Grade Level:
Elementary, Middle School, High School
Ecological Concepts: Adaptation,
Behavior
Arizona Science Standards: Science as Inquiry; Life
Science
Materials:
1) Binoculars
2) Stopwatches
3) Writing/drawing materials
BACKGROUND
Many animals, including mammals, birds, reptiles, fish, insects and
other invertebrates, have adapted to the stresses of the Sonoran Desert.
Desert adaptations can be manifested in behavior, size, shape, or
physiology. The highest priorities for any desert dweller are to survive
the heat and lack of water. Most animals accomplish this by a combination
of behavior, anatomy, and physiology. For example, small desert rodents
are usually only active at night (behavior), have eyes capable of
seeing in the dark (anatomy), and have a metabolism that retains almost
all water ingested through food (physiology).
Other animals are active during the day. A jackrabbit has large ears
with a high density of blood vessels to release body heat. This keeps
the animal from overheating. Reptiles, which are ectotherms,
need heat to become active and to digest food, but even they have
limits as to how much heat they can withstand. When it's too hot,
lizards seek shade. Larger animals tend to be active during the day
because a large body can dissipate heat faster. A large animal has
a larger volume to surface body ratio than a small animal, keeping
the body from absorbing heat quickly.
Early morning, late evening, and night are the active times for many
desert dwelling animals. There are trade-offs, however. Some animals
have to be active during the day to find food and mates, and are thus
adapted for daytime conditions, such as jackrabbits, lizards, and
snakes. In the hottest parts of the summer, rattlesnakes do more hunting
at dawn and dusk.
The closer an urban area is to relatively undisturbed desert, the
more animals will spend at least some time in the urban area. But
almost all areas are habitat for fence lizards (Urosaurus),
hummingbirds, most insects, scorpions, spiders, and some rodents.
The lizards, hummingbirds, and many insects and spiders are active
during the day. As summer progresses and the heat rises, the active
times become more concentrated in the morning and evening. Rodents
and scorpions tend to be most active at night, as do most moths. Areas
nearer to undisturbed desert will have jackrabbits, javelina, coyotes,
pocket mice, kangaroo rats, a wider variety of insects, and many more
reptiles. Reptiles include rattlesnakes of various species, chuckwalla
lizards, horned toads, Gila monsters, whiptail lizards, and desert
tortoises. NOTE: Be extremely cautious around wild animals. All wild
vertebrate animals are legally protected and cannot be captured without
permits from Arizona Game and Fish.
Fish live in the water, of course, and it might be thought they are
not affected by the desert conditions, but they are. Over the ages,
desert dwelling fish have adapted to seasonal low water periods, high
water temperature, sudden monsoon-caused floods, and higher salinity
levels. Fish adaptations are also behavioral, anatomical, and physiological.
Pupfish can tolerate very high salinity levels because of their physiology.
Small fish such as spikedace (Meda fulgida) and longfin dace
(Agosia chrsogaster) can withstand sudden floods that wash
away and kill non-desert fish species.
GUIDED INQUIRY
Observation/Exploration Period: Observe animals in
your habitat. Observe at different times of the day, and in the early
morning and late evening, if possible. Observe places such as burrows,
in leaf litter, and other microhabitats
used that may protect the animal from the heat. Behaviors to look
for are those such as birds sleeking their feathers to insulate their
bodies from the sun's rays, and panting, a form of evaporative cooling.
Notice which animals are active when, where they are (in a tree, in
the sun, on the ground, in the shade), how long they perform a behavior,
what color the body is, and body size and shape.
Group Discussion and Question Period: Some possible
questions are: How do body shape and body size affect an animal's
ability to survive desert heat? Are large insects more active during
the day than small ones? Which animals drink lots of water and which
don't need to? How do animals survive desert heat? Does an animal
behave differently in the morning compared to the afternoon?
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 fence lizards
(Urosaurus) behave differently in the morning than
in the afternoon?" The hypothesis could be, "If fence lizards
need heat to be active and we watch lizards during the morning
and afternoon, then we will observe more activity in the afternoon
when the temperature is hotter."
Sample Experiment Design: Split into groups of two
or three. Each group watches a different fence lizard. Use eyes
and perhaps binoculars to observe lizards. Watch the lizards
in the morning and afternoon for a set period of time, such
as twenty minutes. The independent
variable is time of day, morning versus afternoon.
The dependent
variable is the length of time or number of times
the chosen behavior is observed during the set time period.
Before starting, you will need to carefully define "behavior"
and what behaviors are to be recorded. Your initial observations
will give you some ideas of what to expect and which behaviors
will be easiest to accurately record. Some ideas: In the sun,
in the shade, on the ground, on a rock, in the grass, on a fence,
on a tree, under litter; sitting still, running, doing push-ups
(fence lizards, usually males, do push-ups to warn off other
males and impress females).
To limit this experiment to testing only one factor, observe the lizards on only one day. If you choose to observe on different days, each day should be considered a new experiment. Do not combine the data from different days, unless you are proficient in higher-level statistics. By collecting and analyzing data on one day you are controlling for other factors such as temperature, day length and cloud cover. In order to have replicates observe at least three lizards in the habitat, at the same time. Each lizard will be a replicate.
Sample Prediction: Lizards will be more active in the afternoon than the morning.
Record Results: Record the length of time for each behavior, or record the number of times the behavior occurred.
Sample Analysis of Data and Presentation: Make a bar graph with the time of day (morning versus night) on the x-axis and the raw number of times for the behavior (or total length of time per behavior) on the vertical axis. For students who can divide, calculate the average number of times for each behavior or length of time. 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.
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MORE:
(1) Elementary:
(a) Observe other commonly found animals in the
habitat, such as grackles, pigeons, Inca doves (small species of
dove), ants, crickets, spiders (jumping spiders are great!), or
butterflies.
(2) Middle School:
(a) Find the mean,
median,
mode,
and range
of the data.
(b) Use sweep nets to collect aerial insects. Sweep
net the same places in the early morning and then the afternoon.
Use forceps to gently sort the insects and then categorize them.
Compare morning and afternoon insect types and numbers.
(3) High School:
(a) Calculate the standard
deviation of the averaged data.
(b) Do a T-test
on behavior numbers or length of time, comparing morning and afternoon.
(T-test is a standard statistics test comparing means
of two samples). |
