Population Ecology



Population Ecology

POPULATION DYNAMICS: How populations change in size, density, and age distribution

Three Patterns of Dispersion that Populations Exhibit:

RANDOM CLUMPED UNIFORM

[pic] [pic][pic] [pic]

** MOST COMMON**

Measuring and Modeling Population Growth

POPULATION DENSITY: How many organisms live per unit of space

Calculating population density:

D=N/S

Where: D=density N=number of individuals S=space

Solve: There are thirty five mice on five acres of land, what is this mouse population’s density?

Solve: There are about 325 million people living in the United States. The land area of the U.S. is about 9.8 million km2. What is the population density of the U.S.?

Of Bangladesh if there are 155,000,000 people and the land area is about

130,000 km2?

Factors that govern changes in population size include four variables:

Births

Deaths

Immigration

Emigration

Calculating birth and death rates (given as a percent):

____# births___ x 100

Total population

___# deaths____ x 100

Total population

Calculating population change:

Population change = (births + immigration) – (deaths + emigration)

Solve: What would be the overall population change for people in a given area if 12,300 people were born, 5,000 people died, 8,700 people immigrated, and 4,100 people emigrated?

Calculating r : population growth rate (or percent change in population size):

(births + immigration) – (deaths + emigration)

Growth Rate = -------------------------------------------------------------- x 100

(percent change) n

Where n = initial population size

Solve: What was the growth in the population for the problem above if the initial population was 1.2 million? Express your answer as a percent.

Instead of using total numbers of births and deaths per year, demographers can use crude birth and death rates which is the number of births or deaths per 1000 people in a year.

Calculating annual rate of population change using crude birth and death rates:

Rate of Natural Increase (%) = birth rate – death rate x 100

1000

Example: Madagascar’s crude birth rate is 37.9 and crude death rate is 7.9. What is Madagascar’s natural rate of increase? (express your answer as a percent)

Calculating doubling time: Rule of 70

Doubling time = ____70____

% growth rate

Calculate how long it will take each of the following populations to double according to each growth rate:

World – growth rate: 1.2%

U.S. – growth rate: 0.7%

Zimbabwe – growth rate: 4%

If the numbers of births and immigrations are higher than those of deaths and emigration, then the population will have=

POSITIVE GROWTH (+ OR INCREASING)

If the numbers of deaths and emigrations exceeds the numbers of births and immigrations, then the population will have=

NEGATIVE GROWTH (- OR DECREASING)

If deaths and emigrations equals births and immigrations then=

ZERO GROWTH OR ZPG

Factors that affect growth include:

If a population is only influenced by births (natality) and deaths (mortality) =

CLOSED

If a population is influenced by all four factors=

OPEN

Different Types of Population Growth

Exponential:

**CONTINUOUS REPRODUCTION,

NOT CHECKED BY LIMITING FACTORS

(STARTS SLOW – SPEEDS UP!)

**J-SHAPED CURVE

Logistic:

**RAPID THEN STEADY THEN LEVELS OFF,

CHECKED BY LIMITING FACTORS

**S-SHAPED CURVE

BIOTIC POTENTIAL: maximum rate a population

can increase under ideal conditions.

Intrinsic rate of increase= r: rate at which a population

would grow if it had unlimited resources.

Carrying capacity = K: the maximum number of individuals of a

given species that can be sustained indefinitely in a given area

ENVIRONMENTAL RESISTANCE: all factors that act to limit

the growth of a population (NO population can grow indefinitely!!!)

LIMITING FACTORS

FIG 9 – 4 (pg 166)

Population Density Affects Population Growth

OVERSHOOT: exceeding carrying capacity resulting in DIEBACK

FIG’S 9 – 5 AND 9 – 6 (pgs 166 – 167)

Density INdependant Factors: affect a population’s size regardless of its density

Examples include:

“HUMAN ACTIVITIES”, TEMP CHANGES,

NATURAL DISASTERS

Density DEpendant Factors: affect a population’s size as population density increases

Examples include:

DISEASE, COMPETITION, PREDATORS

Survivorship Patterns of Populations

Species with different reproductive strategies tend to have different life expectancies.

SURVIVORSHIP CURVES: show the percentages of the members of a population surviving at different ages.

Three types of curves show: Early loss, Late loss, and Constant loss

Early loss: LOW SURVIVORSHIP, MANY OFFSPRING BUT

FEW SURVIVE

Late loss: HIGH SURVIVORSHIP, FEW OFFSPRING BUT

MANY SURVIVE

Constant loss: IN-BETWEEN

FIG 9 – 11 (pg 171)

Population Change Curves

There are four different types of population fluctuations:

STABLE: A species whose population size fluctuates around the carrying capacity.

IRRUPTIVE: A species whose population size occasionally explodes.

CYCLIC: A species whose population size undergoes cyclic fluctuations.

IRREGULAR: A species whose populations change in size with no recurring pattern.

FIG 9 – 7 (pg 168)

Reproductive Patterns of Species: Opportunists and Competitors

(Opportunists): _r____ - selected species: species with a high rate of population increase (r). They reproduce early and put most of their energy into reproduction.

(Competitors): __K___ - selected species: species that reproduce late in life and have a small number of offspring with fairly long life spans

FIG 9 – 9 (pg 169)

Characteristics of K strategists vs. r strategists: FIG 9-10

K strategist vs. r strategist

Fewer larger offspring many small offspring

High parental care/protection little or no parental care/protection

Later reproductive age early reproductive age

Most offspring survive to reproductive age most offspring die before reproductive age

Larger adults small adults

Adapted to stable conditions adapted to unstable conditions

Lower growth rate (r) high growth rate (r)

Population stable around K populations fluctuates

Specialist niche generalist niche

High ability to compete low ability to compete

Late successional species early successional species

Predator/Prey Relationship:

[pic]FIG 9 – 8 (pg 168)

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