BIOS 5970: Plant-Herbivore Interactions
Dr. Stephen Malcolm, Department of Biological Sciences
•  D. POPULATION & COMMUNITY
DYNAMICS
•  Week 12. Community Dynamics:
–  Lecture summary:
•  Community patterns
•  East African grazing succession
•  Keystone species
•  White-sand forests
–  Nutrient availability
•  Shifts through time
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 12: Community Dynamics
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2. Community patterns: dependent or
independent of population processes?:
•  Howe & Westley ask:
–  “To what degree do strong ecological
interactions between pairs or guilds of plants
and animals account for differences among
natural communities?”
–  “Are the immigrations, extinctions, and different
reproductive successes of organisms that
underlie differences in community composition
dependent on interactions between species, or
independent of them?”
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 12: Community Dynamics
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3. Grazing
Succession:
•  “East Africa now
harbors the last
extensive remnants of
ecosystems that once
covered much of North
and South America,
Asia and Australia.”
•  Fig. 10-9: kongoni in tallgrass savanna near Nairobi,
Kenya and zebra in grazed
grasslands of SerengetiMara plains in SW Kenya.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 12: Community Dynamics
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4. Succession and
herbivory:
•  Wildebeest and zebra
in grasslands of
Tanzania.
–  Plate 4, Begon et al.,
(2006).
•  Herbivory is the
process most
important to the
structure of such
communities.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 12: Community Dynamics
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5. Intensity of herbivory:
•  Herbivory is comparatively constant in these
grassland communities & can be responsible
for biomass losses of >90% a year.
•  In contrast, most plant communities are
characterized by <10% biomass loss per
year due to herbivory.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 12: Community Dynamics
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6. Effects of experimental
manipulation of herbivory:
Fig. 3a. Grass biomass inside and
outside fences in short (○), medium
(●) & tall (△) grasslands.
Fig. 1. Grass height when grazed (●) or fenced (○)
in (a) short grassland, (b) medium grassland
(McNaughton, 1984. Am. Nat. 124: 868).
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 12: Community Dynamics
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7. McNaughton cont’d:
Fig. 3b. Grass height inside and
outside fences in short (○), medium
(●) & tall (△) grasslands.
Fig. 3c. Max. biomass against max.
height in fenced (●---) & grazed (○ )
grassland.
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 12: Community Dynamics
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8. Species diversity
•  These grass communities support heavy
grazing and a diversity of herbivore species
because the large ungulate herbivores vary
in their diets and distributions.
•  Large rumen, or intestinal volumes, allow
buffalo, zebra, and large antelopes, like
eland, to eat a wider range of plant species,
than the smaller and more selective
antelopes, such as gazelles.
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9. Seasonal variation:
•  Large geographical and seasonal variability
in plant community composition and growth
also help to make these communities
diverse and dynamic.
•  Grazing succession is the result of larger
ungulate herbivores stimulating growth of
plants that progressively smaller ungulates
can exploit.
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10. Effects of grazer size:
•  Different sized species tend
to feed together to take
advantage of the food
resources made available:
–  e.g. topi (90-140 Kg) with
eland (450-700 Kg) or
Grant’s gazelles (42-68
Kg).
–  This succession is shown
for wildebeest (200-228
Kg) and Thompson's
gazelles (18-25 Kg) in
Fig. 10-10.
Fenced-senescent
Unfenced-flushing
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Dietary niche partitioning among large
herbivores in east Africa
grazers
non
grazers
NMDS = nonmetric multidimensional scaling
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11. Are grazers mutualists?
•  Unlikely, because such compensatory
growth cannot result in higher fitness than
grasses that are protected with fences from
herbivory.
–  Unless competition has a greater negative effect
than herbivory?
•  Selection by intense herbivory could also
increase indirect competition because it
would favor unpalatable plant species.
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12. Keystone species:
•  “..animal or plant species with a pervasive influence
on community composition.”
•  “Removal or extinction of keystone species profoundly
changes the competitive relationships, and
consequently the relative abundances, of other
species in a community.”
–  The most famous example is that of Paine (1966) who
showed in a marine community that removal of a predatory
starfish freed mussels to outcompete 11 species of limpets,
clams, and mussels and led to a much less diverse
community.
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13. Keystone mutualists:
•  Mutualists can also
be keystone
species:
–  E.g. the uncommon
canopy tree,
Casearia
corymbosa,
supports 6 spp. of
fruit disperser in
Costa Rica,
including masked
tityra and toucan
(Fig. 10-11).
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14. Casearia corymbosa:
•  This is a keystone mutualist because it
produces fruits in December when other
trees do not and so supports a community of
bird fruit dispersers (including its primary
disperser).
•  Loss of this tree could lead to a widening
community impact with progressive loss of
many tree species through time.
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15. Tropical forest communities:
•  Influence of soil attributes on plant-animal
interactions:
–  Including leaf-feeders, flower-pollinators and
seed-dispersers.
•  Lowland tropical forests have diverse &
dense vegetation, poor soils, high rainfall, &
rapid ecological succession in gaps caused
by soil exposure from treefalls, landslides
and other disturbances:
–  bombs, napalm, floods, clearing etc.
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16. White-Sand Forests:
•  Forest plant biomass
can vary from 6 (whitesand forests) to 80 Kg/
m2 .
