Lec 29 (Succession) Flashcards
What is succession?
Succession is the outcome of ecological processes…
Succession in of itself isn’t a process. It is the outcome of different ecological processes.
Succession is is the outcome of different ecological
processes, shifts in? (6 of them)
- Species dominance
- Species evenness
- Species diversity
- Species composition
- Soil amount and composition
- Nutrient reservoirs/flows
What species will be found in locations
undergoing succession?
–Dispersal
–Niche requirements
– Competition
– Exploitation
– Associated mutualists
Examples of Succession: Primary Succession at Glacier Bay…
-Succession after glacial disturbances can take
centuries to millennia.
- At the glaciers, the number of the plant species grew rapidly for the first 200 years and then leveled off
- Trees, tall shrubs, and mosses attained max diversity in a century
- Low shrubs and herbs continued to grow in diversity for 1,500 years
- Soil depth increased during the first 200 years
Chronosequence
a series of communities or ecosystems representing a range of ages or times since disturbance
Time Scale of Succession…
Primary succession? (Glacial bay)
Secondary succession? (Forest)
Succession in intertidal communities?
Succession in deserts?
Primary succession (Glacial Bay) can required 1,500 years
Secondary forest (fire) succession can require 200 years
Succession in intertidal communities can take
1.5 years
….Succession in desert streams can occur on a
scale of weeks!
Ecosystem properties can change during the
course of succession such as?
– Biomass
– Primary production
– Respiration
–Nutrient retention
A Model of Ecosystem Recovery (4 step process)
- A reorganization phase… of 10 to 20 years, during which the forest loses biomass and nutrients, despite accumulation of living biomass
- An aggradation phase… of more than a century, when the ecosystem accumulates biomass, eventually reaching peak biomass
- A transition phase… during which biomass declines
somewhat from the peak reached during the aggradation phase - A steady-state phase… when biomass fluctuates around a mean level
How Does Succession Occur? (Mechanisms of Success)
Three models:
1. Facilitation
- Tolerance
- Inhibition
What is the Facilitation model?
The facilitation model proposed that many species attempt to colonize newly available space but only species with particular characteristics can establish.
• Species capable of colonizing new sites are pioneer
species.
- Pioneer species modify environment so that it becomes less suitable for them but more suitable for species found in later successional stages.
- Replacement of early successional stages until resident species no longer facilitate colonization by other species.
What is the tolerance model?
The tolerance model proposed that the initial
stages of colonization not limited to few pioneer species.
• Juveniles of dominant species at climax can
establish in earliest successional stages.
• Species colonizing early in succession do not
facilitate colonization by other species.
• Climax community established when no more
species tolerant of environmental conditions
colonize.
What is the inhibition model?
The inhibition model proposed that any species
can colonize area during early stages of succession.
• Early occupants modify environment to make
area 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.
Mechanisms of Succession Following Deglaciation (Glacier Bay)
In the Glacier Bay, Alaska (primary succession) no single mechanism determines succession.
-Used both inhibition and facilitation
Mechanisms of Succession in a Boreal Forest
Forest fire is an important driver of forest changes
through time in Boreal forest.
- Many spruce require fire to release seeds from cones.
- Creates high light conditions for aspen seedlings
- Early hardwood species (e.g. aspen) replaced with conifers such as spruce and fir. Both allow aspen to grow rapidly after fire.
