SUCCESSION

Changes in the ecosystem

Changes occur all the time in an ecosystem. Trees die and new trees take their place. Young animals are born as the older ones die.

As long as there are not majordisturbances the ecosystem will remain essentially the same.

The natural stability of an ecosystem keeps it from undergoing major changes is called homeostasis.

SUCCESSION

It’s important to understand the changes in an ecosystem so that we can understand how the ecosystem will react to the changes that human activity tends to bring about.

VOCABULARY

Pioneer species: the first species to appear during the process of succession, usually grasses & weeds.

Climax community: the stable mature community

Homeostasis: natural stability in an ecosystem, resists transformation & helps it recover from stresses.

SUCCESSION

Succession is the process of community development over time.

A mature community will still change but its overall appearance will remain the same.

PRIMARY SUCCESSION

change in species over time that has not been inhabited by organisms. starts from bare rock.

Lichens are the most important element in the initial community called the pioneer community.

Lichens are important early pioneer species. Lichen is a species of alga and fungi that live together in a symbiotic relationship.

Lichens secrete an acid that breaks down the rock to begin soil formation.

If the process of succession occurs without any disturbances, the species will form the climax community. This is the last stage of succession

Each biome has its own climax community. The climax community for PA is the oak-hickory forest as well as the beech, hemlock & maple forest of Northern PA forest.

SECONDARY SUCCESSION

change in species composition and ecosystem overtime already within a pre-existing community.

Some animals can survive all stages of secondary succession. Most animals appear only in certain stages and disappear with others.

Repeated disturbances will prevent an area from returning to its climax community.

EXAMPLES OF SECONDARY SUCCESSION

1. Abandoned farms

2. Burned or cut forests

3. Heavily polluted streams

4. Areas affected by flood waters.

FIRE MAINTAINED COMMUNITIES

Fires can be set by lightning, storms or human activity. Burned areas undergo secondarysuccession.

Some communities are immuneto fire. For example, the lodgepole pine tree needs temperatures of above several hundreds degrees to germinate their seeds.

ECOSYSTEM DISTURBUANCES

A ___________________ can change an ecosystem both physically & biologically.

Disturbances can be natural or due to ________________ _______________________.

Repeated ________________________ will prevent an area from returning to its_______________ community.

NATURAL DISTURBANCES

Volcanic eruptions

2. Tornadoes

3. ________________________

4. Floods/Drought

5. Natural Wildfires

Now…read the chart with a partner.

HUMAN DISTURBANCES

YELLOWSTONE FIRE 1988

DISTURBANCES WITH LONG TERM EFFECTS

Ecosystems if left undisturbedwill eventually return to their climax community through the process of succession. Perhaps we should just let nature alone. There are three reasons why this does not solve our problems.

1. We can’t leave the Earth undisturbed for any length of time. We need it too much.

2. Human activities may alter an ecosystem that it can not return to its natural state.

3. The length of time that it takes for succession to occur is hundreds if not thousands of years. Succession is of little practical use to us.

ECOSYSTEM DEGRADATION

Ecosystems degrade when humans disturb them. Usually some of the species that once lived there can no longer survive so the biodiversity is reduced. Below are a few examples.

1. Putting out fires.2. Timber Cutting3. Killing Carnivores