OVERVIEW
The Station d'Etudes des Gorilles et Chimpanzés (SEGC)
was established 12 km into the Lopé Reserve, central Gabon,
in 1983 by Caroline Tutin and Michel Fernandez, following the
completion of a nationwide survey of gorillas and chimpanzees
(Tutin & Fernandez, 1984). The census had revealed numbers
far higher than anybody had expected and in the light of this
it was decided to undertake a study of sympatric gorillas and
chimpanzees. The Lopé was chosen because, at the time,
it was the only one of Gabon's five faunal reserves actively protected
by staff from the Ministry of 'Eaux et Forêts'. The construction
and running costs of SEGC were, and continue to be financed by
the Centre International de Recherches Medicales de Franceville
(CIRMF), an institution co-funded the Gabonese government, ELF
Gabon and the 'Cooperation Française'. SEGC is also affiliated
to two other institutions: the University of Stirling, Scotland
and the Ministry of 'Eaux et Forêts', Gabon.
What was initially planned as a two year field study of the ecology
and behaviour of gorillas and chimpanzees has evolved into a long
term study of many aspects of forest ecology. SEGC continues to
receive core funding from CIRMF but additional support for the
station in the form of grants has come from L.S.B. Leakey Foundation,
the World Wide Fund for Nature, the World Society for the Protection
of Animals; whilst The Wildlife Conservation Society (formerly
the New York Zoological Society) has supported the presence of
one researcher (LW) at SEGC since January 1989.
In the early days the emphasis at SEGC was on gorilla and chimpanzee
ecology. Most field days involved many hours trying to locate
apes by following their feeding trail. In addition to Caroline
Tutin and Michel Fernandez, who were based permanently at SEGC,
a number of students joined the team to work on either gorillas
or chimpanzees.
Since 1989 the research goals at SEGC have become more diverse
and the emphasis today has switched to the rain forest ecosystem
as a whole, rather than concentrating on just one or two animal
species.
The aim of this document is to give a synthesis of what has been
achieved over the years and to give some idea of the future direction
of research at SEGC. After a review of the history of scientific
research at Lopé, major findings on the flora and fauna
are presented. The importance of scientific research for management
of the Reserve and role that the SEGC has played in developing
methodologies and in training are described. Finally, future directions
of research at SEGC are briefly outlined and the publication resulting
from research at the station are listed in an Appendix.
A BRIEF HISTORY OF SCIENTIFIC RESEARCH IN THE LOPE RESERVE
Early research in the Lopé Reserve was botanical. It was
the area's savannas, enclosed within tropical rain forest, which
caught the interest. Aubreville published a number of papers speculating
on the origins of the savanna forest mosaic in the Lopé
Region (e.g., Aubreville, 1967). Later Descoings (1974) spent
time in the region identifying and mapping different species assemblages
in the savanna in the north of the Reserve and those further east
towards Booué (Fig. 1). However, up until the early 1980's
there was only limited botanical work in the forests of Lopé,
and no research on animals had been done.
In 1982 Richard Oslisly and his colleagues began a study of the
archaeology of the region. Our knowledge of the history of human
occupation in the Lopé area, which is thought to date back
at least 350,000 years, is due almost wholly to their detailed
and on going study which has documented several stone age cultures,
the arrival of metallurgy about 2500 years ago and the appearence
of the current populations about 700 years ago (e.g., Oslisly
1993, 1995; Oslisly & Fontugne, 1993; Oslisly & Peyrot,
1992 a, b).
In 1982, Patrice Christy, an ornithologist, made the first of
many visits to the Lopé which have resulted in a comprehensive
inventory of bird species occurring in northern parts of the Reserve
(Christy & Clarke, 1994).
In 1983 Michael Harrison, undertook a 9-month study of the ecology
of black colobus, Colobus satanas, in forest bordering
the savanna in the north of the Reserve (Harrison, 1986; Harrison
& Hladik, 1986; see Fig. 1). During the course of his study
he undertook monthly follows of a focal group of black colobus,
collected specimens of all colobus foods for identification, and
established three botanical transects along which he measured
and identified all trees with circumference ³50 cm at breast
height (1.3 m) in an area of 2 hectares. In addition he measured
food availability for colobus by following phenology patterns
of leaf, flower and fruit production.
Also in 1983, Michel Fernandez and Caroline Tutin began the long-term
study on gorillas and chimpanzees at the Station d'Etudes des
Gorilles et Chimpanzés. The small research station, which
houses 4-6 people, is located on the forest edge in the north
of the Reserve (Fig. 1). The study of the ecology of apes (Gorilla
g. gorilla & Pan t. troglodytes ) has monitored diet and
seasonal movements of sympatric gorillas and chimpanzees over
a 12 year period.
Figure 1: Location of the Lopé Reserve
and various sites mentioned in the text.
It is impossible to study the biology of any animal without an
understanding of its habitat. So the ape study has involved identification
of the plant species consumed or otherwise used (e.g., for nest
construction [both species] or during tool use [chimpanzees]).
In addition we have undertaken habitat analyses in order to try
to understand seasonality of food choice (determined in part by
availability) and ranging. Liz Williamson, the first doctoral
student to complete field work at SEGC, identified and measured
all trees with diameter at breast height (dbh, - measured at 1.3
m above the ground, or above buttresses) ³ 10 cm on five
botanical transects (one 1-km line transect and four elephant
paths) covering 4 hectares (Williamson, 1988). Williamson found
that the most common tree species in the SEGC study area was new
to science, and it was described in her honour as Cola lizae
(Sterculiaceae). This was the first of a number of new species
to be described from collections in Lopé, the most recent
of which are Conceveiba macrostachys (Euphorbiaceae), a
new genus for Africa and the most common tree in the forest in
the centre of the Reserve; Dialium lopense (Caesalpiniaceae),
which is one of the dominant trees in the forest galleries in
the savannas in the north of the Reserve, and Engomegoma gordonii
(Olacaceae), a new genus described in 1995 which is amongst the
10 dominant large trees in the south of the Reserve.
The SEGC research team began to collect plant phenology data
in 1984 and this data set continues to be collected regularly.
It has been of great help in the quest to understand the lives
of gorillas and chimpanzees, and indeed for other rain forest
mammals and birds, to have a record of fruit production in particular
(e.g., Tutin et al., 1991a). Rogers and Williamson (1987) undertook
stem counts of Marantaceae and Zingiberaceae along Williamson's
1-km line transect and demonstrated the abundance of plants of
these two families in the understory (cf. Wrangham et al., 1993).
The work at SEGC continues to track the ecology of gorillas and
chimpanzees and is gradually diversifying into a detailed study
of pattern and process in the Lopé ecosystem. Upwards of
60 publications have resulted from this work (see appendix).
Between 1985-1987 Jan Reitsma, established four 1-hectare plots
in different parts of Gabon. One was in the Lopé Reserve,
about 30 km to the south-west of SEGC. He identified and measured
all trees and lianes ³ 10 cm dbh and identified all plant
species (of any size) in two 10 m x 10 m sub-plots within each
of the four sites (Reitsma 1988). Lopé was the least species
diverse of Reitsma's four plots and he suggested that this was
related to poor soils and low rainfall. One surprising feature
of the plot in Lopé was that it contained several large
Sacoglottis gabonensis (Humiriaceae) trees. This species
was thought to be restricted principally to the coastal sedimentary
basin and had not previously been recorded so far inland (Williamson
1988 also recorded the presence of scattered individuals in the
SEGC study area).
In 1986 Marcel Alers and Allard Blom, began a study of the ecology
and behaviour of forest buffalo, Syncerus caffer nanus,
in the northern part of the Lopé Reserve. As part of this
study they undertook classification and mapping of savanna areas
between Lopé village and SEGC. They divided the savannas
into five types based on plant species composition. Erosion and
moisture content of the soil were two of the main physical features
which determined savanna vegetation type. They produced a simplified
vegetation map.
In 1989 Lee White began a doctoral study of the effects of commercial
logging on rain forest vegetation and wildlife. This marked the
first time that activities of SEGC were extended out of the main
ape study area to the Reserve as a whole. At the same time, Gordon
McPherson of the Missouri Botanical Garden made a first collecting
trip to the region and he has continued to collaborate closely
on the botanical inventory of the Reserve ever since.
For the logging study five sites with different logging histories
were identified. Botanical inventories and mammal censuses were
undertaken using methods adopted from similar studies elsewhere,
with some adaptation as appropriate to ecological conditions in
Lopé and the aims of the study - see Figure 1. When it
became evident that there were important vegetation differences
between sites that could not be explained by recent disturbance,
the logging study evolved into an investigation of vegetation
history and the effects of differences in vegetation composition
on mammalian biomass (White, 1992).
From 1989 we began to diversify the research program to look
at other species which shared the apes' habitat. We intensified
long-term data collection on the biology of forest elephants and
and three more PhD theses were completed, one looking at habitat
preferences and nest building of chimpanzees (Wrogemann, 1992),
one on the biology of grey-cheeked mangabeys (Cercocebus albigena
) (Ham, 1994) and one on the role of gorillas as seed dispersers
(Voysey, 1995 ). In 1993, Alphonse Mackanga-Missandzou, the first
Gabonese national candidate for a PhD in wildlife ecology, began
a study of the wildlife and vegetation of the forest-savanna contact
zone.
In 1992 a regional conservation program funded by the European
community, ECOFAC, selected Lopé as the protected area
in Gabon in which it would operate. The goal of ECOFAC is to promote
the conservation of tropical forests through the development of
sustanable economic activities within local comunities. At Lopé
the main development project is the introduction of eco-tourism
which creates jobs and opens a viable source of income to local
people. In addition, ECOFAC has funded both ecological and sociological
research in the Reserve in order to create a data-base that will
allow informed management decisions to be made. Michel Fernandez
directs ECOFAC Gabon and close links exist with SEGC.
Research on the Lopé gorillas suffered a set-back in 1993
when Porthos, the adult male 'silverback' of SEGC's focal gorilla
group died as a result of an attack by another gorilla. His group
broke up and his previous home range in the centre of our study
area has remained practically devoid of gorillas. We continue
to monitor the study area routinely - since the length of time
it takes before the area is colonised by a new group may tell
us a great deal about the dynamics of gorilla populations. However,
the absence of gorillas and the start of ECOFAC have resulted
in a shift in emphasis of research at SEGC.
