Biodiversity, Species Interactions,
and Population Control
Chapter 5
Core Case Study: Southern Sea Otters: Are
They Back from the Brink of Extinction?
 Habitat
 Hunted: early 1900s
 Partial recovery by the late 2007
 Why care about sea otters?
• Ethics
• Keystone species (Eat sea Urchins)
• Tourism dollars
Science Focus: Why Should We Care
about Kelp Forests?
 Kelp forests: one of the most biologically diverse
marine habitat
• One blade of kelp can grow 2 feet in a single day
 Major threats to kelp forests
• Sea urchins
• Pollution from water run-off
• Global warming (changing of the water’s
temp)
Species Interact in Five Major Ways
 Interspecific Competition: over same resources
 Predation
 Parasitism:
• one gains, one loses (not always death)
 Mutualism: both gain
 Commensalism: one gains, the other gets no
benefits
Most Species Compete with One Another
for Certain Resources
 Competition for same limited resources
(food, shelter, space)
 Competitive exclusion principle: no 2
species can occupy exactly the same
ecological niche for very long
Most Consumer Species Feed on Live
Organisms of Other Species (1)
 Predators may capture prey by
• Walking
• Swimming
• Flying
• Pursuit and ambush
• Camouflage
• Chemical warfare
Most Consumer Species Feed on Live
Organisms of Other Species (2)
 Prey may avoid capture by
• Camouflage
• Chemical warfare
• Warning coloration
• Mimicry
• Deceptive looks
• Deceptive behavior
Some Ways Prey
Species Avoid
Their Predators
(a) Span worm
(c) Bombardier beetle
(e) Poison dart frog
(g) Hind wings of Io moth
resemble eyes of a much
larger animal.
(b) Wandering leaf insect
(d) Foul-tasting monarch butterfly
(f) Viceroy butterfly mimics
monarch butterfly
(h) When touched,
snake caterpillar changes
shape to look like head of snake.
Stepped Art
Fig. 5-2, p. 103
Predator and Prey Species Can Drive
Each Other’s Evolution
 Intense natural selection pressures between
predator and prey populations
 Coevolution
Some Species Feed off Other Species by
Living on or in Them
 Parasitism
 Parasite-host interaction may lead to coevolution
 Host’s point of view: parasites bad
 Population level POV: promote biodiversity,
keep populations in check
In Some Interactions, Both Species
Benefit
 Mutualism
 Nutrition and protection relationship
 Gut inhabitant mutualism: vast armies of
bacteria, break down food
 How is a Cow like a termite?
 Cooperation between species?
In Some Interactions, One Species
Benefits and the Other Is Not Harmed
 Commensalism
 Epiphytes
 Birds nesting in trees
 Army ants and silverfish
5-2 How Can Natural Selection Reduce
Competition between Species?
 Concept 5-2 Some species develop
adaptations that allow them to reduce or avoid
competition with other species for resources.
Some Species Evolve Ways to Share
Resources
 Resource partitioning
 Reduce niche overlap, increase species
diversity
 Use shared resources at different
• Times
• Places
• Ways
Competing Species Can Evolve to
Reduce Niche Overlap
Sharing the Wealth: Resource Partitioning
Blackburnian
Warbler
Black-throated
Green Warbler
Cape May
Warbler
Bay-breasted
Warbler
Yellow-rumped
Warbler
Stepped Art
Fig. 5-8, p. 107
Fruit and seed eaters
Insect and nectar eaters
Greater Koa-finch
Kuai Akialaoa
Specialist
Species of
Honeycreepers
Amakihi
Kona Grosbeak
Crested Honeycreeper
Akiapolaau
Maui Parrotbill
Apapane
Unkown finch ancestor
Fig. 5-9, p. 108
Honey creepers on Hawaii

Evolved into different species, each
concentrating on different food resources

Evolutionary divergence-speciation
5-3 What Limits the Growth of
Populations?
 Concept 5-3 No population can continue to
grow indefinitely due to:
• limitations on resources
• competition among species for those resources.
Populations Have Certain
Characteristics (1)
 Populations differ in
• Distribution
• Numbers
• Age structure
 These values are Population dynamics
Populations Characteristics can change
 due to:
• Temperature change
• Presence of disease, organisms or harmful
chemicals
• Resource availability
• Arrival or disappearance of competing species
Most Populations Live Together in
Clumps or Patches (1)
 Different types of population distribution:
• Clumping
• Uniform dispersion (what would cause this?)
• Random dispersion (what would cause this?)
Most Populations Live Together in
Clumps or Patches (2)
 Why clumping?
