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Animal Biodiversity and Conservation 24.2 (2001)
© 2001 Museu de ZoologiaISSN: 1578–665X
Life–history and ecological distribution
of chameleons (Reptilia, Chamaeleonidae)
from the rain forests of Nigeria:
conservation implications
G. C. Akani1, O. K. Ogbalu1 & L. Luiselli2,3,*
Akani, G. C., Ogbalu, O. K. & Luiselli, L., 2001. Life–history and ecological distribution of chameleons (Reptilia,
Chamaeleonidae) from the rain forests of Nigeria: conservation implications.
Animal Biodiversity and Conservation,
24.2: 1–15.
AbstractAbstract
AbstractAbstract
Abstract
Life–history and ecological distribution of chameleons (Reptilia, Chamaeleonidae) from the rain forests of
Nigeria: conservation implications.—
Five species of chameleons were observed in the continuous forest zone
of southern Nigeria:
Chamaeleo gracilis gracilis
Hallowell, 1842
, Chamaeleo owenii
Gray, 1831
, Chamaeleo
cristatus
Stutchbury, 1837
, Chamaeleo wiedersheimi
Nieden, 1910, and
Rhampholeon spectrum
(Bucholz
1874). Many original locality records are presented for each species. One species is apparently rare and
confined to montane habitats (
C. wiedersheimi
), another species is relatively common and its habitat is
generalist (
C. gracilis
), and the other three species are vulnerable and limited to specific micro–habitats. Female
R. spectrum
had clutch sizes of two eggs each and exhibited a prolonged reproductive season with oviposition
likely occurring during the late phase of the dry season. Females of both
C. cristatus
(clutch sizes: 11–14 eggs)
and
C. owenii
(clutch sizes: 15–19 eggs) have a shorter reproductive season with oviposition occurring most
probably at the interphase between the end of the wet season and the onset of the dry season, and female
C. gracilis
(clutch sizes: 14–23 eggs) appeared to exhibit two distinct oviposition periods (one at the interphase
between the end of the wet season and the onset of the dry season, and one at the peak phase of the dry
season). Diets of four sympatric species of chameleons consisted almost exclusively of arthropods. There were
significant inter–group differences at either intra–specific level (with the females of the two best studied
species, i.e.
R. spectrum
and
C. gracilis,
having a wider food niche breadth than males) or inter–specific level
(with a continuum of dietary specialization from the less generalist (
C. cristatus
) to the more generalist (
C.
gracilis
). However, “thread–trailing” experiments indicated that activity patterns of Nigerian chameleons were
relatively similar among species. The overall abundance of chameleons (as estimated from the number of
specimens observed in the time unit of field effort) was relatively similar in three contrasted habitat types, but
lizards were more abundant in the mature secondary forest. When greatly altered by massive logging activity,
the overall abundance of chameleons in the mature secondary forest habitat declined only slightly, whereas the
species diversity declined drastically. This was an effect of (i) the simultaneous extinction of three of the four
species originally present in the forest plot, and of (ii) the rapid increase in abundance of a single species (
C.
gracilis
) as a response to habitat alteration. The conservation implications of all these data are also discussed.
Key words: Chameleons, Habitat, Feeding habits, Activity, Comparative ecology, Conservation status.
ResumenResumen
ResumenResumen
Resumen
Estrategia vital y distribución ecológica de camaleones (Reptilia, Chamaeleonidae) de los bosques húmedos de
Nígeria: implicaciones en la conservación.—
Se observaron cinco especies de camaleones en la zona de bosque
ininterrumpido del sur de Nigeria:
Chamaeleo gracilis gracilis
Hallowell, 1842
, Chamaeleo owenii
Gray, 1831
,
Chamaeleo cristatus
Stutchbury, 1837
, Chamaeleo wiedersheimi
Nieden, 1910 y
Rhampholeon spectrum
(Bucholz 1874). Se presentan muchos registros de localidad originales para todas las especies. Una especie es
aparentemente rara y está confinada a los hábitats montañosos (
C. wiedersheimi
), otra especie es relativamente
común y generalista en cuanto al hábitat (
C. gracilis
), y las otras tres especies son vulnerables y están limitadas
a microhábitats específicos. El tamaño de cada puesta de la hembra de
R. spectrum
fue de dos huevos,
mostrando una prolongada estación reproductora con oviposición durante la última fase de la estación
2Akani et al.
