Biology topic 7 succession

What is succession?

the gradual change in an ecosystem over time from a simple to a more complex community

What causes succession?

Changes in biotic and abiotic conditions make the environment less hostile for new species and less sutible for previous species

How does succession affect biodiversity?

Biodiversity changes continually as new species colonise and others are outcompeted

What is primary succession?

Occurs on newly formed or exposed land with no initial life , such as bare rock from cooled lava or dried up lakebeds

What are pioneer species?

First species to colonise bare land, often mosses and lichens. They tolerate extreme conditions and being soil formation

How do pioneer species form soil?

Their death and decay form basic soil (humus) allowing other species to grow

What species arrive after pioneer species?

Small plants and grasses whos seeds arrive by wind or animals. Their death increases soil depth and nutrient content

How do grasses and small plants stablise the enviroment?

Their roots hold soil in place preventing erosion and making conditions less hostile

What species arrive after grasses ?

Larger plants, shrubs and small trees that grow in deeper, nutrient rich soil with more water

What is a climax community?

A stable complex ecosystem dominated by large trees and containg a variety of plant and animal species

How do human activities affect succession?

Mowing and grazing interrupt succession an dmaintain earlier stages

How does mowing prevent succession?

Mowing removes young shrubs and tree shoots so only grass persists

How does grazing prevent succession?

Live stock eat new shoots, halting succession and maintaining grassland

Why might conservation involve halting succesion?

Intermediate stages e.g grass land support many species not found in climax communities

Why can climax communties reduce biodivercity?

Dominant species outcompetes other and abiotic conditions change making the environment unsuitable for some species

Why are intermediate habitats important?

They support species not found in climax communities including rare or threatened species such as pollinators

Describe what happens in primary succession?

Primary succession beings on newly formed or exposed land with no soil

Pioneer species colonise first becouse they tolerate harsh abiotic conditions

Pioneer species die and decompose to for humus creating first soil

Soil allows small plants and grasses to grow, their death increases soil depth and nutrients

As soil imroves larger plants shrubs and small trees colonise due to hostil conditions

A climax community forms when the enviroment supports large trees and stable, complex ecosystem

What is secondary succession?

Occurs on land where an existing community has been removed but soil remains, such as after a fire, flood or human disturbance

How is secondary succession different from primary succession?

secondary succession starts with soil already present, so it is faster than primary succession and does not require pioneer species to create soil

What events can trigger secondary succession?

Fire , storms, floods , deforestation, agraculture

Why is secondary succession faster than primary succession?

soil, nutrients , seeds , microorganisms and organic matter are already present so conditions are less hostile

What happens after grasses colonise?

Shrubs and small trees grow as soil structure improves and competition increases

What is the end point of secondary succession?

Climax community , similar to the one before the disturbance unless humans manage or halt succession