Stratification means:

The correct answer is Option (1) → Vertical distribution of different species occurring at different levels

In an ecosystem such as a forest, plants of different heights occupy different layers. Trees form the top layer, shrubs the next, and herbs and grasses the bottom layer. This vertical distribution of different species occupying different levels is called stratification.

(1) Vertical distribution of different species occurring at different levels — Correct. This is stratification.

(2) Horizontal distribution of different species occurring at different levels — Incorrect. Stratification is about layers one above another, that is vertical, not horizontal.

(3) Transfer and movement of food and energy between different trophic levels — Incorrect. This describes energy flow through a food chain, not stratification.

(4) Unidirectional movement of food and energy from higher trophic levels — Incorrect. Energy does flow in one direction, but from the lower trophic levels (producers) to the higher ones. In any case this is energy flow, not stratification.

NCERT Extract:
Ecosystem – Structure and Function – …