1. Chapter 4 Populations

2. Properties of Populations Population: a group of organisms of 1 species in the same area 1) Population Size (usually estimated) 2) Population Density = how crowded a popltn. is Expressed as # of individual. per area or volume

3. Properties of Populations (con’t) 3) Dispersion = the spatial distribution of individuals 3 types: A) Even (due to social interactions) B) Clumped (due to resource availability) C) Random (due to seed dispersal by wind or birds)

4. Population Dynamics Reflects changes in size and composition of popltn. Birth Rate: # births in 1 period of time US = ~4.2 million/year Death Rate: # deaths in 1 period of time US = ~2.5 million/year Life Expectancy: average length of life US = 72 (male); 79 (female)

5. Population Dynamics (con’t) Age Structure: distribution of individuals of different ages in a popltn. As % young increases, growth rate increases Survivorship Curves: show likelihood of survival at different ages throughout lifetime

6. Population Growth Rate Growth Rate: the amount by which a popltn. changes over time Calculated by: Growth Rate = Birth rate – Death Rate Depends on: 1) birth rate 2) death rate 3) immigration (moving in) 4) emigration (moving out)

7. Exponential Growth Describes a popltn. that grows rapidly after only a few generations Larger popltn. = faster growth In reality, resources will run out Limiting Factor: a factor that restrains popltn. growth

8. Logistic Growth Describes a realistic popltn. (birth/death rates vary with popltn. size) Accounts for limiting factors Carrying Capacity: the maximum # of individuals the environment can support over time

9. Population Regulation Factors in place to help control popltn. size 2 Types: 1) Density-dependant: depend on popltn. density i.e. availability of resources 2) Density-independent: popltn. density does not matter i.e. weather, floods, etc.