Limnology
Lab Reports
Biology
3371; Dr. Dirnberger; Kennesaw State University |
Lab
#2 - Trophic dynamics
Your report should include methods
(brief), results and
discussion sections (also include the
this page in place of an introduction).
Be sure to focus your
discussion
addressing the central question, hypotheses, and predictions.
Observations:
Nutrient loading has long been know to
affect
primary productivity and phytoplankton standing crop in aquatic systems
(a "bottom-up" effect). Ecologist studying interactions between trophic
levels have suggested that trophic levels higher than phytoplankton
could
also effect phytoplankton. For example, more
piscivorous fish would decrease planktivorous fish, which in turn would
increase zooplankton and thereby decrease phytoplankton (a "top-down"
effect
known as the "trophic cascade hypothesis"). Historical data on
Allatoona
indicates that productivity and phytoplankton vary dramatically over
the
lake, potentially providing a test of the top-down versus bottom-up
hypotheses.
Central Question:
Which hypothesis best explains spatial
variation in chlorophyll concentration
within Lake Allatoona?
Hypothesis:
1) Spatial patterns chlorophyll
concentration over 4 sites is a function of primary productivity
resulting from the distribution of nutrients.
2) Spatial patterns chlorophyll
concentration over 4 sites is a function of grazing resulting from the
distribution of zooplankton.
Also consider that both or neither of the
above hypotheses could be supported by our data.
Predictions:
You must come up with predictions for
this
lab. We are not measuring fish abundance in this lab so we can test
only
the next trophic level above phytoplankton when examining the top-down
hypothesis (i.e. zooplankton). You should decide which measures are
best
to use for your comparisons (e.g. productivity in m2 or m3,
zooplankton
in individuals/m2 or individuals/m3, relative
abundance
of small and large bodied zooplankton, phytoplankton size, nutrient
type,
etc.) and justify your choices in your discussion.
When you write your report, remember to
try to use more than one angle (i.e. different aspects of the data set)
to
support your argument.
Click
here for help on how to crunch the numbers for this lab
Use at least one of the following
references
(or others) to support your point:
Brett M.T. and Goldman
C.R.
1996. A meta-analysis of the freshwater trophic cascade. Proc.
Natl.
Acad. Sci. 93:7723-7726.
http://www.pnas.org/cgi/reprint/93/15/7723.pdf
Drenner, R, W, and K.D.
Hambright.
2002. PISCIVORES, TROPHIC CASCADES AND LAKE MANAGEMENT.
http://faculty-staff.ou.edu/H/Karl.D.Hambright-1/Hambright_Reprints/Drenner&Hambright'02-TSWJ.pdf