húmeda. Las hembras de
C. cristatus
(tamaño de puesta: 11–14 huevos) y
C. owenii
(tamaño de puesta: 15–
19 huevos) tienen una estación reproductora más corta y la oviposición se da con mayor probabilidad en la
interfase entre el final de la estación húmeda y el inicio de la estación seca, y la hembra de
C. gracilis
(tamaño
de puesta: 14–23 huevos) presenta dos periodos distintos de oviposición (uno en la interfase entre el final de
la estación húmeda y el inicio de la estación seca y el otro durante el período más seco de la estación seca). Las
dietas de cuatro especies simpátricas de camaleones consistían prácticamente de forma exclusiva en artrópodos.
Había diferencias significativas dentro del grupo tanto a nivel intraespecífico (con las hembras de las dos
especies mejor estudiadas, es decir
R. spectrum
y
C. gracilis,
con un extenso nicho alimentario más amplio que
los machos) o interespecíficas (con una continua especialización alimentaria desde los menos generalistas (
C.
cristatus
) a los más generalistas (
C. gracilis
). Sin embargo los experimentos “thread–trailing” indican que los
patrones de actividad de los camaleones de Nigeria eran relativamente similares entre especies. La abundancia
de camaleones (estimada a partir de el número de especímenes observado en la unidad de tiempo de esfuerzo
de campo) era relativamente similar en tres tipos de hábitats contrastados, pero el bosque secundario maduro
fue el hábitat donde los lagartos fueron más abundantes. En cuanto al hábitat del bosque secundario, cuando
estaba fuertemente alterado por una fuerte explotación forestal, la abundancia de camaleones disminuía sólo
ligeramente, mientras que la diversidad de especies disminuía de forma drástica. Esto era debido a: (i) la
extinción simultánea de tres de las cuatro especies originalmente presentadas en el bosque, y (ii) el rápido
incremento en abundancia de una única especie (
C. gracilis
) como respuesta a una alteración del hábitat. Se
discuten las implicaciones de estos datos sobre la conservación.
Palabras clave: Camaleones, Hábitat, Hábitos alimentarios, Actividad, Ecología comparada, Conservación.
(Received: 5 VI 01; Conditional acceptance: 17 IX 01; Final acceptance: 10 X 01)
1 Dept. of Biological Sciences, Rivers State Univ. of Science and Technology, P. M. B. 5080, Port Harcourt (Rivers
State), Nigeria.
2 F. I. Z. V., via Olona 7, I 00198 Rome, Italy.
3 Inst. of Environmental Studies DEMETRA, Via dei Cochi 48/b, I 00133 Rome, Italy.
* Corresponding author: Luca Maria Luiselli, F.I.Z.V., via Olona 7, I 00198 Rome, Italy.
E–mail: lucamlu@tin.it
Animal Biodiversity and Conservation 24.2 (2001) 3
Introduction
Chameleons are certainly among the most
conspicuous lizards of Afro–tropical rainforest
habitats (DE WITTE, 1965; BÖHME, 1985) and they
have undergone a remarkable adaptive radiation
in montane habitats of the central–western region
of Africa, particularly Cameroon (BÖHME & KLAVER,
1981; BÖHME, 1985; BÖHME & SCHNEIDER, 1987;
KLAVER & BÖHME, 1992; LAWSON, 1993; WILD, 1993,
1994; NECAS, 1994). The rainforest zone of southern
Nigeria is ecologically connected with the western
Cameroon forests, and the whole region is an
important hot–spot for conservation because many
species of flora and fauna are endemic in the
area (KINGDON, 1990).
Although information on chameleons in
Nigeria–Cameroon rainforests is scarce (but see
WILD, 1993, 1994), many species are known to
suffer from the multiple conservation problems
in the area (WILD, 1993, 1994), to the extent that
the conservation status of a lot of these species
herein is unknown (see NARESCON, 1992 for
Nigeria). At Niger Delta, the various species of
chameleons are nowadays very rare (POLITANO,
1998; AKANI et al., 1999; AKANI & LUISELLI, 2001)
and many populations have recently disappeared
from many sites (OJONUGWA, 1973; AKANI et al.,
1999). In a recent study (AKANI & LUISELLI, 2001) it
was found that over 80% of adult local people
interviewed about these species reported never
to have seen a chameleon. Information about
chameleons in other parts of Nigeria is also very
scarce (but see PASQUAL, 1937; DUNGER, 1967a;
BUTLER, 1986; REID, 1986).
