plant ecology - chapter 12 disturbance & succession
TRANSCRIPT
Plant Ecology - Chapter 12
Disturbance & Succession
Succession
Temporal patterns in communitiesReplacement of species by others within particular habitat (colonization and extinction)Non-seasonal, continuous, directional
Degradative succession
Decomposers breaking down organic matterLeads to disappearance of everything, species included
Autotropic succession
Does not lead to degradationHabitat continually occupied by living organisms
Two types of autotropic succession
Allogenic succession
Autogenic succession
Allogenic succession
Serial replacement of species driven by changing external geophysical processes
Examples:1) silt deposition changing aquatic habitat to terrestrial habitat2) increasing salinity of Great Salt Lake
Autogenic succession
Change of species driven by biological processes changing conditions and/or resourcesExample: organisms living, then dying, on bare rock
Autogenic succession can occur under 2 different conditions
In an area that previously did not support any communityPrimary successionExample: terrestrial habitat devoid of soil
In an area that previously supported a community, but now does notSecondary successionExample: terrestrial habitat where vegetation was destroyed, but soil remained
Disturbances
Relatively discreet event in time that causes abrupt change in ecosystem, community, or population structureChanges resource availability, substrate availability, or the physical environment
Disturbances
Intensity, size, frequencySmall disturbances of low intensity are much more frequent than large disturbances of high intensity
Disturbances
GapsFireWindWaterAnimalsEarthquakes, volcanoesDiseaseHumans
Primary succession
Volcanic eruptions
Glaciers
Secondarysuccession
Floods
Fires
Rate of succession
Primary - slow - may take 1000s of years
Secondary - faster - fraction of the time to reach same stage
Autogenic succession begins…
First community comprised of r-selected species - pioneer species
r-selected species
Good colonizersTolerant of harsh conditionsReproduce quickly in unpredictable environs
Example: lichens
r-selected species
Primary - colonized by seeds, spores, via wind, waterSecondary - wind-dispersed seeds, seed banks
Pioneer species
Carry out life processes and begin to modify habitat
Extract resources from bare rockBreak up/fragment rock with rootsCollect wind-blown dust, particlesWaste products accumulateDie and decomposeSoil development begins
Continuing change
Colonizers joined by other species suited for modified habitatEventually replace colonizersBetter competitors in modified habitatLess r-selected, more K-selected
More change
Communities may gradually become dominated by K-selected speciesGood competitors, able to coexist with others for long periods of time
Stability
Communities may become stabilized on some scaleReach equilibrium (dynamic)Little or no change in species composition, abundance over long periods of timeClimax communityEnd stage of succession
Will climax stage be reached?
Rarely is climax stage reached quicklySlow succession most common, climax stage almost never achievedCommunity usually affected by some major disturbance (e.g., fire) before climax stage is reachedResets succession, forces it to start again from some earlier stage
Terrestrial succession
Relay Floristics
Relay Floristics
Predictability of SuccessionDeterministic- process with a fixed outcome
Community restorationvia succession?