Tropical forests cover only about 6% of the Earth's surface, and yet they house between 50-80% of our planet's estimated 5 to 30 million plant and animal species. The key to this tremendous species richness lies in the stability of the tropical forests themselves where climactic conditions have remained relatively constant for 60 million years. Sophisticated plant and animal adaptations, developed through natural selection, allowed for diversification into highly specialized niches.
OUTCOME
The student should be able to identify and describe adaptations that are important to an individual species' role in the community; infer the consequences of altering population sizes within a tropical forest community; and understand that organisms in an ecosystem are interdependent.
ACTIVITY
Materials Needed:
Paper plates Construction paper flower and leaf symbols
Index cards stating "Ant Bird Dropping" Index cards stating "Death Certificate"
Passion flower vine with 6 leaves Research Data Sheet
Markers Rules Sheet posted
Background:
Species illustrated in this activity:
Katydid - This herbivore insect, related to the grasshopper and the cricket, hides from predators with its leaf green coloration and by keeping still using a camouflage technique.
Heliconius Butterfly - The caterpillars feed on passion flower vine leaves, eating the toxins that make them inedible to predators such as the ant bird. Female butterflies safely flutter around army ant columns to find and eat ant bird droppings which contain amino acids required for their eggs to develop.
Passion Flower Vine - This vine has evolved many adaptations to avoid being eaten and is a site where butterflies lay their eggs. This vine (without leaves, until game 3) should be placed somewhere in the room. Two inch strips of green paper will work as vines.
Army ants - These social insects travel through the forest consuming every small creature that cannot get away from their advancing 100 foot wide mass. The raids, which may last a couple of weeks, move by day. When not on a raid, army ants will stay in one place for almost three weeks during which time they lay their eggs. After these eggs hatch, producing larvae, the raids begin anew to feed the hungry young.
Ant birds - As many as ten different kinds of ant birds fly along above the front of the army ant swarm, feeding on insects that ants have caught and on those that are escaping the swarm.
ROUND #1:
1. Select students (see Table 3 for numbers) to portray butterflies and katydids. Each of these students receives a paper plate, which they keep on the sidelines of a large playing field.
2. Select a designated "ecologist," who will tally the number of survivors from each of the games on the Research Data Sheet (Table #2). Place this chart where everyone can review it during the game.
3. Tell the students that they must collect and deposit onto their own plate on the sideline, two food symbols, ONE AT A TIME, from those scattered at the center of the play area. Have everyone note that there is not enough food for all insects to survive. Write on the board the following rules: once you have collected one food symbol, bring it to your plate on the sidelines.
RULES FOR ROUND 1
* Butterflies collect flowers, the source of nectar.
* Butterflies must beat their wings and say "flap" as they fly through the forest;
* Katydids must hop and say "boing" as they collect leaves.
4. Let the students play out this scenario until no food remains.
5. Have the ecologist tally up the number of survivors (those students who collected the appropriate two food symbols) and place them on a chart. Conclude that competition can limit population size in a habitat.
ROUND #2:
1. Return all food symbols to the center area.
2. Tell the katydids and heliconius butterflies that they will repeat Game #1 with this addition: The insect-eating birds have entered the forest! Remind the insects that they are to search for flowers if they are butterflies, or leaves, if they are katydids, collecting two food symbols (one at a time). Give one death certificate to each of the insects.
3. Select students to be ant birds (see the correct number needed on Table #3) and instruct them that during this game, the ant birds are to flap their wings calling "ant birds" as they hunt for katydids. Butterflies and ant birds cannot tag a katydid when it is not in motion. Add this to your rules on the board.
RULES FOR ROUND 2
* Ant birds flap their wings and call "ant bird"
* Ant birds cannot tag a katydid not in motion.
* Ant birds must tag two insects, one at a time, and escort each separately to the sidelines.
* Each ant bird must collect a death certificate.
4. Each ant bird must tag 2 insects, one at a time, and escort the prey to the sidelines, (one at a time,) whereupon the insect must surrender its death certificate symbol to the ant bird. Each ant bird must collect two death certificates.
