Population Ecology

Ecology - Study of interactions among organisms and their

environment

Conservation biology, environmentalism:

preservation of natural world

• Biosphere

• Ecosystems • Community

• Population

• Organism

ECOSYSTEM LEVELEucalyptus forest

COMMUNITY LEVELAll organisms ineucalyptus forest

POPULATION LEVELGroup of flying foxes

ORGANISM LEVELFlying fox

ORGAN SYSTEM LEVELNervous system

ORGAN LEVELBrain

Brain Spinal cord

Nerve

TISSUE LEVELNervous

tissue

CELLULAR LEVELNerve cell

MOLECULAR LEVELMolecule of DNA

Figure 1.1

Population Ecology

• Population- how to measure?

• Growth rates: J shaped, S shaped

• K, r, and reproductive strategies

• Human population

• Population density = number of individuals in a given area or volume

• count all the individuals in a population

• estimate by sampling

How are populations measured?

• mark-recapture method depends on likelihood of recapturing the same individual

• The dispersion pattern of a population refers to the way individuals are spaced within their area

– Clumped - – Uniform: – Random: no pattern

Figure 35.2C

• Idealized models describe two kinds of population growth1. exponential growth

2. logistic growth

How do populations grow?

• A J-shaped growth curve, described by the equation G = rN, is typical of exponential growth– G = the population growth rate– r = the intrinsic rate of increase, or an organism's

maximum capacity to reproduce– N = the population size

Figure 35.3A

0 5 10 15 20

0

500

1000

1500

Time (years)

Pop

ula

tion s

ize

r = 0.06

r = 0.02

r = 0

r = -0.05

high intrinsicrate of increase

low intrinsicrate of increase

zero populationgrowth

negative intrinsicrate of increase

2. Logistic growth is slowed by population-limiting factors

K = Carrying capacity is the maximum population size that an environment can support

Figure 35.3B

• logistic growth curve

– K = carrying capacity– The term

(K - N)/K accounts for the leveling off of the curve

Figure 35.3C

declining birth rate or increasing death rate

• The regulation of growth in a natural population is determined by several factors – limited food supply

– the buildup of toxic wastes

– increased disease

– predation

Multiple factors may limit population growth

Density Dependent Factors

• Competition

• Predation

• Parasitism

• disease

Density Independent Factors

• Natural disasters

• Weather

• Seasonal cycles

• Human activities

– About every 10 years, both hare and lynx populations have a rapid increase (a "boom") followed by a sharp decline (a "bust")

Figure 35.5

• Survivorship curves plot the proportion of individuals alive at each age

• Three types of survivorship curves reflect important species differences in life history

Figure 35.6

• An organism's life history is the series of events from birth through reproduction to death

• Life history traits include

– the age at which reproduction first occurs

– the frequency of reproduction

– the number of offspring

– the amount of parental care given

– the energy cost of reproduction

Evolution shapes life histories

• Principles of population ecology may be used to – manage wildlife, fisheries, and forests for

sustainable yield– reverse the decline of threatened or endangered

species– reduce pest populations

• In 1890, a group of Shakespeare enthusiasts released about 120 starlings in New York's Central Park

The Spread of Shakespeare's Starlings

• Today: over 100 million starlings, spread over N. Amer.

Current

1955

1945

1935 1925

1925

1935

19151905

19251935

1945

1955Current

• The starling population in North America has some features in common with the global human population

– Both are expanding and are virtually uncontrolled– Both are harming other species

Why We Live in Interesting Times…

Pre 2000 A.D.1. More youth than elderly2. More rural than urban

Post 2010 A.D.1. More elderly than youth2. More urban than rural

People alive 1950-2050 A.D. have seen:1. Highest growth rate (2.1%/year)2. Population double during their lifetime

More people have lived in the last 100 years, than in all of human history before 1900!

Thomas Malthus (1798)

• Populations grow geometrically while supporting resources grow arithmetically

• Population, if not purposefully checked (“preventative checks”), would outpace resources and lead to unplanned “positive checks” that would return population to sustainable levels

“An Essay on the Principle of Population”

HUMAN POPULATION GROWTH

Earth's population: 6 billion (Oct 12, 1999)

Every second, five people are born and two people die, a net gain of three people.

Every day, +250,000 = 2 x Champaign-Urbana

This year, +87,000,000 = Mexico

This decade +1,000,000,000 = China

• doubled three times in the last three centuries

• about 6.1 billion and may reach 9.3 billion by the year 2050

• improved health and technology have lowered death rates

THE HUMAN POPULATION

• The history of human population growth

Figure 35.8A

Figure 35.9B

RAPID GROWTH

Kenya

Male Female

Percent of population Percent of population Percent of population

SLOW GROWTH

United States

Male Female

ZERO GROWTH/DECREASE

Italy

Male Female

Ages 45+

Ages 15–44

Under15

Under15

Ages 45+

Ages 15–44

Also reveals social conditions, status of women

• The age structure of a population is the proportion of individuals in different age-groups

• The ecological footprint represents the amount of productive land needed to support a nation’s resource needs

• The ecological capacity of the world may already be smaller than its ecological footprint

• Ecological footprint in relation to ecological capacity

Figure 35.8B

U.S.

China

India

Russia

Japan

U.S.

China

India

Russia

Japan

Per capita CO2 emissions(metric tons of carbon)

Total CO2 emissions(billion metric tons of carbon)

0 1 2 3 4 5 6 0 0.5 1 1.5

5.48

0.75

2.65

2.51

0.29

1.49

0.91

0.39

0.32

0.28

• What next?

Figure 2.10x