Ecosystem Balance

Ecosystem Balance E2 Ecological Succession

Ecological Succession Organisms affect the environments in which they live • Some changes are helpful • Plants help form soil by breaking down rocks • Some changes are harmful • Species can alter environment so that a niche disappears • Replaced by new niches to which differentspecies are better adapted. • Cause their own destruction • Other forces can also change the environment • Forest fire, volcanic eruptions, earthquakes, floods

Ecological Succession • As environments change, the community living in that environment changes • In many cases, different communities follow one another in a definite pattern. • Primary Succession • The sequence of communities forming in an originally lifeless habitat. • On lava after it has cooled and hardened • Bare rock exposed by a retreating glacier

Primary Succession • Primary Succession is an orderly process • First – colonization by new organisms and formation of soil. • Rocks are colonized by lichens – a fungus and an alga living in a mutualistic relationship • Lichens secrete acids that breakdown the rock and form organic material • Rocks are also broken down by weathering caused by wind, rain, and frost • The lichen and weather form soil

Primary Succession • Next – after soil has formed, grasses and small plants begin to grow • Seeds are carried to the habitat by wind or animals • Plantroots continue to break down rocks • Dead leaves also help soil formation • In time, plants grow dense and tall enough to block the sun from the lichens • The lichen community is replaced by the grass community

Primary Succession • Next – grass community survives for many generations • Makes the soil deeper and more fertile • Allows for the growth of non-wood plants and shrubs with deeper roots • In time this foliage becomes tall and dense enough to form a heathmat that blocks the sun from grasses

Primary Succession • Next – when the soil is deep enough, pines or other trees with shallowroots move in • As trees move in, the community changes again. • Trees shade out the shrubs and grasses • Finally – broadleaf and hardwood trees begin to grow and replace the pines • Hardwood forest is the final stage of succession. • It changes very little over time • Climax community – A community that doesnot undergo further succession

Primary Succession Pioneer Community Climax Community • Lichen • Grasses • Shrubs Heath Mat Pine Trees Hardwood Forest

Secondary Succession • Primary succession occurs only on freshly exposed rock or places where all the organisms and soil have been removed or destroyed • However, most disturbances are not that drastic • Secondary succession – occurs where a disturbance eliminates most organisms but does not destroy the soil • Example: A forest fire will kill trees and plants, but leave the soil. • Living things can quicklycolonize areas created by these types of disturbances

Secondary Succession • Resembles the later stages of primary succession • Usually begins at the grasses or shrub stage

Incomplete Succession • Many habitats never develop climax communities • It takes several hundred years to complete the process of succession • If disturbances occur more frequently than that, the area cannot complete the succession • Example: A Grasslands Habitat • Continuous or periodic disturbances kill seedling shrubs and trees • Succession never progresses past the grass community

Aquatic Succession • Succession also occurs in aquatic habitats • Newly formed lake where water has few nutrients • Reeds and other water plants grow near the shore • Organic matter begins to collect in the lake • Provides nutrients for more plants • Sediment accumulates on the bottom of the lake • More organisms can survive • Water plants cover the surface of the lake

Aquatic Succession • Lake fills with sediment and becomes a marsh • Land plants colonize the marsh • Marsh becomes a meadow • Meadow ultimately turns into a forest

Section Review • Answer the questions in the section review

Ecosystem Balance