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BIODIVERSITY, SPECIES
INTERACTIONS, AND
POPULATION CONTROL
Chapter 5
CORE CASE STUDY: SOUTHERN SEA OTTERS: ARE
THEY BACK FROM THE BRINK OF EXTINCTION?
 Habitat
 Live in giant kelp forests (California, West Coast)
 Prey on many kelp-eating shellfish
 Hunted: early 1900s
 Fur traders
 Competition with local shell-fisherman
 Partial recovery (still endangered, though)
 FWS declared endangered, numbers grew from 50 to 2,654
 Why care about sea otters?
 Ethics
 Tourism dollars
 Keystone species
 Control population of shellfish that would otherwise exploit the
kelp forests
SOUTHERN SEA OTTER
Fig. 5-1a, p. 104
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.
SPECIES INTERACT IN FIVE MAJOR WAYS
 Interspecific Competition- members of different species
compete for resources
 Predation-one species feeds directly on another
Symbiotic Interactions
 Parasitism-one species uses a another as a host to gain
nutrients in a way that it harms the host. Usually on or
in the host
 Mutualism- interactions between two different species
in which both species benefit from each other
 Commensalism- interaction between 2 species where
one species benefits and the other is neither helped
nor harmed (neutral)
MOST SPECIES COMPETE WITH ONE
ANOTHER FOR CERTAIN RESOURCES
 Competition:
 Actual fighting
 Mostly one species becoming more efficient at gaining
resources
 Remember every species occupies a special ecological
niche
 Some niches overlap
 When they both require the same resources
 The greater amount of shared resources, the more intense
competition
OVERLAPPING NICHES RESULT IN…
When one species is much more efficient at
obtaining resources, the other must either:




Move (if possible)
Alter (reduce or shift) its niche through natural
selection
Suffer population decline
Become extinct
SOME SPECIES EVOLVE WAYS TO SHARE
RESOURCES
 Resource partitioning
 Using only parts of resource
 Using at different times
 Using in different ways
These different species of birds feed on different parts of the spruce tree to
partition their resources. Some feed on different insect species
Black burnian
Warbler
Black-throated
Green Warbler
Cape May
Warbler
Bay-breasted
Warbler
Yellow-rumped
Warbler
Fig. 5-2, p. 106
SPECIALIST SPECIES OF HONEYCREEPERS
Honeycreepers of
Hawaii descended
from one
common
ancestor, now
have
differentiated in
beak shapes to
partition their
resources
Fig. 5-3, p. 107
MOST CONSUMER SPECIES FEED ON LIVE
ORGANISMS OF OTHER SPECIES
 Predators capture prey several ways
 Herbivores:
 Swim, walk, fly up to plants they feed on
 Carnivores:
 2 options: pursuit and ambush
 Cooperative hunting: pack of lions hunting giraffes
 Camouflage:
 Hide in plain sight and ambush
 Examples: praying mantis, snowy owls
 Chemical warfare:
 Poisonous snakes and spiders (examples)
PREDATOR-PREY RELATIONSHIPS
Fig. 5-4, p. 107
PREY SPECIES HAVE EVOLVED WAYS TO
AVOID PREDATORS
 Exceptional ability to run, swim, fly away
 Highly developed senses (sight and smell)
 Protective physical features:
 Shells
 Thick bark
 Spines
 Thorns
 Lizard tails
 Break off when attacked and give extra time to escape
PREY SPECIES HAVE EVOLVED WAYS TO
AVOID PREDATORS
 Camouflage
 Chemical Warfare




Poison
Irritants
Foul-smelling, bad tasting
Squids, octopus emit ink clouds to confuse predators
 Warning coloration
 Mimicry
 Non-harmful prey that mimic more risky prey
 Ex. The Viceroy butterfly looks and acts like monarch which is
poisonous
 Deceptive looks and behavior
 Moths, blow fish
(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. 5-5, p. 109
SCIENCE FOCUS: THREATS TO KELP
FORESTS
 Kelp forests: biologically diverse marine habitat
 Extract the substance algin from kelp for use as a
renewable resource
 Used in toothpaste, cosmetics, ice-cream, and more
 Major threats to kelp forests
1. Sea urchins- feed on kelp
2. Pollution from water run-off
3. Global warming
PURPLE SEA URCHIN
Fig. 5-A, p. 108
PREDATOR AND PREY INTERACTIONS
CAN DRIVE EACH OTHER’S EVOLUTION
 Intense natural selection pressures between predator
and prey populations
 Both prey and predator evolve adaptations to survive
 Coevolution
 Definition: when two species interact with each other over a
long period of time, changes in the gene pool of one species
can lead to changes in the gene pool of the other species.
