LAB 3 HABITAT DIVERSITY & ARTHROPOD COMMUNITIES

Transcription

1 LAB 3 HABITAT DIVERSITY & ARTHROPOD COMMUNITIES 1 Introduction: During your first lab, you conducted a field sampling to assess the adequacy of sampling a population of foxtail (Setaria sp.). I also asked you to make a step up to the next level of ecological organization by considering some characteristics of the plant community. In particular, you were to tally the species richness of each field, calculate species diversity for each, and then compare the two fields. During your third lab, you will continue to consider communities, but instead of just characterizing one community, you will characterize two the plant community and the arthropod community (insects and spiders). In addition, I want you to think about how characteristics of the plant community might influence those of the arthropod community. Today s Objectives: 1) To characterize the plant communities of two different habitats. 2) To characterize the arthropod communities of two different habitats. 3) To develop species diversity indices for the habitats sampled. 4) To measure the degree of similarity of the two habitats. 5) To relate structural and species diversity of the plant community with the diversity of the arthropod community. Today s activities: Today s lab will be based upon the following paper: Allan, J. David, Harvey J. Alexander, Ronald Greenberg Foliage arthropod communities of crop and fallow fields. Oecologia 22: (on EReserves via the library website; the password is hosea) You will randomly sample and compare two areas for plant and arthropod diversity. 1) a recently planted field of switchgrass (Panicum virgatum) that has low species richness but possible moderate foliage height diversity and 2) an old field with greater species richness but perhaps less consistent foliage height diversity. Methods There will be five teams of 3 people. Each team will have separate self-selected people to conduct the foliage sampling (2) and the arthropod sampling (1) The latter will assist with the plant sampling upon completion of recording the arthropods in the plot. Note: This lab does not require that you know all of the plant and insect species, but that you can reliably recognize and distinguish among different species. 1) Using 2, 50 meter measuring tapes, you will set up a grid in both areas. 2) Using a random numbers table, select coordinates and lay down the 1 meter square. 3) Make 10 sweeps with the insect net. Place end of net in killing jar and loosely screw on lid. 4) When insect have succumbed to the fumes, dump them out into the sorting tray. 5) Sort by type and the number of each type that are similar. 6) After the quadrat has been sampled for insects, the plant team will: a. Count and record the number of individuals for each plant species, b. Estimate the proportion of foliage by area which has attained a height in one of three categories; < 15 cm, 15-45cm, >45 cm. 7) Sample 2 quadrats for each habitat.

2 2 We will combine data from the whole lab, therefore, it is up to you to coordinate amongst yourselves and agree on how you will designate each species of insect or plant. We will assign one person as curator for the insects and one as a curator for the plants who will then record a description and perhaps a name (e.g. black and yellow beetle, or bug species # 2). Individuals who discover each new species may want to name their species. Calculations required 1. Plant Species Richness for each field. 2. Insect Species Richness for each field Diversity (evenness) calculations (3-5): 3. Though Allan et al. (1975) refer to the following as measures of diversity, they are technically calculations of evenness. They are the Shannon-Weaver index divided by the log of N. In this instance, N = 3 per plot (3 different foliage heights). a) Using the methods described by Allan et al. on page 2, calculate the mean foliage height evenness. To do so, calculate the foliage height diversity for each plot. (You will have 3 percentages for each plot. Be sure to convert these to decimal fractions.) Then divide by the log of 3. (see note on page 3 about consistently using the same base for taking the logs of numbers.) Average the foliage height evenness for the 10 quadrats. 4. Calculate the mean Shannon-Weaver evenness index for the plants sampled using the equation on page 3 Allen et al. s paper). This is not the Shannon-Weaver diversity index! The equation from the paper is : S - pi loge pi e = i = 1 loges Where S = the number of species. First Calculate the top half of the equation. This is the formula for H, the Shannon-Weaver diversity index that is on page 6 of Lab #1. If you are not a wiz with MS-Excel, then use the n log n table I ve provided. (For the long form of the index, it does not matter what logarithmic base is used, as long as the same base is used in both the numerator and denominator. The table I supply for the shortcut method is base 10.) Second After you have calculated the top half of the equation, divide by log 10 S, where is S is the number of species. Note Since the shortcut uses base 10, then you should divide by log 10 S. Your answer should be less than Calculate the mean Shannon-Weaver evenness index (as described above for plants) for the arthropods sampled. 6. Calculate the community coefficient of similarity (page 8 from Lab #1) for both the plants and arthropods.

3 7. Calculate the ratio of species. number of predators for each habitat. Use the # of individuals, not the # of number of herbivores 3 The Write-up - This is your first lab report for. Here s what I want. 1) Write a short (1-2 paragraphs) introduction describing the 2 habitats and provide hypotheses regarding which habitat should have a greater species richness and species evenness of insects. Be sure to provide reasoning to support your selection of hypotheses. 2) No methods section. 3) In your results section, clearly present the a. Plant Species Richness for each field b. Insect Species Richness for each field c. Mean Shannon-Weaver evenness index for foliage height diversity (both habitats). d. Mean Shannon-Weaver evenness index for plant species (both habitats). e. Mean Shannon-Weaver evenness index for arthropod species (both habitats). f. The community coefficient of similarity for plants and arthropods (to compare habitats). [For 3c, d, & e calculate the Shannon-Weaver evenness separately for each plot, then report mean + S.E. for each field.] 4) In your discussion, address the following; A. Consider the results of Allan et al.. In the second sentence of their discussion, they compare their results for crop and fallow fields. Fallow fields have: More species Few individuals (per species) Higher evenness Proportionally more predator individuals. Which of the fields you sampled corresponds to their crop field and which corresponds to their fallow old field? Where did you find the greatest total number of insects, the mowed field of foxtail, or the goldenrod field? How do your results compare to theirs? Elaborate. B. Can you detect any patterns or relationships between the arthropod diversity and a) plant species richness, b) foliage height diversity or c) plant species evenness either within or across the two fields? number of predators C. What is the ratio of for each of the fields? (Use total number of number of herbivores individuals, not the number of species.) Does it seem to be related to the plant species or structural diversity of the field?

4 4 The following articles (available through JSTOR) may provide information to compare and contrast with for your discussion. Siemann, Evan, David Tilman, John Haarstad and Mark Ritchie Experimental tests of the dependence of arthropod diversity on plant diversity. The American Naturalist. 152(5): Siemann, Evan, John Haarstad and David Tilman Dynamics of plant and arthrodpod diversity during old field succession. Ecography 22:

5 5 DATA SHEET FOR SPECIES AREA CURVES AND HABITAT DIVERSITY HABITAT TYPE PLOT NUMBER _ PLANTS ARTHROPODS

6 6 DATA SHEET FOR SPECIES AREA CURVES AND HABITAT DIVERSITY HABITAT TYPE PLOT NUMBER _ PLANTS ARTHROPODS