Question

which of these will cause a cascading effect or trophic cascade in an ecosystem?
the gain of a new species in an ecosystem
the loss of any one species in an ecosystem
no change in any factors in a thriving ecosystem

Explanation:

A trophic cascade is a chain of effects on organisms at different trophic levels in an ecosystem. The loss of a species (a keystone species or any species with interactions) disrupts food webs/ecological relationships, causing changes across levels (e.g., predator loss leads to prey overpopulation, affecting lower trophic levels). Gaining a new species may or may not cause a cascade (depends on its role, not always cascading), and no change in factors means no cascade. So the loss of any one species is most likely to cause a trophic cascade.

Answer:

the loss of any one species in an ecosystem