Corporate participation plays an increasing role in Open Source Software (OSS) development. Unlike volunteers in OSS projects, companies are driven by business objectives. To pursue corporate interests, companies may try to dominate the development direction of OSS projects. One company's domination in OSS may 'crowd out' other contributors, changing the nature of the project, and jeopardizing the sustainability of the OSS ecosystem. Prior studies of corporate involvement in OSS have primarily focused on predominately positive aspects such as business strategies, contribution models, and collaboration patterns. However, there is a scarcity of research on the potential drawbacks of corporate engagement. In this paper, we investigate corporate dominance in OSS ecosystems. We draw on the field of Economics and quantify company domination using a dominance measure; we investigate the prevalence, patterns, and impact of domination in the evolution of the OpenStack ecosystem. We find evidence of company domination in over 73% of the repositories in OpenStack, and approximately 25% of companies dominate one or more repositories per version. We identify five patterns of corporate dominance: Early incubation, Full-time hosting, Growing domination, Occasional domination, and Last remaining. We find that domination has a significantly negative relationship with the survival probability of OSS projects. This study provides insights for building sustainable relationships between companies and the OSS ecosystems in which they seek to get involved.