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Essentials of Ecology 3rd. Ed.
Chap. 7 Predation, grazing
and disease
鄭先祐 (Ayo)
國立臺南大學 環境與生態學院
生物科技學系 生態學 (2008)
Predation, grazing and disease
7.1 introduction
 7.2 Prey fitness and abundance
 7.3 the subtleties (微妙之處) of predation
 7.4 predator behavior: foraging and
transmission
 7.5 population dynamics of predation
 7.6 predation and community structure

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7.1 Introduction

Three main types of predator
‘true’ Predators
 Grazers
 Parasites

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7.2 prey fitness and abundance


The fundamental similarity between predators,
grazers and parasites is that each, in obtaining
the resources it needs, reduces either the
fecundity or the chances of survival of individual
prey and may therefore reduce prey abundance.
When the sand-dune willow was grazed by a
flea beetle in two separate years (1990 and
1991) the reduction in the growth rate of the
willow was marked in both years (Fig. 7.1), but
the consequences were rather different.
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
Fig.7.1 Relative growth rates of a number of
different clones of the sand-dune willow in 1990
and 1991.
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7.2 prey fitness and abundance
Only in 1991 were the plants also subject
to a severe shortage of water.
 Thus it was only in 1991 that reduced
growth rate was translated into plant
mortality:

80% of the plants died in the high grazing
treatment,
 40% died in the low grazing treatment,
 But none of the ungrazed control plants died.

6

Fig. 7.2 The proportion of males of male pled flycatchers
infected with Trypanosoma (blood parasites) amongst
groups of migrants arriving in Finland at different times. 7

Fig. 7.3 Long-term population dynamics in laboratory
population cages of a host (Indian meal moth) , with and
with (a) or without (b) its parasitoid (parasitoid wasp).
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
Fig. 7.3 Long-term population dynamics in laboratory
population cages of a host (Indian meal moth) , with and
with (a) or without (b) its parasitoid (parasitoid wasp).
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7.3 the subtleties of predation
7.3.1 interactions with other factors
 7.3.2 compensation and defense by
individual prey
 7.3.3 from individual prey to prey
populations

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7.3.1 interactions with other factors



Californian salt marsh, where the parasitic plant,
dodder (Cuscuta salina) attacks a number of plants
including Salicornia (Fig.7.4).
Salicornia tends to be the strongest competitor in
the marsh, but it is also the preferred host of dodder.
The distribution can therefore only be understood
as a result of the interaction between competition
and parasitism (Fig. 7.4)
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Salicornia virginica→

Fig. 7.4 The effect of dodder (Cuscula salina) on
competition between Salicornia and other
species in a southern Californian salt marsh.
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
Fig. 7.4(b) over time, Salicornia decreased and
Arthrocnemum increased in plots infected with dodder.
(c) Dodder suppress Salicornia and favor Limonium and
Frankenia.
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(a)Worm burdens of birds
that are shot for ‘sport’,
which may be taken as
a representative
sample of the whole
population.
(b)Worm burdens of
those found killed by
predators.

Fig. 7.5
infection with a
nematode
worm parasite
makes red
grouse more
susceptible to
predation.
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7.3.2 compensation and defense
by individual prey
Compensatory plant responses
 Defensive plant responses (Fig. 7.7)

Fig 7.6
compensatory
plant responses
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
Fig. 7.7 (a) Phlorotannin content of Ascophyllum
nodosum plants after exposure to simulated herbivory
or grazing by the snail Littorina obtusata.
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



Fig. 7.8 (a)
percentage leaf
area consumed by
chewing herbivores
and (b) number of
aphids per plant,
measured on two
dates in three field
treatments.
Overall control,
damage control
(tissue removed by
scissors)
Induced (caused
by grazing of
caterpillars.
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
Fig7.8c fitness of plants in the three treatments.
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7.3.3 from individual prey to prey
populations
Compensatory reactions amongst
surviving prey (Fig. 7.9)
 But compensation is often imperfect (Fig.
7.10)
 Predators often attack the weakest and
most vulnerable (Fig. 7.11)

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Fig. 7.9
Fertilizer, predation 影響顯著
No fertilizer, predation影響不顯著
Fig. 7.9 Trajectories of
numbers of grasshoppers
surviving for fertilizer and
predation treatment
combination in a field
experiment.
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
Fig. 7.10 when Douglas fir seeds are protected
from vertebrate predation by screens.
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
Fig. 7.11 (a) the proportions of different age
classes of Thomson’s gazelles in cheetah and
wild dog kills is quite different from their
proportions in the population as a whole.
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

