Lab 7 - Food Webs PDF

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Name Oyinda Adeyemo

LAB EXERCISE 7:

Trophic Levels and Food Webs Introduction Food webs are visual representations of the complex tropic interactions in an ecosystem. Organisms are often categorized based on their food source into the following designations:

Autotrophs (producers): organisms that can synthesize their own food molecules Heterotrophs: organisms that must acquire their food from a different source Primary consumers: heterotrophs that consume the producers Secondary consumers: heterotrophs that consume primary consumers Tertiary consumers: heterotrophs that consume secondary consumers

Within a food web, a single species can occupy more than one of these positions, depending on the variety of species it consumes. For example, you likely have eaten producers (a salad for example), primary consumers (chicken or beef), and secondary or tertiary consumers (salmon or tuna). It’s not impossible that you did this in a single day, or even in a single meal. These designations therefore are not meant to be static, but a tool to help understand the trophic interactions that determine how energy and nutrients are moved by organisms in an ecosystem. Experiment This lab will require you to create a food web using several species and a description of what they eat. ACTIVITY 1: MAKING A FOOD WEB

Using the following organisms and their descriptions, create a food web that follows each species and uses arrows to denote consumption. Arrows always follow the movement of energy, and as such they should always point from the eaten to the eater (from prey to predator). Each organism and each trophic interaction must be represented. Phytoplankton: microscopic organisms that use sunlight to convert CO2 to sugar Zooplankton: tiny organisms that feed on phytoplankton Small fish: various species of bony fish that feed on zooplankton Krill: small, shrimp-like organisms that feed on phytoplankton and zooplankton Jellyfish: free-floating species that eats small fish and zooplankton Squid: fast swimming species that easts small fish Sea turtle: large aquatic turtles that eat jellyfish and small fish Large fish: various species of bony fish that feed on smaller fish Sea lion: marine mammal that feeds on small fish

Sea bird: marine bird species that feed on small fish

Large shark: feeds on small and large fish, sea turtles, sea lions, and jellyfish Killer whale: toothed whale that feeds on small and large fish and sea lions

Baleen whale: massive whale species that feed on

Quaternary consumers

hese images into the food web below.

Tertiary consumers

Secondary consumers

Primary consumers

Producers

Questions 1.

Which species occupied more than two trophic levels within your food web? Killer whale and large shark

2.

Which species do you think would be the most abundant in a marine ecosystem? Squid, small fish

3.

Which species do you think would be the least abundant in a marine ecosystem? phytoplankton

4.

Often, we expect the larger species to occupy the highest positions in a food chain. Were there exceptions to this?

Yeah, the Baleen whale was a large species but ate zooplanktons, making it not at the top of the food chain

5.

What was the highest trophic level in your food web? What species occupied that trophic level? Quaternary. Turtle, large shark, and killer whale

Thought Question: 6.

Why were there so many trophic levels in this ecosystem? Compare this marine ecosystem with a terrestrial ecosystem like an African Savanna. Which species are primary consumers andcan how limit The heterotrophs are the the primary consumers and they limitdo thethey length of a the foodlength chain if of they all go extinct causing other consumers, the inability to feed on them

that food chain?

ACTIVITY 2: ENERGY IN THE ECOSYSTEM Food webs are most helpful when used to visualize how energy flows through an ecosystem. This activity will simulate this flow of energy up the food web. Autotrophs will be producing their own energy while all other species will acquire energy from their food. One point that should be noted: energy is always being lost, by every organism in the food web. Chemical energy in food is lost as it is used during cellular respiration and ultimately leaves the organism as heat that dissipates from its body. Throughout this activity be sure to note that there is no recycling of energy back to the producers. Energy flows, it does NOT cycle. Questions 7.

Where did the producers in your food web acquire their energy? From the sunlight and CO2

8.

It is estimated that only 10% of the energy in any particular trophic level moves to the next trophic level. Given this, if the producers of an ecosystem are able to acquire 1,000 Kjoules (don’t worry about what a joule is) of energy, how much of that energy would be acquired by the tertiary consumers?

1%

9.

This does NOT mean that a pound of shark meat has less energy than a pound of salmon. What does it mean instead? It means that 1% of the energy is transferred into the shark.

10.

Thought question: Where did all of this “lost” energy go?

They go into digestion of the food and the animal living.

*Use the video to help answer questions 7 – 10...