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Population Ecology
Chapter Overview Questions
 What
are the major characteristics of
populations?
 How do populations respond to changes in
environmental conditions?
 How do species differ in their reproductive
patterns?
POPULATION DYNAMICS AND
CARRYING CAPACITY
 Most
populations live in clumps although other
patterns occur based on resource distribution.
Figure 8-2
(a) Clumped (elephants)
Fig. 8-2a, p. 162
(b) Uniform (creosote bush)
Fig. 8-2b, p. 162
(c) Random (dandelions)
Fig. 8-2c, p. 162
Changes in Population Size:
Entrances and Exits
 Populations
increase through births and
immigration
 Populations
emigration
decrease through deaths and
Limits on Population Growth:
Biotic Potential vs. Environmental
Resistance
 No
population can increase its size
indefinitely.


The intrinsic rate of increase (r) is the rate at
which a population would grow if it had unlimited
resources.
Carrying capacity (K): the maximum population
of a given species that a particular habitat can
sustain indefinitely without degrading the habitat.
Exponential and Logistic Population
Growth: J-Curves and S-Curves
 Populations
grow rapidly with
ample
resources, but
as resources
become limited,
its growth rate
slows and levels
off.
Figure 8-4
Environmental
Resistance
Carrying capacity (K)
Biotic
Potential
Exponential
Growth
Time (t)
Fig. 8-3, p. 163
Exponential and Logistic Population
Growth: J-Curves and S-Curves
 As
a population
levels off, it
often fluctuates
slightly above
and below the
carrying
capacity.
Figure 8-4
Overshoot
Number of sheep (millions)
Carrying capacity
Year
Fig. 8-4, p. 164
Exceeding Carrying Capacity: Move,
Switch Habits, or Decline in Size
 Members
of
populations which
exceed their
resources will die
unless they adapt or
move to an area with
more resources.
Figure 8-6
Number of reindeer
Population
overshoots
carrying
capacity
Population
Crashes
Carrying
capacity
Year
Fig. 8-6, p. 165
Population Density and Population
Change: Effects of Crowding
 Population
density: the number of individuals
in a population found in a particular area or
volume.

A population’s density can affect how rapidly it
can grow or decline.
• e.g. biotic factors like disease

Some population control factors are not affected
by population density.
• e.g. abiotic factors like weather
Types of Population Change
Curves in Nature
 Population
sizes may stay the same, increase,
decrease, vary in regular cycles, or change
erratically.




Stable: fluctuates slightly above and below carrying
capacity.
Irruptive: populations explode and then crash to a
more stable level.
Cyclic: populations fluctuate and regular cyclic or
boom-and-bust cycles.
Irregular: erratic changes possibly due to chaos or
drastic change.
Types of Population Change
Curves in Nature
 Population
sizes often vary in regular cycles
when the predator and prey populations are
controlled by the scarcity of resources.
Figure 8-7
Population size (thousands)
Hare
Lynx
Year
Fig. 8-7, p. 166
Case Study: Exploding White-Tailed
Deer Populations in the United States
 Since
the 1930s the white-tailed deer
population has exploded in the United States.

Nearly extinct prior to their protection in 1920’s.
 Today
25-30 million white-tailed deer in U.S.
pose human interaction problems.


Deer-vehicle collisions (1.5 million per year).
Transmit disease (Lyme disease in deer ticks).
Reproductive Patterns:
Opportunists and Competitors
 Large
number of
smaller offspring with
little parental care (rselected species).
 Fewer, larger
offspring with higher
invested parental
care (K-selected
species).
Figure 8-9
Carrying capacity
K
K species;
experience
K selection
r species;
experience
r selection
Time
Fig. 8-9, p. 168
Reproductive Patterns
 r-selected
species tend to be opportunists
while K-selected species tend to be
competitors.
Figure 8-10
Cockroach
r-Selected Species
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
Fig. 8-10a, p. 168
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
Fig. 8-10b, p. 168
Survivorship Curves:
Short to Long Lives
 The
populations
of different
species vary in
how long
individual
members typically
live.
Figure 8-11
Late loss
Early loss
Age
Fig. 8-11, p. 169
Animation: Life History Patterns
PLAY
ANIMATION