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-crab-migration.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: Reproduce Slowly: 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 Dramatic change from high birthrates and death rates to low rates 3 stages