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Community Ecology. Chapter 9. Succession. Temporal patterns in communities Replacement of species by others within particular habitat (colonization and extinction) Non-seasonal, continuous, directional. Degradative succession. Decomposers breaking down organic matter
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Community Ecology Chapter 9
Succession • Temporal patterns in communities • Replacement of species by others within particular habitat (colonization and extinction) • Non-seasonal, continuous, directional
Degradative succession • Decomposers breaking down organic matter • Leads to disappearance of everything, species included
Autotropic succession • Does not lead to degradation • Habitat 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 habitat • 2) increasing salinity of Great Salt Lake
Autogenic succession • Change of species driven by biological processes changing conditions and/or resources • Example: organisms living, then dying, on bare rock
In an area that previously did not support any community Primary succession Example: terrestrial habitat devoid of soil In an area that previously supported a community, but now does not Secondary succession Example: terrestrial habitat where vegetation was destroyed, but soil remained Autogenic succession can occur under 2 different conditions
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 colonizers • Tolerant of harsh conditions • Reproduce quickly in unpredictable environs • Example: lichens
Pioneer species • Carry out life processes and begin to modify habitat • Extract resources from bare rock • Break up/fragment rock with roots • Collect wind-blown dust, particles • Waste products accumulate • Die and decompose • Soil development begins
Continuing change • Colonizers joined by other species suited for modified habitat • Eventually replace colonizers • Better competitors in modified habitat • Less r-selected, more K-selected
More change • Communities gradually become dominated by K-selected species • Good competitors, able to coexist with others for long periods of time
Stability • Communities become stabilized • Reach equilibrium • Little or no change in species composition, abundance over long periods of time • Climax community • End stage of succession
Will climax stage be reached? • Rarely is climax stage reached quickly • Slow succession most common, climax stage almost never achieved • Community usually affected by some major disturbance (e.g., fire) before climax stage is reached • Resets succession, forces it to start again from some earlier stage
