Researchers must map combined effects of invasive species, climate change and human activities in South Africa

Invasive species are the second biggest threat to biodiversity conservation in South Africa - a fact matched, say researchers, by the number of research papers done on the topic. This is relative to other threats like pollution, climate change, overharvesting or changes in habitat.

These threats to ecosystems are what scientists also call drivers of global change, which is the study of how the Earth, as a system, changes with all the interactions between human activities and other physical, chemical and biological processes.

In a recent book chapter, researchers looked at exactly how much research is being done in South Africa on biological invasions, which is when species like plants or animals are introduced into a new area where they thrive, become established and potentially harm other surrounding species or the environment. 

They also looked at research on how this driver interacts with other drivers.

Looking through research papers published between 2000 and 2018 on the “Web of Science” database, they found 1149 relevant studies.

Their review of the studies showed that land-based (terrestrial) research focussed more on changes in habitat, while freshwater research centred on pollution, and marine and estuary research looked mostly at overharvesting.

They also found that phenomena that are well-documented globally to affect biodiversity or ecosystem services, are not well-documented in local South African studies. For example, they only found 5 papers looking at ocean acidification, which disrupts food chains and harms sea life. This happens because excess carbon dioxide in the atmosphere, from human activities like burning fossil fuels, dissolves in seawater.

Habitat changes, such as fires or climate changes, lead to the growth of invasive species. They said that carbon dioxide has increased by around 40%, and it could be creating better conditions for alien plants to grow in. But, there is very little research done on this issue in South Africa. 

They found 21 papers looking at how different drivers interact. Most of these focussed on linking habitat changes and invasive species. But, very few papers looked at 3 or more drivers at the same time. The authors say this suggests more research into how drivers of global change interact to affect ecosystems is needed in South Africa.

The South African authors acknowledge that it will be difficult to develop a full picture of how global change drivers interact in South Africa, but said existing local research on invasive species can already inform studies in this complex field.

Abstract

In this chapter, we assess how much research in South Africa has been directed towards biological invasions relative to other elements of global change. Using Web of Science, we systematically reviewed literature relevant to South African ecosystems published between 2000 and 2018 and relating to biological invasions, climate change, overharvesting, habitat change, pollution, and/or atmospheric CO2. We identified 1149 relevant papers that were scored in terms of their coverage of drivers and driver interactions that affect biodiversity or ecosystem services. A strong spatio-temporal effect was observed on research effort. Firstly, effort differed between realms, with habitat change, pollution and overharvesting receiving the largest research focus within terrestrial, freshwater and marine/estuarine realms respectively. Secondly, certain globally well-studied phenomena were not documented in local literature (e.g. there were fewer than five papers on ocean acidification). We identified 21 different interactions between drivers, with the interactions between invasive species and habitat change (for example altered fire regimes in invaded landscapes) being the most prominent. However, fewer than 4% of papers addressed interactions between three or more drivers. This suggests that while the importance of understanding driver interactions is recognised, there has been little in the way of researching the compound effects of driver interactions in South African ecosystems. The long-cited statement that invasive species pose the second-largest threat to biodiversity conservation, behind habitat change, matches the relative research output for this driver in South Africa. Developing a comprehensive quantitative picture of the relative importance of global change drivers will nonetheless be challenging, not only in the unambiguous delineation of drivers, but also due to the unequal availability of research results at comparable spatial and temporal scales. The relative maturity of work on invasive species could provide a basis for exploring such complex interactions and thus contribute to overcoming such barriers.

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