Size Selective Predation

Overview

A lower level aquatic food web contains photosynthesizing phytoplankton or algae, various sizes and types of zooplankton, and carnivorous small fish as well as phytoplankton eating fish.  The consumer relationships among these organisms are often based on size, larger organisms eat smaller organisms, and the mechanism for consumption also determines the predator-prey relationships.  This activity explores the mechanisms of prey size and the method of how predators capture prey.  Various types of balls will represent prey and students, the predators; will have different tools to capture the different balls (prey).

Instruction Time

One 45-minute class period.

Objectives

• Students will physically experience the predator’s ability to capture prey, based on the prey’s size.
• Students will have various adaptations that enable them to only select and capture certain prey based on prey size, which simulates predator prey interactions within a food web.
• Students simulate the competition for food within a food web. 

Materials

• Ten wiffle balls
• Ten tennis balls
• Five basket balls or soccer balls
• Ten hacky sack balls
• Ten rubber bouncy balls
• Masking tape or duct tape
• Five tongs (chemistry/food tongs)
• Five tweezers
• Ten spoons (two per person)
• Size Selective Predators Handout

Procedure

1. Assign student partners.
2. Move desks out of center area of the classroom or use a gym or outdoor space such as a tennis court.
3. Each pair of students is given a tong, tweezers, spoons, or masking tape that is used as a food capturing apparatus.  Students may not use their hands to capture the balls (prey).  The masking tape will be folded in a way that the sticky side of the tape is used to pick up the prey.  The spoons are placed in each hand and used together to capture prey.
4. The balls are randomly placed in the center of the room and the students’ stand at the perimeter of the classroom either in a circle or on either side. 
5. When the teacher yells “GO” the predator student in the pair will WALK to the balls to capture one ball at a time using only their food-capturing tool.  YOU CANNOT USE YOUR HANDS.  Once the student picks up the prey they must carry it back to their partner, who holds the prey.  The predator student returns to capture more prey. 
6. Predators must work individually and can’t kick or move the prey other than using their specific tool.
7. After all the prey are captured; students will record their capture numbers and type of prey in their data table.
8. Repeat once more with the same food-capturing tool and same predator. Record data.
9. Students will then switch roles and the former predator will now hold the prey.  Students will also obtain a different food-capturing tool. Repeat trials. Record data.
10. Answer analysis questions.

Analysis Questions

1. List the types of prey that you caught. Compared to the total number of available prey species, what percentage were you able to collect?
2. What challenges did you encounter while hunting prey, relative to the food-capturing tool? Did these challenges influence your ability to survive?
3. Did your food-capturing tool allow you to catch a single type of prey or many different species of prey? What type of tool would allow for a better chance of survival, one that catches many types or a tool, which catches a single species?
4. Besides the method of how you captured your prey what other issues affected your ability to catch prey?
5. If your prey capture tools were the only ones being used by the entire class, what would happen to the prey if you were able to collect over time? In other words, would the species you were catching become more or less abundant relative to others? Harder or easier to find and collect amongst the pile of prey balls?
6. Imagine now that there were predators attempting to catch and eat you, and further, that you became easier to catch when you yourself were hunting prey. Would this likely affect the number of prey you were able to capture (increase or decrease)?
7. What if predators were able to remove most of you and your peers who were hunting for certain prey items. In other words, you, the predator were “overfished”? Would the prey item you were able to collect become more or less abundant compared to other prey items over time?
8. Consider a situation where nutrients were not limiting, in other words they were available in excess abundance. If the prey balls were phytoplankton, then this would stimulate their growth and could lead to more prey items than you could reasonably eat. If these nutrient additions were the result of human activities, what is the scientific term that describes such a situation (see “How are food webs changing” in explore section for answer)?

Lesson Resources

Student Handout

National Science Education Standards

K-12 Unifying Concepts and Processes
-Systems, order, and organization
-Evidence, models, and explanation
-Form and Function
9-12 C Life Science
-Interdependence of organisms

Aquatic Model Mania

Overview

Scientists often use models to study naturally occurring systems that may be too complex to bring into the laboratory. Scientists spend a great deal of time building, testing, comparing and revising models, they are one of the principal instruments of modern science.  Marine biologists can’t always study aquatic food webs in their natural environment so a model simulating the environmental conditions of an aquatic food web allows scientists to study this system and all its variables. This activity explores how nutrient availability and other environmental conditions affect the dynamics of an aquatic food web.

Instruction Time

One 45-minute class period.

Objectives

• Students will observe the interactions of the components of an aquatic food web based upon the availability of nutrients.
• Students will use a model, which represents an aquatic system of nutrients, phytoplankton, zooplankton, and detritus.
• Students will manipulate the various components of the aquatic system to see the dependency upon one another.

Materials

• Computer with access to the internet
• Model Handout

Procedure

1. Students will go the website: https://www.planktoneer.com/applet/
   
2. Following the instructions on the Aquatic Modeling handout (available below) students will manipulate the various components of a food web model and immediately see the effects on the other elements of the food web.
3. After studying and manipulating the model students will answer the questions in the handout. 