•  White-sand forests
(caatinga & heath) are
scrub forests with
drought-adapted trees
& <60% of the biomass
in roots (Fig. 10-12).
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17. Nutrient cycling in white-sand forests:
•  Nitrogen and phosphorus shortages may be
compensated for by catching leaf litter as it falls.
•  Dan Janzen (1974 Biotropica 6(2): 69-103):
–  A great paper!
–  Argued that resource-limited plants will not be able to
replace leaves easily and so should be evergreen during
drought with obvious adaptations to reduce water loss.
•  How will this influence the white-sand community?
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18. Janzen’s predictions:
•  1. Tough foliage heavily defended by
chemicals.
•  2. Minimal herbivory.
•  3. Low numbers and low biomass of
herbivores.
•  4. Extremely rare carnivores at the top of
food chains:
–  Because herbivores are uncommon.
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19. Janzen’s predictions:
•  These predictions are supported by:
–  Low species diversity in white-sand forests.
–  Black acidic rivers loaded with humic acids:
•  Tannins and other phenolic acids.
–  Undecomposed plant matter, suggesting very
high levels of plant secondary defenses.
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20. Nutrient-poor forests continued:
•  Doyle McKey:
–  Ph.D. student of Janzen at Univ. Michigan.
–  Tested Janzen’s predictions.
•  Observed black colobus monkeys (Colobus satanas)
as herbivores feeding on plants in the white-sand
forests of Cameroon in west Africa.
•  Compared with C. badius (red colobus) and C.
guereza (black-and-white colobus) feeding on leaves
of trees in the richer soils of Uganda in central Africa.
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21. Differences between soils in Cameroon
and Uganda (Table 10-3):
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22. McKey’s results:
•  Cameroon monkeys avoided most common
trees and fed selectively on rare deciduous
trees and uncommon herbaceous vines:
–  Not the common, well-defended evergreen
species.
–  37% of food was leaf material, 53% seeds.
•  Ugandan monkeys had a 75% leaf diet from
common trees and ate fewer seeds and the
population was 10x larger than in Cameroon.
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23. Janzen-McKey:
•  The rationale developed by Janzen (1974) and McKey et al.
(1978, Science 202: 61-64) was later used by Bryant et al.
(1983) and Coley et al. (1985) in their carbon:nutrient
balance and resource availability hypotheses.
•  McKey et al. (1978) state:
–  “Janzen (1) reasoned that the cost of replacing materials eaten by
herbivores would be greater in areas of nutrient-poor soils than
for plants growing on sites richer in nutrients. He predicted that
vegetation growing on impoverished white-sand soils would be
found to contain greater concentrations of herbivore-deterrent
toxic secondary compounds (such as tannins, saponins, and
alkaloids) than would vegetation growing on more nutrient-rich
soils.”
•  (1) D.H. Janzen (1974) Biotropica 6: 69-103.
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24. Community, ecosystem, landscape and
biome shifts through time:
•  As abiotic conditions change through time so
their impact will shift patterns of species
diversity and interactions within
communities.
•  For example, increased aridity shifts
vegetation from forests to savannas and
steppes and so the herbivore community
shifts from a predominance of browsers to
mostly grazers.
•  Figs. 9-7, 9-8.
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Figure 9-7: Increased aridity 19-5 million years ago (Miocene)
generated shift from forest to savanna to steppe and change
in herbivores from browsers to grazers.
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Figure 9-8: Shift in North American, Miocene
horse evolution from browsers to grazers.
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References
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Begon, M., Townsend, C.R., and Harper, J.L. 2006. Ecology: From Individuals, to Ecosystems. 4th
edition. Blackwell Publishing Ltd., 738 pp
Bryant, J.P., Chapin III, F.S., and Klein, D.R. 1983. Carbon/nutrient balance of boreal plants in relation
to vertebrate herbivory. Oikos 40(3): 357-368.
Coley, P.D., Bryant, J.P., and Chapin, F.S.III 1985. Resource availability and plant antiherbivore
defense. Science 230: 895-899.
Howe, H.F., and Westley, L.C. 1988. Ecological Relationships of Plants and Animals. New York:
Oxford University Press, 273 pp.
Janzen, D.H. 1974. Tropical blackwater rivers, animals, and mast fruiting of the Dipterocarpaceae.
Biotropica 6(2): 69-103.
Kartzinel, T.R., P.A. Chen, T.C. Coverdale, D.L. Erickson, W.J. Kress, M.L. Kuzmina, D.I. Rubinstein,
W. Wang, & R.M. Pringle. 2015. DNA metabarcoding illuminates dietary niche partitioning by African
large herbivores. PNAS 112(26): 8019-8024.
McKey, D., Waterman, P.G., Mbi, C.N., Gartlan, J.S., and Struhsaker, T.T. 1978. Phenolic content of
vegetation in two African rain forests: Ecological implications. Science 202: 61-64.
McKey, D.B., Gartlan, J.S., Waterman, P.G., and Choo, G.M. 1981. Food selection by black colobus
monkeys (Colobus satanas) in relation to plant chemistry. Biol. J. Linn. Soc. 16: 115-146.
McNaughton, S.J. 1984. Grazing lawns: Animals in herds, plant form, and coevolution. Am. Nat.
124(6): 863-886.
Paine, R.T. 1966. Food Web Complexity and Species Diversity. Am Nat. 100(910): 65-75.
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