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CHAPTER 10
Community Ecology
1
Learning Outcome
1. Describe the predation, cannibalism and
mutualism
2. Explain the types of defense mechanism in
carnivore relationship
3. Distinguish between the functional types
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What is Predation?
 The transfer of energy and nutrients
in community.
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Example of Predation
 1. Herbivory
 2. Carnivory
 3. Parasitism
 Predator numbers are dependent on prey
and predator may regulate number of prey
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Predation (Fitness)
 Fitness of predator
– is the ability to capture the prey
 Fitness of prey
- is the ability to elude or hide from
predator
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Predation- Mechanism
Plant Herbivore System



Defoliation and consumption of fruits/seeds
Defoliation – destruction of plant tissue (leaf, bark,
stem, sap, roots)
Feeding on seeds can be detrimental but it helps
their dispersal (seed) mostly via feces
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Predation- Effect on Prey (Plant) Fitness
 The effects of the predation are
strong at the juvenile stages of
plant development
 Grazers concentrate on young
leaves and thus remove
nutrients
 Loss of nutrients – young leaves
and meristems are dependent
structures – get nutrients from
reserves in roots and other
tissue
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Predation- Plant response after defoliation

Defoliation and subsequent growth alter the trees
physiologically
1.
2.
3.
4.
Can cause changes in hormonal growth regulators that
control bud dormancy
Causes increased attack by insects and disease (plant is not
established yet)
Reduces resources available to reproduction (loss of nutrient
and mature cell)
In some instances in coniferous trees defoliation causes
death because these trees do not have physiological traits
that allows them to recover
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Plant response after defoliation
Example 1 (-ve):
 Plant response after attack by predator
- Plant attacked by a moth (Alsophila
pometaria)
- Leaves are smaller and canopy area is
reduced as much as 30 – 60%
 Some trees end up with only 20-40% of
original leaf area
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Example 2 (-ve):
 Aphids that suck sap can
cause reduction in growth
rate and biomass by 25%
Example 3 (+ve):
 Defoliation can be beneficial
for some grasses where
grazing
stimulates
production
by
removing
older tissue that have low
rate of photosynthesis –
exposes younger leaves to
light
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Effects on Herbivore Fitness
 Herbivore biomass, consumption and reproduction are
correlated to primary production
 For herbivore the quality of food is low (low in N) but not
quantity (high in number)
 Low quality food – tough woody, fibrous and
indigestible
 High quality – young, soft and green or storage
organs (roots, tubers, seeds)
 Food of herbivore is low quality and also hindered by plant
defences – makes food unavailable, hard to digest,
unpalatable, and toxic
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1. Prey Defenses- chemical defences
Example 1(venom and pheromone):
 Snakes (venom) – to avoid predators or capture prey
 Fish e.g. sea lamprey release pheromones that act as
alarm and induces fright and flight
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Prey Defenses- chemical defenses
Example 2 (secretion):
 Arthropods/amphibians/reptiles – take up secretions to
repel predators like birds/mammals/other insects
 Copious amounts – strongly odorous secretion and
easily detectable
 Secretion of slimy substance/mucous may come out
of body wall – millipede
 May be released in air – beetles
 Sprayed as in grasshoppers and stink bugs
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Prey Defenses- chemical defenses
Example 3 (odor and toxic secondary substance)
 Skunks and shrews’ odor – produce secretions that discourage
predation cause bad smell

Toxic secondary substances – in arthropods – eg saponins,
glossypol, cynogenic glycosides



