1. Why Study Diets??

2. The Life of a Diet Sample Background to foraging Why is it important to analyze diets? Collecting diet samples Identifying diet components Quantitative description of diet samples

3. Holling’s Disc Equation C.S. “Buzz” Holling Holling, C. S. 1959. The components of predation as revealed by a study of small mammal predation of the European pine sawfly. Canadian Entomologist 91:293–320. Rate of Energy Gained = (λe – s)/(1 +λh) λ = rate of encounter with diet item e = energy gained per encounter s = cost of search per unit time h = average handling time Search Encounter Pursuit Capture Handling

4. Predation rates ↑ with ↑ prey densities happens due to 2 effects: 1.Functional response by predator -Type 1 -Type 2 -Type 3 2.Numerical response by predator -Reproduction -Aggregation Holling’s Observations

5. Functional Response Type I passive predators

6. Functional Response Type II Handling time limited

7. Functional Response Type III Learned response

8. Functional Response Functional response = same # of predators in area; behavioral change

9. Numerical Response ↑ predation due to ↑ predators Two Potential Mechanisms 1. ↑ prey density = ↑ consumption = ↑ predator reproduction = ↑ rate of consumption (↑ reproduction) 2. Attraction of predators to prey aggregations ("aggregational response")

10. Numerical Response + + = = Increased Reproduction

11. Aggregational Response Numerical Response

12. Hollings equation relates diet information to energy and time spent foraging More specific physiological energetic needs can be described using Bioenergetics Numerical Response

13. Bioenergetics (Respiration, Digestion, Activity) + (Excretion) + } (Reproduction, Δ Growth) Consumption = From Kitchell et al. 1977

14. Why Collect Diets? 1.Fish’s energy: growth and reproduction 2.Aquaculture: assess stock foraging 3.Resource managers: stocking, habitat assessment 4.Environment: indicate change in habitat, population densities

15. Environmental Change An example from my research

16. Little Rock Lake Whole Lake Manipulation

17. Little Rock Lake Results

18. Collecting Fish Active sampling techniques (seine, short term gill nets, angling, shocking) Beware of biases -postcapture digestion -regurgitation (stressed fish) -atypical foraging behavior in traps Long term gill net, fyke net, minnow trap

19. Collecting Diets Collect diets by: 1. Gastric Lavage 2. Stomach Removal -Remember fish size, population density

20. Experimental Strategies 1.Diel patterns (predators and prey) 2.Seasonal patterns (predators and prey) 3.Fish size/gender 4.Digestion rates -slow = over represented (mouse bones) -fast = under represented (earthworms) -correct for these by determining gut passage time for each diet item

21. Identifying Diet Items Categorize diet items What is the question you are asking? -More specific taxonomic keying is more information but could be wasted time Broken items: count body parts (# of heads) Sub-sample small diet items

22. Enumerating the Diet The “Big 3” 1. Frequency of occurrence 2. % composition by number 3. % composition by weight Diet Indicies

23. Frequency of Occurrence Percent of individual diets that contain one or more of a specific diet item Presence/absence indicator - Example: 12/15 walleye diets contain crayfish, frequency of occurrence =.8 = 80% High frequency of occurrence ≠ energetically important, rather selectivity of a group of individuals

24. % Composition by Number The number of an individual diet item relative to the total number of items in the diet/diets -Example 1: Brown trout #1: Amphipod = 3 Fantail darter = 1 Amphipod % composition by number = ¾ =.75 = 75%

25. % Composition by Number Brown trout #1Brown trout #2Brown trout #3 -Example 2: Sampling event #1: # midge larvae = 3 # total diet items = 11 Midge % composition by number (for this sampling event) = 3/11 =.27 = 27%

26. Weight of one type of diet item relative to the total diet weight 1.Wet weight: quicker to obtain 2.Dry weight: more energetically informative Can be calculated similarly to examples shown for % composition by number % Composition by Weight

27. Diet Indicies Index of Relative Importance (IRI) IRI = (% number + % weight)(FO) Consistency Overlap Selectivity *all of these are arbitrary units!

28. Isopod Diptera Fantail Darter Amphipod