Lab Goals:  

1.  Collect field data to determine the dispersion pattern of an organism of your choice.   

2.  Develop an observational hypothesis in the field and then functional hypotheses to explain the dispersion pattern you found.    

Data Processing:  Prepare a table like the one in the lab manual (Table 4C.1).  You will use the mean number of organisms per plot to get the Poisson probability from  Table 4C.4.  After making the table, prepare a graph as in Fig. 4C.4.  You can compare your observed line to the random (= Poisson) and to the uniform and contagious lines in Fig 4C.5.  Keep in mind that the mean number of organisms per plot will impact the shape of the curve, as shown in Fig. 4C.3.   At this point you can judge what kind of distribution the organism you counted showed, but you don't have a statistical test yet.  The best test to use is the chi-square statistical test listed under section 3.2 Variance-to-Mean Ratio in Chap 4C.  This is not your usual chi-square calculation, and you need to use the equation given (eq. 10).  All you need for this test is the variance, s² , and mean calculated from the raw data.  After finding your chi-square value, use Figure 4C.6 to determine if you have a random, clumped, or uniform dispersion.  The variance, s² is just the standard deviation, s, squared.   You can calculate this on your TI calculator or using SYSTAT.   Although this test uses a chi-square statistic, don't try doing the chi-square test you used in genetics--the test is not the same.

Interpretation:  Each group needs to present their conclusions about the dispersion pattern they found.  Your group will develop two functional hypotheses that could explain the dispersion pattern you found (i.e., if you found a clumped pattern, you need two different hypotheses that could explain why that organism would be clumped).  The hypotheses should represent two different alternatives to explain the pattern.  One can be presented as your main hypothesis, and I want you to develop an experiment that would allow you to test your hypothesis (you are not going to do the experiment, just describe what you could do).  The other hypothesis will be an alternative hypothesis that could also account for the same data pattern--you do not need an experiment for this alternative hypothesis.  Remember, your hypotheses will be educated guesses, thus the more  you learn about the biology of the organism you examined, the better your hypothesis can be.  For example, you might want to find out how offspring are produced, how they disperse, how the adults mate, or how long they live.  This information should be in basic field guides to plants and animals in the library.   You can also search for full-text articles through the Research Database links at the Torreyson library.  JSTOR is great for ecology--just select Ecology where it asks for the journals you want searched--these are full-text articles.  Wilson Web, SpringerLink, and Proquest also have ecology articles.  You can search by the organism or the subject (dispersion, clumped distribution or whatever).   BIOSIS has references and some full-text articles.  The General information about dispersal is in your Textbook in chapter 9.  A google image search can help with finding images and the web page from the USDA will help with information about the plant you studied...sorry I don't have a central site for animals, but just google them and look for sites from universities (.edu) or goverment (.gov).  

 Presentation: Each group will present their results in class this week.  Everyone in the group needs to contribute to the oral presentation of this project or the next one...if you don't say much or anything this time, be sure to be the major speaker next time.    The presentation should include the sections listed below (maybe one for each group member?).  I would also like you to hand in a written copy of your data summary (raw data, data summary, graphs, and a list of the references you used), the name of the organism you worked with, and the main and alternative hypotheses of your group (of course, I'd like it done on a word processor, or you can just print your powerpoint slides and add the raw data on a separate sheet).  The written copy is due before your presentation.  Bring your presentation to class on a CD (check to make sure it opens before you come to school).  

   Here is an example about earthworms, one about spiders, and another about a plant.  Check these out for the things you like and the things you don't like--like most student presentation, there are good things about these, but there are errors as well, but they give you an idea of what presentations can include. 

Introduction and Methods states what you did, the species examined, and your method of data collection.  You should include information on how and why the species was chosen, but we did not really approach the data collection with a hypothesis to be tested...we set out to document a pattern of dispersion for a particular species.  You may state any predictions you made about its dispersal, but you don't have to state a hypothesis here in the introduction (unless you already knew enough about your organism that you proposed a reasonable hypothesis before you started collecting data).  You should give enough information about how you sampled that someone could go out and sample the same organism in the same way that you did.    

Results where you state what you found, and refer to your data summaries or figures.  Remember, as a good scientist, I won't believe what you tell me until you clearly show me the data.   A good way to state your data would be:  We expected 30 plots with 0 individuals, but found 60 (see Table), suggesting an aggregated dispersion pattern. In addition we found more plots with 6 individuals than expected by the Poisson (see Table), also indicating an aggregated dispersion pattern.

Conclusion: Your conclusion will begin with a statement about how your organism was distributed.  From there, you will need to refer to our textbook and sources from the library and the web to help explain your result. Of course, you won't know for sure why your organism is distributed in a particular manner, but you can propose a hypothesis explaining why the organism you chose was distributed the way it was.  You will also need at least one alternative hypothesis that could also explain the result you found.  Use the literature presented in your text to support your argument and specifically make reference to your text by page number.  This section will be graded on how well you integrate the results of your study with what is currently known about both the organism you studied and the dispersion of organisms in general as presented in your text.  References need to be listed at the end of the presentation. 

I will grade the presentation on (1) introduction and methods--do you clearly state how you did the project and why you chose a particular organism?  (2) the accuracy of your data analysis and the clarity with which you present the data results to the class (i.e., can you explain the numbers to the class clearly); (3) the logic and originality of the hypotheses you propose to account for the dispersion pattern you document, and whether you demonstrate your understanding of established knowledge about dispersion patterns in general and the specific organism you worked with through effective use of reference material; and (4) overall clarity of presentation--do you speak directly and loudly enough to be heard by the class? (5) written copy turned in before presentation.