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SUCCESSION. HOW DO ECOSYSTEMS RESPOND TO CHANGE?. A change in structure ensures a change in function and species composition . Ecological succession is the gradual and fairly predictable change in species composition of an area over time.
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HOW DO ECOSYSTEMS RESPOND TO CHANGE? • A change in structure ensures a change in function and species composition. • Ecological succession is the gradual and fairly predictable change in species composition of an area over time. • some species colonize and their populations become more numerous • other species populations decline and disappear.
Primary Succession • Lifeless area. • Pioneer species (lichens and mosses) create soil (chemical and physical weathering). • Young soils support bacteria, fungi, insects, and small worms (adds organic material to soil as they die). • Perennial grasses and herbs. • All early successional plants grow low to the ground, can establish large populations quickly under harsh conditions.
Primary Succession • After hundreds of years the soil matures (deep and fertile) and midsuccessional species grow. • These species include: herbs, grasses, and low shrubs and later include trees that require lots of sunlight.
Primary Succession • As midsuccessional stage species grow and create shade areas they are replaced by late successional species. • Primary succession occurs fastest in humid tropical areas and slowest in dry polar areas.
Terrestrial Primary Succession Boreal Forest Biome Climax Community Balsam fir, paper birch, white spruce Pine, spruce and aspen Heath mat Small herbs and shrubs Exposed rocks become colonized by lichens and mosses to create a soil. May take hundreds to thousands of years to establish a fertile soil
Secondary Succession • Occurs where soil or bottom sediment remains where an area has been disturbed or destroyed. • Abandoned farmlands, burned or cut forests, heavily polluted areas, land that has been dammed or flooded.
Secondary Succession Temperate Deciduous Forest Biome Mature Oak-Hickory Forest Young Pine Forest Shrubs Perennial weeds and grasses Annual Weeds
Species Found at Various Stages of Succession Early Successional Species Rabbit Quail Ringneck Pheasant Dove Bobolink Pocket Gopher Midsuccessional Species Elk Moose Deer Ruffed grouse Snowshoe hare Bluebird Late Successional Species Turkey Martin Hammond’s flycatcher Gray squirrel Wilderness Species Grizzly bear Wolf Caribou Bighorn Sheep California condor Great horned owl
Table 8-1Page 158 Table 8-1 Ecosystem Characteristics at Immature and Mature Stages of Ecological Succession Characteristic Ecosystem Structure Plant size Species diversity Trophic structure Ecological niches Community organization (number of interconnecting links) Ecosystem Function Biomass Net primary productivity Food chains and webs Efficiency of nutrient recycling Efficiency of energy use Immature Ecosystem (Early Successional Stage) Small Low Mostly producers, few decomposers Few, mostly generalized Low Low High Simple, mostly plant herbivore with few decomposers Low Low Immature Ecosystem (Late Successional Stage) Large High Mixture of producers, consumers, and decomposers Many, mostly specialized High High Low Complex, dominated by decomposers High High
How Do Species Replace One Another? • 1. Facilitation – promotion of growth due natural enrichment of soil. • 2. Inhibition – early successional species can hinder the establishment and growth of other species. Removal of the inhibitors by fire, bulldozer or other disturbance is the only way to allow other species to establish. • 3. Tolerance – late successional plants are unaffected by plants at earlier stages.
What is the Role of Disturbance in Succession? • A disturbance is a discrete event in time that disrupts an ecosystem or community. • Natural disturbances = fires, hurricanes, tornadoes, droughts, and floods. • Anthropogenic disturbances = deforestation, overgrazing, and plowing. • Disturbances create openings for opportunistic species to colonize areas and change the community structure of an area.
What is the Role of Fire in Succession? • Fires start by lightening in the following biomes: savanna, temperate grasslands, chaparral, temperate rain forest, and northern coniferous forest. • Fire burns older trees by burning biomass and releasing seeds as cones open in intense heat = ensures regeneration.
Fire Suppression • Fire suppression can be very dangerous. It allows for the build up of large quantities of flammable underbrush and undergrowth. • It allows conifers to grow very large and store energy as biomass. • BOTH contribute to fuel for the fire, making a moderate forest fire catastrophic!
Is Succession Predictable? • General patterns of succession are predictable. • Research indicated that there is no ecological plan leading to ecological balance or equilibrium. • Succession can be highly variable, chaotic, and unpredictable. • We do know there will be changes to structure, function, and species composition that will continue to change over time due to facilitation, inhibition, and tolerance. • The Earth’s ecosystems are dynamic and resilient. Research shows that ecosystems with high diversity in primary producers are the most resilient ecosystems.
Succession in Volcanic Areas • Krakatau – August 27, 1883 (Sundra Strait between Sumatra and Java)
KRAKATAU • 10:02 am explosion (100-150 megatons of TNT) • The sound of the explosion traveled at the speed of sound around the world 7 times. • Blackened sky with showers of ash and heavy, suffocating sulfur filled the sky and rained down on the previous tropical rainforest ecosystem. • Island collapsed causing a 40 meter high tsunami along the shores of Java and Sumatra killing 40,000 people. • Krakaktau had been replaced by an undersea crater 7 km long and 270 m deep. • All traces of life were extinguished!
SUCCESSION OF KRAKATAU • Rakata the southern remnant of of Krakatau survived as a sterile obsidian-laced pumice island. • Life quickly re-established. • Spiders “ballooned” making their way to the island “aeolian plankton”
SUCCESSION OF KRAKATAU • Other organisms that undergo long-distance dispersal as hitchikers include: springtails, crickets, earwigs, barklice, bacteria, fungal spores, nematode worms, and mites. • Organisms that fly on their own include moths, butterflies, dragonflies, true flies, beetles, birds, bats, and wasps. • The monitor lizard and reticulated python swim. • Rafting on logs and branches occurred by insects, snakes, frogs, and small mammals. • Waterspouts can pick up fish and transport them to lakes and streams. • Seeds pass through the guts of birds and mammals. Pioneer plants (morning glory) and grasses moved in first, then Casuarina pine, and now it is covered entirely by Asian rain forest, but NOT the climax community that existed prior to the eruption. • As the biodiversity of primary producers, so did the biodiversity of the food web.
Primary Succession on a Newly Established Volcanic Island Primary Succession – involves the gradual establishment of biologic communities in an area that has not been occupied by life before.
Secondary Succession on Krakatau Secondary Succession – involves the re-establishment of a biotic community in an area where a biotic community was previously present.
Population Dynamics • Population numbers are becoming more stable a Century after the eruption. • The composition of the populations are less stable. • E.O. Wilson “The thick green forests offers testimony to the ingenuity and resilience of life”
