29. Succession Flashcards
succession
the outcome of ecological processes (not a process itself): shifts in
- species dominance
- species evenness
- species diversity
- species composition
- soil amount and composition
- nutrient reservoirs/flows
processes involved in succession
- dispersal
- niche requirements
- competition
- exploitation
- associated mutualists
primary succession at Glacier Bay
- succession after glacial disturbances can take centuries to millennia - chronosequence created using 8 study sites - rapid increase in first years since disturbance and eventually almost levels out
chronosequence
a series of communities or ecosystems representing a range of ages or times since disturbance - plot number of plant species against years since disturbance
differences in colonization
can be attributed to the life histories of species - ex. lichens can colonize earlier than trees
secondary succession in boreal forest
community is already established and soil remains in disturbance (forest fires) - aspen roots generally survive fires, jack pines release seeds –> able to live in disturbed habitat better - chronosequence shows basal area (density) of species against time since fire
succession in rocky intertidal communities
intermediate-sized boulders have the greater diversity - after storm, first green algae, then red algae - rapid succession
time scale of succession
- primary succession (glacial bay) can require 1500 years
- secondary (forest fire) succession can require 200 years
- succession in intertidal communities can require 1.5 years
- succession in desert streams can occur in weeks
succession in shallow lakes
succession on two time scales - lakes also experience succession over geological time scales (more obvious in shallow organic lakes) - sediment slowly settles and fills lake into a marsh - can become bog or land
ecosystem properties that change in succession
- biomass
- primary production
- respiration
- nutrient retention
ecosystem changes at glacier bay
depth of all major soil layers changed with different times during succession and overall increased
ecosystem changes on Hawaiian islands
- primary succession on lava flows
- total soil nitrogen and carbon peaks about 100 years after and then declines due to leaching of nutrients into groundwater
ecosystem change after deforestation
sites with logging had sharp decrease in biomass, but once succession was allowed to proceed, biomass increased
model of ecosystem recovery
- reorganization phase
- aggradation phase
- transition phase
reorganization phase
(10-20 years) forest loses biomass and nutrients, despite accumulation of living biomass
aggradation phase
(>100 years) ecosystem accumulates biomass, eventually reaching peak
transition phase
biomass declines somewhat from the peak
steady-state phase
biomass fluctuates around a mean level
3 models for mechanisms of success
- facilitation model
- tolerance model
- inhibition model
facilitation model
many species attempt to colonize newly available space but only species with particular characteristics can establish (pioneer species), replacement of early successional stages until resident species no longer facilitate colonization by other species
pioneer species
capable of colonizing new sites, modify environment so it becomes less suitable for them but more suitable for species found in later successional stages
tolerance model
- initial stages not limited to pioneer species
- juveniles of dominant species at climax establish in earliest successional stages
- species colonizing in early succession do not facilitate colonization by other species
- climax community established when no more species tolerant of the environmental conditions colonize
inhibition model
- any species can colonize during early succession
- early occupants modify environment to make it less suitable for any species
- early colonizers inhibit colonization by later arrivals
- climax community long-lived species resistant to damage by physical or biological factors