Our new themes are most concerned with vegetation changes which
have occurred since the last ice age (that is, the last 20,000
years or so) and their implications for rain forest mammals. Lopé
is ideal for such studies, because the mosaic of forest and savanna,
which occurs in the north of the Reserve, resembles the vegetation
of much of tropical Africa as it was after the last glacial peak,
when forest was expanding out of a few rain forest refugia into
open grasslands. The juxtaposition of forest and savanna opens
up a window into the past. A new emphasis on archaeology, in collaboration
with Richard Oslisly at the Natural History Museum in Paris, has
begun to highlight the important role humans have played in forest
history, particularly over the last 2500 years. At the same time,
the long term ecological data sets are gradually coming into their
own, highlighting possible implications of the rapid climate change
the world is experiencing today. Our research may eventually allow
us to predict future changes in rain forest vegetation in Africa.
SUMMARY OF RESEARCH FINDINGS AT SEGC
Many researchers have passed through the Lopé Reserve
and through the continued presence of the field station at SEGC
the published and unpublished results of the work of these assorted
scientists have been compiled into an extensive data base. This
can be divided into four broad categories: Inventories; Vegetation
Description, Dynamics and History; Ecology and Behaviour of large
mammals; and Long-term Data Sets. Major findings are described
below emphasising links between fields of research and the application
of these findings to management of the Lopé Reserve and
of tropical rain forest ecosystems.
1) Inventories
There has been no concerted attempt to compile a comprensive
biological inventory in the Reserve. A list of large and medium
sized mammals based on field observations and supplemented by
examination of dead animals, includes 45 forest dwelling species
(Tutin et al., in preparation). Systematic inventories have not
been made of small mammals.
The majority of researchers have taken an interest
in the botany of the Reserve and more recently ECOFAC has supported
systematic botanical collection aimed at producing a plant species
list for the Reserve. It can be argued that a detailed botanical
inventory is the building block for all ecological research. In
Lopé, early research focussed on primate ecology but in
order to understand the ecology of primates it was vital to identify
and describe the distribution of food species and to document
patterns of plant food production in their habitat (e.g., Tutin
et al., 1991 a, 1994). If one is to make meaningful comparisons
across different sites detailed botanical inventories are essential
(Mitani et al., 1994).
In addition, compilation of a detailed botanical inventory is
a form of research in itself. Species composition will reflect
both the diversity of habitats and the vegetation history of the
site. The process of compiling a species list contributes to our
understanding of vegetation types and is a useful means of training
research assistants. The process also encourages collaboration
between field sites and taxonomists working in herbaria worldwide,
and in this way stimulates the ongoing process of describing and
cataloguing the numerous species as yet unknown to science.
Tutin et al. (1994) recorded 676 species in the SEGC study area
which covers about 50 km2 in the north of the Lopé Reserve
(see Figure 1) and predicted that the total count would rise to
about 1400. We have been able to compile a record of all botanical
collections made in the Reserve by contacting botanists known
to have worked there. During the course of daily field work we
systematically collect all fertile plants with which we are unfamiliar.
In addition, we undertake specific collecting trips to particular
habitats or more remote areas. Plants are dried in the field.
One specimen is kept for the field herbarium at SEGC. A second
replicate is kept in Gabon for the National Herbarium in Libreville
(LBV). A third is sent to the ECOFAC collection currently being
established by Jean Lejoly at Université de Bruxelles Libre
and all other replicates go to Missouri Botanical Garden (MO),
in view of our profitable, long-term collaboration with Gordon
McPherson at that institution.
To date we have a list of about 1250 collections to add to our
own, numbering just over 1500, making a total of over 2750 for
the Reserve. These have been entered into a database at SEGC.
A total of at least 1286 species of plant from 116 taxonomic families
have been collected in the Reserve. A number of collections have
been made close to, but not within the Reserve, mostly in the
Forêt des Abeilles to the east. This forest is dominated
by plants in the Caesalpiniaceae - a vegetation type which dominates
eastern and southern parts of the Lopé Reserve, but in
which we have done limited collecting to date. If these collections
from close to the Reserve, but not within its physical limits,
are added (Gordon McPherson, personal communication; Chris Wilks,
personal communication; and Gesnot, 1994) a further 67 species
and one additional family are added to the list. The list includes
8 new species and one new genus (and a second which is new for
Africa) and 26 new records for Gabon. The list of plant species
will continue to rise for many years to come.
In addition to the plant list there is a comparable list of 345
bird species known to occur within the Reserve. Many of these
are restricted to specific habitats such as savanna, mature forest
or the galleries along the River Ogooué. Many of the species
found in savanna are specialists which would disappear if this
habitat is not maintained (see below).
Further inventories are planned as part of the ECOFAC program.
An inventory of reptiles and amphibia is underway, and work on
insects will be undertaken in the future.
2) Vegetation Description, Dynamics and History
a) Vegetation Types
Vegetation studies have been undertaken in several parts of the
Lopé Reserve on five 5-km botanical transects, using the
methods subsequently adopted by ECOFAC. There were between 81-160
species of tree and liane ³ 10 cm dbh per 2.5 ha transect
sample (Figure 3). In addition there were marked differences in
species composition between sites. For example, Table 1 compares
the first ten species ranked by basal area for the five transects.
Table 1: Species ranked in the first 10
by basal area on at least one transect. |
Species |
Family |
Site |
|
|
1 |
2 |
3 |
4 |
5 |
Aucoumea klaineana |
BURSERACEAE |
1 |
1 |
1 |
2 |
1 |
Cola lizae |
STERCULIACEAE |
2 |
|
|
|
2 |
Pentaclethra macrophylla |
MIMOSACEAE |
3 |
7 |
3 |
|
4 |
Pentaclethra eetveldeana |
MIMOSACEAE |
4 |
|
|
|
6 |
Dacryodes buettneri |
BURSERACEAE |
5 |
4 |
5 |
1 |
5 |
Lophira alata |
OCHNACEAE |
6 |
|
|
|
3 |
Diospyros polystemon |
EBENACEAE |
7 |
|
| |
8 |
Hylodendron gabunense |
CAESALPINIACEAE |
8 |
|
|
|
|
Ganophyllum giganteum |
SAPINDACEAE |
9 |
|
|
|
|
Pycnanthus angolensis |
MYRISTICACEAE |
10 |
|
|
|
|
Santiria trimera |
BURSERACEAE |
|
2 |
2 |
9 |
|
Coula edulis |
OLACACEAE |
|
3 |
6 |
4 |
|
Sacoglottis gabonensis |
HUMIRIACEAE |
|
5 |
|
|
|
Augouardia letestui |
CAESALPINIACEAE |
|
6 |
|
5 |
|
Sindoropsis le-testui |
CAESALPINIACEAE |
|
8 |
|
6 |
|
Conceveiba africana |
EUPHORBIACEAE |
|
9 |
4 |
|
|
Desbordesia glaucescens |
IRVINGIACEAE |
|
10 |
|
|
|
Scyphocephalium ocochoa |
MYRISTICACEAE |
|
|
7 |
3 |
|
Staudtia gabonensis |
MYRISTICACEAE |
| |
8 |
| |
Strombosiopsis tetrandra |
OLACACEAE |
|
|
9 |
7 |
|
Staudtia kamerunensis |
MYRISTICACEAE |
|
|
10 |
|
|
Strombosia zenkeri |
OLACACEAE |
|
|
|
8 |
|
Cylicodiscus gabonensis |
MIMOSACEAE |
|
|
|
10 |
|
Xylopia quintasii |
ANNONACEAE |
|
|
|
|
7 |
Scottellia coriacea |
FLACOURTIACEAE |
|
|
|
|
9 |
Ceiba pentandra |
BOMBACACEAE |
|
|
|
|
10 |
Figure 3: Species Area Curves for plants ³ 10 cm dbh on
the five transects.
By a combination of field observation and data analysis using
two types of multivariate analysis (Two-way Indicator Species
Analysis [TWINSPAN] [Hill, 1979a] and Canonical Community Ordination
[CANOCO] [Ter Braak, 1988 - an extension of DECORANA - Hill, 1979b])
21 vegetation types found in different proportions on one or more
of the transects were defined. Of these, six are major habitat
types while others (described in full in White, 1992) cover smaller
areas.
1) Savanna - vegetation maintained by annual fires, dominated
by grasses, with shrubs such as Crossopteryx ferruginea, Nauclea
latifolia and Bridelia febrifuga patchily distributed
in some areas. Large continuous areas of savanna are restricted
to low altitude areas, whilst small isolated patches occur either
around these zones, or on hill tops with altitude of about 250-450m.
2) Colonising Forest - occurs adjacent to savannas in areas protected
from fire. Shrubs such as Psidium guineensis, Psychotria
vogeliana and Antidesma vogelianum become common as
well as the trees Aucoumea klaineana, Lophira alata
and Sacoglottis gabonensis. Ground vegetation is dominated
by grasses.
3) Monodominant Forest - dominated by Aucoumea klaineana
and Lophira alata, but with other characteristic species
(e.g., Klainedoxa gabonensis ). Many individuals
are crooked or branch low and most are smaller than is usual for
their species. Ground vegetation is sparse, but some herbs may
become established, notably Aframomum longipetiolatum
and Megaphrynium spp.
4) Marantaceae Forest - where trees are better formed, canopy
cover is increased but dominated by Aucoumea klaineana
and Lophira alata . Ground vegetation is more diverse
and herbs abundant including Haumania liebrechtsiana, Aframomum
sp. ?nov and Megaphrynium spp.
5) Mixed Marantaceae Forest - in which greater numbers of other
tree species are present adding to the structural complexity and
species diversity of the forest in which Aucoumea klaineana
and Lophira alata are no longer dominant. Herbaceous plants
of the Zingiberaceae and Marantaceae are abundant.
6) Mature Forest - increased tree diversity including species
associated with more ancient forest (e.g., Coula edulis,
Sindoropsis le-testui, Desbordesia glaucescens )
(cf. de Saint Aubin, 1963). Densities of Marantaceae and Zingiberaceae
herbs are low.
b) Effect of vegetation on animal abundance.
