Ecological Disturbances and Succession SC.912.L.17.4 Describe changes in ecosystems resulting from seasonal variations, climate change and succession. By Dr. Suris Soto

What Is Disturbance? A disturbance Is an event that changes a community Removes organisms from a community Alters resource availability

Natural Human-Caused Disturbances They are common in ecosystems Fire Hurricanes Floods Volcanic Eruptions Are the most widespread agents of disturbance Usually reduces species diversity Humans also prevent some naturally occurring disturbances Deforestation and land cleared Farming Urbanization (Developments)

Ecological Succession Is the gradual sequence of community and ecosystem changes after a disturbance One community of organisms replaces another

Types of Ecological Succession: Primary succession Occurs where no soil, (barren terrain) exists when succession begins No pre-existing plant or animal life Examples: After volcanic eruption, retreating glacier (natural), abandon parking lot (human-caused) Secondary succession Begins in an area where soil remains after a disturbance Some organisms may still be there Examples: After a flood, hurricane, tornado (natural) or after land cleared for farming, deforestation (human-caused)

Primary Succession ---- No Soil, barren rock Glacier Retreating Volcanic Eruption Abandon parking lot

Secondary Succession after a fire Is a significant disturbance in most terrestrial ecosystems Is often a necessity in some communities (a) Before a controlled burn. A prairie that has not burned for several years has a high propor- tion of detritus (dead grass). (b) During the burn. The detritus serves as fuel for fires. (c) After the burn. Approximately one month after the controlled burn, virtually all of the biomass in this prairie is living. Figure a–c

The large-scale fire in Yellowstone National Park in 1988 Demonstrated that communities can often respond very rapidly to a massive disturbance (a) Soon after fire. As this photo taken soon after the fire shows, the burn left a patchy landscape. Note the unburned trees in the distance. (b) One year after fire. This photo of the same general area taken the following year indicates how rapidly the community began to recover. A variety of herbaceous plants, different from those in the former forest, cover the ground. Figure 53.22a, b

Secondary Succession

Pioneer species Always the first species to move into a devastated area Must be able to live on limited resources Must be able to live in barren rock They include Bacteria Lichens Lichens are a symbiosis (close relationship) of a fungus and a green algae Each organisms depends on each other for survival (mutualism) Fungus anchors lichen to a surface, absorbs water and nutrients, and protects the algae from direct sunlight. The algae performs photosynthesis to make its own food and also feed the fungus As lichens grow, they make break down rock , help form soil. When it dies it decomposes enriching the soil.

Pioneer species Mosses Lichens Bacteria

Primary Succession

Climax community Fairly stable community Marks the end of succession in an area Organisms present depend on the climate and physical features of the area Ex. In areas with little rain the climax is a grassland Nothing lasts forever: A new disturbance can happen at any time Disturbances in climax communities can lead to secondary succession or primary in the event of volcanic eruption covering the soil with lava, hardened to rock

Draw it yourself:

Fire Flood Earthquake Change of seasons Which of the following is not a possible cause of secondary succession? Fire Flood Earthquake Change of seasons

Which of the following is an example of primary succession? Lichens growing on rocks after a volcanic eruption Grasses growing after a forest fire Oak trees replacing pine trees in a forest Nonnative species introduced into a climax community

Which term refers to final forest’s development? Pioneer forest Secondary forest Climax forest Conifer forest