Challenges to Anticipate and Solve:
Allergic reactions: Students should be asked about allergies to bee stings and pollen. Those with potential negative reactions should be
assigned to tasks that reduce their risks.
Weather: Especially in the spring, there are days when this activity will not work because the insects will not be active if it is
raining, too cloudy, and/or too cool (under 10oC). A back-up plan should be in place for an indoor activity that can be alternated with this one.
However, it is still possible to do the floral assessments.
Comments On the Lab Description:
Introducing the Lab to Your Students.
I usually begin with at least one 45 minute lecture on pollination ecology and coevolution of mutualism in the classroom portion of
my courses. On the day of lab, the approach differs in different classes. For all, we start with careful observation of the flowering
species chosen and its visitors. For the freshman biology majors, we then divide into three groups (visitation, phenology, and
visitors) to start the natural history observations, to be compiled and followed up on, OR we start with group observations and
brainstorming questions. Students then decide on a question to investigate in a group of about 3.
Comments On the Activities in the Lab.
Since temperature, wind, and how sunny the day is all greatly influence insect activity, it is good to have a back-up activity that could
be substituted for the pollination observations.
Suggested Back-up Activity:
Willing, R. P. 2000. A Simulated Pollination Exercise. Pages 469-473, in Tested studies for laboratory teaching,
Volume 21. S. J. Karcher (ed.). Proceedings of the 21st Workshop/Conference of the Association for Biology Laboratory
Education (ABLE), 509 pages.
Facilitating Development of Student Questions:
Students are sometimes stymied when asked to ask questions (even though they were too good at it when they were five!).
Feinsinger et al (1997) suggest the following guidelines for questions:
- The question chosen should be answerable within the time allotted.
- Questions of “How? Which? How many? and Where?” are
likely to be answerable. The “Why?” questions may
be more natural and more beguiling, but are rarely
answerable directly through hands-on investigation.
The other questions are likely to generate many “Whys?" for
- Questions must fit the following criteria:
- Elements must be measurable and controllable.
- COMPARISON-TYPE questions will be easiest to address, given time and equipment.
- Compare things that common sense and prior knowledge suggest will be different, or where finding no differences
should be interesting. Do NOT choose questions that have obvious answers, or you won’t want to waste your time.
- Choose a question that you find somewhat tantalizing - neither too obvious, nor too tedious in methodology.
Hypothesis: Develop an hypothesis - a tentative explanation for what we observe
- Must be TESTABLE and FALSIFIABLE.
- Should be specific - not “temperature will affect visitation rates” but “increased temperatures will increase visitation rates.”
- CAN DISPROVE, BUT CAN NEVER PROVE TRUE!!!! There may be other explanations.
Investigation: Design an experiment to test the hypothesis
- Define variables:
- Dependent variable - response to treatment,
- Independent variable - manipulated factor - should be only one in order to isolate effect of variable on response,
- Controlled variables - all other factors that might influence response should be held constant,
- Outline procedure:
- Treatment level,
- Record carefully steps to be performed.
- Determine controls - independent variable held at an established level, or omitted.
- Predict outcome based on hypothesis - If...Then...
Examples of questions students have investigated:
A. SHORT TERM STUDIES
- Do small insect visitors visit more flowers on one plant than do larger visitors? If so, what effects would this have on cross pollination?
TECHNIQUES: “Eyeball ID” of visitors, visitation observation, data analysis.
- Which visitors are the most “faithful” to the target species (i.e. visit only that species)? What effects would faithfulness, or floral constancy,
have on the amount of pollen “wasted?"
TECHNIQUES: “Eyeball ID,” following visitors, collection of pollen load in staining gel, microscopic analysis of pollen loads, sampling
of pollen on the slide, creation of pie-graph of load for each species of visitor.
- How far between target species plants do the pollinators move for their next visit?
TECHNIQUES: “Eyeball ID,” following visitors, estimation of distances between target species plants visited, counting numbers of
flowers visited on each plant.
- Where is most of the pollen carried on the insect visitors?
TECHNIQUES: Collection and preserving of insects, careful swabbing of body parts with staining gel, sampling of pollen on the slide,
- Do flowers in large patches attract more visitors than isolated flowers or flowers in small patches?
TECHNIQUES: Mark and observe flowers in patches of different sizes, “Eyeball ID,” visitation observations,
- Do flowers with larger petals attract more visitors than flowers with smaller petals?
TECHNIQUES: Clip petals to reduce size (nail clippers) of experimental group, and observe flowers of different sizes, “Eyeball ID,”
- Do flowers near an artificial display of similar flowers attract more visitors than more isolated flowers?
TECHNIQUES: Set up control and experimental plots with and without artificial flowers of similar size, color, and shape as target
species, “Eyeball ID,” visitation observations.
B. EXTENDED STUDIES
Comments On the Uses of This Lab Activity in Different Courses at Millikin University.
- Do flowers that have not been visited last longer than visited (and possibly pollinated) flowers?
TECHNIQUES: Preparation of exclosure to prevent visitation, hand pollination, phenology observations.
- Do flowers in large populations produce more seeds than more isolated flowers?
TECHNIQUES: Locate sites with high and low populations of target species, collect seed, calculate percentage of seed set,
- Are flowers more likely to be visited at certain times of day?
