Food Webs

Trophic Levels

    -First level

        -Primary Producer

    -Second level

        -Primary consumers

    -Third level

        -Secondary consumers

    -Fourth level

        Tertiary consumers

    -It ends with what we call Top Predators

-Primary consumers, or herbivores (plant eaters), are animals such as rabbits, grasshoppers, deer, and zooplankton that eat producers, mostly by feeding on green plants.

• Secondary consumers, or carnivores (meat eaters), are animals such as spiders, hyenas, birds, frogs, and some zooplankton-eating fish, all of which feed on the flesh of herbivores.

• Third- and higher-level consumers are carnivores such as tigers, wolves, mice-eating snakes, hawks, and killer whales (orcas) that feed on the flesh of other carnivores.

• Omnivores such as pigs, foxes, cockroaches, and humans, play dual roles by feeding on both plants and animals.

• Decomposers, primarily certain types of bacteria and fungi, are consumers that release nutrients from the dead bodies of plants and animals and return them to the soil, water, and air for reuse by producers. They feed by secreting enzymes that speed up the break down of bodies of dead organisms into nutrient compounds such as water, carbon-dioxide, minerals, and simpler organic compounds.

• Detritus feeders, or detritivores, feed on the wastes or dead bodies of other organisms, called detritus (“di-TRI-tus,” meaning debris). Examples include small organisms such as mites and earthworms, some insects, catfish, and larger scavenger organisms such as vultures.

When you are in elementary school you learn about food chains. A food chain is a simple linear hierarchy of food. Food chains are not the full picture. We are more advanced than that. We learn about food webs.

A food web connects many species, Some species can fill many positions. They can be primary, secondary and tertiary consumers. Also tertiary consumers can also be the food for simpler consumers like secondary consumers.

Lets take a second to talk about thermodynamics and entropy!

Thermodynamics says energy cannot be created nor destroyed. Energy can only be converted. Every time energy is converted some is lost as an unusable form. That is entropy.

Every time energy is transferred some is lost as heat. We can feel this when we exercise. The more physical activity you complete the more calories you use. You are taking chemical energy and converting that to kinetic energy (movement). This transfer of chemical energy to movement releases heat and your body temperature starts to rise. Since we cannot exceed 98.6F/37C, our body sweats to cool us off.

All energy on earth comes from the sun. The sun is sending a lot of solar energy towards the earth every day. Photosynthetic organisms are only able to capture 1% of that energy and convert it into chemical energy. Without photosynthesis making chemical energy for us none of us would exist. 

Because there is an energy loss each time energy is transferred, there is less available energy within each trophic level.

For example Primary consumers (Herbavors) are only able to capture 10% of the energy available in primary producers. Secondary consumers are only able to capture 10% of the energy available in primary consumers, and so on.

We call the ability to transfer energy from the previous trophic group Ecological efficiency. In reality ecological efficiency ranges from 2% to 40%. The average is 10%.

Net Primary Productivity is how much chemical energy a primary producer can store not accounting for the energy it uses to survive.

NPP = GPP - R, where R is energy used in respiration. NPP measures how fast producers can provide the chemical energy stored in their tissue that is potentially available to other organisms (consumers) in an ecosystem.

Lets talk about the Estuaries and Swamp lands in Los Angeles.

Why would estuaries be important to an ecosystem?

Class activity: Food web/ Food Chain