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Population Growth Chapter 5 How do ecologists study populations? • Geographic range: where are they distributed? • Density and distribution: in what manner are they distributed? • Growth rate: how is the population increasing or declining? • Age structure: males and females? number at reproductive age? Geographic range: manatees and dugongs Patterns of distribution: why??? Clumped distribution • Food – clumped around food source • Protection or shelter • Small differences in habitat: shade, soil, wind, water • Patchy resources! Uniform distribution • Can be caused by competition for resources • Some organisms have specialized mechanisms… • Creosote bushes release terpines, chemicals which inhibit growth of other plants around • Tree planting • Farming Random distribution • Happens when none of these factors exist • Least common in nature because biotic factors usually cause other type • Homogeneous habitats (same all over) • Wind dispersal of seeds • Water dispersal of larvae Population growth • Birth rate, death rate, immigration, emigration • Resources are often the driver: food, water abundance or shortage, overcrowding Exponential population growth What caused human population expansion? Logistic population growth • Stages: exponential growth, growth slows down, growth stops • Carrying capacity: number of organisms the area can support Limiting factors • Any factor that slows or stops the growth of a population • Determine the carrying capacity • Can be biotic or abiotic: availability of food or water, parasitism or disease, competition and predation, natural disasters such as floods or droughts Density dependent limiting factors • Act strongly when population density reaches a certain level • Competition, predation, parasitism and disease, hunting, overcrowding stress • Tend to be the BIOTIC limiting factors Density independent limiting factors • Affect all populations equally, regardless of population size or density • Drought, floods, unusual weather such as hurricanes, wildfires • Tend to be ABIOTIC limiting factors Invasive species • Any non-native species that is introduced to an ecosystem • Accidental in intentional introductions • Don’t have the usual limiting factors because the species didn’t evolve there: – No natural predators – No biological controls – Often short life-history species (rapid growth, lots of reproduction Examples: • Brazilian pepper trees outcompete our mangroves • Brown hoplo “armored catfish” in St. Johns River are outcompeting native fish we eat • Jellyfish brought in ballast water of ships • Invertebrates attached to oil rigs moving from ocean to ocean Demography: study of human populations • When you refer to “demographics” it usually means: ages, genders, ethnicities, socioeconomics • Age structure very important: how many members of the population are reproducing? The Demographic Transition • Stage 1: high birth rate and high death rate • Stage 2: high birth rate, but death rate begins to fall • Stage 3: birth rate falls to meet the death rate Factors that influence human birth and death rates: nutrition, sanitation, medical treatment, education, higher standard of living Countries by population Top 400 urban areas in 2006: 1 million + • Humans have a clumped distribution • Notice that Florida has 3 dots! Fertility rate by country: number of children (0-8) More people = less resources • Food competition: shortages, prices • Other resources: fuels, water, space, trees • Impact on the environment: – Deforestation – Air pollution – Water pollution – Overcrowding What can we do? What should we do? • Write a 1 page essay about human population growth • Should we address population as a society, or leave it up to individuals? • What are some of the things that we can do?