Differences in vegetation type have a profound influence on densities
of many animal species, particularly large mammals such as forest
elephant, Loxodonta africana cyclotis and western lowland
gorillas, Gorilla g. gorilla (White, 1994 a). Table 2
gives the large mammal biomass for transects 1-5. There are great
differences between sites and these are mainly due to differences
in vegetation composition of the five sites (White, 1994 a).
Site 1, the SEGC main study area, which is dominated by Marantaceae
Forest, had the highest mammalian biomass yet recorded for a tropical
rain forest. This was due mostly to the high forest elephant density,
which averaged 3 km-2 over a period of three
years, with seasonal peaks almost double this. This illustrates
the importance of Marantaceae Forest for elephants and there is
evidence that it is equally important for several other large
mammal species, particularly gorillas and mandrills (see White
et al., 1995).
Table 2: Estimated species biomass for the study sites.
Species Estimated Biomass (kg km-2) |
|
Site 1 |
Site 2 |
Site 3 |
Site 4 |
Site 5 |
Cercopithecus nictitans |
81 |
25 |
59 |
87 |
61 |
Cercopithecus pogonias |
11 |
4 |
12 |
9 |
14 |
Cercopithecus cephus |
12 |
3 |
7 |
19 |
8 |
Cercocebus albigena |
35 |
12 |
30 |
41 |
51 |
Colobus satanas |
114 |
109 |
36 |
92 |
102 |
Mandrillus sphinx |
15 |
48 |
82 |
67 |
8 |
Gorilla gorilla |
78 |
39 |
31 |
23 |
55 |
Pan troglodytes |
27 |
8 |
43 |
19 |
16 |
Sub-total |
(diurnal primates) |
373 |
250 |
300 |
358 |
315 |
Loxodonta africana |
5225 |
1916 |
523 |
1742 |
2961 |
Potamochoerus porcus |
99 |
347 |
105 |
204 |
81 |
Cephalophus monticola |
1 |
6 |
5 |
5 |
1 |
Red duikers |
39 |
74 |
47 |
85 |
64 |
Cephalophus sylvicultor |
51 |
P |
17 |
34 |
59 |
Hyemochus aquaticus |
P |
2 |
1 |
|
|
Neotragus batesi |
P |
P |
P |
|
|
Syncerus caffer |
71 |
P |
214 |
119 |
|
Sub-total |
(ungulates) |
5486 |
2343 |
696 |
2286 |
3166 |
Squirrels |
4 |
4 |
7 |
4 |
4 |
TOTAL |
5863 |
2597 |
1003 |
2648 |
3485 |
P = present but not recorded on censuses.
New research in gallery forests and forest islands isolated in
the savanna has shown that mammalian biomass in the forest-savanna
contact zone is even higher than in Marantaceae Forest, exceeding
5970 kg km-2. However, in this habitat type the proportion made
up by each species is different, with elephants becoming less
dominant and buffalo, pigs, duikers and mandrills achieving much
higher densities.
c) Mapping vegetation types.
Considering the marked differences in animal densities in different
vegetation types, if we are to estimate the size of populations
of different animal species within the Lopé Reserve we
need to map the distribution of vegetation types. Mapping has
been undertaken on two scales. First, using aerial photographs
which already existed and radar images commissioned by ECOFAC,
a simplified vegetation map of the whole reserve has been produced
(Figure 4). Second, a more detailed map of the main SEGC study
area in the north of the Lopé Reserve has been produced
in order to study the relationship between different vegetation
types (Figures 5 & 6).
Figure 4: Simplified vegetation map of the Lopé Reserve
Figure 5: Part of the Lopé Reserve showing the area
covered by the detailed vegetation map.
Aerial photographs from 1982 and radar images taken in 1992 were
available for the whole of the Reserve, and there were also some
aerial photographs from 1957 (all three at 1:50,000 scale). On
aerial photographs and radar images it was possible to distinguish
Savanna and the major forest types. A 1:10,000 scale map was produced
by tracing visible vegetation boundaries from 1:50,000 scale aerial
photographs and radar images and enlarging. Locations of water
courses, old logging loads and major elephant trails were marked
onto these maps using unpublished records from SEGC, aerial photographs
and an existing topographic map and by direct mapping using a
sighting compass and a 'topofil' measure. The entire SEGC study
area was then walked and each vegetation type was mapped with
the aid of a compass, topofil and GPS unit, by walking its perimeter.
The vegetation map is presented in Figure 6 at a scale of about
1:150000.
Figure 6: Detailed vegetation map of part of the Lopé
Reserve.
d) Vegetation dynamics.
This map clearly demonstrates the relationship between Colonising,
Monodominant and the two types of Marantaceae Forest. In almost
all locations where there is Colonising Forest isolated within
the main forest block, there are successive rings of Monodominant,
Marantaceae and Mixed Marantaceae Forest. This is in line with
the theory that these vegetation types are linked on a succession.
In order to try to explain the large variation in botanical composition
between sites the following model was developed:
It is generally accepted that global climatic fluctuations associated
with ice age maxima and minima have caused changes in the distribution
of forest vegetation in Africa (e.g., Hamilton, 1976, 1982; Maley,
1991): during maxima the African climate became cooler and drier
and forest vegetation retreated into a series of isolated refugia;
and during minima the climate became warmer and wetter and forests
expanded. In some places forest composition today reflects these
pre-historic changes. De Foresta (1990) described forest vegetation
close to savanna isolates in the Makaba region of the Oriental
Mayombe, Congo, and concluded that the characteristic formation
"forêt clairsemée à Marantaceae",
which had previously been described close to savannas in Cameroun
(Letouzey, 1968), was evidence for recent colonisation of savanna
by forest vegetation. This forest type occurs at Lopé,
where it is generally close to savannas, extending up to 10-15
km from the modern savanna edge, although isolated patches exist
further away. Aubreville (1967) suggested that savanna areas
in Lopé had previously been more extensive, and that they
had been recolonised by forest spreading from refuges to the north
and south. Data from our research, and information on Lopé
savannas (Oslisly, 1993; J. Maley, personal communication), suggest
the following scenario, very much in line with that put forwards
by Aubreville:
After the last major dry climatic phase (ice age maxima) around
18,000 years BP (e.g., Hamilton, 1982; Maley, 1991), when much
or all of the area might have been savanna, forest vegetation
started to re-colonise around 12,000 years BP. Maximum extension
of the forest occurred in the middle Holocene (7-4,000 BP), at
which point the Lopé savannas would probably have been
much reduced. Savannas probably then re-opened between 3-4,000
BP, expanding during a marked arid phase between 2500 - 2000 BP
(Maley, 1992), when they were probably more extensive than today.
The return of more humid conditions between 1400 - 1500 BP (Maley,
1992) would have initiated a new phase of forest re-colonisation,
which may be what we see underway today in Lopé, in places
where fire does not interfere with the succession.
During arid periods it is generally accepted that the climate
also became cooler and that montane vegetation descended to about
450-500m altitude (Hamilton 1976, 1982; Maley et al, 1990).
Hence, forest cover was retained on mountains of about this height,
whilst lower hills became covered by savanna. In addition, species
composition of some of the gallery forests currently isolated
in savanna in the north of the Reserve suggests that some of these
are ancient and probably also survived through at least the most
recent arid phase. Once climatic conditions became favourable
once again, forest species spread out from major forest refugia
to the north and south of Lopé, and from forested mountain
tops and any galleries that remained. As the forest advanced
the last areas to be recolonised were hill-tops, and many of these
retain isolated patches of savanna on their crowns, which will
presumably slowly disappear if protected from fire.
Tree species such as Lophira alata, Aucoumea klaineana
and Sacoglottis gabonensis are able to establish in
savanna edge conditions. They form a Colonising Forest extension
that provides shade, moderating the extremes of temperature and
humidity experienced in open savanna. Early colonising individuals
have low, round canopies and branch low down, but successive generations
of seedling grow taller and branch higher to escape from the shadow
of their predecessors. As more individuals become established
canopy cover increases, and there is a corresponding increase
in relative humidity and rates of organic deposition, whilst soil
temperatures come to resemble those found within the forest. Soil
quality improves, and new species are able to become established
forming a post-colonising formation. Increased shade reduces the
competitive advantage of grasses and new species of herbs and
shrubs appear.
As the process continues and more species establish, conditions
become favourable for the growth of herbs such as Haumania
liebrechtsiana, Megaphrynium spp. and Aframomum
spp., i.e. Marantaceae Forest, characteristic of many savanna/forest
areas (de Foresta, 1990; Letouzey, 1968). Haumania liebrechtsiana
densities increase until it forms a tangled carpet smothering
the ground and climbing up to 10m or more in dense towers that
can engulf small trees. This formation may persist for long periods,
as the ground cover interferes with establishment of the next
generations of trees. Marantaceae forests have characteristic
low stocking densities of trees, especially medium sized trees
whose crowns form the middle canopy (de Foresta, 1990; Letouzey,
1968), giving them an open appearance (see photographs in: de
Foresta 1990, p.335; Letouzey 1968, p.225) and there are sometimes
extensive areas (up to about 1ha) with few or no trees at all
(de Foresta, 1990).
There is a gradual build-up of canopy cover in Marantaceae forest,
which results in decreased light levels and a decrease in herb
densities, and new tree species invade which are characteristic
of Mixed Forest. As these become established the succession proceeds
towards Mature Closed Canopy Forest, characterised by increased
dominance of the Caesalpiniaceae, Olacaceae and Myristicaceae,
and further decreased herb densities.
Following this model, the vegetation in the Lopé is a
dynamic formation which has been in constant flux for thousands
of years. The situation today is a snapshot in time and the vegetation
will continue to evolve. As a consequence, there is a complex
mosaic of vegetation types, particularly in northern parts of
the Reserve close to the savanna, which reflects the recent expansion
of forest into savanna areas. Each vegetation type is a stage
of the succession from savanna to mature forest, and as such they
are all inter-related.
If one assumes that Monodominant Forest results from savanna
colonisation and evolves into Marantaceae Forest, one can see
clearly from the detailed vegetation map the evolution of the
landscape: areas which are now occupied by Monodominant Forest
were once Savanna; areas which are now occupied by Marantaceae
Forest would then have been Monodominant or Colonising Forest.
