Brussels’ Gucci Gulch

Over the past decades, studies on interest groups in the EU have increased noticeably. However, the available literature focusses mainly on the micro-level, which examines individual groups. Research into the systems of interest groups, so-called populations, at the macro-level remains underrepresented. A variety of theories, originating from the US, explain differences in the development of interest group populations. The Population Ecology Theory of Lowery and Gray is the most prominent example in contemporary political science, often applied through the cross-sectional ESA model. While its application to the EU has been limited by fragmented data sources, the Transparency Register now offers an opportunity to conduct a comprehensive large-n study. The present paper utilizes this possibility to identify variables that facilitate the mobilization of corporate interest groups and shape the density of their populations. For this purpose, an adapted ESA model tests five hypotheses. Results highlight the importance of two different variables. First, the density of corporate interest group populations increases with higher constituency, operationalized by annual turnover. This relationship is limited by density dependence, proving that populations only increase to a certain point until competition among similar interest groups limits further growth. It further shows that the EU interest group system has reached a point of maturity, which was not verifiable a decade ago. The second variable that has a significant relationship with density is policy participation. Having more expert groups to participate in the policy-making process, brings more interest groups to Brussels. Further explorative findings highlight the differences between corporate and social interest groups. It becomes evident that their mobilization processes vary substantially and can therefore not be explained by the same approaches. Future research can link the gained knowledge with micro-level studies, focus more on the mobilization of social interest groups and further specify the independent variables of the ESA model.