The contribution of a keystone species to its ecosystem is significant, as it plays a critical role in maintaining the structure and diversity of that ecosystem. A keystone species can influence population dynamics, such as predator-prey relationships, and affect the availability of resources for other organisms. For example, sea otters are considered a keystone species because they help control sea urchin populations, which in turn allows kelp forests to thrive. The presence or absence of a keystone species can lead to substantial changes in ecosystem health and stability.