Download Section 14.3: Population Density and Distribution

Section 14.3:
Population
Density and
Distribution
Biology
Objectives
• How is the number of individuals that live in a
defined area described?
• How do geographic dispersions of a population
show how individuals in a population are spaced?
• How are density and geographic dispersal
characteristics of a population?
• Describe the three basic types of survivorship curves
in relation to reproductive strategies.
Population Density
• Scientists need to measure a species’ population
• By collecting data about a population in a
particular area, scientists can calculate the
population density for that area
• Population Density: measurement of the number of
individuals living in a defined space
• Ratio of number of individuals that live in a
particular area to the size of the area
• # of individuals / area (units2)
Population Density
• Calculation of population densities allows scientists
to notice any changes in population
• This can lead scientists to understand if a population
density change is due to
o Environmental Factors
o Normal variation in the life history of a species
• Allows changes to be made if needed
Geographic Dispersion
• Studying how individuals of the same species
interact and how different species interact in
regards to their population density
• Population Dispersion: the way in which individuals
of a population are spread in an area or a volume
Population Dispersion
• Clumped Dispersion
o Individuals live close
together or in groups
o Facilitates mating
o Give protection
o Access to food resources
increases
Population Dispersion
• Uniform Dispersion
o Territorial disputes and
intra-species competition
o Due to limited resources
o Individuals live at specific
distances from one
another
Population Dispersion
• Random Dispersion
o Individuals are spread
randomly within an area
o In plants can be due to
windblown seeds
Survivorship Curves
• General diagram showing the number of surviving
members over time from a measured set of births.
o Measuring the number of offspring born in a year
o Follow through until death
o Gives life history of a species
• The number of individuals surviving from year to
year decreases, but a substantial portion will live a
full life and reproduce
Survivorship Curve
Survivorship Curve
• Type I
o Low level of infant
mortality
o Population will generally
survive to old age
• Parental care for young
o Ensures offspring stay
alive until can survive on
own.
• Seen more often in
large mammals
Survivorship Curve
• Type II
o Rate of survivorship is
equal at all ages of the
organism’s life
o Equal chances of living
and dying from disease
or predation
• Birds, small mammals,
and some reptiles
Survivorship Curve
• Type III
o Very high birth rate
o Very high infant mortality
rate
• Many offspring will die
from predation, but
some will survive to
adulthood and
reproduction
• Invertebrates, fish,
amphibians, plants
Output
1. Draw and label a diagram showing the three
population dispersion patterns.
2. Use the Frayer model demonstrated in class to
explain Type I, Type II, and Type III survivorship
curves.