Transcript Ecology 3 Population Ecology Ppt

Population Ecology
Ecology
What Factors Affect
Population Growth?
• Millions of red crabs live in Christmas Island in the Indian
Ocean. Each year, the entire adult crab population
migrates from forest to sea to breed, making daily life a
bit tricky for human residents!
What factors
could influence
the growth or
decline of the red
crab’s population
size?
Penguins!
• What factors could affect the size of
penguin populations in Antarctica?
• http://video.nationalgeographic.com/video/
kids/animals-pets-kids/birds-kids/penguinemperor-parenting-kids/
• http://dsc.discovery.com/tv-shows/frozenplanet/videos/criminal-penguin.htm
How do Ecologists Study
Populations?
• Geographic Range=the area inhabited by
a population.
• A population’s range can vary enormously
in size, depending on the species.
North Carolina Black Bear
Population Range:
1971—About 4,000 bears
occupied approximately 2.5
million acres
2008—About 11,000 bears
lived on almost 10 million
acres
How do Ecologists Study
Populations?
Population
Density=number of
individuals per unit
area.
• Populations of
different species often
have very different
densities, even in the
same environment.
Population Distribution
• Population Distribution=how individuals in
a population are spaced out.
What type of Population
Distribution is seen in
Penguins?
Population Growth Rates
• Population Growth=Birth Rate-Death Rate
• A population’s growth rate determines whether the
size of the population increases, decreases or stays
the same.
• Hydrilla populations tend to stay the same size over
time in its native
range in Indonesia.
• The Hydrilla population
in Florida, by contrast,
has a high growth rate.
What factors are influencing
The growth rate of Hydrilla?
Population Growth-Migration
Births + Immigration =
• Immigration vs.
Population ↑
Emigration
• A population may
grow if individuals
move into its range
(Immigration).
• A population may
decrease if individuals
move out of its range
(Emigration).
Deaths + Emigration =
Population ↓
Exponential Growth
• If you provide a population with all the food
and space it needs, protect it from
predators and disease, and remove its
waste products, what will happen?
How many bacteria will
there be in 6 more days?
(1.0 X 1013)
That is
10,000,000,000,000!
Exponential Growth
The size of each generation is larger than
the generation before it. The larger a
population gets, the faster it grows! This is
called exponential growth.
In ideal conditions,
all species will
exhibit exponential
growth, resulting in
a J-shaped growth
curve.
Logistic Growth
• Natural populations don’t grow exponentially for long.
Sooner or later, something stops exponential growth.
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Phase 1: Exponential growth
Phase 2: Growth slows down
Phase 3: Growth stops
This produces an “S-shaped”
curve
• (NOTE: This does not mean the species dies out—
only that the growth of the population stops.)
Carrying Capacity
• When the birth rate and death rate are the same
and when immigration equals emigration,
population growth stops.
• It may still rise and fall somewhat, but the ups and
downs average out at its’ carrying capacity.
• Carrying Capacity is
the maximum number
of individuals that a
particular environment
can support for an
extended period of time.
What is the carrying capacity of
deer on WallaWalla Island?
Limiting Factors
• A limiting factor is a factor that limits the growth
of a population. They determine the carrying
capacity of an environment for a particular
species. These may include:
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Competition
Predation
Parasitism & Disease
Natural disasters
Severe weather
Density-Dependent Limiting
Factors
• Density-dependent
Limiting Factors operate
strongly only when the
population density
reaches a certain level.
• These include:
• Competition
• Predation and Herbivory
• Parasitism
• Disease
• Stress from overcrowding
The relationship between Lynx and
Snowshoe hare illustrates how predation
can affect population growth.
Density-Independent Growth
Factors
• Density-Independent
Limiting Factors affect
all populations—no
matter how big or small
they are.
• These include:
• Severe weather events
such as hurricanes or
drought
• Floods
• Wildfires
• Natural disasters
What would be limiting
factors for Emperor
Penguins?
• What factors would
influence the size of
Emperor Penguin
populations?
Keystone Species
• Sometimes changes in the population of a
single species, called a keystone species
can cause dramatic changes in the
structure of a community.
Sea otters are a keystone species on the
northern California coastlines and their favorite
food is sea urchins. Sea urchins are herbivores
whose favorite food is kelp, giant algae that
grow in undersea “forests”. Sea otters were
nearly eliminated due to hunting. When that
happened, however, sea urchin populations
skyrocketed and they ate all the kelp. Without
kelp to provide habitat, many other animals
disappeared. When otters became protected,
the ecosystem slowly recovered.
Organisms in Antarctica
• Which of the following is the keystone
species of Antarctica?
Krill
Skua
Chinstrap
Penguin
Adelie
Penguin
Leopard
Seal
Emperor
Penguin