Final answer:
Intervenor groups are external stakeholders with the power to disrupt project development, often forming in response to changes in society and influencing public policy through campaigns and lobbying.
Step-by-step explanation:
The external stakeholders who are not part of a project but possess the power to significantly influence or disrupt its development are known as intervenor groups. These stakeholders often form due to external events or disturbances, such as changes in social norms, environmental factors, or technological advances. They can become highly active participants in public policy debates, using various strategies to advance their viewpoints, which might include lobbying, media campaigns, and influencing public perception through the dissemination of information and opinion polls.
An example of such a group is the Environmental Defense Fund, which has used its influence to support regulations on pollution, backed by public opinion polls that align with their stance. These groups, as described by disturbance theory, come together in response to changes and wield their power to affect projects and public policy through collective action efforts.