BIOL 2060 Lecture Notes - Lecture 22: Climax Community, Superorganism, Models 1
3 May 2018
School
Department
Course
Professor
Mechanisms of Succession
March 7, 2016
Clements (1916): likened succession to the predictable development of an organisms and called
the climax community a “superorganism”
• Each wave of species in a successional sequence facilitated the establishment of the next
wave
• Predictable serial replacement until climax community is reached
Gleason (1926): argued that succession proceeded more dynamically and “individualistic”
• Less predictable
• Based on species characteristics, external conditions and chance
• Outcome is not always the same climax community, even under similar environmental
conditions
CLEMENTS MODEL:
• Single predictable sequence to a single climax community
• Rock Lichen Annual Herb Perennial Herb Scrubs Forest
Objection 1 : too simplistic
• Local environmental conditions and species interactions matter
• *polyclimax = several possible endpoints
• intermediate community types are possible *pattern-climax
Objection 2 : not always predictable
• dispersal affects sequence and climax; chance events
Most modern ecologists lean towards Gleason’s succession model:
• outcome of succession is influenced by…
o environmental conditions
o dispersal limitations
o species interactions
o chance events
• communities are groups of individuals, not a superorganism
• climax concept is useful, but not a deterministic model
Egler (1954): presented two alternative views of how succession may work based on Clement’s
and Gleason’s models
1. Relay Floristics – based on facilitation
-weeds enter immediately after cropland is abandoned
-waves of species is followed by successive waves of other species
-width of line represents relative abundance (increases through time)
2. Initial Floristics – based on tolerance
-most species are always present but change in abundance over time
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Gleason (1926): argued that succession proceeded more dynamically and individualistic : less predictable, based on species characteristics, external conditions and chance, outcome is not always the same climax community, even under similar environmental conditions. Clements model: single predictable sequence to a single climax community, rock lichen annual herb perennial herb scrubs forest. Objection 1 : too simplistic: local environmental conditions and species interactions matter, *polyclimax = several possible endpoints intermediate community types are possible *pattern-climax. Objection 2 : not always predictable: dispersal affects sequence and climax; chance events. Egler (1954): presented two alternative views of how succession may work based on clement"s and gleason"s models: relay floristics based on facilitation. Waves of species is followed by successive waves of other species. Width of line represents relative abundance (increases through time: initial floristics based on tolerance. Most species are always present but change in abundance over time.