In order to attain conservation programs for
chameleons, this study provides basic information
on the ecology and habitat distribution of free–
ranging populations of several species inhabiting
the rainforest region in Nigeria.
The aims of the study are twofold: to analyse
the food niche of sympatric species, their diurnal
activity, and changes in the community composition
at a forest site before, and after, timbering; and to
present records for new sites of these species.
Data on their conservation problems are
presented and some solutions suggested. No
attempt is made to review the distribution range
of species (see for instance, TALBOT, 1912; PASQUAL,
1937; ROMER, 1953; DUNGER, 1967a, 1967b; BUTLER,
1986; REID, 1986; AKANI et al
.,
1999), but only new
records data set are presented.
Materials and methods
Study areas
Chameleons were studied at different forest
habitats of southern Nigeria as follows: moist
lowland forest, deltaic freshwater swamp–forest,
and coastal mangrove (see LUISELLI et al., 2000
for a detailed description of the area and LUISELLI
& ANGELICI, 2000 for the territories used during
field surveys). Field work was performed from
September 1994 to April 2001. The whole area
has a tropical climate, with the wet season from
May to September, and dry season from October
to April. The rainfall peak is in June–July, and
the driest period between late December and
February. Annual precipitation averages between
2,000 and over 3,000 mm per year. The air
temperature is generally high (average around
27–28°C), and varies little throughout the year.
The annual range of the monthly average
temperature varies only between 3°C and 3.5°C.
The human population density is high, and the
landscape is characterised by fragmented patches
of rainforest interspersed within a sea of urban
centres, industry, farmlands and plantations
(POLITANO, 1998).
Field methods
Observations of free–ranging chameleons were
made opportunistically during more general
surveys for other forest vertebrates (mainly snakes;
for the general survey methods, see LUISELLI &
ANGELICI, 2000; LUISELLI et al
.,
1998, 1999, 2000).
For this paper, the following variables were
recorded each time a chameleon was observed:
Site
A GPS “Garmin 12” was used. Habitat type,
time of day, and species of each chameleon sighting
were also recorded.
Biometry
Snout–vent length (SVL) with a calliper to the
nearest ± 1 mm. Chameleons were individually
marked with a number painted in white on the
back, a useful method for short–term reptile
studies (e.g. see LUISELLI et al., 1996), including
chameleons (KAUFFMANN et al., 1997; CUADRADO,
1998). The marked specimens were also sexed.
Body mass was not systematically recorded.
Diet
Faeces from free–living specimens of chame-
leons were examined for this study. To obtain
faeces from free–ranging specimens while
minimizing handling (which may produce stress
and damages to the handled animals),
chameleons captured from the wild were kept
separately into small terraria until defecation
occurred. Faeces were analysed in the laboratory.
Prey were sorted, and identified to the lowest
taxonomic level possible, and measured (to
± 0.1 mm) under a binocular microscope 10×40
equipped with a micrometer. As in a previous
chameleon study (PLEGUEZUELOS et al., 1999),
characteristic body parts of arthropods
(mandible width for Orthoptera, head width in
Coleoptera, Diptera, Hemiptera, Hymenoptera,
Mantodea, and Odonata; chelicera length for
arachnids) were measured in order to estimate
4Akani et al.
the size of the prey, but attempts failed in some
cases when prey fragments were broken and/or
difficult to size. Diet analysis was performed on
a species and sexual basis, and summarised by
absolute frequency (i.e. numbers of prey
belonging to a given prey type) and by frequency
of appearance of a given prey type in the pellets
(i.e. numbers of faecal pellets where a given
prey type was observed). Diet data reported
here were recorded from a single study site
(Eket, Akwa–Ibom State).
Reproductive data
Clutch sizes of females were determined by
palpation in some cases (two cases in
C. gracilis,
two cases in
C. cristatus,
two cases in
C. owenii,
six cases in
R. spectrum
), and by dissection in
other cases, when the females were found dead
in the field (four cases in
C. gracilis,
and two
cases in
C. owenii
).