 Interact over a long period of time
 Bats and moths: echolocation of bats and sensitive hearing of
moths
COEVOLUTION: A LANGOHRFLEDERMAUS
BAT HUNTING A MOTH
Fig. 5-6, p. 110
SOME SPECIES FEED OFF OTHER SPECIES
BY LIVING ON OR IN THEM
 Parasitism
 Parasite is usually much smaller than the host
 Parasite rarely kills the host
 Mostly draw nourishment from host and gradually weaken
them over time
 Parasites may have a negative reputation, but they
never-the-less add to species biodiversity
 May live inside or outside host
 Examples: tapeworms, ticks, sea lampreys, fleas,
mistletoe plants
PARASITISM: TROUT WITH BLOOD-SUCKING SEA
LAMPREY
Fig. 5-7, p. 110
MUTUALISM
 Two interacting species benefit each other by doing so
 Examples:
 Bees/butterflies/mosquitos/hummingbirds and flowering
plants (pollination)
 Clownfish and sea anenomes
 Oxpeckers and black rhinoceros
 Gut inhabitant mutualism: beneficial bacteria in digestive
systems
 Note: mutualism is not a cooperative agreement.
 Unintentional benefit by exploiting each other
 Each species is in it for themselves
MUTUALISM: OXPECKERS CLEAN RHINOCEROS;
ANEMONES PROTECT AND FEED CLOWNFISH
Fig. 5-9, p. 111
COMMENSALISM
 Interaction where one species benefits and the other is
neither helped, nor harmed (just neutral)
 Examples:
 Epiphytes: “air plants” attach themselves to trunks or branches
of large trees
 Gain better access to sunlight, nutrients; gain a solid base on
which to grow
 Birds nesting in trees
Bromeliad Epiphyte
5-2 WHAT LIMITS THE GROWTH OF
POPULATIONS?
 Concept 5-2 No population can continue to grow indefinitely
because of limitations on resources and because of
competition among species for those resources.
MOST POPULATIONS LIVE TOGETHER IN
CLUMPS OR PATCHES (1)
 Population: group of interbreeding individuals of the
same species
 Population distribution
1.
2.
3.
Clumping
Uniform dispersion
Random dispersion
MOST POPULATIONS LIVE TOGETHER IN
CLUMPS OR PATCHES (2)
Why clumping?
1. Species tend to cluster where resources are
available
2. Groups have a better chance of finding clumped
resources
3. Protects some animals from predators
4. Packs allow some to get prey
POPULATIONS CAN GROW, SHRINK, OR
REMAIN STABLE (1)
 Population size governed by
 Births
 Deaths
 Immigration
 Emigration
 Population change =
(births + immigration) – (deaths + emigration)
 Negative value means population is shrinking
 Positive value means population is growing
 0 means stable
POPULATIONS CAN GROW, SHRINK, OR
REMAIN STABLE (2)
 Age structure: Distribution of individuals among
various age groups in a population
 Can have strong effects on how fast a population grows or
shrinks
 Age groups described as:
 Pre-reproductive age
 Reproductive age
 Post-reproductive age
 Population most likely to grow fast the more
individuals there are in the reproductive age group
AGE STRUCTURE GRAPHS
Why is taking gender into account important? Would a population grow
faster with more men than women or women than men at reproductive
ages? What does this depend on?
SOME FACTORS CAN LIMIT POPULATION
SIZE
Range of tolerance
 Variations in physical and chemical environment
 Some individuals within a population can be slightly
more tolerant (see next slide
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
 Precipitation
 Nutrients
 Sunlight, etc
TROUT TOLERANCE OF TEMPERATURE
Fig. 5-13, p. 113
LIMITING FACTORS CONTROL
POPULATION SIZES
 Important Land Limiting Factors:
 Precipitation/water
 Soil nutrients
 Temperature
 Important Aquatic Limiting Factors
 Temperature
 Sunlight
 Nutrient availability
 Dissolved oxygen levels
 Salinity
NO POPULATION CAN GROW INDEFINITELY:
J-CURVES AND S-CURVES (1)
 Size of populations controlled by limiting factors:
 Light
 Water
 Space
 Nutrients
 Exposure to too many competitors, predators or infectious
diseases
 There will always be limits to population growth
 No population can grow indefinitely
NO POPULATION CAN GROW INDEFINITELY:
J-CURVES AND S-CURVES (2)
Environmental resistance
 All factors that act to limit the growth of a population
 Determines a population’s carrying capacity
Carrying capacity (K)
 Maximum population a given habitat can sustain
 When populations near the (K), growth RATE begins to
slow/decline
NO POPULATION CAN GROW INDEFINITELY:
J-CURVES AND S-CURVES (3)
Exponential growth (J-curve)
 Starts slowly, then accelerates to carrying capacity
when meets environmental resistance
Logistic growth (S-curve)
 Decreased population growth rate as population size
reaches carrying capacity
LOGISTIC GROWTH OF SHEEP IN TASMANIA
Note how the population size fluctuates, it never truly stabilizes. Overshoot usually
occurs, knocks the population back down, and up again.
