Final answer:
A trophic cascade is a series of changes in predator-prey relationships affecting the composition and abundance of organisms across different trophic levels in an ecosystem.
Step-by-step explanation:
The best definition of a trophic cascade is: A series of predator-prey relationships that result in changes in the abundance or composition of species at different trophic levels. When a change occurs at one trophic level, it can lead to subsequent changes in the ecosystem, such as the alteration of population sizes or biodiversity at other levels. Trophic cascades are important in understanding how ecosystems function and respond to changes in species dynamics and environmental impacts.