Biology 213 Chapter 53 Introduction to Ecology: Population Ecology Part 1.

Biology 213 Chapter 53Introduction to Ecology:

Population Ecology Part 1

You will be able to…

• List various fields of study in Ecology• Explain what factors change populations• Calculate population rate changes• Compare and contrast density-dependent to

density-independent factors

Ecology:

Oikos = home Ology = study ofIntegrates all biological fields

1.Organismal ecology: physiology, behavior, interactions with environment

2.Population ecology: factors affecting groups of individuals in an area.

3.Community ecology: interactions between species in an area

4. Ecosystem ecology: biotic and abiotic interactions; E flow & chem. Cycles

5. Landscape ecology: exchange of E & materials across multiple ecosystems

6. Global ecology: biosphere: regional exchange of E & materials affecting entire functioning & distribution of organisms wotldwide.

Ecology & evolution: changes in environment impacting populations’ alleles over time.

Ecology & environmental issues

Complexity of Nature: Why are some species present in an area?Dispersal difficulties (accessibility?)Behaviour limits distribution (habitat preference)?Biotic factors: competition/parasitism/predation/etcAbiotic factors:

Chem: H2O, O2, pH, salinity, nutrients

Phys: Macro & micro climate: Temp, light, fire, soil composition, moisture

• Estimate: one million years to get from 2.5 million to human population of ~ 5 million people in 6000 B.C. (2x)

• population did not reach 500 million until almost 8,000 years later -about 1650 A.D (100x)

• doubled roughly once every thousand years or so• reached a billion ~ 1850, doubling in 200 years• reached two billion around 1930 – doubling in 80

years• 1970’s it reached 4 billion ~ 40 year doubling time• Today’s population ~ 7 billion

What factors have allowed human population

to increase so rapidly?

• Population size

• Population density

• Patterns of dispersion

• Demographics

• Population growth

• Limits on population growth

Ecologists study population trends rather than individual organisms.

Properties of populations include

• Population density– # individuals of a species per unit

at a given time

• Population dispersion (spacing)– How are individuals distributed in a habitat?

– Why would this be important to know if you were studying a population?

– What does a dispersion pattern tell you?

Individual members distributed in a # of

different ways:

• Clumped -

• Uniform -

• Random -

Why would a clumped population pattern form?

individuals _____________ to each other, or __________________________________.

What factors encourage a uniform population pattern?

individual organisms actively _____ each other or all _________________________________

What abiotic or biotic features would encourage a random population pattern?

Rare in nature - occurs in absence of strong attractions or repulsions among individuals.

Dispersion patterns and density may change over time

Habitat changes: food, nutrients, water, sunlight (plants)

Age / size / developmental stages change:

• Four factors that produce changes in population size

Natality: birth rate

Mortality rates

Mortality rate of cheetahs

Increased Infant

Mortality• Is the cheetah

dangerously inbred?• Majority of deaths in

wild due to predation.• Future for cheetah

population?

How a population changes:

in # of individuals

in a certain period of time

N =

r =

How a population changes:

in # individuals / time

N = # individuals r =

* Per 1,000 individuals

Growth rate =

Example: N = 300,000 humans:3,000 births + 1,500 deaths in one year

r = (birth rate) – (death rate)

Example: N = 300,000 humans:

r = (birth rate) – (death rate)

r =

r =

Example: N = 300,000 humans:

r = 0.005 x 100 = 0.5% increase

rN = 0.5 x 300,000

rN =

If r is positive, increase in pop.

If r is negative, pop. is decreasing

If r = 0, population is stable

Are there other factors besides birth and death

and

size of a population

that can change a population?

Immigration• What causes

immigration biologically?– Favorable factors

Factors encouraging immigration:New environment made available

–Natural disasters large and small–Competitive or predatory species goes

extinct / moves away–Climate change or new resources–Hitch-hiking (“alien” species)

Less competition in new area

Succession after a disaster

Immigrants have an opportunity to invade:Reduced competition

Factors that encourage successful immigration:

Distribution methods:

• dispersal is at or near ground level vs. aerial dispersal

• dispersers actively engage in searching, or not

• dispersers able to orient toward preferred habitat from some distance, or not

Wind dispersing Golden Orb spiders

Emigration

Unfavorable Factors:*Excessive competition: mates or food

*Lack of resources

*Disease

*Avoidance of in-breeding

Population change includes immigration and emigration:

r = (birth rate) – (death rate) plus

(immigration – emigration)

e.g. Example: N = 300,000 humans:3000 births + 1500 deaths in one year

3,000 immigrated into the area

9,000 emigrated out of the area

r = (b – d) + (i – e)b – d = (10/1000) – (5/1000) = 0.005

i – e = 1/1000 – 3/1000

= 0.001 – 0.003 = -0.002

r = (b – d) + (i – e)

= (0.005) + (-0.002) = 0.003 x 100 = 0.3%

Growth rate: rN = (0.3%)(300,000)

= 900 more people in the population

Intrinsic rate of increase (rmax)

Maximum rate at which species or

population can increase under ideal

conditions

• Exponential population growth

Exponential population growth

According to Malthus:• Population, when unchecked, increases in a

geometrical ratio. 

