SEE-U 2000: Biosphere 2 - Module 3:Exercise 3

## Exercise 3: Intraspecific Vigor and Diversity along a Resource Gradient
Module 3: Natural Selection and Evolution

#### First of the Shared Activities — Data is Shared Between all Biomes

### Your Question

1. Does intraspecific diversity differ between the heart of a species’ range and in the more peripheral areas of its range?

### Background

On first glance, the world looks green and the same species of plants seem to be everywhere. In actuality, nearly all plants have extremely specific humidity, climate, soil, space, pollination, and disturbance requirements that must be met.

Some have suggested that the heart of a species range is defined by the most favorable combination of the above environmental features. The heart of a species’ range could also be said to have the most vigorous individuals in the population. If this hypothesis is supported, then natural selection mediated via intraspecific competition is likely the most important force influencing the individuals in this population.

In direct contrast, some recent work (Smith et al., 1998) has suggested that it may be the edges of a species’ range that have the greatest morphological and genetic diversity. In this case, the individuals that are living at the edges of the desired habitat are most stressed. As a consequence, these individuals are probably not very strongly influenced by intraspecific competition. Instead, they may be most strongly limited by environmental factors.

Today we’ll be using plant morphology to test these ideas. The centers of a species’ distribution will be defined on a local scale rather than a larger spatial scale. To these ends, we shall focus on tree species that are strongly limited by moisture. The within population variation in morphology of species that are sensitive to moisture may vary with decreasing moisture levels. You should work with your instructor to determine which species would be most appropriate for each site.

Our activity today explores the influence of distance from the most preferred habitat of a species and the amount of within-population morphological variation. The variation within a species must be genetically encoded and heritable to have a selective value. If it is not, then it cannot be selected upon.

There is the possibility that the results that we find are in fact not genetically based and may instead be environmentally mediated. Keep both of these explanations in mind as we do today’s activity. As you analyze your data, try to come up with explanations for why the results that you obtained exist. Are they due to short-term environmental or longer-term evolutionary influences? Explain your conclusions.

References:
Smith et al. Science 276:1855-1857 (June 20, 1998)

### Objectives

1. Comprehension of the basics of scientific methodology
2. Understanding of how to adhere to and implement a mostly predesigned scientific experiment
3. Better knowledge of the role of natural selection in structuring populations and its importance in understanding ecology
4. Insight into some of the proximate mechanisms for natural selection
5. Increased familiarity with the local biome and how it creates the conditions under which natural selection operates
6. Understanding of how the same processes of natural selection act across many different biomes
7. Knowledge of why reducing resource quality and quantity affect intraspecific diversity
8. Understanding of the different sources for intraspecific variation, and how to differentiate among them

### Your Assignment

1. Before the start of field time, confer with labmates to design the experiment that you wish to perform—not all lab groups in the class have to have the same design nor do they have to use the same species to collect the data, but it would be advised.
   1. You will need to determine hypotheses to be tested (see below) the species, how to determine the location of the heart of the range, the determinant of the resource gradient (elevation, water, soil type, etc.), the morphological character that will be used, and how the range of diversity will be quantified
   2. Likely the most useful determinant of distribution is elevation or distance from a water source for a mesic (wet) tree species
   3. Likely the most useful sampling method is to sample repeatedly at the “heart of the range” and then to sample repeatedly at the “periphery of the range”, using samplings of a set size at each sampling area to determine which individuals will be included in the test—the centers of individual sampling events at each location would have to be separated by a set distance
2. Before going into the field, you will need to log onto eBiome and print off a data page from the Morphological Intraspecific Diversity input screen that you will use for data entry
3. You should then go to the field and collect morphological diversity data using whatever methodology and characters you choose and input the data (if possible) into the GPS units in the field when the data are collected (or write it down on sheets if not possible)
4. In early afternoon, you should return to the computer lab, input your data into eBiome, determine what types of data that you would like to later download from eBiome that were collected across all the biomes, and then conduct statistical analyses on the resulting data
   1. Appropriate statistical tests would include a determination of the population variance within a sample
   2. Statistical analyses of the variances should be kept very simple like an F-test (Section 8.3 and Box 8.1 in Sokol & Rohlf 1981) of the hypotheses of equal variances—if more than two groups are included then use either a Hartley’s Fmax-test (Section 13.3 and Box 13.1) or a log-ANOVA (a.k.a. Scheffe-Box test) which is less sensitive to departures from normality (probably a major concern with these data, Section 13.3 and Box 13.1)
   3. Additionally, a t-test should also be performed if the data are continuous or a Chi-square if they are discrete to determine whether the means of the two samples also differ—at most if the groups desire to do an analyses using more than two groups, the statistical procedure could be an ANOVA. You would then group sites together based on whether they were in the heart of the species’ range or whether they were peripheral
5. Communication between the biomes should occur between students—possibly talking about their outcomes and why they think they obtained them
   1. Discuss whether the trends that you obtained were a result of genetic differences between different sampling points along the transect or whether they were due to changes that were mediated by the environmental differences and as such are not genetically fixed
   2. Provide reasons for your conclusions from point A above.

