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Community and Population
Ecology
Chapter 6
Good Morning!
Place your portfolio containing your
paper and sources on the front table
and then sign in using the red pen.
Why Should We Care about the American
Alligator?
Fig. 6-1, p. 108
Core Case Study: American Alligator
 Highly adaptable
 Only natural predator is humans
 1967 – endangered species list
 Successful environmental comeback
 Keystone species
6-1 How Does Species Diversity Affect
the Sustainability of a Community?
 Concept 6-1 Species diversity is a major
component of biodiversity and tends to increase
the sustainability of communities and
ecosystems.
Species Diversity
 Species richness combined with species
evenness
 Niche structure
 Varies with geographic location
 Species richness declines towards poles
Sustainability and Environmental Change
 Inertia or persistence
 Constancy
 Resilience
Science Focus: Community Sustainability
 No certain definition of sustainability
 Do communities need high inertia and high
resilience?
 Communities may have one but not the other
 Equilibrium is rare
Richness and Sustainability
 Hypotheses
• Does a community with high species richness
have greater sustainability and productivity?
• Is a species-rich community better able to recover
from a disturbance?
 Research suggests “yes” to both
6-2 What Roles Do Species Play in a
Community?
 Concept 6-2 Based on certain ecological roles
they play in communities, species are described
as native, nonnative, indicator, keystone, or
foundation species.
Ecological Niche
 Species occupy unique niches
 Native species – those normally found living
and thriving in a particular community
Spanish moss in the south
 Nonnative species – plants, animals, fungi
• Spread in new, suitable niches
Deliberately Introduced Species
Purple looselife
European starling
Marine toad
Water hyacinth
African honeybee
(“Killer bee”)
Japanese beetle
Nutria
Hydrilla
Salt cedar
(Tamarisk)
European wild boar
(Feral pig)
Fig. 9-11a, p. 193
http://dnr.wi.gov/invasiveS/fact/loosestrife.htm
http://www.npwrc.usgs.gov/resource/plants/loosstrf/index.htm
http://www.maxshores.com/kudzu/
Kudzu
Fig. 9-12, p. 194
http://aaabeeremoval.com/photogallery_africanbeeswarm.htm
http://www.invasivespeciesinfo.gov/animals/afrhonbee.shtml
http://www.desertusa.com/mag98/sep/stories/kbees.html
Accidentally Introduced Species
Sea lamprey
(attached to lake trout)
Formosan termite
Argentina fire ant
Zebra mussel
Brown tree snake
Asian long-horned
beetle
Eurasian muffle
Common pigeon
(Rock dove)
Asian tiger mosquito
Gypsy moth larvae
Fig. 9-11b, p. 193
Indicator Species
 Early warning system – tell about harmful
changes in biological communities
 Birds – found everywhere; affected by habitat
problems including pesticides
 Butterflies – associate with various plant species
becoming vulnerable to habitat loss
 Amphibians – multiple reasons; complex and
interacting
Case Study: Why Are Amphibians
Vanishing? (1) – See latest article
 Habitat loss and fragmentation
 Prolonged drought
 Pollution
 Ultraviolet radiation
 Parasites - chytrid fungi
Life Cycle of a Frog
Young frog
Adult frog
(3 years)
sperm
Tadpole develops into
frog
Sexual
reproduction
Eggs
Fertilized egg
development Organ formation
Tadpole
Egg hatches
Fig. 6-3, p. 112
Case Study: Why Are Amphibians
Vanishing? (2)
 Viral and fungal diseases
 Climate change
 Overhunting
 Nonnative predators and competition
 Why we should care
Keystone Species
 Significant role in their food web
 Elimination may alter structure, function of
community
 Pollinators
 Top predators
Foundation Species
 Create habitats and ecosystems
 Beavers
 Elephants
 Seed dispersers
http://www.morning-earth.org/Graphic-E/Interliv-Two.html
great overview
http://www.naturehaven.com/elephantbottom.html Elephant site
Science Focus: Why Should We
Protect Sharks?
