Succession. Ecological Succession Natural ecological restoration –Primary succession – gradual...

Succession

Ecological Succession

• Natural ecological restoration– Primary succession – gradual

establishment of biotic communities in lifeless areas where there is no soil or sediment

– Secondary succession – series of communities with different species develop in places containing only soil or bottom sediment

Primary Succession

• In the beginning…– No soil = no

nutrients– Over time rock

weathers

Hundreds and thousands of years later…

Primary Succession

• Early pioneer plant species– Species arrive and

attach themselves to inhospitable patches of weathered rock• Lichens, mosses

– Help form soil by trapping wind-blown soil particles and detritus• Add waste and dead

bodiesHundreds and thousands of years later…

Primary Succession

• Mid-successional plant species– Soil becomes deep

and fertile enough to hold moisture

– Supports the growth of herbs, grasses, and low shrubs

– Creates shade which causes mosses and lichens to die

– Trees replace grasses and shrubs

Primary Succession

• Late successional plant species– Species that can

tolerate shade– Bare rock ultimately

becomes a complex forest

Aquatic Primary Succession

• Newly created small pond• Influx of nutrients via runoff

Secondary Succession

• Some soil remains in a terrestrial system or sediment in an aquatic system

• Ecosystem has been– Disturbed– Removed– Destroyed

Secondary Succession

• New vegetation can germinate usually within a few weeks – Seeds already in

the soil or imported by wind, birds, and other animals

• Climax community – stability

Similarities• Primary and secondary succession– Tend to increase biodiversity– Increase species richness and interactions

among species

• Primary and secondary succession can be interrupted by– Fires– Hurricanes– Clear-cutting of forests– Plowing of grasslands– Invasion by nonnative species

Species Replacement

• Facilitation – one set of species makes an area suitable for species with different niche requirements– Less suitable for itself (mosses and lichens)

• Inhibition – some early species hinder the establishment and growth of other species– Pine needles make soil acidic

• Tolerance – late succession plants are largely unaffected by plants at earlier stages of succession

Succession Doesn’t Follow a

Predictable Path• Traditional view – Balance of nature and a climax

community

• Current view – Ever-changing mosaic of patches of

vegetation–Mature late-successional ecosystems • State of continual disturbance and change

Living Systems Are Sustained through Constant Change

• Inertia, persistence– Ability of a living system to survive

moderate disturbances

• Resilience – Ability of a living system to be restored

through secondary succession after a moderate disturbance

• Tipping point – Any additional stress can cause the system

to change in an abrupt and usually irreversible way that often involves collapse