The rock outcrops are probably a result of erosion during savanna
conditions (see Schwartz et al., 1990).
The research of Richard Oslisly and his colleagues on the history
of Iron Age populations, who arrived in the area about 2500 years
ago, has particular bearing on vegetation dynamics. At Lopé,
Marantaceae Forests extend up to 20km from the savanna edge in
places (Fig. 4) and are then replaced by 'Closed Canopy Forests'
with increased species diversity and structural complexity and
decreased densities of Marantaceae and Zingiberaceae herbs. Oslisly
& Dechamps (1994) found evidence of fires about 20 km south
of the current savanna-forest interface in Lopé, which
dated from 1,400 - 1,500 BP. These were closely associated with
remains of iron smelting furnaces which dated from the same period
and it is likely that the fires were caused by humans. Two tree
species identified from the charcoal, Sapium ellipticum
and Erythroxylum sp., are currently restricted to the
forest-savanna mosaic. This suggests that the savannas extended
further south at this time. Recent discoveries of iron age villages
far from the present day savannas, close to the transition between
Marantaceae Forest and Closed Canopy Forest, and dated back at
about 1800 years BP (Oslisly & White, unpublished data) provide
further evidence that savannas extended far to the south of their
current distribution at Lopé. All of these sites are located
in mature forest types with open understorey. The age of these
recent archaeological finds suggests that the current distribution
of Marantaceae Forest at Lopé is most likely to be a result
of changes in the vegetation during the last dry phase of the
recent Holocene, which started about 3000 BP and lasted to 2500/2000
BP (Maley, 1992).
If this is so, there would have to have been a period between
then and now when savannas fires were absent, or rare, allowing
the forest to advance up to 20 km into the savanna. This would
be unlikely if human populations continued to live in the area,
since they would burn savannas regularly. However, Oslisly (1993,
1995) reports evidence of a population crash at about 1400 BP
which lasted until about 700 BP: there are numerous archaeological
remains from the Lopé area both before and after this period,
but no evidence of human activity anywhere in central Gabon between
these dates. Such a population crash, coinciding as it did with
a relatively humid period in Africa's climatic history (see Maley,
1992), would have allowed the forest to advance rapidly into the
savanna from its southern limit at the time. This scenario suggests
that much of the vegetation in the Lopé Reserve was savanna
up to 1500 years ago. This area is delimited today by the distribution
of Marantaceae Forests (Fig. 4). Today these forests support the
highest known mammalian biomass of any rainforest (White, 1994
a).
The age of some of the younger vegetation types can be estimated
using evidence from old aerial photographs and data on the growth
rates of indicator tree species. The Colonising phase lasts for
about 50 - 100 years before the transition to Monodominant Forest.
Monodominant Forests probably last for another 100 years or so,
gradually evolving into Marantaceae Forest. The transition from
Marantaceae Forest to Mixed Marantaceae Forest probably takes
about 200 years and the evolution of Mixed Marantaceae Forest
into older forest types with more open understory probably takes
300 - 500 years. Succession in rocky areas is slower. Individuals
of Diospyros zenkeri up to 30 cm dbh occur in Mixed Rocky
Forest - according to growth data (see above) these are about
597 years old. Presence of rock outcrops indicates that the surrounding
area was once savanna, since the erosion necessary to reveal outcrops
does not occur under forest conditions (Schwartz et al., 1990).
These dates are best guesses for the moment. We are currently
awaiting the results of a project using 13C analyses (which use
measures of 13C in the soil to distinguish between landscapes
dominated by Savanna or Forest species) combined with 14C dating
of charcoal in soil profiles, which should allow us to date these
transitions with some precision.
Using the preliminary estimates of the age of different vegetation
types vegetation changes in the SEGC / ECOFAC area from the present
to 1500 years BP have been reconstructed (Figures 7 - 11).
Figure 7: Vegetation map of SEGC and ECOFAC areas; present
(Legend applies to Figures 7 - 11).
Figure 8: Vegetation map of SEGC and ECOFAC; situation 75-100
years ago.
Figure 9: Vegetation map of SEGC and ECOFAC; situation about
250 years ago.
Figure 10: Vegetation map of SEGC and ECOFAC; situation
about 700 years ago.
Figure 11: Vegetation map of SEGC and ECOFAC; situation
about 1400 years ago.
This reconstruction shows that about 75 -100 years ago there
was a lot more Colonising Forest than today, suggesting a corresponding
reduction in the number of savanna fires. This probably corresponds
to a trend for villages to move out of the Reserve towards the
Ogooué River under the colonial 'regroupment' policy, begun
in the late ninteenth century (Pourtier, 1989). About 250 years
ago there was a high proportion of Monodominant Forest, corresponding
to a period, probably about a century before, when there was another
period without fires. Alternatively, this may represent a gradual
movement of the forest-savanna border during a period of irregular
fires due to low population density (Richard Oslisly, personal
communication). The situation about 700 years ago reflects the
situation at the end of the 700 year absence of human populations
when savanna fires lit by the new arrivals (Oslisly 1995) would
have stopped colonisation and set much of the young Colonising
Forest back to Savanna. The situation about 1400 years ago corresponds
to the beginning of the hiatus. Some gallery forests which were
thin or non-existant are indicated by the presence of rock outcrops.
In others, densities of Caesalpiniaceae species today indicate
that they survived through this period of maximum savanna extension.
It is probable that the situation just before the hiatus was
little changed from the arrival of metalurgists, about 2500 years
ago (Oslisly & Fontugne, 1992). This arrival coincided with
a dry climatic phase which lasted from about 3000 to 2500-2000
years ago (Maley, 1992), during which fires of human origin may
well have penetrated the forest, driving it south away from the
population centre along the River Ogooué. Hence, vegetation
distribution in the Reserve at this time probably corresponded
to that portrayed in Figure 12.
Figure 12: Simplified vegetation map for the Reserve, as it
is thought to have been about 2000 years ago.
Figure 13 shows profile diagrams which document the process of
savanna colonisation. Note that all but three of the species colonising
the savanna in these figures are dispersed by animals (see below).
Table 3 shows the densities of the commoner shrubs and seedlings
in Savanna and Colonising Forest - all the species with animal
dispersed fruits represent foods which will attract animals out
of the forest into open areas where they are more easily viewed
by tourists.
Figure 13: profile diagrams in Savanna and Colonising Forest.
(horizontal and vertical scales are the same. All individuals
³ 5 cm dbh in a 5m strip along a line-transect are drawn)
a) Savanna
b) Colonising Forest (about 15 years since last fire).
c) Colonising Forest ( about 50 years since last fire)
Table 3: abundance of species which occurred at least five times
in Savanna or Colonising Forest plots. (Sav = number of individuals
in 5 savanna plots; Col = number of individuals in 5 Colonising
Forest plots; Disp = Dispersal mode (A - animal, W - wind, ? -
unknown).
Species | Family
| Sav | Col
| Disp |
| | |
| |
Psidium guineense | MYRTACEAE
| 25 | 311 | A
|
Aucoumea klaineana | BURSERACEAE
| 2 | 144 | W
|
Uapaca guineensis | EUPHORBIACEAE
| - | 73 |
A |
Psychotria vogelianum | RUBIACEAE
| - | 59 |
A |
Barteria fistulosa | PASSIFLORACEAE
| - | 39 |
A |
Crossopteryx febrifuga | RUBIACEAE
| 281 | 24 | W
|
Duboscia macroceras | TILIACEAE
| - | 22 |
A |
Klainedoxa gabonensis | IRVINGIACEAE
| - | 22 |
A |
Triumfetta cordifolia | TILIACEAE
| - | 20 |
A |
Swartzia fistulosa | CAESALPINIACEAE
| - | 17 |
A |
Lophira alata | OCHNACEAE
| - | 16 |
W |
Antidesma vogelianum | EUPHORBIACEAE
| 1 | 14 | A
|
Psorospermum tenuifolium | HYPERICACEAE
| - | 13 |
A |
Tetracera podotricha | DILLENIACEAE
| - | 8 | A
|
Ouratea flava | OCHNACEAE
| - | 7 | A
|
Pauridiantha efferata | RUBIACEAE
| - | 7 | A
|
Citrus sp. | RUTACEAE
| - | 5 | A
|
Hippocratea myriantha | HIPPOCRATACEAE
| - | 5 | W
|
Pavetta puberula | RUBIACEAE
| - | 5 | A
|
Psychotria venosa | RUBIACEAE
| - | 5 | A
|
Vitex doniana | VERBENACEAE
| - | 5 | A
|
Lippia multiflora | VERBENACEAE
| 8 | - | ?
|
| | |
| |
Other species |
|
1 |
70 |
|
|
|
|
|
|
|
TOTALS |
318 |
891 |
|
|
|
|
|
|
Moving further along the succession we pass through Monodominant
Forest, which is essentially a natural plantation of Okoumé,
into Marantaceae Forest. Plants belonging to the families Marantaceae
(arrowroot) and Zingiberaceae (gingers) are a major component
of the understorey in certain tropical African forests, to the
extent that 'Marantaceae Forest' is a recognised forest type in
some areas (e.g. de Foresta, 1990; Hawthorne, in press; Koechlin,
1964; Letouzey, 1968; Maley, 1990; Rogers & Williamson, 1987;
Swaine, 1992; White, 1992).
Several species of Marantaceae and Zingiberaceae provide important
food items for apes (Gorilla gorilla & Pan
troglodytes ), mandrills (Mandrillus sphinx ) and
elephants (Loxodonta africana ) in the forests of central
Africa (Badrian & Malenky, 1984; Carroll, 1988; Hoshino, 1986;
Jones & Sabater-Pi, 1971; Kano, 1983; Kano & Mulavwa,
1984; Malenky & Stiles, 1991; Rogers & Williamson, 1987;
White et al., 1995; Wrangham et al., 1991, 1993).