Fig. 5-15, p. 115
SCIENCE FOCUS: THREAT ON
CALIFORNIA’S SOUTHERN SEA OTTER
 Low reproductive rates
 Sexual maturity between 2-5 years old
 1 pup per yea
Threats






Predation from Orcas
Parasites from cat litter
Thorny -headed worms from seagulls
Toxic algal blooms
Biomagnification from PCB’s
Oil Spills
They serve as indicator species
why?
POPULATION SIZE OF SOUTHERN SEA OTTERS
OFF THE COAST OF SO. CALIFORNIA (U.S.)
Fig. 5-B, p. 114
CASE STUDY: WHITE TAILED DEER
POPULATIONS
 White Tailed Deer were greatly threatened in the early
1900’s
 Due to habitat destruction and hunting
 Laws were passed in 1920’s-30’s to protect remaining
deer
 Methods used included
 Restricted hunting
 Elimination of predators
 Protection methods worked too well
 Population boom
CASE STUDY: WHITE TAILED DEER
 Problems with deer population explosion
 Deer are exploiting suburban areas (feeding on
suburbanite’s gardens and farmer’s land)
 Spreading Lyme disease to humans (via ticks)
 Increased vehicular accidents, human fatalities
 Control methods:
 Hunting re-opened
 Spray predator-scented sprays as a scare tactic
 Trapped and moved
 Birth control darts
POPULATION CRASH AFTER EXCEEDING
CARRYING CAPACIT Y
 Some populations temporarily exceed the ( K) known as
OVERSHOOT
 A drastic crash may occur if there is a reproductive time
lag
 Period needed for the birth rate to fall and for the death
rate to rise in response to over consumption
 This is known as a population
Crash, or dieback
CARRYING CAPACIT Y IS NOT FIXED
Factors may increase or decrease (k)
Seasonality
Presence/absence of predators
Abundance/scarcity of competitors
Habitat degradation
SPECIES HAVE DIFFERENT
REPRODUCTIVE RATES
 Some species reproduce many, small offspring
 Do not need to provide significant parental care
  Why not?
 Many offspring = greater chances of survival
 The number of pre-reproductive deaths will most likely
always remain less than the total offspring produced
 Conserves time/energy for parent offspring
 Some species reproduce later in life and have few
offspring
 Mature slowly
 Require parental care
Which are most susceptible to
extinction? Why?
SURVIVORSHIP CURVES
http://apbiology.chsd218.richards.schoolfusion.us/modules/groups/homepagefiles/gwp/805395/918350/File/Unit_01_Ecolo
gy/Survivorship_Curves.swf?sessionid=44c50c7ebdcd89a975e40de7289bbd56
REPRODUCTIVE STRATEGIES (R & K)
R - Unstable environment, density
independent
small size of organism
energy used to make each individual is
low
many offspring are produced
early maturity
short life expectancy
each individual reproduces only once
type III survivorship pattern
in which most of the individuals die
within a short time
but a few live much longer
K - Stable environment, density
dependent interactions
large size of organism
energy used to make each individual is
high
few offspring are produced
late maturity, often after a prolonged
period of parental care
long life expectancy
individuals can reproduce more than
once in their lifetime
type I or II survivorship pattern
in which most individuals live to near the
maximum life span
http://www.bio.miami.edu/tom/courses/bil160/bil160goods/16_rKselection.html
REPRODUCTIVE PATTERNS
 r-selected species tend to be opportunists while K-selected species
tend to be competitors.
Figure 8-10
R-SELECTED VS. K-SELECTED
POPULATION DENSIT Y
Population Density: number of individuals in a
population found in a particular area or
volume
DENSIT Y-DEPENDENT VS DENSIT Y
INDEPENDENT FACTORS
Density Dependent factors
 Have a greater effect as a population increases in density
 Examples: infectious disease, competition, space,
predation, parasitism
 Musical Chairs!