Some arthropods can take in the above substances and infuse in
their tissue
The monarch caterpillar feeds on milkweed (cardiac glycosides) –
when birds eat the caterpillar they fall sick or even die
Toxic secondary substances in plants – alkaloids, terpenes,
phenolics, cynogenic steroids, mustard oil, glycosides, tannins,
resins
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2. Prey Defenses- warning coloration
Warning Coloration (Aposematic Coloration)
 Animals that possess pronounced toxicity (toxins) and other
chemical defences (sting) often possess warning coloration
– bold colors or designs
 Bees/wasps’ (sting) serve notice to danger .
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3. Prey Defenses- mimicry
 One sp resembling another species for predator
avoidance – usually live in the same habitat
(mimic and model)
 Eg: Passiflora (plant) have evolved glandular
outgrowths on its stipules that mimic the size,
shape and colour of Heliconius sp (butterfly)
eggs
– female butterfly will reject shoots that carry
eggs of other females so the plant receives a
measure of protection by egg mimicry.
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Prey Defenses- mimicry
 1. Batesian (harmless vs harmful)
 Harmless species (mimic) imitate the warning signals
of a harmful species (model) directed at a common
predator
 Predator leaves to avoid model (harmful)– it also
avoids mimic (harmless)
 The Ash Borer (Podosesia syringae), a moth of the
Clearwing family (Sesiidae), is a Batesian mimic of
the Common bee
- it resembles the bee, but is not capable of stinging.
Podosesia syringae
(mimic)
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Bee (model)
Prey Defenses- mimicry
 2. Mullerian (two or more harmful sp.)
 Mutual resemblance of two or more harmful species,
that are not closely related and share one or more
common predators, have come to mimic each other's
warning signals
 Usually members of the same genus and family
 eg the viceroy butterfly mimics the monarch butterfly
(distasteful to birds)
Model
Mimic
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Viceroy butterfly
Monarch butterfly
Prey Defences- mimicry
(different phylogenetic lines)
 Some butterflies and butterfly larvae posses eye spot
patterns that suggest the eye of snakes or eyes of
large avian predators (that attack small birds)
 Juvenile lizards & snakes mimic highly unpalatable
millipedes,
 insect larvae mimic snakes
 snakes even mimic snakes
 Models and mimics are from different phylogenetic
lines
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4. Prey Defences- Cryptic Coloration
 Concealing Coloration or protective coloration
 Allows prey to hide from predators
 Involves pattern, shape, posture, movement and
behavior that make prey less visible
 Common among fish, reptiles and ground nesting birds
 Stick insects – resemble stick or twigs
Ibexes in the Israeli desert.
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Lizard fish (to the right of the green rock),
Big Island of Hawaii
Stick insect
Leaf insect
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5. Prey Defences- Flashing Coloration
 Butterflies, grasshoppers, birds and ungulates display
visible color patches when disturbed and put predator to
running away
 Colour may distract and disorientate predators
 In deer the colours may signal to provide group
organization when confronted by predator
Harmless Scarlet king
snake
Poisonous Coral snake
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6. Prey Defences- Armour & Weapon
 Clams, armadillos, turtles, beetles withdraw in their
armour, coats or shells
 Porcupines/hedgehogs/echidnas – have modified hairs
(quills) – sharp and painful
Armadillos
Echidnas
Hedgehog
Porcupines
Armadillos
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Armadillos
Porcupines
7. Prey Defences- Alarm call
(Behavioral Defences)
 Alarm call – when a predator is sighted
- If alarm exposes the caller it attracts
predator attention away from
conspecific (same sp.) or
- could attract more conspecifics for
cooperative defence
 Alarm calls do function to warn close
relatives eg in squirrels
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Belding’s Ground Squirrel
Prey Defences- Alarm call
(Behavioral Defences)

1. Alarm calls do bring in number of potential
prey that respond by mobbing (grouping) or
harassing predator
- e.g. harassment of owls by small birds
 The mobbing may be at a safe distance
or by direct attack

The distraction display diverts attention of
predators from eggs and young – very common
in birds

2. Living in groups is the most simplest defense
– sudden movements of flight or running away
in many directions will confuse predator
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8. Prey Defences- Predator Satiation

Synchronization of births/eggs
predation of new born
to
reduce

Most offspring are produced in a short period
of time to enhance their numbers

e.g. strategy employed by caribou and
wildebeest
- Collective defense of young by breeding
adults
- Production of increase number of prey so
that predator only takes a fraction of them
- Remaining young will grow quickly beyond
size easily handled by predator
caribou
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wildebeest
Cannibalism
-Terrestrial cannibal (50% herbivorous)
-Aquatic/marine cannibal (predaceous)
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Cannibalism (Intraspecific Predation)
 Definition:
- killing or consumption of
- either all or part of the individual
- that is from the same sp.
 Common in animal kingdom and even
in humans
 50% of terrestrial cannibals are
herbivorous – most appropriate to
encounter shortage of protein.
- E.g. snail
CoelophysisCannibalism became a
way of surviving 28
Cannibalism (Intraspecific Predation)
 in aquatic and marine habitats cannibalistic species are
predaceous
i) Usually cannibalism is found in stressed populations
(rabbit, sea lion, hippo)/facing starvation/hunger (lion,
tiger)
ii) Crowded/dense population even when food is
available (hippo)
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Cannibalism (Intraspecific Predation)
Potential cannibal?
 Not all individuals in a population become cannibals
– usually older and larger individuals
 In some species of organisms the young may
cannibalize or consume older or bigger
individuals
Why?
 Cannibalism is a mechanism to regulate/control
their population that reduces intraspecific (same
sp.) competition as food gets scarce
 E.g. Larger crocs prey on the juveniles, which
keeps their numbers stable, and their other food
sources and resources from becoming scarce.
How long?
 Usually
short
term
extinction of species
so
no
chance
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of
Cannibalism (Intraspecific Predation)
 Cannibalism promotes selective fitness
advantage, increase longevity
 Eliminates potential intraspecific
competition and provides a meal
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Mutualism
Symbiotic
Non symbiotic
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Mutualism

