1. Background to Foraging

2. C.S. Buzz Holling aka "the man" Functional response was developed based on a 1959 paper These eating These

3. Sometimes called the disk equation cause this is how he originally developed the model

4. Holling Processes of Predation –Search –Encounter –Pursuit –Capture –Handling

5. Holling’s Disk Equation 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 Energy gained per time invested per item

6. Functional Response Energy gained per time invested per item

7. Functional Response Type I passive predators (spiders) Type II most typical: predator saturation (Daphnia). Type III Learning – occurs in predators which increase their search activity with increasing prey density (bass/goby)

8. Numerical Response Predators increase in abundance as prey density increases. Two Potential Mechanisms 1. Increased rate of predator reproduction when prey are abundant 2. Attraction of predators to prey aggregations ("aggregational response")

9. Diets Goals – Explained in lecture, applied in lab Why are diets important? How do we get diet data? What do we do with diet data?

10. Why are diets important? What information do they tell us? What questions do they answer? Fish’s view –Source of energy (bioen) Managers view –Stocking Aquaculture –Nutrients As an indicator of environmental change –Nutrient loading, change in pop density

11. How do we get diets? Fish collection: –what should we be cautious of? Sources of error/ bias due to methods selection? Regurgitation Post capture digestion Alteration in behavior due to capture –Traps Did you use bait?

12. Sampling strategies Diel effects Seasonal effects –Both of the above affect predator and prey behavior Fish size –Ontogenetic shifts? What age/size class is your diet representing? Things to consider/keep in mind

13. Sampling strategies cont… Digestion rates –Too fast - protozoans Under representation in diets Could be determined by watching behavior in a tank –Too slow Over representation in diets Could be solved by determining gut passage times Do stomach contents accurately depict the fish’s diet?

14. Removal of gut contents Puking Dissection

15. Identification of Diet Components Crushed/digested organism –Find characteristic structure for each organism Level of identification depends on the research question –Higher resolution=greater time investment

16. Quantitative diet description Frequency of Occurrence Percent composition by number Percent composition by weight

17. Frequency occurrence What proportion of the diets contained one or more of a given food type Describes presence absence –Example: 18/22 bluegill contain chironomid, frequency of occurrence =.82 or 82% lower frequency occurrence = selective or opportunistic feeding

18. Frequency of occurrence Drawbacks High frequency of occurrence may not mean this diet item is of nutritional importance, only that it is consumed with some regularity Example: benthic fish and algae

19. Percent Composition by number Number of food items in a group relative to total number of diet items consumed (%) Potential for fragmentation, count a characteristic part of prey item –Dragonflies have four wings, so 4 wings = 1 dragonfly Percent composition by number + estimates of feeding rates = effects of predators on prey

20. Percent Composition by Weight Weight of each type as a percentage of the total weight of the diet –Wet and dry weights can be used Dry are more precise and offer more information about nutritional value Remember some component of the diets have already been digested!!!! begins to identify food importance in fish nutrition

21. Further Analysis and Interpretation Selectivity indices: Do fish feed at random or preferentially? Diet overlap indices

22. Laboratory Groups of two/three “work up” 1-2 diets –Fill out data sheet including weight of each diet item Combine data with other groups Analyze the diets –Freq occ, % comp by number, % comp by weight

23. Amphipods

24. Isopod