In the Lopé, young leaves and pith of five species, Aframomum
sp.? nov. (Zingiberaceae), Haumania liebrechtsiana, Megaphrynium
velutinum, M. macrostachyum and Hypselodelphys
violacea (Marantaceae) are eaten throughout the year by lowland
gorillas (Gorilla g. gorilla) and chimpanzees (Pan t.
troglodytes) (Rogers et al., 1990; Tutin & Fernandez,
1993 b; Williamson et al., 1990). When fruit is scarce,
both species of ape at Lopé increase their consumption
of these foods. In addition, gorillas eat large quantities of
the aquatic Marantaceae, Marantochloa cordifolia, but only
during the annual dry season when fruit was scarce (Rogers et
al., 1988; Tutin et al., 1991a). Parts of 14 other
species of Marantaceae and Zingiberaceae are eaten less frequently
(Tutin & Fernandez, 1993 b; Williamson et al., 1990),
but the five species named above are amongst the 'keystone' foods
of the apes at Lopé; that is, they play prominent roles
in sustaining apes through periods of food (i.e.fruit) scarcity,
and are reliably available all year (Terborgh, 1986). As well
as providing crucial foods, 62% of gorilla night nests (N=2435)
are built using one or more of these species as nesting materials
(Tutin et al., 1995).
Occurrence of dense stands of plants in the families Marantaceae
and Zingiberaceae in some African rain forests has been attributed
to factors other than savanna colonisation: association with permanent
water (e.g. Rogers & Williamson, 1987; Wrangham et
al., 1993); forest disturbance (Calvert, 1985; Carroll, 1988);
fire (Hawthorne, in press; Swaine, 1992); and elephants (Calvert,
1985; Guillaumet, 1967); although in some central African forests
there is no obvious explanation for their occurrence (D. Harris,
Central African Republic, pers.comm.).
Figure 14 illustrates these next stages in the succession:
Figure 14: Profile diagrams for Monodominant and Marantaceae
Forest.
(horizontal and vertical scales are the same. All individuals
³ 5 cm dbh in a 5m strip along a line-transect are drawn)
a) Monodominant Forest
b) Marantaceae Forest
e) Patterns of fruit production
Patterns of fruit production in the forest in the Lopé
Reserve are highly seasonal (see Fig. 15). The short dry season
(January / February) is the period of maximum fruit availability
whilst in the long dry season (mid-June to mid-September) is a
time of scarcity for frugivorous mammals. This has a serious impact
on behaviour of some species. For example, gorillas shift their
diet to certain Marantaceae and Zingiberaceae species and range
less widely, whilst chimpanzees split into small silent groups
in an attempt to maintain the fruit content of their diet (Tutin
et al., 1991a).
Some plant species fruit over prolonged periods and hence their
fruits are available during much of the year (Tutin et al., 1991a;
White, 1994b; White et al., 1993). Others however have distinct
fruiting periods, which can cause predictable movements of some
large mammals (see below). Plants which provide a reliable source
of food in the period of fruit scarcity (known as 'keystone' foods)
are of particular importance. For example, at SEGC the bark of
Iroko (Milicia excelsa ) is an important food for gorillas
during the long dry season when fruit availability is at a minimum.
However, this species is a valuable commercial wood much sought
after by loggers. Even a light exploitation which involved removal
of many of the Iroko trees could have a severe effect on gorilla
densities.
Another lesson that comes out of these phenological studies is
the important role played by animals as seed dispersers. Almost
75% of plant species in Lopé rely on animals to disperse
their seeds - what will be the result if over-hunting kills most
of the large mammals and birds ?
Figure 15: Number of plant species fruiting per month in the
Lopé Reserve.
(Data recorded on monthly fruit fall counts along five 5-km line
transects - see Fig. 1. Taken from White 1994 b)
3) Ecology and Behaviour of Large Mammals.
a) Gorillas and Chimpanzees.
I. Diet
Data on ape diet have been collected by observation of feeding,
examination of feeding trail left by apes and analysis of faeces.
To date we have identified 220 foods of gorillas and 182 of chimpanzees
(Tutin & Fernndez, 1993b; Williamson et al., 1990). For both,
fruit is the most important food class although seeds, leaves,
flowers and insects are also eaten regularly. Figure 16 compares
the diets of Lopé gorillas and chimpanzees in terms of
the relative proportions of different food classes.
Figure 16. Comparison of gorilla and chimpanzee diet at Lopé
Both gorillas and chimpanzees eat fruit regularly and remains
of at least one species of fruit were found in 96% of 5200 gorilla
faeces and in 98% of 3150 chimpanzee faeces examined. Dietary
overlap is high with 139 foods eaten by both apes. Overlap is
highest for fruit foods and only 8% of gorilla fruits and 10%
of chimpanzee fruits are not shared. The degree of overlap is
lowest for animal foods although insect remains were found in
30% of faeces of both species. Chimpanzees use tools to obtain
honey from bees nests and to catch ants in arboreal and subterranean
nests while gorillas, who have not been seen to use tools in the
wild, eat a variety of ant species that life in accessible nests
(Tutin & Fernandez, 1992; Tutin et al., 1995). Chimpanzees
at Lopé, but not gorillas, also kill and eat vertebrates
and to date we have identified six prey species including three
arboreal monkeys.
Both gorillas and chimpanzees harvest the majority of their plant
foods from trees, climbing to heights of 40m many times each day
to obtain fruit and leaves.
Mountain gorilla ecology is well documented from long-term studies
in Rwanda and Zaire and their diet, in contrast to that of the
Lopé gorillas, is almost entirely folivorous. Few succulent
fruit are available in their montane habitat. It is now clear
from research at Lopé and from studies of gorillas in tropical
forests in CAR and Congo, that fruit are a prefered food of gorillas
and are eaten whenever available. The Lopé gorillas are
the most frugivorous population studied to date, due probably
to the botanical diversity of their habitat. Their diet resembles
that of the Lopé chimpanzees much more than that of mountain
gorillas.
The importance of fruit for apes at Lopé means that their
diets vary greatly from month to month as most fruit are produced
seasonally (Tutin et al., 1991a). We have also documented large
inter-annual variations in the amount of ripe fruit available
due to failures of crops in some years. Figure 17 illustrates
both seasonal and inter-annual variation in the availability
of fruit foods.
Figure 17. Means and Standard Deviations of the Number of Tree
Species bearing ripe fruit, 1986 - 1991.
Figure 18. Seasonal variation in gorilla
and chimpanzee diet at Lopé.
a) Mean Number of Fruit Species / Sample
b) Mean Monthly Foliage Score
Seasonal variation in ape diet is illustrated by the pattern
of diversity of fruit eaten each month (mean number of fruit species
per faecal sample) and by the mean monthly foliage scores (the
proportion of the faecal sample composed of non-fruit foods measured
on an 8-point scale), as shown in Figure 18. When fruit is scarce
during the annual dry season both gorillas and chimpanzees eat
larger amounts of pith and young leaves of herbaceous plants.
Chimpanzees maintain a higher intake of fruit than do gorillas
and concentrate on the oily flesh of the palm nut (Elaeis guineensis)
which fruits asynchronously. Gorillas, but not chimpanzees, eat
large amounts of the inner bark of Iroko during the dry season,
as mentioned in the previous section, and also much pith from
two acquatic herbs. Chimpanzees eat some palm nuts throughout
the year but gorillas only eat Iroko bast and pith of acquatic
herbs during the dry season suggesting that their 'keystone' foods
are not preferred.
Thus, although gorilla and chimpanzee diets at Lopé are
similar, they diverge when the preferred food of both species
(succulent fruit) is scarce with gorillas being more folivorous
than chimpanzees.
Fruit is a high quality food being rich in easily digested sugar.
The preference for fruit is not surprising as, in contrast to
other food classes such as leaves and pith, fruit are 'designed'
to be eaten: the plant's reward to a potential seed dispersers.
Apes are seed dispersers 'par excellence' as their large body
size means that they swallow many seeds which are excreted intact.
Ben Voysey's study showed that in addition to transporting seeds
away from the parent tree, gorillas deposit seeds of some tree
species in ideal conditions for germination and seedling growth.
Gorillas defecate beside their night nests and nests are usually
built in light gaps where the herbs preferred for nest construction
are common. Germination rate and seedling survival after 2 years
was significantly greater at nest-sites than for seeds that fell
below parent trees or that were left in dung deposited beside
paths in the forest (Voysey, 1995).
II. Social Organisation
Chimpanzees and gorillas at Lopé show the species-typical
forms of social organisation: the former has large communities
numbering 20-100, with approximately equal numbers of males and
females, but associate in temporary sub-groups that change membership
frequently; gorillas live in cohesive social groups led usually
by a single fully adult male. It has been proposed that gorillas
are the only great ape able to live in permanent groups because
they do not eat fruit as, when fruit is a major part of the diet,
competition for limited supplies of food imposes high costs. The
flexible social group of chimpanzees allows adjustment to different
levels of fruit availability, forming large sub-groups when fruit
is abundant but foraging alone when fruit is scarce. The data
on gorilla diet at Lopé pose a challenge to this hypothesis
on the evolution of social systems of the great apes but, there
are indications that gorillas do indeed suffer from intra-specific
feeding competition by lacking the social flexibility of chimpanzees.
One line of evidence comes from a comparison of food processing
techniques of the two apes which shows that gorillas ingest fruit
with a minimum of pre-ingestion processing (separating digestible
from indigestible parts) and swallow large seeds to maximise food
intake rate (Tutin & Fernandez, 1994). In contrast, chimpanzees
are 'fussy' feeders, rejecting indigestible fruit skin and swallowing
fewer seeds. These differences cannot be explained by the larger
body size of gorillas as, when feeding on abundant herbaceous
plants, gorillas and chimpanzees use identical laborious processing
techniques to selectively feed on the digestible fraction of developing
leaves or the heart pith from a stem and reject the tougher parts.
Gorillas' non-selective rapid feeding on succulent fruit may be
provoked by competition with their ever present conspecifics for
limited supplies of preferred food. There are behavioural consequences
as gorillas rest and sleep for longer periods than do chimpanzees
and engage in social behaviour at much lower rates: a lethargy
induced by post-ingestion food processing.
Gorillas at Lopé have larger home ranges (15-30 km2)
and longer day ranges (Mean = 1.5 km) than do mountain gorillas.