 Remove injured, sick animals
 Many are gentle giants
 Provide potential insight into cures for human
diseases
 Keystone species
6-3 How Do Species Interact?
 Concept 6-3A Five basic species interactions –
competition, predation, parasitism, mutualism,
and commensalism – affect the resource use
and population sizes of the species in a
community.
 Concept 6-3B Some species develop
adaptations that allow them to reduce or avoid
competition for resources with other species.
Interspecific Competition
 No two species can share vital limited resources
for long
 Resolved by:
•
•
•
•
Migration
Shift in feeding habits or behavior
Population drop
Extinction
 Intense competition leads to resource
partitioning
Resource Partitioning of Warbler Species
Fig. 6-5, p. 115
Number of individuals
Resource Partitioning and Niche
Specialization
Species 1
Species 2
Region
of
niche overlap
Number of individuals
Resource use
Species 1
Species 2
Resource use
Fig. 6-4, p. 1
Predation
 Predator-prey relationship
 Predators and prey both benefit – individual vs.
population
 Predator strategies
 Prey strategies
How Species Avoid Predators
Span worm
Wandering leaf insect
Poison dart frog
Viceroy butterfly mimics
monarch butterfly
Bombardier beetle
Hind wings of io moth
resemble eyes of a
much larger animal
Foul-tasting monarch
butterfly
When touched, the
snake caterpillar
changes shape to look
like the head of a snake
Fig. 6-6, p. 116
Parasitism
 Live in or on the host
http://mybloatingrelief.com/parasites/
 Parasite benefits, host harmed
 Parasites promote biodiversity
 http://www.youtube.com/watch?v=rLtUk-W5Gpk
 http://www.morning-earth.org/Graphic-E/InterlivTwo.html
Mutualism
 Everybody benefit by unintentional exploitation
 Nutrition and protection
 Gut inhabitant mutualism
Examples of Mutualism
Oxpeckers and black rhinoceros
Mycorrhizae fungi on juniper
seedlings in normal soil
Clown fish and sea anemone
Lack of mycorrhizae fungi on
juniper seedlings in sterilized soil
Commensalism
 Benefits one with little impact on other
 Bromeliad
6-4 How Do Communities Respond to
Changing Environmental Conditions?
 Concept 6-4A The structure and species
composition of communities change in response
to changing environmental conditions through a
process called ecological succession.
 Concept 6-4B According to the precautionary
principle, we should take measures to prevent or
reduce harm to human health and natural
systems even if some possible cause-and-effect
relationships have not been fully established
scientifically.
Ecological Succession
 Primary succession
 Secondary succession
 Disturbances create new conditions
 Intermediate disturbance hypothesis
 Ecological
succession
Ecological Succession
Exposed
rocks
Lichens
and
mosses
Small herbs and shrubs
Jack pine,
black spruce,
and aspen
Balsam fir, paper
birch, and white
spruce climax
community
1. It is an orderly process of COMMUNITY development; it
normally proceeds in a predictable, orderly direction; it
represents the gradual replacement of populations by
others that are better adapted to the existing
conditions.
2. It results from modification of the physical environment
by the populations that interact to makeup the
community thus, succession is community controlled;
the physical factors of the environment and climate
determine the pattern and the rate of change; the
climate and immediate environment often set the limit
as to how far development can proceed
Fig. 6-9, p. 119
3. The end result of succession is a stabilized ecosystem
which is in balance with the climate and environment of the
area; under these conditions the maximum number of
organisms (biomass) and their symbiotic (nutritional)
interactions are balanced or maintained with the energy
available to the system.
Thus, the strategy of succession as a short term process is
very much like the strategy of long-term evolutionary
development of the biosphere. It results in HOMEOSTATIC
balance of organisms with the physical environment WITH
THE BENEFIT of achieving a means of effectively dealing
with the constant changes or pertubations presented by the
environment.
