bios 5970: plant-herbivore...
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BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 12: Community Dynamics Slide - 1
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
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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?”
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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 tall-grass savanna near Nairobi, Kenya and zebra in grazed grasslands of Serengeti-Mara plains in SW Kenya.
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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.
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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.
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6. Effects of experimental manipulation of herbivory:
Fig. 1. Grass height when grazed (●) or fenced (○) in (a) short grassland, (b) medium grassland (McNaughton, 1984. Am. Nat. 124: 868).
Fig. 3a. Grass biomass inside and outside fences in short (○), medium (●) & tall (△) grasslands.
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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.
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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
Dietary niche partitioning among large herbivores in east Africa
BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 12: Community Dynamics Slide - 11NMDS = nonmetric multidimensional scaling
grazers
non grazers
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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 (white-sand 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.
References • 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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