Biodiversity,
Species
Interactions,
and Population
Control
Chapter 5
This Chapter is divided into
4 main concepts
• 5-1 How Do Species Interact?
• 5-2 How Can Natural Selection Reduce
Competition between Species?
• 5-3 What Limits the Growth of
Populations?
• 5-4 How Do Communities and
Ecosystems Respond to Changing
Environmental Conditions?
Core Case Study:
Southern Sea
Otters: Are They
Back from the Brink
of Extinction?
• Habitat
• Hunted: early
1900s
• Partial recovery
• Why care about
sea otters?
– Ethics
– Keystone
species
– Tourism
dollars
5-1 How Do Species Interact?
• Concept 5-1 Five types of
species interactions—
competition, predation,
parasitism, mutualism,
and commensalism—
affect the resource use
and population sizes of
the species in an
ecosystem.
Most Species Compete with One
Another for Certain Resources
• Competition-for limited
resources
• Most competition involves one
species becoming more
efficient at obtaining resources
than another species.
Greater the overlap
=more competition
Competitive Exclusion Principle
Gause’s Law (Gause’s Principle)
• Some species share their niche, but no
two species can occupy exactly the
same niche for very long.
• This causes both species to have
limited resources.
• One (or both) species must change
their niche (if possible)
P. Caudatum
are
outcompeted,
they die.
Most Consumer Species Feed on Live
Organisms of Other Species
• Predators may
capture prey by
–
–
–
–
Walking
Swimming
Flying
Pursuit and
ambush
– Camouflage
– Chemical warfare
• Prey may avoid
capture by
–
–
–
–
–
–
Camouflage
Chemical warfare
Warning coloration
Mimicry
Deceptive looks
Deceptive behavior
Some Ways Prey Species Avoid Their Predators
•
http://www.teachersdomain.org/asset/tdc02_vid_defense/
Science Focus: Why Should We Care
about Kelp Forests?
Kelp forests: biologically
diverse marine habitat
• Major threats to kelp forests
– Sea urchins
– Pollution from water run-off
– Global warming
Predator and Prey Species Can
Drive Each Other’s Evolution
• Predator and prey populations exert intense
natural selection pressures on one another
• Prey develop traits that make them harder to
catch...predators face selection pressures that
favor traits to catch prey
Coevolution: Populations of two species
interact and exert selective pressure forcing
species to adapt. EX: Caribbean crab/snail and
bats/moths (moths can hear the ultrasonic hunting
calls of the bat)
• Remember, coevolution is an example
of populations responding to changes
in environmental conditions.
• Species cannot design strategies to
increase their chances of survival.
»
Some Species Feed off Other
Species by Living on or in Them
• PARASITISM
• EX: tapeworms, mosquitoes,
mistletoe plants,
sea lampreys, ticks,
and cowbirds
• Parasite-host interaction
may lead to coevolution- nature’s way of
controlling populations and biodiversity
Parasitism
Tree with Parasitic Mistletoe
Trout with Blood-Sucking
Sea Lampreys
In Some Interactions, Both Species
Benefit
• Mutualism
• Nutrition and protection relationship
• Gut inhabitant mutualism
In Some Interactions, One Species
Benefits and the Other Is Not Harmed
• Commensalism
• Epiphytes(take no nutrients
from the tree EX: mosses, ferns,
orchids)
• Birds nesting in trees
Bromeliad on Tree
Symbiosis
• Symbiosis and coevolution
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.
How Can Natural Selection Reduce
Competition between Species?
• Resource partitioning
• Reduce niche overlap
• Use shared resources
at different
– Times
– Places
– Ways
Sharing the Wealth:
Resource Partitioning
Specialist
Species of
Honeycreepers
(an example of
evolutionary
divergence)
5-3 What Limits the Growth of
Populations?
• Concept 5-3 No population
can continue to grow
indefinitely because of
limitations on resources
and because of competition
among species for those
resources.
What Limits the Growth of Populations?
• Populations differ in
–
–
–
–
Distribution
Numbers
Age structure
Density
• Population dynamics: how populations change in
response to changes in environmental conditions.
• Changes in population characteristics due to:
–
–
–
–
Temperature
Presence of disease organisms or harmful chemicals
Resource availability
Arrival or disappearance of competing species
Most Populations Live Together in
Clumps or Patches
• Look at how populations
are distributed or
dispersed
– Clumping
– Uniform dispersion
– Random dispersion-pretty
rare
Dispersion Patterns
• Random
(smaller
plants)
• Clumping
(flocks)
• Uniform
(trees)
Why clumping?
– Species tend to cluster where resources
are available
– Groups have a better chance of finding
clumped resources
– Protects some animals from predators
– Packs allow some to get prey
– Temporary groups for mating and caring
for young
Populations
• Can Grow, Shrink, or Remain Stable
–
–
–
–
Births
Deaths
Immigration
Emigration
• Age structure: proportion of individuals at
various ages
– Pre-reproductive age
– Reproductive age
– Post-reproductive age
No Population Can Grow Indefinitely
• Biotic potential -capacity for population
growth under ideal conditions
– Low…Large animals like elephants
– High… Small organisms like insects
• Intrinsic rate of increase (r)- population
growth with unlimited resources
• Individuals in populations with high r
–
–
–
–
Reproduce early in life
Have short generation times
Can reproduce many times
Have many offspring each time they reproduce
Limiting Factors
• Size of populations limited by:
– Light
– Water
– Space
– Nutrients
– Exposure to too many competitors, predators
or infectious diseases
– There are always limits to population
growth in nature….Sustainability!!!
