• POPULATION = a group of interbreeding organisms (same species) that live in the same place at the same time and compete for the same resources.

• Resources = food, water, shelter, mates, and so on . . . • resources  pop. size • resources  pop. size

The population size of a species in a given space at a given time is determined by the interplay between

BIOTIC POTENTIAL ENVIRONMENTAL RESISTANCE

and .

Biotic potential

= growth rate with unlimited resources.

Four variables change population size: 1.NATALITY = birth rate 2.MORTALITY = death rate 3.IMMIGRATION = rate of organisms moving in 4.EMIGRATION = rate of

DENSITY DEPENDENT FACTORS =

affect a populations’ size depending on its population density.

1. Predation 2. Disease 4. Space

Populations change in response to environmental stress or changes in environmental conditions.

1. In size = # of individuals 2. Density = # of individual / specific space 3. Age distribution = proportions / age group 4. Dispersion =

Clumped (elephants) Uniform (creosote bush) Random (dandelions)

DENSITY INDEPENDENT FACTORS =

affect a populations’ size regardless of its population density.

1. Weather 2. Earthquakes 3. Floods 4. Fires R-strategists populations are . . . Natural disasters

No population can grow indefinitely!

Every environment has a CARRYING CAPACITY = the maximum number of individuals of a given species that can be sustained indefinitely in a given space.

2.0

1.5

1.0

.5

1800 1825 1850 1875 Year 1900 1925

Factors that affect carrying capacity:

1. Competition with/in and between species.

2. Natural and human caused catastrophes.

3. Immigration and emigration.

4. Seasonal fluctuations in food, water, shelter, and nesting sites.

A population that has few if any resource limitations grows exponentially.

EXPONENTIAL GROWTH starts out slowly and then proceeds faster and faster as the population increases. “J” population growth curve

Time (t)

LOGISTIC GROWTH involves initial exponential growth and then there is a steady decrease in growth as the population encounters environmental resistance and approaches carrying capacity and levels off.

K

“S or sigmoid” population growth curve

Time (t)

K Transitional phase Plateau phase Exponential phase Time (t)

Opportunistic or r-Selected Species cockroach dandelion

Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species

Competitor or K-Selected Species elephant

Fewer, larger offspring

saguaro

High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species

REPRODUCTIVE STRATEGIES Carrying capacity

K

K species; experience K selection r species; experience r selection Time

SURVIVORSHIP CURVES

Reindeer on St. Paul Island • 41 mi 2 • Started with 25 Reindeer (4 males and 21females) • No predators • 200 mi from mainland so no on or off • No hunting

Start with 25 1938= 2046 deer 1950= 8 deer Growth Rate of 16% Did bounce back to a steady 250 deer End Result

Birth and Death Calculations

Crude Birth Rate

(CBR)= # of births per 1000 individuals/yr CBR=(Births/Pop. Size)x1000 The world CBR is 20.3

Crude Death Rate

(CDR) = # of deaths per 1000 individuals/yr CDR= (Deaths/Pop. Size)x1000 The world CDR is 9.6

More Calculations

Natural Increase Rate in %

(NIR) NIR = (CBR-CDR)/10

Doubling Rate

= how many years it will take to double the population DR= 70/NIR

Density

= # of individuals in a given area D= Pop./ Area

IB Acronyms for Countries • • •

MEDC=

More Economically Developed Country

LEDC=

Country Less Economically Developed

NIC=

Newly Industrialized Country