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 predator
Grazer
Parasites
parasitoids
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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
 Males that arrive earlier 
more successful at finding
mates
Proportion of males of male pied
flycatchers infected amongst
groups of migrants arriving in
Finland at different times
 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
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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 cycle
Assume: 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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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
(c) 2001 by W. H. Freeman and
Company
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.
 By December 7th
 Give me your weekly diet
 A one to two paragraph
reflection on your eating
habits
 Include as much locationalinformation about the
product that you know
 A one to two paragraph
reflection on the
relationship between what
you eat and ecology
 Be detailed. A “salad” is
not enough.
 Think about what you are
eating
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