Transcript Population Growth Rate

POPULATION ECOLOGY
Objectives:
• I will be able to describe differences between exponential
and logistic models of population growth.
• I will be able to discuss characteristics of human population
growth.
Intro:
On a scrap piece of paper sketch two graphs:
1. Linear growth graph
2. Exponential growth graph
What will you plot on the x-axis?
What will you plot on the y-axis?
Give your graphs appropriate titles.
Population Ecology
Population = organisms of the same species that live in the same
area and interbreed.
Size of a population (N) = total number of individuals in the
population.
Density of a population = total number of individuals per area
occupied (i.e. 100 mosquitos/m2).
Dispersion = describes how individuals in a population are
distributed (clumped, uniform, or random).
Dispersion Patterns
What distribution pattern do you see?
What causes
these populations
to use this
pattern?
Population Sizes Fluctuate Over Time
• Due to environmental conditions (presence of predators,
immigration/emigration, availability of nutrients, etc.).
Growing
Shrinking
Boom and bust
Exponential Population Growth: “J-curve”
• Occurs under ideal conditions when there are no limits to the
size to which the population can grow (unlimited water, food,
living space, etc.).
• Rare.
Exponential Growth
d = delta or change
N = Population size
t = time
rmax = maximum rate of increase
Population Size, N
Growth Rate of E.
coli
Time
(hours)
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Logistic Population Growth: “S-curve”
• Occurs when resources and space are limited.
• Carrying capacity = maximum number of organisms of a
population that the environment can support for indefinite
period of time.
• Factors that limit carrying capacity = limiting factors.
• Types of limiting factors: density-dependent and densityindependent .
Label the following limiting factors as density-dependent or densityindependent:
earthquake
food and water availability
flood
disease or parasites
competition or crowding
frost
Logistic Model
carrying capacity
Some
populations
do not have
a stable
carrying
capacity
Logistic Growth
d = delta or change
N = Population Size
t = time
K =carrying capacity
rmax = maximum rate of increase
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Population Reproductive Strategies
r-selected species
K-selected species
• Exhibit J-shaped curve,
• Opportunistic species that quickly
invade a habitat,
• Short maturation and lifespan,
• Many small offspring,
• No parental care,
• High death rate.
•
•
•
•
•
Exhibit S-shaped curve,
Long maturation & lifespan,
Few large offspring,
Extensive parental care,
Low death rate.
• Population Survivorship Curves describe how
mortality
of individuals in a species
varies during
Survivorship
curves
their lifetimes.
1000
Human
(type I)
Survival per thousand
Hydra
(type II)
100
Type II.
Constant mortality
rate throughout life
span.
Oyster
(type III)
10
1
0
25
Type I.
High death rate in
post-reproductive
years.
50
75
Percent of maximum life span
100
Type III.
Very high early
mortality but the few
survivors then live
long (stay
reproductive).
Closer Look at Human Population Growth
Demographics = study of human population growth
characteristics such as:
• Growth rate = the difference between death rate and birth
rate.
• Fertility = number of offspring a female produces in her
reproductive years.
• Age structure = concerned with how many individuals are in
their pre-reproductive, reproductive, and post-reproductive
years.
• Mobility = movement of individuals in or out (in =
immigration, out = emigration).
Age Structure Diagrams = show the abundance of individuals of each age.
Which country shows slow growth, rapid growth, and no growth?
Male
Female
Afghanistan
10 8
6 4 2 0 2 4 6
Percent of population
Age
85+
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
8 10
8
Male
Female
Male
Female
Age
85+
80–84
Italy
75–79
United 70–74
65–69
States 60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
6 4 2 0 2 4 6 8
8 6 4 2 0 2 4 6 8
Percent of population
Percent of population
Always examine the base before making predictions about the
future of the population.
• The human population began exponential growth 1000 years
ago due to increases in food supply, reduction in disease,
reduction in human waste, and expansion of habitat.
• Today the human population is no longer growing
exponentially but is still increasing rapidly.
• Global carrying capacity for humans is not known.
• Ecological footprint = total land and water area needed for all
the resources a person consumes.
1.7 hectares (4 acres) per person = sustainable
US average per person = 10 hectares (25 acres)
Note: 1 hectare = 10,000 square meters or 2.5 acres
MATH CONNECTION
•
Use the table below to calculate the population growth rate of a hypothetical
population where the carrying capacity (K) = 1,500 individuals and the maximum
rate of increase per year ( rmax) is 1.0. Give your answers to the nearest whole
numbers.
Population Size (N)
500
1000
1500
2000
Population Growth Rate
(Individuals per Year)