Transcript 1. What is a population? Distinguish between

Chapter 52 Reading Quiz
1.
2.
3.
4.
5.
A group of individuals of the same species
hanging out in the same area at the same
time is called a ____.
A bunch of nesting penguins would exhibit
which pattern of dispersion?
Describe under what condition “zero
population growth” occurs.
The maximum population that a particular
environment can sustain is called ______.
The world population increases by about
how many people per year?
1. What is a population? Distinguish between
density and dispersion.
• Population  individuals of one species
simultaneously occupying the same general
area, utilizing the same resources, and
influenced by similar environmental factors
• Density  the number of individuals per
unit area or volume
• Dispersion  the pattern of spacing among
individuals within the geographical
boundaries of the population 
2. How do scientists measure density?
• May count all the individuals in a sample of
representative plots; estimates become
more accurate as sample plots increase in
size or number
• May estimate by indirect indicators such
as number of nests or burrows, or by
droppings or tracks
• May use the mark-recapture method 
3. Describe the various patterns of
dispersion.
1.
Clumped pattern  “patchy” groupings of
organisms
2. Uniform pattern  spacing of individuals
is even
3. Random pattern  spacing of animals
varies in an unpredictable way
- very uncommon in nature 
4. What is demography? Why is it important
to study the age structure and sex ratio of a
population?
• Demography  the study of the vital
statistics affecting population size
• Age structure  relative numbers of
individuals of each age in a population
• Sex ratio  the proportion of individuals
of each sex found in a population 
5. Overview the various survivorship curves,
and list examples.
• Type I curve  flat during early and
middle life and drop suddenly as death
rates increase among the older individuals
• Type II curve  intermediate with
mortality being more constant over the life
span
• Type III curve  show very high death
rates for the young followed by lower
death rates after individuals have survived
to a certain critical age 
6. Overview how life histories are diverse yet
exhibit patterns.
• Life history  an organism’s schedule of
reproduction and death
- life histories often vary in parallel with
environmental factors
- tropical birds lay fewer eggs than those
in higher latitudes, which reflects the
number of offspring that can successfully
be fed (parent birds can gather more food)

7. Describe the concept of a trade-off between
reproduction and survival. What does this have to do
with offspring produced, number of matings, and age
of maturation?
• Relates to the principle of allocation
• Episodes of reproduction 
- semelparity: invest most in growth &
development, then reproduce before dying
- iteroparity: fewer offspring produced over many
seasons
• # of offspring per episode
• Maturation age  balances the cost between
current reproduction and survival plus future
reproduction 
8. Describe the conditions for the
exponential model of population growth.
• Describes an idealized population in an
unlimited environment
• Birth rates must be higher than death
rates
• Produces a J-shaped curve 
9. Describe the concept of “carrying
capacity” and logistic population growth. How
does this model fit with real populations?
• The “carrying capacity” of a habitat is the
maximum stable population size that the particular
environment can support over a relatively long time
period
• A “logistic population growth” model assumes the
rate of population growth (r) slows as the
population size reaches the carrying capacity of
the environment
• Some assumptions do not hold true for all
populations 
Ex: Populations approach carrying capacity
smoothly 
10. Differentiate between K-selected
populations and r-selected populations.
• K – selected  “equilibrium populations”
- live at a density near the limits of their
resources
• r – selected  “opportunistic populations”
- more likely to be found in variable
environments where population densities
fluctuate or in open or disturbed habitats
where individuals have little competition 
11. Describe how density-dependent factors
regulate population growth.
• A density-dependent factor intensifies as
the population size increases, affecting
each individual more strongly
• Seen in intraspecific competition, where
two or more individuals of the same species
rely on the same resource
• Ex: disease, competition 
12. Describe the effects of densityindependent factors on population size.
• Density-independent factors are
unrelated to population size and affect the
same percentage of individuals regardless
of the size of the population
• Ex: weather, climate, natural disasters 
13. How are most populations in nature
regulated?
• A mix of density-dependent and densityindependent factors probably limits the
growth of most populations
• Many populations remain fairly stable in
size, close to the carrying capacity
determined by the density-dependent
factors
• Show short-term fluctuations due to the
density-independent factors 
14. Describe how some populations have
regular boom and bust cycles.
• Lemmings have a 3 – 5 year cycle
• Snowshoe hares have a 9 – 11 year cycle
• Crowding may regulate cyclical population by
affecting the organisms endocrine systems (stress
due to high density)
• May result from a time lag in response to densitydependent factors, causing the population to
overshoot and undershoot the carrying capacity
• Cicadas have a 13 – 17 year cycle, probably an
adaptation to reduce predation 
15. Overview the history of human population
growth.
• The human population has been growing
exponentially for centuries (since 1650) but will
not be able to forever
• The advent of agriculture 10,000 years ago
increased birth rates and decreased death rates
• Better sanitation and nutrition since Industrial
revolution
• Scientists can not agree on what the carrying
capacity of humans on earth might be…hopefully it
will be a smooth leveling out once we get there 