| Author | Message | ||
     Mark Howe Moderator Username: unclemark Post Number: 459 Registered: 08-2003 |
Diversity index applet: http://www.mdsg.umd.edu/programs/education/interactive_lessons/biofilm/studnt1a. htm Still looking for a simple spreadsheet. | ||
| Mark Howe Moderator Username: unclemark Post Number: 456 Registered: 08-2003 |
One of the most important pieces of ecological data we can use is an index of diversity. I have settled on the pie diagram as the easiest way to present diversity on a map, and I still think it may prove to be the most valuable tool. Last night a discussion on diversity index brought back memories. I started with Wikipedia and came up with following with some paraphrasing and interpretation. We will try it out on fish and see what we get. Species richness -- simply the number of species present, no use of relative abundance. (Easy) Simpson's diversity index -- the sum of the fraction of organisms squared; therefore a total of the fractions for all species will equal one, but the sum of the square of the fractions will be the index. The fraction of organisms is the number of individual organisms of a given species to the total number of all organisms in the sample. [Edward Hugh Simpson] http://www.countrysideinfo.co.uk/simpsons.htm | ||
| Mark Howe Moderator Username: unclemark Post Number: 294 Registered: 08-2003 |
You want to lump the species counts together by trawl station. You want the average number of fish found at a given station. You want to compare them on a map. Dissolve: Within your table selected by species: Take the Station as the dissolve field: Take the Count as the statistics field and the mean as the statistics type. The output table gives you what you want. The average number of fish found at each trawl station in your data. Since all trawls should cover the same area, the results will be a function of density. [the area is 16ft wide by 1000m long, or thereabouts] |
