Administrational note first

Received from: Antoine, Alaa (El Chiekh Ali), Richard, Mireille, Angie. The rest?

All thus far: want quizzes, and one or two midterm exams

Remember: 12% of quizzes done; at least one exam (30%)28

Not acceptable for evaluation: attendance, comments

Paper Tell me: your hypothesis. Your timeline. Deadline: one week

from today.

Project Tell me: your hypothesis. Your methodology. Your timeline.

Deadline: one week from today.

Final syllabus will be signed by both of us

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example 12% - done (quizzes)

30% - Final exam

30% - research paper

18% - 5 quizzes (3.6 % each)

10% - homework

Total – 100%

Research paper Due in one week: Hypothesis &

timeline Hypothesis: Climate change

will result in decreased productivity for olive trees in Lebanon

Methodology [how do you plan on answering your question? What readings? What sub questions?] – 5% - due…?

Draft: - 10% - due…? Final: 15% - due…?

Signed: student: _______________________Prof: _______________________

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Documentaries – must see

Thursday December 2nd, 12.30 to 2.00 pm: Microcosmos

Thursday December 9th, 12.30 to 2.00 pm: Food, Inc.

Location for both: Hariri Auditorium

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Remember:

True predatorGrazerParasitesparasitoids

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Prey fitness and abundance Fundamental similarity between (true)

predators, grazers, and parasites is…?

… each reduces either the fecundity or chances of survival of individual prey and may therefore reduce prey abundance.

Studied the Relative growth rates (changes in height) of a # of different clones of sand-dune willow – subjected to herbivory at different intensities, in 1990 and 1991. 1991: also drought -> greater mortality

Studied pied flycatcher

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Prey fitness and abundance

Proportion of males of male pied flycatchers infected amongst groups of migrants arriving in Finland at different times

Males that arrive earlier more successful at finding mates

Later arrivals disproportionately infected with a blood parasite

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Prey – Predator

Need to compare prey populations in the presence and absence of predators

Rely on observation and experiments (both artificial and natural experiments)

What is the impact of the Indian meal moth with and without a parasitoid wasp? – wasp reduced moth abundance to 1/10th

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Prey-Predator

Predators can reduce prey abundance – as we have seen

But they do not necessarily reduce prey abundance

There are subtleties of predation – like what?

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More than just: prey dies, predator

reproduces Interactions with other factors

Grazers and parasites (in particular) make prey more vulnerable to other form of mortality Interaction between competition and parasitism

Infection or grazing more susceptible to predation Red grouse: birds killed by predators in the

spring and summer had more gut nematode parasite

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More than just: prey dies, predator

reproduces Compensation and defense by individual

prey Individual plants can compensate in a variety

of ways for the effects of herbivory Remove leaves other leaves have more sun

more photosynthesis Herbivory attacks plants use stored reserves

– shifting root: shoot ratio Or compensatory regrowth of defoliated plants

when buds are stimulated to develop Or plants can increase their production of

defensive structures or chemicals

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What is the cost/benefit?

Snails grazed on the brown seaweed for a few weeks substantially increased [ ] of phlorotannins reduced snail grazing. [clipping the plants did not have the same effect. Why?] End result: snails eat less. Plants have less eaten. At a cost.

Lifetime fitness of wild radish plants Grazed by caterpillars response induced

protected plants from other herbivores; increased fitness > control

Leaf-damage controls [equivalent amount of biomass removed using scissors] plants had 38% lower fitness than overall controls

Overall control [undamaged]

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What about the populations – not just

the individual From individual prey to prey populations

General rule: predators are harmful to individual prey

What are the effects of predation on a population of prey?! - not always so predictable Impacted / influenced by food availability.

When food is tight, and competition is intense, predation may…

…relieve competitive pressures and allow individuals to survive who may not have been able to 13

True predators

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How do predators forage?

We’ve talked a bit about what happens after a predator finds a prey

What happens to establish that contact?

Different types of foraging

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Different types of foraging Active predators seeking … Sit and wait predators Direct parasite transmission Transmission between free-living stages of a parasite

shed by a host and new uninfected hosts

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Foraging behavior Where to eat?

How to balance risk of predation?

How long to remain in one location?

What about other competing predators?

And what to eat?

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Optimal diet model Optimal diet model:

Any predator will include the single most profitable type of prey in its diet [highest net rate of energy intake] – but then what? How to choose?

Predators with handling times that are typically short compared to their search times should be generalists (broad diet)

Predators with handling times are long relative to their search times should be specialist.

