14.2 Measuring and Modeling Population Change

• Read p.660 – 670

• Practice Questions!

– P.664 #1

– P.665 #2

– P.668 #3, 4

Carrying capacity

• The maximum number of organisms that can be sustained by available resources over a given period of time

"population dynamics," and the main natural determinants.

- changes in population characteristics

- natality (birth rate)

- mortality (death rate)

- immigration

- emigration

Biotic potential

• maximum reproductive rate under ideal conditions (or, intrinsic rate of natural increase)

• Example: Under ideal conditions, a population of bacteria can grow to more than 10 in 24 h.

• Limiting Factor: the name applied to an essential resource that is in short supply or unavailable, and prevents an organism from achieving this potential

Fecundity: theoretical maximum number of offspring that could be produced by a species in one lifetime– Example: Mice have the ability to produce over a dozen

offspring every 3 weeks.

Fertility: the number of offspring actually produced by an individual during its lifetime, affected by food supply, disease, mating success, etc.

Factors limiting reproductive potential include:

• Migration

• Disease

• Food availability

• Mating success

Population change

[(births + immigration) (deaths + emigration)] x100

initial population size

CLOSED POPULATION

• A population whose growth is influenced only by natality and mortality

OPEN POPULATION

• A population whose growth is influenced by natality, mortality and migrations

the equation used to calculate the population change of an open

population.

the equation used to calculate the population change of a closed

population.

SURVIVORSHIP CURVES

                                                             

                                                                                                

Type I Survivorship

• A population showing low mortality rates until the individuals are past their reproductive years

• Example: Elephants are slow to reach sexual maturity and have few offspring.

Type II Survivorship

• These species show a uniform risk of mortality during their lifetime.

• An example is birds, where predation is a constant concern, but some level of parental care is given for a time.

Type III survivorship pattern

• A population with very high mortality rates among the young and very low mortality rates among sexually mature adults

• Sea turtles are an example: a female lays hundred of eggs each year, but less than 1% survive to adulthood. Those that do can live for hundreds of years.

POPULATION GROWTH MODELS

Geometric growth• A population that grows

rapidly during breeding season, then declines through the year until the next breeding season

• Exponential growth occurs under ideal conditions. Ex: when a population is first starting out and resources are plentiful

Exponential growth

• reproduction is continuous throughout year (i.e., no breeding season)

• constant growth rate

• examples: yeast, bacteria, humans

Logistic growth

• As population continues to grow, food, water,light and space can limit population growth.

• When the carrying capacity is reached, reproduction slows and the death rate increases.

• Equilibrium is reached.

• Logistic growth represents the effect of the carrying capacity on the growth of a population.

• Is the most common growth pattern in nature.