Download Models of Population Growth

Models of
Population Growth
Chapter 8
Carrying Capacity
Carrying capacity (K) is the number of
individuals that can be sustained in a given
space.
Growth Curves
Two population growth curves:
J-shaped (exponential)
S-shaped (logistic)
Unlimited Growth Model
Unlimited resources. Not realistic due to
carrying capacity.
Density-dependent Growth
Model
Resources become more and more limiting.
Environmental
resistance
Population size (N)
Carrying capacity (K)
Biotic
potential
Exponential
growth
Time (t)
Logistic Growth Model
Population growth
is SLOWED by
limiting factors:
1. Densitydependent
2. Densityindependent
Density-Dependent Factors
Factors include: Competition, Predation, Disease
Pause and Think
What’s going on here?
Exponential increase in population size
(number of bacteria).
Doubling every 20 min.
This assumes resources are unlimited.
J-shaped curve – unrealistic due to
carrying capacity
Pause and Think
What’s going on
here?
P. aurelia and P. caudatum both show
exponential growth early on, then their
growth slows down.
Resources are becoming more and more
limited, which in turn affects growth.
Carrying capacity is reached.
In a mixed culture, P. aurelia becomes a
dominating species after 5 days. The
growth of P. caudatum declines at this
time. P. aurelia must be a better
competitor for resources.
Predator-Prey Cycles
Low # predators = high # prey
As # prey increase, # predators increases
High # predators = low # prey
As # prey decrease, # predators decrease
Think-Pair-Share
Which population peaks first in each cycle —
predator or prey? Why?
Population Curves in Nature
Think-Pair-Share
What is happening to the populations?
Activity 1
How/why did this lead to a population
explosion?
Industrial
Revolution
(1800)
Activity 2
How did this lead to a population decline?
WWII
(1939-1945)
Activity 3
How did this lead to a population increase?
Medicine
and
Sanitation
Pause and Think
What’s going on
here?
Reproductive Strategies
Organisms can be divided into two
categories of "strategies" for reproduction
and survival:
r–strategist species
K–strategist species
© Brooks/Cole Publishing Company / ITP
r–strategist species
r–strategist species tend to live in
environments where resources are not
limiting.
Such species tend to have high intrinsic rates
of growth (high r).
‘Quick and Many’
• r-selected species are short-lived and
produce very large numbers of offspring.
• r-selection is directed to quantity of
offspring (they put most of their energy into
numbers).
The letter ‘r’ comes from the equation for
population growth where r = rate of increase
per generation.
K–strategist species
K–strategist species tend to do well in competitive
conditions and live in environments where resources
are limiting.
They tend to have lower intrinsic rates of growth and
characteristics that enable them to live near their
carry capacity (population size near K).
‘Slow and Few’
• K-selected species produce small numbers of
offspring at less frequent intervals
• In general, K-selection is for quality of
offspring (they put most of their energy into
development).
The letter ‘K’ comes from the equation for
population growth where K = carrying
capacity of a habitat.
Carrying capacity
K
Number of individuals
K species;
experience
K selection
r species;
experience
r selection
Time
Revisual
Revisual
Revisual
Characteristics of r–Strategist
Species
© Brooks/Cole Publishing Company / ITP
Characteristics of K–Strategist
Species
Fig. 10–7b
© Brooks/Cole Publishing Company / ITP
Biozone
146 – Factors Affecting Population Size
147 – Calculating Change in Population Size