· Scale/extent: size of the disturbed area · Intensity: measure of the strength of the disturbance · Frequency: how many disturbances per unit time
-Succession is the predictable changes in species composition after an environmental disturbance.
What is primary succession?
-Succession that starts with bare ground without previous inhabitants--no seed bank, no diapausing insects, etc...This might include glacial retreat revealing new ground; a volcanic eruption creating new land or destroying everything in an area.
What is secondary succession?
-Succession in a Community where the previous community or climax community has been removed. This can include human disturbance, or disturbance from fires, floods, severe storms, etc... -Regeneration following a disturbance: remove vegetation, not the soil.
What is autogenic succession?
-Succession based on biotic modification of the environment.
What is allogenic succession?
-Changes in species composition associated with abiotic changes in the environment, such as global drying or warming trends that change an area's vegetation.
What were the steps of succession in Clements view?
Nudation: exposure of the soil surface Migration: of seeds, propagules, seed bank... Germination Competition Reaction: autogenic effects of plants on the environment Stabilization: results in a climax community
What is an example of Cyclic Succession?
-In desert scrub communities, for example, creosote bush (Larrea tridentata) is a dominant species. Birds and rodents shelter in Larrea, leaving droppings and seeds of other species. When Opuntia cactus seeds germinate they grow well under Larrea. Larrea eventually seneces, exposing Opuntia. Opuntia falls over and eventually dies, leaving open space where Larrea colonizes best.
What are the two methods of studying succession?
Toposequence: study communities of different ages that have had similar disturbances. Main problem is that humans can't control conditions at the establishment of the sequence. This may partially be solved by replicated observations within community age groups. Chronosequence: follow a community from the initial disturbance through time. Here the main problem is that this takes a long time, longer than the lifetime of most ecologists!
What were the 3 models of successional processes that Connell and Slatver proposed?
-Facilitation: early species facilitate colonization of later species. Later species - stronger competitors for resources, exclude early species. -Tolerance: first-come, first-served. All species can colonize regardless of other species present. Competition, longevity determine climax community. -Inhibition: early species inhibit/ block colonization by later species. Random colonization order is important. Longevity drives succession.
What is the easiest, most direct way of testing the 3 models of succession?
-By removing early species and monitoring the rate of colonization of later species.
What did Walker and Chapin's study of succession show?
-They found a combination of factors affecting successional sequence. Alder (N-fixing plant) reduces the nutrient limitations on spruce and aiding its colonization. However, net effect of alder was inhibitory. Alder has dense canopy, blocking out sunlight for spruce. Alder leaf litter inhibits spruce germination. Herbivores preferred alders over spruce.
What did the study at Glacier Bay show?
-It showed primary succession. Plant species rapidly increased early, then decreased over time. -Soil depth, organic content, moisture, and nitrogen increased.
What are the 4 predictable patterns in succession?
1. Communities are most diverse, complex, and productive at intermediate stages. 2. Ratio biomass / productivity increases. Biomass increases, productivity increases. 3. Net accumulation biomass slows, stops. 4. Greater proportion nutrients in organic matter than soil.
What were the 5 dynamic processes in Clements succession model?
1.Initial exposed soil 2.Colonization: arrival of seeds, organisms 3.Competition 4.Reaction: effects of organisms on the environment 5.Stabilization: results in a climax community
Clement's model of succession showed what?
-It showed a facilitation model: colonists modify habitat, help aid in the settlement of next species until climax community is achieved.
What did Gleason's model of succession propose?
-It proposed that facilitated interactions between species are not that important. Instead, he argued that stochastic events, who got there first, is more important in succession.
What did Egler add to Gleason's model of succession?
-Egler added that the longevity of species is determined by competition.
What are two sorts of processes to recover from a disturbance?
(1) Founder Controlled: would rely more on stochastic factors..which species colonized a place first.. and this would correlate with vagility (2) Dominance Controlled: control would relate more to competitive ability
________ of plants influence their place in the sere.
Characteristics of early species?
-Good colonizers, grow rapidly.
Characteristics of late species?
-Tolerate poor resources, dominate competition.
Late successional species have usually what characteristics?
-They have larger seeds and seedlings. -Seed mortality rate is inversely proportional to seed weight. Lighter seeds have higher mortality than heavier seeds.
Inhibition is common in what type of succession?
What was Clement's view of succession leading to the same climax community?
-Viewed succession as uni-directional and predictable. -Many seres in different local environments converge into the same climax community. -End point (climax) is determined by topography and climate.
What argument was used to reject the monoclimatic theory of succession?
-Variation in size of disturbance and conditions in early succession can lead to alternative stable states.
The monoclimatic theory was replaced by what?
-It was replaced by open continuum within a region, where climax communities represent a continuum of vegetation types.
How do you "jump-start" succession and move it faster?
-Accelerate arrival of seeds.
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