Transcript Chapter 4: Population Biology

Chapter 4:
Population
Biology
Population
• group of organisms,
all of the same
species, that live in
a specific area
How fast do populations
grow?
• Not linear growth – so it is
not a straight line
• Graph- starts to increase
slowly, then resembles a Jshaped curve
• Initial increase slow, b/c #
of organisms that
reproduce is small
• Increases b/c the total # of
individuals that can
reproduce has increased
Is Growth Limited?
• J-shaped growth curve illustrates exponential
population growth
• Exponential Growth – means that as a population
get larger, it also grows at a faster rate
What Can Limit Growth?
Population growth does have limits
• Limiting Factors – food, disease,
predators, or lack of space will
Cause population growth to SLOW
• Under these conditions the
population may stabilize in a S-shape
growth curve
Carrying Capacity
• the number of organisms of one species
that an environment can support
indefinitely
• Developing population – more births than
deaths and the population increases until
the carrying capacity is reached or passed
• When a population overshoots the
carrying capacity, limiting factors come
into affect
• Deaths begin to exceed births and the
population falls below the carrying
capacity
Reproduction Patterns
• Life-History Pattern- organisms
reproduction pattern
• Slow life-history pattern – slow rate of
reproduction and produce relatively
few offspring
– Ex. Elephant
• Fast life-history pattern – reproduce
rapidly and produce many offspring in
a short period of time
– Ex. Mosquito
Rapid Life- History Patterns
• Common among organisms in changeable
or unpredictable environments
• Organisms have:
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Small body size
Mature rapidly
Reproduce early
Short life span
• reproduction rises rapidly then decline
when environment becomes unsuitable
• population survives and will reproduce
again when the environment is favorable
Slow Life- History Patterns
large species that live in more stable environments
– Elephants, Bears, Whales, Humans, and plants
(trees)
• reproduce and mature slowly
• long-lived
• maintain population sizes at or near carrying
capacity
Density Factors and
Population Growth
3 Patterns of Dispersal:
1. Random
2. Clumped
3. Uniform
Density-Dependent Factors
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disease
competition
predators
parasites
food
• increasing affect
as the population
increases
• Example- corn
fields
• Crops grow close
together
• Disease can
spread rapidly and
kill off the whole
crop
Density-Independent
Factors
can effect most populations regardless of
their density
• Most are abiotic factors
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Volcanic eruptions
Temperature
Storms
Floods
Drought
Chemical Pesticides
Major habitat destruction
Usually affect smaller organisms more
– Example – Mosquitoes – severe winters kill the
adults of most species
Population Size
• limited by abiotic and biotic factors
• controlled by various interactions
among organisms that share a
community
• Predation – can effect population
size in minor and major ways
• Locusts eat
acres of lettuce
on a farm
• Brown snake
introduced into
Guam, there
were no native
predators, and it
preyed freely on
native birds –
drastic effect on
the population
size
• predator- prey relationships are known to
experience cycles or changes in their numbers
over periods of time
• prey population increases and there is more food
for the predator, so the predator population
increases
• predator population increase and predation
increase, therefore – the prey population
declines.
• With less food, the predator population decrease.
• Cycle starts again
Competition within a Population
• density dependent factor
• few individuals compete for
resources, usually no problems
• When population increase and the
demand exceeds the supply, the
population size decreases
Crowding and Stress
• populations become
crowded, individuals
exhibit stress
• stress symptoms
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Aggression
decrease in parental care
decreased fertility
decreased resistance to
disease
• all have negative effects
on a population
Human Population
•
Demography – study of human population size
– density and distribution
– movement
– Birth and death rates
Human Population Growth
• Humans change their environment
• Developed methods for producing
more food
• infant mortality rate decreased
• clean water
• All enable people to live longer and
produce more offspring
• Population Grows
Calculating Growth Rate
• Birthrate – number of live births per 1000
population in a given year
• Death rate – number of deaths per 1000
population in a given year
• Immigration – movement of individuals into a
population
• Emigration – movement of individuals out of a
population
Calculate a population’s growth
rate by
• (Birthrate + Immigration Rate) – (Death rate +
Emigration Rate) = Population Growth Rate
• PGR = (B + I) – (D + E)
• Immigration and emigration are not always
accurate use:
• PGR = Birthrate – Death rate
• Positive Growth Rate
– unless the growth rate becomes
negative the population continues
to grow, just slower
• Doubling Time
– time needed for a population to
double in size
• Age Structure
– refers to the portions of the
population that are in the different
age levels