How Populations Grow / Exponential Growth/ Logistic Growth/ J-shape vs S-shape

Populations grow based on the differences between WHAT that increase population size and those that decrease population size

FACTORS

In natural populations, immigration and emigration are approximately WHAT - WHAT have the largest effect on population size and growth

In natural populations, immigration and emigration are approximately EQUAL - BIRTH RATE AND DEATH RATE have the largest effect on population size and growth

Lag Phase

where population isn’t ACTIVELY reproducing and there are few individuals to REPRODUCE

Growth phase

Fastest reproduction (exponential) B>D

Transitional phase

Where growth is SLOWING down, but STILL GROWING (environmental resistance now playing a part)

Stationary phase

B = D

Death phase

D > B, entire population may die

Exponential growth

• Growth curves for WHAT or WHAT

• WHAT shape

• The highest possible per capita growth rate represents an organism’s WHAT which is the WHAT rate of growth possible given unlimited resources and ideal living conditions

• Growth curves for MIRO-ORGANISMS or CLOSED POPULATIONS

• J-shape

• The highest possible per capita growth rate represents an organism’s BIOTIC POTENTIAL (r) which is the INTRINSIC rate of growth possible given unlimited resources and ideal living conditions (growth is exponential at the intrinsic rate of increase)

Ex: Bacteria have a doubling time of 20 min.   After 36 h, if growth continued at this rate, the entire earth would be blanketed in bacteria 10 cm thick.  In the next hour, the blanket would be deeper than we are tall.

Logistic growth

• Growth curve for a population which has reached WHAT capacity and is in stable WHAT

• Carrying capacity is the WHAT

• Carrying capacity occurs at the WHAT

• WHAT curve

• Growth curve for a population which has reached CARRYING capacity and is in stable EQUILIBRIUM

• Carrying capacity is the maximum size the environment can sustain over an extended period of time.  

• Carrying capacity occurs at the stationary phase where the birth rate = death rate

• S-shaped curve

J-shaped growth curves

• Organisms whose populations are regulated by WHAT factors

• Periods of rapid WHAT, rapid pop. decline

• The population’s size at any time is determined by the WHAT of time it experiences a WHAT growth rate

• Found in WHAT and WHAT

• Organisms whose populations are regulated by DENSITY INDEPENDENT factors

• Periods of rapid EXPONENTIAL GROWTH, rapid pop. decline

• The population’s size at any time is determined by the LENGTH of time it experiences a POSITIVE growth rate

• Found in INSECTS and ALGAE POPULATIONS

S-shaped growth curves

• Organisms that are affected by WHAT factors display s-shaped (sigmoidal) growth curve - the population will remain WHAT

• Changes in conditions will cause numbers to WHAT, but periods of WHAT are rare

• When populations are small, the WHAT may be so small that they go by unnoticed, and the increase appears to be WHAT until the population gets bigger.

• when population growth ceases due to WHAT factors, the population has reached its WHAT - a state of dynamic WHAT (steady state)

• Organisms that are affected by DENSITY-DEPENDENT factors display s-shaped (sigmoidal) growth curve - the population will remain STABLE

• Changes in conditions will cause numbers to FLUCTUATE, but periods of EXPONENTIAL GROWTH are rare

• When populations are small, the DENSITY-DEPENDENT may be so small that they go by unnoticed, and the increase appears to be EXPONENTIAL until the population gets bigger.

• when population growth ceases due to DENSITY-DEPENDENT factors, the population has reached its CARRYING CAPACITY (K) - a state of dynamic EQUILIBRIUM (steady state)

Every organism needs “space” that is taken up - wastes build up and cause WHAT, predators will increase in number because there is WHAT

Every organism needs “space” that is taken up - wastes build up and cause DISEASE, predators will increase in number because there is PLENTY of FOOD

As population increases, eventually, to reach WHAT B = D (B decreases)

CARRYING CAPACITY

• Fecundity (ability to reproduce) will WHAT as population WHAT

• The total number produced per female WHAT

• Females attain maximum WHAT older

• Fecundity (ability to reproduce) will DECREASE as population INCREASES

• The total number produced per female DECREASES

• Females attain maximum FECUNDITY older

Survivorship - as density increases, the survivorship curves will change so that at WHAT densities, fewer organisms WHAT

Survivorship - as density increases, the survivorship curves will change so that at HIGH densities, fewer organisms SURVIVE

As population increases environmental resistance (combination of density independent and dependent factors) will WHAT

Increase

when a population is at its carrying capacity it may show WHAT changes in population

CYCLIC changes

Although S-shaped growth curves will reach and tend to maintain WHAT, populations tend to produce more offspring than the environment can support → WHAT around carrying capacity with some years having much more environmental resistance than other → selective pressure → Evolution

Although S-shaped growth curves will reach and tend to maintain CARRYING CAPACITY, populations tend to produce more offspring than the environment can support → OSCILLATE around carrying capacity with some years having much more environmental resistance than other → selective pressure → Evolution