GEOG 235. Biogeography
	Dispersal Mechanisms Exercise

Introduction

In general, species may be dispersed passively or actively. Passive dispersal includes being blown by the wind, directed by gravity, or floated upon water. Hitchhiking on animals--including humans, being collected and buried by animals, and being passed through the digestive tract of a bird or mammal are also effective, passive means of dispersal. Active dispersal means moving under one's own powers of locomotion: being forcibly ejected from a seed pod; or flying, walking, swimming.

This exercise asks you to examine different mechanisms for dispersal displayed among the plants (and possibly animals) of your local environment and see if there are correlations between habitat types or growthforms and dispersal mechanisms.

Objective 1: To observe in the field and record in field notes a variety of dispersal mechanisms in the local flora and fauna.

Objective 2: To seek a pattern between dispersal mechanisms and growthforms or habitat types.

Objective 3. To formulate and test hypotheses about dispersal mechanisms and growthforms or habitat types.

Time required: One to two hours in the field. One or two more hours to analyze and write up report.

Field Work

1. Find two distinctly different habitats. The habitats might be as different as a field and a woodlot, a roadside or vacant lot and a well tended garden.
2. Begin a page of field notes. [Your notes should begin with a description of where you are, the date and time of your observations, the weather conditions, and the names of people with whom you are working.]
3. Search each habitats and find about ten different specimens of fruits or seeds in each. Try to collect from a variety of growthforms at each site.
4. Sketch and describe each propagule in your field notes.
5. Note the growthform of the parent plant. Try to identify to species at least one representative of each type.
6. Record the likely means of dispersal (e.g., wind, gravity, hitchhiking, serving as food for birds, etc.) for each.
7. Describe the habitat from which the specimens were collected or observed. A sketch map or profile of vegetation would be helpful.

Analysis

• Which habitat would you suspect selects for the "better" dispersers? Why?
• What dispersal mechanism or mechanisms that you observed do you think is a property of "good" dispersers? Why?
• Construct a matrix similar to the one below to analyze your data for patterns.

  

• Does there appear to be a correlation between one or more dispersal types and a particular habitat type? If so, what is the apparent correlation?

• Formulate one or more hypotheses about the apparent correlation.
  • The null hypothesis (H₀) is that there is no difference between dispersal mechanisms in different the habitats.

Discussion

Find distribution maps for the two species with different dispersal mecahnisms that you identified.(Look in a field guide or in the Flora of Virginia.) Describe and compare the geographic distribution patterns of the two. Does there seem to be any correlation between dispersal capability and geographic distribution? Why might there be a correlation; or, why not?

Final Report:

• The final report should include the results of your analysis and a discussion section. It should be well written and typed. Neat diagrams or sketch maps may accompany the text where appropriate.
• Attach field notes and sketches.
• Prepare a well considered, honest evaluation of the field experience. Did it meet the objectives set forth above? Did you gain anything from the experience? Was the time allotment about right? How could the exercise be improved?