Community Ecology Chapter 9 Succession n Temporal patterns

Community Ecology Chapter 9

Succession n Temporal patterns in communities Replacement of species by others within particular habitat (colonization and extinction) Non-seasonal, continuous, directional

Degradative succession n n Decomposers breaking down organic matter Leads to disappearance of everything, species included

Autotropic succession n n Does not lead to degradation Habitat continually occupied by living organisms

Two types of autotropic succession n Allogenic succession n Autogenic succession

Allogenic succession n Serial replacement of species driven by changing external geophysical processes n Examples: n n 1) silt deposition changing aquatic habitat to terrestrial habitat 2) increasing salinity of Great Salt Lake

Autogenic succession n n Change of species driven by biological processes changing conditions and/or resources Example: organisms living, then dying, on bare rock

Autogenic succession can occur under 2 different conditions n n n In an area that previously did not support any community Primary succession Example: terrestrial habitat devoid of soil n n n In an area that previously supported a community, but now does not Secondary succession Example: terrestrial habitat where vegetation was destroyed, but soil remained

Primary succession n Volcanic eruptions n Glaciers

Secondary succession n Floods n Fires

Rate of succession n Primary - slow - may take 1000 s of years n Secondary - faster - fraction of the time to reach same stage

Autogenic succession begins… n First community comprised of r-selected species - pioneer species

r-selected species n n Good colonizers Tolerant of harsh conditions Reproduce quickly in unpredictable environs Example: lichens

Pioneer species n Carry out life processes and begin to modify habitat n n n 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 n n 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 n n Communities gradually become dominated by K-selected species Good competitors, able to coexist with others for long periods of time

Stability n n n 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? n n 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

Terrestrial succession

Lake or pond succession