1. Unit 3 Notes Biotic Potential vs. Environmental Resistance

2. 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

3. 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

4. Comparison

5. 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)

6. 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)

7. r-strategists vs. K-strategists r-strategistsK-strategists EnvironmentAdvantage if less stable Advantage if more stable SizeSmallerLarger Life SpanShorterLonger Age at first reproduction YoungerOlder OffspringMoreFewer Parental CareLittle or noneLong and involved Population Stability Wild fluctuationsMostly stable

8. 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

9. 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

10. Survivorship Curves