What is primarily affected by the disruption caused by dams?

The disruption caused by dams primarily affects wildlife migration. Dams can alter river ecosystems and create barriers that prevent fish and other aquatic species from moving freely along rivers to their spawning grounds. This alteration of natural water flow changes habitats significantly, and many species that rely on the unimpeded movement through these waterways may struggle to thrive.

In addition to physical barriers, changes in water temperature, sediment flow, and the chemistry of the water can further impact wildlife populations and their migration patterns. Efforts such as fish ladders and other mitigation strategies can be implemented, but they do not always fully replicate the natural conditions required for many species to migrate successfully. Hence, the ecological impact on wildlife migration is a significant concern when considering the consequences of dam construction and operation.

In the context of the other choices, while human transportation, tourism revenue, and agricultural output can indeed be affected by dams, the most direct and often discussed impact in relation to ecological studies is wildlife migration.