Transcript Chapter 9

Chapter 9
Population Dynamics,
Carrying Capacity, and
Conservation Biology
Key Questions
• How do populations change in size,
density, and makeup?
• What is the role of predators in
controlling population size?
• What is conservation biology?
• How can we live more sustainably?
Major Characteristics of a
Population
Populations can change in…
1. Size (number of individuals)
2. Density (number of individuals in a
certain area)
3. Dispersion (spatial pattern)
4. Age distribution
Dispersion
Clumped
(elephants)
Uniform
(creosote bush)
Random
(dandelions)
These changes are called…
• Population Dynamics!
-occur in response to environmental
stress OR changes in
environmental conditions
What Limits Population
Growth?
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Births
Deaths
Immigration (to a new area)
Emigration (out of an area)
Population change = (births + immigration) – (deaths + emigration)
Populations
• Populations vary in biotic potential
(growth)
• Intrinsic rate of increase (r)-rate
at which a population would grow if
it had unlimited resources
High intrinsic rate of increase
populations…
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Reproduce early in life
Short generation times
Reproduce many times
Many offspring each time they
reproduce
Example…
• FLIES!-high intrinsic rate of
increase/biotic potential
• Without control, there would be 5.6
trillion flies within 13 months
• Within a few years, flies could cover
the surface of the earth!
Of course…
• This is not realistic because
no population can grow
indefinitely
• There are always limiting
factors!
Environmental Resistance
• all limiting factors
• together the biotic potential and
environmental resistance determine
the carrying capacity
POPULATION SIZE
© 2004 Brooks/Cole – Thomson Learning
Population Size
Growth factors
(biotic potential)
Abiotic
Favorable light
Favorable temperature
Favorable chemical environment
(optimal level of critical nutrients)
Biotic
High reproductive rate
Generalized niche
Adequate food supply
Suitable habitat
Ability to compete for resources
Ability to hide from or defend
against predators
Ability to resist diseases and parasites
Ability to migrate and live in other
habitats
Ability to adapt to environmental
change
Decrease factors
(environmental resistance)
Abiotic
Too much or too little light
Temperature too high or too low
Unfavorable chemical environment
(too much or too little of critical
nutrients)
Biotic
Low reproductive rate
Specialized niche
Inadequate food supply
Unsuitable or destroyed habitat
Too many competitors
Insufficient ability to hide from or defend
against predators
Inability to resist diseases and parasites
Inability to migrate and live in other
habitats
Inability to adapt to environmental
change
A Few More Terms
• Carrying Capacity (K)-number of
individuals that can be sustained in a
given space
• Minimum viable population (MVP)minimum population size needed to
support a breeding population (below
MVP, extinction is likely)
Exponential and Logistic
Growth
• A population has exponential growth
when it has few/no resource limitations
(J-shaped curve)
• Logistic growth- exponential population
growth that approaches carrying
capacity and levels off (S-shaped curve)
© 2004 Brooks/Cole – Thomson Learning
Population size (N)
Population size (N)
K
Time (t)
Exponential Growth
Time (t)
Logistic Growth
What Happens If Population
Size Exceeds Carrying
Capacity?
• Overshoot-exceeds carrying capacity
• Dieback-happens unless individuals
change resources or move to another
area
• Humans are not exempt from this!
• Potato fungus in Ireland; 1 million died/3
million emigrated
2.0
Number of sheep (millions)
Overshoot
1.5
1.0
.5
1800
1825
1850
1875
Year
1900
1925
How Does Density Affect
Population Growth?
• Density-independent population
controls (do NOT depend on size of
population): floods, fires, hurricanes,
habitat destruction, pesticides
• Density-dependent population
controls (depend on size of
population): competition, predation,
disease, parasitism
Population Curves in Nature
• Stable: fluctuates slightly above and
below carrying capacity (undisturbed
areas)
• Irruptive: fairly stable with occasional
explosions
• Irregular: chaotic, no recurring pattern
• Cyclic: regular cycles
Natural Population Curves
Do Predators Control
Population Size?
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YES!
Lynx-Hare Cycle:
Shortage of hares reduces lynx population
Hare population builds up because there
are fewer predators
• Lynx population increases because there
are more hares
• Cycle begins again
Two Ideas About Lynx-Hare
Cycle
• Top-down control hypothesis:
lynx controls hare population
• Bottom-up control hypothesis:
hare controls lynx population
Population size (thousands)
160
140
Hare
120
Lynx
100
80
60
40
20
0
Year
Reproductive Patterns and
Survival
• Asexual reproduction: all offspring are
exact copies (clones) of a single parent
• Sexual reproduction: combination of
gametes (97% of species)
• r-selected species
• K-selected species
Reproductive Patterns
r-selected: opportunist species; high
intrinsic rate of increase; reproduce early;
algae, bacteria, rodents, insects
• Many offspring each time they reproduce
• Reproduce at young age
• Short generation times
• Little or no parental care
• Short life-spans
• Irregular and unstable changes in
population size
r-Selected Species
cockroach
dandelion
Many small offspring
Little or no parental care and protection of offspring
Early reproductive age
Most offspring die before reaching reproductive age
Small adults
Adapted to unstable climate and environmental
conditions
High population growth rate (r)
Population size fluctuates wildly above and below
carrying capacity (K)
Generalist niche
Low ability to compete
Early successional species
Reproductive Patterns,
continued
• K-selected: competitor species;
mammals, long-lived plants, birds of
prey
• Reproduce late in life
• Few offspring
• Long generation times
• Nurture and protect their young
• Logistic growth curve
K-Selected Species
elephant
saguaro
Fewer, larger offspring
High parental care and protection of offspring
Later reproductive age
Most offspring survive to reproductive age
Larger adults
Adapted to stable climate and environmental
conditions
Lower population growth rate (r)
Population size fairly stable and usually close
to carrying capacity (K)
Specialist niche
High ability to compete
Late successional species
Carrying capacity
Number of individuals
Figure 9-9
Page 196
r species;
experience
r selection
Time
K
K species;
experience
K selection
Survivorship Curves
• Shows the number of survivors of each age
group for a species
3 Types:
1. Late Loss Curves: high survivorship to a
certain age, then high death rate (elephants,
humans)
2. Constant Loss Curves: constant death rate at
all ages (songbirds)
3. Early Loss Curves: survivorship is low early
in life (r-selected species)
Percentage surviving (log scale)
100
10
1
0
Age
Conservation Biology
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Started in the 1970s
Uses science to take action to preserve
species and ecosystems
3 principles
1. Biodiversity is necessary to all life on earth
and should not be reduced by humans
2. Humans should not disrupt vital ecological
processes
3. The best way to preserve earth’s
biodiversity is to protect ecosystems