Chapter 52—Population

Ecology

Essential Questions

• How do we measure a population?

• How do populations change over time?

• What factors affect population density, distribution & age structure?

• What are the limits to growth of a population?

• How many humans can the Earth support?

I. Characteristics of Populations

• Population

– group of individuals of same species in same

general area

• rely on same resources

• interact

• interbreed

• Population Ecology

– study of populations in relation to environment

– environmental influences on population

density & distribution, age structure, and

variations in population size

What environmental factors affect a population?

Population Density• How do we measure how many individuals in a

population?

– number of individuals in an area (sample plots)

– mark & recapture methods • N= (# marked in 1st catch x total # in 2nd catch) / # recaptures in 2nd catch

– organism evidence (nests, burrows, tracks, feces)

Mark & Recapture Example:

• 50 marked in 1st catch

• 2nd catch of 100, 10 are already marked

• How many in the population?

N= 50 x 100 / 10

N = 500

Patterns of Dispersal

- Spacing patterns within a population

Provides insight into the

environmental associations & social interactions of individuals in population

Figure 50.2

Clumped Pattern (most common)

WHY?

Uniform Pattern

• May result from direct interactions between individuals in the

population →→→→territoriality

Changes to Population Size

• Adding & removing individuals from a population

– birth

– death

– immigration

– emigration

Demography• Study of factors that affect growth & decline of

populations

– vital statistics & how they change over time

What does this tell you about the

population?

Life Table

Survivorship Curve

- Graphic representation of life table

Conclusions?

Survivorship Curves

• What does this tell about survival & strategy of a species?

Figure 50.3

Reproductive Table• Fertility schedule

– age-specific summary of reproductive rates

for females

Why track only females?

Would a different species have a similar reproductive pattern?

II. Population GrowthChange in population = births – deaths

• Exponential model (ideal conditions; assumes unlimited resources)

dN = rmaxNdt

N = # of individuals

r = rate of growth

t = time period

growth increasing at constant rate

Figure 52.8

Exponential Growth Rate

• Characteristic of populations introduced to a new environment or rebounding from a catastrophe

Whooping crane

coming back from near extinction

African elephant

protected from hunting

Carrying Capacity

• Can populations continue to grow exponentially?– of course NOT!

– what sets limit?

• Carrying Capacity (K)– maximum population

size that environment can support with no degradation of habitat

– not fixed; varies with changes in resources

Logistic growth

What happens as N

approaches K?

Figure 52.11

Incorporates effect of

population density on rate of increase

dN = rmaxN (K-N/ K)

dt

Logistic Model of Growth

Doesn’t fit the

pattern of many natural populations

Life History Traits• K-selection = density dependent

• r-selection = density independent

K-selection

r-selection

mortality constant

Reproductive Strategies

• K-selection—maximizes K (pop. size)

– have few offspring & invest a lot of

energy in raising them to reproductive age

• primates

• r-selection—maximizes r (growth rate)

– have many offspring & invest little in their survival

• insects

Trade-OffsNumber &

size of offspring

vs.

Survival of offspring or

parent

Parental Survival

The cost of larger broods to both male & female parents

Figure 52.6

III. Population-Limiting Factors

Regulation of population size

• Limiting factors

– density independent

• environmental disturbances

– density dependent

• food supply

• competition

• predators

• Population cycles

– population fluctuations

Dungeness crabs, ocean

currents, & cannibalism

Limits to growth• Negative feedback prevents unlimited

growth

Density dependent—death rate rises as birth rate falls

Density independent–no change in death rate or birth rate

What does it mean to be density dependent or density independent?

Figure 52.13

Effects of Increased Population

Density

Figure 52.14

Decreased Fecundity

Decreased Survivorship

Figure 52.15

Loss of habitat, predation, climatic changes affecting food availability

Population dynamics• Complex interaction of biotic & abiotic

influences

Decline of Northern Pintail

Example: Isle Royale studies

Moose population on small island in Lake Superior

Why so unstable?

wolvesstarvation

winter loss

Figure 52.17

Predator – prey interactions

• Population cycles

Figure 52.19

IV. Human Population Growth

What factors have contributed to this exponential growth pattern?

Where in the world is most of the population growth occurring?

Figure 52.20

Demographic Transition

What do the data imply about population growth in these countries?

Figure 52.21

High birth and

death rates →

Low birth and

death rates

Age Structure

• Relative number of individuals of each ageWhat do the data imply about population growth in these countries?

Figure 52.22

Ecological Footprint

Based on land & water area appropriated to produce all resources a country consumes & to absorb all wastes it generates

Is the human population near carrying capacity?

2011 = ~6.9 billion

K = 10–15 billion??

deficit

surplus

Figure 52.23