Snowshoe Hare and Canada Lynx

Population: a group the same species that live in the same place at the same time

Resources: food, water, shelter, space and mates

In theory populations can grow to an infinite size, but they are limited by resources

This causes individuals to compete for resources (remember intraspecific and interspecific competition!).

Population Growth

There are 4 main factors controlling population sizes:Natality - births increase

the populationMortality - deaths

decrease the populationImmigration - movement

of individuals into an area increases the population

Emigration - movement of individuals out of an area decreases the population

Factors that Control Populations

Carrying capacity: maximum number of individuals of a species that can be sustained indefinitely in a given space

No population can grow indefinitely! Resources = Limited!!

Carrying Capacity

Limiting Factors of PopulationsFactors (biotic or abiotic) which prevent

population numbers from growing too large and overrunning an ecosystem.

Example: Disease/ parasitesdisastershunting & predationcompetition for resources (food, oxygen, nutrients)

“J” population growth curveExponential growth = starts out slow and

then proceeds faster and fasterOccurs when a population has few resource

limitationsSudden collapse

('diebacks')

Patterns of Population Growth

“S” growth curve (S for sigmoid) Initially shows

exponential growth then levels off at the carrying capacity.

Occurs when a population has limited resources.

Results in stable population

Patterns of Population Growth

J Curve vs. S Curve

Population DynamicsA look at the factors that tend to increase or

decrease the size of a populationThe population size is determined by the interplay

of biotic potential and environmental resistance.

Biotic potential- growth rate with unlimited resources

Environmental resistance - all the factors acting jointly to limit population growth

Biotic Potential vs. Environmental Resistance

Biotic potential(Growth Factors)

Environmental resistance(Decrease Factors)

Favorable light, temperature

High reproductive rate

Adequate food supply Ability to migrate

habitatsAbility to adapt to

environmental change

Too much or too little light and temperature

Low reproductive rateInadequate food supplyInability to migrate

habitats Inability to adapt to

environmental change

Biotic Potential vs. Environmental Resistance

Density Dependent Factors Density dependent factorsDepend on the size of the populationEffects of the factors increase as the population growsAct as negative feedbackTend to be bioticTwo categories:

Internal factors = Within a single species limited resourcesreduced fertility rates

External factors = between speciespopulations of predators or preydiseases spread more easily in densely-populated

areas

Density Independent FactorsDo NOT depend on the size of the populationTend to be abioticEffect the population regardless of its sizeExamples:

1. Weather2. Earthquakes3. Floods 4. FiresR-strategists are most affected by these factors

Reproductive Strategies r

Unstable environment K

Stable environmentSmall sizeMany offspring are

producedEarly maturity Short life spanEach individual

reproduces onceType III survivorship

curveAffected by density

Independent

Large sizeFew offspring producedLate maturity (long

parental care)Long life spanIndividuals reproduce

more than once Mostly type I survivorship

curveAffected by density

dependent

Survivorship CurvesType I - high survival rate of the young, live

most of their expected life span and die in old age. (ex. Humans)

Type II - relatively constant death rate, could be due to hunting or diseases. (ex. coral, squirrels, honey bees and many reptiles)

Type III - have many young, most of which die very early in their life. (ex. plants, oysters and sea urchins).

Survivorship Curves

Pop QuizWhat does parental care have to do with the shape

of these curves? What density dependent factor will always affect

the population of white tailed deer in Wisconsin? (Only at certain times in the year)

What do you think the survivorship curve would be for a white-tailed deer population?