Download Lecture 8

10/23/2015
Bio122
Lecture 8 (10/15/15)
I. Predation & Herbivory (con’t)
A. Prey Defenses
B. Induced defenses
C. Co-evolution
D. Effects of predation on communities
II. Parasitism (Ch 14)
A. Symbiosis
1. Definition
2. Types (parasitism, mutualism, commensalism)
B. How common are parasites?
C. Parasitism vs. predation
1. Higher reproductive rates
2. Don’t usually kill host
3. Specialized to few hosts
4. Can live inside or on host
D. Parasite defenses
1. Immune
2. Biochemical
3. Mutualists
E. Host counter-defenses & co-evolution
F. Ecological effects of parasites
1. Survivorship
2. Extinction
3. Geographic range
4. Growth
5. Reproduction
6. Population cycles
7. Species interactions
8. Community structure
III.
Commensalism (Ch 15)
Costs to defense
• Trade off between producing defensive
structures or substances and growing and
reproducing
– (and immune responses—pathogen defense may
come at a cost to predator defense)
• Differential allocation of defenses (based on
the vulnerability of particular tissues or
stages)
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Plant Defenses Against Herbivory
Plant Defenses Against Herbivory
Compensation
Consumption
can be
beneficial
• Removal of older canopy leaves
may decrease shading on younger
leaves, increasing photosynthesis
• Following herbivory, plants often:
– Utilize stored reserves
– Alter the distribution of newly
synthesized material
Secondary plant substances
• By products of primary
metabolic pathways in
plants—not directly
involved in growth or
photosynthesis
• Ex:
(AKA negative allelopathy--biochemicals that influence the growth,
survival, and reproduction of other organisms)
– Chemical flavor of spices
(clove, nutmeg, cinnamon)
– Terpenoids (peppermint oil,
catnip)
– Alkaloids (nicotine,
morphine, cocaine,
caffeine, cannabis,
hallucinogenic cacti,
chemotherapeutic plants)
– Many others!
Field gentian (Gentianella campestris)
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periwinkle plant
(catharanthus rosea)
AND
taxanes made from
the bark of the Pacific
Yew tree (taxus)
What other defenses does this cactus have?
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Bryozoan predators
Co-Evolution
(Evolutionary Arms Race)
AKA: The Red Queen Hypothesis
"Well, in our country," said Alice, still panting a little,
"you'd generally get to somewhere else — if you run
very fast for a long time, as we've been doing."
"A slow sort of country!" said the Queen. "Now, here,
you see, it takes all the running you can do, to keep in
the same place. If you want to get somewhere else,
you must run at least twice as fast as that!"
Inducible defense -> spines
Inferring an arms race from fossils
Co-evolution
Shells of fossil gastropods
Difficult to infer coadaptation from fossils because we can’t observe interactions
• Some herbivores evolve to produce enzymes
to detoxify or behavior to avoid toxins or
defense structures
But we can use characteristics that reflect predator-prey interactions
Milkweed contains
alkaloids and latex
and hair on the leaves
to deter herbivores
Monarchs and other
insects (beetles and
moths) feed on milkweed
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Effects on Communities
When a shell is repaired
following a failed predation
attempt, it leaves a clear
pattern evident in fossils
Gastropods “cement”
themselves to the substrate
as an adaptation against
predators
Gastropods with thickened
or narrowed apertures are
better able to survive
predation events
The incidence of shell repair
increases through time,
suggesting predation is
becoming more intense
The incidence of mobile
gastropods that lack a
means of attachment
decreases over time
The incidence of thickened
or narrowed apertures
increases over time
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Effects on Communities
Direct = predator directly decrease abundance of a species
Direct = predator directly decrease abundance of a species
Indirect = predator decreases abundance of a species which affects
the abundance of one or more other species
 Cascading effects
Indirect = predator decreases abundance of a species which affects
the abundance of one or more other species
 Cascading effects
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Interspecific Interactions
Philip Henry Goss (Victorian naturalist)
(1810-1888)
Simple Classification of Intimate Interspecifc Interactions
Interaction
Type
Guest
(Symbiont)
Host
Commensalism
+
0
Mutualism
+
+
Parasitism
+
-
How common are parasites?
• Parasites ≥ 50% of biodiversity
“There is nothing funny in the thought that
even man, who was made in the image of God,
bears about in his vital organs various forms of
loathsome creatures, which riot on his fluids
and consume even the very substance of his tissues.”
Typical consumer-resource interactions
• Consumers benefit (+) and resources don’t (-)
good situation (+)
Parasites
Free living
bad situation (-)
Figure 14.10 Coevolution of the European Rabbit and the Myxoma Virus (Part 1)
Most species are vulnerable to >1 parasite
species (but parasites are highly specialized)
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Figure 14.10 Coevolution of the European Rabbit and the Myxoma Virus (Part 2)
Parasitism can reduce host survivorship
Figure 14.15 Parasites Can Reduce Their Host’s Geographic Range
Enslaver Parasites: A Case Study
Some parasites can alter the behavior of
their host in order to complete their life
cycles.
Parasitism can lower host growth rates
Parasites can decrease host’s reproduction
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Figure 14.17 Parasites Can Alter the Outcome of Competition
Parasites can influence host population cycles
Parasites can alter behavior
Ex - Killifish become more conspicuous
Parasites can alter predator-prey interactions
Conspicuous behaviors
30
25
2
20
15
10
5
0
0
500
1000
1500
2000
Intensity of infection
2500
Lafferty and Morris 1996
Ecology
Figure 14.18 Parasites Can Alter the Physical Environment
Parasites can alter predator-prey interactions:
Ex – infected killifish become more vulnerable
to predators
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