Unit 3 NotesBiotic Potential vs. Environmental Resistance

Biotic Potential Reproductive capacity (r)- a measure of

biotic potential; rate that members of a population reproduce if unlimited For an organism to survive past the early life

stages and become part of the reproducing population is called recruitment

Each organism will have a different amount Humans may only have one offspring per year,

while fish may lay 100s of eggs in a year

Environmental Resistance We very rarely see unlimited population

growth due to biotic and abiotic factors influencing environmental resistance Biotic Factors are predators, parasites,

competitors, and lack of food Abiotic Factors include unusual

temperatures, moisture, light, fire, just to name a few

Comparison

Reproductive Strategies Produce massive numbers of offspring,

leaving survival to kill off most of the young Results in low recruitment (what is

recruitment again?) High reproductive rate High mortality rate Small organisms Sometimes called r-strategists

r-strategists: organisms that have a high “r” value (or “reproductive” value)

Reproductive Strategies Produce low numbers of offspring, but

provide care and protection to allow the organism to survive to adulthood Organisms are well-adapted to their

environment Low reproductive rate Low mortality rate Often called K-strategists

K-strategists: populations that fluctuate around the carrying capacity (also called “equilibrial” species)

r-strategists vs. K-strategists

r-strategists K-strategists

Environment

Advantage if less stable

Advantage if more stable

Size Smaller Larger

Life Span Shorter Longer

Age at first reproduction

Younger Older

Offspring More Fewer

Parental Care

Little or none Long and involved

Population Stability

Wild fluctuations

Mostly stable

Survivorship Curves Life History: characteristics such as

age at first reproduction and the length of life that determine survivorship curves

Survivorship Curves demonstrate the number remaining from a group of organisms all born at the same time, shown decreasing over time until the maximum life span for the species is met

Survivorship Curves Type I

Low mortality rate throughout life, and most live to old age

Type II Intermediate mortality and life

expectancy Type III

Produce many offspring, with early mortality rate

Survivorship Curves