The vertical distribution of different species occupying different levels in an ecosystem, as in a forest, is called:

Stratification refers to the vertical layering of plants and animals in a community. Different species occupy different heights or levels, depending on their needs for light, space and food. It is one of the main features of community structure and is most clearly seen in forests, especially tropical rainforests.

In a tropical rainforest, the following layers are commonly seen:

Emergent layer: a few very tall trees that rise above the rest, reaching 50-60 metres or more. Eagles and some monkeys live here.

Canopy: the dense upper layer formed by the crowns of most trees, which receives most of the sunlight. Most of the forest's animals, such as birds, monkeys and insects, live here.

Understorey: smaller trees and shrubs that grow in the shade below the canopy.

Forest floor: the dark ground layer, with herbs, ferns, fallen leaves and decomposers such as fungi, bacteria and earthworms.

Stratification helps reduce competition, because species in different layers use different resources. It also creates many micro-habitats, increasing biodiversity.

Vertical stratification is also found in lakes and oceans. In a lake, for example, there are zones based on light and temperature: the upper, well-lit zone where photosynthesis happens (the photic zone), and the deeper, darker zone (the aphotic zone). In temperate lakes, the water separates into a warm upper layer (epilimnion), a middle layer with a sharp change in temperature (thermocline or metalimnion) and a cold lower layer (hypolimnion) in summer.

Why not the other options?

• ✗Succession is the gradual change in the species of a community over time.
• ✗Zonation usually refers to horizontal changes in communities, such as along a seashore or up a mountain.
• ✗Biomagnification is the increase in concentration of toxic substances at higher levels of a food chain.