Grade Level:
Elementary, Middle School, High School
Ecological Concepts: Predation,
Herbivory
Arizona Science Standards: Science as Inquiry; Life Science
Materials:
1) Grass or other seeds of different sizes
2) Clear plastic drink cups*
3) Writing/drawing materials
4) Magnifying lenses*
5) Insect field guide*
*May be borrowed from SCENE.
BACKGROUND
There are many species of ants in the Sonoran Desert. Some are carnivorous,
some grow and eat fungi, and other species eat mostly plant seeds
found in their habitat. Different types and sizes of seeds are available
at different times of the year, depending on the plants in the area.
Most ant species build their living spaces, called colonies, underground.
This is where the eggs are laid, hatch, and the larvae
are cared for. Seed eating ants bring seeds back to the colony. When
ants find a source of food, many of them will keep going to the food
until it is gone. This is an ant trail. A good way to find a colony
is to follow an ant trail back to the colony opening. Unusable food
parts and other garbage from the colony are placed in piles outside
the opening to the colony.
GUIDED INQUIRY
Observation/Exploration Period: Survey your habitat (and adjacent
grounds, if necessary), and map where ant colonies are found.
What size are the ants? What items do they seem to be carrying?
Also make note of the potential food sources near the colonies. Time
of year could influence what food items are available.
Group Discussion and Question Period: What do ants eat? Do
they prefer certain foods? Do seed eating ants prefer some seeds instead
of others?
Important aspects of guided inquiry are encouraging students to
generate multiple
hypotheses, and letting students make decisions about
what data are important and create their own data sheets.
Keeping these ideas in mind, the sample in the box below illustrates
how ONE OF MANY possible investigations around this topic might develop.
Sample
Hypothesis : Let’s use the question, "Do
ants in our habitat prefer a certain size of seed?" Our
hypothesis could then be, "Ants that normally prefer to
eat seeds will prefer large seeds to small ones, because large
seeds provide more food per seed." Or, "As seed
size increases, more of those seeds are chosen by the ants."
Sample Experiment Design: We need to set up a fair test
of what characteristic, if any, of seeds is attractive to ants.
To do that, we want to test one characteristic, or factor, at
a time. A single factor would be one like size or shape. To
test our hypothesis about the independent
variable, seed size, we need seeds of different
sizes. If possible, collect seeds (grass seeds are best) from
the habitat area to use. If not, purchase seeds of two noticeably
different sizes but similar shape and color to control
for these other factors. You also need to control for ant species
by using the same ant species for each seed pile. Count out
ten seeds of each size and mix twenty seeds together. Make five
sets of mixed seeds. In the habitat find five areas that have
ant trails or visible ant colonies opening above ground. If
you have lots of colonies to choose from, randomly
choose the ones to use. Each ant colony is an experimental
unit and by using more than one colony we are replicating
the units being treated.
For observation purposes, the best kind of seed eating ant in
the Sonoran Desert is the large red ant, genus Pogonomyrmex
(Pogo, for short). Place a mixed seed pile along the ant
trail or within 1 meter of the colony opening. Move away a meter
or so and observe the ant behavior for a set period of time.
Be careful not to disturb the ants.
Let the piles sit for about five to ten minutes before recording
data so the ants in the area can settle down and find the piles.
Groups of two-four students can watch individual piles and record
data. If nothing happens for a while you can put clear plastic
cups over the seed piles with an opening cut in the side to
allow ants in but keep birds and other seedeaters out, and then
check the piles the next day.
Sample Prediction: Ants will take more large seeds than
small seeds.
Record Results: Count the number of each seed size that
is taken by ants of each colony separately.
Sample Analysis of Data and Presentation: Calculate
the total number of seeds of each size taken by ants. The raw
data, total number of seeds taken of each size, can be presented
as a bar
graph or pie
chart. The seed sizes can be listed on the horizontal
axis and number of seeds on the vertical axis. For students
who can divide, calculate the average
number of seeds of each size taken by all ant colonies. Graph
the average number on the vertical axis.
Discussion: Was your hypothesis supported? If yes, go
on to test other hypotheses. If not, why not? What did happen?
Why? This is a great opportunity to revise your hypothesis and
do another test. |
MORE:
(1) Elementary:
(a) Many ants collect nectar. Do a similar experiment
using shallow bowls with different concentrations of sugar. (See
Attract a
Hummingbird activity.)
(b) Try other kinds of possible foods ants may
collect. Your initial observations will give you ideas.
(c) Test seed shape by using seeds of the same
size and color but different shape (round versus oval).
(2) Middle School:
(a) Find the mean,
median,
mode,
and range
of the data.
(b) Test different seed sizes. How large (maximum)
a seed will ants take? How small (minimum) a seed?
(3) High School:
(a) Calculate the variance
and standard
deviation of the averaged data.
(b) Weigh the seeds of each size group. Mark the
seeds with dots of different colored paint. Go through the refuse
piles near the colonies to see if you can find any of the marked
seed coats (usually only the inner seed itself is eaten; the exterior
coat is discarded). This is a good way of making sure ants took
the seeds, and not some other animal. |
