Ecology Lesson #5: Succession: The Process of Change see pages 408-410 in your text. succession comes from the Latin, succedere, meaning to follow after DEFINITION: the gradual and directional process of species change in a community. Succession can be thought of as the evolution of a given landscape and the biotic / abiotic factors within that area communities change through time in response to many influences:
ABIOTIC FACTORS Climatic Events: ice ages, droughts, floods, el nino, global warming Natural Disasters: fires, tornadoes, hurricanes, earthquakes, floods Human Activities: urban sprawl, pollution, deforestation, mining BIOTIC FACTORS: disease, competition, immigration /emigration/ extinction
What is primary succession? Primary succession the establishment of living things in an area that was previously lifeless. Pioneer species- the first species to colonize an area (usually lichens and mosses but sometimes higher plants), begin the process of soil formation. Pioneer species establish biogeochemical cycles that pave the way for larger plant species. *Volcanic eruptions are good examples involving primary succession. Following the eruption, there is no life in the blast zone. Eventually, however, pioneer species of plants do establish themselves, beginning the course of succession. Example: Hawaiian Islands
Primary succession might follow a volcanic eruption
A variety of lichens pictured here grow on bare rock. The lichens break the rock down to form a soil substrate from which plants can grow
Primary succession can also occur on man made structures:
What is secondary succession, and how does it differ from primary succession? Secondary succession the changes and / or replacement of plant and animal species in an area where food webs and biogeochemical cycles are already well established. Example: Mt. St.Helens eruption 1980.
Secondary succession results in the transition of a community from pioneer species to climax species (species that define an area) Because soil may already be present, the rate of secondary succession is faster than primary succession. Secondary succession also indicates changes in community composition following disturbances. Floods, hurricanes, and fires are all examples of naturally occurring disturbances. Notice, however, that none of these completely wipes out the life that was in the area. Not only do plants and animals survive these disturbances, but some need them to be able to continue to live there. For example, some prairie plants NEED fire before they can germinate.
Flooding along the Mississippi river
Hurricane damage along the Florida Coast
As seen here, controlled fires can be a necessary measure that directs succession
*Climax community - a stage of succession in which changes are usually slow and subtle but at times can be extreme. Climax communities are characterized by several dominant species of plant and animal. Example: the major biomes of the world
Traditional farming involves creating disturbance and then fighting secondary succession. Plowing is a prime example of disturbance, but it can't eliminate underground plant parts seeds left in the soil from previous years (even 100 years or more) seeds of nearby plants seeds blown in from far away Weeds are pioneer species; if farming is discontinued, these colonizing plants will reclaim a field.
A summary of changes that occur during succession: Pioneer species colonize a bare or disturbed site. Soil building. Changes in the physical environment occur (e.g., light, moisture). New species of plants displace existing plants because their seedlings are better able to become established in the changed environment. Newly arriving species alter the physical conditions, often in ways that enable other species to become established. Animals come in with, or after the plants they need to survive. Eventually a climax community that is more or less stable will become established and have the ability to sustain itself. Disturbances can affect the process of succession at various stages (primary, secondary or the climax state).