GEOG 442

Biogeography

Analysis of Biodiversity Patterns

In this lab, you'll examine species richness counts for different organisms in different locations on the North American continent to see if you can pick out environmental gradients that covary with the species richness gradients. Some of these run more or less north-south and others run east-west. It might help if you consulted an atlas while doing these analyses, as regional context gives clues. Your biogeography text and notes and any introductory physical geography text would be helpful resources, too.
 

Getting Your Data

To get the data on which this lab is based, click here. You will be asked what to do with the file, since it's an Excel spreadsheet, not a web page. Select Save File As and then specify where you'd like to keep it. If you're doing this at home, stash it anyplace you normally keep data. If you're in our labs, please save it to a disk of some sort, because the student files on the system are purged each week. You can temporarily save it in the D: drive (and it's okay to create a folder in the D: drive with your last name, so you can find your work to save later!

If you find that you can't open the spreadsheet with your Excel program at home, it may be that you have an older version of the program, which won't work with the newer edition. Here is the same spreadsheet saved as an Excel 5.0/95 file.

If that doesn't work, you could try importing it as a comma-separated value (CSV) file by clicking here. It's ugly but usable, and you can pretty it up on your own. CSV files can be imported by Excel, OpenOffice, Works, and pretty much any spreadsheet or database program, so this would be the one to try if you don't use Microsoft products.

 

Mammal Quadruped Diversity in Central and North America

Now you have your data, what do you do with them? First, take a look at Columns A and B, the ones highlighted in light blue. Column A shows the latitude of 22,500 square mile quadrats throughout Central and North America. Column B shows the number of mammalian quadrupeds that showed up in species counts within each of those quadrats. To see the pattern in the numbers, select the "Chart Wizard" from the Excel toolbar (it looks like a little bitty bar graph done in garish colors) or go to the Insert menu and select Chart.

Under Standard Types, pick XY (Scatter) and then select the box that shows a bunch of dots on an X-Y graph without any lines connecting them. Then, select Next > from the buttons on the bottom of the chart wizard.

Under Data Range, write in A4:B51 and indicate that the series is in columns. Then, hit Next > again. Under Titles, come up with a name for your chart and enter it in the Chart Title box. Under Value (X) axis, put latitude. Under Value (Y) axis, put in # of spp/quadrat. If you're feeling fancy, you can play around with Gridlines and Legend, but you don't really need to.

For Chart Location, select As object in Sheet1. Then, you hit Finish, and poof! the graph pops up in your spreadsheet somewhere, probably someplace inconvenient. You can click on any white space area inside your graph and you'll see small black boxes materialize at each corner and at the midpoints of your border. Then, you can move it wherever you like by putting the cursor in the white spaces, holding down the left mouse button, and dragging the whole thing where you want to put it. You can then fiddle with the shape of it, too. By clicking on one of the border black boxes, you can stretch or compress the whole graph so that it takes on a pleasing shape. Something else really helpful: Try right-clicking on one of the data points (it may take a couple tries) and then select Add Trendline. A box will come up. Select the Polynomial button and request a 6th order polynomial (this will create a cascade of three slight convexities and three slight concavities in the trend line, which does a good job running down the middle of the trend of dots. The equation would look like this:

          Y = a + b₁X¹ + b₂X² + b₃³ + b₄X⁴ + b₅X⁵ + b₆X⁶ + E

When you're happy with it, have a look at the pattern you've created.

In simple English, what is the relationship between latitude and species richness (just the eyeball interpretation)?

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Now, the hard part. Why do you think this relationship exists? What is it about latitude that might affect richness? You may want to rummage around in your notes or in Chapter 2 for some ideas.

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Pay attention to the level of departure of points above and below the trend line. Where is the disparity the widest (rough latitude range)? Take a look at a map of climates in North and Central America to surmise which side of the continent the "too low" and the "too high" data points must be. Here is a helpful map: http://apollo.lsc.vsc.edu/classes/met130/notes/chapter17/graphics/climate_west.jpg. A succinct summary of the Köppen climate system on which the map is based can be found at: http://www.meteorologyclimate.com/koppenclassification.htm What are the two climates on either end of the North American continent where the divergence from the trend line is greatest? So, which other factor acts with the energy aspects of latitude to set the maximum species richness of a latitutde?

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Tree Richness Gradients along Transects in North America

In columns F, G, H, and I of your spreadsheet, you have latitude and longitude and species richness data for ten locations along each of three transects, or sampling lines. Each location is roughly in the center of a large quadrat (70,000 square kilometers). The number of species of trees that were counted within those quadrats is given. You'll notice that for each quadrat, either latitude or longitude (Column G) is more or less the same: The top set of ten comes from a transect running from the West Coast at roughly 37° N to the East Coast at roughly 33° N. The two transects below it run due north/south, one at 118° W and the other at 80° W.

First, let's deal with the W/E transect. Again, you'll create an X-Y graph by activating the Chart Wizard. Again, pick XY (Scatter) but this time select the "Scatter with data points connected by lines" option (probably in the bottom row of sample boxes on the left side) and hit Next. In Data Range, put in H4:I15 and select Series in Columns. Again, hit Next.

In Titles, name your chart in Chart title. Value (X) axis should read longitude, while Value (Y) axis should read # spp/quadrat. Again, Place chart As object in Sheet1 and hit Finish. Again, move your chart where you want and morph its shape to make it somewhat æsthetic.

In clear English, how might you describe the relationship between longitude and species richness along this west to east transect across the United States?

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What is going on along that transect that might affect richness?

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Now, do the same for the second transect, which runs from Southern California to Canada's Northwest Territories along the 118° meridian. This time, your data range runs from H18 to I27, and you'll use latitude as the label for the X (horizontal) axis.

Briefly, how might you describe the relationship between latitude and species richness along this south to north transect across the United States along this western meridian?

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Once more, with vigor, do a graph for the third transect. This one runs from Florida to Baffin Island along the 80° meridian, and your data range from H30 to I39. The X axis will be labeled latitude.

Again with terseness, how might you describe the relationship between latitude and species richness along this south to north transect across the United States along this eastern meridian?

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Now, the fun part: Compare and contrast the patterns you see along these two north/south transects.

How do the two patterns resemble one another? What might be driving that similarity?

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In which ways do they differ? Look especially at the height of the curves and then the shape of the drop off in species (where they're concave and where they're convex and the latitudes at which these deviations from a straight line relationship take place).

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What is going on to explain the differences in the two latitude/richness curves? You may need to dust off your introductory physical geography textbook (what? you sold it?! how could you DO that?!!!) for clues somewhere in the climate section.

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first placed on the web: 11/03/03
last revised: 10/28/08
© Dr. Christine M. Rodrigue