Chapter 5 Part 2
Bell Work
• Imagine you have been
hired to oversee the
maintenance of a forest.
– How would you evaluate
the health of the forest?
– What actions would you
take to keep the forest
healthy?
– What might be a threat to
the health of the forest?
Broad and Narrow Niches
• Generalist species
• Specialist species
– What is better? Depends…
• Environmental conditions consistent – favors
specialists. Fewer competitors, food plentiful
• Rapidly changing environmental conditions –
favors generalists… More adaptable.
Ecological Niches and Adaptation
r and K selected species
No Population Can Grow Indefinitely
• Biotic potential –
capacity for
population growth
under ideal
conditions
– Larger organisms
tend to have low
potential
Population Growth
• Exponential growth – population that
increases at a fixed rate
– J-Curve
• Logistic growth – rapid exponential
population growth followed by a steady
decrease in population growth
– S-Curve
Population Growth
Exponential Growth
• Intrinsic rate of
increase (r) – rate
the population of a
species would grow
if it had unlimited
resources
Exponential Growth
• Individuals in populations
with high r
– Reproduce early in life
– Have short generation
times
– Can reproduce many times
– Have many offspring each
time they reproduce
Logistic Growth
• Environmental resistance –
combination of all factors that act to limit
the growth of a population
• Carrying capacity (K) – maximum
population of a given species that a
habitat can sustain indefinitely without
being degraded
Logistic Growth
Phases of Logistic Growth Curve
1. Lag Phase – little initial growth.
2. Rapid Growth Phase
3. Stable Phase – stabilizing factors limit
growth
Species Reproductive Patterns
• r-Selected species, opportunists – species with
a capacity for a high rate of population increase
– Many small offspring
– Little to no parental care or protection
– Reproductive opportunists
• K-selected species, competitors – reproduce
later in life and have a small number of offspring
with fairly long life spans
– Few large offspring
– High parental care
Positions of r- and K-Selected Species on the
Logistic Population Growth Curve
Transitioning between exponential
and logistic curves…
• Carry capacity isn’t fixed
– Varies depending on climate and season
– Unpredictable changes can be devastating to the
species AND the habitat
• Reproductive time lag – period needed
for the birth rate to fall and the death rate to
rise in response to resource
overconsumption
– May lead to overshoot
– Dieback (crash)
r-Curve Fluctuations
Types of Population Change
• Stable – population fluctuates slightly
above and below its carrying capacity
– Characteristic of undisturbed rain forests
– Late loss curve
• Irruptive – short-lived rapidly reproducing
species
– Linked to seasonal changes in weather or
nutrient availability
– Algal Blooms
– Early loss curves
Logistic Curve Fluctuations
Types of Population Change
• Cyclic fluctuations, boom-and-bust
cycles
– Top-down population regulation
• Controlled by predation
– Bottom-up population regulation
• Controlled by scarcity of one or more resources
• Irregular – changes in population size with
no recurring pattern
– chaos
Top-down Regulation
Your Turn!
• Make a K selected  r selected
continuum on your desk
• Organize your cards ON YOUR OWN
• Discuss with partner
Survival Strategies
• Which organisms were difficult to
classify? Why?
Survival Strategies
• K selected
• r selected
•
•
•
•
•
•
Red-tailed hawk
Coyote
Western rattlesnake
Roadrunner
Kangaroo Mouse
Whiptail lizard
Ecological Succession
• In 1988 large
areas of
Yellowstone
Park burned to
the ground.
• How do you
think the park
looked the
following
spring?
Ecological Succession
• The “dead” forest
began to change
• New plant growth
began
Succession
• Succession
– 1. Gradual
development of a
community of
organisms over time
– Succession
• A. Takes place in all
communities
• B. Takes place over
time
Primary Succession
• Primary Succession
– A. Takes place after an ecosystem is
completely destroyed, including its soil
– B. There is no soil in this area, usually just
bare rock
• Example: volcanic eruption
Steps in Primary Succession
• 1. After an volcanic
eruption, lava covers
the land and hardens
into rock
Primary Succession
• 2.Lichens begin to form on rocks
– A. Lichens-plant like organism that is a
fungus and algae
– B. Acids from the lichens begin to break
down the rock
– C. These pieces of broken rock and the
remains of dead lichens start forming soil
Pioneer species- first organisms to grow in
a succession
example-lichens
Primary Succession
• 3. After many years
– A. The soil is deep enough for mosses to
grow
– B. Mosses replace lichens
– C. Tiny organisms like insects live the in the
lichens and mosses
• Their remains add to the soil
Primary Succession
• 4. Over time
– Soil layer thickens
• Moss is replaced by
ferns
– Next
• Growth of grasses
and wildflowers
– Once the soil is deep
enough:
• Shrubs and small
trees come into the
area
Primary Succession
• 5. After hundreds or
even thousand of
years
– The soil may be deep
enough to support a
forest
• The final stage of
succession is the
climax community
Primary Succession
Secondary Succession
• Secondary Succession
– Changes that takes place after an
environment is disrupted in some way (the
soil must remain intact)
• Example-forest fire, hurricane, farm land left
unused
Secondary Succession
• 1. fast growing
grasses and nonwoody plants appear
Secondary Succession
• 2. Larger shrubs move in
Secondary Succession
• 3. Fast growing trees
(such as pines) move
in
• 4. These are followed
by slower-growing
hardwood trees
Secondary Succession
• 5. As new plants take
root and grow,
animals begin
moving back in the
ecosystem
• Succession ends with
a climax
community (when
species have
adapted to the
average conditions in
that area)
Secondary Succession