5. Remember, ant birds cannot tag a katydid when they are not in motion. Explain to everyone that the katydids are camouflaged by their green coloration as long as they are carrying a green leaf, but that motion such as travel across the forest gives their position away. Katydids may remain motionless for no more than six seconds per run across the forest.
6. Secretly tell only the butterflies that they taste awful and make the ant bird very sick because as caterpillars, the butterflies ate toxins found in the passion flower vine leaves.
The butterflies secretly inform the predator (the ant bird) of the toxins once the butterfly has been escorted to the sidelines and handed a death certificate. The captured butterflies are out of the game, but the ant bird who got sick learned a lesson and now, if they had first captured a butterfly, will only eat katydids.
7. Let the students play out the game. Repeat Round #2 if needed.
8. Have the "ecologist" tally and record the number of survivors, and the leaves and flowers that remain.
9. Explain the heliconius butterfly's chemical defense to all the students.
10. Compare the results of Round 1 to Round 2.
ROUND #3:
1. Reveal to the students that relationships between species can be quite complex and that dependencies may not be apparent at first glance. For example, the heliconius butterflies, which safely fly around because they are distasteful to eat, require the proteins found in ant bird droppings in order for their eggs to develop and so must follow the ant birds.
2. As in Round #2, place all leaves and flowers in the center area. Pass out two droppings cards to each student. Katydids again must find two leaves and may use camouflage for protection from the ant bird. As before, ant birds must collect 2 death certificates from the katydids, but in addition, they will each carry 2 droppings symbols, one to be dropped immediately upon tagging a katydid. (Add the rules to your list on the board.)
RULES FOR ROUND 3
* Butterflies now collect only 1 flower plus 1 ant bird droppings card,
but rather than returning to the plate, they must take their flower to the Passion Flower Vine where they will "lay" their eggs by writing their name on one of the leaves.
* Army ants must stay connected with their arms locked together and
surround an animal one at a time to "kill" their victim.
3. The remaining students (see Chart #) enter the forest as army ants, social insects which depend on each other for protection and for success on foraging raids. The army ants will show their dependence upon one another by marching in a line with their arms locked together. Allow the army ants to practice their raid march before starting Round #3. To kill their victim, army ants must surround the animal completely, but they must not run.
4. Any creature, including katydids and butterflies, that is surrounded by army ants becomes a victim and must go immediately to the sidelines.
5. When all the butterflies have laid their eggs or are dead, tally the survivors.
6. Evaluate the impact of the army ants on the community. Was it advantageous to the butterflies to follow an ant bird for its droppings? Explain that this is just one example of the interconnectedness of animals and plants in the tropics. What are some other examples?
7. What are some examples of interdependent animals and plants that live near you?
Answers will vary.
TABLE #1 MATERIALS REQUIRED
CLASS SIZE 16 24 35
Flowers 7 10 13
Leaves 10 15 20
Paper Plates 10 14 21
Antbird Droppings 6 8 10
Death Certificates 10 14 21
TABLE #2 RESEARCH DATA SHEET
The following Research Data Sheet can be copied on the chalkboard or a large sheet of paper and used to tally survival results from each game for late discussion.
ORIGINAL # NUMBER OF SURVIVORS
FLOWERS GAME #1 GAME #2 GAME #3
LEAVES
KATYDIDS
BUTTERFLIES
ANTBIRDS
ARMY ANTS
TABLE #3:
NUMBER OF STUDENTS NEEDED TO PORTRAY EACH SPECIES
CLASS SIZE 16 24 35
Butterflies 4 6 8
Katydids 6 8 13
Antbirds 3 4 5
Army Ants 2 5 8
Ecologist 1 1 1
EXTENSIONS
*Create a food web.
*Design an 18" x 24" poster summarizing this activity.
GRADING CRITERIA
* Describe adaptation methods used by various individuals in the tropics.
* Define the characteristics of the organisms and how they interact in their system.
