difficult to control the natural spread of species, therefore preventing alien species introductions is paramount. However, preventing the introduction of all alien species to a new area is difficult to achieve. Therefore, prioritising alien species for prevention efforts is an essential component of responding to biological invasions which will allow decision makers to more carefully allocate limited resources and time to species with the potential to result in severely negative impacts. Incorporating a holistic prioritisation approach based not only on alien species with a high-risk of invading new areas, but also the pathways which facilitate their introduction and the areas which are most at risk of being invaded is beneficial for decision makers in targeting priority species for prevention efforts. I developed a methodology, integrating these three aspects (species, pathways and sites), to select priority species to target for prevention efforts and identified areas most at risk of being invaded by these species using climatic suitability modelling to select priority targets for prevention efforts. Additionally, I used climatic models and pathway information to identify potential points of first introduction and sites of first naturalisation to target for active and passive surveillance endeavours. Solenopsis invicta Buren (the red imported fire ant) was identified as a potentially high-risk species posing serious ecological and socio-economic threats for Durban. I then explored opportunities for strategic response planning for Solenopsis invicta for Durban, South Africa. In doing so, I identified key priorities to help decision makers initiate strategic response planning for a potential incursion of this species to Durban. The research presented in this study outlines approaches that can assist with the prevention, prioritisation, and preparedness in responding to alien species in urban environments.