Transcript Populaton Growth ppt

Ecology
Population Growth
Population Growth
– Any organism provided ideal growing
conditions will experience rapid population
growth
– Larger it gets, faster it grows – exponential
growth curve
– Darwin calculated if all the offspring of 1
pair of elephants were to survive and
reproduce, after 750 yrs there would be 19
million elephants
Why doesn’t exponential
growth happen for long?
Sooner or later, you will run out of
resources.
 Competition for resources
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– deer population for example
Logistic Growth
– Lets introduce a few animals to a new
environment
– at first the population begins to grow
slowly
– Soon the population grows rapidly –few
die, many produced
– Population growth begins to slow –
growing still, but slower – why is this
happening?
Carrying Capacity
Carrying Capacity
The largest # of
individuals an
environment can
support
Logistic Growth
– When birthrate and deathrate are equal,
population growth stops
– Steady state – population size stays the
same (averages out)
Logistic Growth
– Draw a line through the middle of steady
state – carrying capacity
– Carrying capacity is the average of the
steady state
– Factors at this point keep the population
from getting any bigger – food,
overcrowding, competition
Logistic Growth
Occurs when resources become less available
(Slows population growth rate)
Slow population growth rate due to
1.
Decrease in birthrate
2. Increase in deathrate
3. Immigration decreases
4. Emigration increases
Density Dependent Limiting
Factors
– factors that control population size operate
more strongly on large populations than
small ones
– Competition, predation, parasitism, and
crowding
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Competition
– struggle for food, water, & space
Density Dependent Limiting
Factors
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Predation
– Just about every species serves as food for
some other species
– Predators vs. Prey
Density Dependent Limiting
Factors
 Prey
– defenses
–Poison chemicals
–Shells
–Poison skins
–Camouflage
–Behaviors such as mimicry
Poison
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Batesian mimicry
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Monarch butterfly
or viceroy
butterfly?
Mertensian mimicry
(Warning coloration)
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Coral snake or King snake?
Camouflage in nature
Industrial
melanism of the
peppered moth
Shells as
Defense
Slime as Defense
Limiting Factors
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Growth of many species is controlled by
density dependent and density
independent limiting factors.
Density Dependent Limiting
Factors
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Counterdefenses
– Monarch butterfly caterpillars have evolved
the ability to avoid certain plant poisons
– Predator population varies with prey
population
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Large # of prey = large # predators = small #
prey
Density Dependent Limiting
Factors
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Symbiosis means living together
– Parasitism – one benefits, one is hurt  
– Commensalism – one benefits, one not
affected  
– Mutualism - both benefit  
Density Dependent Limiting
Factors
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Crowding and Stress
– crowding helps parasites travel from host
to host
– Most animals have built in need for certain
amount of space – hunting, nesting,
territory (fish for example)
– Increase fighting = decrease breeding
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Make Love Not War
Limits to population growth
Limiting Factor – causes population growth to decrease
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Density Dependent Limiting Factors
Factors which work best with a large dense population
Interspecific competition
Intraspecific competition
Predation
Disease
Parasitism
Density Independent Limiting Factors
Tornado, hurricane, drought, temperature
Human disturbance (Clear-cutting forests or damming rivers)
Competition
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Competitive exclusion principle
No two species can occupy the same niche
in the same habitat at the same time
Interspecific competition occurs between
two species for similar resources
Intraspecific competition occurs within a
species for similar resources
Why Competition?
Limited resources
 Food
 Water
 Space
 Shelter
 Mates
 Sunlight
Predation
Prey have evolved defense mechanisms to
prevent predation
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Poison (Monarch butterflies & Dart frogs)
Mimicry
Camouflage
Shells
Slime
Density Independent Limiting
Factors
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Because population size does not
matter in these instances, these natural
occurances are called densityindependent limiting factors.
Density Independent Limiting
Factors
Long hot dry weather
 Frosts
 Happen regardless of how large the
population is
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Density Independent Limiting
Factors
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Boom and Bust Growth Curves
– Populations grow exponentially then crash,
then back again
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Aphids feed on plant buds that can be washed
away in a rain storm
Human Population Growth
Exponential growth due to:
 Agriculture
 Industry
 Better healthcare / medicine
 Reduced death rate
 High birth rate
Human Population Growth
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Human populations tend to increase
over time
– About 500 years ago, human population
began growing exponentially.
– Today, it has slowed in the US and parts of
Europe, but not in most of the rest of the
world
– China, India, Africa, and Latin America
Demography
The scientific study of human populations
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Birthrates
Deathrates
Age structure
U.S. Age Distribution
South Africa Age
Distribution
South Africa and U.S.