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ESA 2014 A massive and a tiny herbivore species drive patterns of plant community structure and landscape heterogeneity

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ESA 2014 A massive and a tiny herbivore species drive patterns of plant community structure and landscape heterogeneity

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My 2014 ESA talk on the role of termites and elephants in shaping plant communities and landscape heterogeneity. On one hand, termites and elephants change plant communities by themselves. Termites create mounds which have different soil, nutrients, and water availability. These mounds form separate plant "islands" that are home to distinct plant communities. Elephants, meanwhile, eat mostly trees and shrubs, and this diet can also change plant communities by reducing the numbers and abundance of certain plant species.

Together, however, it appears that these two species also affect each other. Elephants reduce trees, which means there are fewer resources available for termites. As a result, termites form fewer mounds in areas where elephants are present. This changes landscape-scale patterns in plant communities.

My 2014 ESA talk on the role of termites and elephants in shaping plant communities and landscape heterogeneity. On one hand, termites and elephants change plant communities by themselves. Termites create mounds which have different soil, nutrients, and water availability. These mounds form separate plant "islands" that are home to distinct plant communities. Elephants, meanwhile, eat mostly trees and shrubs, and this diet can also change plant communities by reducing the numbers and abundance of certain plant species.

Together, however, it appears that these two species also affect each other. Elephants reduce trees, which means there are fewer resources available for termites. As a result, termites form fewer mounds in areas where elephants are present. This changes landscape-scale patterns in plant communities.

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ESA 2014 A massive and a tiny herbivore species drive patterns of plant community structure and landscape heterogeneity

