Download Species Diversity

Fish Species Diversity in Flat Bank Creek
Important: Safety gear in this lab is quite different from a lab investigation. You must have appropriate foot and
skin protection a s discussed in class to enter the creek. Flat Bank is used by an abundance of wildlife so E. coli counts
have occasionally been high. Drinking the water is definitely a bad idea. Showering after working in the creek is
strongly recommended. Any cuts, scratches or abrasions should be washed and disinfected as soon as possible. I will
have clean water, disinfectant and band aids available on site but that will be temporary field treatment. You will
want to repeat the process at home later.
Mathematic measures of species diversity can be used to comparatively evaluate ecosystem health. Investigators
obtain samples from different ecosystems for comparison or from the same ecosystem at different points in time.
Changes in diversity can be used as indictors of ecosystem health since high species diversity is interpreted as high
health. There are many diversity indices and as mathematic models they all have their strengths and weaknesses. The
Shannon Diversity Index (Shannon-Weaver, Shannon-Wiener) is very commonly used. Shannon, a famous World War II
code breaker, developed his index in the early 1950’s to evaluate information transferred by telephone lines. His index
quickly found ecological applications. It includes the two most important components of diversity, number of species
and the population evenness between those species. An important note: the actual species present have no bearing on
calculated species diversity! It doesn’t matter whether they’re cockroaches or koala bears; it’s all about the numbers.
Theoretically then, you can compare species diversity between completely different communities.
We will continue our investigation of Flat Bank Creek by determining its current fish species diversity. True species
richness and evenness values are challenging to determine for difficult to sample communities like fish. Sampling effort,
which includes the skill of the sampling team and number of capture attempts will influence results. Additionally,
sampling method influences results because different methods are more efficient at capturing different species. Some
species are difficult to capture with any method and remain uncounted even though they are an important community
member, usually apex predators. As sampling continues in a community the chance of encountering new species
decreases as most species have already been collected. Only rare and difficult to capture species remain. This
“discovery curve” can be plotted (total species collected by number of samples) to get an estimate of species richness
without catching all of them. This does not help with relative abundance though so species richness values gained by
discovery curves cannot be used in calculating species diversity. Discovery curve data can be used as a stand-alone
summary statistic that helps paint a picture of the community with more dimensionality when used with diversity
indices. These challenges make precise evaluations of species diversity difficult but much like determining stock
assessment by mark-recapture studies rough but accurate measures have value both in understanding community
structure and for making management decisions.
As amateur ichthyologists with very little knowledge of fish species in the creek you will run into the problem of
having different sampling teams identifying species consistently. I will be available and shuttling between teams to help
you with identification but I won’t always be with your team when you need identification help. The best way to do this
is by using a dedicated shore bound photographer. Before each seine haul the photographer takes a picture of an ID
sheet, Sample 1 Barry’s Team, for example. Then your photographer takes a QUALITY photo of each species collected.
Make sure that the sequence of photos match the sequence of abundance data in your records. That isn’t that
important for diversity calculations but it reflects the fish community so you want it to be as accurate as possible.
Another shore bound team member can collect relative abundance data for each sample. I will post photos or links to
photos of all species collected. You will be able to identify any species that we miss in the field later from these photos.
Two additional shore bound members can collect environmental data: water and air temperature, dissolved oxygen, pH
and turbidity. Remaining team members can help with sorting fish from the net.
Once you have your data you can calculate species richness using a discovery curve and species diversity using
Shannon’s Index. Calculate species diversity using the Shannon index (H’) with the following equations.
ni
pi = N
S
H' = –
 pi (ln (pi))
i=1
(equation 1)
"i" is each species
ni = number of individuals of species "i"
N = total number of individuals of all species
pi = relative abundance of species "i" (see equation 1)
S = total number of species
H' = The Shannon Diversity Index (see equation 2)
(equation 2)