Population Ecology

1
Chapter 8

• Population Ecology
• (continued)

2
POPULATION DYNAMICS AND CARRYING CAPACITY

• Most populations live in clumps although other
  patterns occur based on resource distribution.

Figure 8-2
3
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.

4
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.
• Members of populations which exceed their
  resources will die unless they adapt or move to
  an area with more resources.

Figure 8-4
5
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
6
(No Transcript)
7
(No Transcript)
8
Chapter Overview Questions

• What are the major characteristics of
  populations?
• TODAY
• How do populations respond to changes in
  environmental conditions?
• How do species differ in their reproductive and
  survivorship patterns?

9
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 populations 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

10
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
11
Hare
Lynx
Population size (thousands)
Year
Fig. 8-7, p. 166
12
(No Transcript)
13
Environmental Resistance
Carrying capacity (K)
Population size (N)
Biotic Potential
Exponential Growth
Time (t)
Fig. 8-3, p. 163
14
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
  1920s.
• 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).

15
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.

16
Chapter Overview Questions

• What are the major characteristics of
  populations?
• How do populations respond to changes in
  environmental conditions?
• NEXT
• How do species differ in their reproductive and
  survivorship patterns?

17
REPRODUCTIVE PATTERNS

• Some species reproduce without having sex
  (asexual).
• Offspring are exact genetic copies (clones).
• Others reproduce by having sex (sexual).
• Genetic material is mixture of two individuals.
• Disadvantages males do not give birth, increase
  chance of genetic errors and defects, courtship
  and mating rituals can be costly.
• Major advantages genetic diversity, offspring
  protection.

18
Sexual Reproduction Courtship

• Courtship rituals consume time and energy, can
  transmit disease, and can inflict injury on males
  of some species as they compete for sexual
  partners.

Figure 8-8
19
Reproductive PatternsOpportunists and
Competitors

• Large number of smaller offspring with little
  parental care (r-selected species).
• Fewer, larger offspring with higher invested
  parental care (K-selected species).

Figure 8-9
20
Carrying capacity
K
K species experience K selection
Number of individuals
r species experience r selection
Time
Fig. 8-9, p. 168
21
Reproductive Patterns

• r-selected species tend to be opportunists while
  K-selected species tend to be competitors.

Figure 8-10
22
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
Fig. 8-10a, p. 168
23
K-Selected Species
Saguaro
Elephant
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
24
Hare
Lynx
Population size (thousands)
Year
Fig. 8-7, p. 166
25
(No Transcript)
26
Survivorship Curves Short to Long Lives

• The way to represent the age structure of a
  population is with a survivorship curve.
• Late loss population live to an old age.
• Constant loss population die at all ages.
• Most members of early loss population, die at
  young ages.

27
Survivorship Curves Short to Long Lives

• The populations of different species vary in how
  long individual members typically live.

Figure 8-11
28
Late loss
Constant loss
Percentage surviving (log scale)
Early loss
Age
Fig. 8-11, p. 169
29
Survivorship Curves Short to Long Lives

• Are Humans a . ?
• Early loss population, die at young ages.
• Constant loss population die at all ages.
• Late loss population live to an old age.

30
Conservation Biology Sustaining Wildlife
Populations

• Investigate human impacts on biodiversity

• Ideas for maintaining biodiversity

• Endangered species management

• Wildlife reserves and ecological restoration

• Ecological economics

• Environmental ethics

• Wildlife management

31
Human Impacts on Ecosystems

• Habitat degradation and fragmentation

• Ecosystem simplification

• Genetic resistance

• Predator elimination

• Introduction of non-native species

• Overharvesting renewable resources

• Interference with ecological systems

32
Figure 9-12Page 200
Environmental Stress
Organism Level
Population Level
Population Level
Disruption of energy flow through food
chains and webs Disrupted biogeochemical cycles
Lower species diversity Habitat loss or
degradation Less complex food webs Lower
stability Ecosystem collapse
Physiological changes Psychological
changes Behavior changes Fewer or no
offspring Genetic defects Birth
defects Cancers Death
Change in population size Change in age
structure (old, young, and weak may
die) Survival of strains genetically resistant
to stress Loss of genetic diversity and
adaptability Extinction
33
(GO TO MARK RECAPTURE SIMULATION CD)
34
Critical Thinking 8 Half-Life of Plutonium-239

• PROBLEM If we start with 100 grams of
  Plutonium-239, how much will we have after
  12,000, 24,000, and 96,000 years ?
  (Plutonium-239 has a half-life of 24,000 years)
• First... We know that the equation that describes
  a half-life decay is
• Y Yoekt
• For this problem, Yo 100 g but we dont know
  what k is yet.
• From the half-life, we know that when t 24,000
  there will be half of the Plutonium left (50 g)
  so
• 50 g 100 g ek24,000
• 0.5 ek24,000

35
Critical Thinking 8 Half-Life of Plutonium-239
(page 2)

• Now remember that ln (ex) x and
  ln (0.5) just a
• So lets take the natural log (ln) of both sides
  to get ride of the e ...
• ln (0.5) ln (ek24,000)
• -0.6931 k 24,000
• k -0.6931 / 24,000 -2.89 x 10-5
• So our equation is
• Y Yoe-2.89 x 10-5 t

36
Critical Thinking 8 Half-Life of Plutonium-239
(page 3)

• So Y Yoe-2.89 x 10-5 t
• All we have to do is let t 12,000 or 24,000 or
  96,000 years
• Y(12,000) 70.7 g
• Y(24,000) 50.0 g
• Y(96,000) 6.25 g

37
DUCKWEEK EXPONENTIAL GROWTH
To solve for the intrinsic rate of increase (r)
Y Yoert Y final count Yo initial count T
time between counts Solve for r intrinsic
rate of increase. (See example on board)
38

• To solve for the intrinsic rate of increase, r
  
• Pick two duckweed counts at the points at
  beginning and end of linear region of increase,
  Y and Yo
• Let t be the number of days between those points
• Solve for r
• EX Day 16 27 fronds
• Day 19 39 fronds
• t 3 days
• 39 27 er3 (see work on board)
• r 0.1225
• or 12.25 growth rate

DUCKWEEK EXPONENTIAL GROWTH EXAMPLE
39
DUCKWEED LAB (in addition to questions on
Tuesday)- Calculate the intrinsic rate of
growth, r, for each of your duckweed
populations. - Create a table that summarizes
these calculations. - Include the calculations
table with your Duckweed questions. -
Graph label each curve on your graph with
its intrinsic rate of growth, r