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Population Ecology

Size, Growth, and Regulation

Associated Reading: 26.1 - 26.2, 26.4

Courtesy of Joe Robertson, Wikimedia Commons

Courtesy of National Oceanic and Atmospheric Administration

Terms to Know

•Habitat •Population •Community •Ecosystem •Biotic Factors •Abiotic Factors

Biotic Potential

•Biotic potential: Maximum rate of increase in a

population under ideal conditions

•Varies between species

•In nature, biotic potential is rarely reached

Population Growth Our hypothetical mouse population

•2,000 individuals

•Reproduce every month

•1,000 births every month

•200 deaths every month

•Birth rate (b) = # of births Total population size

•Death rate (d) = # of deaths Total population size

b = d = 1,000 2,000

200 2,000

= 0.5 = 0.1

Changes in a Population Over Time

Rate of change in population size during a

given period of time

•AKA: natural rate of increase

•How quickly a population is growing with each

generation

•Takes into account both births and deaths

r = b - d

r = 0.5 - 0.1 = 0.4

Growth Rate (r)

Population growth per unit time

(G)

Growth rate

(r)

Total population

(N)

x =

Population Growth (G)

G represents the number of individuals added to a population in the specified time frame

Month 1 2,000 x 0.4 = 800 mice added + 800 2,800 mice in population by month 2

Month 2 2,800 x 0.4 = 1,120 mice added +1,120 3,920 mice by month 3

Month 3 ???

Apply What You Know

TIME

PO

PU

LATI

ON

SIZ

E Exponential Growth

Population growth per unit time

(G) Growth rate

(r)

Total population size

(N) x =

Proportion of resources not

yet used x

Logistic Growth

An S-shaped growth curve stabilizes at carrying capacity

The S-Curve of Logistic Population Growth

Overshooting Carrying Capacity

= Environmental Resistance

Limits on Growth of Populations

Limiting factor: any essential resource that is in short supply

Total population size

Area of the habitat =

Malheur County 9,930 acres in the SE corner of Oregon

Home to ~10,000 deer

Image courtesy of Google Maps

Density

Images courtesy of Pixabay.com

Density-Independent Factors

•Factors unaffected by population density.

•Natural disasters, climate changes, etc.

Image courtesy of U.S. Fish and Wildlife Service

Image courtesy of U.S. Fish and Wildlife Service Public Domain

Image by Karunakar Rayker via Flickr CC BY 2.0

Density-Dependent Factors

•Logistic growth equation deals with density-dependent controls

•Limiting factors become more intense as population size increases

Images courtesy of Pixabay.com and OpenStax.org

Predator-Prey Cycles

Human Populations

Current World Population ←Awesome website alert! Click here for a

real time estimation of the earth's population

Human Population Growth

The Demographic Transition

Age Structure Diagram for Sweden

Replacement Level Fertility (RLF)