Other things being equal: predator should have a broader diet in an unproductive environment than in a productive environment

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Predator-Prey interactions: a

tendency to cycleAssume: large population of prey; lotka-

volterra model

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Factors Changing Equilibrium

Isoclines The prey isocline increases (r/c) if:

Reproductive rate of the prey (r) increases or capture efficiency of predators (c) decreases, or both: the prey population would be able to support the

burden of a larger predator population

The predator isocline (d/ac) increases if: Death rate (d) increases and either

reproductive efficiency of predators (a) or c decreases: more prey would be required to support the

predator population

Predator-prey cycles in practice

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(c) 2001 by W. H. Freeman and Company

The Functional Response

A more realistic description of predator behavior incorporates alternative functional responses type I response: rate of consumption per

predator is proportional to prey density (no satiation)

type II response: number of prey consumed per predator increases rapidly, then plateaus with increasing prey density

type III response: like type II, except predator response to prey is depressed at low prey density

Disease dynamics and cycles

Cycles are also apparent in dynamics of many parasites

Start with basic reproductive rate

Transmission threshold – for disease to spread: R0 > 1

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Start 0 No predator lives alone

Predators are affected by other predators Competitive reduction in the consumption

rate per individual as predator density increases Mutual interference Increased rate of emigration Prey may hide more

Impacts: fecundity. Growth. Mortality. Of individual predators. Intensifies as predator density increases.

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Crowding with prey too

Prey too are also subject to crowding

Prey crowding: prevents their abundance from reaching as high as level impacts predator abundance

Damping effect on any predator-prey cycle. What does that mean?

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Patches.

Metapopulations. Remember them?

Catch: differences between the patches tend to stabilize the interaction, to dampen any cycles that might exist. Why?

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Predators and prey in patches

Predatory mite (Typhlodromus occidentalis) feeds on a herbivorous mite (Eotetranychus sexmaculatus) which feeds on oranges interspersed amongst rubber balls in a tray

Why?

To create ‘patches’

First introduced a prey population with 20 females per tray, then introduced 2 female predators

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Without its predator, the mites stabilized their pop

With the predator, the predator increased, killed all the prey, then died

Predator-prey dynamics were unstable

What about when patchy?

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In each experimental tray, 4 oranges, half exposed, are distributed at random among the 40 positions in the tray. Other positions are occupied by rubber ball.

Each orange is wrapped with paper and its edges sealed with wax. The exposed area has been divided into numbered sections to facilitate counting the mites.

Then further modified to facilitate dispersal of prey and not predators

Each tray has 120 possible food positions

Shading represents relative density of six-spotted mites at each position…

…and dots indicate presence of predatory mites

A spatial mosaic of habitats allows predators and prey to coexist

Predator-prey patches

Natural population example: Starfish eat mussels Mussels eat planktonic larvae Planktonic larvae continuously colonizing new

areas Clumps of mussels that are heavily preyed

upon – get dislodged by heavy seas – mussels die

End result: same mosaic

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Take home message?

Predator-prey dynamics can take a wide variety of forms

We can understand this variety by seeing it as a reflection of the way in which different aspects of predator-prey interactions combine to play out variations of an underlying theme

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Predation and community structure

Predator-mediated coexistence When predation promotes the coexistence of

species that might otherwise exclude one another Eurasian pygmy owls – only on 4 islands Five islands w/o predatory owl: 1 species (coal tit) w/ owl: coal tit had two larger tit species (willow tit

and crested tit) Why? Coal tit is better competitor; but 2 larger

species less affected by predation from owl; owl reduces the competitive dominance

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Levels of predation

Zebu cattle: no-grazing control and 4 grazing intensities in sites in Ethiopia More species occurred at intermediate levels of

razing then where there was no grazing or heavier grazing

As a generalization: selective predation should favor an increase in species number in a community as long as the preferred prey are competitively dominant, although species numbers may also be low at very high predation pressures

balance

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Quizzes – 4 left

December 1 – chapters 5 and 7

December 10 or 15

January 5

January 19

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homework

http://www.eatinganimals.com/

“Animal agriculture makes a 40% greater contribution to global warming than all transportation in the world combined; it is the number one cause of climate change.”

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Food…Homework

In one week (7 days), write down everything that you consume, including cigarettes, gum, etc.

Include as much locational-information about the product that you know

Be detailed. A “salad” is not enough.

Think about what you are eating

By December 7th

Give me your weekly diet

A one to two paragraph reflection on your eating habits

A one to two paragraph reflection on the relationship between what you eat and ecology

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