Similarly, and intuitively, a sample with one species has life, but no diversity. The SW index is not the tool for this set. Tom Cuba
> In the limit as p goes to 0, log(p) goes to -infinity. The Shannon-Wiener > terms are equal to p*log(p) and 0*(-infinity) is defined as 0, which goes > along with intuition, no species would have to be zero diversity. > > ************************************************************* > Robert Matlock > Assistant Professor > Department of Biology > CSI/CUNY > 2800 Victory Boulevard > Staten Island, NY 10314 > 718-982-3869 > Fax 718-982-3852 > > > -----Original Message----- > From: Ecological Society of America: grants, jobs, news > [mailto:[email protected]] On Behalf Of Maria Van Dyke > Sent: Thursday, July 16, 2009 5:39 PM > To: [email protected] > Subject: [ECOLOG-L] Shannon-Wiener Div Index Question - dealing with zero > species per plot?? > > Dear ECO loggers, > I have a question about utility of the Shannon-Wiener diversity index in > regards to sampling units that have no species in them at a given sampling > time. Normally this would get a value of zero, however with Shannon-Wiener > a > sampling unit that has only one individual of one species would also earn > the value of zero when input into the formula -∑(1*ln1) = > -∑(1*0) = 0; > therefore there becomes an issue of two different species scenarios having > the same values (0 for no species individuals and 0 for 1 ind of one > species). > For example: > I am studying substrate preferences of ground nesting bees in which I > created three different substrate treatment types for bees to nest in. In > all, I have 20 plots that have the 3 different treatments (subplots) > within > each plot. I sampled all subplots of all plots 7 times throughout the bee > flight season. During some rounds I would collect no bees from a subplot > and > therefore have no species to calculate diversity from in my data set. How > do > I deal with these subplots that actually had no (zero) bee species in > them? > I would use Simpson Diversity instead but I am interested in rare species > so > I thought it would not be sensitive enough. > > I know this is somewhat of a strange predicament b/c the data sets that > Shannon-Wiener is usually applied to normally have at least one species > per > plot at the very least but the nature of my study forces me to deal with > these true zero values. > > Has anyone out there had to deal with this before? I am open to any and > all > suggestions or varying approaches. Is there a better index to use for this > analysis? I intend to use the results from diversity to calculate evenness > as well. Please enlighten me > > Maria Van Dyke > Department of Environmental Sciences > University of Virginia >
