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Exams. Preview – second half. Today: Foraging and Diets Next Week: Exotics and 2 nd half of fish ids plus quiz on Moyle and Light 1996 plus first draft of papers are DUE for P.Rev . Spring Breek 1 st week back: Bioenergetics Lab Peer review due

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slide2

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

why collect diets
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
what can parameters about a fish can we measure that relate to feeding

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?

slide6

Discussion

What parameters about a fish can we measure that relate to feeding?

Lists:

slide7

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

slide8

Discussion

What environmental factors influence fish feeding?

Lists:

Lists:

slide9

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

slide10

Discussion

What biotic factors influence fish feeding

Lists:

Lists:

slide11

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

example

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

holling s disc equation
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.

holling s disc equation1
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.

holling s observations
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

functional response
Functional Response

Type I passive predators

functional response1
Functional Response

Type II Handling time limited

functional response2
Functional Response

Type III Learned response

functional response3
Functional Response

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

numerical response
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")

numerical response1
Numerical Response

+

=

Increased Reproduction

+

=

numerical response2
Numerical Response
  • Aggregational Response
numerical response3
Numerical Response
  • Hollings equation relates diet information to energy and time spent foraging
  • More specific physiological energetic needs can be described using Bioenergetics
organisms are not chemicals

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

slide26

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.

collecting fish
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

collecting diets
Collecting Diets
  • Collect diets by:

1. Gastric Lavage

2. Stomach Removal

-Remember fish size, population density

experimental strategies
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

identifying diet items
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
enumerating the diet
Enumerating the Diet
  • The “Big 3”

1. Frequency of occurrence

2. % composition by number

3. % composition by weight

  • Diet Indicies
frequency of occurrence
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
composition by number
% 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%

composition by number1
% 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

composition by weight
% 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
diet indicies
Diet Indicies
  • Index of Relative Importance (IRI)

IRI = (% number + % weight)(FO)

  • Consistency
  • Overlap
  • Selectivity

*all of these are arbitrary units!

slide38

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

slide39

Trichoptera (Caddisfly)

Ephemeroptera(Mayfly)