5.1 Populations I. What is a population? A. Def- made up of a group of organisms (same species) that live together in one place at one time & interbreed. 1. Can be large or small B. Important because populations of different species interact & affect one another 1. including human populations

II. Population Growth A. Factors that affect growth 1. Births 2. Deaths 3. Immigration a. movement of individuals into a population 4. Emigration a. movement of individuals out of a population

B. Exponential Growth 1. More births than deaths 2. Causes a J-shaped curve when graphed 3. Numbers increase by a certain factor in each successive time period 4. Starts slowly when small population 5. Increases speed as population gets larger a. ex- bacteria 1. 1 bacteria, copies itself every 30min.=10 million bacteria in 10 hrs.

C. Logistic Growth 1. Populations do not grow unchecked forever 2. S-shaped curve when graphed 3. Limiting factors a. food availability, predators, & disease 4. Ecosystems can only support so many organisms a. Carrying capacity 1. the largest population an environment can support 5. Eventually birth rate = death rate, which = no more growth

6. Density-dependent factors a. variable affected by number of organisms present in an area 1. not enough nesting sites for birds = less birds born 7. Density-independent factors a. affect a population regardless of population density 1. weather, fire, floods

III. Factors that affect population size A. Abiotic 1. Most important- weather & climate a. harsh weather slows growth rate B. Biotic 1. Often density dependent a. Crowding causes stronger influence 2. Food (ex- grass or other animals) a. plenty = growth, scarce = decline 3. Predators a. too many = decline 4. Bacteria & disease

5. Humans affect populations 1. cause populations to decrease a. disrupt habitats, introduce disease, or introduce non native species IV. Human Population A. More than 7 billion B. Decreased death rate 1. Reasons - better sanitation, hygiene, disease control, & agricultural technology C. Industrial Revolution 1. Rapid increased growth of human population

D. Beginning to put pressure on Earth’s ecosystems 1. possibly 9 billion humans in 50yrs. E. Science & technology 1. agricultural tech. has allowed efficient production of crops. a. more food = more people 2. Medical advances a. Vaccines allow more children to grow to adulthood