Home ranges of neighbouring groups overlap extensively and no
gorilla group has exclusive access to any area (Tutin et al.,
1992; Tutin, in press). These differences seem to be related directly
to the frugivorous diet of the Lopé gorillas. Averge size
of gorilla groups at Lopé is 10, a figure that differs
little from that of 12 for mountain gorillas in Rwanda. However,
maximum group size at Lopé is 16 compared to groups of
up to 40 in montane habitats. Data on group size from studies
of gorillas in tropical rain forest in Congo and CAR suggest smaller
mean group size than at Lopé and no groups of more than
16 members have been seen. Limited fission-fusion of gorilla groups
has been recorded at both these sites but not at Lopé although
group spread is often great. While it is not yet clear whether
or not a fundamental difference in social organisation exists
between folivorous and frugivorous populations of gorillas, it
does appear that maximum group size may be constrained by within
group competition for food which is stronger for frugivorous gorillas
in tropical rain forest habitats.
b) Diurnal Monkeys
In addition to gorillas and chimpanzees, seven species of diurnal
primate occur at Lopé. One, the endemic suntailed guenon
(Cercopithecus solatus) has a limited distribution in the
south of the Reserve and occurs neither in the SEGC study area
nor in the zone selected for ecotourism. Detailed studies have
been made of grey cheeked mangabeys (Cercocebus albigena)
and of black colobus (Colobus satanas) by Rebecca Ham (Ham,
1994) and Mike Harrison (Harrison, 1986; Harrison & Hladik,
1986) and data have been collected opportunistically on the other
four species: mandrills (Mandrillus sphinx), spot nosed
guenon (Cercopithecus nictitans), crowned guenon (Cercopithecus
pogonias) and moustached guenon (Cercopithecus cephus).
Biomass data for all of the primates are shown in Table 2.
Diets of five of the six monkey species are dominated by fruit,
the exception being colobus with a diet dominated by seeds. However,
all species have diverse diets and eat young leaves, flowers and
insects as well as fruit and seeds. Dietary overlap is extensive
both between the frugivorous monkey species and with apes.
The largest species, mandrills, are terrestrial and have a complex
and, as yet, poorly understood social structure. Mandrills visit
the SEGC study area mostly during the annual dry season when supergroups,
or hordes, of up to 700 individuals arrive and forage widely through
the area for periods up to ten days before moving on (Rogers et
al., in prep.). Solitary male mandrills are seen occasionally
throughout the year.
The five smaller, arboreal, species are often found in mixed
species, or polyspecific, groups. They vary in their choice of
associates and in the percentage of time they remain in polyspecific
groups. The costs and benefits of associating with another species
are complex but an analysis of data from Lopé suggests
that important benefits in detecting and avoiding predators, notably
crowned hawk eagles, accrue (Ham, 1994).
Sweep censuses of natural forest fragments within the savanna
zone were conducted monthly for two years and showed that the
primates differed in their propensity to use this atypical habitat.
Total biomass of primates was similar to that found in the adjacent
continuous forest but four species (chimpanzees, mandrills, moustached
guenons and spot nosed guenons) were more common and two (gorillas
and crowned guenons) were less common in the savanna dominated
habitat (Tutin et al., submitted). These data are of interest
in reconstructing the likely history of the different primate
species during past times when, as a reslt of climate change,
savanna dominated vegetation was widespread.
c) Elephants
Elephants are common at Lopé dominating the biomass (see
Table 2) and feed on many fruits eaten by gorillas and chimpanzees
(Williamson, 1988). Systematic observations of elephants in the
forest have been recorded since SEGC was established. This opportunistic
data set developed into a more intensive study and has proved
very interesting. Similar methods to those adopted for the ape
study were applied to elephants and some equivalent data has resulted.
Elephants at Lopé are opportunistic frugivores eating fruit
of at least 80 plant species as well as a wide variety of leaves
and bark. There is a group of about 20 tree species whose large
seeds are only dispersed by elephants. This includes several major
timber species, such as Moabi (Baillonella toxisperma)
and Douka (Tieghemella africana).
Elephants eat large quantities of soil digging into cliffs or
under exposed tree roots along streambeds to create salines which
are then frequented by a large variety of other forest mammals.
Analysis of soil from salines showed a tendency for selection
of areas rich in minerals (sodium, calcium and iron) but results
were not consistent. To investigate geophagy by elephants, we
set up a 'cafeteria' where mineral salts were mixed with earth
in known concentrations in 100 litre dustbins sunk into an abandoned
saline. In the first experiment, elephants tasted all four minerals
(a control bin with no additives was ignored) but showed a very
marked preference first for iron then for sodium. As the iron
was placed (at random) closest to the elephants' path, a second
cafeteria trial is currently underway.
Relatively little is known about the biology of forest elephants
but our studies at Lopé have demonstrated that they have
a very different social organisation to savanna elephants. Females
live in small groups with their offspring and males tend to be
solitary. Hence forest elephants may be more susceptible to poaching
than their savanna relatives, since related females in a savanna
elephant group will adopt and care for young orphans whose mothers
have been killed by poachers (as is more and more the case as
large male tuskers are decimated over Africa), but if a forest
elephant female is killed all of her dependant offspring will
die. Such background information is vital if management of elephant
populations is to be envisaged in the future.
A case of particular interest at Lopé is the seasonal
movement of elephants to feed on the fruit of Ozouga, Sacoglottis
gabonensis. As noted above, S. gabonensis is a species
which was not known to occur in the interior of Gabon until recently.
It is common in a limited block towards the western border of
the Reserve (see below) but then absent or uncommon until the
coastal sedimantary basin, 120 km to the west. During the fruiting
season (September to November) elephant densities increase dramatically,
peaking at above 5 km-2 (see Figure 16). Figure
17 shows the distribution of 'Sacoglottis Forest'.
Figure 16: The relationship between Sacoglottis gabonensis
fruit availability measured on fruit-fall transects and elephant
density.
(dung counts along a 5-km line transect are taken as an index
of abundance cf. Barnes et al., 1995)
Knowing the density in forest types surrounding the Sacoglottis
Forest, White (1994c) calculated that all the elephants in an
area of about 3000 km2 move into Sacoglottis
Forest to feed on its fruit. This entails movements of at
least 50 km for some individuals, illustrating the importance
of Sacoglottis Forest for elephants in the Lopé.
Figure 17: Distribution of Sacoglottis gabonensis in
the Lopé Reserve.
4) Long-term Data Sets.
Data from Congo has shown that Mahogany trees can live to over
850 years old (M. Fay, pers. comm.). This illustrates the time
scale on which forest management needs to be considered. How fast
does an Okoumé or a Moabi grow ? To answer such a question
we must undertake long-term studies. Field stations such as Lopé
are in a unique position to coordinate this. At Lopé there
are a number of examples of successful long-term studies:
a) The SEGC research team began to collect plant phenology data
in 1984 and this data set continues to be collected regularly.
It has been of great help in the quest to understand the lives
of gorillas and chimpanzees, and indeed for other rain forest
mammals and birds, to have a record of fruit production in particular
(e.g., Tutin et al., 1991a). However, this data set has had possibly
greater, unexpected, importance simply as a long term phenology
study. Analysis of 8 years of phenology data (Tutin & Fernandez,
1993 a) showed that for eight major gorilla and chimpanzee food
species minimum temperatures in the long dry season (June-September)
are the trigger for flowering. It seems that 19°C is the
threshold. In the two years that minima did not reach this figure
there was little or no fruit set. In the two years when there
were aseasonal minima below 19°C there was aseasonal fruiting.
Temperatures of 20°C are not sufficiently low to trigger
flowering. Therefore, if dry season temperatures increase by a
degree or two due to global warming, some important tree species
in Lopé, and presumably other African countries, may cease
to produce fruit. There will be serious implications for the animals
that eat their fruit, as well as for the trees themselves. Hence,
the Lopé data set has taken on a global importance as a
means to evaluate the effects of climate change on the African
tropical forest ecosystem.
b) Botanical transects and plots established over the last 12
years have been revisited periodically. In all 3598 individuals
of 181 species have been remeasured at least once to date. There
is a great deal of variation in growth rate between tree species.
Xylopia aethiopica, a species characteristic of disturbed
vegetation, showed the most rapid mean increase (0.91 cm per year)
and Diospyros zenkeri grew extremely slowly (0.05 cm per
year). Hence, a Xylopia aethiopica of 10 cm diameter is
probably little over 10 years old but a Diospyros zenkeri
would take about 200 years to reach this diameter.
The overall mean growth rate for Okoumé was 0.72, which
suggests that it takes about 100 years for an Aucoumea
to grow from seed to an exploitable diameter of 70 cm. However,
it seems that growth rates for small individuals are slower. According
to Figure 18, it should take about 125 years for an Aucoumea
to reach 30 cm dbh, a further 25 years to reach 50 cm and another
15 years to reach 70 cm dbh. Hence, a total of 165 years to reach
an exploitable size. Foresters tend to base their calculations
on a mean growth rate of 1 cm per year. The discrepancy may be
due to the fact that most forestry studies are on large individuals.
Regardless, if the Lopé figures are representative forestry
practice will have to be changed if harvests are to be maintained
at sustainable yields.
Figure 18: Growth rates for Aucoumea klaineana.
c) Today climate change (induced by our pollution) may be occurring
faster than at any point in the last 10,000 years (Houghton et
al., 1990). In a recent paper published in Science, Phillips &
Gentry (1994) surveyed tropical forests worldwide and found evidence
of increased turnover rates (mortality and recruitment) in all
tropical rain forest regions in the last decade. One possible
explanation is that increased levels of atmospheric carbon dioxide
have accelerated plant production. If this is actually happening
it will have wide ranging implications for conservation of biodiversity.
Species composition in tropical forests worldwide will gradually
shift in favour of fast growing trees and lianes.
The data set used in their study included only two sites in Africa,
one in Ghana and a second in Nigeria. No data was available for
the forests of central Africa, which make up about 10% of the
World's rain forests. Long term data from Lopé enables
us to contribute to the study. Botanical plots established in
1984 and 1986 by Williamson (1988) and Reitsma (1988) respectively
were checked for tree mortalities in 1990 and again in 1994. Trees
were scored as living or dead. In 1994 they were also re-measured
(see above).
Mortality rates in the six samples are compared in Table 4.
Table 4: Mortality rates in six botanical samples followed
for 10 years.