• Environmental resistance: combination
of all factors that limit the growth of a
population
• Carrying capacity (K)= Biotic Potential
+ Environmental resistance
• Exponential growth-J Curve
• Logistic growth-S Curve
Limiting factors!!
When a Population Exceeds Its Habitat’s
Carrying Capacity, Its Population Can Crash
• Carrying capacity: not fixed…can change
during seasons or years
• Reproductive time lag may lead to overshoot
– Dieback (crash)-time needed for birth rate to
fall and death rate to rise in response to
resource overconsumption
• Damage may reduce area’s carrying
capacity. Ex overgrazing
Exponential Growth, Overshoot, and
Population Crash of a Reindeer
Moose and Wolf Population on Isle Royale
• http://vicksta.com/wolf%20and%20moose
%20graph7.html
Different Reproductive Patterns
• r-Selected species, opportunists
– Capacity for high rate of population
increase
– ex. Small, lots of offspring, no parental
care
• K-selected species, competitors
– Reproduce later in life, small # of
offspring, long life span
– Large mammals, birds of prey
Positions of r- and K-Selected Species on
the S-Shaped Population Growth Curve
GROSS!!!!
Genetic Diversity Can Affect the Size
of Small Isolated Populations
• Founder effect -colonize new habitat, limits genetic
diversity
• Demographic bottleneck- only a few survive a catastrophe
such as a fire. Limits gene pool
• Genetic drift- Random changes in gene pool - certain
individuals breed more than others and their genes
dominate gene pool (founder effect is one cause)
• Inbreeding- Individuals in a small population mate with one
another. Can occur due to a demographic bottleneck. Can
increase frequency of defective genes.
Minimum viable population size- # of individuals needed
for long term survival of the population – important when
studying endangered species.
Population Density Can Affect
Population Size
• Density-dependent population controls
– Predation
– Parasitism
– Infectious disease
– Competition for resources
• Density-Independent
– Floods, hurricanes, extreme temperatures,
drought, fire, pollution, habitat destruction
Patterns of Variation in
Population Size
• Stable- slight fluctuations in carrying
capacity
• Irruptive- High peak then crash to stable
lower level (ex: seasonal changes-die in
winter)
• Cyclic fluctuations (boom-and-bust cycles)
regular cycles of population
– Top-down population regulation
– Bottom-up population regulation
• Irregular – severe weather?
Cyclic fluctuations for the
Snowshoe Hare and Canada
Lynx
Humans Are Not Exempt from Nature’s
Population Controls
• Ireland
– Potato crop in 1845, 1 million people died, 3 million
migrated
• Bubonic plague (Cats of Borneo!!)
– Fourteenth century, 25 million killed
• AIDS
– Global epidemic, 25 million killed between 1981 and
2007
Case Study: Exploding White-Tailed Deer
Population in the U.S.
• 1900: deer habitat destruction and
uncontrolled hunting
• 1920s–1930s: laws to protect the deer
• Eliminated the predators
• Current population explosion for deer
– Lyme disease
– Deer-vehicle accidents
– Eating garden plants and shrubs
• Ways to control the deer population
SOMETHING TO THINK ABOUT…
• Are the deer to blame
for invading farms and
yards/gardens?
OR
Are people to blame for
eliminating the predators
and moving into the deer’s
habitat?
Counting Populations
• See interactive of mark and recapture
of butterflies (Miller ppt)
• Random sampling
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 • Natural ecological
restoration
Ecosystems
– Primary
Change over
succession
Time: Ecological
– Secondary
Succession
succession
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
• Occurs very slowly!
Primary
Ecological
Succession
Secondary Succession
• 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 Succession
Some Ecosystems Do Not Have to Start
from Scratch: Secondary Succession
• Both 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 HOW AND AT WHAT RATE
SUCCESSION OCCURS
1- facilitation- one set of species makes an area
suitable for another, but less suitable for itself. EX:
mosses/lichen break up soil which enables grasses
to come in and crowd them out.
2- inhibition- when some early species hinder the
growth of others. Plants may release toxins –
succession halted until area is disturbed.
3- tolerance- late successional plants are unaffected
by plants at earlier stages because they are not in
direct competition.
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
• Mt St Helens succession (10 min)
Living Systems Are Sustained
through Constant Change
• Inertia, persistence
– Ability of a living system to survive moderate
disturbances. (grasslands/fire low persistence,
rainforest high persistence due to high biodiversity)
• Resilience
– Ability of a living system to be restored through
secondary succession after a moderate disturbance
(grasslands and fire-high resilience, rainforest low
resilience if cut down)
• Tipping point- when you have passed the point of
no return- an irreversible point)
Core Case Study:
Southern Sea
Otters: Are They
Back from the
Brink of
Extinction?
• Habitat
• Hunted: early
1900s
• Partial
recovery
• Why care
about sea
otters?
– Ethics
– Keystone
species
– Tourism
dollars
Why Are
Protected Sea
Otters Making a
Slow
Comeback?
• Low biotic potential
• Prey for orcas
• Cat parasites
• Thorny-headed worms
• Toxic algae blooms
• PCBs and other toxins
• Oil spills
Population Size of Southern Sea Otters
Off the Coast of So. California (U.S.)
• http://www.teachersdomain.org/asset/tdc0
2_vid_arctic/