TECHNIQUES: Visitation observations throughout time flowers are open, compilation of class data for diurnal (daily) flowering
and visitation profiles.
- What is the relationship between size of active pollinators and ambient temperature?
TECHNIQUES: Sorting visitors into 3 size classes, observe flowers on several different days at about the same time,
measurement of air temperature, visitation observation, compilation of class data.
- What is the relationship between size of active pollinators and ambient temperature?
TECHNIQUES: Sorting visitors into 3 size classes, observe flowers on several different days at about the same time, measurement
of air temperature, visitation observation, compilation of class data.
- What is the relationship between the relative time of flowering of an individual in the population (early, middle, or late),
probability of visitation, and seed set?
TECHNIQUES: Mark flowers open at 3 different times within the flowering period for that target species, visitation observations,
seed collection, calculation of seed set, compilation of class data.
- Do pollen grains from different individuals germinate and grow at a faster rate than self-pollen in self-compatible species?
Does temperature affect rates of germination and/or growth of pollen?
TECHNIQUES: Hand pollination, stigma dissection and staining with basic fuchsin gel, microscopic examination of style.
This lab activity is used in four different courses at Millikin University. In a spring semester non-majors course, Local Flora, with 18 students,
we do one two-hour lab at a park across the street when spring beauties are in flower following a two hour lecture and discussion on pollination,
including showing David Attenborough’s “Birds and Bees” video from the Private Life of Plants series. Pairs of students spend ten minutes
watching a patch of flowers, and then brainstorm questions. We get back together as a group and share “favorite” questions, then choose
one or two to work on as a class, form a testable hypothesis, and plan an investigation to test it. The question chosen usually deals with
which flowers are more likely to be visited, comparing color, patch size, patch position in sun or shade, or flower height. The brainstorming
and planning take about 30 minutes, and the investigation takes another 30 minutes. Each pair of students can get in two ten-minute
observation periods, which results in a sample size large enough for statistical comparisons. We compile the data, and then students write
a scientific report on the class-generated question and experiment.
The lab activity is used differently in our spring freshman biology major’s course, Attributes of Life, with five lab sections, each with 16 students.
The lab is preceded by one or two lectures on coevolution of plants and pollinators and a pre-lab assignment. On lab day, in each
lab, students are divided into three groups to examine the natural history of pollination of spring beauty, crabapple, or buckeye flowers. One
group assesses flowering phenology, one group estimates visitation rates, and one group examines visitors for pollen, all using the sample
experiments included with this module. Data are compiled from all five labs and posted for all to use. Some years students are asked to
write a paper estimating probability of visitation of a flower by the visitors most likely to be effective (based on pollen load composition).
Data from all three groups are necessary to know how long the flower is open, which visitors are most frequent, and which are likely to carry
pollen. Students are required to come up with a list of questions generated by their observations and those of the class as part of their
discussion sections. In some years, a second lab period is devoted to designing and carrying out an investigation of a question generated
by the student, and then the write-up is of the student-generated project rather than about the class data. When we have a data from two
or more years, such as for spring beauty and buckeye flowers, we plan to present the natural history information in an introductory
lecture/discussion on the site rather than spending the two-hour lab collecting more of that data. We can then start the brainstorming and
student-generated hypothesis testing.
In our Field Ecology course, which is a summer immersion experience at Lake Shelbyville, Illinois, for 10-12 non-majors, we include the lab activity
much like it is used in Local Flora. However, students have a full day to complete the investigations of questions they generate, and can further
develop hypotheses in a two-day, individual follow-up project.
In Plant Biology, a fall course for 12-16 junior and senior undergraduate students, students work in pairs on a prairie species. One three-hour
lab is devoted to observing visitation, examining flowers, acquiring pollen samples, generating questions, developing hypotheses, and designing
an experiment to test the hypothesis chosen. Projects are discussed and approved, and investigations are undertaken outside of class. A
formal scientific report is required.
Comments On Questions for Further Thought:
Students often mix seed dispersal and pollen dispersal - for example, when I ask them to bring me a flower with wind dispersed pollen,
nearly all bring me a dandelion. It is important to stress the timing and source of pollen versus seeds.
Students also often have difficulty with mathematical manipulations - even with figuring the number of visits per flower observed
during a ten-minute period. It is often better to lead them through the development of a formula to figure rates than to present them
with one (as in the example in section 6C).
The last several questions for further thought, and the questions generated by students, make good group discussion material.
Comments On the Assessment of Student Learning Outcomes:
Extensive notes on course assessment are in the Teaching Resources sector
of TIEE under the keyword "Assessment"
Comments On the Evaluation of the Lab Activity:
Comments On Translating the Activity to Other Institutional Scales:
Since transportation is not necessary, this outdoor activity can be adapted for much larger groups on large campuses.
Landscape beds can be used, or trees with large, attractive flowers, like redbud, crabapple, hawthorn, and buckeye.
This activity can be useful for non-majors in local flora and field ecology immersion classes, as well as junior and senior biology majors in upper
level Plant Biology. Also adaptable for younger students, with more emphasis on observations and not pollen removal from insects.
Different approaches have been effective, including:
- Natural history observations as major part of lab, generating list of questions.
- Natural history observations as one lab, with spin-off projects to address questions raised in follow-up lab.
- Natural history information given about system chosen, with student-generated questions addressed in experiments designed and carried out in lab.