A massive and a tiny herbivore species drive
patterns of plant community structure and
landscape heterogeneity
Grace Charles
UC 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 grassland Kari Veblen

Striking heterogeneity at the landscape scale
Low termite mound

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

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

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 keystones
Termite 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

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

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?
Tree density/ HA
Termite mound
footprint (m2) per plot
Megaherbivore presence
+ _

Do megaherbivores influence termite
abundance?
R2 = 0.78
0.56** -0.28**
R2 = 0.31
0.84***

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 Young
Kari Veblen
Corinna Riginos
Duncan Kimuyu
Field assistance:
Mathew Namoni
Jackson Ekadeli

Questions?