Last class

• Some expressed apathy – not sure if people can change

• Some weren’t sure change should happen, perhaps the earth would be better without us.

• Energy sources• Information = power

Energy in EcosystemsHow does the energy received from the sun move through living things on our Earth?

Energy in EcosystemsIn order to understand how energy flows in an ecosystem, we must first organize living things in a certain way. The term trophic level refers to a way of categorizing living things according to how they gain their energy.

Solar EnergyWe have already learnedin the Weather Unit thatabout 30 % of the sun’senergy that reachesEarth is reflected by the air, clouds and surface of the planet. 70% of this energy is absorbed. This energy can be used by living things.

AutotrophsSome organisms can maketheir own food from sunlight and nutrients in the air and soil. The bunchgrass and algae are examples of these kinds of organisms. Some types of bacteria can also do this. These types of organisms are called autotrophs (or producers).

Primary ConsumersThe second trophic level contains organisms that feed on the producers. These organisms are referred to as primary consumers (also called herbivores).Grasshoppers and krill are examples of these types of consumers. They rely on autotrophs for their source of energy.

Secondary ConsumersAt the third trophic levelwe find animals that relyon the primary consumersas their source of energy.Consumers at the third trophic level are referred to as secondary consumers (also called carnivores) The spotted frog and crab are examples of secondary consumers.

Tertiary ConsumersThe fourth trophic levelis made up of animalsthat eat secondary consumers to obtain theirenergy. The red-tailedhawk might eat the spotted frog and the sea otter could eat the crab. These animals at the fourth trophic level are called tertiary consumers (also carnivores).

DetrivoresDetrivores (also called decomposers)Are consumers. Theyobtain their energy by eating detritus which is the bodies of small dead animals, dead plant matter, and animal wastes. Detrivores feed at every trophic level and make up their own important food chains. Detrivores such as earthworms and beetles are also an important energy source for consumers such as birds.

Food ChainIn our example we can see how energy flows from one livingthing to another. A food chain is a step by step sequencelinking organisms that feed on each other, starting with a food source, such as a producer or detritus, and continuing with a sequence of consumers.

Food WebIn nature, manyanimals are partof more than onefood chain and eatmore than one kindof food to meet their energy requirements. A food web is a model of the feeding relationships among organisms in an ecosystem.

An Example: The GrouseLook at the grouse inthe model at the right. The grouse mayis seeds. In this case,the grouse would be a primary consumer.But the grouse can also eat a butterfly.In that case it would be secondary consumer. There are only two examples of the possible food chains that the grouse could belong to.

Time to Practice

Checklist1. Define and use correctly the

following terms: trophic level, autotrophs (producers), primary consumers (herbivores), secondary consumers (carnivores), tertiary consumers (carnivores), detrivores, food chain, food web

2. State how much of solar energy is absorbed by Earth.

Practice1. Fill in the blanks with the appropriate words.a) The term used to categorize living things according to how

they gain their energy is trophic level.b) Of all the energy that falls on Earth from the sun, the

percentage that reaches the surface is 70%.c) The name given to green plants, bacteria, and all living

things that can make their own food from sunlight, and nutrients found in the soil and air is autotrophs (producers).

d) These living things are found at the second trophic level. The obtain their energy from green plants. The general name given to them is primary consumers (herbivores).

e) Another term for carnivores is secondary consumers.f) Carnivores are found at the third trophic level.g) Those consumers that eat secondary consumers and are

also carnivores are the tertiary consumers and they are found at the fourth trophic level.

Practice1. Fill in the blanks with the appropriate

words.h) Another word for decomposers is detrivores. Two examples of these living things are earthworms and beetles.i) The name given to a step by step sequence linking organisms that feed on each other is food chain.j) A more accurate model of feeding relationships in a food chain is the food web.

Practice2. The diagram shows a simple food chain.

For each of the living things you see in this diagram, give the ecology term that could be applied to it.Grass: autotroph (producer).Insect: primary consumer (herbivore).Frog: secondary consumer (carnivore).Snake: tertiary consumer (carnivore).

Practice3. The diagram shows a food web.a) If the trout was to serve as a primaryconsumer, what would beits food?b) For example a), what type of consumer would the hawk be and at what trophic level would it be?c) If the trout aced as a secondary consumer, what would be its food?d) For example c), what type of consumer would the eagle be and what would be its trophic level?

Practice3. The diagram shows a food web.

a) If the trout was to serve as a primary

consumer, what would be its food?Phytoplankton

Practice3. The diagram shows a food web.

b) For example a), what type of consumer would the hawk be and at what trophic level would it be?The hawk would be a secondary consumer and it would be at the third trophic level.

Practice3. The diagram shows a food web.

c) If the trout aced as a secondary consumer, what would be its food?Mayfly or dragonfly.

Practice3. The diagram shows a food web.

d) For example c), what type of consumer would the hawk be and what would be its trophic level?The hawk would be a tertiary consumer and it would be at the fourth trophic level.