NEW AIM: How do scientists describe population growth?

Population Ecology- The study of changes in population size and the factors that regulate it.

Population- group of individuals of a single species that occupy the same general area

1. Rely on same resources

2. Influenced by the same biotic and abiotic factors

3. High likelihood of interbreeding

AIM: How do scientists describe population growth?

Let’s look at population growth of bacteria starting from a single bacterium

- binary fission every 20 minutes under ideal conditions

Q: How many will there be after 36 hours?

AIM: How do scientists describe population growth?

Let’s look at population growth of bacteria starting from a single bacterium

- binary fission every 20 minutes under ideal conditions

Graph it:

Q: How many will there be after 36 hours?

A: 2108 (enough to cover the planet one foot deep)

2n Where n = # of divisions

AIM: How do scientists describe population growth?

1. Exponential Growth Model

(J-shaped curve)

What does the rate of growth depend on in this model?

The number of individuals ONLY

So why is Earth not covered in bacteria?

AIM: How do scientists describe population growth?

2. Population limiting factors- environmental factors that restrict population growth

Ex. Fur seals on St. Paul Island

AIM: How do scientists describe population growth?

2. Population limiting factors- environmental factors that restrict population growth

Ex. Fur seals on St. Paul Island

1. Uncontrolled hunting until 1925

2. Population jumped until 1935

- Almost exponential3. Population stabilized

- Some hunting- limited breeding grounds

AIM: How do scientists describe population growth?

2. Population limiting factors- environmental factors that restrict population growth

3. Logistic Growth Model

(S - shaped curve)

Q: How does the logistic model differ from the exponential model?

AIM: How do scientists describe population growth?

2. Population limiting factors- environmental factors that restrict population growth

3. Logistic Growth Model

(S - shaped curve)

Q: How does the logistic model differ from the exponential model?

A: It accounts for limiting factors in the environment

AIM: How do scientists describe population growth?

2. Population limiting factors- environmental factors that restrict population growth

3. Logistic Growth Model

(S - shaped curve)

Carrying capacity (K)- max. population the environment can support without degrading the habitat

Determined by:The species itself and the environment (resources available, predation, etc…)

AIM: How do scientists describe population growth?

- environmental factors that restrict population growth

When is growth rate the lowest?

When is it the highest?

NO POPULATION FITS EITHER MODEL PERFECTLY

1. When population is small or large

Limited number of individuals and then limited resources

1. Population at intermediate level relative to carrying capacity.

2. Plenty of resources

2. Population limiting factors

3. Logistic Growth Model

AIM: How do scientists describe population growth?

Population limiting factors- environmental factors that restrict population growth

Human Population

We have a major problem here. What is our future? The number one problem on this planet for humans and many, many other species is our own overpopulation.What is the solution?

AIM: How do scientists describe population growth?

Population ecology

Exponential growth model

Logistic Growth Model- S-shaped

- NO limiting factors

Review

- Growth rate determined by population size and type of organism

- J-shaped

- Population limiting factors

NO POPULATION FITS EITHER MODEL PERFECTLY

AIM: How do scientists describe population growth?

Let’s look at some specific population limiting factors and examples.

NEW AIM: What are some of the factors that limit population growth?

Population limiting factors

1. Biotic factors

a. Competition among members (intraspecific)

Song Sparrow Population Experiment(small island in British Columbia)

Fig. 35.4A

- add food

- Clutch size increased

- food supply, water, space, energy (oil), mates, etc…

AIM: What are some of the factors that limit population growth?

Population limiting factors

1. Biotic factors

a. Competition among members (intraspecific)- food supply, water, space, energy (oil), mates, etc…

Competition for space…

AIM: What are some of the factors that limit population growth?

Population limiting factors

1. Biotic factors

a. Competition among members (intraspecific)i. food supplyii. space (territory)

A. Dispersion patterns1. clumped

2. uniform

3. random

AIM: What are some of the factors that limit population growth?

Dispersion patterns

AIM: What are some of the factors that limit population growth?

Population limiting factors

1. Biotic factors

b. Health- increased spread of disease with increased pop. density- accumulation of waste

AIM: What are some of the factors that limit population growth?

Population limiting factors

1. Biotic factors

c. Predation

Fig. 35.5

“boom-and-bust” cycles

As the hare population increases, so does the Lynx population, which will cause the hare population to decrease and in turn the lynx population decreases, etc…

AIM: What are some of the factors that limit population growth?

Population limiting factors

1. Biotic factors

d. Physiological factors

White-footed mouse experiment

1. Enclose in a small field

2. Reproduce quickly to 30 or 40

3. Reproduction declines and pop. stabilizes around 404. Add more food and water

- no change

RESULT: high population induces stress syndrome (hormonal changes)

- sexual maturity delayed, reproductive organs shrink, depressed immune system

AIM: What are some of the factors that limit population growth?

Population limiting factors

2. Abiotic factors

a. Climate and weather

Ex. Aphids

- insects that feed on phloem sap of plants

1. Exponential growth in spring

2. Rapid die out in hot, dry summer

3. A few individuals survive and reproduce when conditions improve

What happens to mosquitoes and grasshoppers during winter?

- die out completely, leaving only fertilized eggs

Fig. 35.4B

AIM: What are some of the factors that limit population growth?

Population limiting factors

2. Abiotic factors

b. Fire, flood, etc…

AIM: What are some of the factors that limit population growth?

Population limiting factors

1. Biotic factorsa. Competition among members

- food supply- space

b. Healthc. Predationd. Physiological factors

2. Abiotic factors

a. Climate and weatherb. Natural disasters

Almost all populations are regulated by a mixture of these and other factors

(25-year study of the song sparrow)

Fig. 35.4C