Transect | N(1)
| % Mort. | N(2)
| % Mort. | % Mort.
|
| | 1990
| | 1994
| 1994* |
| | |
| | |
1 | 361 |
1.39 | 331 | 2.27
| 2.08 |
2 | 230 |
1.09 | 215 | 1.28
| 1.20 |
3 | 338 |
1.08 | 316 | 1.74
| 1.63 |
4 | 421 |
2.30 | 363 | 2.48
| 2.14 |
5 | 187 |
1.69 | 168 | 1.93
| 1.74 |
6 (1 ha plot) | 396
| 1.46 (1986-90) | 370
| 1.99 | 1.86
|
| | |
| | |
N (1) = Number of trees in sample; N (2) = Number of trees remaining
after first period; % Mort. 1990 = % mortality per year (Number
dead by 1990 /total number in original sample x number of years
between samples); % Mort. 1994 = % mortality per year (Number
dead between 1990-1994 /number in 1990 sample x number of years
between samples); % Mort. 1994* = % mortality per year (Number
dead between 1990-1994 /number in original sample x number of
years between samples)
On all six transects there was increased mortality in the more
recent period. To allow for the fact that some trees would have
been recruited in the intervening period a second calculation
was undertaken, calculating mortality in the second period as
a percentage of the total number of individuals at the beginning.
In this case all but one of the samples showed increased mortality.
The sample is small and the result may be a coincidence. It
could be that the difference, if real, is due to infections which
established after trees had been injured by slashes or labelling,
although there is no reason to expect this to differ between the
two periods. However, I find it very sinister to think that
there is a possibility that changes in the atmosphere induced
by humans are killing trees in a remote forest in Central Gabon
and that differences can be detected on such a short time scale.
5) Application of Research at Lopé to
Management.
Considering the importance of forestry in the Gabonese economy
since the turn of the century it is surprising that ours was the
first detailed study of its ecological impact of selective logging
in the country. We found that damage levels were relatively low,
typically about 10%. Most animal species did not seem to be disturbed
by logging, but chimpanzees were a notable exception. It seems
that even logging resulting in these low damage levels leads to
a marked decline in chimpanzee density which lasts for 15 years
or more after logging (White & Tutin, in press). This unexpected
finding has major implications for conservation of chimpanzees,
since the majority of Africa's forests will be subject to logging
in the next few decades. We hope now to undertake a more detailed
study of why logging has such drastic effects on chimpanzees,
as well as to use our baseline studies before and during logging
to monitor forest regeneration. In addition we have started a
genetic study of selected tree species - are tall straight Okoumé
trees of this form because of their environment, or is it (at
least in part) genetically programmed ? This is certainly the
case for South American mahoganies, which have become large, bent
shrubs in areas where the tall straight individuals were exploited
for centuries (Styles & Khosla, 1976). The results of some
of these studies could have profound bearing on forestry practice.
Our data on elephant movements related to the fruiting of Scaoglottis
will enable the Ministry of Eaux et Forêts to make a special
effort to police the area where Sacoglottis occurs during
the fruiting season in order to minimise disturbance to the elephants.
In addition, we can make use of this seasonal concentration to
monitor population trends over a relatively large area and to
facilitate elephant viewing by tourists.
6) Contributions to the Development of Survey
Methodologies.
Caroline Tutin and Michel Fernandez were the first researchers
in African rain forests to undertake a nation-wide animal survey
based on line-transect methodologies. Richard Barnes later took
their study as a model and modified their methods to census elephants
(Barnes et al.,1995). Our interest in the refinement of inventory
methods continues. Studies of decay rates of ape nests or elephant
dung piles are vital if line-transect data are to be converted
into animal densities. However, such studies require long periods
of time for data collection, and are therefore costly to initiate.
They can, however, be incorporated at relatively low cost into
the day to day activities at a research station such as Lopé.
For example we have analysed gorilla nesting behaviour and nest
decay rates and examined the implications for censusing (Tutin
et al., 1995) and have published the results of the monitoring
of 1282 elephant dung piles in different months in order to investigate
seasonal differences in decay rate (White, 1995).
In addition, botanical inventory methods developed at SEGC have
been adopted by the Wildlife Conservation Society and the ECOFAC
program. Hence, for the first time we will be able to make direct
comparrisons of botanical composition and species diversity between
sites where data has been collected in the same way, ensuring
direct comparability.
7) Training.
Knowledge is nothing unless you share it. Researchers do so in
publications but an obvious extension of this is actual training.
Many field stations are obliged to train field assistants in order
to undertake their day to day data collection, but more formal
links need to be forged if training is to extend beyond this.
Training can be academic, practical or fall some way between these
two extremes. There are three examples from Lopé
I) Tourist guides: since the start of ECOFAC a tourist program
has been initiated which involves guides from the local community
accompanying tourists into the Reserve. Apart from rudimentary
knowledge gleaned on logging chantiers these guides had little
knowledge of the animals and plants of the rain forest. Between
1992-94 a team of 14 guides were trained to the point where they
are eloquent in their explanations of plants, animals and ecological
processes of interest to tourists. SEGC has played a major role
in this training process. The initial training process was to
have future guides working as field assistants at the research
station. As they gained in experience more intensive training
was undertaken to include subjects such as archaeology, ornithology
and psychology.
II) Personnel from the Ministry of Eaux et Forêts undergoing
training at the National forestry school (ENF) or at Garoua in
Cameroon have to undertake brief ecological studies as part of
their course. When appropriate researchers at SEGC supervise these
projects. To date five such projects have been conducted at Lopé
on subjects related to ape and elephant ecology.
III) Advanced studies: It is hoped that with time there will
be more Gabonese doctoral candidates in wildlife and conservation
biology. Alphonse Mackanga-Missandzou, currently in charge of
the Eaux et Forêts brigade at Lopé and homologue
to the ECOFAC project manager, is the first national candidate
for a doctorate in wildlife biology and has collaborated closely
with researchers at SEGC on a study of the vegetation and wildlife
of the forest-savanna boundary.
FUTURE ACTIVITIES OF SEGC.
1) New directions for long-term data sets.
Whilst the emphasis of research at SEGC has gradually expanded
from its early focus on gorillas and chimpanzees, data on these
two species is and will continue to be collected systematically.
SEGC has been monitoring the daily lives of gorillas and chimpanzees
in Lopé for 12 years and has been a pioneer in research
on apes in central Africa. This long term data set allows us to
undertake studies not possible elsewhere. For example, the death
of the silverback male Porthos and the disappearence of his group
from our central study area may allow us to assess the rate at
which gorillas would be expected to expand their ranges out of
forest refugia, and hence to explain some anomalies of gorilla
distribution in African rain forests. New genetic techniques will
allow 'fingerprints' to be made from DNA extracted from naturally
shed gorilla hairs. Since 1992 we have collected hairs from gorilla
nests at Lopé and these will be analysed at the Centre
International de Recherches Médicales de Franceville. The
genetics laboratory at CIRMF run by Dr. Jean Wickings with Sonia
Schmerl and Tim Williams are developing methods that will permit
individual identification of gorillas in the SEGC study area.
These data will complement the field data and lead to significant
advances in our understanding of ranging, social structure and
local demography. The CIRMF/Lopé group, in collaboration
with colleagues at field sites in CAR, Congo, Zaire and Cameroun,
have begun an analysis of genetic variation across the entire
range of gorillas in Africa. The presence and support of a modern
medical research laboratory in the same country as the field site
has already lead to fruitful collaborations in studies of parasitology
(Landsoud Soukate et al., 1995; Bain et al., 1995).
We will also continue to collect routine data on all of the species
of large mammal we encounter in the forest in Lopé, to
provide baseline studies of little known species and to facilitate
more detailed studies in the future.
Our phenology sample of 597 trees is reaching its 10th year,
whilst studies on tree mortality and growth rates have been underway
for 11 years. Samples for both of these studies will gradually
be enlarged and routine monitoring of these data sets will become
a more important aspect of daily activities. The possible spin
offs to understanding the implications of global climate change
which we detailed above should certainly justify any increased
effort here.
2) Forest and human history in central Gabon.
The Lopé region provides a unique opportunity to study
forest dynamics and the history of human populations in the forest.
The work of Richard Oslisly and his colleagues has shown the Lopé
to have a rich archaeological record with the greatest concentration
of sites in central Africa. Human presence in the area has left
a record of cultural changes from the early Stone Age through
the Neolithic to the Iron Age. Against a background of major climate
change over the past 25,000 years, Man and the rain forest ecosystem
have interacted in an on-going dynamic process. In the coming
years this will be the basis of a major research effort, combining
archaeological exploration, analysis of pollen preserved in marshes,
_13C profiles in strategically chosen sites and mapping of current
vegetation distributions. We believe this will greatly add to
understanding of forest history and that there will be significant
management applications.
3) New species and habitats.
As baseline data are collected on plants and animals, shorter
term studies on different species become a viable possibility.
As we have done in the past, we will encourage students to undertake
work on interesting species, or questions which have evolved from
our own research. Making use of all the background information
which is available other researchers may be able to come in for
shorter periods and address fundamental questions which, elsewhere,
would require many years of study.
4) Understanding how the forest functions.
A major obstacle to sustainable forest management in African
rain forests is the lack of knowledge of the natural history of
any of the commercially exploited tree species. In almost every
case we do not know how fast they grow, what pollinates
them, what disperses their seeds or what conditions their seeds
need for growth. For years foresters have said that an Okoumé
tree grows to maturity in 40 years. New data from our work suggests
it is closer to 165 years. We also believe that Okoumé
is unable to regenerate in the forest, but needs open savanna
or large clearings in the forest to be able to establish. Okoumé
is perhaps the most studied timber species in Africa . . . . . .
A major new thrust to our research, and a logical extension of
our inventory work, will be to collect baseline information on
the natural history of as many plant species as possible. This
will be an ongoing process which, in the long term, create an
invaluable data base and contribute to our ability to manage and
protect African rain forests.
5) Training.
By nature of the fact that Lopé has a diverse fauna and
flora, which has been effectively protected in its natural state;
because there are unusually high densities of many animals, including
elephants, gorillas and chimpanzees (three focal species for conservation
efforts); and because we have a wealth of background information;
Lopé is an ideal site for training in tropical ecology.
