1

Biology 101

Lecture 3: Populations

Learning Objectives

1. Understand the differences between population size,

density, age structure, and distribution.

2. How does age structure affect population growth?

3. Recognize the different dispersion/distribution patterns

found in nature.

4. What factors affect population growth? What limits it?

5. What is the difference between exponential and

logistic growth?

6. Compare/contrast density dependent and

independent controls.

7. Differentiate between the three survivorship curves.

2

Salmon in California

Data from Peter Moyle, UC Davis

Less than 1% of original populations remain

Outline

Populations

1. Size and growth

a. Exponential

b. Logistic

2. Age structure

3. Distribution

a. Clumped

b. Uniform

c. Random

4. Density

5. Survivorship

3

Age Structure Diagrams

Shows age distribution of a population

Rapid

Growth

Slow

Growth

Zero

Growth

Negative

Growth

Otter age structure

Otters released in Oklahoma in 1960s & 1990s

BARRETT, D. A., & LESLIE JR., D. M. (2012). Spatio-Temporal

Variations in Age Structures of a Partially Re-established

Population of Northern River Otters (Lontra canadensis).

American Midland Naturalist, 168(2), 302-314.

4

Discuss: Western populations had more young

otters than eastern populations. What does this mean?

Distribution

clumped • Clumped populations:

– Suitable physical, chemical, and biological conditions are patchy, not uniform.

– Resources patchy

– Social groups

5

Distribution

• Rare in nature

• Result of fierce

competition for very

limited resources

uniform

45.1

Distribution

• Uniform environmental

conditions

• Members are neither

attracting nor repelling

each other

random

45.1

6

Human Population Growth

• What kind of growth?

Life Table for the US Human

Population in 2001

7

Survivorship Curves

• represent age-specific patterns of death for a

given pop in a given environment

• Each species has a characteristic curve.

• Three types of curves are common in nature.

45.5

Figure 45.11

Page 809

•Type I: low death rates early in life and through midlife,

with a sharp increase in death rate among older-age

groups (e.g., humans).

8

Fig. 45-11a, p.809

Figure 45.11

Page 809

•Type I: low death rates early in life and through midlife,

with a sharp increase in death rate among older-age

groups (e.g., humans).

•Type II: fairly even mortality rate throughout life of

organism (e.g., birds).

9

Fig. 45-11b, p.809

Figure 45.11

Page 809

•Type I: low death rates early in life and through midlife,

with a sharp increase in death rate among older-age

groups (e.g., humans).

•Type II: fairly even mortality rate throughout life of

organism (e.g., birds).

•Type III: high death rates early in life followed by a sharp

decline of death rates for the survivors (e.g., fish and

many insect populations).

10

Fig. 45-11c, p.809

Homework

• Study for Quiz #1 Wed

– Scientific method

– Evolution

• Pre-lab: due at the beginning of lab

– Lab packet this week