Transcript Diapositive 1

Role of western lowland gorilla (Gorilla gorilla gorilla) to dispersal and regeneration of commercial trees in southeast Cameroon
Charles-Albert Petre 1,2,3, Roseline Beudels 2, Nikki Tagg 3, Jean-Louis Doucet 1
1
Laboratory of Tropical and Subtropical Forestry, Unit of Forest and Nature Management, Gembloux Agro-Bio Tech, University of Liege, 2 Passage des Déportés, 5030 Gembloux, Belgium
2 Royal Belgian Institute of Natural Sciences, Conservation Biology Section, 29 rue Vautier, 1000 Brussels, Belgium
3 Projet Grands Singes (PGS) of the Center for Research and Conservation (CRC) of the Royal Zoological Society of Antwerp (RZSA), Koningin Astridplein 26, 2018 Antwerp, Belgium
Introduction
Methodology
• Tropical ecosystems are strongly influenced by animals through seed dispersal;
• Many dispersers including the western lowland gorilla (WLG) are declining in population size : WLG is
listed as critically endangered (IUCN, 2011);
• Logging concessions encompass more than the half of WLG range;
• Indirect effects of timber exploitation are amongst the main drivers of WLG population decline (Morgan &
Sanz, 2007).
 Widespread wildlife/ape-friendly logging practices represent the major challenge for their long term
survival
 Determining the role of WLG to dispersal and regeneration of commercial trees would encourage forest
managers to strengthen WLG conservation in their concessions
Study site: northern periphery of Dja Biosphere Reserve; 32.4 km²; 1.18 weaned gorilla/km²
Sampling period: 24 month (October 2009 to September 2011)
Sample size: 446 dung piles; 391 deposition sites; 23 daily path lengths; 1211 retention time markers
 Deposition site characterization: canopy openness estimates by hemispherical photography; Basal area
 Theoretical dispersal distances and seed shadow:
Retention time: captive gorillas fed with wild fruits; Dung collection twice a day (9 am & 5 pm)
Daily path length: trail follow between consecutive nest sites
 Gut passage effect on germinability: gut passed seeds sown in a field nursery; Semi-controlled
experiment (gut passed seeds vs seeds discarded from fruit pulp)
Results
Global seed dispersal:
• 55 species identified : tree (41), shrub (1), liana (6), herb (7) + ≈ 40 undidentified morphotypes
• Dispersal of 20.7% of the tree community (41/199 spp)
• 93.1% of dung piles contained intact seeds
• Capacity gut size of up to 9 cm3 (Anonidium mannii, Annonaceae)
Dispersal of commercial tree species:
• Dispersal of six tree species exploited by logging companies (Tab. 3).
• The Tali (E. suaveolens) was previously thought to be an autochorous species (e.g.: Kouadio, 2009).
• The large seed size of Longhi abam (C. lacourtianum) and Ozanbili k (A. klaineanum) restrict the
number of potential dispersers to large capacity gut size species
Table 3. Qualitative dispersal of commercial tree species
Table 1. Quantitative description of seed dispersal
Mean
Minimum
Maximum
2.8 (2.1)
0
12
10.3 (8.7)
1
34
93.07
52.2 (58.8)
309.5 (212.6)
25
0.16
31
100
225.44
1396
Number of species dispersed (± SD)
- individual dung pile
- month
Percentage of dung piles containing seeds
Number of seeds per 100g of faeces (± SD)
Weight of dung piles analyzed (g) (± SD)
Volume of seeds
3
< 1 mm
3
Day
35.7
54.4
3.3
6.6
Young secondary forest
Secondary forest
Light gap
Inundated forest
Night
39.7
4.5
50.3
5.5
Total
37.7
29.5
26.8
6.05
45
40
Mean
Standard deviation
35
30
25
20
Seed deposition sites:
• Bimodal dung production rate (Todd et al., 2008):
50% during daily displacements & 50% at nest sites
• During daily displacements faeces are produced
mainly in closed canopy secondary forest (54.4%) and
open canopy young secondary forest (35.7%) (Tab. 2)
• Almost all nest sites are found in light gaps and young
secondary forest (50.3 & 39.7% respectively; Tab. 2)
• Canopy openness above individual nests is
significantly higher than any other sites (pair-wise
comparisons, U Mann-Whitney , p < 0.05; Fig. 1).
 Most of the seeds are dispersed in sites where light is
not a limiting factor
5
0
YSF
SF
IF
NS
Figure 1. Canopy openness of the different habitat types
Cumulative percentage
• Retention time: 54.3 h ± 28.9 [<8-192].
The gut passage rate of seeds depends on seed size, with
small seeds being retained for longer periods than larger
one (ANOVA, F = 51,373, df = 2, p < 0.05; Tukey post-hoc
test, p < 0.05; Fig. 3).
Large seeds
Medium seeds
Small seeds
75
50
Seed size (mm)
Aningré A
Bilinga
Diana T
Longhi abam
Ozanbili K
Tali
Pouteria altissima
Nauclea diderrichii
Celtis tessmannii
Chrysophyllum lacourtianum
Antrocaryon klaineanum
Erythrophleum suaveolens
Sapotaceae
Rubiaceae
Ulmaceae
Sapotaceae
Anacardiaceae
Caesalpiniaceae
Semi-heliophilous
Heliphilous
Semi-heliphilous
Semi-heliophilous
Heliphilous
Heliphilous
medium
very small
medium
large
large
medium
N.A.
