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Populations

Populations. Chapter 5. In Your Notebook. Look at the picture on page 128 Identify and Explain three factors that could cause a change in the number of red crabs on Christmas Island. Chapter Mystery. Read the chapter mystery on page 129

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Populations

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  1. Populations Chapter 5

  2. In Your Notebook • Look at the picture on page 128 • Identify and Explain three factors that could cause a change in the number of red crabs on Christmas Island.

  3. Chapter Mystery • Read the chapter mystery on page 129 • Hypothesize why the rabbits turned into a plague in Australia.

  4. How Populations Grow • Hydrilla in Florida • Used in home aquariums • Farmer threw in canal • Taking over native plants • Costs $$$$ to control

  5. Describing Populations • Population – group of organisms of a single species that lives in a given area • Studied using • Geographic Range • Density and Distribution • Growth Rate • Age Structure

  6. Describing Populations • Geographic Range • The area inhabited by a population • Can be large • Cod in Western Atlantic ranges from Greenland to North Carolina • Can be small • Bacteria on rotting pumpkin

  7. Describing Populations • Density • The number of individuals per unit area • Distribution – page 131

  8. Describing Populations • Growth Rate • Determines if the size of the population increases, decreases or stays the same • If the number of species in a given area remains basically the same over a large amount of time the growth rate is zero • Hydrilla in Florida has high growth rate • Cod in Atlantic have negative growth rate

  9. Describing Populations • Age Structure • The number of males and females of each age a population contains • Important because: • Must reach a certain age before you can reproduce • Only females can reproduce

  10. Population Growth • Factors that affect population size: • Birthrate • # born • Death rate • # that die • Immigration rate • Moving in • Emigration rate • Moving out

  11. Exponential Growth • What happens when you provide a population with everything it needs? • Food, shelter, protection from predators • Will the population increase, decrease or stay the same? • How? • Population produces offspring and those offspring produce offspring, etc.

  12. Exponential Growth • The size of each generation is larger than the one before • The larger a population gets, the faster it grows • Under ideal conditions with unlimited resources, a population will grow exponentially.

  13. Exponential Growth • Read “Organisms That Reproduce Rapidly” on Page 133 • How are these graphs the same/different?

  14. In Your Notebook • Read the Analyzing Data Box on Page 135 • Calculate the number of rabbits/generation • Generation 1: 1 pair of rabbits = 6 offspring • Generation 2: 3 pair of rabbits = 18 offspring • Construct a graph of your data • Answer: What type of growth is the rabbit population going through after 5 years?

  15. Logistic Growth • Natural populations don’t grow exponentially forever • What happens?

  16. Logistic Growth • Occurs when a population’s growth slows and then stops, following a period of exponential growth • Reasons: • Birth rate decreases • Death rate increases • Immigration decreases • Emigration increases

  17. Logistic Growth • Populations eventually reach their carrying capacity • The maximum number of individuals of a particular species that a particular environment can support

  18. In Your Notebook • One Minute Response • How are exponential growth and logistic growth related?

  19. 5.2 Limits To Growth • A situation that causes the growth rate of a population to decrease is called a limiting factor. Some limiting factors depend on the size of the population. Other limiting factors affect all populations in similar ways, regardless of the population size.

  20. In Your Notebook • Imagine a small island that has a population of five rabbits. How might each of the following factors affect the rabbit population? a. climate b. food supply c. predation

  21. In Your Notebook • Now imagine another small island that has a population of 500 rabbits. How would the same factors affect this population? • Climate, food supply, predation • Which of the factors depend on population size? Which factors do not depend on population size?

  22. Limiting Factors A factor that controls the growth of a population • Determines the carrying capacity • Some depend on population density, others do not

  23. Density-Dependent Limiting Factors • Affect populations when number of organisms per unit area reaches certain level • Does not affect small, scattered populations • Types • Competition • Predation • Herbivory • Parasitism • Disease • Stress from overcrowding

  24. Density-Dependent Limiting Factors • Competition • Fight for food, water, space, sunlight and other essentials • The more individuals in a given area – the faster the resources are used up • Can also occur among members of different species that attempt to use similar or overlapping resources

  25. Density-Dependent Limiting Factors • Predation, Herbivory and Human Predators

  26. Density-Dependent Limiting Factors • Parasitism and Disease • Parasites weaken or kill their host • If host population is large – parasites easily spread • CPV virus killed all but 13 wolves, only 3 were female so moose population skyrocketed. But, dense population of moose allowed winter ticks to run rampant so moose began to die

  27. Density-Dependent Limiting Factors • Stress from overcrowding • Fighting among themselves weakens ability to resist disease • Can cause females to abandon, kill or eat their own offspring

  28. In Your Notebook • Mystery Clue • What factors do you think could limit the size of a rabbit population?

  29. Density-IndependentLimiting Factors • Affect all populations, no matter what size • Hurricanes, droughts, floods, wildfires, etc. • Sometimes hard to tell difference • When moose population got large a snow storm covered their food source • Might not have had as big of an impact if population had been smaller

  30. Controlling Introduced Species • Hydrilla population controlled in natural environment • Plant-eating insects and fish might eat it • May be weakened by pests or diseases • Those limiting factors aren’t present in US so population grows out of control • Have tried herbicides and mechanical removal • Grass carp introduced to eat it • They must be sterile. Why?

  31. In Your Notebook • Make a T-Chart listing and describing limiting factors

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