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Changes in Ecosystems:Ecological Succession
succession
Gradual process of change and replacement in a community.
Succession usually emphasizes plant community changes, but these in turn cause succession in animal species.
What drives ecological succession?
How is the presence of later-succession species dependent upon early ones modifying the environment so that it is favorable to the later?
How do animal communities respond to plant succession?What happens when taller grasses take over a field?What happens when trees start moving in?
2 types:
primary succession –
succession where no ecosystem has existed before (rocks, sand dunes)
secondary succession – disturbed or disrupted area (flood, farmland, volcano)
Definition:
• Natural, gradual changes in the types of species that live in an area; can be primary or secondary
• The gradual replacement of one plant community by another through natural processes over time
Trends in Succession
require large inputs of nutrients and also tend to lose nutrients.
stages are dominated by "weedy" species which reproduce quickly, but often die young. Most of their energy goes into reproduction. There are relatively few species in early stages.
Climax stages more complex, with many species. They create a favorable environment for many species. decomposition rates are roughly equivalent to new production. Nutrients are cycled efficiently, and rarely leave the ecosystem. Individual organisms are longer-lived, since they invest more resources in themselves and less in producing offspring.
Primary Succession
Begins with bare rock exposed by
geologic activity (glacial melt, volcanic eruption)
rock -> lichen -> moss -> grass -> shrub -> trees -> climax forest
Bare stone, but a hint of algae on its face and a bird dropping on top. Those, plus weathering,
prepare the stone for lichens.
Stone colonized by lichens, which bit by bit dissolve the rock into nutrients. Life creates environment.
Stone covered with moss wherever light can reach. Lichens
dead under moss, feeding moss.
A crevice in a boulder shows three stages of succession. Lichen, followed by mosses, and the makings of soil caught in the crevice. Seeds will follow
On weathered wood, algae, lichens, and mosses show three stages in succession.
Succession usually emphasizes plant community changes, but these in turn cause succession in animal species.
What drives ecological succession?
How is the presence of later-succession species dependent upon early ones modifying the environment so that it is favorable to the later?
How do animal communities respond to plant succession?What happens when taller grasses take over a field?What happens when trees start moving in?
Pines slowly climb a volcano cone after eruption. They've climbed
about 10,000 years.
A seedling saltbush pioneers volcanic cinders
Sagebrush and a single pine colonize the cinder barrens left from an eruption
Primary Succession
• Begins in a place without any soil – Sides of volcanoes– Landslides– Flooding
• Starts with the arrival of living things such as lichens that do not need soil to survive
• Called PIONEER SPECIES
Primary Succession
• Soil starts to form as lichens and the forces of weather and erosion help break down rocks into smaller pieces
• When lichens die, they decompose, adding small amounts of organic matter to the rock to make soil
Pioneer species are the first to colonize a community. These species make the area habitable for other species.
http://botit.botany.wisc.edu
http://www.saguaro-juniper.com/
Primary Succession
• Simple plants like mosses and ferns can grow in the new soil
http://uisstc.georgetown.edu
http://www.uncw.edu
Primary Succession
• The simple plants die, adding more organic material
• The soil layer thickens, and grasses, wildflowers, and other plants begin to take over
http://www.cwrl.utexas.edu
Primary Succession
• These plants die, and they add more nutrients to the soil
• Shrubs and tress can survive now
http://www.rowan.edu
Primary Succession
• Insects, small birds, and mammals have begun to move in
• What was once bare rock now supports a variety of life
http://p2-raw.greenpeace.org
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:Earth's way to bandage wounds
Where land has been scarred by fire or disturbance such as plowing, it will soon be covered again with green. Secondary succession is incredibly fast compared to primary succession. Soil is already there, with nutrients. Seeds are already there, seeds of earlier occupants, windblown seeds of pioneer species which exploit disturbed soil (living bandages). After a fire, many seeds germinate in the fire's sudden heat that have waited years for the opportunity. Global warming is already changing the mix of species in temperate zones, and will continue.
A birch tree begins to colonize a farm field from the edge in. Smaller deciduous trees, such as birch and aspen, are among the first to reclaim
cleared land
A mountain riverbed is dotted with willows and seedlings. They will all be swept away by flood next summer. In the
background, a logged slope is regenerating conifers.
Lakes and ponds
Lakes are at the bottom of their watersheds so that lakes accumulate the nutrients that runoff the watershed, causing drastic changes in lake ecosystems over time. Lakes change over time in a process know as eutrophication, typically going from clear lakes (few nutrients, so few nutrients) to turbid lakes (many nutrients resulting in thick blooms of phytoplankton and little or no oxygen
in deeper waters).
Lakes are slowly, gradually filled in by decaying vegetation and runoff fill, and eventually become peat bogs (muskeg
A fallen hemlock tree has become a nurse-log with tree saplings growing out of it, above the mosses that prepared the way.
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
Fire & Succesion
Fire plays a complex role in succession. A fire stops the progression of succession and sets the stage for new, secondary succession as plants take root and grow in the soil enriched by the mineral ashes of their predecessors. In some cases, however, fire plays an even more important role. It maintains the climax community by removing competitors that would move the climax to a different type of community.
http://www.marietta.edu/~biol/biomes/succession.htm
