Zonation, succession and change in ecosystems

Zonation is a change in species composition across space along an environmental gradient.

A change in species composition across space along an environmental gradient.

Altitude, latitude, tidal level, and soil depth.

Biodiversity generally decreases as altitude increases because conditions become colder, windier, and growing seasons shorten.

A gradual change in an abiotic factor across space (e.g., tidal exposure, altitude, moisture, light).

Abiotic conditions change, species have tolerance limits, and competition affects where species survive.

The low tide zone, because it is submerged most of the time and conditions are more stable.

Tidal level on a rocky shore (high tide zone → mid tide → low tide).

Transects (often with quadrats at intervals) to record changes across a gradient.

Because abiotic conditions change across space, species have tolerance limits, and competition excludes less adapted species from some zones.

Abundance (number of organisms).

A transect is a straight line laid across an environmental gradient along which observations are made at intervals.

Species distribution and abundance along a transect; kite width indicates abundance and position shows where the species occurs.

The range of abiotic conditions a species can survive and reproduce in; outside the range it cannot persist.

Local scale (e.g., rocky shores, forests) and global scale (e.g., climate zones and biomes).

Succession that starts on bare rock/land with no soil present.

Succession is the process of change in species composition and community structure over time.

Biodiversity, biomass, and soil depth/nutrients (also food web complexity).

Resilience is the ability of an ecosystem to resist disturbance or recover and return to a stable state after disturbance.

Seral stages progressing toward a climax community.

Pioneer species are the first organisms to colonise a barren environment; they tolerate harsh conditions and start soil formation.

Recovery. Resilience describes how well an ecosystem bounces back after disturbance, not whether disturbance happens.

Succession that starts after disturbance where soil already exists (e.g., after fire or farming).

By keeping ecosystems at early stages through farming, grazing, or urban development.

Primary starts with no soil (bare rock). Secondary starts with soil present after disturbance.

Biomass increases, biodiversity increases, soil depth/nutrients increase, and food webs become more complex.

Because soil, nutrients, and often seeds/roots are already present, so recovery can start immediately.

Large storages (e.g., biomass, soil nutrients) act as buffers, allowing the system to keep functioning if inputs are temporarily disrupted.

It helps plan ecosystem restoration by predicting which stage comes next and estimating recovery time after disturbance.

A climax community is the final, stable community in equilibrium with the environment, with maximum biodiversity for that area.

Resilience is the ability to resist disturbance or recover and return to a stable state after disturbance.

Lichens and mosses (also algae).

Succession is change over time; zonation is change over space.

More species and interactions create complex food webs with multiple pathways, so loss of one species is less damaging.

Species change the environment over time (e.g., soil and shade), making conditions suitable for different species to replace them.

Biodiversity and large storages (also redundancy and negative feedback).

Deforestation and urbanisation (also intensive agriculture or repeated grazing).

Primary = from scratch (bare rock, no soil). Secondary = soil already there (just disrupted).

After a volcanic eruption or retreating glacier, succession can start on bare rock with lichens and mosses.

Redundancy is when multiple species perform similar roles; it increases resilience because another species can replace a lost function.