Exams

1. Exams

2. Preview – second half Today: Foraging and Diets Next Week: Exotics and 2nd half of fish ids plus quiz on Moyle and Light 1996 plus first draft of papers are DUE for P.Rev. Spring Breek 1st week back: Bioenergetics Lab Peer review due Quiz on bioenergetics paper (Kitchell 1977) 2nd week back: Kitchell’s Cabin field trip

3. Foraging and Diets

4. Why Collect Diets? • Food webs are a big part of ecology • Fish’s energy: growth and reproduction • Aquaculture: assess stock foraging • Resource managers: stocking, habitat assessment • Environment: indicate change in habitat, population densities

5. Group discussion questions What environmental (abiotic) factors influence fish feeding? What can parameters about a fish can we measure that relate to feeding? What biotic factors influence fish feeding?

6. Discussion What parameters about a fish can we measure that relate to feeding? Lists:

7. Discussion What parameters about a fish can we measure that relate to feeding? Lists: -At distance react to food -measure stomach contents (counts, weight, volumetric) -Gape -how long it takes for a fish to swallow prey -rates, number per time - attempts per diet item - angle of attack - are there other fish around

8. Discussion What environmental factors influence fish feeding? Lists: Lists:

9. Discussion What environmental factors influence fish feeding? Lists: pH temp Time of day season light level DO Substrate Fishing pressure Lists: pollution reproductive cycle nest guarding Flow velocity turbidity Physical Habitat Salinity

10. Discussion What biotic factors influence fish feeding Lists: Lists:

11. Discussion What biotic factors influence fish feeding Lists: Prey abundance Size of prey Size of predator Competition Gill rakers, mouth placement, and other morphology Indirect competition (common predator) Level of production Specialist or generalist or omnivore Experience Maturity Gender Vegetation Lists: Community Composition

12. I think the darker the water gets the harder it will be to find food, and the relationship should be linear! General factor: Turbidity Assumptions?: For all visual feeders Example: You are both crazy, think about when it gets foggy, you can't see crap, little increases in turbidity have a way bigger effect, but then once it gets cloudy fish just use other senses! No way, fish don't care if it gets a little muddy, up to a point, then they can't see anything! Distance till fish reacts to prey Distance till fish sees prey...huh? Water Clarity or Turbidity

13. Holling’s Disc Equation • Rate of Energy Gained = (λe – s)/(1 +λh) 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.

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

15. Holling’s Disc 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 C.S. “Buzz” Holling • Search • Encounter • Pursuit • Capture • Handling 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.

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

17. Functional Response Type I passive predators

18. Functional Response Type II Handling time limited

19. Functional Response Type III Learned response

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

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

22. Numerical Response + = Increased Reproduction + =

23. Numerical Response • Aggregational Response

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

25. Prey eaten Prey eaten Prey density Prey density Organisms are not chemicals! Ecological interactions are highly organized Reaction vat model Foraging arena model Prey behavior limits rate Predator handling limits rate Big effects from small changes in space/time scale Slide from Villy Christensen, IncoFish Workshop 2006

26. Foraging Arena Theory “There is a horrific linkage between getting food and being food, and this creates a severe trade-off relationship” – Walters and Martell Chalk board! Hiding places – under a rock, water too shallow for preds, dark profundal zone, in a school – but low food Arena – high food, little protection.

27. How we do it

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

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

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

31. 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

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

33. 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

34. % 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%

35. % Composition by Number Brown trout #1 Brown trout #2 Brown trout #3 -Example 2: How to calculate WRONG: 3/11 midges = 0.272 RIGHT: (0.25+0.25+0.33)/3 = 0.276

36. % Composition by Weight • 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

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

38. How does a fish decide what to eat? Electivity: what's the proportion of item an in the environment compared to the proportion in the stomach? If an items is rare in the environment but prevalent in diets, it is selected for. How do we measure that? Must also measure invertebrates

39. Trichoptera (Caddisfly) Ephemeroptera(Mayfly)

40. Non-biting Midges Black Flies Crane Flies Diptera (Flies)

41. Amphipods

42. Isopod