Transcript chapter9

Population Ecology
G. Tyler Miller’s
Living in the Environment
14th Edition
Chapter 9
Key Concepts
Factors affecting population size
Species reproductive patterns
Species survivorship patterns
Conservation biology and
human impacts on ecosystems
Population Dynamics and Carrying
Capacity
 Population
dynamics
 Biotic potential (intrinsic rate of increase [r])
 Environmental resistance
 Carrying capacity
 Exponential and Logistic Growth
 Population Density
Population Distribution
Clumping: Most
common. Safety in
numbers, social
interaction, mating
and caring for
young, resources
are clumped
Uniform: Not as
common. Used
because of scarcity
of resources
Random: Quite
rare. Can be hard
to determine
between truly
random or largely
“clumpy”
Fig. 9-2 p. 164
What goes up must come down
1. Increases in population: through
birth or immigration
2. Decreases in population: through
death or emigration.
Change in Population
Births + Immigration
Deaths + emigration
Age Structure
• What is expected to happen if a large % of the population is under the
age of 10?
Growth will remain stable, then increase in 10-20 years
• What is expected to happen if a large % of the population is between the
ages of 20 and 40?
Growth will increase within 10 years
• What is expected to happen if a large % of the population is over the age of
65?
Growth will decrease
• What is expected to happen if there is an equal distribution in age?
Growth remain stable
What stage are you?
• Pre-reproductive stage: Those not through
puberty; reproductively immature.
• Reproductive stage: Those who are capable of
reproduction
• Post-reproductive stage: Organisms that are
too old to reproduce.
• Remember: while males are capable of
reproduction longer, “survival of the fittest” can
prevent them from breeding once they are too
old.
Abiotic
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•
•
•
•
Not living
Sunlight
Temperature
Climate
Chemical
environment
vs.
Biotic Factors
•
•
•
•
•
•
Living factors
Reproduction rates
Food supply
Habitat
Resistance to disease
Ability to adapt to
change
Factors Affecting Population Size
Biotic potential =
growth
Environmental
resistance =
decrease
Fig. 9-3 p. 166
Exponential and Logistic Growth
Boom then
Bust
Boom then
Stable
Logistic Growth
Population size (N)
Environmental
resistance
Carrying capacity (K)
Biotic
potential
Exponential
growth
Time (t)
Going up…
•Intrinsic rate of increase (r) is the rate the
population would grow at if it had unlimited
resources.
•Can be seen as the “boom” of the population.
•r species: reproduce early in life, reproduce often,
have many offspring each time.
Coming Down
• Overshoot occurs when the population
“booms” and is too great for the resources to
support
• Overshoot is followed by dieback, or the
sudden decrease in population
• Reproductive time lag: the amount of time it
takes for the birth rate to fall and death rate
to rise. If the time lag is too long,
environmental damage can occur which
further limits the carrying capacity.
Population Density Effects
Density-dependent controls: Limits populations that are
too high. Examples: competition for food, shelter, water;
disease; parasites
•Density-independent controls: Decreases population
regardless of size. Examples: weather, temperature,
natural disasters, habitat destruction
Natural Population Curves
Fig. 9-7 p. 168
Who’s in control here?
• Top-down control: Population is limited by
the predator.
• Bottom-up control: Population is limited by
the food source of the prey.
• Example: Hare population is controlled
either by the lynx killing it (top-down) or by
large numbers of hare using up their food
source (bottom-up)
Let’s talk about sex…
• Asexual reproduction: does not require
sperm/egg. Mitosis – cell splitting. Bacteria
reproduce this way. Only 3% of all species use
this form
• Sexual reproduction: requires sperm/egg, but
not necessarily intercourse/copulation
• Disadvantages:
– Males don’t give birth
– Increased chance of genetic defect/error
– Courtship and mating rituals can be complex
• Advantages: (get your mind out of the gutter!)
– Genetic variety/diversity
– Parents can divide responsibilities
What species are you?
Carrying capacity
Number of individuals
K species;
experience
K selection
r species;
experience
r selection
Time
Species
r
k
• Found at bottom of population
curve
• Reproduce early in life
• Reproduce frequently
• Large numbers of offspring
• Little to no parental care
• Boom and bust populations
• Examples:
–
–
–
–
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Frogs
Cockroach
Dandelions
Mice
Most insects
• Found at top of population
curve
• Reproduce later in life
• Reproduce less frequently
• Have less offspring at one time
• Lower infant mortality
• Logistic graph (stable at top)
• Examples:
–
–
–
–
Humans
Elephants
Whales
Long-living plants (oaks, rain
forest trees)
The Role of Predation in Controlling
Population Size
 Predator-prey cycles  Top-down control
 Bottom-up control
Fig. 9-8 p. 168
Reproductive Patterns and Survival
 Asexual reproduction  r-selected species
 Sexual reproduction  K-selected species
Fig. 9-10 p. 170
Survivorship Curves
1. Early loss: high
infant mortality
(fish, frogs)
2. Constant loss:
death rate even
among all ages
(song birds)
3. Late loss: low
infant mortality
(humans,
elephants)
Fig. 9-11 p. 171
Isolation isn’t best…
• Problems when small, isolated populations exist.
1. Founder effect: small group is geographically
isolated. May not have the genetic diversity to
survive (coloring, fur cover, etc)
2. Demographic bottleneck: only a few surviving
individuals may not have the genetic diversity to
rebuild the population
3. Genetic drift: some individuals breed more and
dominate the gene pool (wolves)
4. Inbreeding: related individuals in an area mate. Can
increase genetic defects.
Oops! I did it again…
Past mistakes that need stopped:
1. Reducing biodiversity by destroying, fragmenting and
degrading habitats
2. Reducing biodiversity by simplifying natural
ecosystems (monocultures – one type)
3. Unintentionial strengthening of pest species and antibiotic resistant bacteria
4. Elimination of natural predators (wolves, cougars,
buffalo, eagles)
5. Over-harvesting renewable resources
6. Interfering with natural cycles in natural
7. Over dependence on fossil fuels
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
Learning from Nature
 Dependence on Nature
 Interdependence
 Unpredictability
 Limited resources
 Recycle wastes
See Connections p. 173