1. Chapter 27-29
Population Growth

2. 27.1 How Are Populations Distributed In Space And Time?
Organisms arrange themselves in space in many different ways.
Ecologists recognize three major types of spatial distribution:
Clumped
Uniform
Random

3. 27.1 How Are Populations Distributed In Space And Time?
Individuals in many populations clump together in groups, and include social groups such as elephant herds, wolf packs, lion prides, flocks of birds, and schools of fish.
clumped
(a)
Clumped distribution
Fig. 27-1a

4. 27.1 How Are Populations Distributed In Space And Time?
Creosote bushes release chemicals into the soil around them that inhibit germination of seeds from other plants.
uniform
(b)
Uniform distribution
Fig. 27-1b

5. 27.1 How Are Populations Distributed In Space And Time?
Trees and other plants in rain forests may be randomly distributed.
random
(c)
Random distribution
Fig. 27-1c

6. 27.2 How Do Populations Grow?
A simple equation for the change in population size within a given period is as follows:
(births – deaths) + (immigrants – emigrants) = change in population size

7. 27.2 How Do Populations Grow?
A constant growth rate increases population size rapidly (continued).
If the per capita growth rate r remains constant, the number of people added to the population increases each year.
population growth in the first year (rN) is 0.10 x 10,000 = 1,000 people; at the end of year 1, the population has 11,000 people.
This pattern of continuously accelerating increase in population size is exponential growth.

8. 27.2 How Do Populations Grow?
A population’s growth rate depends on patterns of reproduction.
Every species has a built-in capacity for population growth, but the speed of this potential growth varies among species, dependent upon the following factors.
The age of first reproduction
The frequency of reproduction
The average number of offspring produced each time
The length of an organism’s reproductive life span
The organism death rate

9. 27.2 How Do Populations Grow?
Some species produce large numbers of offspring quickly.
The harmless bacterium Staphylococcus is found on the human body.
Each bacterial cell can divide every 20 minutes, doubling the population three times each hour.
The larger the population growth, the more cells there are to divide.

10. 27.2 How Do Populations Grow?
J-shaped exponential growth curves in bacteria
bacteria
time (minutes)
number of bacteria
1,200
1,100
1,000
900
800
700
600
500
400
300
200
100
,024 2,048
number of individuals
Exponential growth curves are J-shaped
(a) 60
120
180
240
Bacteria
time (minutes)
Fig. 27-2a

11. 27.2 How Do Populations Grow?
Other species produce fewer but longer-lived offspring.
The golden eagle is a long-lived, rather slowly reproducing species.
Figure 27-2 compares the potential population growth of eagles with that of bacteria, assuming no deaths.
All three curves on this figure are J-shaped, indicating exponential growth.

12. 27.2 How Do Populations Grow?
J-shaped exponential growth curve in eagles
number of eagles (i)
number of eagles (ii)
time (years)
2,000
1,800
1,600
1,400
1,200
1,000
800
600
400
200
eagles
0 2 4 30
,314 2,504 4,770 9,088 17,314 8
12 18
,066 1,764
(i)
Reproduction begins at 4 years
(ii)
number of individuals
Reproduction begins at 6 years
(b)
Eagles 5 10 15 20 25 30
time (years)
Fig. 27-2b

13. 27.2 How Do Populations Grow?
The effects of death rates on population growth
2,500
bacteria
No deaths
10% die between doublings
2,000
25% die between doublings
1,500
number of individuals
1,000
500 1 2 3 4 5 6
Fig. 27-3
time (hours)