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Why Clumping?
1. Species tend to cluster where resources are available
2. Groups have a better chance of finding resources
3. Protects some animals from predators
4. Packs allow some predators to get prey
How do populations change over time?
Population Ecology # of individuals of a species in an area AND how/why those # change over time Effected by: – Resource competition– Predation– disease
Population Density
# of individuals Area or volume
Determined by external factors (habitat/resources)What is the population density of 200 birds in
Population Density
Population Density
• What is the population density of 200 birds in 20 square miles?
• What about 200 birds in 5 square miles?
• Which area is more densely populated?
Limits on Population GrowthPopulation Increase (+)• Births (b)• Immigration (i)
Population Decrease (-)• Death (d)• Emmigration (e)
Growth Rate (r) (also termed rate of change)
r = b - d• If r (+), population size • If r (-), population size • If r (0), b=d, stationary population
size
Biotic Potential
Maximum rate at which a population can increase when there are no limits on its rate of growth
Biotic Potential is Influenced by:
1. Reproduction age2. Reproductive
periods3. # of offspring4. Care of offspring
GENERALLY…
Organisms with a high biotic potential:
1. Reproduce early in life2. Have short generation times3. Can reproduce many times4. Have many offspring each time
they reproduce
GENERALLY…
Small organisms have large biotic potentialEX: Housefly – descendants = 5.6 trillion in 13 mo. Bacteria dividing in ½ every 30 min.
Exponential Growth
Results when organisms are growing at biotic potential
Time (t)
Po
pu
lati
on
siz
e (N
)
Exponential Growth
Environmental Resistance
All factors acting jointly to limit the growth of a populationPopulation size determined by:
1. Biotic potential2. Environmental resistance
Environmental Resistance
Unfavorable environmental conditions due to resource availability
As environmental conditions deteriorate, b and d
Carrying Capacity (K)
Largest population that can be maintained given fixed resources - S (sigmoid) shaped curve (logistic Growth)
• Reflects influence of Env. Resistance• Populations rarely stays at K• If it rises above K, pop will crash
Time (t)
Po
pu
lati
on
siz
e (N
)
K Carrying capacity
What Happens When Populations Exceed Carrying
Capacity
• Members of populations which exceed their resources will die unless they adapt or move to an area with more resources.
Minimum Viable Population (MVP)
Estimate of smallest # of individuals necessary to ensure the survival of a population
Reproductive Strategies
r-strategists• Life based on r
(growth rate -r)• Rapidly increase
numbers• Below carrying
capacities for long periods of time
k-strategists• Life based on
carrying capacity (k)
• Live in a state of equilibrium
• Close to carrying capacity
Figure 9-9Page 196
Nu
mb
er o
f in
div
idu
als
Time
Carrying capacity
K species;experienceK selection
r species;experiencer selection
K
Reproductive Patterns
r strategists (based on study)
• + Live in disturbed environments.• + Ecological generalists.• + Have populations that fluctuate rapidly in size.• + Do not compete well against other species• + Are widely distributed.• + Are slow to respond to ecological opportunities
but live in wide varieties of environments.• + Are short-lived.• + Have many, relatively small young.• + Have short periods of embryonic development.• + Reach adulthood rapidly• + Small sized adults.• + Invest little or no parental care in young.• + Reproduce once per lifetime.• + Early successional species.
r-selected species
Once established – population crash because 1)Changing environment2)Invasion by more competitive
speciesGo through regular BOOM and bust cycles
k strategists (based on study)
• + Live in stable environments.• + Ecological specialists.• + Have populations stable in size.• + Compete well against other species.• + Are restricted in distribution and where they can
live.• + Take rapid advantage of ecological opportunities but
live in specific types of environments.• + Are long-lived.• + Have few, relatively large young.• + Have long periods of embryonic development.• + Reach adulthood slowly.• + Large sized adults.• + Invest intensive parental care in young.• + Reproduce throughout lifetime• + Late successional species.
K-selected species
Do well when pop. size is near KTypically follow logistic growthThrive in constant environment
Many organisms have
reproductive patterns
between the extremes of r &
K, or change from one to the
other depending on environment*
Reproductive strategy may give temporary advantage
BUT the availability of suitable
habitat determines ultimate population size
Factors Affecting Population Growth/Population Density
Density Independent Limiting Factors
• Floods• Fires• Hurricanes• Unseasonable
Weather• Habitat Destruction
Density Dependent Limiting Factors
• Competition• Predation• Parasitism• Disease
Fig. 5-13, p. 113
Lower limit of tolerance
Higher limit of tolerance
No organisms
Few organisms Abundance of organisms
Few organisms
No organisms
Po
pu
lati
on
siz
e
Zone of physiological
stress
Optimum rangeZone of
physiological stress
Zone of intolerance
Low Temperature High
Zone of intolerance
Range of Tolerance