chapter 9 mutualism 鄭先祐 生態主張者 ayo [email protected]
TRANSCRIPT
Chap.9 Mutualism 2
RoadMap
• Mutualism: an association between two organisms that benefits both
• Seed dispersal mutualism: disperser acquires a meal and the plant gets its seed dispersed
• Through mutualism, species are better able together to secure resources or better able to defend themselves
• Mutualism is difficult to model; models tend to result in runaway densities
Chap.9 Mutualism 3
RoadMap
• Mutualism between two species can affect the entire community
• Commensalism is an association between two species that benefits only one, with the other species unaffected
Chap.9 Mutualism 4
9.1 Plant-Pollinator Mutualism• Most frequent type of mutualism (Figure 9.1)
– 45% of all studies of mutualism
– Coevolved systems
• Selective pressures for plants to develop intimate relationship with pollinators (Figure 9.2)– More than 900 species of Ficus exist and virtually all
must be pollinated by its own species of agaonid wasp
– Yucca plants and yucca moths - highly coevolved
– The distribution of each species is controlled by the availability of the other species
• Ex. Yucca flower abortion if too many eggs are laid
Chap.9 Mutualism 5
Pro
port
ion o
f m
utu
alis
m a
rtic
les
0.5
0.4
0.3
0.2
0.1
0
Pollination Seeddispersal
Ant-plantprotection
Mycorrhizal Ant-insectprotection
Grazing Nutritional Other
•Fig. 9.1 Frequency of articles on different forms of mutualism published in 675 papers.
Chap.9 Mutualism 6
Fig. 9.2 Blastophaga psenes, a tiny fig wasp, which crawl inside the captifig in California to lay her eggs.
Chap.9 Mutualism 7
• Cheating in pollination– In the Bogs of Maine
• Grass-pink orchid produces no nectar, but mimics the nectar-producing rose pogonia
• Some Bombus species cheat by biting through the base of the flowers, taking the nectar without entering the plant nor assisting with pollination
Chap.9 Mutualism 8
9.2 Seed Dispersal
• Seed dispersal systems account for almost 30% of all mutualisms– In tropics some fruits are dispersed by birds that are
frugivorous• Fruit provides balanced diet for birds
• Birds disperse seeds
• Mechanisms for attraction
– Birds and mammals - attractive colors, and odorless (Birds)
– Nocturnal bats - give off pungent odor
Chap.9 Mutualism 9
• Seed dispersal mechanisms are not as obligatory as plant-pollinator systems– Performed by more generalist agents
– Wide array of adaptations• Ex. parrot beaks to crack and peel fruits
• A berry-eating fish from the Amazon. Ex. Figure 9.3
Chap.9 Mutualism 10
A Variety of Mutualisms• Mutualisms and resources
– Neotropical leaf-cutting ants and fungus (Figure 9.4)
• Typical ant colony: 9 million
• Typical biomass of colony: Equivalent to a the biomass of a cow
• Typically cuts the equivalent of a cow's daily requirement of fresh vegetation
• Leaf-cutting ants harvest 17% of the total leaf production in the forest
• Ants take cut vegetation underground to grow special fungal crops (nature's farmers?)
• Fungus grows specialized structures called gongylidia, which serve as food for the ants
Chap.9 Mutualism 11
Fig. 9.4 Leaf-cutting ants Atta cephalotes, in South America, chew up leaves and cultivate fungus gardens underground.
Chap.9 Mutualism 12
• Leaf-cutting ants and the parasitic fungus, Escovopsis– Escovopsis can infest the ants' fungi gardens,
destroying the fungi inside
– A mutualisitic streptomyces• Occurs on the bodies of ants
• Produces antibodies that keep Escovopsis in check
Chap.9 Mutualism 13
Nitrogen
• Vital to plant and animal growth– Most species can not fix atmospheric nitrogen
– Fixation is carried out by soil bacteria and archaebacteria
• Most live in the roots of plants
• Mutualistic relationship with plant
• Excess nitrogen is available to plant
• Ex. Rhizobia bacteria in legumes– Figure 9.5
Chap.9 Mutualism 14
Mutualism under harsh environmental conditions
• Strong facultative mutualism
• Leguminous shrub, Retama, and an understory plant, Marrubium vulgare– Grow in a semiarid region of Spain
– Retama shades Marrubium, provides favorable microclimate
– Marrubium enhances the availability of water for Retama
Chap.9 Mutualism 15
Retama Marrubium
Leaf
mas s
(g)
0
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5
15
0.0
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0.6 3
2
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Leaf
mass
(g)
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are
a (
cm
/g)
2N
cont e
nt
(g /
pla
nt)
Leaf
are
a (
cm
/g)
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N c
ont e
nt
(g /
pla
nt)
+M -M +R -R
Environment
•Fig. 9.6
Chap.9 Mutualism 16
Mutualism and protection from natural enemies
• Common example: ants and aphids(Figure 9.7)– Aphids feed on plant sap and excrete
honeydew
– Ants drink the honeydew and in return protect the aphids
Chap.9 Mutualism 17
Mutualism and herbivory
• Ants protect plants from herbivores
• Common in the tropics– 377 myrmecophytic plants per hectare in a
Brazilian Rain Forest (Fonseca and Ganade, 1996)
– 312 ant-plant associations at a single coastal site in Mexico (Rico-Grey, 1993)
Chap.9 Mutualism 18
Fig. 9.8 Thorns on Acacia collinsii in Paloverde National Park in Costa Rica.
