Biodiversity, Species Interactions, and Population Control
Southern Sea Otter
Fig. 5-1a, p. 104
5-1 How Do Species Interact?
• The interactions between species in an ecosystem
affect:
• the resource use in an ecosystem and
• population sizes of the species in an ecosystem.
Five types of Interactions
• Interspecific Competition
• Predation
• Parasitism
• Mutualism
• Commensalism
Five types of Interactions
• Interspecific Competition
• Predation
• Parasitism
• Mutualism
• Commensalism
Interspecific Competition
• Species compete for limited resources like
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Water
Food/Nutrients
Light
Habitat/Space
Five types of Interactions
• Interspecific Competition
•Predation
• Parasitism
• Mutualism
• Commensalism
Predation
• Predators may capture prey by
1. Walking
2. Swimming
3. Flying
4. Pursuit and ambush
5. Camouflage
6. Chemical warfare
Predator-Prey Relationships
Fig. 5-4, p. 107
Avoiding Predation
• Prey may avoid capture by
1. Run, swim, fly
2. Protection: shells, bark, thorns
3. Camouflage
4. Chemical warfare
5. Warning coloration
6. Mimicry
7. Deceptive looks
8. Deceptive behavior
(b) Wandering leaf insect
Fig. 5-5b, p. 109
(c) Bombardier beetle
Fig. 5-5c, p. 109
(d) Foul-tasting monarch butterfly
Fig. 5-5d, p. 109
(e) Poison dart frog
Fig. 5-5e, p. 109
(f) Viceroy butterfly mimics monarch
butterfly
Fig. 5-5f, p. 109
(g) Hind wings of Io moth resemble
eyes of a much larger animal.
Fig. 5-5g, p. 109
(h) When touched, snake
caterpillar changes shape to look
like head of snake.
Fig. 5-5h, p. 109
Predator and Prey Interactions Can
Drive Each Other’s Evolution
• Intense natural selection pressures between
predator and prey populations
• Coevolution
• Interact over a long period of time
• Example - Bats and moths: echolocation of bats and
sensitive hearing of moths
Coevolution: A Langohrfledermaus
Bat Hunting a Moth
Fig. 5-6, p. 110
Five types of Interactions
• Interspecific Competition
• Predation
•Parasitism
• Mutualism
• Commensalism
Parasitism
• Parasitism – species feed off other species or live on
or in them
• Parasite is usually much smaller than the host
• Parasite rarely kills the host
• Parasite-host interaction may lead to coevolution
Parasitism: Trout with Blood-Sucking Sea Lamprey
Fig. 5-7, p. 110
Parasitism: Tapeworm in Human Eye
Five types of Interactions
• Interspecific Competition
• Predation
• Parasitism
•Mutualism
• Commensalism
Mutualism
• Mutualism – both species benefit
• Nutrition and protection relationship
• Clownfish and anemone
• Gut inhabitant mutualism
• Bacteria in our intestines
• Not cooperation: it’s mutual exploitation
Mutualism: Hummingbird and Flower
Fig. 5-8, p. 110
Mutualism: Oxpeckers Clean Rhinoceros; Anemones
Protect and Feed Clownfish
Fig. 5-9, p. 111
Five types of Interactions
• Interspecific Competition
• Predation
• Parasitism
• Mutualism
•Commensalism
Commensalism
• Commensalism
• One species benefits, one not
harmed
• Bromeliad (air plant) in tree
• Birds nesting in trees
What Limits the Growth of
Populations?
• No population can continue to grow indefinitely
because of
• limitations on resources and
• competition among species for those resources.
Most Populations Live Together in
Clumps or Patches
• Population: group of interbreeding individuals of the
same species
• Population distribution
1. Clumping (ex. Flocks of birds)
2. Uniform dispersion
3. Random dispersion
Generalized Dispersion Patterns
Fig. 5-12, p. 112
Most Populations Live Together in
Clumps or Patches
• Why clumping?
1.
2.
3.
4.
Species cluster where resources are available
Clumps have a better chance of finding resources
Protects some animals from predators
Packs allow some to get prey
Population of Snow Geese
Fig. 5-11, p. 112
Population Growth and Decline
• Population size governed by
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Births
Deaths
Immigration
Emigration
• Population change =
(births + immigration) – (deaths + emigration)
Population Growth and Decline
• Age structure
• Pre-reproductive age “kids”
• Reproductive age “adults”
• Post-reproductive age “elderly”
• Sizes of each group will drive the growth or decline of
population in the future
• Example: A population with 70% of kids will most
likely have a population growth spike as those kids
become adults
Some Factors Can Limit Population
Size
• Range of tolerance
• Variations in physical and chemical environment that
impact a population’s ability to survive and reproduce
• Temperature, Rain, Nutrients…
Trout Tolerance of Temperature
Fig. 5-13, p. 113
Some Factors Can Limit Population
Size
• Limiting factor principle
• Too much or too little of any physical or chemical
factor can limit or prevent growth of a population,
even if all other factors are at or near the optimal
range of tolerance
“Population can only
grow as much as its
scarcest resource!”
