Grade Level:
Elementary, Middle School, High School
Ecological Concepts: Biodiversity,
Species
richness
Arizona Science Standards: Science as Inquiry; Life Science
Materials:
1) Magnifying lenses/loupes*
2) Catch boxes*
3) White cloth
4) Forceps*
5) Writing/drawing materials
6) Aspirator,
optional
7) Berlese
funnel, optional
8) Sweep net
9) Field measuring tape*
10) Insect field guides*
*May be borrowed from SCENE.
BACKGROUND
Insects are six-legged arthropods
with exoskeletons.
They are found in almost every ecosystem worldwide. Some are carnivores,
others herbivores,
omnivores,
parasites,
or parasitoids.
Insects occupy many niches
and microhabitats.
They are not always obvious, but every habitat has insects of some
sort.
Insects inhabit almost all areas of the Earth. Which types and species
occupy an area will vary depending on the biotic
and abiotic
characteristics of the habitat. Also, the number and types of insects
found in a habitat change over time. Potential factors causing these
changes are birth, death, immigration,
and emigration.
These factors in turn are influenced by what is available in the habitat
for the insects to be able to live and reproduce.
GUIDED INQUIRY
Observation/Exploration Period: Examine the habitat
for insects or signs of insects, or other arthropods such as spiders,
mites or isopods. Signs include spider webs, cocoons, partially eaten
leaves, eggs on the plant leaves or stems, mines
on the leaf surface, galls
on leaves or stems, holes in the ground, exoskeletons, dead insects,
and insect frass (feces). Look on and under plants, inside leaves,
in the air using a sweep
net, in plant debris (leaf litter) on the ground, on
fences or other structures, and in the soil itself.
Group Discussion and Question Period:
Why do some plants or parts of plants have more insects than others? Why don't we see many insects on some plants? What insects are in the soil? How many different kinds of insects are in the habitat? Does time of day or year change what insects will be here? What insects are in our habitat? Do some places in the habitat have more insects than other places?
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, "Why do some areas of the habitat
have more insects than other areas?" Our hypothesis might
be, "Areas of the habitat with more plants will have more
insects because the food they need is there." Or, "As
the amount of plant biomass
increases, the number and types of insects will increase."
Sample Experiment Design: The original placement
of plants in the schoolyard habitat was human-caused, but where
insects will be found, how many, and what species are unknown
until a survey is done. To get beginning, or baseline, data,
we need to set up a method for collecting it. To test the hypothesis
that insects prefer places with more plants, we set up an experiment
to test the independent
variable of plant
density. The dependent
variable is numbers/species of insects found.
Survey: Map out the habitat, drawing in the
plants and any other permanent structures. Divide the habitat
into sections of the same size and shape. Each area will be
randomly searched for actual insects or signs of insects.
Figure 1. A habitat area divided into more or less
equal sections.
Split the students into groups. Each group takes a white tray,
a net, a hand lens, forceps, paper and pencil, and any other
insect collecting equipment available. Each group picks an area
of the habitat to search for insects and other arthropods. Look
over the plants for actual insects or signs of insects. If possible,
place the white tray under a section of the plant and shake
it enough to shake loose some insects. Other members of the
group can be using forceps,
aspirators,
sieves
and nets
to collect insects off leaves, on the ground, in the soil, and
in the air. Be careful, for your safety and for that of the
insects. Release insects once the data are collected.
Sample Prediction: The types and numbers of
insects will be higher in areas of the habitat with more plants.
Record Results: Record the number of plants
and what species they are for each section of the habitat. Categorize
insects according to general body characteristics (e.g., beetles,
moths, other arthropods). At this point it is not necessary
to know the names of the insects. Count how many insects of
each type you found.
Sample Analysis of Data and Presentation: Graph
the total number of insects for each area of the habitat and
the numbers of each type of insect on a bar
graph, with plant density on the horizontal axis
and insect numbers 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) Use soil sieves to sort through the soil and
look for insects. Count as above.
(b) Spread out leaf litter on trays and look for
insects. Use a Berlese
funnel. Count as above.
(2) Middle School:
(a) Within each habitat area randomly
choose five smaller areas to survey for insects. Continue as above.
Each smaller area is an experimental
unit, yielding five replicates.
(b) Find the mean,
median,
mode
and range
of the replicated sub-areas of the habitat. Do this by adding the
numbers from each sub-area within an area together to get a total
number for the area, and then average that total number by dividing
by the number of sub-areas.
(c) Categorize sub-areas of the habitat as high,
medium or low plant density based upon number of plants. Compare
the numbers of insects based upon the density of plants in each
area. Graph plant density on the horizontal axis and insect number
on the vertical axis.
(3) High School:
(a) Calculate the variance
and standard
deviation of the averaged data of the five sub-areas
in Extension (a) above.
(b) Conduct the counts at different times of day
or year. Test for a correlation
between the two variables, number of insects and time of collection.
Draw a scatter
plot and calculate the sample correlation
coefficient. This will yield data indicating what changes
are occurring over time in the community of insects in the habitat.
Map the data onto a map of the habitat.
(c) Calculate the volume
of each plant. Measure the height, length and depth of each plant.
Use the volume
of a sphere if plant structure more closely matches a sphere shape.
A volume measurement will yield an estimate of the plant biomass
in the area. Calculating the biomass available for insects will
give a more accurate representation of plant density, as compared
to just counting the number of plants in the area.
(d) Calculate species
richness of insects for each habitat area or each plant
species.
(e) Do a T-test
of species richness per plant unit volume. (T-test is a standard
statistics test comparing means of two samples.)
(f) Black
light the area at night. Collect, sort, and count the
insects. Compare daytime and nighttime species richness.
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