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Chapter 5 POPULATIONS Lab Biology CP Red Crabs on Christmas Island in the Indian Ocean- What assumptions can you make about this population??? http://animal.discovery.com/videos/fooled-by-nature-christmas-island-crabmigration.html What problems does this population impose on other populations?? Chapter 5: POPULATIONS • 5.1: How Populations Grow • 5.2: Limits to Growth • 5.3: Human Population Growth 5.1 How Populations Grow What is a Population? • A population is a group of organisms of a single species that lives in a given area How do Ecologists Study Populations??? • • • • 1.) Geographic Range 2.) Density and Distribution 3.) Growth Rate 4.) Age Structure 1. Geographic Range • Geographic Range: – The area inhabitated by a population – Can vary in size • Small - Bacteria in a rotting pumpkin (<1 cubic meter) • Large - Cod in the Atlantic (hundreds of miles) 2. Density and Distribution • Population Density: – The number of individuals per unit area – Vary in densities • Distribution: – How individuals in a population are spaced out across the range of the population • 1.) Randomly • 2.) Uniformly • 3.) Clumps (most concentrated) 3 Types of Population Distribution 3. Growth Rate • Growth rate determines whether the size of a population increases, decreases, or stays the same. • Examples: – Zero growth rate: • When the population size stays the same – Positive growth rate: • Population increases – Negative growth rate: • Population decreases 4. Age Structure • Age structure: – The number of males and females of each age a population contains – WHY? • Because most plants and animals can’t reproduce until a certain age • Only females reproduce What factors affect population growth? • • • • 1.) Birthrate 2.) Death rate 3.) Immigration 4.) Emmigration Reasons for 3 & 4: – Food shortage – Overcrowding – Looking for mates Why does a population grow? • Has food • Has space • Protection from predators • Protection from disease • Has removal of waste products Exponential Growth • Exponential Growth: – The size of each generation of offspring will be larger than the generation before it – The larger the population gets, the faster it grows – Under ideal conditions, a population will grow exponentially Rates of Growth • Reproduce Rapidly: – Bacteria • 1 day = 4,720,000,000,000,000,000 individual cells • Reproduce Slowly: – Elephants • 1 offspring every 2-4 years Logistic Growth • Logistic Growth: – Occurs when a population’s growth slows then stops, following a period of exponential growth – 3 Phases: • Phase 1 – Exponential Growth • Phase 2 – Growth slows down • Phase 3 – Growth stops – When birthrate and death rate are the same – When emigration equals immigration Carrying Capacity • Carrying Capacity: – The maximum number of individuals of a particular species that a particular environment can support 5.2 Limits to Growth Limiting Factors • Limiting factors: – A factor that controls the growth of a population – Determine the carrying capacity of an environment for a species – Examples: • • • • • • Competition Predation Parasitism Disease Natural disaster Unusual weather How might each of these factors increase the death rate in a population? Density Dependent Limiting Factors • Operates strongly only when population density reaches a certain level • Examples: – – – – – – 1. Competition 2. Predation 3. Herbivory 4. Parasitism 5. Disease 6. Stress from overcrowding 1. Competition • Organisms compete for: – – – – Food Space Water sunlight 2 & 3. Predation and Herbivory • Predator-prey relationships – Cycle up and down over time • Herbivory effects – Herbivores are predators to plants – Cycle up and down • Humans as predators 4 & 5. Parasitism and Disease • Parasites make their hosts weak and may cause disease or death How does predation affect population growth? Density-Independent Limiting Factors • Affect all populations in similar ways, regardless of population size and density • Examples: – – – – Hurricanes Droughts Floods Wildfires Controlling Introduced Species • How to control runaway populations??? – Remove them – Herbicides • Problems: – Only temporary solution – Expensive 5.3 Human Population Growth Has human population size changed over time? • Tends to INCREASE • Reasons: – Medication – Sanitation Patterns of Human Population Growth • Demography: – The scientific study of human populations – Predicted by: • Birthrates • Deathrates • Age structure The Demographic Transition • Demographic Transition: – Dramatic change from high birthrates and death rates to low rates – 3 stages