9.4

• What is an ecosystem?

  An ecosystem is a community of living organisms interacting with one another and their physical surroundings.
• How do ecosystems vary?

  Ecosystems vary in size.
• What is a key characteristic of all ecosystems?

  All ecosystems are self-sustaining.
• What is the largest and most complex ecosystem called?

  The biosphere.
• What are the three main components of the biosphere?

  • Hydrosphere
  • Lithosphere
  • Atmosphere
• What do food chains and food webs illustrate in an ecosystem?

  They show the flow of energy in an ecosystem.
• What are the two main classifications of organisms in food chains?

  • Producers: first in the chain
  • Consumers: higher in the food chain
• What are the types of consumers in an ecosystem?

  Carnivores, omnivores, herbivores, parasites, scavengers, detritivores, and decomposers.
• What is the usual type of food chain?

  • Predator / prey
  • Shows predators eating prey
  • Prey is usually smaller than the predator
• What characterizes a parasite / host food chain?

  • Less common type
  • Large organism is the host
  • Parasite feeds off the host
• How do detritivores and decomposers function in ecosystems?

  • More complex in areas with lots of detritus
  • Decomposers are a major energy source for detritivores
  • Enable nutrients to be returned to the environment
• What do decomposers convert organic matter into?

  Inorganic matter.
• How is energy passed in a food chain?

  • Energy and nutrients are passed from one organism to another
  • An animal passes on about 10 percent of the energy it receives
  • Results in a pyramid of numbers
• What does the pyramid of numbers in a food chain indicate?

  It shows many organisms at the bottom and few at the top.
• What is a food web?

  • A community may contain numerous species
  • Each species is involved in several different food chains
  • Food chains are interconnected to form a large network
• What is a trophic level?

  Each feeding level of a food web.
• What are the first and higher trophic levels in a food web?

  Producers are the first trophic level, and consumers are higher trophic levels.
• What is the role of herbivores in trophic levels?

  Herbivores are the second trophic level.
• What is the role of first-order carnivores in trophic levels?

  They feed on herbivores and are in the third trophic level.
• Can organisms function at multiple trophic levels?

  Yes, organisms may function at multiple trophic levels.
• What is a keystone species?

  • A species that plays a critical role in maintaining the structure of their ecosystem
  • Example: Sea stars as top predators
• What was the experiment involving sea stars in a rock pool?

  • Sea stars were removed from one rock pool
  • Two types of barnacle and mussel began to dominate
  • Limpets were outcompeted, decreasing from 15 to 8 species
• How can some species be considered keystone species based on their habitat effects?

  • They affect their habitat significantly
  • Example: Elephants preserve savannahs by eating young trees