Fiddling with Estimating Populations -
Pre-site Activities/Teacher
Led
Grade Level: 7
Content
Area: Science and Math
Time to Complete: 45 minutes
Title of
Lesson: Fiddling with Estimating
Populations
South Carolina State Standards
Addressed:
Science
|
II.B.1.a. |
Analyze the basic
characteristics and needs
of living things. |
|
II.D.1.a. |
Describe characteristics
of populations. |
|
II.D.1.c. |
Distinguish between
habitat and niches. |
|
II.D.2.a. |
Analyze the role of
producers, consumers,
and decomposers in an
ecosystem. |
|
II.D.2.c. |
Analyze energy flow in a
food chain and its
relationship to the food
web. |
|
II.D.3.b. |
Analyze the effects of
overpopulation within an
ecosystem on the amount
of resources available. |
Math
| III.E. |
Connect patterns, relationships, and
functions with other aspects of mathematics and with other
disciplines |
| V.B. |
Estimate, construct, and use
measurement to describe and compare phenomena. |
| VI.D. |
Construct, read, and interpret
tables, graphs, charts, and other forms of displayed data. |
Lesson Description:
The following activity was designed for
teachers to introduce the organism, the
Fiddler Crab, and to show how
individuals and therefore populations
fit into an ecosystem. The
students will find out the average of
individuals in a given area.
Focus Question For Students:
|
1. |
What is a population?
|
|
|
It is
made up of all individuals of a
particular species that occur
together at a given space in
time. |
|
2. |
What makes up an ecosystem?
|
|
|
Animals
populations interact with one
another as well as with their
environment to form an
ecosystem. |
|
3. |
Why do scientists use the metric
system? |
|
|
They use it as a way to
standardize measurements by
having one basic measurement
system. |
Culminating Assessment:
See
Post-site
Activities
Material/Equipment/Resources:
Teacher Preparation:
| 1. |
Complete steps in "Plan Your Discovery". |
| 2. |
Complete the pre-site activity prior to
the field trip (an on-site visit with a naturalist at the park can
be arranged to go over the activity if desired). |
| 3. |
Read background information. |
Background Information:
The Fiddler Crab (Uca) lives in large
colonies in the mud flat areas of the salt marsh. It belongs to the Phylum
Arthropoda—the same as spiders and insects. Biologists estimate herds of 1
million Fiddler Crabs per acre. They are approximately 1 inch in diameter
(2.54 cm). The male is larger than the female and has one greatly enlarged
claw which is usually located on the right side. Males use this claw
primarily to attract females to their burrows for mating. It may also be
used as a weapon and to scare off other males. If it happens to be torn off
by a rival male or a predator, the smaller left claw will develop into a new
large claw while a smaller replacement grows from the old stub. Crabs have
hard shells that do not grow with them. Therefore, they periodically have to
make new soft shells underneath the old hard shell. The hard shell then
breaks open along the back and the crab pulls itself free. It will then
inflate this soft shell with seawater and harden it by extracting minerals
from the seawater. This process is known as molting.
Fiddler crabs use their small claw to spoon
up mud. They then suck the water out from in between the grains of sand and
filter this water for detritus, which is composed of rotting Spartina grass
and the fungus and bacteria that are doing the decomposition. The burrow,
which is dug in the mud, serves several purposes. It protects the crab from
incoming tides, protects it from predators such as birds and blue crabs, and
is used for mating. Each fiddler crab has it own burrow. Fiddler crabs
scurry into their burrows very quickly when they sense danger. Once inside,
the crabs will plug up the entrance to the burrow using little pellets of
mud; this will keep out the predators that enter the marsh with the rising
tide from entering the burrows.
A population of Fiddler Crabs is made up of
all individuals of that species that occur together at a given place and
time. Their populations as well as other animal populations interact with
one another and their environment forming an ecosystem. Many of these
interactions can be determined and discussed. The role Fiddler Crabs play in
an ecosystem can be determined by looking at their place in the food web as
a consumer as well as discussing its niche in an ecosystem.
The major source of energy for most
ecosystems is sunlight. The sunlight that enters an ecosystem is used by
producers through photosynthesis. An example of this is the marsh grass
which grows throughout the salt marsh. It is able to use the sunlight as
energy which in turn feeds something else. When this marsh grass dies, the
Fiddler Crabs can then consume this detritus (dead stuff) and the food chain
continues on from there with animals eating the crabs, and so on. Food is
not an unlimited resource however. There is only so much food to support an
ecosystem. A population can only grow as big as the resources around it will
allow it to. This is referred to as the carrying capacity. There are other
factors which contribute to limiting a population—the availability of water,
space, and shelter. Other abiotic factors can contribute as well such as
quantity of light, air, and water; range of temperature; salinity, water
pressure; and soil composition. The impact humans have on the environment is
often a negative one which also contributes to a reduced “carrying capacity”
or maximum number of existing animals that can survive.
Procedures:
|
1. |
Read background information and share with class as
an introduction. The
instructor should describe the fiddler crab’s physical
characteristics, where and how it lives, some of its habits, and how
they fit into the larger ecosystem (see background information).
Students who have visited a salt marsh may be familiar with the
fiddler crab and may have comments for the class. |
|
2. |
Divide the students into groups of four.
|
|
3. |
Each group should cut out one square plot from the
cardboard (for example: a 2 in. x 2 in. plot or 4 in.2
). |
|
4. |
Pass out one “X” Colony sheet to each group. Each “X” represents
one individual in a population in the measured area (3 m. x 4 m.).
|
|
5. |
Each student randomly throws the square onto the
colony sheet and outlines it where it falls. When finished there
should be 4 squares drawn on the page, some may overlap.
|
|
6. |
Count the X’s in each outlined square and divide by
the # of square plots drawn on the page (4). This will give the
students the average number of X’s per meter squared. |
|
7. |
The students now need to find out the size of the
area our “X” colony lives in. Multiply the length by the width (4
m. x 3 m.). Multiply the average number of individuals by the
area. This will give you the total estimate of the X’s. |
|
8. |
Last, count each “individual” on the “X” colony sheet
to see how close the estimate is to the ACTUAL number of
“individuals.” |
|
|
Notes:
To simplify
calculations, the measurement of meters will be used although the
students are measuring out the plots in inches. A 2 in. x 2 in.
plot will be considered as a 1m x 1m plot. |
|
