Lab 2 Paper: Diet Tracing in Ecology

Question 1

The observation of the stomach/gut contents of predators has an extensive history within the field
of dietary tracing. Imagine we are observing the stomach/gut contents of a chinook salmon.
Please provide one advantage of visual observations over other methods and one disadvantage
with some justification.

Answer 1

Provide insight to the variation over the daily or weekly feeding habits of an animal, not seen with no robust longer-term analyses. It is also the only method that can consistently identify different life stages of prey, because you can visually see them

This means that it is not good for long term time scale studies. It is biased towards material that doesn’t get digested. What is left in stomach is all you can see

Question 2

There are five light stable isotopes typically used in research (CHNOS). What do each of these
stable isotopes reveal about diets?

Answer 2

C consumption of different primary producers’ – C3 or C4 plants or phytoplankton

N can be used for this same purpose as well, producers lacking N can be identified

S can be used to distinguish between marine and freshwater or benthic vs pelagic prey

H can be used for contribution of terrestrial vs aquatic prey

Little is known about the use of O as a trophic marker

Question 3

How might the effectiveness of a diet tracing method be tested?

Answer 3

With DNA sampling, you can first conduct a test on a mock community where you know the output. And test the effectiveness of what it identifies in the sample.

Experimentally feeding organisms mono-culture diets and testing the ability to detect the amino acids present in the organism

Overall, they suggest conducting many more experiments where known diets, isotopes, molecules are fed and then test the accuracy of all methods on the given organims

Question 4

Suppose we are doing a study on the diets of yellowtail rockfish in Howe Sound. We are
conducting visual inspections of the gastrovascular cavity as well as sequencing the DNA to get
a broad overview of the diet. When we encounter visual northern anchovy remains, we get DNA
readings for several groups of marine diatoms. What is the most reasonable interpretation of this
result?

Answer 4

The anchovy is visually detected in the gastrovascular cavity so we know that it is part of the diet.

The DNA may not have picked up the anchovy due to using primers that are not optimal for anchovy detection

The detection of diatoms in the diet make perfect sense, given that anchovy have a diet mainly in plankton, the DNA is being detected in the diet of the anchovy which the rockfish has now eaten