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MILLER/SPOOLMAN
LIVING IN THE ENVIRONMENT
17TH
Chapter 5
Biodiversity, Species
Interactions, and Population
Control
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. Clumping
2. Uniform dispersion
3. 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
Population of Snow Geese
Fig. 5-11, p. 112
Generalized Dispersion Patterns
Fig. 5-12, p. 112
(a) Clumped (elephants)
Fig. 5-12a, p. 112
(b) Uniform (creosote bush)
Fig. 5-12b, p. 112
(c) Random (dandelions)
Fig. 5-12c, p. 112
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
• Post-reproductive age
Some Factors Can Limit Population
Size
• Range of tolerance
• Variations in physical and chemical environment
• 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
Lower limit
of tolerance
Few
organisms
Abundance of organisms
Few
organisms
No
organisms
Population size
No
organisms
Higher limit
of tolerance
Zone of
Zone of
intolerance physiological
stress
Low
Optimum range
Temperature
Zone of
Zone of
physiological intolerance
stress
High
Fig. 5-13, p. 113
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
No Population Can Grow Indefinitely:
J-Curves and S-Curves (2)
• Environmental resistance
• All factors that act to limit the growth of a population
• Carrying capacity (K)
• Maximum population a given habitat can sustain
No Population Can Grow Indefinitely:
J-Curves and S-Curves (3)
• Exponential growth
• Starts slowly, then accelerates to carrying capacity
when meets environmental resistance
• Logistic growth
• Decreased population growth rate as population size
reaches carrying capacity
Logistic Growth of Sheep in Tasmania
Fig. 5-15, p. 115
Number of sheep (millions)
2.0
Population
overshoots
carrying
capacity
Carrying capacity
1.5
Population recovers
and stabilizes
1.0
Exponential
growth
Population
runs out of
resources
and crashes
.5
1800
1825
1850
1875
Year
1900
1925
Fig. 5-15, p. 115
Science Focus: Why Do California’s Sea
Otters Face an Uncertain Future?
• 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.)
Fig. 5-B, p. 114
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
• Current population explosion for deer
• Spread Lyme disease
• Deer-vehicle accidents
• Eating garden plants and shrubs
• Ways to control the deer population
Mature Male White-Tailed Deer
Fig. 5-16, p. 115
When a Population Exceeds Its Habitat’s
Carrying Capacity, Its Population Can Crash
• A population exceeds the area’s carrying capacity
• Reproductive time lag may lead to overshoot
• Population crash
• Damage may reduce area’s carrying capacity
Exponential Growth, Overshoot, and
Population Crash of a Reindeer
Fig. 5-17, p. 116
Population
overshoots
carrying
capacity
Number of reindeer
2,000
1,500
Population
crashes
1,000
500
Carrying
capacity
0
1910
1920
1930
Year
1940
1950
Fig. 5-17, p. 116
Species Have Different Reproductive
Patterns (1)
• Some species
•
•
•
•
Many, usually small, offspring
Little or no parental care
Massive deaths of offspring
Insects, bacteria, algae
Species Have Different Reproductive
Patterns (2)
• Other species
•
•
•
•
•
•
•
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
Humans
Elephants
Under Some Circumstances Population
Density Affects Population Size
• Density-dependent population controls
•
•
•
•
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
Population Cycles for the Snowshoe Hare and
Canada Lynx
Fig. 5-18, p. 118
Population size (thousands)
160
Hare
Lynx
140
120
100
80
60
40
20
0
1845
1855
1865
1875
1885
1895
1905
1915
1925
1935
Year
Fig. 5-18, p. 118
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
• No bottom sediment in an aquatic system
• Takes hundreds to thousands of years
• Need to build up soils/sediments to provide
necessary nutrients
Primary Ecological Succession
Fig. 5-19, p. 119
Exposed
rocks
Lichens
and
mosses
Small herbs
and shrubs
Heath mat
Balsam fir,
paper birch,
and white
Jack pine,
spruce
forest
black spruce,
community
and aspen
Fig. 5-19, p. 119
Lichens and
Exposed mosses
rocks
Small herbs
and shrubs
Heath mat
Jack pine,
black spruce,
and aspen
Balsam fir,
paper birch,
and white
spruce forest
community
Stepped Art
Fig. 5-19, p. 119
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
Fig. 5-20, p. 120
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. 5-20, p. 120
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
Stepped Art
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
•
•
•
•
•
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).