Lesson Resources

Student Handout

National Science Education Standards

9-12 C Life Science
-Molecular basis of heredity
-Biological evolution

Real Time with Bay Buoys

Overview

The National Oceanic and Atmospheric Administration’s (NOAA) Chesapeake Bay Interpretive Buoy System (CBIBS) is a network of observing platforms (buoys) that collect meteorological, oceanographic, and water-quality data and relay that information using wireless technology to the community. The latest data from key points up and down the Bay are available to examine current conditions as well as observe environmental trends over a year or many years.

Using real time data from CBIBS, students can investigate the environmental conditions, which allow aquatic food webs to exist or perish. In any food web, terrestrial or aquatic, it is the photosynthetic organisms that support the upper trophic levels.  Algae are photosynthetic organisms that support the zooplankton and fish populations in the Bay.  The Bay Buoys measure the presence of algae through chlorophyll-a values. Harmful concentrations of chlorophyll, as a general guide, above 50 ug/l represents a significant algal bloom, and above 100 ug/l represents a severe bloom. Excess algae, usually caused by an excess of nutrients, which stimulate their growth, can also make the water cloudy, or increase turbidity, blocking the light needed by underwater grasses to survive. These damaging algae blooms, which can also produce toxins in some cases, are collectively known as harmful algal blooms.  If algal blooms exist in an area they can destroy an entire food web.

Instruction Time

1-2 45-minute class periods.

Objectives

• Students will analyze real time data from buoys in the Chesapeake Bay to determine habitat quality.
• Students will determine the presence of algal blooms based on chlorophyll a levels obtained from real time data and anticipate these effects on the food web.
• Students will predict trends based on various environmental parameters from the Bay buoys, and then utilize the aquatic model to prove or disprove their hypothesis.

Materials

• Real Time with Bay Buoys Handout (available below)
• Computer

Procedure

Have students go through the following instructions (also provided in the student worksheet below), which are a guided exploration of data available from moored buoys.

Below is a map of the Chesapeake Bay and the locations of the buoys. 

1. Go to the website: https://buoybay.noaa.gov/

2. In the yellow band located at the top of the page mouse over the word “OBSERVATIONS” and click on “Parameters Measured.”

3.  Read the two paragraphs under Chlorophyll-A and answer the following questions.

a.  What is actually measured by the buoys when determining the amount of chlorophyll-a and what are the units?

b.  Excess algae blooms are caused by ____________________________________.

c.  What are two negative effects of a severe algal bloom?

d.  As a general guide, what concentration of chlorophyll constitutes a severe algal bloom that can be harmful to the environment?

4.  In the right hand column on the “Parameters Measured” page, find the Buoy Status Box. Click on every station and read the value of chlorophyll-a.  Write down the stations having the lowest and highest values and give the values.

e.  Is either station having an algal bloom? If yes, then list the station(s).

5.  Locate the “Parameters Measured” page and read the two sections on Dissolved Oxygen, then answer the following questions.

f.  What does the amount of dissolved oxygen (DO) measure?

g.  What are the units that DO is measured in?

h.  At what DO levels will sensitive organisms like fish, feel stressed? ____________.

i.  In your own words, explain how temperature, salinity, and photosynthesis each affect the amount of dissolved oxygen in the water.

j.  What are the three causes of low dissolved oxygen levels in the Chesapeake Bay?

6. Go back to the Buoy Status box on the top right-hand side of the page.  Click on all the stations and read the values for DO.  List all stations and the DO values in which fish may be stressed.

7.  Let’s consider one more parameter, water salinity.  Find Salinity on the “Parameters Measured” page.  Read the paragraph and answer the following questions.

k.  What processes control salinity in the Bay?

l.  Why is salinity important for living organisms in the Bay?

8.  Using the Buoy Status box on the top right-hand side of the page.  Click on the S (Susquehanna) and N(Norfolk) stations.  Record the values for DO, Water Temperature, and Water Salinity.

m.  Based on this data, is temperature or salinity more influential in determining the range of dissolved oxygen seen in the Chesapeake Bay?

n.  What else could be contributing to the low DO levels at the Norfolk Buoy (refer back to the DO paragraphs on the parameters measured page)?

9.  Lets now look to see if there is a correlation between Chlorophyll and Dissolved Oxygen at the Annapolis Buoy over a longer period of time, from the first of May through September 1^st. Under the “OBSERVATIONS” heading click on “Data Graphing Tool.”  For Date Range, select “Custom Date Range” and enter the begin date as May 1^st of this year and the end date of September 1^st. Select the platform as Annapolis, the X-axis, as Time and the Y-axis as Chlorophyll.   Click on the load button.  Record approximate date ranges of higher chlorophyll values, above 40 ug/l.  Next change the Y-axis to dissolved oxygen and click on load link.  Record any date ranges where dissolved oxygen is below 5 mg/l.

o.  Do any of the date ranges between chlorophyll and DO overlap?  List these overlap dates.

p.  How would you expect high chlorophyll levels affect the aquatic food web? Sketch two simple trophic pyramids (similar to those in the Learn and Explore sections of the online module), one representing a food web you would expect at chlorophyll 10 ug/L, and a second for a food web at chlorophyll 100 ug/L.

p. Conversely, if high chlorophyll levels led to low DO levels, how would you expect this to affect the Chesapeake Bay food web? Sketch a simply trophic pyramid you would expect under conditions of high chlorophyll, but also low DO.

Lesson Resources

Real Time With Bay Buoys Handout

National Science Education Standards

9-12 B Physical Science
-Structure of atoms
9-12 C Life Science
-Interdependence of organisms