Daily activity and foraging habits
A continuous monitoring procedure of a few
specimens encountered in the field was applied,
thus devising a monitoring protocol quite
equivalent to the “thread–trailing” strategy
developed to study activity of tortoises (BREDER,
1927; HAILEY & COULSON, 1999). Three specimens,
from three different species (
C. owenii, C. gracilis,
C. cristatus
), were “thread–trailed”, for 14 days
each, five hours every day (i.e. for a total of
70 hours of trailing for each specimen), by
remaining at approximately 10 m distance, so as
not to interfere in the chameleon’s normal
activities. Binoculars (8x40) were also used to
facilitate observations.
Population abundance and structure
Population abundance and structure of
chameleons were studied at three forest patches
situated in the surroundings of Calabar (Cross
River State). All these areas were surveyed during
the dry seasons of 2000 (area B) and 2001 (area
C), and both 1998 and 2001 (area A). Area A
(50x30 m) was a mature secondary forest in the
first year of study (1998), but was partially affected
by industrial timbering activities during the second
year of study (2001, when about 40% of the
former wooded surface was cut). This allowed us
to test for the effects of habitat reduction on
animal abundance and species composition. Area
B (approximately 120x10 m) was a riparian
woodland growing along the banks of the Rhoko
River. Area C (40x40 m) was a secondary bush–
grassland mosaic, with plants of 50–150 cm height,
surrounded by plantations (of cassava and
pineapples) and farmlands. All these areas are
virtually flat, at elevations of 300 m a.s.l. (area A),
385 m a.s.l. (area B) and 320 m a.s.l. (area C). In
order to compare the abundance patterns of
chameleons in the three areas, a “time–
constrained–searching” protocol was applied. To
do this, each area was carefully explored for a
total of 45 hours by two researchers, each moving
independently, both by day (hrs 07.00–16.30 h)
and at night (20.30–00.30 h). A balance was
maintained between diurnal and nocturnal
samplings at each area (50% of survey time for
both diurnal and nocturnal searches). Roosting
sites of each individual were noted on a scaled
map of the study site.
Niche width and niche overlap
These variables were estimated by using
SIMPSON’s (1949) diversity index and PIANKA’s (1986)
symmetric equation index which ranges from 0
(no overlap) to 1 (total overlap). In both cases,
the different Orders of–prey types were used as
operative taxonomical units to calculate niche
widths and overlaps.
Statistical analysis
An SPSS (version for Windows) computer package
was used for all statistical analyses. All tests
were two tailed, and alpha was set at 5%. Mean
values +/- one standard deviation are provided.
Results
Species distribution and types of habitats
Five species of chameleons (
Rhampholeon
spectrum, Chamaeleo cristatus, C. owenii, C.
gracilis gracilis, C. wiedersheimi
) were found at
the following sites:
Rhampholeon spectrum spectrum
(Bucholz 1874)
Sites. Akwa–Ibom State: Eket (riverine forest
along the River Kwa–Ibo (= Quo–Ibo); 04°50' N,
07°58' E), Stubbs Creek Forest Reserve
(04°49' N, 08°00' E); Cross River State: Iko–
Esai Forest (along the Rhoko River banks,
70 km N of Calabar; 05°28’ N, 08°23’ E),
Osomba (05°21’ N, 08°24’ E), Oban (05°18’ N,
08°34’ E), Itu (05°14’ N, 07°59’ E), Ikpan Forest
(30 km N of Calabar; 05°00'–05°15' N, 08°35'–
08°45' E), Akpabouyoh (04°50' N, 08°22' E);
Benue State: :
: :
: Ogoja (06°40’ N, 08°47’ E).
Habitat. The species is very common in wet
forests with closed canopy (primary as well as
mature secondary forests) either at sea level
(e.g., Stubbs Creek Forest Reserve) or on hills
(e.g., Oban). During daylight it was always
observed on the ground, whereas it was observed
on low bushes at night–time.
Rhampholeon
sp.
Sites. Rivers State: :
: :
: Bonny Island (04°25' N,
07°15' E).
Habitat. Three undetermined
Rhampholeon
were found in the stomachs of two snakes (the
colubrids
Rhamnophis aethiopissa
and
Hapsidophrys
lineatus,
cf. LUISELLI et al., 2000, 2001) which were
captured at the coastal barrier island forest of
Animal Biodiversity and Conservation 24.2 (2001) 5
Bonny island.
These specimens were most probably
spectrum,
but as digestion was too advanced to
positively identify species level, they have been
placed separately from ascertained records of
R.
spectrum
in this section.
