module 14 Flashcards
Communities are in
constant flux
communities appear
and what changes
Appear stable in short-term Change over Long-Term Environmental Conditions Competition Facilitation
community development is
chaotic, cyclical, or directional (succession)
Succession
Gradual, Ordered, Directional change in plant and animal communities in an area following a disturbance or the creation of new substrate
Basic Succession – F.E. Clements
follows orderly series of species replacement
does not guarantee outcome (single climax)
Primary Succession
Sequence of communities developing in newly exposed habitat devoid of life
Succession only from Immigrants
Secondary Succession
Sequence of communities developing in habitats in which the climax has been disturbed or removed
Succession from Immigration or Seed Bank
Autogenic Succession
organisms change environment to
time scale
Temporal succession of species at a location driven by processes operating within community
- Organisms Change Environment to harm/favor others
- Time Scale – Life of Organisms
- biotic factors
Allogenic Succession
Temporal succession of species at a location driven by external influences which alter conditions
- Massive Disturbances, Environmental Shifts
- Time Scale – Time scale of disturbance
Sere
A series of stages of community development in a particular area leading to a stable state, or Climax
final Seral Stage
may be….
- Climax
- -Final Seral Stage
- -Endpoint of a successional sequence
- -A Community that has reached a steady state under a particular set of environmental conditions
- May be definitive or Tenuous
Seres are different for and are determined by
-Different for each environment
-Determined by surrounding:
Vegetation
Nutrients
Soil Characteristics
Etc.
Sand Dunes
- Soils Unstable/Shifting
- Low Nutrient Content
- 1st colonizers:
- -Stabilize soil
- -Add Organic material
old fields
Old Fields
- -Soils More Stable
- -Higher Nutrients
- quicker to colonize
closed community
Closed Community
- Clementsian View
- Species closely associated
- Ecological limits of Individual Species = Ecological Limits of Community
- Ecotones Distinct
- -Transition between communities well defined
open community
- Gleasonian View
- Species distributed independently
- No Natural Boundaries
Climax – Early Studies
Determined solely by
climate
-Similar Climaxes within the Same Regions
Clementsian Climax
-how many climaxes
Identified 14 climaxes in North America
-2 grasslands, 3 scrub, and 9 forest
All others were interrupted seral stages
-Fire, animals, soils, topography
Sub-climaxes could persist unchanged for long periods
-Due to “unnatural” disruptions to seral stages
Present Day Climax
Early Ideals Questioned or Dismissed for Open Community Concept
-local climaxes
Communities Vary Continuously over Gradients
Continuum Index
change in community composition based on environmental gradient
Succession begins with
disturbance or creation of new habitat
-Opens areas for Colonization of New Species
succession driven by
Driven By Plants Differential Ability to:
- colonize
- compete
Disturbances definitions
- Any Process that limits plants by destroying plant biomass (Grimes 1977)
- Any discrete, punctuated, killing, displacement, or damaging of ≥ 1 individuals that creates opportunity for new individuals (Sousa 1984)
- Any relatively discrete event that disrupts structure & changes resources, substrate availability, or physical environment (White & Pickett 1985)
types of disturbances
- Physical Disturbance
- Biological Disturbance
succession disturbances
Set Back Succession
Remove all Life from area
Eruption of Mt. St. Helens
Old Field Succession
Changes Fast Initially
Slows over time
Slow Growing Plants
Colonization occurs from:
areas surrounding disturbed area
areas some distance away from disturbed area
seed bank
Disturbance may leave individuals remaining alive
Colonization Primary Force in Succession
-Succession directed by Species’ Ability to:
Cope with Environmental Conditions
Often Low Nutrients
Disperse into Disturbed Areas
Modify Environment
Pioneer species
have the best combination of what
Species that are among the first to become established
Best combination of Coping & Dispersal
Often Determine Successive Colonizers
best colonizers are
slower colonizers are
Best Colonizers often worst Competitors
- Weeds
- -Invade Quickly But are short lived
- -Generally do not persist past 1 year
Slower Colonizers (grasses) Do persist -Thrive After death of weeds
Major determinants of organisms in seral stage
Life History of Organisms
Are Organisms Built for dispersal or competition?
Evolutionary History of Species
Nature of Changes
Mechanisms of Succession
Pioneer Species Effect Future Colonizers
Clements – 1 Mechanism
Connell & Slayter (1977) Presence of one species effects the probability of establishment of a second in 3 ways: Facilitation Inhibition Tolerance
Facilitation
Many species may attempt to colonize newly available space.
-Only certain species will establish.
Pioneer Species modify environment so it becomes:
-Less suitable for themselves
-More suitable for species of later successional stages.
Autogenic processes inherent in driving process
-Addition of Organic Material
-Breakdown of Substrate to Soil
Key process in Primary Succession
Tolerance
Initial occupants neither increase nor decrease the ability of other species to colonize
-Initial stages of colonization are not limited to pioneer species.
–Generally Better Nutrients & Soil remain
Change driven primarily by Allogenic Processes
-Early successional species do not facilitate later successional species.
Inhibition
Early occupants modify the environment in ways that makes it less suitable for both early and late successional species.
- Early arrivals inhibit colonization by later arrivals.
- Assures late successional species dominate an area
- They live a long time & resist damage by physical and biological factors.
Succession driven Primarily by Allogenic Processes
-Autogenic Processes present but impede change
Founder Effect
- Two Supremely Competitive Species Colonize area
- Propogules of neither species competes with adults of other
- The species that establishes first determines community structure & direction of succession
animal species _____ with plants
-Continuation of Succession
–Woody Species Increase
1st small shrubs -> Small Trees ->Large Trees
-Animal Species Increase with Plants
Primary Succession in Glacier Bay
4 Stages
- Pioneer Stage – blue-green algal mats, lichens, liverworts, forbs, limited willows, cottonwoods, spruce, & Dryas
- Dryas stage – Thick mat of Dryas, few willows, alders, spruce. ~ 30 years after Retreat
- Alder Stage – Alder dominated, ~ 50 YAR
- Spruce Climax – ~ 100 YAR
Ecosystem Changes During Succession
-soil depth and organic content
- Substantial changes in ecosystem structure during succession at Glacier Bay.
- Total soil depth and depth of all major soil horizons show significant increase from pioneer community.
- organic content, moisture, and N concentrations all increased.
- Physical and biological systems are inseparable.
Climax & Environment
rate of change and rate of adaptation
-Climax occurs when Community & Physical Environment reach Equilibrium
Rate of Change of Environment < Rate of adaptation of Existing Organisms
- Climax Remains Until Disturbance Occurs
- Subtle Changes Continue even at Climax
- -Births, Deaths, & Growth Processes
- -Less Dramatic than succession
