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
Sacoglottis gabonensis
Autranella congolensis
Balanites wilsoniana
Detarium macrocarpum
Drypetes gossweileri
Irvingia gabonensis
Irvingia grandifolia
Irvingia robur
Ndoki, Congo – Blake, 2009
Klainedoxa gabonensis
Mammea africana
Maranthus sp.
Ornphalocarpum elatum
Panda oleosa
Tridesmostemon ornplalocarpoides
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:
Found in a variety
of habitats
consume and defecate
large quantities of
seed - an average of
228 woody plant seeds
per defecation
- Move 11 billion
seeds per year
have long gut
passage times
have large home
ranges – up to 3000
km2 in the Kalahari
Sands, Southern
Africa
our question
What is the spatial
scale at which savanna
elephants disperse
megafaunal fruit?
gut passage + movement data
Steps:
1.
2.
3.
4.
identify our megafaunal fruit
get gut passage rate
analyses movement data
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
Type
Type I
Elephants
fruit fleshy
Apocynaceae
Carissa macrocarpa
not known
U
fruit maximum length between 4-10cm
Arecaceae
Rapphia australis,
not known
U
Hyphaene petersiana;
21500
Y
Hyphaene coriacea;
156
Y
Borassus aethiopum
not known
Y
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
Euphorbiaceae
Schinziophyton
12500
Y
5405
Y
number of seeds: 1-5
(15)
Balanitaceae
Type Ib
Consumed by
fruit fleshy
fruit maximum length between 3-4cm
number of seeds: 1
seed mass > 2000
rautanenii
Anacardiaceae
Sclerocarya birrea
(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
Type
Type II
Consumed by
Elephants
fruit maximum
fruit fleshy
length > 10cm
(6)
number of seeds:
Rubiaceae
Gardenia volkensii
Y
Strychnaceae
Strychnos spinosa; Strychnos
U
pungens
U
Bombacaceae
Adansonia digitata
Y
Bignoniaceae
Kigelia africana
I
Capparaceae
Cladostemon kirkii
U
Mimosoideae
Faidherbia albida;
Y
Albizia brevifolia;
U
Acacia erioloba;
Y
Acacia nilotica;
Y
Acacia haematoxylon
U
Piliostigma thonningii;
Y
Tamarindus indica
Y
Swartzia madagascariensis
U
numerous
fruit dry
(8)
Caesalpinoideae
Papilionoideae
14 species
our question
What is the spatial
scale at which savanna
elephants disperse
megafaunal fruit?
gut passage + movement data
Steps:
1.
2.
3.
4.
identify our megafaunal fruit
get gut passage rate
analyses movement data
dispersal curve estimation
Seed passage experiments with
sanctuary elephants
observations
When foreign they
were initially destroyed
Type 1
Type 2
•rolled underfoot
•taste preference
gradient
Type 1
gut passage +
Cumulative Number of Mango Seeds Recovered
25.0
20.0
gut transit = 66 hours
15.0
10.0
5.0
0.0
0.0
10.0
20.0
30.0
40.0
50.0
60.0
Time Elapsed (h)
Gut Transit of Mango Seeds (Mangifera indica) through
the gut of 4 elephants (2 males, 2 females)
70.0
Type 2
gut passage +
1.20
Proportion of Total Melon Presence Score
1.00
0.80
gut transit = 96 hours
0.60
0.40
0.20
0.00
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
Time Elapsed (h)
Gut Transit of Melon (Cucumis melo) through
the gut of 2 elephants (1 males, 1 females)
90.0
100.0
our question
What is the spatial
scale at which savanna
elephants disperse
megafaunal fruit?
gut passage + movement data
Steps:
1.
2.
3.
4.
identify our megafaunal fruit
get gut passage rate
analyses movement data
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
Median Distance Traveled (km)
6.00
5.00
4.00
3.00
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
Distance (km)
50
(14 x)
40
30
20
90th %= ~15km 10
Median = 4.4km
0
12.00
24.00
1d
36.00
48.00
2d
60.00
72.00
3d
84.00
96.00 108.00 120.00 132.00 144.00 156.00 168.00 180.00 192.00
Time (hours)
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
Distance (km)
Max =49km
40
30
90th % =11.6km
20
Median =3.6km
10
0
12.00
24.00
1d
36.00
48.00
2d
60.00
72.00
3d
84.00
96.00 108.00 120.00 132.00 144.00 156.00 168.00 180.00 192.00
Time (hours)
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.
2.
3.
4.
identify our megafaunal fruit
get gut passage rate
analyses movement data
dispersal curve estimation
25
Percentage of Seeds
20
15
10
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