Transcript Food Webs and Chains

FOOD WEBS AND CHAINS
7th Grade Science
OBJECTIVES
• Define and give examples of organisms at different
trophic levels
• Describe how energy flows in a food chain.
• Explain why producers must outnumber consumers in a
balanced ecosystem.
PRODUCERS
• Food chains begin with producers
• organism that makes its own food
• Green Plants use energy from the Sun to create food through
photosynthesis
• Make up Trophic Level in an ecosystem
• Examples: Grass, Trees, and Algae
CONSUMERS
•
Organism that get their energy by eating other organisms
•
“YOU” cannot make your own food, no matter how hard you try!
•
Must obtain energy from other sources to live and grow (EAT!!!!!)
• All animals, including humans are consumers
PRIMARY CONSUMER
• First consumer in Food Chain
• Obtain energy directly from “Producers”
• a.k.a—”HERBIVORES” or plant eaters
• Land Ecosystem Herbivores include:
• Cows, Deer, and Grasshoppers
• Aquatic Ecosystem Herbivores include:
• Shrimp, Minnows, and Snails
LAND ECOSYSTEM HERBIVORES
AQUATIC HERBIVORES
SECONDARY CONSUMERS
• Eat Primary Consumers
• Include “Carnivores” (meat eaters)
• Lions, Tigers, Coyotes, and Wolves
TERTIARY CONSUMER
• Eats “Secondary Consumer”
• Includes: Carnivores and Omnivores
• Carnivores:
• Only eat meat
• Omnivores
• Eats both meat and plants
• Examples of Omnivores:
• Humans and Bears
DECOMPOSERS
• Last link in a food chain
• Break down nutrients in dead organisms and return essential chemicals to
earth:
• Nitrogen (N), Carbon (C), and Phosphorous (P)
• In land ecosystems, chemicals are released into soil.
• In aquatic ecosystems, chemicals are dissolved in water.
• Essential part of an ecosystem because:
• Producers absorb nutrients to make food
• Most common Decomposers are:
• Bacteria and Fungi
ENERGY FLOW
• Where do you get energy to read, come to school, hunt, and play ball?
• Eating what? Food!!
• All energy as you already know, comes from the Sun
• Producers absorbs the energy and uses “Photosynthesis” to make food
• 50% of energy absorbed from Sun is used to live and grow
• Unfortunately not all energy is transferred to consumer, due to heat “loss”
• Only around 10% of energy is transferred from producer to consumer
BALANCED ECOSYSTEM
•
Producers outnumber consumers greatly
•
More Specifically:
• Producers outnumber Primary Consumers
• Primary Consumers outnumber Secondary Consumers
• Secondary Consumers outnumber Tertiary Consumers and so on…….
•
Since energy decreases 10% with each Trophic level, it is very important for higher level
consumers to eat a lot to get enough energy to survive.
•
Example:
• Even though a mouse only has to eat a few stalks of grass to have energy, a snake
must eat several mice to survive. To take this one step further, a hawk has to eat
even more snakes!
TROPHIC PYRAMID
FOOD WEBS
•
Used to represent the complex food relationships between organisms in an ecosystem.
• Network of interconnecting food chains
FOOD WEB #2
END OF CLASS REVIEW
• How much energy is transferred from one trophic level to the next?
• Describe a Balanced Ecosystem.
• Where do producers get their food and how?
• What are the 3 types of consumers? How do they get their food?
• Describe a food web