Unit 3 Notes
Biotic 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
Mostly stable
Wild fluctuations
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

Low mortality rate throughout life, and most
live to old age
 Type

II
Intermediate mortality and life expectancy
 Type

I
III
Produce many offspring, with early mortality
rate
Survivorship Curves