Intermediate Disturbance Hypothesis Challenged: What Science Now Says About Biodiversity

The intermediate disturbance hypothesis (IDH), proposed by Joseph Connell in 1978, holds that biodiversity peaks at moderate levels of ecological disturbance such as storms, fires, or treefalls that prevent dominant species from crowding out others. However, a 2001 review by Mackey and Currie found that the predicted hump-shaped curve between disturbance and diversity appears in only a minority of real-world systems, with many habitats showing other patterns entirely. Ecologist Jeremy Fox argued in 2013 that the standard mechanisms used to explain the hump do not reliably predict one, calling for the hypothesis to be abandoned. What remains scientifically supported is a narrower principle: some level of disturbance is necessary for diversity in any habitat where a single competitor can eventually dominate. The key variable is the ratio of disturbance frequency to the time a dominant species needs to outcompete rivals, rather than a universal hump-shaped relationship.