Life System and Environmental & Evolutionary Biology II

Lab 9: Island Biogeography Computer Laboratory.


Island biogeographic theory suggests that there is a relationship between the size of an area and the number of species it can be expected to contain, as well as that the number of species found in an area is a function of the rate at which new species can colonize the area and the rate at which they are lost from the area. The objective of this lab is to examine island biogeography theory in the context of nature reserves run by the US Park Service.


For this exercise we make use of an extensive database on the flora and fauna on lands of the US National Park Service. These lands include National Parks (NP), National Recreation Areas (NRA), National Monuments (NM), and National Historic Sites and Places (NHS and NHP). You can use this database to test two fundamental aspects of island biogeographic theory:

  1. Species richness should be a positive linear function of park size. In other words, if we plot the number of species in US Parks versus the parks area, we should be able to fit a straight line through the slope, and the line’s slope should be positive.
  2. If we compare data from mainland and island parks, the relationships between area and species richness should be positive for both, but the intercepts should be different.

The database is entitled NPFAUNA and can be accesses interactively through the Internet at If you are using a PC the entire database can also be downloaded and run as an executable file.

When you have accessed the site, use your browser to select "search a database by name". To gather the data you need, first click a mouse on the name of the park. You will see some cursory information on the park, including its area, then you will see a series of taxon-oriented groups (amphibians, mammals, etc.). If you click on any of these buttons, you will generate a list of all the species in that taxonomic group that occur in the park. This is how you will obtain your two key data points: park area and species richness.

For this exercise, I would like to focus on three taxonomic groups. One I choose (amphibians), and 2 you choose. Of the two you choose, one should be on of the groups categorized in the database (reptiles, mammals, birds, fishes, and plants). The second group should be a subset of amphibians - an order or family.

The easiest way to record the data is to make a set of columns with the following headings: Park name, park area (record this in hectares: 1 ha = 100m X 100m), and the number of species recorded. Then choose a set of mainland parks and island parks to compare. The parklands in the Pacific Ocean represent the most extensive group of island parks in the US system and probably are the best to use. Therefore, tally species for:

American NP
Channel Islands NP
Hawaii Volcanoes NP
Haleakala NP
Kalaupapa NHS
NP of American Samoa

Click on each of these parks and then record the number of species present and the size of the park. Then do the same for mainland parks. I suggest the parks in the southeast US, which, although quite different from the Pacific Islands, are nonetheless more ecologically similar to the Pacific Island parks than are those in the rest of the database, which are mostly in the arid western US. Quantify species for:

Big South Fork NR/NRA
Colonial NHP
Everglades NP
George Washington Birthplace NM
Great Smokey Mountains NP
Mammoth Cave NP
Shenandoah NP
Valley Forge NHP

Now plot species richness by park area for mainland and island parks. Both species number and park area should be converted to log10-units prior to plotting to ensure that the relationship is linear. You will need a calculator to do this. Remember that species richness is dependent on park area (it is the Y variable), and park area varies independently of species richness (it is the X variable).

The key attributes of the species-area relationship are the slope and the y-intercept of the line describing the relationship. Specifically, you will need to estimate the parameters a and b for the equation describing the line:

Y = a +bX

The statistic b describes the slope of the relationship and tells you how much of a change in Y (number of species) exists for a unit change in X (area). The statistic a is the Y-intercept and is the value of Y at X = 0. These two statistics uniquely define a line.


  1. Is the general prediction of increasing species richness with park area borne out in both the island and mainland setting? What factors do you think underlie the basic pattern of increasing species richness with park area?
  2. Why should the intercept be lower for the island sites versus the mainland sites?
  3. What is the value of calculating a line through the data?
  4. Surely you observe some noise in the relationships for both the island and the mainland plots. What might account for this noise?
  5. Did the data on a subset of amphibians display the same relationship between species richness and area as did the amphibians as a whole? Was this surprising? Why?
  6. Did the broad taxa that you chose (e.g. fish, plants) show the expected relationship? Why might this be?
  7. Consider the mainland data for amphibian richness. If the parklands lost, on average, 90% of their area (e.g. 10,000 ha to 1,000, or 1,000 to 100), according to your calculations, by what percent would species number change?
  8. Given your results, do you think that scarce conservation funds that could be used to buy a finite amount of land would be better spent to enlarge a small park or a large park (if the goal was to protect as many species as possible)?
  9. How might isolation effects differ among taxa (e.g. amphibians vs. plants)? Why?