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Population Ecology
• Ecology: study of the interactions of organisms with
each other & with the physical environment
• Population: all organisms of same species that live in
a particular area
• Community: all of the different populations in a given
area
• Ecosystem: all of the different populations in a given
area including living (biotic) & nonliving
(abiotic) parts
• Biosphere: portion of Earth’s surface where life exists
Patterns of Population Growth
•
Each population has particular patterns of growth
•
Population size can stay the same, increase or
decrease according to per capita rate of increase
(growth rate)
•
Biotic potential:
Highest possible per capita rate
of increase for a population
Patterns of Population Growth
•
Factors affecting biotic potential:
1. Average number of offspring per
reproduction
2. Chances of survival until age of reproduction
3. Age at first reproduction
4. How often each individual reproduces
•
Population growth patterns can be exponential
or logistic
Patterns of Population Growth
• Exponential patterns
of population growth
result in a J-shaped
curve because growth
rate is increasing
• Logistic growth
patterns result in an
S-shaped curve
because
environmental
resistance
Patterns of Population Growth
• Environmental resistance: all those environmental
conditions that prevent populations from
achieving their biotic potential
–
–
–
–
Limited food supply
Accumulation of waste products
Increased competition
Predation
• Carrying capacity: number of individuals of a
species that a particular
environment can support
Survivorship Curves
• Type I curve: individuals
survive past midpoint &
death comes near end
of maximum life span
• Type II curve: survivorship
decreases at a constant
rate throughout life
span
• Type III curve: most
individuals die young
Human Population Growth
• Growth in less developed
countries is in exponential
growth phase
– Ex. Latin America, Africa,
Asia
– Population growth is
expanding rapidly
– Majority of people live in
poverty
• Growth in more
developed countries has
leveled off
– Ex. North America, Europe
– Population growth is low
– Good standard of living
Human Population Growth
•
Suggestions to reduce population growth explosion in
LDC (less developed countries):
1. Establish or strengthen family planning practices
(birth control)
2. Reduce desire for large families
– Provide education
– Raise status of women
– Reduce child mortality
– Improve economic stability
3. Delay onset of childbearing
Age Distributions
•
Age-structure diagrams
divide the population into
three groups:
1. Preproductive
2. Reproductive
3. Postreproductive
•
LDC population continues
to grow as long as there
are more young women
enter reproductive years
than older women leaving
them (unstable age
structure).
Regulation of Population Growth
•
Factors that regulate population growth consist
of two types of life history patterns:
1. Opportunistic patterns
–
–
–
–
–
–
Small individuals
Many offspring
Mature early
Short life span
Little or no care of offspring
Ex. Insects, weeds
2. Equilibrium patterns
– Large individuals
– Large populations
– Slow to mature
– A lot of care of offspring
– Long lifespan
Ex. Birds, mammals
Regulation of Population Growth Cont.
• Density-independent factors
– Abiotic factors (weather, natural disasters)
– Effects population all the same
– Opportunistic life history pattern
• Density dependent factors
– Biotic factors (competition, predation, parasitism)
– Effects depend on size of population
– The more dense a population, the faster a disease
might spread
– Equilibrium life history pattern
Competition
• Occurs when members of a different species try to utilize
a resource that is in limited supply
– Light, space, nutrients
• Ecological niche: role organism plays in the community
that includes its habitat & interactions
with others
• Habitat: where an organism lives
• Competition exclusion principle: no two organisms can
occupy the same niche at the same
time when resources are limited
• Resource partitioning reduces competition by dividing
the feeding niches.
Predation
•
Predation occurs when
one organism feeds on
another (prey)
•
Predator-prey cycling
can occur if:
1. The predator population
overkills the prey & forces
a decline in predators.
2. The prey population has
huge booms of population
growth beyond their
carrying capacity which
results in a crash.
Predator population
declines due to lack of
food.
Antipredator Defenses
• Prey have evolved strategies to escape predation
• Coevolution: two species adapting in response to
selective pressure imposed by each other
–
–
–
–
Sharp spines of cacti
Pointed leaves of holly
Leathery leaves of oak tree
All discourage predation by insects
• Prey escape predation by utilizing camouflage,
poisonous secretions, fright, flocking together, warning
coloration, and mimicry.
Mimicry
•
•
1.
2.
Occurs when one species
resembles another species
or an object in environment
to escape predation
There are 2 types of mimicry:
Batesian mimicry: prey that
is not harmful mimics another
species that is harmful.
Ex. Flower fly & beetle will
look like stinging wasp
Mullerian mimicry: both
species that look alike have
good defenses
Ex. Bumble bee & wasp
Symbiosis
•
Refers to close interactions between members of two
different species
•
Three types of symbiotic relationships are:
1.
2.
3.
Parasitism:
(+) (-) the parasite gets nourishment from
another organism called the host.
Ex. Leeches, ticks, tapeworms
Commensalism: (+) (0) one species benefits, the other species
is neither harmed nor helped.
Ex. Barnacles on whales, clownfish/anenomes
Mutualism:
(+) (+) both species in the association benefit.
Ex. Ants & bullhorn acacia tree, plants &
animal pollinators