Spatial dynamics of termite mounds

AB Davies1, SR Levick2, GP Asner2, MP Robertson1, BJ van Rensburg1 & CL Parr3

1Centre for Invasion Biology, Department of Zoology and Entomology, University of Pretoria2Department of Global Ecology, Carnegie Institution, Stanford, USA

3Department of Ecology, University of Liverpool, UK

SR Levick

African savannas

• Highly variable environments

WC Oosthuizen

African savannas

• Highly variable environments• Spatial heterogeneity important

– Ecological functioning– Biodiversity– Ecosystem resilience

WC Oosthuizen

Savanna heterogeneity

• Induced by several factors– Fire– Climatic events (variable rainfall)– Herbivory

Termite mounds• Create heterogeneity

Termite mounds• Create heterogeneity• Alter soil properties

Termite mounds• Nutrient hotspots

– Support richer, more nutritious vegetation– Focal feeding sites

Termite mounds• Understanding their spatial patterns

– Densities– Spatial patterning

Termite mounds• Understanding their spatial patterns

– Densities– Spatial patterning

• Enable better understanding of heterogeneity and savanna functioning

Mapping mounds• Carnegie Airborne Observatory (CAO)

– Remote sensing system designed to study the 3D structure and function of ecosystems

– Integration of light detection and ranging (LiDAR) and hyperspectral imagery

Mapping mounds

Mapping mounds

Mapping mounds• Map mound dynamics across space

– Densities– Mound structure – Spatial patterning

Mapping mounds• Map mound dynamics across space

– Densities– Mound structure – Spatial patterning

• Mapped mounds across an entire river catchment – the N’waswitshaka

Results

5 km

Ripley’s K function

Ripley’s K function

60 m

Mapping mounds

Stream order effects

1 2 3 4 5 6 7120

140

160

180

200

220

240

260

280

300

Stream order

Nea

rest

mou

nd (m

)

Crest patterns

5 km

Crest patterns

520 540 560 580 600 620 640

0.0

0.5

1.0

1.5

2.0

Precipitation (mm/yr)

Mou

nd d

ensi

ty (

ha)

0.8 1.0 1.2 1.4 1.6

0.0

0.5

1.0

1.5

2.0

Mound height (m)

Mou

nd d

ensi

ty (

ha)

10 20 30 40

0.0

0.5

1.0

1.5

2.0

% woody cover

Mou

nd d

ensi

ty (

ha)

MAM MDG PaHM SDM v

0.0

0.5

1.0

1.5

2.0

Soil type

Mou

nd d

ensi

ty (

ha)

Decreasing clay content

What this means…• Mounds are on crests

– Where matrix vegetation is of poor quality

WC Oosthuizen

What this means…• Mounds are on crests

– Where matrix vegetation is of poor quality– Evenly spaced on these crests

WC Oosthuizen

What this means…• Spatial distribution

– High densities of large colonies in nutrient rich (dry) savanna

WC Oosthuizen

What this means…• Spatial distribution

– High densities of large colonies in nutrient rich (dry) savanna

– Associated with high levels of woody cover

WC Oosthuizen

What this means…• Spatial distribution

– High densities of large colonies in nutrient rich (dry) savanna

– Associated with high levels of woody cover• Induce positive feedback loops

– Maintaining nutrient rich savanna

WC Oosthuizen

Acknowledgements

DST/NRF Centre of Excellence for Invasion Biology Carnegie Institution for Science Andrew Mellon Foundation South African National Parks