Savanna Landscapers? assessing the seed dispersal service provided by elephants
Bunney, Katherine and Bond, William Botany Department, University of Cape Town Pleistocene Extinctions Percentage of genera that have gone extinct over the last 100,000 years.
Giant Kangaroos Enormous Wombats and Rhino-like Marsupials
Mastodons, Mammoths, Ground Sloths, Glyptodonts, Native Horses, Large Camels
Focus has always been on Forest elephants.
Forest elephants been established as forest gardeners, consuming more seeds from more species than any other taxon of large vertebrate disperser
Identified at least 14 woody species relied exclusively on elephants for their dispersal.
No such study has been undertaken for the African Savanna elephants.
Elephant-like proboscidean megaherbivores originated in Africa 60 million years ago
Potential for co-evolution between megafaunal fruit and large vertebrates should be higher in Africa than anywhere else.
Megafaunal Fruits Dispersed by the African forest elephant
Lope, Gabon – White, 1994 Ndoki, Congo – Blake, 2009
Sacoglottis gabonensis Klainedoxa gabonensis Autranella congolensis Mammea africana Balanites wilsoniana Maranthus sp. Detarium macrocarpum Ornphalocarpum elatum Drypetes gossweileri Panda oleosa Irvingia gabonensis Tridesmostemon ornplalocarpoides Irvingia grandifolia Irvingia robur
rely exclusively on elephants for their effective dispersal Sacoglottis gabonensis Irvingia grandifolia Panda oleosa Mammea africana
Dispersal Distance
?
Long distance dispersal (LDD) - one of the most important contributors to seed dispersal effectiveness.
No data on the spatial scale at which the African savanna elephants disperse seeds.
One might guess at their efficacy:
consume and defecate large quantities of seed - an average of Found in a variety 228 woody plant seeds of habitats per defecation - Move 11 billion seeds per year
have large home ranges – up to 3000 have long gut km2 in the Kalahari passage times Sands, Southern Africa our question What is the spatial scale at which savanna elephants disperse megafaunal fruit?
gut passage + movement data
Steps:
1. identify our megafaunal fruit 2. get gut passage rate 3. analyses movement data 4. dispersal curve estimation
Identifying South Africa’s megafaunal fruits
Used Operational definition developed by Guimares et al (2008)
South African woody flora (n = 1126) was divided into two types.
Type 1) fleshy fruits that are 4–10 cm in diameter with up to 5 large seeds(generally >2.0 cm diameter)
Type 2)fleshy/dry fruits that are greater than 10 cm in diameter and have numerous (>) small seeds.
Type 1
Megafaunal Fruit Description Family Species Seed Mass Consumed by Type Elephants
Apocynaceae Carissa macrocarpa not known U Type I fruit fleshy fruit maximum length between 4-10cm Arecaceae Rapphia australis, not known U Hyphaene petersiana; 21500 Y number of seeds: 1-5 Hyphaene coriacea; 156 Y (15) Borassus aethiopum not known Y
Balanitaceae Balanites aegyptiaca; 1150 Y Balanites maughamii; 826.84 Y
Boraginaceae Cordia grandicalyx not known U
Chrysobalanaceae Parinari curatellifolia 3315 U
Flacourtiaceae Rawsonia lucida 81.33 U
Ochnaceae Ochna glauca not known U
Papilionoideae Cordyla africana 10000 Y
Sapotaceae Mimusops zeyheri; 291.4 U Vitellariopsis marginata not known U Strychnaceae Strychnos cocculoides 476 U
Type Ib fruit fleshy fruit maximum length between 3-4cm Euphorbiaceae Schinziophyton 12500 Y number of seeds: 1 rautanenii
seed mass > 2000 Anacardiaceae Sclerocarya birrea 5405 Y (2) 17 species Identifying South Africa’s megafaunal fruits
Used Operational definition developed by Guimares et al (2008)
South African woody flora (n = 1126) was divided into two types.
Type 1) fleshy fruits that are 4–10 cm in diameter with up to 5 large seeds(generally >2.0 cm diameter)
Type 2)fleshy/dry fruits that are greater than 10 cm in diameter and have numerous small seeds.
