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Chapter 8Chapter 8
Population EcologyPopulation Ecology
POPULATION DYNAMICS AND POPULATION DYNAMICS AND CARRYING CAPACITYCARRYING CAPACITY
Most populations live in clumps although other Most populations live in clumps although other patterns occur based on resource distribution.patterns occur based on resource distribution.
Figure 8-2Figure 8-2
Changes in Population Size: Changes in Population Size: Entrances and ExitsEntrances and Exits
Populations increase through births and Populations increase through births and immigrationimmigration
Populations decrease through deaths and Populations decrease through deaths and emigrationemigration
Age Structure: Young Populations Age Structure: Young Populations Can Grow FastCan Grow Fast
How fast a population grows or declines How fast a population grows or declines depends on its age structure.depends on its age structure. Prereproductive agePrereproductive age: not mature enough to : not mature enough to
reproduce.reproduce. Reproductive ageReproductive age: those capable of : those capable of
reproduction.reproduction. Postreproductive agePostreproductive age: those too old to : those too old to
reproduce.reproduce.
Limits on Population Growth: Limits on Population Growth: Biotic Potential vs. Environmental Biotic Potential vs. Environmental
ResistanceResistance
No population can increase its size No population can increase its size indefinitely.indefinitely. The intrinsic rate of increase (The intrinsic rate of increase (rr) is the rate at ) is the rate at
which a population would grow if it had unlimited which a population would grow if it had unlimited resources.resources.
Carrying capacity (Carrying capacity (KK): the maximum population ): the maximum population of a given species that a particular habitat can of a given species that a particular habitat can sustain indefinitely without degrading the habitat.sustain indefinitely without degrading the habitat.
Fig. 8-3, p. 163
EnvironmentalResistance
Time (t)
Po
pu
lat i
on
si z
e (N
)
Carrying capacity (K)
ExponentialGrowth
BioticPotential
Fig. 8-4, p. 164
Carrying capacity
Year
Nu
mb
er o
f sh
eep
(m
illi
on
s)Overshoot
Fig. 8-6, p. 165
Nu
mb
er o
f re
ind
eer
Populationovershootscarryingcapacity
Carryingcapacity
Year
PopulationCrashes
Exceeding Carrying Capacity: Move, Exceeding Carrying Capacity: Move, Switch Habits, or Decline in SizeSwitch Habits, or Decline in Size
Over time species may increase their Over time species may increase their carrying capacity by developing adaptations.carrying capacity by developing adaptations.
Some species maintain their carrying Some species maintain their carrying capacity by migrating to other areas.capacity by migrating to other areas.
So far, technological, social, and other So far, technological, social, and other cultural changes have extended the earth’s cultural changes have extended the earth’s carrying capacity for humans.carrying capacity for humans.
Types of Population Change Types of Population Change Curves in NatureCurves in Nature
Population sizes may stay the same, increase, Population sizes may stay the same, increase, decrease, vary in regular cycles, or change decrease, vary in regular cycles, or change erratically.erratically. StableStable: fluctuates slightly above and below carrying : fluctuates slightly above and below carrying
capacity.capacity. IrruptiveIrruptive: populations explode and then crash to a : populations explode and then crash to a
more stable level.more stable level. CyclicCyclic: populations fluctuate and regular cyclic or : populations fluctuate and regular cyclic or
boom-and-bust cycles.boom-and-bust cycles. IrregularIrregular: erratic changes possibly due to chaos or : erratic changes possibly due to chaos or
drastic change. drastic change.
Types of Population Change Types of Population Change Curves in NatureCurves in Nature
Population sizes often vary in regular cycles Population sizes often vary in regular cycles when the predator and prey populations are when the predator and prey populations are controlled by the scarcity of resources.controlled by the scarcity of resources.
Figure 8-7Figure 8-7
Fig. 8-7, p. 166
Po
pu
lati
on
siz
e (t
ho
usa
nd
s)
Year
LynxHare
Case Study: Exploding White-Tailed Case Study: Exploding White-Tailed Deer Populations in the United StatesDeer Populations in the United States
Since the 1930s the white-tailed deer Since the 1930s the white-tailed deer population has exploded in the United States.population has exploded in the United States. Nearly extinct prior to their protection in 1920’s.Nearly extinct prior to their protection in 1920’s.
Today 25-30 million white-tailed deer in U.S. Today 25-30 million white-tailed deer in U.S. pose human interaction problems.pose human interaction problems. Deer-vehicle collisions (1.5 million per year).Deer-vehicle collisions (1.5 million per year). Transmit disease (Lyme disease in deer ticks).Transmit disease (Lyme disease in deer ticks).
REPRODUCTIVE PATTERNSREPRODUCTIVE PATTERNS
Some species reproduce without having sex Some species reproduce without having sex (asexual).(asexual). Offspring are exact genetic copies (clones).Offspring are exact genetic copies (clones).
Others reproduce by having sex (sexual).Others reproduce by having sex (sexual). Genetic material is mixture of two individuals.Genetic material is mixture of two individuals. Disadvantages: males do not give birth, increase Disadvantages: males do not give birth, increase
chance of genetic errors and defects, courtship chance of genetic errors and defects, courtship and mating rituals can be costly.and mating rituals can be costly.
Major advantages: genetic diversity, offspring Major advantages: genetic diversity, offspring protection.protection.
Sexual Reproduction: CourtshipSexual Reproduction: Courtship
Courtship rituals Courtship rituals consume time and consume time and energy, can transmit energy, can transmit disease, and can disease, and can inflict injury on males inflict injury on males of some species as of some species as they compete for they compete for sexual partners.sexual partners.
Figure 8-8Figure 8-8
Fig. 8-9, p. 168
r species;experiencer selection
Time
Nu
mb
er o
f in
div
idu
als
KCarrying capacity
K species;experienceK selection
Fig. 8-10a, p. 168
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
r-Selected SpeciesCockroach
Dandelion
Fig. 8-10b, p. 168
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
K-Selected Species
SaguaroElephant
Survivorship Curves: Survivorship Curves: Short to Long LivesShort to Long Lives
The way to represent the age structure of a The way to represent the age structure of a population is with a population is with a survivorship curvesurvivorship curve.. Late loss populationLate loss population live to an old age. live to an old age. Constant loss populationConstant loss population die at all ages. die at all ages. Most members of Most members of early loss populationearly loss population, die at , die at
young ages.young ages.
Survivorship Curves: Survivorship Curves: Short to Long LivesShort to Long Lives
The populations The populations of different of different species vary in species vary in how long how long individual individual members typically members typically live.live.
Figure 8-11Figure 8-11
Fig. 8-11, p. 169
Per
cen
tag
e su
rviv
ing
(lo
g s
cale
)
Age
Early loss
Late loss
Constant loss
