2.5A Zonation Notes

1. Zonation occurs as abiotic and biotic conditions vary across space, resulting in distinct zones where particular species dominate.
2. It represents a spatial pattern (not temporal like succession) and is often observed in ecosystems such as rocky shores, sand dunes, mountains, and forests.
3. It describes how biotic communities (plants, animals, and microorganisms) change in response to abiotic factors such as:
   1. Elevation (altitude)
   2. Latitude
   3. Tidal level
   4. Soil horizons
   5. Distance from a water source
   6. Temperature, moisture, and light intensity

Factors Influencing Zonation

Changes in Abiotic Factors

1. Elevation (altitude): Temperature and oxygen levels decrease, changing vegetation types from tropical forests at low altitude to alpine tundra higher up.
2. Latitude: Sunlight intensity and temperature vary from the equator to the poles, influencing global biome zonation.
3. Tidal level: In coastal ecosystems, exposure to air, salinity, and wave action varies between high and low tide zones.
4. Soil composition: Soil pH, salinity, and nutrient availability differ between areas, creating patterns in plant distribution.
5. Distance from water source: Moisture availability affects vegetation density and type, as lush vegetation near rivers transitions to arid desert farther away.

Changes in Biotic Factors

1. Competition: Species compete for light, space, or nutrients, influencing their zonal distribution.
2. Predation: Predators may restrict the range of prey species to specific zones.
3. Mutualism: Certain plants may only grow in areas where their symbiotic species (e.g., pollinators or mycorrhizae) exist.

Examples of Zonation

1. Rocky Shore Zonation

1. The rocky intertidal zone provides a clear, observable example of zonation.
2. Conditions vary sharply from the upper shore (exposed, dry, salty) to the lower shore (submerged, stable, oxygen-rich).
3. Species distribution:
   1. Spray zone: Exposed to air most of the time; inhabited by lichens and periwinkles.
   2. High tide zone: Alternates between wet and dry; barnacles and limpets dominate.
   3. Middle tide zone: Submerged for longer periods; mussels, seaweed, and chitons thrive.
   4. Low tide zone: Constantly submerged; anemones, sea urchins, and kelp are abundant.

2. Mountain Ecosystems

1. As altitude increases:
   1. Temperature decreases and oxygen levels drop.
   2. Plant communities transition from tropical forest → montane forest → alpine grasslands → lichens and mosses.
2. Each band supports species adapted to that altitude’s conditions.

3. Coastal Dune Zonation

1. Sand dune systems exhibit gradual changes from the shore inland:
   1. Embryo dunes: Closest to the shore; few species (e.g., sand couch, sea rocket).
   2. Foredunes: Dominated by marram grass that stabilizes the sand.
   3. Fixed dunes: Contain shrubs and herbs like sea buckthorn and wild rose.
   4. Dune slacks: Low-lying areas between dunes; moisture supports diverse flora.
   5. Wooded dunes: Farther inland, trees like oak and birch dominate.

Scales of Zonation

1. Local Scale:
   1. Observed within ecosystems (e.g., rocky shore, sand dunes).
   2. Determined by microclimate and soil differences.
2. Global Scale:
   1. Seen across continents (e.g., from tropical to polar biomes).