Population Ecology
What is a Population?
An interbreeding group of the same species
living in the same general area
• may be distinguished by natural or
arbitrary boundaries
Population Density vs Dispersion
• the number of
individuals per unit
area or volume
• the pattern of
distribution of
individuals
Patterns of Dispersion
What is the
pattern for the
population on the
previous slide?
On the title slide?
Population Dynamics
Demographics
Life table: age-specific summary
of survival pattern of a population
Survivorship Curve
Survivorship Curves
I – Fewer offspring
and low mortality
until old age due
to parental care.
II – Death rate is
relatively
constant
throughout the
life span.
III – Many offspring
& high mortality
in young due to
lack of parental
care.
Reproductive Rates
• focus on females
• reproductive
tables:
age-specific
summary
Semelparity vs Iteroparity
• reproduce once
• reproduce repeatedly
• MANY offspring
• FEW offspring
• most offspring die
• most offspring survive
• offspring are “on their own”
• Offspring are cared for
Population Growth Rate
Change in
Births (B) – Deaths (D) = population
size per unit
time (DN/Dt)
•
Per capita birth rate (b): average # offspring produced
by individual
•
Per capita death rate (m): used for expected # of deaths
•
Per capita rate of increase (r)
rN = bN – mN = DN/Dt
Simplifying the Population Growth Rate
rN = bN – mN = DN/Dt
r=b–m
• r > 0 : population is growing
• r < 0 : population is shrinking
• r = 0 : zero population growth (ZPG)
Exponential
Growth
J-Curve Growth
r is steady & positive
Maximal growth rate
Abundance of resources
Logistic Growth Model
carrying capacity (K):
Max population size
habitat can sustain
Logistic Model & Real Populations
Growth rate decreases approaching K
or
Population size overshoots K, then decreases as a result
Trade-offs in life history
Trade-off between reproduction
and survival
Invest in numbers of offspring
or in provisions to offspring?
• K–selected competitive species
• r-selected opportunistic species
Regulation of Population Growth
Density-independent factors:
• unrelated to population density
Density Dependent Factors:
• change in response to population density
• decrease birth rates and/or increase death rates
closer to the carrying capacity
Density Independent vs
Density Dependent Growth
Population Dynamics
Fluctuate due to changes in weather & climate, resources,
predator population size, pathogens
Human Population Growth
Why the Population Explosion?
Industrial Revolution
Medical & Biotechnology Revolution
Human Growth Rate is Decreasing
The Demographic Transition
• high birth & death rates
• high birth, low death rates
(population expansion)
• low birth &
death rates
Key: education
of women!
Age Structures
• useful for predicting future population growth
Ecological Footprint
•
surface area required to sustain each person
(at current levels of consumption)
Worldwide Energy Use
One person in the U.S. consumes more than 20
times the resources of a person living in an LDC.