Biology 2108 Laboratory Exercises: Variation in Natural Systems

Transcription

1 Biology 2108 Laboratory Exercises: Variation in Natural Systems Ed Bostick Don Davis Marcus C. Davis Joe Dirnberger Bill Ensign Ben Golden Lynelle Golden Paula Jackson Ron Matson R.C. Paul Pam Rhyne Gail Schiffer Heather Sutton Kennesaw State University Department of Biology and Physics LABORATORY 4 Ecology: Variation within Ecological Communities (Part 1)

2 OVERVIEW OF LAB Observations: Forests within the same region often vary dramatically in species composition. This is easily observed within our county, where forest patches vary in many ways, the most obvious being the relative number of pines and hardwoods. A possible explanation for these differences comes from observations on changes in species composition over long periods of time. In many ecosystems, species composition changes over many years in fairly predictable ways. This process is known as ecological succession. To explain difference in the communities of two nearby forests stands we will test the following hypothesis based on this ecological succession model: Forest stands that differ in the length of time since major disturbance will differ in species composition. For forest communities in this region, the last major disturbance was most likely agriculture. By the early 20 th century, most of the land in the region was agricultural, with cotton as the major crop. With severe soil erosion and infestation of the cotton boll weevil, farming became unprofitable and the land has slowly returned to forest. Over the next two weeks we will measure physical and biological factors within two nearby forest stands to test the model of ecological succession. Specifically we will address the following questions: Do the two forest stands differ in the time since disturbance (and if so, which one is older )? (Week 1) How are these two successional stages different in species composition (hardwood vs. pines, amount of undergrowth, species diversity)? (Week 1 & 2) Can differences in environmental factors explain how ecological succession occurs? (Week 2) SAMPLING IN FOREST AREAS A AND B The class will be divided into several groups and each group will sample plots in one of two different forest areas that appear to differ with respect to plant species composition (arbitrarily named Forest A and Forest B). Your instructor will show you the general areas within which plots (quadrats) will be established and sampled. Ropes have been divided into 10 meter units. To establish a 100 square meter plot, stretch a rope out on the ground in a square with the 10 m marks on the rope as the corners. Each group of students will collect data in five 100 m 2 quadrats in Forest Area A or B as follows: - In order to estimate the relative time since a major disturbance, we will measure the circumference of all pines found in the quadrats (on the assumption that the circumference reflects the ages of the pines). Because pines are abundant in each forest area and are primarily of a single species (the Loblolly Pine, Pinus taeda), we will use the age of these trees to determine which forest is older (i.e. existed longer since the last major disturbance). - In order to determine how are these two successional stages different in species composition, count all pines and of all hardwood trees that are over 45 cm in circumference in each quadrat. Pine seedlings are more tolerant of high light and dry, poor soils than are hardwoods.

3 RAW DATA TABLE Plot 1 No. of Pines >45 cm No. of Hardwoods >45 cm Circumference of all pines (cm): Plot 2 Plot 3 Plot 4 Plot 5 COMBINED CLASS DATA The pine circumference data from the two forest areas will be compared using a t-test. This will be done in order to confirm our assumption that the two forest areas chosen differ with respect to time since a major disturbance. Mean Circumference of Pines in Forest Area A: (cm) Standard Deviation: Mean Circumference of Pines in Forest Area B: (cm) Standard Deviation t-test P-value: The numbers of pines & hardwood trees (> 45 cm) in forest areas A and B will be compared using a chi-square contingency table test of independence as follows: Area A Area B Pines Hardwoods chi-square test P-value:

