Ecological SuccesionEcological Succesion

SuccessionSuccession

Do ecosystems ever change?Do ecosystems ever change? Were there ALWAYS forests?Were there ALWAYS forests? SUCCESSIONSUCCESSION is the name given to a is the name given to a

predictable series of changes in an predictable series of changes in an ecosystem over timeecosystem over time– Organisms themselves can change Organisms themselves can change

the environment (ex. Nutria burrows)the environment (ex. Nutria burrows)– The new environment becomes no The new environment becomes no

longer suitable for the longer suitable for the originaloriginal group group of organismsof organisms

– One set of organisms gradually One set of organisms gradually replaces another…replaces another…

Forces of ChangeForces of Change What factors can cause What factors can cause

ecosystems to change?ecosystems to change?– VolcanoesVolcanoes– FloodsFloods– HurricanesHurricanes– Human activityHuman activity– DiseaseDisease– DroughtDrought– FireFire

Stages of successionStages of succession– PIONEERPIONEER stage (ex. Moss, stage (ex. Moss,

Water Plants)Water Plants)– CLIMAXCLIMAX community (ex. community (ex.

Mature rainforest)Mature rainforest)

Primary & Secondary Primary & Secondary SuccessionSuccession PRIMARYPRIMARY Succession Succession

– When the starting point is When the starting point is an an abioticabiotic environmentenvironment

VolcanoVolcano FloodFlood

SECONDARYSECONDARY SuccessionSuccession– When an existing When an existing

ecosystem is disturbedecosystem is disturbed Fire/lightningFire/lightning DiseaseDisease HurricanesHurricanes Human activitiesHuman activities

Ecosystem recovers after a major Ecosystem recovers after a major volcanic eruption in Mount St. Helensvolcanic eruption in Mount St. Helens

• 1973: The Mountain Peak 10 years before eruption

• 1983: 3 years after eruption

• 2000: Vegetation re-growth around the volcano

Gradual ChangesGradual Changes Wetland SuccessionWetland Succession

– p36-37p36-37– As water plants colonize, sediments are As water plants colonize, sediments are

trapped by the roots, and the ecosystem trapped by the roots, and the ecosystem becomes drierbecomes drier

– As the environment dries out, water plants As the environment dries out, water plants can no longer compete for resources, and can no longer compete for resources, and larger “land” plants colonize, which shade-larger “land” plants colonize, which shade-out the other plantsout the other plants

Forest SuccessionForest Succession– Fires & tree-falls create opportunities for Fires & tree-falls create opportunities for

different species to colonize (ex. different species to colonize (ex. Yellowstone National Park)Yellowstone National Park)

– Tree falls create Tree falls create canopy gapscanopy gaps (sunlight (sunlight comes in, allowing other plants to colonize)comes in, allowing other plants to colonize)

Wetland SuccessionWetland Succession

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Wetland SuccessionWetland Succession

© 2003 John Wiley and Sons Publishers

Fig 10.7 Diagram of bogsuccession.

Wetland Succession

Sedges and floating plants close over the open water,

trapping sediments in

their roots, and gradually

drying out the pond.

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Forest SuccessionForest Succession

Primary SuccessionPrimary Succession

Transects

Because of the change in availability of sunlight and water, there is a predictable pattern of change in the vegetation as you walk from a field into a forest. This

transitional zone between ecosystems is called an ecotone.