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Ecology (BIOL 250) Lecture 14: Succession and Stability
Today’’s Outline
  Introduction
  Primary Succession
  Secondary Succession
  Disturbance
 Ecosystem Recovery
  Mechanisms of Succession
  Community and Ecosystem Stability
Announcements
Introduction
  Succession: Gradual change in plant and animal
communities in an area following disturbance.
–  Primary succession on newly exposed geological
substrates.
–  Secondary succession following disturbance that does not
destroy soil.
  Climax Community: Late successional community
that remains stable until disrupted by disturbance.
Introduction
Primary Succession
at Glacier Bay
  Reiners et.al. studied changes
in plant diversity during
succession.
–  Total number of plant species
increased with plot age.
–  Species richness increased
rapidly in early years of
succession and more slowly
during later stages.
  Not all groups increased in density
throughout succession.
Primary Succession
Primary Succession
at Glacier Bay
at Glacier Bay
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Primary Succession
Secondary Succession
at Glacier Bay
in Temperate Forests
  Chapin (1994) documented 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.
  Studies often find the number of woody plant
species increases during secondary forest
succession.
–  Other studies show increases in bird diversity
across successional sequence closely paralleled
increase in woody plant diversity.
  In addition, organic content, moisture, and N
concentrations all increased.
–  Physical and biological systems are inseparable.
Model of Ecosystem Recovery
Model of Ecosystem Recovery
  Biomass Accumulation Model
  Reorganization (10-20 yrs)
–  Forest loses biomass and nutrients.
  Aggradation (100+ yrs)
–  Ecosystem reaches peak biomass.
  Transition
–  Biomass declines from peak.
  Steady-State
–  Biomass fluctuates around mean.
Model of Ecosystem Recovery
Models of Ecosystem Recovery
Mechanisms of Succession
Three Models
– Facilitation
– Tolerance
– Inhibition
Facilitation
  Proposes many species may
attempt to colonize newly available
space.
–  Only certain species will establish.
  Colonizers “Pioneer Species” modify
environment so it becomes less suitable
for themselves and more suitable for
species of later successional stages.
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Model of Ecosystem Recovery
Successional Mechanisms
Tolerance
in Rocky Intertidal Zone
Tolerance
  Initial stages of colonization are not limited to
pioneer species.
–  Early successional species do not facilitate or
inhibit later successional species.
Inhibition
  Early occupants of an area modify the
environment in a way that makes it less
suitable for both early and late successional
species.
  Sousa investigated mechanisms behind
succession of algae and barnacles in intertidal
boulder fields.
–  If the inhibition model is in effect what should
happen?
–  If the inhibition model is in effect, early
successional species should be more vulnerable to
mortality. Why?
–  Early arrivals inhibit colonization by later arrivals.
Successional Mechanisms
in Primary Succession on Volcanic Substrate
  1980 - Mt St. Helens, Washington
erupted.
–  Disturbance set stage for succession.
  Avalanche debris, hot volcanic ash and
pumice killed all plant life.
Community and Ecosystem Stability
  Stability: Absence of change.
  Resistance: Ability to maintain structure and
function in face of potential disturbance.
  Resilience: Ability to recover from
disturbance.
Community and Ecosystem Stability
Community and Ecosystem Stability
Park Grass Experiment
  Hertfordshire, England
Park Grass Experiment
–  Studied effects of fertilizer
treatments.
  Continued for 150 years.
  Silverton(1987) investigated
ecosystem stability.
  Dodd (1995) showed that although community
stability is present, populations of individual species
can change substantially.
–  Stability depends on resolution an area is investigated at.
–  Used community composition
variability as measure of stability.
–  Represented composition as
proportion of community
consisting of each plant form.
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