The Strategy of Ecosystem Development, Eugene P. Odum
Science 18 April 1969: Vol. 164. no. 3877, pp. 262 - 270
Primary Ecological Succession
Lichens
Exposed
and mosses
rocks
Small herbs
and shrubs
Heath mat
Jack pine,
black spruce,
and aspen
Balsam fir, paper
birch, and white
spruce climax
community
Fig. 6-9, p. 119
Secondary Ecological Succession
Annual
weeds
Perennial
weeds and
grasses
Shrubs
and pine
seedlings
Young pine forest with
developing understory
of oak and hickory
trees
Mature oak-hickory forest
Fig. 6-10, p. 120
Succession’s Unpredictable Path
 Successional path not always predictable toward
climax community
 Communities are ever-changing mosaics of
different stages of succession
 Continual change, not permanent equilibrium
Precautionary Principle
 Lack of predictable succession and equilibrium
should not prevent conservation
 Ecological degradation should be avoided
 Better safe than sorry
6-5 What Limits the Growth of
Populations?
 Concept 6-5 No population can continue to
grow indefinitely because of limitations on
resources and because of competition among
species for those resources.
Population Distribution
 Clumping – most populations
 Uniform dispersion
 Random dispersion
 http://www.biology.iupui.edu/biocourses/n100/im
ages/39dist.gif
Why Clumping?
 Resources not uniformly distributed
 Protection of the group
 Pack living gives some predators greater
success
 Temporary mating or young-rearing groups
Populations Sizes Are Dynamic
 Vary over time
population = (births + immigration) - (deaths + emigration)
 Age structure
• Pre-reproductive stage
• Reproductive stage
• Post-reproductive stage
Limits to Population Growth (1)
 Biotic potential is idealized capacity for growth
 Intrinsic rate of increase (r)
 Nature limits population growth with resource
limits and competition
 Environmental resistance
Population Growth Curves
Population size (N)
Environmental
resistance
Carrying capacity (K)
Biotic
potential
Exponential
growth
Time (t)
Limits to Population Growth (1)
 Carrying capacity – biotic potential and
environmental resistance (Number of individuals of a
given species that can be sustained indefinitely in a
given area)
 Exponential growth - logarithmic increase
 Logistic growth – exponential growth followed by
steady decrease over time until population size
levels off. Due to population meeting environmental
resistance and approaching carrying capacity
Number of sheep (millions)
Logistic Growth of Sheep Population
2.0
Overshoot
Carrying Capacity
1.5
1.0
.5
1800
1825
1850
1875 1900
Year
1925
Fig. 6-12, p. 121
Overshoot and Dieback
 Population does not transition smoothly from
exponential to logistic growth
 Overshoot carrying capacity of environment
 Caused by reproductive time lag
 Dieback, unless excess individuals switch to
new resource
Number of reindeer (millions)
Exponential Growth, Overshoot and
Population Crash of Reindeer
Population
Overshoots
Carrying
Capacity
2,000
Population
crashes
1,500
1,000
500
Carrying capacity
0
1910
1920
1930
Year
1940
1950
Fig. 6-13, p. 122
Different Reproductive Patterns
 r-Selected species
• High rate of population increase
• Opportunists
 K-selected species
• Competitors
• Slowly reproducing
 Most species’ reproductive cycles between two
extremes
Humans Not Exempt from Population
Controls
 Bubonic plague (14th century) – Ebola like
symptoms
 Famine in Ireland (1845) – led to emigration to
the United States (through 1848)
 AIDS – major player in population decline
 Technology, social, and cultural changes
extended earth’s carrying capacity for humans
 Expand indefinitely or reach carrying capacity?
Case Study: Exploding White-tailed Deer
Populations in the United States
 1900: population 500,000
 1920–30s: protection measures
 Today: 25–30 million white-tailed deer in U.S.
 Conflicts with people living in suburbia