No Population Can Grow Indefinitely:
J-Curves and S-Curves
• Size of populations controlled by limiting factors:
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Light
Water
Space
Nutrients
Exposure to too many competitors, predators or
infectious diseases
No Population Can Grow Indefinitely:
J-Curves and S-Curves
• Environmental resistance
• All factors that act to limit the growth of a population
• Carrying capacity (K)
• Maximum population a given habitat can sustain
• Calculated by looking at the limiting factors
No Population Can Grow Indefinitely:
J-Curves and S-Curves
• Exponential growth
• Starts slowly, then accelerates to carrying capacity
when meets environmental resistance
• Known as “J” curve due to shape
• No limiting factors yet
No Population Can Grow Indefinitely:
J-Curves and S-Curves (3)
• Logistic growth
• Decreased population growth rate as population size
reaches carrying capacity
Yellow line = calculated
theoretical carrying capacity
Green = actual population
Logistic Growth of Sheep in Tasmania
Fig. 5-15, p. 115
When a Population Exceeds Its Habitat’s
Carrying Capacity, Its Population Can Crash
• A population can “briefly” exceed (overshoot) the
area’s carrying capacity due to:
• Reproductive time lag
• If it greatly overshoots the carrying capacity, the
result is:
• Population crash and
• Damage may reduce area’s new carrying capacity
Exponential Growth, Overshoot, and
Population Crash of a Reindeer
Fig. 5-17, p. 116
Species Have Different Reproductive
Patterns
• Some species
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Many, usually small, offspring
Little or no parental care
Massive deaths of offspring
Ex. Insects, bacteria, algae
Species Have Different Reproductive
Patterns
• Other species
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Reproduce later in life
Small number of offspring with long life spans
Young offspring grow inside mother
Long time to maturity
Protected by parents, and potentially groups
Ex. Humans, Elephants
Under Some Circumstances Population
Density Affects Population Size
• Density-dependent population controls
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Predation
Parasitism
Infectious disease
Competition for resources
Several Different Types of Population
Change Occur in Nature
• Stable
• Irruptive
• Population surge, followed by crash
• Cyclic fluctuations, boom-and-bust cycles
• Top-down population regulation
• Bottom-up population regulation
• Irregular
Humans Are Not Exempt from
Nature’s Population Controls
• Ireland
• Potato crop in 1845
• Bubonic plague
• Fourteenth century
• AIDS
• Global epidemic
5-3 How Do Communities and Ecosystems
Respond to Changing Environmental
Conditions?
• Concept 5-3 The structure and species composition
of communities and ecosystems change in response
to changing environmental conditions through a
process called ecological succession.
Communities and Ecosystems Change over
Time: Ecological Succession
• Natural ecological restoration
• Primary succession
• Secondary succession
Some Ecosystems Start from Scratch:
• Primary Succession
• No soil in a terrestrial system or no bottom sediment
in an aquatic system
• Takes hundreds to thousands of years to build up
soils/sediments to provide necessary nutrients
• Ex. – Bare rock after a glacier retreats
Primary Ecological Succession
Fig. 5-19, p. 119
Some Ecosystems Do Not Have to Start from
Scratch
• Secondary Succession
• Some soil remains in a terrestrial system or bottom
sediment remains in an aquatic system
• Ecosystem has been
• Disturbed
• Removed
• Destroyed
• Ex – old farmland, forest fires
Natural Ecological Restoration of Disturbed Land
Fig. 5-20, p. 120
Secondary Ecological Succession in Yellowstone Following
the 1998 Fire
Fig. 5-21, p. 120
Some Ecosystems Do Not Have to Start from
Scratch: Secondary Succession (2)
• Primary and secondary succession
• Tend to increase biodiversity
• Increase species richness and interactions among species
• Primary and secondary succession can be interrupted by
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Fires
Hurricanes
Clear-cutting of forests
Plowing of grasslands
Invasion by nonnative species
Science Focus: How Do Species Replace One
Another in Ecological Succession?
• Facilitation
• Inhibition
• Tolerance
Succession Doesn’t Follow a
Predictable Path
• Traditional view
• Balance of nature and a climax community
• Current view
• Ever-changing mosaic of patches of vegetation
• Mature late-successional ecosystems
• State of continual disturbance and change
Living Systems Are Sustained through
Constant Change
• Inertia, persistence
• Ability of a living system to survive moderate
disturbances
• Resilience
• Ability of a living system to be restored through
secondary succession after a moderate disturbance
• Some systems have one property, but not the other:
tropical rainforests
Three Big Ideas
1. Certain interactions among species affect their use
of resources and their population sizes.
2. There are always limits to population growth in
nature.
3. Changes in environmental conditions cause
communities and ecosystems to gradually alter
their species composition and population sizes
(ecological succession).