3.2 Life History Strategies

^^Life History:^^ series of events from birth through reproduction to death

Life history strategies are…

• shaped by microevolution
• operating through natural selection
• adapted for the specific environment

Life History Strategies Influence Growth Rate of a Population, Including

• age of first reproduction
• number of offspring
• amount of parental care given to offspring
• energy cost of reproduction

2 Patterns of Reproduction

1. r-Selection

   1. Energy into reproduction not survival

   2. poor competitors

   3. ^^Opportunists^^--take advantage of favorable conditions, changes in environment

   4. when favorable conditions are gone, population may crash

   5. populations go through irregular or unstable cycles

   6. characteristics:

      1. small-bodied
      2. reproduce when young → many offspring → low survival
      3. little to no parental care
      4. Exponential growth
      5. unpredictable environments
      6. controlled by density- independent factors
      7. exhibit type III survivorship curve

   7. examples

      1. bacteria
      2. algae
      3. most annual plants
      4. dandelions
      5. most insects
      6. cockroaches
      7. rodents
      8. oysters

2. K-Selected

   1. energy into long term survival

   2. High parental care

   3. good competitors

   4. thrive best in ecosystems with fairly constant environmental conditions

   5. populations remain close to carrying capacity (K) over long periods of time

   6. characteristics

      1. larger-bodied
      2. Late reproduction→fewer offspring→most survive
      3. high parental care
      4. live in predictable environments
      5. controlled by density dependent factors
      6. exhibit type I survivorship curve

   7. examples

      1. Humans
      2. Large trees
      3. Polar bears
      4. Elephants
      5. Most mammals/birds

Survivorship Curve