(< 1 mm3)
(13 x 8 x 8)
(31 x 15 x 9)
(21 x 20 x 13)
(17 x 10 x 6)
Hawthorne (1995)
Aningré A
Bilinga
Diana T
Longhi abam
Ozanbili K
Tali
6.6
156.0
46.0
2.0
1.8
1.2
Occurrence
No. month
(± 6.5)
(± 115.3)
(± 25.6)
(± 2.4)
(± 3.0)
(± 1.7)
Mean % of faees
11.1
60.3
56.0
29.9
7.0
41.6
1
4
2
5
7
4
No. seeds dispersed/month/ha
(± SD)
38.2
1116.5
253.7
10.4
13.8
8.2
(± 0)
(± 457.6)
(± 42.3)
(± 6.2)
(± 18.5)
(± 5.5)
Gut passage effect:
• Viability of seeds after gut passage ranges from 8.7 to 93.1%, nonetheless about half of all species
tested retain viabilities higher than 75% (Tab. 5).
• Germination trials reveal that germination success is not affected by gut passage for any of the 8
species tested; in contrary it enhances the success for half of them (Fig. 3) including C. lacourtianum
(Longhi abam).
100
90
N
Y SF: y oung secondary f orest; SF: secondary f orest; IF: inundated
f orest; NS: nest site; N: nest
100
Trait at seedling stage1
Mean no. seeds dispersed/100g
(± SD)
15
10
Family
Table 4. Quantitative dispersal of commercial tree species
minimum = Ficus spp and Nauclea spp ; maximum = Anonidium mannii
Table 2. Dung encounter rate per habitat types (%)
Canopy openness (%)
9 cm
Species
1
Percentage of germinated seeds
1
1
Commercial name
Gut passed
Control
*
*
*
80
Figure 3.
Germination success of
seeds passed through
the gut compared to
control seeds removed
from fruit pulp.
(* significant differences
at 5% level; chi2 test).
70
60
50
40
*
30
20
10
0
A. klaineanum
C. lacourtiana
D. macrocarpa
H. zimmereri
M. tenuifolia
M. arboreus
P. microcarpa
T. abut
Species tested: Antrocaryon klaineanum, Chrysophyllum lacourtianum, Duboscia macrocarpa, Heisteria zimmereri, Monodora tenuifolia, Myrianthus arboreus,
Pseudospondias microcarpa & Trichoscypha abut.
Table 5. Viability of seeds found in fresh faeces
25
• Daily path length: 1923m ± 630.4 [498-2904 m]
0
0
24
48
72
96
120
144
168
192
Hour
Figure 2. Cumulative percentage of seed
deposited in faeces after one feeding event
 Ingested seeds could then potentially be dispersed far
away from the parent tree, along a path as long as 23
km (2.9 km x 8 days).
>75%
7spp
C. lacourtianum (93.1), Cissus dinklagei (88.9), Trichoscypha abut (80.0), Heisteria zimmereri (79.2),
Pseudospondias microcarpa (78.8), Ficus sp (78.7), Marantochloa filipes (75.8)
50 – 75%
4 spp
Monodora tenuifolia (66.3), Myrianthus arboreus (64.4), A. klaineanum (63.4), Desplatia sp (58.6)
25 – 50%
3 spp
Uapaca sp (36.8), E. suaveolens (35.7), Duboscia sp (33.9)
<25%
1 sp
Vitex sp (8.7)
Conclusion
This study reveals that WLG are important dispersers as they disperse seeds of many species at large spatial scale, in large quantities, and with unaffected or enhanced germination success. These seeds have a high
probability of being dispersed in sites with high light intensity which would be very suitable for the six commercial tree species dispersed by WLG since they are are light demanders at the seedling stage. In addition to
deposition site suitability, WLG should contribute significantly to the dynamics of E. suaveolens (Tali), C. lacourtianum (Longhi abam) and A. klaineanum (Ozanbili K) due to the very limited set of potential dispersers.
Conservation of WLG is therefore highly relevant to ensure ecological and commercial function of the concerned forest ecosystems, and for natural forest regeneration, a consideration which should encourage logging
companies to strengthen wildlife/ape management in their concessions.
References
Hawthorne WD. 1995. Ecological profiles of Ghanaian forest trees. Tropical Forestry Paper 29, Oxford Forestry Institute, Oxford, UK. 345p.
IUCN. 2011. IUCN Red List of Threatened Species. Version 2011.1. <www.iucnredlist.org>. Downloaded on 13 May 2011.
Kouadio LY. 2009. Mesures sylvicoles en vue d’améliorer la gestion des populations d’essences forestières commerciales de l’Est du Cameroun [Ph.D. dissertation]. Gembloux (Belgium): University of Liege-GxABT . 278p.
Morgan D, Sanz C. 2007. Best Practice Guidelines for Reducing the Impact of Commercial Logging on Great Apes in Western Equatorial Africa. Gland, Switzerland: IUCN SSC Primate Specialist Group (PSG). 32p.
Todd AF, Kuehl HS, Cipoletta C, Walsh PD. 2008. Using dung to estimate gorilla density: modeling dung production rate. International Journal of Primatology 29: 549-563.
Corresponding author: Charles-Albert Petre - 2 Passage des Déportés, 5030 Gembloux, Belgium - [email protected]