Changes in Ecosystems: Ecological Succession

Definition: Natural, gradual changes in the types of species that live in an area The gradual replacement of one plant community by another through natural processes over time

Examples: A glacier recedes, leaving bare earth. First lichens colonize the area. They are eventually replaced by tundra plants and animals. A building is demolished. Mosses, the grasses, then shrubs, and eventually trees cover the area.

Types of Succession Primary Succession – The sequence of communities that inhabit a lifeless environment. –Sides of volcanoes

Types of Succession Primary Succession – The sequence of communities that inhabit a lifeless environment. –Sides of volcanoes –Receding glacier

Types of Succession Primary Succession – The sequence of communities that inhabit a lifeless environment. –Sides of volcanoes –Receding glacier –Newly formed island

Types of Succession Primary Succession – The sequence of communities that inhabit a lifeless environment. –Sides of volcanoes –Receding glacier –Newly formed island –Abandoned parking lot

Types of Succession Primary Succession – The sequence of communities that inhabit a lifeless environment. –Sides of volcanoes –What happens after the lava cools down??

Primary Succession PIONEER SPECIES arrive and colonize the area. Pioneer species are able to survive in harsh environments. They can survive without soil. Pioneers tend to thrive in areas of intense sunlight and scarce water.

Primary Succession Lichens are a common pioneer. Lichens are a mutualistic relationship between a fungus and an algae. The algae is photosynthetic (autotroph) and the fungus holds water and absorbs nutrients from the rocks. Over time the lichens break down the rocks.

Primary Succession As the water freezes and thaws, it breaks the rocks up further. Lichens die and accumulate in the cracks. These lichens decompose and create soil. Mosses will begin to grow on the rocks.

Primary Succession Mosses grow and die, adding to the soil. The mosses will shade the lichens, which will die out. Eventually, enough soil will be there to support grasses and weeds. The grasses will shade out the mosses. The grasses and weeds grow and die, increasing the depth of the soil.

Primary Succession Shrubs and bushes will eventually replace the grasses. The grasses will be shaded out and die. Eventually, the soil will become deep enough to support larger trees. The tall trees will shade out the shrubs and bushes.

Primary Succession The point where the ecosystem stops changing is called a climax community. What was once bare rock now supports a wide variety of species.

Climax Community A stable group of plants and animals that is the end result of the succession process Does not always mean big trees –Grasses in prairies –Cacti in deserts –Sawgrass in the Everglades –Wildflowers and short trees in the tundra

Primary succession can be seen happening in any lifeless area. If left alone, New York City would turn into a cement filled woodland.

Primary Succession This is a SLOW process. It may take hundreds of years for the ecosystem to go through all of the stages of primary succession. Each community alters its environment. Those alterations make it possible for the new community to take over.

Secondary Succession Begins in a place that already has soil and was once the home of living organisms Occurs faster and has different pioneer species than primary succession Example: after forest fires

Secondary Succession The pioneer would be grasses and weeds. The changes in the ecosystem would follow the same sequence we saw in primary succession. However, the progression from pioneer to climax community would occur much faster.

Fires Fires are a natural part of many ecosystems. –They clear out underbrush, leaving rich ash behind. –Some species of trees need fire for their seeds to germinate.

Slash Pines Subclimax community

Secondary Succession Example: – after a forest fire –after a flood

Secondary Succession Example: – after a forest fire –after a flood –after a hurricane

Secondary Succession Example: – after a forest fire –after a flood –after a hurricane –An abandoned field or building