Transcript BIOL 4120: Principles of Ecology Lecture 17: Community Ecology

Recap
Food web structure influences the stability of
communities
Constancy and resilience; diversity and stability
Communities can switch between alternative stable
states
Alternative stable states
Trophic levels are influenced from above by predation
(top-down control) and from below by production
(bottom-up control)
An example of forest zonation
Topographic distribution of forest communities in the Great Smoky
Mountains National Park (west-facing) OH: red- oak-pignut hickory
OCH: chestnut oak-chestnut heath OCF: chestnut oak-chestnut forest
ROC: red oak-chestnut H: Helmock forest; P: pine; F: Frazir fir; SF:
spruce-fir; S: Red spruce; GB: grassy balds HB:Heath balds
Patterns of co-occurrence for 4 plant species on a landscape along a
gradient of altitude
BIOL 4120: Principles of Ecology
Lecture 16: Ecological
Succession and Community
Development
Dafeng Hui
Room: Harned Hall 320
Phone: 963-5777
Email: [email protected]
August 27, 1883
Island of Krakatau
Volcano erupted followed
by tsunamis
Catastrophe  natural lab
Ecologists studied the
colonization of species
Source islands: Sumatra
and Java (40km from
Krakatau)
Sea-dispersal arrived first
(10 of 24 by 1886)
Others, wind-dispersed
grasses and ferns and
moved away from beach
Then wind-d trees, birds
and bats arrived …
Plants dispersed by
physical forces are
the first to arrive in
primary succession
Outline (Chapter 19)
16.1 The concept of the sere includes all the
stages of successional change
16.2 Succession ensures as colonists alter
environmental conditions
16.3 Succession becomes self-limiting as it
approaches the climax
16.1 Community structure changes
through time
Grazed grassland in
1942
aspen and maple in
1972
Successional
changes over 30
years in a western
Pennsylvania field.
Cropland or
Grazed grassland
 grasses,
goldenrod, weedy
herbaceous plants
 shrubs
(blackberry,
hawthorn) fire
cherry, pine,
aspen  forest of
maple, oak, cherry
or pine.
Cleaning of oakhornbeam forest
30 years after
7 years after
95 years after
15 years after
150 years after
Succession
Definition: The process of gradual and (seemingly)
directional change in the structural of the community
through time (from open field to forest)
Temporal change in community structure
Sere (from the word series): The sequence of
communities from grass to shrub to forest
Seral stage: each of the changes is a seral stage, is a
point of continuum of vegetation through time,
can be short or long (1 or 2 yrs to several decades)
Climax community: ultimate association of species
achieved
William Sousa
Process of succession in a
rocky intertidal algal
community in southern
California (by W. Sousa)
Use concrete blocks for
algae to colonize
Panel b shows succession
Early successional species
(pioneer species):
High growth rate, small
size, high degree of
dispersal, high rates of
population growth
Late successional species:
Species dominance change along time
Low rate of dispersal,
slower growth rate, larger
and live longer
(competition?).
Hubbard Brook Experimental
Forest, New Hampshire
Process of succession after
forest clearing
Prior to forest clearing, beech
and sugar maple seedling
dominate understory
Following clearing, pin cherry,
yellow birch etc. will replace.
After many years, sugar maple
and beech will dominate.
Primary succession (example
before, a site unoccupied by a
community) and
Species dominance change along time
secondary succession (this
example, occurs on previous
occupied site after disturbance,
remove part or all vegetation)
Primary succession occurs on
newly exposed substrates
Primary succession begins on sites that never have supported a
community, such as rock outcrops and cliffs, sand dunes, and
newly exposed glacial till.
Primary
succession
on a coastal
sand dune
colonized
by beach
grass
Later on,
shrub, then
trees (pines
and oak if
they can
survive)
Primary succession occurs on
newly exposed substrates
Glacier Bay fjord complex in southeastern Alaska. Ice retreats,
primary succession occurs
Secondary succession occurs after
disturbances
Terrestrial environment:
Oldfield succession in the Piedmont region of North Carolina by
Dwight Billings in the late 1930s
Abandoned farmland
1st yr: crabgrass, 
horseweed
2nd yr: horseweed, 
white aster and ragweed
3rd yr: broomsedge,
pine seedling
5-10th yr pine
Later oak and ash
Decline in pine and increase in hardwood (oak and hickory)
Plant life history influence old-field succession
Tolerance and inhibition interact with life history to shape details of the
species sequence during succession.
Oosting and Keever, Duke University, 1950s, old field study, Piedmont, NC
Old field on the Piedmont of North Carolina. Abandoned agricultural
fields undergo a series of successional changes. (shrubs start to
replace annual plants)
The climax community
Friderick Clements (1916, 1936): Monoclimax hypothesis
view community as a highly integrated superorganism, the
process of succession represents gradual and progressive development of
community to ultimate or climax stage (similar as development of an
individual organism)
Clements’ climax community (Closed system):
Community is like an organism, it arises, grows, matures, and dies.
Seres are different stage of development, ultimately lead to similar
climax community
Fourteen climaxes:
2 grassland: prairie and tundra
3 scrub: sagebrush, desert scrub and chaparral
9 forest: pine-juniper woodland to beech-oak forest
The climax community
New views consider climax communities represent a continuum of
vegetation types (open system)
Communities were ordered along
a continuum index
Continnum index: scale of an
environmental gradient based on
the changes in physical
characteristics or community
composition along the gradient
Stages in the sere will lead to
sugar maple climax community,
but so-called climax vegetation
actually represents a continuum
of forest types
Curtis and McIntosh (1951)
16.2 Succession ensures as colonists
alter environmental conditions
Two factors determines a species’s present in a sere:
1.How readily it invades a newly formed or disturbed habitat
2. Its response to environment over the course of succession
Early pioneering species hypothesis
F. Egler (1954):Initial floristic composition
Succession at any site depends on which species gets there
first. No species is competitively superior to another. Once the
original dies, the site becomes available to others.
Joesph Connell and Ralph Slatyer (1977): three models
(facilitation model, inhibition model, and tolerance
model)
Mechanisms of Succession
Alder facilitates succession by
adding nitrogen to soils
Alder trees harbor nitrogen-fixing
bacteria in their roots, providing
nutrient to soils, facilitate the
establishes of nitrogen-limited
plants such as spruce, which will
replace alder later.
Facilitation, inhibition, and invasive
species
Mycorrhizae fungi and plants: mutualistic sybmioses
Fungi can facilitate or inhibit plant growth (positive and negative)
Effects are larger in home-home than home-foreign
(Black cherry, Maple with soil microorganisms)
The differing adaptations of early and
late successional species
Early-stage species
and later inhabitants
tend to have different
strategies of growth
and reproduction.
Early-arriving species:
High dispersal ability.
(dandelion, milkweed)
Climax species: large
size, slow growth, but
shade-tolerance as
seedling (oak, maple)
The survival of tree seedlings
in shade is directly related to
seed weight
16.3 Succession becomes self-limiting as it
approaches the climax
Succession continues until the
addition of new species to the
sere and the exclusion of
established species no longer
change the environment of the
developing community.
The progression from small to
large growth form modifies the
conditions of light, temperature,
moisture and soil nutrients.
Conditions change slowly after
the vegetations achieves the
largest growth form that the
environment can support.
Final dimensions of a climax
community are limited by climate
independently of events during
succession.
Succession becomes self-limiting as it approaches
the climax
Time required for succession from a new or disturbed habitat to a climax
community depends on nature of climax and initial quality of habitat
Mature oak-hickory climax forest from old field in North Carolina: 150 yrs
Climax stage of grasslands in western North America: 20-40 years
Humid tropics, reach climax within 100 years from clear cut, but may take
a few more centuries to achieves a fully mature structure and species
composition.
Sand dune  beech-maple climax, up to 1,000 years
Climax is an elusive concept:
Communities also change in response to climate change, hunting, fire, and
logging, disappearance of keystone consumers (wolf, passenger pigeon)
and trees (chestnuts, eastern hemlock)
Climax communities under extreme environmental
conditions
Fire is an important
feature of many climax
communities, favoring
fire-resistant species
and excluding species
that would otherwise
dominate.
Longleaf pine after a
fire
Seedling may be badly
burned, but the
growing shoot is
protected by the long,
dense needles.
Grazing pressure also modify a climax community
Grassland can be turned into
shrubland by intense grazing
Herbivivores may kill or severely
damage perennial grasses and allow
shrubs and cacti that are unsuitable
for forage to invade.
Selective grazing
Some species prefer to feed on areas
previously grazed by others. Both
zebras and Thompson’s gazelles feed
on Serengeti ecosystem of east
Africa, but eating different plants.
In North America, cattle grazing may
lead to invasion by alien cheatgrass,
which promote fire.
Transient and cyclic climaxes
Succession is a series of changes leading to a stable climax, whose
character is determined by local environment. Once established, a
beech-maple forest perpetuates itself, and its general appearance
changes little despite constant replacement of individuals within the
community.
Transient climaxes: such
as communities in
seasonal ponds – small
bodies of water that
either dry up in summer,
or freeze solid in winter.
The extreme seasonal
changes regularly
destroy the communities
that become established
in the ponds each year.
On African savannas, carcasses of large mammals are devoured by a
succession of vultures including: large, aggressive species  smaller
species that glen smaller bits of meat from bone  species that cracks
open bone to feed on marrow.
Cyclic climax:
Suppose, for example, species A can only germinate under species B, B only
under C, and C only under A. The relationships create a regular cycle of
species dominance in the order of A, C, B, A, C, B, A, …, in which the length
of each stage is determined by the life span of the dominant species.
Cyclic succession is usually driven by stressful environmental conditions.
When high winds damage
heaths and other types of
vegetation in northern
Scotland, shredded foliage and
broken twigs create openings
for further damage, and soon a
wide swath is opened in the
vegetation.
Regeneration occurs on the
protected side of damaged area
while wind damage further
encroaches on exposed
vegetation.
Temporal: wind damage and
regenerate, cycling
Spatial: mosaic patches
The End
18.4 Succession is associated with autogenic
changes in environmental conditions
Environmental changes can be grouped into two classes:

Autogenic (direct result of organisms within community)
• Created by organisms in community


Light in a forest
Allogenic (a feature of physical environment)
• Created by physical environment
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Elevation on a mountain (decline temperature with elevation)
Stress in a salt marsh, seasons
Succession: changes in community structure through time;
specifically, changes in species dominance.
During plant succession, it creates autogenic environmental
change in a place
Both primary and secondary succession, colonization alters
environmental conditions
How do autogenic environmental changes influence succession?

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During plant succession, it creates autogenic
environmental change in a place. For example, light
environment (vertical distribution)
Initial colonization, the light at ground level is high,
seedlings are able to establish themselves.
As plants grow, their leaves intercept sunlight, light
availability declines from canopy to ground levels,
reducing light to short plants
The reduction in light enables fast-growing plants to
out-compete the other species that dominate the site
Sun-adapted, shade-intolerant plants exhibit high rates
of photosynthesis and growth under high-light
conditions (Under low light, they can not survive).
Only shade-tolerant species exhibit much low
photosynthesis rate and growth under high-light
conditions, are able to continue photosynthesis and
growth, and survival under low-light (trade-off)


In the early stage, shade-intolerant species
dominate because of their high growth rate.
They grow and shade the slower growing,
shade-tolerant species.
As time progresses and light level decline below
the canopy, seedlings of the shade-intolerant
species can’t grow and survive in the shaded
conditions. At this time, although shadeintolerant species dominate the canopy, no new
individual are being recruited. In contrast,
shade-tolerant species will germinate and grow,
and replace the old, dead shade-intolerant spp.

Example of succession
• 1st
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• 2nd
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Early successional
species, pine,
eventually dominate
only in canopy
Pine seedling
regeneration declines
as light decreases in
the understory
Shade tolerant species
(oak and hickory)
seedlings established
Shade intolerant pines
die out due to no
seedlings
Shade tolerant take
over
Density of species change
18.6 Species diversity changes during
succession
In addition to shifts in species dominance, patterns of
plant species diversity change over the course of
succession.
Comparison of species diversity at different sites within
an area that are at different stages of succession;
such groups of sites are:
Chronosequences (or chronoseres)
For example, farmland abandoned at different times
(herbaceous: crabgrass, horseweed, broomsedge;
wood: pine, oak)
Colonization and replacement processes
Changes in plant diversity during secondary succession of
an oak-pine forest in Brookhaven, New York.
Species richness increases into the late herbaceous stage, declines
into the shrub stage, then increases in the early forest stages, then
decreases thereafter.
Colonization increases species richness, replacement decreases spp
richness.
Normal growth rate
Double growth rate
Hypothetical succession involving five plant species (Huston, ORNL)
Species diversity increases initially as new species colonize the site. As
autogenically changing environments and competition result in the
displacement of early successional species, diversity declines
Pattern of succession under three different
disturbance frequencies
High to
low?
Intermediate disturbance hypothesis: community with
intermediate disturbance has large species diversity
18.7 Succession involves heterotrophic
species
Not only autotrophic component
of community (plant
succession) show succession,
changes in heterotrophic
component of the community
also occur.
Decomposition (treesoil)
Tree fall  bark beetle, wood
boring beetle  fungi broke
down lignin bacteria 
predator insects (centipedes,
mites, pseudoscorpions,
beetles)  fungi  moss and
lichens  seedlings
As plant succession advances, changes in structure and composition of
the vegetation result in changes in the animals life that depends on
vegetation as habitats.
18.8 Systematic changes in community structure
occur as a result of allogeneic environmental change
at a variety of timescales
Shifting patterns of community structure in response
to autogenic environmental changes often occur
at time scales relating to the establishment and
growth of the vegetation.
Purely abiotic environmental change can produce
patterns of succession over time scales ranging
from days to millennia.
Lawrence
Lake, MI
Short-term change: temporal changes in abundance of dominate
phytoplankton species during the period of May to Oct every year.
Optimal temperature controls the abundance
Paleoecology: study of distribution and abundance of ancient
organisms and their relationship to the environment
Pleistocene was
an epoch of
great climate
fluctuations
(1.8m to 10k yr
BP).
7 ice-sheet (4 in
N. America 3 in
Europe)
advanced and
retreated.
Cold state, tundralike vegetation
dominated; glaciers retreated, lightdemanding forests(birch, pine) advanced.
As soil improved, climate warmed, shadetolerant trees (oak, ash) dominated.
Last great ice
sheet reached
maximum
advance at
18,000 BP
Paleoecology: study of distribution and abundance of ancient
organisms and their relationship to the environment
Pleistocene was
an epoch of
great climate
fluctuations.
7 ice-sheet
advanced and
retreated.
Last great ice
sheet reached
maximum
advance at
18,000 BP
Study fossil: bone, insect exoskelecton, plant part pollen grains
Post-glacial
migration of
four tree
species
Numbers are
thousands of
year before
present
Changes in
distribution of
plant
communities
during and after
the retreat of
the Wisconsin
ice sheet
(pollen
analysis).
mixedhardwood and
oak-hickorysouthern pine
shrieked
Southern pine
expanded