Type 2
Megafaunal Fruit Description Family Species Consumed by Type Elephants Type II fruit maximum fruit fleshy Rubiaceae Gardenia volkensii Y length > 10cm (6) Strychnos spinosa; Strychnos number of seeds: Strychnaceae U pungens U numerous Bombacaceae Adansonia digitata Y
Bignoniaceae Kigelia africana I
Capparaceae Cladostemon kirkii U
fruit dry Mimosoideae Faidherbia albida; Y (8) Albizia brevifolia; U Acacia erioloba; Y Acacia nilotica; Y Acacia haematoxylon U
Caesalpinoideae Piliostigma thonningii; Y Tamarindus indica Y Papilionoideae Swartzia madagascariensis U
14 species our question What is the spatial scale at which savanna elephants disperse megafaunal fruit?
gut passage + movement data
Steps:
1. identify our megafaunal fruit 2. get gut passage rate 3. analyses movement data 4. dispersal curve estimation
Seed passage experiments with sanctuary elephants
observations
When foreign they were initially destroyed Type 1
•rolled underfoot •taste preference gradient Type 2
Type 1 gut passage +
25.0
20.0
15.0 gut transit = 66 hours
10.0 CumulativeNumber ofMango Seeds Recovered 5.0
0.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 Time Elapsed (h)
Gut Transit of Mango Seeds (Mangifera indica) through the gut of 4 elephants (2 males, 2 females) Type 2 gut passage + 1.20
1.00
0.80 gut transit = 96 hours
0.60
0.40 ProportionofTotal PresenceMelon Score
0.20
0.00 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 Time Elapsed (h)
Gut Transit of Melon (Cucumis melo) through the gut of 2 elephants (1 males, 1 females) our question What is the spatial scale at which savanna elephants disperse megafaunal fruit?
gut passage + movement data
Steps:
1. identify our megafaunal fruit 2. get gut passage rate 3. analyses movement data 4. dispersal curve estimation
+ movement data
Thanks to Save the Elephants!
•Timbavati APNR/KNP
•Telemetry data on thirty eight radio-collared wild elephants (27 males, 11 females)
•8-year collection period
7.00
R² = 0.957 6.00
5.00
4.00
3.00
MedianDistance Traveled (km) 2.00
1.00
0.00 0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00 180.00 200.00 Time (hours)
Median Distance Travelled over Time for 38 elephants (27 males, 11 females) 80
70
Max =65km
60
50
(14 x)
40 Distance (km) Distance 30
20
90th %= ~15km 10 Median = 4.4km
0 12.00 24.00 36.00 48.00 60.00 72.00 84.00 96.00 108.00 120.00 132.00 144.00 156.00 168.00 180.00 192.00 Time (hours) 1d 2d 3d 4d 5d 6d 7d
Box and whisker plot of distance across different time intervals. The lower and upper sides of boxes indicate 10th and 90th percentiles. Lines within boxes mark the medians. Whiskers indicate the maximum dispersal distances. Distance travelled for each interval a result of 50 time series across each of 38 elephants 27 males, 11 females) 80
70
60
(14 x) 50
Max =49km
40 Distance (km) Distance 30
90th % =11.6km 20
Median =3.6km 10
0 12.00 24.00 36.00 48.00 60.00 72.00 84.00 96.00 108.00 120.00 132.00 144.00 156.00 168.00 180.00 192.00 Time (hours) 1d 2d 3d 4d 5d 6d 7d
Box and whisker plot of distance across different time intervals. The lower and upper sides of boxes indicate 10th and 90th percentiles. Lines within boxes mark the medians. Whiskers indicate the maximum dispersal distances. Distance travelled for each interval a result of 50 time series across each of 38 elephants 27 males, 11 females) our question What is the spatial scale at which savanna elephants disperse megafaunal fruit?
gut passage + movement data
Steps:
1. identify our megafaunal fruit 2. get gut passage rate 3. analyses movement data 4. dispersal curve estimation
25
20
15
10 Percentage ofSeeds
5
0 0 4 9 13 17 22 26 30 35 39 43 48 52 56 61 65 Dispersal Distance (km) Dispersal curve estimation Curves of dispersal distance were estimated by substituting values of seed gut passage time by corresponding values of elephant displacement in that time (Westcott et al. 2005, Campos Arceiz et al., 2008).
Dispersal Curves for Type 2 megafaunal fruits How do savanna elephants compare to forest elephants?
10 x greater dispersal distance (Campos Arceiz et al.,2008) some thoughts
seed dispersal distance is linked to home range which in turn is linked to water availability
longer dispersal tail
Males always show longer max. dispersal distances How unique is the service African savanna elephants provide?
highly unique service – 65000m
50m
500m
850m
Maximum seed dispersal distances for different disperser functional groups. conclusions elephants bring about extremely long distance dispersal. distances of 30km and over have formerly been treated as extreme LDD events that happen very infrequently – once in a population in a year (Nathan, 2008). in areas with elephants: this is likely to enable rapid movements in response to climate change – mobile link between vegetation types – enhances genetic diversity. in areas without elephants: dispersal failure is a risk – range reductions or clumped and aged populations might result.
I am hoping to further explore these consequences.
Thank you for listening.
Thanks also to:
Prof. William Bond my Supervisor Michelle Henley and the Save the Elephants Foundation Elephant Whispers Sanctuary in Hazyview