Fig. 7.11 (b) age influence the probability for
Thomson’s gazelles of escaping when chased by
cheetahs
(c) when prey zigzag to escape chasing cheetahs,
prey age influences the mean distance lost by the
cheetahs.
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7.4 predator behavior: foraging and
transmission
Active predators
Sit-and -wait
Direct parasite
Transmission
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7.4.1 foraging behavior

Behavioral ecology
The evolutionary, optimal foraging approach
 Applying the optimal foraging approach to a
range of foraging behaviors
 Predictions of the optimal diet model

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choosing between habitats




the conflict between increasing input
and avoiding predation.
Fig. 7.13
The types of
foraging decisions
considered by
optimal foraging
theory
(a) choosing
between habitats
(b) the conflict
between increasing
input and avoiding
predation.
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patch
stay-time decisions
optimal diets



patch
quality and competitor density
(c) patch stay-time
decisions
(d) the ideal free decisionthe conflict between patch
quality and competitor
density
(e) optimal diets
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7.5 population dynamics of predation




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7.5.1 underlying dynamics of predator-prey
interactions: a tendency to cycle (Fig. 7.15)
7.5.2 predator-prey cycles in practice (Fig. 7.18,
19)
7.5.3 disease dynamics and cycles (Fig. 7.20)
7.5.4 crowding (Fig. 7.21)
7.5.5 predators and prey in patches (Fig. 7.22,
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7.5.1 underlying dynamics of predator-prey
interactions: a tendency to cycle

Fig. 7.15 the
underlying tendency for
predators and prey to
display coupled
oscillation in
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abundance
7.5.2 predator-prey cycles in
practice

Fig 7.18a parthenogenetic female rotifers and
unicellular green algae in laboratory cultures.
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
Fig. 7.18b the snowshoe hare and the Canada lynx.
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
Fig. 7.19a the main species and groups of species in the
boreal forest community of North America, with trophic
interactions.
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
Fig. 7.19
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7.5.3 disease dynamics and cycles


Fig. 7.20 (a) reported cases of measles in England and
Wales from 1948 to 1968, prior to the introduction of mass
vaccination
(b) reported cases of pertussis (whooping cough) in England
and Wales from 1968 to 1982. Mass vaccination was
introduced in 1956
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7.5.4 crowding

Fig. 7.21 host immune responses are necessary for
density dependence in infections of the rat with the
nematode. Survivorship is independent of initial doses in
mutant rats without an immune response.
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7.5.5 predators and prey in patches
Dispersal and asynchrony dampen cycles
 Stabilizing metapopulation effects in
Huflaker’s mites (Fig. 7.22) and in starfish
and mussels.

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

Fig. 7.22 predator-prey interactions between the mite
Eolentranychus sexmaculatus and its predator, the mite
Typhlodromus occidentalis.
(a) Population fluctuations of Eotetranychus without its
predator.
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
Fig. 7.22b a
single oscillation
of the predator
and prey in a
simple system.
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
Fig. 7.22c sustained oscillations in a more
complex system.
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


Fig. 7.23 a metapopulation structure can increase the
persistence of predator-prey interactions.
(a) the parasitoid attacking its bruchid beetle (甲蟲) host lived
on beans either in small single cells or in combinations of cells.
(b) The predatory ciliate(纖毛蟲) feeding on the bacterivorous
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ciliate in bottles of various volumes.
7.6 predation and community structure
Predator-mediated coexistence: predation as
an interrupter of competitive exclusion
 For example, pigmy owls occurred on only
four of the islands.

The five islands without the predatory owl were
home to only one species, the coal tit (山雀)
 However, in the presence of the owl, the coal tit
was always joined by two larger tit species.

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
Fig. 7.24 mean species richness of pasture vegetation in
plots subjected to different levels of cattle grazing in two
sites in the Ethiopian highlands.
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Questions
動物的掠食行為，必然是「最佳策略」嗎？
為何是？為何不是？
 按「本利分析」結果的策略，就是「最佳
策略」嗎？
 請按生態與演化的觀點，扼要討論。

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問題與討論
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