Chapter 5: Populations 5-1: How Populations Grow Characteristics of Population 1. Geographic Distribution: “range”, area inhabited by a population 2. Density: # of individuals per unit of area 3. Growth Rate: Increase, Decrease, or Stay the Same Population Growth • 3 Factors that affect population growth – # of births (birth rate) – # of deaths (death rate) – # entering and # leaving • Immigration: movement of individuals into an area (growth) • Emigration: movement of individuals out of an area (decrease) Exponential Growth • Exponential Growth: individuals reproduce at a constant rate – Ideal conditions with unlimited resources are necessary for exponential growth. Ex: One bacteria cell reproduces every 20 minutes How many bacteria 20 min later? How many another 20 min later? How many after another 20 min? How many after one day? Logistic Growth • Logistic Growth: when population growth slows or stops (due to decreased availability of resources) • Carrying Capacity: The largest number of individuals that an environment can support 5-2: Limits to Growth Limiting Factors • Limiting Factor: Causes population growth to decrease 1. 2. 3. 4. 5. Competition Predation Parasitism/Disease Extreme Climates Human Disturbances Density Dependent Factors • Density Dependent Limiting Factors – depends on population size and density • Factors act most strongly when population is large and dense – Ex: Competition: compete for resource – Ex: Predation: one catches & feeds on another; population rise and fall in tandem – Ex: Parasitism: organisms take nourishment at expense of host, weakening or killing host. Density-Independent Factors • Density –Independent Limiting Factors: affect all populations, regardless of size – EX: weather, natural disaster, seasons, and humans 5-3 Human Population Growth Human Population Growth • Size of human population increased with time • Started slow, grew rapidly due to: – – – – Agriculture Industry Medicine Sanitation Patterns of Population Growth • Demography: scientific study of human populations • “The Demographic Transition” – a dramatic change in birth and death rates – – – – In developing countries birth and death rates are high As country develops, death rate is lowered Population increases and birth rate is lowered U.S, Japan, and much of Europe have completed the transition Age Structure • Age Structure Diagram: graph the numbers of people in different age groups in a population – Used to predict future population growth Future Population Growth • Estimated human population in 2025? – 7.8 Billion People • Estimate human population in 2050? – 9 Billion People • If the human population growth doesn’t slow down it could seriously damage the environment and global economy.