Chapter 5

Populations

Populations• members of the same species that reside

in the same area

Characteristics of populations

1. Geographic distribution:

Where do they live?

2. Density:

How many are found in a given unit of area?

3. Growth rate:

How quickly do they grow?

Daisy population

Factors affecting population growth?

1. Birth rate: number of offspring

per time period2. Death rate:

number of deaths per time period

3. Migration rate movement in and out of populations in a period of time• Immigration: in• Emigration: out

Exponential growth

• Occurs when individuals in a population reproduce at a constant rate

• Only under ideal conditions

Activity

• Assume 2 flies (one male and one female) start reproducing.

• Assume constant rate reproduction.• Assume each female lays 120 eggs (½

male ½ female).• Calculate the total population at the end of

6 cycles.• Graph your results.• Create a curved fit.

Result?

1. 2 flies

2. 120 offspring (60 females)

3. 14,400

4. 864,000

5. 51,840,000

6. 3,110,400,000

Logistic growth• Occurs when a population’s growth rate slows or

stops, following a period of exponential (geometric) growth

• Carrying capacity: largest number

that a given environment

can support

Click image to play video.

• What can slow down exponential growth?

Limiting factors• cause population growth to stop

• Density-dependent factors depend upon population size:– Competition– Predation– Parasitism– Disease

Competition• Occurs when 2 species occupies the same

niche & habitat

• What are some things they compete for?

Competition

• Using this 1990 census map of US population densities, what can one deduce at resource competition between the different parts of the country? How can competition explain

population size in nonhuman species?

Predation

• Predator: one that consumes or exploits a particular species for self gain

• Prey: one that is consumed or exploited

• What would you expect to happen to prey populations if the predator numbers increased or if predator numbers decreased?

Figure 5-7 Wolf and Moose Populations on Isle Royale

60

50

40

30

20

10

01955 1960 1965 1970 1975 1980 1985 1990 1995

2000

1600

1200

800

400

0

2400

Moose Wolves

Describe the relationship between the wolf and moose populations shown in the graph.

Predator-Prey relationships

Parasitism and Disease

• Both deplete the host organism of vital minerals and nutrients to sustain life.

• Death of the organism results in the decline of population size.Heart worms (roundworms) as

exposed by a veterinarian

Density-independent factors

• Limiting factors on population size,

regardless of the

number of individuals

in the population– Weather– Natural disaster– Seasonal cycles– Human activities (habitat

destruction) Corals that have died from weather changes, leading to increased

water temperature and pollution.

Historical Human Population Growth

Agriculturebegins

Plowingand irrigation

Bubonicplague

IndustrialRevolutionbegins

It took 500,000 years to reach 1 billion & less than 200 years to reach 5 billion.

What might be some reasons why?

What’s the carrying capacity for the human population?

What if it’s right here? ---------------------------

But, what if it’s right here? ---------------------------

(We do know it lowers when pollution occurs)

Age structure diagrams (population profiles):

graphs showing numbers of people in different age groups in the population

U.S. Population Rwandan PopulationMales MalesFemales Females

What conclusions can be drawn from these graphs?

Why do the population growth curves look different between developing and

developed countries?

Demography

• Study of human population size, density and distribution, movement, and its birth and death rates

• Birth rate is the number of live births per 1000 population in a given year.

• Death rate is the number of deaths per 1000 population in a given year.

Calculating how fast populations grow

• Birthrate – Death rate = Population Growth Rate (PGR)

• If PGR > 0, then the population is growing.

• If PGR < 0, then the population is declining.

R/K Selection

• R-strategists the ability to reproduce quickly, small body size, early maturity onset, short generation time and short gestation period. Results in unstable or unpredictable environments

• K-strategists large body size, long life expectancy, and the production of fewer offspring that require extensive parental care until they mature, long gestation period. Results in stable or predictable environments

Animal

Gestation orincubation,

in days (average)

Longevity,in years(record

exceptions)

Ass 365 18–20 (63)

Bear 180–2401 15–30 (47)

Cat 52–69 (63) 10–12 (26+)

Chicken 22 7–8 (14)

Cow 280 9–12 (39)

Deer 197–3001 10–15 (26)

Dog 53–71 (63) 10–12 (24)

Duck 21–351 (28) 10 (15)

Elephant 510–7301 (624) 30–40 (71)

Fox 51–631 8–10 (14)

Goat 136–160 (151) 12 (17)

Groundhog 31–32 4–9

Guinea pig 58–75 (68) 3 (6)

Hamster, golden 15–17 2 (8)

Hippopotamus 220–255 (240) 30 (49+)

Horse 329–345 (336) 20–25 (50+)

Human 253–303 652 (120)

Kangaroo 32–391 4–6 (23)

Lion 105–113 (108) 10 (29)

Monkey 139–2701 12–151 (29)

Mouse 19–311 1–3 (4)

Parakeet (Budgerigar) 17–20 (18) 8 (12+)

Pig 101–130 (115) 10 (22)

Pigeon 11–19 10–12 (39)

Rabbit 30–35 (31) 6–8 (15)

Rat 21 3 (5)

Sheep 144–1521 (151) 12 (16)

Squirrel 44 8–9 (15)

Whale 365–5471 n.a.

Wolf 60–63 10–12 (16)