• Species tend to cluster where resources are
available
• Groups have a better chance of finding clumped
resources
• Herds protect some animals from predators
• Packs allow some predators to get prey
• Temporary groups for mating and caring for
young
Populations Can Grow, Shrink, or
Remain Stable (1)
 Population size governed by
•
•
•
•
Births
Deaths
Immigration
Emigration
 Population change =
(births + immigration) – (deaths + emigration)
Populations Can Grow, Shrink, or
Remain Stable (2)
 Age structure
• Pre-reproductive age
• Reproductive age (if greatest %, greatest growth)
• Post-reproductive age
Excluding emigration/immigration, a population
that has an even distribution amongst the groups
will remain stable.
Population Growth
Rates
 Biotic potential: capacity for pop growth
• Low (elephants, whales)
• High (insects and bacteria)
 Intrinsic rate of increase (r)
• Steepness of curve
 Individuals in populations with high r
•
•
•
•
Reproduce early in life
Have short generation times (adaptable)
Can reproduce many times
Have many offspring each time they reproduce
Environmental resistance
 Environmental resistance:
• Combo of all factors which limit growth
 Size of populations limited by
•
•
•
•
•
Light
Water
Space
Nutrients
Exposure to too many competitors, predators or
infectious diseases
No Population Can Grow Indefinitely:
J-Curves and S-Curves (3)
 Carrying capacity (K)
• Max population sustained
indefinitely
 Exponential growth (j-curve)
• (even 1-2% growth is
exponential)
 Logistic growth (s-curve)
• Rapid growth followed by
leveling off
The first part of any population graph
should be a J
As population nears carrying capacity,
graph should change into an s-curve
No Population Can Continue to Increase
in Size Indefinitely
When a Population Exceeds Its Habitat’s
Carrying Capacity, Its Population Can Crash
 Carrying capacity: not fixed, dependent on
environmental factors (food, conditions)
 Reproductive time lag may lead to overshoot
• Dieback (crash)
 Overshoot Damage may reduce area’s carrying
capacity
Genetic Diversity Can Affect the size,
success of Small Populations
 Founder effect: few individuals start new colony
 Demographic bottleneck: few individuals survive
catastrophe
 Genetic drift: random changes to gene frequencies in
pop that lead to unequal reproductive success
 Inbreeding: increase of defective genes in small pop
 Use above to estimate minimum viable population
size
Population Density and Population Size
 Density independent pop controls
• Mostly abiotic like weather, forest fires…
 Density-dependent population controls
•
•
•
•
Predation
Parasitism
Infectious disease
Competition for resources
5-4 How Do Communities and Ecosystems
Respond to Changing Environmental
Conditions?
 Concept 5-4 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
• Starts from bare rock
• Secondary succession
• Does not start from bare rock
• New home construction (why?)
Some Ecosystems Start from Scratch:
Primary Succession
 No soil in a terrestrial system
 No bottom sediment in an aquatic system
 Early successional plant species, pioneer
 Midsuccessional plant species
 Late successional plant species
Primary Ecological Succession
Lichens and
Exposed mosses
rocks
Small herbs
and shrubs
Heath mat
Balsam fir,
paper birch, and
Jack pine,
black spruce, white spruce
forest community
and aspen
Fig. 5-16, p. 116
Some Ecosystems Do Not Have to Start
from Scratch: Secondary Succession (1)
 Some soil remains in a terrestrial system
 Some bottom sediment remains in an aquatic
system
 Ecosystem has been
• Disturbed
• Removed
• Destroyed
Natural Ecological
Restoration of Disturbed
Land (secondary)
Annual
weeds
Perennial
weeds and
grasses
Shrubs and
small pine
seedlings
Young pine forest
with developing
understory of oak
and hickory trees
Mature oak and
hickory forest
Fig. 5-17, p. 117
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
•
•
•
•
•
Fires
Hurricanes
Clear-cutting of forests
Plowing of grasslands
Invasion by nonnative species
Factors that affect the rate of succession
 Facilitation:
• one set of species makes area makes area
suitable for following species, less for
themselves (mosses/lichens and grasses)
 Inhibition:
• hinder establishment and growth of species
ex: pine trees
 Tolerance:
• unaffected by plants in earlier stages (mature
trees vs shade plants)
Succession Doesn’t Follow a
Predictable Path
 Traditional view
• Balance of nature and a climax community
• Achieves equilibrium
 Current view
• Succession Doesn’t follow a predictable path
• Ever-changing mosaic of patches of vegetation
• Mature late-successional ecosystems
• State of continual disturbance and change, not
permanent equilibrium
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
 Tipping point