Chamaeleo (Trioceros) cristatus
Stutchbury, 1837
Sites. Edo State: Oredo Forest, 18 km SW of
Benin City (06°03' N, 05°12' E); Bayelsa State:
Sagbama (05°10' N, 06°05' E); Rivers State: Upper
Orashi Forest Reserve (04°44' N, 07° 10' E);
Akwa–Ibom State: Eket (riverine forest along
the River Kwa-Ibo (= Quo–Ibo); 04°50' N,
07°58' E); Cross River State: Oban (05°18’ N,
08°34’ E); Osomba (05°21’ N, 08°24’ E); Ikpan
Forest (30 km N of Calabar; 05°00'–05°15' N,
08°35'–08°45' E); Obudu Cattle Ranch (06°37' N,
08°46' E); Iko–Esai Forest (70 km N of Calabar;
05°28’ N, 08°23’ E); Okarara (04°50' N, 08°23' E);
Ekang (05°23' N, 08°39' E).
Habitat. Uncommon. This species was seldom
observed in mature forests and riparian forests,
either at the sea level (e.g. in Niger Delta) or in
hilly areas (e.g., Oban and Obudu). It was most
frequently observed in low, thick, flowering
bushes and, much more rarely, ground–dwelling
in the leaf litter of the forest floor.
Chamaeleo (Trioceros) owenii
Gray, 1831
Sites. Bayelsa State: Sagbama (05°10' N,
06°05' E), Yenagoa (05°12' N, 06°05' E), Taylor
Creek Forest Reserve (05°16' N, 06°11' E); Rivers
State: Upper Orashi Forest Reserve (04°44' N,
07°10' E), Otari–Abua (04°53' N, 06°41' E),
Ahoada (05°04' N, 06°38' E), Buguma Creek
(04°43' N, 06°50' E), Elem–Sangama (04°40' N,
06°39' E), Igbeta–Ewoama (04°34' N, 06°21' E),
Degema (04°48' N, 06°48' E); Akwa–Ibom State:
Eket (riverine forest along the River Kwa–Ibo
(= Quo–Ibo); 04°50' N, 07°58' E); Cross River
State: Calabar (04°47' N, 08°21' E), Ikpan Forest
(30 km N of Calabar; 05°00'–05°15' N, 08°35'–
08°45' E), Itu (05°14' N, 07°59' E).
Habitat. Our original records confirm its
presence at several sites east of the River Niger,
but we failed to find this species in any locality
west of the course of the River Niger. Thus,
based on our data, it is possible that
C. owenii
would be much rarer, if occurring at all, in the
western forests of Nigeria, which is also in good
agreement with the range of this species at the
continental level (e.g., SCHMIDT, 1919). It also
seems that
C. owenii
is found in lowland forests,
along river banks, as well as in forest-plantation
mosaics and in mature secondary forests. A
specimen from the Upper Orashi Forest Reserve
was eaten by the snake
Rhamnophis aethiopissa
(LUISELLI et al.,
2000).
Chamaeleo wiedersheim
I Nieden, 1910
Sites
.
Cross River State: Obudu Cattle Ranch
(06°37' N, 08°46' E).
Habitat. Our single locality record was relative
to two males observed at an open bush sub–
montane area, at the border of a forested site.
Chamaeleo (Chamaeleo) gracilis gracilis
Hallowell, 1842
Sites. Lagos State: Lekki (06°30' N, 04°08' E);
Ondo State: Ashewele (06°48' N, 04°55' E), Ifetedo
(07°27' N, 04°35' E); Delta State: Sapele (05°53' N,
05°42' E), Eku (riverine bushland along the River
Benin; 05°49' N, 06°00' E); Edo State: Ologbo
Game Reserve (05°55' N, 05°27' E), Oluku
(05°59' N, 05°41' E); Bayelsa State: Sagbama
(05°10' N, 06°05' E), Yenagoa (05°12' N, 06°05' E),
Taylor Creek Forest Reserve (05°16' N, 06°11' E),
Zarama–Epie (05°15' N, 06°08' E); Rivers State:
Upper Orashi Forest Reserve (04°44' N, 07°10' E),
Otari–Abua (04°53' N, 06°41' E), Ahoada
(05°04' N, 06°38' E), Odiokwu (05°06' N, 06°37' E),
Degema (04°48' N, 06°48' E), Bonny Island
(04°25' N, 07°15' E), Peterside (04°29' N, 07°10' E);
Anambra State: Onitscha (06°08' N, 06°46' E),
Oguta (AGIP Oilfield forest; 05°58' N, 06°44' E);
Abia State: Blue River banks (20 km N of Aba;
05°14' N, 07°13' E); Akwa–Ibom State: Eket
(riverine forest along the River Kwa–Ibo (= Quo–
Ibo); 04°50' N, 07°58' E), Ikot–Ekpene (05°12' N,
07°45' E), Uyo (05°09' N, 07°51’ E); Cross River
State: Calabar (04°47' N, 08°21' E), Itu (05°14' N,
07°59' E), Akpabouyoh (04°50' N, 08°22' E),
Akamkpa (05°20' N, 08°21' E).
