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Population Ecology
G. Tyler Miller’s
Living in the Environment
14th Edition
Chapter 9
Pages 163-174
Key Concepts
Factors affecting population size
Species reproductive patterns
Species survivorship patterns
Conservation biology and
human impacts on ecosystems
CASE STUDY: Sea Otters
OMG
• live in kelp forests
• eat sea urchins
• hunted in 1900s
• 1977 declared endangered
Increased from 300 to 2800
• keystone species
 protect kelp forest
9-1 Population Dynamics and
Carrying Capacity
OBJ 9.1
 Population dynamics
-study of how populations change in size, density, and age
distribution
-populations respond to their environment
-change according to distribution
Factors Governing Changes
in Population Size
• Four variable
– births, deaths,
immigration and
emigration
• Population Change =
(births +
immigration) –
(deaths + emigration)
OBJ 9.2
Age Structure Stages
• PREREPRODUCTIVE AGE
- Not mature enough to reproduce
• REPRODUCTIVE AGE
- Capable of reproducing
• POSTREPRODUCTIVE AGE
- too old to reproduce
LIMITING FACTOR
ABIOTIC
- temperature
- water
- climate/weather
- soils (mineral component)
BIOTIC
- competition: interspecific and intraspecific
- predation/parasitism
- amensalism
- mutualism
OBJ 9.3
LIMITS TO POPULATION GROWTH:
Resources & Competition
Biotic potential: capacity for growth
Intrinsic rate of increase (r): rate at which a population
would grow if it had unlimited resources
Environmental resistance: all factors that act to limit the
growth of a population
Carrying Capacity (K): maximum # of individuals of a
given species that can be sustained indefinitely in a given
space (area or volume)
Fig. 9-3 p. 166
OBJ 9.4
Exponential and Logistic Growth
EXPONENTIAL GROWTH
LOGISTIC GROWTH
-Population w/few resource
limitations; grows at a fixed rate
- Rapid exp. growth followed by
steady dec. in pop. Growth
w/time until pop. Size levels off
OBJ 9.5
Population Density Effects
OBJ 9.6
 Density-independent controls
- floods, hurricanes, unseasonable weather, fire,
habitat destruction, pesticide spraying, pollution
- EX: Severe freeze in spring can kill plant pop.
regardless of density
 Density-dependent controls
- competition for resources, predation, parasitism,
infectious diseases
- EX: Bubonic plague swept through European cities in
14th century
Natural Population Curves
OBJ 9.7
Fig. 9-7 p. 168
• STABLE
– pop. Size fluctuates above or below its carrying
capacity
– Stable population size
– EX: undisturbed tropical rain forests
• IRRUPTIVE
– pop. Growth occasionally explodes to a high peak then
crashes to stable low level
– EX: Algae, insects
• CYCLIC
– Fluctuations occur in cycles over a regular time period
– EX: Lynx & snowshoe hare
• IRREGULAR
– No recurring pattern in changes of population size
The Role of Predation in
Controlling Population Size
 Top-down control
- lynx preying on hares
periodically reduce the hare
pop.
OBJ 9.8
 Bottom-up control
- the hare pop. may cause
changes in lynx pop.
Fig. 9-8 p. 168
How do Species Reproduce
• ASEXUAL REPRODUCTION
– all offspring are exact genetic copies of a single parent
– Common in single celled species (bacteria)
– Each cell divides to produce 2 identical cells
• SEXUAL REPRODUCTION
– Organisms produce offspring by combining sex cells or
gametes from both parents
– Produces offspring with combination of genetic traits
from each parent
– Provides greater genetic diversity in offspring
• DISADVANTAGES
– Males do not give birth
– Increased chance of genetic errors and defects
– Courtship & mating rituals consume time &
energy and transmit diseases
OBJ 9.10
Reproductive Patterns and Survival
 r-selected species vs. K-selected species
Fig. 9-10 p. 170
Survivorship Curves
OBJ 9.11
•Shows the % of members in a pop. Surviving at different ages
LATE LOSS
-High survivorship to certain age; then
high mortality
-EX: elephants, rhinos, humans
CONSTANT LOSS
-Fairly constant death rate at all ages
-EX: songbirds
EARLY LOSS
-Survivorship is low early in life
-EX: annual plants, bony fish sp.
Fig. 9-11 p. 171
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