### Key Skills

1. Improved ability with Geographic Positioning System (GPS) units
2. Facility using Geographic Information System technology (eBiome)
3. Ability to collect morphological data in the field
4. Competence with identifying several common species of trees in the local biome
5. Skill with t-tests and chi-square statistical tests and knowledge of when to use them
6. Increasing competence in communicating results with others in other biomes

### Timetable

1. Total elapsed time to perform the experiment : Two days
   - Set-up, data collection, data input into eBiome, statistical analyses on locally collected data, and communication between students in different biomes should all be done in one day (Thursday; starting Wednesday at B2C).
   - Talk preparation and presentation should occur on the second day (Friday)
   - The exercise will be performed on a Thursday and the morning of the next day (Friday)—they should be completely finished with the project and have presented the oral report by Friday Noon (Friday at 9 at B2C)
   - The rest of Friday should be spent on designing the individual independent projects in consultation with the instructors and TAs
2. Total elapsed hands-on time : approximately Eleven hours
   - Discussion to construct experiment = 1 hour (Thursday; Wed PM at B2C)
   - Field work time to collect morphological data = 3 hours (Thursday)
   - Data Input into eBiome = 1 hour (Thursday)
   - Statistical tests on locally collected data and interpretation = 1 hour (Thursday)
   - Networked discussion and interpretation = 2 hours (Thursday)
   - Writing of talk = 2 hours (Friday; Thursday PM at B2C)
   - Oral presentation = 1 hour (15 min max/group) (Friday)

### Procedural Notes

1. This experiment could not be portable within the timing of the course, if weather is inclement, the students would have to persevere and collect the data
   - For this reason, woody plant species that are hearty and will not be too strongly affected by rain or wind should be chosen to be the study organism
   - Species should provide the same data in the dependent variables given below, irrespective of the environmental conditions
2. This will be run simultaneously at all of the biomes and will be the first of the Shared Activities
   - Instructors in each biome should frequently communicate as the exercise progresses to ensure that similar species of trees are used as the study organism across each biome
   - Ideally the trees will be of the same genus (e.g., Acer only), although this will probably be impossible, given the disparate biomes included
3. Before this activity, students will be introduced to eBiome and GPS during the first two modules.
4. The need for relatively quick data turnaround, going into and out of eBiome, may be problematic if the database is not centralized
   - For quick activities like this one, where the data are shared between biomes, we will need to adhere to a tight schedule in terms of getting the data to the central organizer if the database is not centralized and input is not web-based
   - There are only three activities, including this one, during which the data are shared between sites
   - More localized activities will not have the need for such a quick turnaround, and the data deposition into eBiome can occur more leisurely

### Materials Needed

1. Computer and printer
   - Need Excel or some other database and statistical analysis package that has the tests of homoscedasticity included
2. High-speed computer connection to the web and access to eBiome
3. Preferably 3 GPS units with ArcView compatibility and data input capability, may have many fewer the first year of the class
4. eBiome needs to be fully developed, with the eventual target of having it web-based and data are immediately (or at a set time lag for data inspection and verification by a third party) input and made available to other students
5. Clipboards, paper, pencil
6. Measuring tape, rulers, calipers, etc. depending on the variables and organisms chosen by the groups.
7. Field appropriate gear