A massive and a tiny herbivore species drive patterns of plant community structure and
landscape heterogeneity
Grace CharlesUC Davis
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?
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
Study site
Semi-arid, Acacia drepanolobium wooded grasslandKari Veblen
Striking heterogeneity at the landscape scale
Low termite mound
MW
C WMWC
WCO
CSix combinations
of large
mammalian herbivores
200m
C = Cattle allowedW = Wildlife allowedM = Mega-herbivores allowed (elephants and giraffes)
Three replicate blocks
KLEE – Kenya Long-Term Exclosure Experiment
MW
C WMWC
WCO
CSix combinations
of large
mammalian herbivores
200m
C = Cattle allowedW = Wildlife allowedM = Mega-herbivores allowed (elephants and giraffes)
Three replicate blocks
KLEE – Kenya Long-Term Exclosure Experiment
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
A tale of two keystonesTermite mounds•Hyperdispersed, highly productive mounds have cascading effects on the productivity of surrounding biotic communities (Pringle 2010)
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
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
• 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
Do termite mounds create heterogeneity in plant communities?
Termites mounds support distinct plant communities
PERMANOVA Vegetation~ Microhabitat P = 0.001***
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
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.
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.
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.
Megaherbivores allowed
Do megaherbivores influence termite abundance?
Termite mound footprint (m2) per plot
Tree density/ HA
Megaherbivore presence
+ _
Do megaherbivores influence termite abundance?
R2 = 0.78
R2 = 0.31
0.56** -0.28**
0.84***
YES
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
-
+
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
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
Thanks!
KLEE: Truman YoungKari VeblenCorinna Riginos Duncan Kimuyu
Field assistance: Mathew Namoni Jackson Ekadeli
Questions?
