esa 2014 a massive and a tiny herbivore species drive patterns of plant community structure and...

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?