• Example: Ants and the Central American acacia trees– Acacia trees provide food and shelter for the ants
inside large thorns
– Ants protect the acacia tree from other insects and vertebrate herbivores
– Ants also trim foliage away from competing plants and kill neighboring plant shoots
– Figure 9.8
Chap.9 Mutualism 19
Fig. 9.9 Soay sheep
• Example: Fungi and plants– Fungi reduce vertebrate herbivory
– Soay Sheep of Hirta Island (in the St. Kilda Archipelago) Figure 9.9
– Sheep overgraze native grasses
– Periodically, sheep population crashes
Chap.9 Mutualism 20
• Mutualism is the chief culprit– The main forage is the grass Festuca rubra
– F. rubra contains an endophyte, the fungus Acremonium, inside its blades
– The fungus produces toxic alkaloids
– These alkaloids function as an anti-herbivory defense
– In return, the fungus obtains food from the plant
– Frequency of infection correlated to grazing pressure. Heavy grazing causes higher infections
– Fungi are in greatest concentration in basal regions. Heavy grazing results in sheep reaching lower blades.
Chap.9 Mutualism 21
Obligate mutualism• A mutualistic relationship, in which neither participant
could survive without the other
• Ex. Lichen: a relationship between algae and fungi– Algae provides the photosynthate
– Fungi provides a safe habitat
• Ex. Many ruminants and symbiotic bacteria– Bacteria break down plant tissue to provide energy for their
hosts
• Ex. The roots of most plants and fungi– Mutualistic association between the fungus and root tissue -
mycorrhizae• Fungi obtain carbohydrates from their host
• Fungi increase access to mineral nutrition and water for the plant
Chap.9 Mutualism 22
9.4 Modeling Mutualism• Uses equations similar to Lotka-Volterra
competition equations
• For facultative mutualism– dN1 /dt = r1N1 [K1 - N1 + N2) / K1]
– dN2 /dt = r2N2 [K2 - N2 + N1) / K2]
• dNi /dt = change in population size of species 1 or 2
• ri = per capita growth rate for species 1 or 2
• Ni = population size of species 1 or 2
• Ki = Maximum population density of species 1 or 2
• = Positive effect of species 2 on species 1 = Positive effect of species 1 on species 2
Chap.9 Mutualism 23
NN 1=0 2=0dN
dt1= 0dN
N2 N N
dNdt
2 2
dt
Facultative mutualism
2=0dNdt
1=0dtdN
2=0dNdt
N1 N1 N1X1
X1
X1
X2X2 X2
Pop
ula
tion d
ensi
ty o
f N
2
—
—
—
—
——a) b) c)1
2
Population density of N1
Fig. 9.10 Graphical models of facultative (a-c) and obligate (d-f) mutualism.
Chap.9 Mutualism 24
• For obligate mutualism– Different equations are needed
– Models of facultative mutualism are, in general, more stable than models of obligate mutualism
– Figure (9.10d-f)
Chap.9 Mutualism 25
Obligate mutualism
Population density of N1
1=0dNdt
2=0dNdt
2=0dNdt
2= 0dNdt
1= 0dNdt
1= 0dNdt
N2 N2 N2
N1 N1N1
Pop
ula
tion d
ensi
ty o
f N
—
—
—
—
—
—d) e) f)N2
N1
Chap.9 Mutualism 26
9.5 Mutualisms and Community Process
• Mutualism can have strong indirect effects on the community– Ex. mycorrhizal fungi and herbivory load
• Pinyon pines and mycorrhizae: Density of needle scale insect, Matsucoccus acalyptus:
• Mycorrhizae can improve pine vigor and/or increase plant investment in antiherbivory defenses
• Density of needle scale insects will decrease
Chap.9 Mutualism 27
• Ex. Endophytes (fungi that live inside leaves) and vascular plant hosts - Defend host against herbivory
• Mycorrhizal fungi and plant species diversity (Figure 9.11)
Chap.9 Mutualism 28
0
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0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14
0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14
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oot
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nt
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mg k
g so
il)-1
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ngth
(m
g
so
il)-1
a)
b)
c)
d)
e)
f)
Number of mycorrhizal fungal species Number of mycorrhizal fungal species
Fig. 9.11
Chap.9 Mutualism 29
9.6 Commensalism
• Commensal relationship: one members benefits and the other is unaffected– Ex. An orchid and a tropical tree: orchids
gain a place to live and the tree gains nothing
– Ex. Cattle egrets and cattle: Cattle stir up insect prey for egrets (Figure 9.12)
Chap.9 Mutualism 30
Ste
ps
per
pre
y
0
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20
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Cow No cow
Feed
ing
s per
min
ute
0
10
•Fig. 9.12
Chap.9 Mutualism 31
• Commensalism in the form of phoresy: association is passive and more temporary transport of one organism by another– The transport of flower-inhabiting mites from bloom to
bloom in the nares of hummingbirds
• Common commensalisms: plant mechanisms of seed dispersal– Ex. Seeds attached to animal fur
– Some mechanims can become an antagonistic relationship
• Pisonia (cabbage tree) produce a very sticky fruit
Chap.9 Mutualism 32
Chap.9 Mutualism 33
Humans in mutualistic relationship
• Humans and Agriculture (Box Photo 1)
• Origins of world's crops (Box Table 1)
• Crops are introduced around the world
• Livestock are domesticated
• Mutualism– Human population has increased
– Crops and livestock populations have increased
– Box Table 2
Chap.9 Mutualism 34
• Side-Effects of Mutualism
1. Pollution of bodies of water
2. Loss of topsoil
3. Depletion of water supplies
4. Salting of the land
5. Desertification
6. Severe loss of wildlife
