Diet Analysis Flashcards
Key idea with food pyramid:
Decreasing Biomass with Increasing Trophic Level
Key concepts associated with the food pyramid:
Not all of the biomass (organisms) at a trophic level are consumed
Metabolism (respiration) reduces available biomass (energy)
Not all of a consumed prey is digested (incorporated into next trophic level)
More efficient to eat at base of food web (Transfer efficiency)
Transfer Efficiency
the proportion of the prey production taken by predators
What is a good transfer efficiency?
25%; most fishes ~10 – 15%
What is the old rule of thumb for transfer efficiency?
Old rule of thumb is 10% per trophic level
Somatic Growth
The mechanism and results of fish adding weight
At the individual level: eating more food
Results in an increase in biomass of the stock
Links size and age
Sampling Considerations
Time of day
Size range of individuals
Areal coverage (different habitats)
Seasonal variation
Annual (or longer) variation
What is the appropriate sample size?
How does one select “representative” samples?
Gut Content Analysis considerations
Identification of prey
Size estimation of prey
Potential biases
Identification of prey includes:
Many keys based on “parts”
DNA barcoding
Size estimation of prey includes:
Relationship of the size of parts to the whole organism
Potential biases to consider:
Digestion rates
All quantitative analysis are ____ and look at___
biased
Percentage by number (%N)
Percentage by weight or volume (%W)
Frequency of occurrence (%F)
Index of relative importance (IRI)
IRI = %F * (%W + %N)
Fullness Index parameters
m = number of stomachs in month
Wi = total weight of stomach contents
Ei = eviscerated weight
Stable Isotope Analysis
An “integrated” perspective on trophic relationships
Different trophic levels and prey types with different stable isotope signatures
Assimilated into predator’s tissues
