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C·I·B Post Doctoral Fellow Dr. Gyan Sharma, core team member Prof. Karen Esler (Department of Conservation Ecology and Entomology, SU) and renowned ecological economist Prof. James N. Blignaut (Department of Economics, University of Pretoria) recently explored the relationships between various socio-economic variables and the prevalence and density of invasive alien species (IAS) using country-level data sets for 172 countries.

They tested whether the abundance and distribution of populations of IAS are correlated with various socio-economic indicators, with the direction of causality being that the state of IAS is determined by socio-economic conditions. The results revealed a positive and statistically significant relationship between the prevalence and density of IAS and the human development index (HDI), the satisfaction with life index and the gross domestic product (GDP) among all the countries tested. Additionally, the density of IAS increased significantly with human-population density, total geographic area, GDP and HDI.

The working group also established a positive relationship between the density of IAS and the top 10 road networks of the world. The study argues that inevitable road development as a consequence of economic growth is therefore also a major concern regarding the spread of invasive species. Precise policies and management practices need to be in place during road construction and management to minimise the propagule pressure of invasives.

While establishing such relations the study also cautioned, however, that the results are likely to be influenced by the sampling factor, whereby affluent countries have more resources to measure and monitor IAS than poorer countries and hence have better records of such, which then indicates a stronger relationship with the level of development.

The study suggests that a new agenda of research in modelling and analysing the economic impacts of biological invasions should be explored through interdisciplinary collaboration between ecologists and economists. This global study gives insight that countries with emerging economies should dedicate funds for invasive species research and management to reduce future costs associated with the management of these species. Resources should be used to support intercontinental cooperation with properly designed research strategies, addressing issues of invasions where current biases can limit our understanding of biological invasions.

For further details: Prof. KJ Esler (

Sharma, G.P., Esler, K.J. & Blignaut, J. (2010). Alien invasives, disposable income and the gentle pursuit of happiness: socio-economic correlates of invasion? South African Journal of Science, 106 (3/4), 1-6.

To view the paper: