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BIOL 4120: Principles of Ecology
Lecture 15: Community
Structure
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: [email protected]
Case study: Global Change
Invasive plant species, the role of herbivores
and Meta-Analysis
Wide spread of invasive species: lack of natural enemies (no
predators, parasites, pathogens)
Results are not conclusive.
John Parker, Georgia
Tech
Question: How native
and introduced
herbivores affect the
abundance of native
and introduced plants.
Papers: 63 studies
Herbivores: bison,
deer, rabbits
One specific study of the herbivores:
Pampas grass (an introduced species to CA) and native jackrabbits
John Lambrinos,
University of
California
Exclude rabbits
decreased grass
survival to 60%,
allow grazing
decreased the
survival to 5%.
Grazing of invasive
species by native
herbivores decreased
survivorship.
What do the results of the metaanalysis tell us?
1.What invasive plant spp encounter
matters (escape of native herbivores at
home, but face new generalist herbivores
that they have not evolved defense)
2.Native species survive better with
native herbivores (co-evo)
3.Single study can’t reveal this
information, as only native or invasive
spp used.
BIOL 4120: Principles of Ecology
Lecture 15: Community
Structure
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: [email protected]
Outline (Chapter 18)
Community structure
15.1 A biological community is an association of
interacting populations
15.2 Measure of community structure include numbers
of species and trophic levels
15.3 Feeding relationships organize communities in
food webs
15.4 Food web structure influences the stability of
communities
15.5 Communities can switch between alternative
stable states
15.6 Trophic levels are influenced from above by
predation and from below by production
15.1 A biological community is an
association of interacting populations
Two contrasting views of the community
Community is defined as groups of species
that occupy a given area, interacting with
each other directly or indirectly.
How important are these interacts? Two
reviews
Organismal (or discrete or holistic) concept:
Clements
Individualistic (or continuum) concept:
Gleason
Organismic (Holistic) concept:
Distribution of species is discrete (associations)
Association: a type of community with
1.
relative consistent species evolved together;
2.
a uniform general appearance;
3.
a distribution that is characteristics of a
particular habitats such as hilltop or valley
Transitional between communities are narrow, with
few species in common (Ecotone)
Suggest a common evolutional history and similar
foundational response and tolerances for
component species
Mutualism and coevolution play important roles in
the species that make up association.
Individualistic (or continuum) concept:
Relationship among co-existing species is
the result of similarities in their
requirements and tolerances, not the
result of strong interactions or common
evolutionary history.
Gradual change in species abundance along
environmental gradient (no associations)
Transitions are gradual and difficult to
detect.
Two views of community
Organismic and
individualistic views
Holistic (discrete) or
continuum
Ecotones
Closed or open communities
Ecotones
Ecotons are
places where
many species
reach the edges
of their
distributions
Locate: sharp
physical
differences
separate distinct
associations
Differences in soil conditions may
result in ecotones
Serpentine soil: soil with high
Mg and asbestos, greenish,
brownish.
The distributions of plant species may be determined by factors other
than their physiological tolerance of soil characteristics
Plant species are
restricted to
particular soil in
nature does not
mean that their
distributions are
determined solely
by their
physiological
tolerance of soil
characteristics.
Competition
McMillon 1956, California
The continuum concept and
gradient analysis
Twelve tree species
occur together in
associations in eastern
Kentucky
But none of them have
the same geographic
range.
At any spot, not form a
closed community
Limits: north and south,
Temperature
West and east:
precipitation
Environmental gradients
Continuum concept.
Gradient analysis
Abundance of each species is plotted on a continuous gradient of
one or more environmental factors.
The dominant tree species of the Great Smoky Mountains show distinct
but overlapping distributions
Many gradient analyses have
revealed open community structure
15.2 Measures of community structure
include numbers of species and trophic
levels
Biological structure of a community is defined by the
mix of species, including both their number and
relative abundance.
Attributes of community structure
1. Species richness: number of species that occur
within the community
2. Relative abundance: counting all individuals of each
species in a number of sample plots within a
community and determining what percentage each
contributes to the total number of individual of all
species.
Tropic rain forests in
Amazon (a), Malaysia (b),
and Northeast Australia (c)
High net primary
productivity (NPP)
High diversity of plant and
animal life
All trees, shrubs
and saplings on 1
50-hectare plot on
a 16-km2 island in
Panama include 300
spp among 240,000
individuals
(dbh>1cm). This
number exceeds all
tree species found
in Canada.
7% land surface, >50%
plant and animal species
10-km2 contain 1500
species of flowing plants
and 750 tree species.
Richest area in Malaysia,
7900 species
90% of all primate species
live in the tropical rain
forest
Tropical forests harbor the greatest species
richness of any communities
Autotrophic
Heterotrophic
Primary producer
Primary consumers
Secondary
consumers
Guild: groups of
species that feed
on similar
resources, have
similar ways of
life.
(leaf eater, stem
borer, root chewer
etc.)
15.3 Feeding relationship organize
communities in food webs
Food web
An abstract representation of feeding
relationships within a community.
Food chain
Grass  grasshopper  sparrow  hawk
A series of arrow, each pointing one species to
another, representing flow of food from prey
to predator.
Food webs describe species
interactions
Food web:
Involve numerical food chains meshed
together.
Hypothetical food web:
Circle: species
Links: arrows from one to
another
Basal species: feed on no
others, but are fed upon by
others
Intermediate species: feed
on others, and are fed upon
Top predator: not subjected
to predator, but prey on other
species.
Trophic levels
A food web for a prairie grassland community in the midwestern US
Effects of species richness on food web
structure
Intertidal mud flat
7 spp
7 links
One omnivory spp
Plant-insect-parasitoids
8 species
12 links
5 omnivory
Species richness and food web complexity
Pitcher plants
communities in
different
regions (Indian
Ocean)
Increasing
species
richness is
associated with
increasing food
web
complexity.
Source of food:
A: live insect
B: dead insect
C: organic
debris
Effect of food web structure on species
diversity
Robert Paine, University of Washington
Sea stars on the community species richness
Some species play more
important role in a
community than others
Removing top predator
reduced species richness
Effect of food web structure on species
diversity
John Terborgh, Duke University
Predator “remove” experiment, rain forest, Venezuela
Dam, water rising, form small islands (0.29-09 ha), too
small to support predators of large herbivores (howler
monkey, green iguanas)
Population density: Monkey 20-40 vs 1000 /km2
amerdillo disappeared
ants: 4-28 colonies vs <1 /4-hectare
 Influence forest regeneration, decreased productivity
and diversity declined (136 m-2 to 39).
Recap
1.Two views of biological community
(organismal and individualistic; closed
and open; discrete and continuum)
2.Ecotone and Gradient analysis
3.Community structure (species richness
and relative abundance)
4.Food web and food chair and stability
of community
Keystone species (consumer)
Consumer species that maintain diversity among
resource species and thereby influence the
structure of a community
Insecticide use (over 8 years) killed carysomelid beetle, goldenrod
Solidago became dominant and shaded out other species.
A variety of food web types
Food webs can be distinguished into different types
Connectedness web: emphasize feeding relationships
among species, portrayed as links in food web
Energy flow web: connections between species are
quantified by the flux of energy between a resource
and its consumer
Functional web: influence on the growth rate of other
species population.
Three types of food web
Limpet
Sea urchin Chiton
Chiton
Limpet
Case study: Indirect effect: Fox predation
on seabirds transforms plant communities
on a subarctic island
Without fox
With fox
Fox predate on sea
birds, less moved to
lands and transfer
less nutrients
Soil fertility and
plant production
drop, and landscape
shift from grassland
to forb- and shrubdominated lands
15.4 Food web structure influences
the stability of communities
Some consumers are keystone species and play an important role
in community structure.
How about the food web structure on stability of communities?
Stability: constancy and resilience
Constancy: a measure of ability of a system to resist change in
the face of outside influences (resistance)
Resilience: ability of system to return to some reference state
after a disturbance.
Resilience means that system may have internal processes that
can compensate for disturbance-induced changes. For
example, increase in birth rate can help population move back
after a population size decreases.
Environmental perturbation can cause a delayed
response in the functioning of a community
Suttle and
Thomsen (Mary
Power lab at UC
Berkeley)
Spring watering:
Any extension of the rainy
season resulting from climate
change is likely to lead to a
reduction of specie richness?
Enhanced
biomass,
especially in the
beginning
How about
species richness?
Suttle et al.
Science 2007
Resilience of communities increases with
diversity
Algae, bacteria,
protozoans,
rotifer (4 trophic)
Lab microcosms
(small water
bottle, two
nutrient levels)
Grow 3 weeks,
then remove 90%
of organisms
Resilience: daily
rate of return to
control biomass
level
Chris Steiner et al., Rutgers Uni. 2006
High productivity, resilience differ little among low, medium and high
diversity
15.6 Communities can switch
between alternative stable states
Resiliency means that a system is able to return to a “reference”
state following a perturbation. Sometimes, however, a system
can have more than one stable reference state.
Predation and prey: upper and lower equilibrium states of prey
population
Stable state: small perturbations are followed by return to the
reference state
Biological community might have multiple stable states:
Two keystone species respond differently to climate change:
Global warming may shift the community to species favors
warming climate
Rainfall  tree grow, dry->fire  grassland community
structure. (shrubland  grassland)
Remove of
organisms in a New
England rocky
intertidal zone
community resulted
in replacement by
one of several
possible new
community
Northern exposure
site dominated by
brown alga
Southern exposure
site by another
barbacle
Replaced original
ones and did not
recover over five
years
15.7 Trophic levels are influenced from
above by predation and from below by
production
The Earth is Green: Hairston, Smith, Slobodkin (1960):
“carnivores depress the population of herbivores that would
otherwise consume most of the vegetation”
Trophic cascade: When the indirect effects of consumer-resource
interactions extend through additional trophic levels of a
community.
Top-down control: when higher trophic levels determine the size
of trophic levels below
Bottom-up control: when the size of trophic level is determined
by the rate of production of its food resource
Trophic structure of a community may be
determined by bottom-up or top-down control
Cases for
bottom-up, topdown control or
both
Mathew Leibold,
Uni. Of Chicago
1997, Survey
Remove or add
herbivore will
influence primary
production
But consumer
production is
related to primary
production
Leibold et al. 1997
Community structure and its response to changes in productivity
depend on the number of trophic levels (Hansson et al. 1998)
Hansson
et al.
Uni. Of
Lund in
Sweden
Tanks
3 or 4
levels
Two
nutrient
conditions
Inorganic
nutrient
Another nice example to demonstrate the
indirect interactions
A tropic cascade from fish
to flowers
Fish have indirect effects on
the populations of several
species in and around
ponds
Knight et al. 2005, Nature
Compared ponds contain
fish compared to ponds
without fish
4 control (no fish)
4 treatment (within fish)
Presence or absence of fish influence dragonfly
density
The presence or
absence of fish also
influence the near
terrestrial communities
Effect on pollinators
Pollinators paid more
visit to a common
plant species that lived
on the edges of ponds
with fish.
Fish have indirect
effects on the
populations of several
species in and around
ponds
The concept of community revisited
Two views of community: organismal (holistic) view and
individualistic (continuum) view
Clements’s Organismal community is a spatial concept: variety
of plant and animal species interacting and influencing the
overall structure
Gleason’s Continuum view is a population concept, focusing on
the response of the component species to the underlying
features of the environment.
An example (demonstrate two views)
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
THE End
Keystone species
Keystone species: a species that has a
disproportionate impact on the community
relative to its abundance.
Remove of keystone species initiates changes
in community structure and results in
significant diversity loss.
Role in community: create or modify habitats,
or influence interactions with others.
Keystone species examples
Coral (Oculina arvbuscula) in the eastern coast
of US
This coral has complex branch and provide
shelter of more than 300 species of
invertebrates
African elephants in the
savannas of southern
Africa
Elephants are destruct
feeders, damage trees,
reduce density of shrubs,
but increase grass
growths.
Change in nutrient level can switch a marine
community between alternate state