BIOS 5970: Plant-Herbivore Interactions
Dr. Stephen Malcolm, Department of Biological Sciences
•  Week 9. Ecology & Evolution of Mutualisms:
–  Lecture summary:
•  Mutualism: a world of
cheerful cooperation?
•  Energetics of bee
foraging
•  Factors limiting plant
reproduction
•  Fruit profitability
•  Dispersal probability
•  Consequences of seed dispersal
Bombus vagans
http://bugguide.net/node/view/470601
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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2. Mutualisms:
•  Charles Darwin noted that Victorians liked to
–  “behold the face of nature bright with gladness”
in a world of cheerful cooperation.
•  Darwin used this attitude to contrast with the
reality in which a mistletoe exploits a bird for
dispersal.
•  But the bird eats the fruit for food and leaves
the sticky seeds in clumps where they
compete intraspecifically for limited
resources.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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3. Mutualism and optimality:
•  Mutualisms between plants and animals are
widespread.
•  Howe & Westley consider the reason why.
•  They use an analysis of costs and benefits
to the interactants.
•  Ideas about optimization borrowed from
economics.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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4. Balancing costs and benefits:
•  Bernd Heinrich
estimated the energetic
costs and benefits of
bee foraging for nectar
and pollen of flowers.
•  Bees with longer
tongues were more
efficient at extracting
nectar than shorttongued bees (Fig. 7-1)
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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5. Bumblebee foraging at flowers:
•  4 Bombus species foraging
at:
–  Long-corolla flowers.
–  Short-corolla flowers (<3mm).
–  Pollen flowers.
•  Partition resources
according to tongue length
(Fig. 7-2).
–
–
–
–
B. vagans >8mm, stippled
B. fervidus >8mm, open
B. terricola <7mm, lined
B. ternarius<7mm, black
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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6. Diversity of pollinator species:
•  Many pollinator species may visit related flower species,
•  E.g. 55 species of sunflowers (Asteraceae) in Illinois:
–  Frequency distribution of species (Fig. 7-3).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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7. Majoring and minoring by bumblebees
•  In the absence of competition bees narrow their foraging
range of flower species (Fig. 7.4A).
•  In the presence of competition bees visit the same most
profitable flowers on subsequent trips (Fig. 7.4B).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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8. Experience and improved handling:
•  Foraging
bumblebees
learn to handle
jewelweed
(Impatiens)
flowers more
accurately with
experience
(Fig. 7-5).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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9. Flower patchiness and residence times:
•  Foraging bees stay
longer in patches of
flowers with most
nectar.
•  They do this by
travelling short
distances after
encountering high
nectar volumes
(Fig. 7-6).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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10. Bee Foraging:
•  6 options for coping with competition:
–  (1) Visit more flower species.
–  (2) Improve nectar-handling efficiency.
–  (3) Extend foraging range rather than switch to
minor foods.
–  (4) Territoriality to defend food resources.
–  (5) Respond to high rewards with short
movements.
–  (6) Respond to lower reward variances rather
than high reward means.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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11. Limiting factors for plant reproduction:
•  Ovule-limited seed production:
–  When abundant pollen grains fail to fertilize eggs.
•  Pollen-limited seed production:
–  When some ovules are not fertilized (like Fig. 7-8).
•  Resource-limited seed production:
–  When fertilized eggs are aborted because light or soil
resources are insufficient.
•  Herbivore-limited seed production:
–  Fertilized ovules eaten by consumers before maturity.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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12. Fruit profitability & dispersal probability:
•  Fruit size and fruit disperser size both influence fruit
profitability and the likelihood that a particular fruit
will be dispersed by a particular disperser.
–  Fig 7-10 - profitability as a
function of fruit size and
bird size (a = 17g, b = 250g,
c = 500 g birds)
–  Profitability P depends on
pulp weight (Fm) nutritional
content (Fn) and the basal
metabolic weight (M0.61)/
exploitation time (T).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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13. Fruit diameter and gape width:
•  Maximum fruit diameters are positively correlated
with bill gape in 36 bird species in the mountains of
Costa Rica (Fig. 7-11).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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14. Fruit size and bird disperser diversity:
•  Large fruited plants have fewer bird species visiting
than small fruited plants (Table 7-3).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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15. Ecological Consequences of Seed Dispersal:
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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16. Seedling recruitment:
•  Product of dispersed seed shadow and probability
of seed/seedling survival (Fig. 7-15).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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17. Pollen dispersion:
•  Pollen follows a negative binomial distribution with most
pollen deposited near its flower source (Fig. 8-2).
•  Higher probability of same species fertilization
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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18. Consequent gene dispersal:
•  Most butterfly
pollinator flights
are <3m
between plants
of Phlox pilosa
(Fig. 8-3).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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19. Patterns of pollen dispersion in plant
communities:
•  Pollinators moved dyed
pollen further in
populations of
chickweed alone
–  (Fig. 8-4 top).
•  Dyed pollen had more
restricted movement in
chickweed when grown
mixed with spring
beauty
–  (Fig. 8-4 bottom).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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20. Constraints on coevolution between plants
and their mutualists:
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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21. Diversity of symbiotic mutualisms:
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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Figure 7-8: Pollinator (fungus gnat)
limitation in jack-in-the-pulpit.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 9: Ecology & Evolution of Mutualisms
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