Food Webs and Energy Pyramids

Objectives

• Identification of the feeding relationships of animals in an ecosystem

• Tracing the flow of energy and nutrients through an ecosystem

• Understanding how organisms in an ecosystem are interrelated

• Understanding the complex and dynamic nature of an ecosystem.

Ecosystems• Biotic Factors: Any living part of an environment.• Abiotic Factors: Any non-living part of an environment.Examples:

Feeding Strategies• Autotroph - organisms that is able to capture energy from sunlight and

use it to produce its own food from inorganic compounds, also called a producer.

• Heterotroph -organisms that obtain food by consuming other living things, also called a consumer.

Feeding Strategies

• Producers/Autotroph- Sunlight is the main energy source for life on Earth.– Definition-organisms that can capture energy

from sunlight and use that energy to produce food.

– Examples:

Feeding Strategies

• Consumers/Heterotrophs • Definition:-organisms that rely on other organisms for their energy and

food.• Examples:

– Herbivores- such as cows, obtain energy by eating only plants.– Carnivores- such as snakes, eat only animals.– Omnivores- such as humans, eat both plants and animals.– Detritivores- such as earthworms, feed on dead matter.– Decomposers- such as fungus, break down organic matter.– Scavengers- such as vultures, consume the carcass of other animals.

Trophic LevelsEnergy, Producers, and Consumers

Trophic Levels

• Producers• Definition- the beginning level in a food chain

that contains organisms that use energy directly from the sun for life processes. For example: Plants and other autotrophs use sunlight to produce sugars and oxygen.

• Examples: plants, some protists (algae), some bacteria (cyanobacteria)

Trophic Levels

• Primary Consumers• Definition- Organisms that obtain nutrients by consuming producers. They

indirectly use energy from the sun that was captured by the producers. For example: when plants are eaten by animals.

• Examples: Rabbits, field mice, birds, and prairie dogs.

Trophic Levels

• Secondary Consumers• Definition- Organisms that obtain nutrients by

consuming other consumers. They indirectly use energy from the sun that was captured by the producers and other consumers.

• For example: Foxes, birds, snakes

Trophic Levels

• Tertiary Consumers and Top PredatorDefinition: Tertiary Consumers are carnivores /organisms that eat only

animals and they feed on secondary and primary consumers.

Examples: Harris’s Hawks, rattlesnakes, dogs, owls, bald eagles, plankton-eating fish, shrew, lions and tigers.

Trophic Levels

• Detritivores– Definition – organisms

that consume dead and decaying organic matter

http://www.bing.com/images

Trophic Levels• DecomposersDefinition: Organisms that break down and obtain energy from dead organic matter.

Examples: Bacteria, fungi, mushrooms, mites, gitterbug, millipede, slug, earthworm, snail, and the dung beetle.

Trophic Levels

Trophic Levels

Food Chain vs. Food WebA food chain is a series of steps in which organisms transfer energy by eating and being eaten.

Food Chain vs Food Web A food web is a network of several interacting food chains.

Dynamic Nature of Ecosystems

Changes in Ecosystem

• Top Down– Owls increase– Mice decline– Grass increases

Changes in Ecosystem• Bottom up– Add fertilizer- more grass– More mice– More owls

Energy PyramidEnergy transfer is only 10% from one trophic level to the next higher trophic level

Lots of producesFew top predators