2.6.1-.2 populations. a look at the factors that tend to increase or decrease the size of a...
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2.6.1-.2 Populations
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Population Dynamics
A look at the factors that tend to increase or decrease the size of a population.
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The population size of a species in a given space at a given time is determined by the interplay between BIOTIC POTENTIAL and ENVIRONMENTAL RESISTANCE.
Biotic potential = growth rate with unlimited resources.
Environmental resistance = all the factors acting jointly to limit population growth.
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POPULATION SIZE
Growth factors(biotic potential)
Favorable lightFavorable temperatureFavorable chemical environment (optimal level of critical nutrients)
Abiotic
BioticHigh reproductive rateGeneralized nicheAdequate food supplySuitable habitatAbility to compete for resourcesAbility to hide from or defend against predatorsAbility to resist diseases and parasitesAbility to migrate and live in other habitatsAbility to adapt to environmental change
Decrease factors(environmental resistance)
Too much or too little lightTemperature too high or too lowUnfavorable chemical environment (too much or too little of critical nutrients)
Abiotic
BioticLow reproductive rateSpecialized nicheInadequate food supplyUnsuitable or destroyed habitatToo many competitorsInsufficient ability to hide from or defend against predatorsInability to resist diseases and parasitesInability to migrate and live in other habitatsInability to adapt to environmental change
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Four variables change population size:
1. NATALITY = birth rate
2. MORTALITY = death rate
3. IMMIGRATION = rate of organisms moving in
4. EMIGRATION = rate of organisms moving out
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Nu
mb
er
of
ind
ivid
uals
Time
Carrying capacity
K species;experienceK selection
r species;experiencer selection
K
REPRODUCTIVE STRATEGIES
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Opportunistic or r-Selected Species
cockroach dandelion
Many small offspringLittle or no parental care and protection of offspringEarly reproductive ageMost offspring die before reaching reproductive ageSmall adultsAdapted to unstable climate and environmental conditionsHigh population growth rate (r)Population size fluctuates wildly above and below carrying capacity (K)Generalist nicheLow ability to competeEarly successional species
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Fewer, larger offspringHigh parental care and protection of offspringLater reproductive ageMost offspring survive to reproductive ageLarger adultsAdapted to stable climate and environmental conditionsLower population growth rate (r)Population size fairly stable and usually close to carrying capacity (K)Specialist nicheHigh ability to competeLate successional species
elephant saguaro
Competitor or K-Selected Species
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SURVIVORSHIP CURVES
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Population density affects population growth.
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DENSITY INDEPENDENT FACTORS = affect a populations’ size regardless of its population density.
1. Weather
2. Earthquakes
3. Floods
4. Fires
. . . Natural disasters
R-strategists populations are most affected by these.
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DENSITY DEPENDENT FACTORS = affect a populations’ size depending on its population density.
1. Predation
2. Disease
3. Availability of food and water
4. Space
Negative Feedback!!
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INTERNAL FACTORS = might include density-dependent fertility or size of breeding territory.
EXTERNAL FACTORS = might include predation and disease.
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Species interactions influence population growth and carrying capacity = SYMBIOSIS
Competition for resources.
High
Low
Rela
tive p
op
ula
tion
den
sit
y
0 2 4 6 8 10 12 14 16 18
Days
Each species grown alone
Parameciumaurelia
Parameciumcaudatum
High
LowRela
tive p
op
ula
tion
den
sit
y
0 2 4 6 8 10 12 14 16 18Days
Both species grown together
Parameciumaurelia
Parameciumcaudatum
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Resource Portioning
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PREDATION
PREY POPULATION
PREDATOR POPULATION
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Span worm Bombardier beetle
Viceroy butterfly mimicsmonarch butterfly
Foul-tasting monarch butterfly
Poison dart frog When touched, the snake caterpillar changes shape to look like the head of a snake
Wandering leaf insect
Hind wings of io mothresemble eyes of a much larger animal
Avoiding predators
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Parasitism
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Mutualism
Oxpeckers and black rhinoceros Clown fish and sea anemone
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Shark and ramora
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Cleaning station
Sabertooth blenny
Cleaner blenny
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Commensalism
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Herbivory
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Population Growth
change in the size of a population over time.
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POPULATION = a group of interbreeding organisms (same species) that live in the same place at the same time and compete for the same resources.
Resources = food, water, shelter, mates, and so on . . .
• resources pop. size
• resources pop. size
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Populations change in response to environmental stress or changes in environmental conditions.
1. In size = # of individuals2. Density = # of individual / specific space3. Age distribution = proportions / age
group4. Dispersion =
Clumped(elephants)
Uniform(creosote bush)
Random(dandelions)
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No population can grow indefinitely!
Every environment has a CARRYING CAPACITY = the maximum number of individuals of a given species that can be sustained indefinitely in a given space.
2.0
1.5
1.0
.5
Nu
mb
er
of
sh
eep
(m
illion
s)
1800 1825 1850 1875 1900 1925Year
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Factors that affect carrying capacity:
1. Competition with/in and between species.
2. Natural and human caused catastrophes.
3. Immigration and emigration.4. Seasonal fluctuations in food, water,
shelter, and nesting sites.
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A population that has few if any resource limitations grows exponentially.
EXPONENTIAL GROWTH starts out slowly and then proceeds faster and faster as the population increases.
Time (t)
Pop
ula
tion
siz
e (N
)
“J” population growth curve
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Bacteria population
8 1024
24 hourslater
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LOGISTIC GROWTH involves initial exponential growth and then there is a steady decrease in growth as the population encounters environmental resistance and approaches carrying capacity and levels off.
“S or sigmoid” population
growth curve
Time (t)
Pop
ula
tion
siz
e (N
)
K
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Time (t)
Pop
ula
tion
siz
e (N
)K
Exponential phase
Transitional phase
Plateau phase
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2,000
1,500
Nu
mb
er
of
rein
deer
1910 1920 1930 1940 1950
Year
1,000
500
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Kaibab Plateau
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Kaibab Plateau