is a positive, reciprocal relationship at the individual
or population level between 2 different species

both species enhance their survival, growth and
fitness

may be symbiotic or non symbiotic
i.
Symbiotic - two organisms live in close physical
association – both derive benefit – at least one
member of the pair cannot lead an independent life
Non symbiotic – the species do not live together,
both members benefit each other – relationship is
either facultative or opportunistic
ii.
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Other Forms of Mutualisms
 1. Obligatory - organisms cannot survive in the
absence of the other partner.
- E.g. fungi and algae that combine to form
lichen are obligate symbiotic
- E.g. yucca moth and yucca plant are obligate
non-symbiotic
 2. Facultative - organism can lead an
independent existence, interacting species
derive benefit without being fully dependent.
 Mutualism is not essential for the survival of
either sp
 Both of the sp will engage when both of the sp
is present
- E.g. Many plants produce fruits that are eaten
by birds. Birds would be the pollinator in
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return.
Obligate Symbiotic- Mycorrhizae
 mycorrhizae is association between a
fungus and plants (roots)
- plant supplies energy (photosynthesis) to
fungi
- fungal hyphae take up mineral nutrients
from the soil and transport them into plant’s
roots
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Obligate Symbiotic- Coral reefs anthozoans+
photosynthetic zooxanthellae


Trophic mutualism
Coral reefs – corraline anthozoans and photosynthetic
dinoflagellates (zooxanthellae)

Zooxanthellae provide the photosynthetic products to the
heterotrophic anthozoans
Coral anthozoans remove, retain and recycle essential nutrients from
the water used by zooxanthellae


The chemical interaction between the coral cells and the
zooxanthellae facilitates crystalization of calcium carbonate
- zooxanthellae help the corals grow
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zooxanthellae
Obligate NonsymbioticYucca moth/plant
Dispersive mutualism
 Yucca flowers are a certain
shape so only
-that tiny moth can pollinate
them.
yucca moth placing
pollen on yucca stigma
 The moths lay their eggs in
the yucca ovary and
- the larvae (caterpillars) live
in the developing ovary and
eat yucca seeds.
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Obligate NonsymbioticAcacia ant/plant
Defensive mutualism

ants protect the plant from herbivores –
at the least disturbance they swarm from
shelters and produce disgusting odours
and attack intruder
Acacia gives ants more than thorns to
live in. She feeds them sweet sap
through special organs called nectaries.
Here three ants sip38
nectar
from their host tree.
Functional responses
Relationship between prey and
predators. 3 types of functional
responses:
 Type I
 Type II
 Type III
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II
III
I
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Type I (Linear)
 The no of prey eaten per predator increases linearly to a
maximum but then suddenly reaches a constant value
when the predator is satiated
 Based on the Lotka-Voltera equation
(dN1/dt = r1N1(K1 – N1)/K1)
 Best demonstrated in the lab
 Exhibit by the long-eared owl (Asio otus) and the
Microtus vole population
Microtus vole
Asio otus
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Type II (cyrtoid)
Corophium
Tringa totanus
 Functional response in which the attack rate increases at
a decreasing rate of prey density until it becomes
constant at satiation.
 Cyrtoid behavioral responses are typical of predators
that specialize on one or a few prey.
 E.g amphipod crustaceans (Corophium) being eaten by a
shorebird (Tringa totanus)
 E.g the 1st instar of spider (Linyphia triangularis) feeding
on Drosophila
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Drosophila
Linyphia triangularis
Type III (sigmoid)
i.
ii.
iii.

No of prey taken is low at 1st,
then the attack rate accelerates and finally
decelerate towards satiation approaching asymptote
Predator may require a learning period (i) to develop
searching and handling skills for a particular food item before
they can feed on it efficiently (ii)

E.g, bay-breasted warbler (Dendroica castanea) feeding on
spruce budworm (Choristoneura fumiferana)
Dendroica castanea
Choristoneura fumiferana
budworm
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