4 LABORATORY 4 Ecology: Variation within Ecological Communities (Part 2) OVERVIEW OF LAB In the second week we will return to the field and collect data on a variety of environmental factors. These "descriptive data" may then be examined in order to determine whether they support the ecological succession model that we tested in the previous week. SAMPLING IN FOREST AREAS A AND B This week, each group will collect data from three 100 meter 2 quadrat plots within either forest area A or B. 1. Determine the amount of light at the four corners of the plot and at the center of the plot using a light meter. 2. Measure topsoil moisture (using a moisture meter) at several cm into the topsoil. 3. Measure top soil temperature (using a thermometer) at several cm into the topsoil. 4. Measure top soil depth (using a ruler) 5. Count the number of trees in each plot (do not include undergrowth plants). 6. Examine the leaves, bark, and branching pattern of the trees to determine the number of species of trees in a plot. Assign a number to each of the tree types ("species") you can distinguish and tabulate the number of each type of tree in the plot. Note that we need not identify each species by name, with the exception of three species: pines, tulip poplars, and dogwoods. These species are easily identified - your instructor will show examples in the forest. 7.Count the number of undergrowth plants as follows: choose one of the four sides of your quadrat and count every undergrowth plant that touches or is below or above that side s rope. N.B.: the class as a whole must be sure to establish clear criteria for distinguishing between undergrowth plants and trees. Repeat the above procedure for your second and third plots. Measure the same variables that you measured in the first plot.

5 SAMPLING IN THE PRE-FOREST AREA Each group (regardless of whether they have been assigned Forest Area A or B) will also sample physical parameters in a recently disturbed area behind the Science Building. The environmental conditions present in Forest Areas A and B have presumably changed since the tree species in each of those forests first germinated. In order to more closely approximate the conditions under which the forest first developed, we will select an area that is younger (i.e. less time since disturbance) than each of the forest areas examined in the previous week. This pre-forest area with very young pines can be thought of as the early successional conditions from which younger of the two forest areas developed. The younger forest from last week can be thought of as the later successional conditions from which the older forest developed. Each group should randomly select two points in this pre-forest area and measure the following parameters at each of these two points: light soil moisture soil temperature soil depth. Return to lab. Data from all groups will be compiled and data analysis will be discussed

6 RAW DATA TABLES: Pre-forest Area Plot: Soil moisture Soil temp. (C ) Soil depth (cm) light Forest Area A Forest Area B Plot Sp. 1 (pine) Sp. 2 (tulip poplar) Sp. 3 (dogwood) Sp. 4 Sp. 5 Sp. 6 Sp. 7 Sp. 8 Sp. 9 Sp. 10 Undergrowth Soil moisture Soil temp. (C ) Soil depth (cm) light 1 light 2 light 3 light 4 light 5

7 WORKSHEET: ANALYSIS OF FOREST DATA Here are some common ways to mathematically describe and characterize populations and communities. For the purpose of this lab, all trees that are not pines will be considered as hardwoods. Mean number of trees per plot Add the number of trees for all plots within a forest area and divide by the number of plots. Species diversity of trees Many measures of diversity consider not only the number of species, but also the evenness in the number of individuals per species. For instance, a plot containing 10 pines and 10 dogwoods would be more diverse than a plot containing 2 pines and 18 dogwoods, despite the fact that both plots contain the same number of species. A commonly used diversity index that mathematically incorporates both species number and evenness is the Shannon Diversity Index: Diversity = - (pi * ln pi) where: = "sum of" pi = the proportion of the total number of individuals occurring in species i ln = "natural log function of" Because different student groups identified species independently of each other, you must calculate diversity for each plot and then calculate the mean diversity from these values. Summary of various physical and biological parameters in three forest areas Mean no. of tot. trees/plot Mean no. of pines/ plot Mean no. of tulip poplars/ plot Mean no. of dogwoods/ plot Mean no. hardwood trees/ plot Mean no. of tree species/ plot Mean no. undergrowth/plot Diversity Index Mean soil moisture Mean soil temperature (C ) Soil depth (cm) Mean light (ft. candles) Forest area: A B Pre-forest area

8 LAB REPORT From the descriptive data collected this week and the results of your test in the first week's lab, write a lab report that addresses the successional model and questions discussed. Your report should include the following sections: INTRODUCTION METHODS AND MATERIALS RESULTS DISCUSSION LITERATURE CITED Your Discussion section should focus on whether the data collected on the relative number of pines and hardwoods, species diversity, and number of undergrowth plants support the hypothesis. Use appropriate environmental data taken in the second week of this study to support your conclusions and explain how ecological succession may occur. (Note that some data may not be relevant to your discussion.) Use the same format for writing a lab report as you have in other labs. In your Literature Cited section be sure to include any references requested by your instructor.