44 lecture ppt

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Biology

Sylvia S. Mader Michael Windelspecht

Chapter 44 Population

Ecology

Lecture Outline

See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into

PowerPoint without notes.

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Outline

• 44.1 Scope of Ecology

• 44.2 Demographics of Populations

• 44.3 Population Growth Models

• 44.4 Regulation of Population Size

• 44.5 Life History Patterns

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44.1 Scope of Ecology

• Ecology

 The study of the interactions of organisms with

• Other organisms and the physical environment

 Habitat - Place where an organism lives

 Population - All the individuals of a species within a

particular space

 Community – Various populations of multiple species

interacting with each other

 Ecosystem - Community interacting with the

environment

 Biosphere - All the communities on Earth whose

(4)

Ecological Levels

4

Organism Population Community Ecosystem

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44.2 Demographics of Populations

• Demography

is the statistical study of a

population

• Demography includes



Population density



Population distribution

(6)

Demographics of Populations

• Density and Distribution



Population Density

- Number of individuals

per unit area



Population Distribution

- Pattern of

dispersal of individuals across an area of

interest



Limiting factors

are environmental aspects

that particularly determine where an organism

lives

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Distribution Patterns of the Creosote Bush

7

Young, small shrubs

b. Clumped

Large shrubs a. Mature desert shrubs

Medium shrubs

c. Random

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Demographics of Populations

• Population Growth



The

rate of natural increase

depends on

• The number of individuals born each year, and • The number of individuals who die each year

(9)

Demographics of Populations

• Population Growth (continued)



Biotic Potential

• The maximum rate of natural increase for a population that can occur when resources are unlimited



Biotic potential depends on factors that influence

the population’s reproduction, including

• The usual number of offspring surviving to reproductive age

(10)

Biotic Potential

10

a. b.

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Demographics of Populations

• Mortality Patterns



A

cohort

• Composed of all the members of a population born at the same time

– Life tables demonstrate how many members of a cohort are still alive after certain intervals of time



Survivorship

• The probability that newborn individuals of a cohort will survive to a particular age

• Survivorship Curves

(12)

A Life Table for a

Bluegrass Cohort

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Demographics of Populations

• Survivorship Curves



Type I

• Characteristic of a population in which most individuals

survive past the midpoint of the life span and death does not come until the end of the life span



Type II

• Death is linear over time (unrelated to age)



Type III

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Survivorship Curves

14

b: © Holt Studios/Photo Researchers, Inc.; c: © Bruce M. Johnson; d: © Digital Vison/Getty RF Images

I I II III III N um ber of S urv iv ors

Percent of Life Span

N um ber of S urv iv ors

Percent of Life Span b. Bluegrasses d. Mosquitoes 1,000 100 10 0

0 50 100

1 million

10,000

100

0

0 50 100

50

Death occurs after midpoint.

Death unrelated to age.

Death comes early on. II N um ber of S urv iv ors

Percent of Life Span a.

c. Lizards

Percent of Life Span

Num b er o f S u rvi vo rs 1,000 100 10 0

0 50 100

1,000

100

10

0

0 100

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Demographics of Populations

• Age Distribution

 The proportion of the population that falls into various

age categories

 There are three major age groups

• Prereproductive • Reproductive • Postreprodutive

 At least three age structure diagrams are possible

• Increasing population • Stable population

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Age Structure Diagrams

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Increasing Population Stable Population Decreasing Population Age Structure

Postreproductive Ages

Reproductive Ages

Prereproductive Ages

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44.3 Population Growth Models

• Two working models for population growth:



Semelparity

• Members of a population have only a single reproductive event in their lifetime

– Ex: insects



Iteroparity

• Members of the population experience many reproductive events throughout their lifetime

(18)

Patterns of Reproduction

18

a. b.

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Population Growth Models

• Exponential Growth



Rate of population growth increases as the total

number of females increases



Biotic potential is having full effect and birthrate is

a maximum during exponential growth



Phases of an exponential growth curve

• During the lag phase, growth is small because the population is small.

(20)

Model for Exponential Growth

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1 2 3 4 5 6 7 8 9 0 Generation Population Size Number of Females 10.0 24.0 57.6 138.2 331.7 796.1 1,910.6 4,585.4 11,005.0 26,412.0 63,388.8 12 28.8 69.1 165.9 398.1 955.3 2292.7 5502.5 13206.1 31694.5 a. 70 60 50 40 30 20 10 10 R = 2.4

exponential growth

lag b. c. Generations P o p u la tio n ( th o u s a n d s )

To calculate population size from year to year, use this formula:

Nt+1= RNt

Nt= number of females already present

R = net reproductive rate

Nt+1= population size the following year

(21)

Population Growth Models

• Logistic growth



Occurs when limiting environmental factors

oppose growth



Phases of a logistic growth curve

• During the lag phase, growth is slow because the

population is small.

• During the exponential growth phase, growth is

accelerating.

• During the deceleration phase, growth slows down.