Furthermore, access is easy (5 hours by train or road from Libreville),
the country is stable politically, and there is a great need for
such a training centre at both national and regional levels. We
feel that in addition to the applied value of long term data sets,
the wealth of baseline data available for Lopé makes it
an ideal site for training in ecological inventory and monitoring
methods.
We are committed to developing this aspect of our work by setting
up firm links with the Ministry of Eaux et Forêts college
just outside Libreville at Cap Esterias. We plan to run annual
field courses for students from the college and to supervise longer
field projects on a regular basis. Much of this can be undertaken
using infrastructure already in place at Lopé, although
new laboratory and classroom facilities will have to be built.
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Appendix: publications resulting from work undertaken at
SEGC.
Articles published in scientific journals and books
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gorillas (Gorilla gorilla gorilla) in Gabon, West Africa.
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Peyrot, B & Oslisly, R. 1986. Recherches récentes
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Tutin, CEG. 1986. La vie des gorilles. Thèmes et
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De Bayle des Hermens R., Oslisly, R & Peyrot, B. 1987
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Hallé, N. (1987) Cola lizae N. Hallé
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Rogers, ME & Williamson, EA. 1987. Density of herbaceous
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19: 278-281.
Tutin, CEG & Fernandez, M. 1987. Gabon: A fragile sanctuary.
Primate Conservation 8: 160-161.
Tutin, CEG & Fernandez, M. 1987. Sympatric gorillas
and chimpanzees in Gabon. AnthroQuest 37: 3-6.
Oslisly, R. 1988 : Gravures rupestres au Gabon: les pétroglyphes
d'Elarmékora. L'Anthropologie, tome 92, n°1,
p.373-374.
Oslisly, R. & Peyrot, B. 1988 Synthèse des
données archéologiques des sites de la moyenne vallée
de l'Ogooué. Nsi, n°3, p.63-68.
Oslisly, R. & Peyrot, B. 1988. La Préhistoire
du Gabon. Ministère de l'Education Nationale du Gabon Press,
52 pp.
Rogers, ME, Williamson, EA, Tutin, CEG & Fernandez, M.
1988. Effects of the dry season on gorilla diet in Gabon. Primate
Report, 22: 25-33.
Williamson, EA, Tutin, CEG & Fernandez, M. 1988. Western
lowland gorillas feeding in streams and on savannas. Primate
Report 19: 29-34.
Gautier-Hion, A & Tutin, CEG. 1989. Mutual attack by
a polyspecific association of monkeys against a crowned hawk eagle.
Folia Primatologica, 51: 149-151.
Oslisly, R. 1990 : Les gravures rupestres de la vallée
de l'Ogooué. Actes du Premier séminaire international
des archéologues du monde Bantou (Libreville, 11-15 Décembre
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Fernandez, M & Tutin, CEG. 1990. Ecologie comparée
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(eds), Edition Masson, Paris.
Rogers, ME, Maisels, F, Williamson, EA, Fernandez, M &
Tutin, CEG 1990. Gorilla diet in the Lopé Reserve,
Gabon: A nutritional analysis. Oecologia 84: 326-339.
Tutin, CEG. & Fernandez, M. 1990. Responses of wild
chimpanzees and gorillas to the arrival of primatologists: Behaviour
observed during habituation. Pp. 187-197 in Primate Responses
to Environmental Change, HO Box (ed), Chapman and Hall,London.
Williamson, EA, Tutin, CEG, Rogers, ME & Fernandez, M.
1990. Composition of the diet of lowland gorillas at Lopé
in Gabon. American Journal of Primatology 21: 265-277.
McPherson, G. & Louis, A. 1991. A new species of Pseudocalyx
(Acanthaceae) from Gabon. Bull. natn. Hist. nat., Paris, 4
eme série, I3, section B, Adansonia, n° 1-2:
57-59.
Tutin, CEG & Benirschke, K. 1991. Possible osteomyelitis
of skull causes death of a wild lowland gorilla in the Lopé
Reserve, Gabon. Journal of Medical Primatology 20:
357-360.
Tutin, CEG & Fernandez, M. 1991. Conservation and ecology
of gorillas and chimpanzees in Gabon. Abstract in Proceedings
of The Great Apes Conference: Conservation of the Great Apes in
the New World Order of the Environment. Ministry of Forestry
& Ministry of Tourism, Post and Telecommunication, Republic
of Indonesia.
Tutin, CEG, Fernandez, M., Rogers, ME, Williamson, EA &
McGrew, WC. 1991 . Foraging profiles of sympatric lowland
gorillas and chimpanzees in the Lopé Reserve Gabon. Philosophical
Transactions of the Royal Society of London B 334 (1270):
179-186.
Tutin, CEG, Williamson, EA, Rogers ME & Fernandez, M.
1991. A case study of a plant-animal interaction: Cola lizae
and lowland gorillas in the Lopé Reserve, Gabon. Journal
of Tropical Ecology 7: 181-199.
Oslisly, R & Peyrot B. 1992. L'arrivée des premiers
métallurgistes sur l'Ogooué (Gabon). The African
Archaeological Review, n°10, p.129-138.
Oslisly, R & Peyrot B. 1992. Un gisement du paléolithique
inférieur: la haute terrasse d'Elarmékora (Moyenne
vallée de l'Ogooué) Gabon: problèmes chronologiques
et paléogéographiques. Comptes rendus de l'Académie
des sciences de Paris, t.314, série II, p.309-312.
Oslisly, R 1992. L'art rupestre au Gabon: les pétroglyphes
de la vallée de l'Ogooué. L'Anthropologie,
tome 96, n°4, p.811-824.
Rogers, ME, Maisels, F., Williamson, EA, Tutin, CEG & Fernandez,
M. 1992. Nutritional aspects of gorilla food choice in the
Lopé Reserve, Gabon. Pp. 255-266 In Topics in Primatology
Volume 2, N. Itoigawa, Y. Sugiyama, G.P. Sackett & R.K.R.
Thompson (eds.) University of Tokyo Press, Tokyo.
Tutin, CEG & Fernandez, M. 1992. Insect-eating by sympatric
lowland gorillas (Gorilla g. gorilla) and chimpanzees (Pan t.
troglodytes) in the Lopé Reserve, Gabon. American
Journal of Primatology 28:29-40.
Tutin, CEG & Fernandez, M. 1992. Status of Chimpanzees
in Gabon. Bulletin of The Chicago Academy of Sciences 15:31.
Tutin, CEG, Fernandez, M, Rogers, ME & Williamson, EA.
1992. A preliminary analysis of the social structure of lowland
gorillas in the Lopé Reserve, Gabon. Pp. 245-254 In Topics
in Primatology Volume 2, N. Itoigawa, Y. Sugiyama, G.P. Sackett
& R.K.R. Thompson (eds.) University of Tokyo Press, Tokyo.
Oslisly, R 1993. Préhistoire de la moyenne vallée
de l'Ogooué (Gabon). Editions de l'ORSTOM, Travaux
et Documents Microédités, n°96.
Oslisly, R. 1993. The Neolithic/Iron age transition in
the Ogooué valley in Gabon: cultural changes. Nyame
Akuma, n°40, p.17-21
Oslisly, R. 1993. Rock art in Gabon: petroglyphs in the
Ogooué river.Rock Art Research, 10, p.18-23.
Oslisly, R & Fontugne, M. 1993. La fin du stade néolithique
et le début de l'âge du fer dans la moyenne vallée
de l'Ogooué au Gabon. Problèmes chronologiques et
changements culturels. Comptes rendus de l'Académie
des sciences de Paris, t.316, série II, p.997-1003.
Tutin, CEG & Fernandez, M. 1993. Relationships between
minimum temperature and fruit production in some tropical forest
trees in Gabon. Journal of Tropical Ecology 9: 241-248.
Tutin, CEG & Fernandez, M. 1993. Composition of the
diet of chimpanzees and comparisons with that of sympatric lowland
gorillas in the Lopé Reserve, Gabon. American Journal
of Primatology 30: 195-211.
White, LJT, Tutin, CEG & Fernandez, M. 1993. Group
composition and diet of forest elephants, Loxodonta africana
cyclotis, Matschie 1900, in the Lopé Reserve, Gabon.
African Journalm of Ecology 31: 181-199.
Ancrenaz, M., Tutin, CEG & Fernandez, M. 1994. Observations
of wild mandrill groups (Mandrillus sphinx ) in central
Gabon. XVth Congress of the International Primatological Society,
Bali, Indonesia, Abstracts.
Breteler, FJ. 1994 Novitates gabonenses (14) Dialium
lopense, a new Leguminosae-Caesalpinioidae from central
Gabon. Bull. Jard. Bot. Nat. Belg. Bull. Nat. Plantentuin Belg.
63: 201-204.
Moisson, PY, Bain, O, Huerre, M & Tutin, CEG. 1994.
Death of a wild silverback lowland gorilla at the Lopé
Reserve, Gabon. XVth Congress of the International Primatological
Society, Bali, Indonesia, Abstracts.
Oslisly, R & Dechamps, R 1994. Découverte d'une
zone d'incendie dans la forêt ombrophile du Gabon ca
1500 BP: Essai d'explication anthropique et implications paléoclimatiques.
Comptes rendus de l'Académie des sciences de Paris,
t.318, série II, p.555-560.
Rogers, ME, Tutin, CEG, Parnell, RJ, Voysey, BC, Williamson,
EA & Fernandez, M. 1994. Seasonal feeding on bark by gorillas:
An unexpected keystone food? Pp. 37-43 in B. Thierry, J. R. Anderson,
J. J. Roeder & N. Herrenschmidt. Current Primatology Volume
1: Ecology and Evolution. Université Louis Pasteur,
Strasbourg - France (1994).
Tutin, CEG. 1994. Reproductive success story: Variability
among chimpanzees and comparisons with gorillas. Pp. 181-194 in,
Chimpanzee Cultures, RW Wrangham, WC McGrew, FBM deWaal
& PG Heltne, Harvard University Press, Cambridge, MA.
Tutin, CEG & Fernandez, M. 1994. Faecal analysis as
a method of describing diets of apes: examples from sympatric
gorillas and chimpanzees at Lopé, GabonTropics 2:
189-198.
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