Plan – Week 3 • Test on 5.1 – Today or Tuesday… • Test on 5.2 (Greenhouse Effect, Carbon Cycle and Climate Change) : Friday • In between….5.3 and Topic G.3: Population Ecology and Invasive Species 5.3 Population Ecology What you need to know about populations (Topic 5.3, SL and HL) • Key Factors which determine population size • You must know how to draw, and interpret, a classical population growth curve • Factors which set limits to population increase What ELSE you need to know about populations (Topic G, SL and HL) • You must understand the impacts of alien species • You must be able to give three examples of alien species in ecosystems • You must outline one example of biological control of an invasive species What ELSE you need to know about populations (Topic G, HL, NEXT YEAR) • You must understand and distinguish between r-strategies and K-strategies • You must understand environmental conditions that favour r- or K-strategies • You must understand a method to estimate population size (catch and release) Let’s start simple… WHAT IS A POPULATION?... Human Population • At what point in human history did the population reach 1 billion people? • It took all of human history up to the early 1800s for world population to reach 1 billion people, and until 1960 to reach 3 billion. Today, the world gains 1 billion people every 11 years. Let’s Review: What is a population? (5.1.1) A group of organisms of one species that interbreed and live in the same place at the same time Key Characteristics of Populations 1: Geographic Distribution Characteristics of Populations 2: Population density The number of individuals per unit area Population Density • Can vary tremendously depending on the species and its ecosystem A field of sunflowers A flock of birds A few saguro cactus Turtles grouped to sun Population Density What are some benefits of living close together or in a clumped population? 1. Help finding food 2. Protection from predators or wind 3. Easier to find species Population Density What are some drawbacks (negatives) of living in a clumped population? 1. Crowded living areas 2. Battles over food/shelter 3. Easier for disease to spread Characteristics of Populations: Evaluating Growth Rate The amount by which a population’s size changes in a given time Let’s imagine a brand new population of…. • Let’s think about how it changes over time…. • How does it arrive in its new habitat? • Which factors will affect population size over time? • You have two minutes… Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com 5.3.1 What are the four factors that affect populations? What affects population size? Number of births (natality) Number of deaths (mortality) Number of individuals that enter (immigration) or leave (emigration) Population Growth • Migration- periodic movements of populations away from and back to their place of origin (not what we are talking about here) • Irregular movements of some individuals out of an area, into a new area, with no return - affects population size • Immigration – movement of individuals into an area Population increases in size • Emigration – movement of individuals out of an area Population decreases in size Population Growth • Why would an animal immigrate to or emigrate from a population? • Competitive pressures on some individuals – To find food, better living conditions, or a mate Evaluating population growth… doing the mathematics… If a population has unlimited food and space and is protected from predators and disease, what will happen to the size of the population? What would population growth looks like on a graph when an population colonizes a new habitat? Draw a graph and explain the shape. Work with a partner. You have five minutes. Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com Time Remaining www.SummitStudies.com It will increase exponentially! Under ideal conditions with unlimited resources and no predation, a population will grow exponentially Some formulae (you don’t need to know these!) (Reference: http://www.nature.com/scitable/knowledge/libr ary/how-populations-grow-the-exponentialand-logistic-13240157 • Exponential growth: • Logistic Growth (Transitional phase): Exponential Growth • Example: Bacteria reproduce in ~20 minutes by splitting in half – 1 bacteria after 20 min = 2 bacteria – 2 bacteria after 40 min = 4 bacteria – 4 bacteria after 60 min = 8 bacteria – In 180 min (3 hours) = 512 bacteria – In one day = 4,720,000,000,000,000,000,000 bacteria Exponential Growth • Exponential growth occurs when the individuals in a population reproduce at a constant rate This is what a graph – Creates a “J” shaped curve – Under ideal conditions with unlimited resources and no predation, a population will grow exponentially of bacterial growth would look like if the growth went unchecked Can exponential growth continue for ever? Write down the factors that set limits to population size You have two minutes… What are factors that set limits to population size? • • • • Competition for resources Build up of toxic by-products of metabolism Increased predation Incidence of disease. Birth and Death Rates • Affected by – Biotic factors • Disease, predators, food, competitors – Abiotic factors • Rainfall, temperature, light, pollution – Can be density dependent or density independent – Can be extrinsic or intrinsic Limits to Growth • Medium Galapagos finch • Droughts (fewer seeds) – Death rate increases – Birth rate decreases • High rainfall (more seeds and caterpillars) – Death rate decreases – Birth rate increases Logistic (Transitional) Growth Phase • Do bacteria cover the planet? • Exponential growth does not continue in populations very long. • As resources become less available, the growth of a population slows or stops • What might cause population growth to stop or slow down? – Predators, loss of habitat, disease, competition for resources: less food, less space etc. Logistic Growth (Transitional Phase) • Logistic growth (transition phase) occurs when population growth slows or stops following a period of exponential growth – Creates an “S” shaped curve • Population growth may slow or stop for a number of reasons: – Birthrate ↓ death rate ↑ immigration ↓ emigration ↑ • At some point, the growth of a population will level off (stabilise, plateau phase) Comparing Exponential and Logistic Growth Carrying Capacity Carrying Capacity (K) • The maximum number of individuals that a particular habitat can support The classical ‘Sigmoid’ Population growth curve Most plant and animal populations follow this type of growth What is happening in this population graph? Finches & Rainfall Some formulae (you don’t need to know these!) (Reference: http://www.nature.com/scitable/knowledge/libr ary/how-populations-grow-the-exponentialand-logistic-13240157 • Exponential growth: • Logistic Growth (Transitional phase): Alien Species What is an alien species? • An alien species is one which arrives in a nonnative habitat, usually as a result of intentional or accidental human activity • Often, they are not well adapted to their new habitat and don’t survive (too far outside their ‘niche’ • MANY have been hugely successful in their new habitat, causing huge ecological and economic damage The Classic Examples: • Zebra Mussels in American Great Lakes • Cane Toads in Australia • Rabbits in Australia • Japanese Knotweed in Europe • Bamboo in Europe There are literally hundreds of thousands more… Example of an Alien Species: The Cane Toad • http://www.youtube.com/watch?v=gYUHnf7U y1k&feature=player_embedded • http://www.youtube.com/watch?v=8q77CIQo dVw Homework (2) http://www.issg.org/database/ welcome/ • The Global Invasive Species DataBase • Use the database to build a factsheet about one invasive species, EITHER from your home country, OR Switzerland You must provide: • Common name and Binomial nomenclature • Native and introduced habitat range • Introductory pathway/vectors • Local dispersal methods • Impacts on local ecosystem and environment • Management strategies • Images What would population growth looks like on a graph when an population colonizes a new habitat? Draw a graph and explain the shape. Work with a partner. You have five minutes. 5.3.2, 5.3.3 A B A 5.3.2, 5.3.3 K = carrying capacity A r = rate of reproduction N0 = starting population B A 5.3.1 What are the four factors that affect populations? Population Growth Population Stability Population Decline What would population growth looks like on a graph when an population colonizes a new habitat? Make the shape of a Sigmoid graph with your hand in the air. Homework (1): Zebra Mussel Webquest (Population Study) http://ats.doit.wisc.edu/biology/ec/pd/t1_a1_b. htm 5.3.1 What are the four factors that affect populations? Population Growth Population Stability Population Decline What would population growth looks like on a graph when an population colonizes a new habitat? Make the shape of a Sigmoid graph with your hand in the air.