• During the stable equilibrium phase, there is little if

(22)

Model for Logistic Growth

22 100 200 300 400 700 600 500

2 4 6 8 10 12 14 16 18 a. b. c. 0 2 4 6 8 10 12 14 16 18 9.6 29.0 71.1 174.6 350.7 513.3 594.4 640.8 655.9 661.8 0 19.4 42.1 103.5 176.1 162.6 81.1 46.4 15.1 5.9 N t K lag deceleration

D N

D t

Growth of Yeast Cells in Laboratory Culture

Time (t ) (hours)

Number of individuals (N)

Number of individuals added per 2-hour period

Nu m b e r o f Y e a s t Cel ls exponential growth stable equilibrium phase Time (hours)

To calculate population growth as time passes, use this formula:

N = population size N/t = change in population size r = rate of natural increase K = carrying capacity

K – N = effect of carrying capacity on population growth = rN

K K – N

(23)

Population Growth Models

• Carrying Capacity



The maximum number of individuals of a

species the environment can continuously

support

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44.4 Regulation of Population

Size

• Density-independent Factors



The population density does not influence

the intensity of the factor’s effect

• Natural disasters

• Density-dependent Factors



The percentage of the population affected

increases as the population density

increases

• Competition

• Predation

• Parasitism

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Density-independent Effects

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Density-dependent Effect

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2,000

1,500

1,000

500

0

1910 1920 1930 1940 1950

N

um

ber

of

R

e

indee

r

exponential growth

decline as a result of sudden resource depletion

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Density-dependent Effects

--Competition

(28)

Density-dependent Effects

--Predation

28

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44.5 Life History Patterns

• Life histories contain characteristics of a

population such as

 The number of births per reproduction

 The age of reproduction

 The life span

 The probability of an individual living the entire life

span

• Each population distributes energy among its life

span, reproduction events, and care of offspring.

• Related species may have different life history

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Parental Care Among Frogs and Toads

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a. Mouth-brooding frog, Rhinoderma darwinii

b. Strawberry poison arrow frog, Dendrobates pumilio

c. Midwife toad, Alyces obstetricans

(a): © Michael Fogden/Animals Animals; (b): © Michael Fogden/Animals Animals; (c): © Tom McHugh/Photo Researchers, Inc.

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Life History Patterns

• r

is the rate of natural increase of a

population.

• K

is the carrying capacity of the

environment.

• Some populations are subject to

r-selection

, and other populations are

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Life History Patterns

• r - Selection

 In unstable or predictable environments, population

growth is controlled by density-independent factors.

 Population size is low relative to K.

• r

- Strategists (opportunistic species)

 Produce large numbers of offspring

 Have a small body size

 Mature early

 Have a short life span

 Do not invest energy in parental care

(33)

Life History Patterns

• K - Selection

 In stable, predictable environments, population size is

controlled by density-dependent factors.

 Population size tends to be near K.

• K

- Strategists (equilibrium species)

 Produce small numbers of offspring

 Have a large body size

 Mature late

 Have a long life span

 Invest energy in parental care

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Life History Strategies

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Opportunistic Species (r-strategist) • Small individuals • Short life span • Fast to mature • Many offspring • Little or no care of

offspring

• Many offspring die before reproducing • Early reproductive age

Equilibrium Species (K-strategist) • Large individuals • Long life span • Slow to mature

• Few and large offspring • Much care of offspring • Most young survive to

reproductive age • Adapted to stable

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Ecology Focus: When a

Population Grows Too Large

• White-tailed deer are prolific breeders

 Female deer breed their first year, and once they start

breeding, produce about two young each year of life.

• A century ago, the white-tailed deer population

was less than half a million

• Today, it is well over 200 million

• Natural predators of deer, such as wolves and

mountain lions, are now absent from most

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Ecology Focus: When a

Population Grows Too Large

• Populations that are too large may suffer

from starvation as they deplete their own

food supply

• For example, after deer hunting was

banned on Long Island, New York, the

deer population quickly outgrew available

food resources

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White-tailed Deer

37

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44.6 Human Population Growth

• The human population is undergoing

exponential growth

 Present size is 6.7 billion people

• The

doubling time

of the human population is

currently estimated at 52 years

• Population Size

 1800 1 Billion

 1930 2 Billion

 1960 3 Billion

 2012 6 Billion

(39)

Human Population Growth

• More-Developed Countries (MDCs)



North America, Europe, Japan, and Australia



Slow population growth



High standard of living



A

demographic transition

(decreased death

rate followed by decreased birth rate) has

(40)

40

Human Population Growth

• Less-Developed Countries (LDCs)



Latin America, Africa, and Asia



Rapid population growth



Low standard of living



Strategies to reduce population growth

• Family planning programs

• Social progress, which may reduce the desire for large families

(41)

World Population Growth

lowest growth highest growth less-developed countries more-developed countries a. b. Bi ll io n s o f P eo p le 1750 2 4 6 8 10 12 0

1800 1850 1900 1950 2008 2250

Year

(42)

Human Population Growth

• Age Distributions



Populations of MDCs and LDCs can be

divided into three age groups

• Prereproductive • Reproductive

• Postreproductive



MDCs and LDCs have different age structure

diagrams

• Many MDCs have a stable age structure • Most LDCs have a youthful profile and are

experiencing population growth

(43)

Age Structure Diagrams

80+ 75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0–4 80+ 75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0–4 0

b. Less-developed countries (LDCs) a. More-developed countries (MDCs)

Millions

postreproductive

reproductive

prereproductive

300250 200150100 50 50 100150200250300

A g e (i n y e a rs ) A g e (i n y e a rs ) postreproductive reproductive

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Human Population Growth

• Population Growth and Environmental

Impact



Environmental impact of a population is

measured in terms of:

• Population size

• Resource consumption per capita

• Resultant pollution due to resource consumption



There are two types of overpopulation

• Overpopulation due to population growth • Overpopulation due to increased resource

consumption

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Environmental Impact Caused by

MDCs & LDCs

Population Hazardous Waste Production Consumption

a. b.

c.

paper

metals fossil fuels

MDCs = more-developed countries LDCs = less-developed countries