Learning Target: Population Density & Distribution
Ch. 14.3 (pp. 436 – 439)
I Can…Explain how population density, dispersion
patterns and survivorship curves, affect the
reproductive strategies of a species.
I Will…
•
•
Calculate the density of a population of organisms
in a given area.
Describe the dispersion pattern of organisms in a
given area.
•
•
•
Infer what type of intraspecies and interspecies
relationships cause specific patterns of dispersion.
Describe the three types of survivorship curves.
Infer connections between survivorship curves and
reproductive strategies.
KEY CONCEPT: Each population
has a density, a dispersion pattern,
and a reproductive strategy.
Population density – is a measurement
of the average number of individuals in
a defined space.
# of individuals = Population density
Area (units2)
e.g. 28 turkeys in a field of 4-square acres is
28 turkeys = 7 turkeys / acre2 or 7 turkeys
4 acres2
per square-acre
NOTE: the unit is squared NOT the number before the unit
Population dispersion – the way in
which individuals of a population are
spread in an area or volume.
Clumped dispersion – individuals live
close together in order to facilitate
mating, gain protection, or access food
resources.
Uniform dispersion – Territoriality
and intraspecies (within species)
competition for limited resources leads
to individuals living at specific
distances from one another.
Random dispersion – Individuals are
spread randomly within an area or
volume. Species often solitary with few
competitors and few natural predators.
Survivorship curve – generalized
diagram showing the number of
surviving members over time from a
measured set of births.
Type I – low level of infant mortality
(death) and population survives to old
age. Common in large mammals and
humans.
Survivorship curve
Type II – Survivorship rate is equal at all
ages of an organism’s life. (Equal chance
of living or dying at anytime)
Common in birds, small mammals, and
reptiles.
Survivorship curve
Type III – Very high birthrate and very
high infant mortality (death) rate.
Common in invertebrates (no backbone),
fish, amphibians, and plants
Survivorship curve
Reproductive strategy – reproductive
practice that provides a survival strategy
for a species.
e.g. Fish (Type III) lay hundreds of eggs
to ensure at least some offspring reach
adulthood without being eaten and are
able to reproduce.