UNIT 3 - POPULATIONS Chapters 8 & 9

8.1: Populations Population—a group of the same species living together in the same place

Features of populations: – Size—number of individuals – Density—number of individuals in an area

– Dispersion—how individuals are arranged in an area Random, even (uniform), or clumped

How Does a Population Grow Populations change over time due to births & deaths – Growth rate—change in population size over time – Growth rate formula: (Births + Immigrants) – (Deaths + Emigrants)

Reproductive potential—maximum number of offspring an individual can produce How Fast Can a Population Grow – Higher in species that produce more young at an earlier age

Exponential growth— populations grow without limits – Makes a J-shaped curve – Ex: bacteria

Carrying capacity—population size where birth rates equal death rates – Maximum number an ecosystem can support – Above carrying capacity = not enough resources, population declines – Below carrying capacity = many resources, population grows What Limits Population Growth

Limiting resources—limit the growth of a population – Food, water, habitat, sunlight

Competition within a population – Direct competition: food, sunlight – Indirect competition: territory, dominance

Patterns of Population Change Density-dependent factors—impact depends on the density of a population – Greater affect on dense populations, less affect on sparse populations – Ex: food, water, disease

Density-independent factors—impact does not depend on population density – Affects entire population – Ex: natural disasters, weather, fire

8.2: How Species Interact Niche—how an organism uses its environment & its role in the environment

Competition Competition—individuals attempt to use the same limiting resource – Can occur within species or between different species

Predation Predation—predator feeds on another organism (prey) Predator’s population size rises & falls with prey’s population size – Ex: snowshoe hare & lynx, moose & wolf

Other Interactions Parasitism—organism that lives in or on another organism (host) Mutualism—two species interact; each provides a benefit to the other Commensalism—one species benefits, the other species is not harmed or helped

9.1: Studying Human Populations Demography—the study of human populations Developed countries have more effect on the environment (resource depletion) Developing countries have the largest increases in population growth

Forecasting Population Size Age structure—the distribution of ages in a population – Shown in a population pyramid

Fertility rate—number of babies born each year per 1000 women – Replacement level is the average number of children that must be born to “replace” Migration—movement of individuals – Immigration (in) & emigration (out)

Declining Death Rates Population increase happened because of declining death rates Contributors to declining death rate: – Improved sanitation – Improved medical care (vaccines, medication – Improved nutrition

Life expectancy—average number of years members of a population are likely to live – 1800’s: 50 years – Today: 67 (higher in developed countries; 78 in U.S.)

9.2: Problems of Rapid Growth Fuel shortages (fossil fuels & wood) – Fuelwood is used for boiling water & cooking Unsafe drinking water – Local water used for drinking, cleaning, sewage Impacts on the land – Shortage of land for crops; urbanization causes suburban sprawl

Managing Population Growth Governments in some countries restrict births – Ex: China’s 1- child rule Provide more education, lower fertility rates

Growth is Slowing Current statistics: – World: 7 billion people, U.S.: 307 million – Took until 1850 to reach 1 billion people – Population should stabilize at 9 – 12 billion people by 2050 Population Growth Video Clip