 Density-Independent Factors
 Does not matter how dense a population is
 Examples: seasonal change, catastrophic event, habitat
destruction
 Think of a population of plants that experience a winter
freeze does not matter if there are 50 members in the
population or 100 members. The freeze will affect the
entire area
4 DIFFERENT T YPES OF POPULATION
CHANGE OCCUR IN NATURE
 Stable- population size slightly fluctuates above and
below (k)
 Ex. Species in undisturbed tropical rainforests
 Irruptive
 Population surge, followed by crash
 Common of short-lived rapidly reproducing organisms
 Cyclic fluctuations, boom-and-bust cycles
 Top-down population regulation
 Bottom-up population regulation
 Irregular- no particular pattern
POPULATION CYCLES FOR THE SNOWSHOE
HARE AND
CANADA LYNX
Cyclic fluctuation patterns
Fig. 5-18, p. 118
ESTIMATING POPULATION SIZES
Scientists need to consider several limitations when attempting
to estimate population sizes
 Mobility/immobility
 Distribution patterns
 Migration rates
 Some methods scientist use to estimate ecological
populations:
 Random Sampling (best for stationary organisms)
 Normally use quadrats
 Mark Recapture
MARK RECAPTURE
P=(M*C)/R
P= estimated population size
M=# of 1 st Sample that were marked
C= Total number caught in 2 nd sample
R= # recaptured (marked) found in sample 2
MARK RECAPTURE EXAMPLE
 A biologist caught 16 cichlid species from a lake and tagged
all of them. He released them back into the lake. A week
later, he went back and caught 13 cichlid fish in the same
lake and found that 4 of them were tagged individuals he had
recaptured. The estimated population of cichlids in the lake
would be:
M=16
C=13
R=4
P= (16*13)/4= 52
This method helps with
estimating mobile species
population sizes
RANDOM SAMPLING EXAMPLE
10
8
Since the area is 4x4, take 4 samples
Find the average number of individuals per
square
4
7
Multiply is times total number of area (16)
Total Sampled = 29
Average/sample = 7.25
Est. Population = 7.25*16 = 116
This method is best for evenly
dispersed, stationary
populations… why?
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
 Ecological succession:
 The normally gradual change in species composition in a
given area after the area has been disturbed o destroyed
in some way
 Response to such instances as
 Fire
 Volcanic eruption
 Climate change
 Clearing of forests
 2 types:
 Primary succession
 Secondary succession
SOME ECOSYSTEMS START FROM
SCRATCH: PRIMARY SUCCESSION
 Establishment of biotic community in a lifeless area
 No soil in a terrestrial system
 No bottom sediment in an aquatic system
 Takes hundreds to thousands of years
 Need to build up soils/sediments to provide necessary
nutrients
 Pioneer species: first species to inhabit the area
 Examples: Moss, Lichens
 Occurs after such instances as
 Volcanic eruption
 Retreating glaciers
 Abandoned highway/parking lot
 Newly created or shallowed pond/reservoir
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
 Some bottom sediment remains in an aquatic system
 Much more common than primary succession
 Restoration is also much faster than in primary
succession
 Occurs after disturbances such as
 Abandoned farmland
 Burned/cut forests
 Heavily polluted streams
 Flooded land
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
ECOLOGICAL SUCCESSION SUCCESSION
 Primary and secondary succession
 Tend to increase biodiversity
 Increase species richness and interactions among species
 Important natural service
 Both (primary and secondary) are examples of ecological
restoration
 Primary and secondary succession can be interrupted by
 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 One set of species makes an area more suitable for other
species and less suitable for itself
 Inhibition Early species hinder the establishment of other species
growth
 Succession can proceed when these species are removed
 Tolerance Plants in the late stages of succession are unaffected/no
direct competition with earlier species
SUCCESSION DOESN’T FOLLOW A
PREDICTABLE PATH
Traditional view- Equilibrium
 Balance of nature and a climax community
 Climax community: dominated by few long-lived plant
species and is in balance with its environment
Current view
 Ever-changing mosaic of patches of vegetation
 Reflects on-going struggle by species
 Mature late-successional ecosystems
 State of continual disturbance and change
LIVING SYSTEMS ARE SUSTAINED
THROUGH CONSTANT CHANGE
 Stability is achieved through change
 Environment is constantly changing, thus to keep it stable,
living systems must parallel the change by change
 2 aspects of stability:
1. Inertia (persistence)
 Ability of a living system to survive moderate disturbances
2. 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
SOME ECOSYSTEMS HAVE ONE OR THE
OTHER: RESILIENCE OR INERTIA
 Ranforests (example)
 High Inertia
 High resistance to
change due to species
diversity and richness
 Once severely
damaged, have low
resilience
 Reaches ecological
tipping point
 Grasslands (example)
 High Resilience
 Low species diversity
makes them susceptible
to destruction
 Because most plant
matter stored in
underground roots, they
may recover quickly via
secondary succession
THREE BIG IDEAS
1.
Certain interactions among species af fect 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).