  1. 1. A massive and a tiny herbivore species drive patterns of plant community structure and landscape heterogeneity Grace Charles UC Davis
  2. 2. Linking ecological drivers and landscape heterogeneity • Landscape heterogeneity is a major driver and maintainer of biodiversity • Conversely, certain subsets of species (keystones) can actually create heterogeneity • What drives the creation and maintenance of landscape heterogeneity? Can keystones interact, and what are the consequences of these interactions?
  3. 3. Savanna ecosystems • Cover around 20% of earth’s land surface • Some of the last repositories of large mammalian fauna • Community structure is highly heterogeneous and is heavily influenced by both biotic and abiotic drivers
  4. 4. Study site Semi-arid, Acacia drepanolobium wooded grassland Kari Veblen
  5. 5. Striking heterogeneity at the landscape scale Low termite mound
  6. 6. KLEE – Kenya Long-Term Exclosure MW O WC C MWC C W 200m Six combinations of large mammalian herbivores C = Cattle allowed W = Wildlife allowed M = Mega-herbivores allowed (elephants and giraffes) Three replicate blocks Experiment
  7. 7. KLEE – Kenya Long-Term Exclosure MW O WC C MWC C W 200m Six combinations of large mammalian herbivores C = Cattle allowed W = Wildlife allowed M = Mega-herbivores allowed (elephants and giraffes) Three replicate blocks Experiment
  8. 8. A tale of two keystones 1. Termites (Odontotermes spp.) •Fungus growing, generalist herbivores/detritivores • Forage for woody biomass, dung, even bone(!)(Freymann 2007) •Mounds have high soil nutrients, water infiltration rates, different soil texture (less clay, more sand and silt) •Herbaceous vegetation on, and surrounding termite mounds is distinct •Mounds are generally treeless
  9. 9. A tale of two keystones Termite mounds •Hyperdispersed, highly productive mounds have cascading effects on the productivity of surrounding biotic communities (Pringle 2010)
  10. 10. A tale of two keystones 2. Elephants •Known to radically affect landscape heterogeneity through reductions in woody stands •Tree and shrub consumption might reduce resource availability to termites
  11. 11. Q1: Do termite mounds create heterogeneity in plant communities? • H1: Plant communities on termite mounds are significantly distinct from those off termite mounds • H2: Because both keystones forage for a common resource, woody biomass, the removal of megaherbivores should increase woody biomass and, in turn, lead to an increase in termite density
  12. 12. Do termite mounds create heterogeneity in plant communities? • Censused plant communities on and off termite mounds in KLEE experimental plots (15/plot) • Vegetation surveys: Presence/absence and percent cover of all plant species within 1m2 quadrats • NMDS analysis of plant communities
  13. 13. Termites mounds support distinct plant communities PERMANOVA Vegetation~ Microhabitat P = 0.001***
  14. 14. Q2: Do megaherbivores influence termite abundance? • H1: Plant communities on termite mounds are significantly different than those off termite mounds • H2: Because both keystones forage for a common resource, woody biomass, the removal of megaherbivores should increase woody biomass and, in turn, lead to an increase in termite density
  15. 15. Do megaherbivores influence termite abundance? Methods • 10m x 200m transects across all KLEE plot area (72,000m of transects in all) to determine termite mound density and aboveground termite mound footprint in plots including and excluding megaherbivores. • Integration with previously collected KLEE datasets on tree density/HA.
  16. 16. Do megaherbivores influence termite abundance? Methods • 10m x 200m transects across all KLEE plot area (72,000m of transects in all) to determine termite mound density and aboveground termite mound footprint in plots including and excluding megaherbivores. • Integration with previously collected KLEE datasets on tree density/HA.
  17. 17. Do megaherbivores influence termite abundance? Methods • 10m x 200m transects across all KLEE plot area (72,000m of transects in all) to determine termite mound density and aboveground termite mound footprint in plots including and excluding megaherbivores. • Integration with previously collected KLEE datasets on tree density/HA.
  18. 18. Megaherbivores allowed
  19. 19. Do megaherbivores influence termite abundance? Tree density/ HA Termite mound footprint (m2) per plot Megaherbivore presence + _
  20. 20. Do megaherbivores influence termite abundance? R2 = 0.78 0.56** -0.28** R2 = 0.31 0.84***
  21. 21. Putting it all together • Termites and megaherbivores interact in profound ways that strongly affect plant community structure and ecosystem heterogeneity • Megaherbivores reduce tree density, and this leads to a reduction in termite mound density and footprint • Megaherbivores reduce the landscape heterogeneity produced by termites by reducing termite mound area • Extirpation of megaherbivores may have profound consequences for large-scale patterns in community composition, community structure, and nutrient cycling - +
  22. 22. Putting it all together • Termites and megaherbivores interact in profound ways that strongly affect plant community structure and ecosystem heterogeneity • Megaherbivores reduce tree density, and this leads to a reduction in termite mound density and footprint • Megaherbivores reduce the landscape heterogeneity produced by termites by reducing termite mound area • Extirpation of megaherbivores may have profound consequences for large-scale patterns in community composition, community structure, and nutrient cycling
  23. 23. Next steps • Exploring multiple scales of landscape heterogeneity- how do we rectify counteracting patterns in heterogeneity? • How do biotic interactions impact belowground communities and overall ecosystem function? • What are the effects of other large herbivores on termite mounds and plant communities? – Cattle also appear to have a strong effect on termite mound density
  24. 24. Thanks! KLEE: Truman Young Kari Veblen Corinna Riginos Duncan Kimuyu Field assistance: Mathew Namoni Jackson Ekadeli
  25. 25. Questions?

Editor's Notes

  • Resource heterogeneity can drive species richness, abundance, and plant animal interactions in savannas (du Toit et al. 2003). Landscape heterogeneity is a major driver/mainter of biodiversity. Conversly, certain subsets including keystones themselves create heterogeneity
  • Savannas cover 20% of earth’s land surface. They support most of the world’s rangeland, livestock, and wild herbivore biomass; last repositories of large mammalian fauna (Scholes & Archer 1997)
    High dry plateau in the rain shadow of mount kenya
  • From satellite imagery, it appears that termite mound density might increase with increasing rainfall and tree density
  • Specialists; ecosystem hotspots; great fossorial refuges
  • 20 transects x 200m x 18 plots; put in more lines
  • 20 transects x 200m x 18 plots; put in more lines
  • 20 transects x 200m x 18 plots; put in more lines
  • Negative/positive sign; this kind of question has usually been asked with natural variation. Few opportunities to actually control for variation; notice two things– variation in plots across gradient, then variation across treatments
  • Plots with megaherbivores vs. plots without
  • Small scale pattern of mounds being treeless; how do these scales interact; adding that layer counteracting forces; multiple scales of landscape heterogeneity – one thing that is special is that it’s a livestock area; cattle are also keystones– don’t have to tell main results
  • ×