• Subsistence increases arithmetically.

Carrying capacity

–Carrying capacity (K) = largest population maintained without degrading environment they live in

–Changes as environment changes• Logistic population curve

(S-shaped curve)

Carrying capacity and logistic population growth

Limiting Factors

Density-dependent factors

–Regulate population growth by affecting large proportion of population as population rises:

Density-dependent factors

–What do you think would impact a population as it got bigger?

• Predation• Disease• Competition• Toxic wastes

Density-dependent factors and negative feedback

• Density-independent factors– Limit population growth but are not

influenced by changes in population density: usually ABIOTIC

– Examples include natural disasters:• Hurricanes• Blizzards• Forest fires• Mudslides• Volcanoes, tsunamis, and earthquakes

Limiting FactorsBiotic and abiotic,

Density dependent or independent

factors that limit a population’s growth:

What would be a limiting factor?

What can you think of that would be a

limiting factor?

Which are biotic and which are abiotic?• increase death rate• decrease birth rate• limits immigration• encourages emigration• Any factors that slows population growth.

How are up & down cycles explained?Can be very complex relationships and factors.

Biology 213 Chapter 53Introduction to Ecology:

Population Ecology Part 2

You will be able to…• Explain what factors change populations

• Calculate population rate changes

• Compare and contrast density-dependent to density-independent factors

• Analyze human population patterns and make predictions about future trends

• Semelparous reproduction–Expend their energy in a

• Iteroparous reproduction–Exhibit ________________________ throughout their lifetimes

Semelparity:

Expend energy to reproduce in one big

effort

Most insects, invertebrates, many annual plants,

and some fish

What’s the advantage?

Iteroparous reproduction

• Expend energy to reproduce in cycles

• Most vertebrates, perennial plants.

• What’s the advantage?

Species exhibiting an r strategy–Emphasizes a high growth rate–Organisms typically have

• small body size• high reproductive rates• short life spans• inhabit variable environments

• Often

Species exhibiting a K strategy–Maintains a population near

carrying capacity (K) of environment–Species often have

• large body size• low reproductive rates• long life spans• inhabit stable environments

• Often

• Survivorship curves–Type I

•Mortality is greatest in old age–Type II

•Mortality is spread evenly across all ages

–Type III•Mortality is greatest among the young

Survivorship curves

Survivorshipcurve for a herring gull population

Source habitats:–Preferred habitats–Local reproductive success is

> local mortality–Local individuals disperse from

source habitats to other regions

• Sink habitats–Lower-quality habitats–Individuals may suffer death or

poor reproductive success–What would make an organism

move then?

Source & sink populations in a hypothetical metapopulation

Human population growth– World population reaches 6,668,926,425 by

May 20, 2008

– Per capita growth rate declined from peak in 1965 of about 2% per year (doubling time 35 years)

– to 1.3% per year (doubling time of 54 years)

– birthrate necessary for zero population growth is 2.1 births per woman

7,000,000,000The year 2011

Human population growth: exponential J-shaped curve so far

logistic population growth

Chapter 53 Clicker Question #4:Often growth cycles of one population affects the cycle of another. As moose populations increase, wolf populations also increase. If we consider the logistic equation for the wolf population:

dN = rN (K-N)dt K

which of the above factors accounts for the strongest impact on the moose population? A. K B. dN C. rN D. dt

Population characteristics

–Highly developed countries• low birth rate• low infant mortality• low fertility rate• long life expectancies• high GNI PPP:

–GNI PPP per capita is the gross national income in purchasing power parity divided by mid-year population.

Population characteristics

–Developing countries• high birth rate

• high infant mortality

• high fertility rate

• short life expectancies

• low GNI PPP

China and India’s populations increasing

What trends do we see world-wide?

Birth rate decline lags behind as death rate decreases: e.g. in Mexico, 1900–2000

• Age structure influences population dynamics

–Possible for country to have replacement-level fertility and still experience population growth

–Young age structure causes a positive population growth momentum as large pre-reproductive age group matures

Age structure diagrams comparing Kenya to USA to Germany

15-to-40 range: reproductive rates are high

“Carrying-capacity" definition of overpopulation:

• not population density, but #’s of people in an area relative to resources capacity to sustain human activities

• a condition of overpopulation might be corrected with no change in the number of people!

• Developing countries tend to have people overpopulation that degrades the environment

• Developed countries have consumption overpopulation that degrades the environment

Ecological Footprint

USA & MexicoOne week’s food supply.

One week’s food costs the American family $341.98

One week’s food

Egypt

Ecuador

Above: Bhutan Below: Chad 

One week’s

food costs the Chad

family $1.23

• China has 22 % of world’s population

• India has 17 % of world’s population

• Both nations are modernizing rapidly

• USA uses has 4.4% of the world population and uses 25% of world’s energy resources

• What happens to global resources when developing countries want to enjoy a developed nation lifestyle like ours?