Habitats. Our records came not only from mature
lowland forests (e.g., Upper Orashi Forest Reserve),
but also from altered forests (Abonnema), bushy
spots surrounding farmlands and plantations (Uyo),
and even derived savannas (Onitscha).
In general, chameleons of genus
Chamaeleo
were observed mainly along paths crossing humid
secondary forests, where, usually, three vegetation
strata were discernible, and with abundance of
lianes and patches of undergrowth as general
features. Counts of buttresses of commercially
felled trees within five hectares from every spot
of capture of chameleons were found to average
3.2 ± 2.7 × ha-1 (
n
= 46, with a range of 0 to
7 × ha-1; e.g. 2 × ha-1 at Oredo, 4 × ha-1 at Zarama,
and 5 × ha-1 at Otari). Most forests where
chameleons were observed had also been dissected
by series of roads created for trucks to cart away
the timber. The forest floor of all these sites had
damp soils and considerable leaf litters in which
eggs or juveniles can be hidden during the
reproductive season (e.g., see BRANCH, 1988).
Habitat alteration may be locally high: for instance,
Oredo forest had a history of fire episodes from
neighbouring farmlands. Chameleons were also
found at seasonally flooded areas: for instance,
Otari forests were subject to seasonal flood from
River Nun and Sombreiro River.
Reproductive biology of females
All the species were oviparous. Females with
shelled eggs were found in February (
n
= 1), May
6Akani et al.
(
n =
4), and June (
n
= 1) in
R. spectrum
; in August
(
n
=1) and September (
n
= 3) in
C. cristatus
; in July
(
n
= 3), August (
n =
1), and September (
n
= 1) in
C. owenii;
in August (
n
= 2), September (
n
= 3),
December (
n
= 1), and January (
n
= 2) in
C.
gracilis
. Thus, based on these preliminary data, it
can be suggested that (i) female
R. spectrum
show a prolonged reproductive season with
oviposition likely occurring during the late phase
of the dry season; (ii) females of both
C. cristatus
and
C. owenii
have a shorter reproductive season
with oviposition occurring most probably at the
interphase between the end of the wet season
and the onset of the dry season; (iii) female
C.
gracilis
have at least two distinct oviposition
periods, one at the interphase between the end
of the wet season and the onset of the dry
season, and one at the peak phase of the dry
season. For this latter species, it could not be
excluded that reproduction may in fact take place
all the year round. Clutch size was invariably two
eggs in six
R. spectrum
, and was respectively 11
and 14 eggs in two
C. cristatus,
17, 15, 17, and 19
eggs in four
C. owenii,
and 19, 15, 21, 23, 16, and
14 in six
C. gracilis.
Diet composition, food niche width and overlap
of sympatric chameleons
A total of 116 chameleons were examined for
food items in their faeces: 47 were
R. spectrum
(23{, 24}), 20 were
C. owenii
(14{, 6}), 15 were
C. cristatus
(9{, 6}), and 34
C. gracilis
(16{,
18}). Results are shown in table 1. Diet
composition of all the four species of chameleons
consisted exclusively of invertebrates (arthrop-
ods), although a case of frog–eating was recorded
in
C. cristatus.
In both
R. spectrum
and
C. gracilis
,
females exhibited a wider food niche width than
males (
R. spectrum,
{
B
= 5.181, }
B
= 7.782;
differences significant at
P
< 0.01 at Mantel
linear test;
C. gracilis,
{
B
= 5.397, }
B
= 10.020;
P
< 0.00001 at Mantel linear test) (fig. 1).
Concerning
C. owenii,
the food niche width of
males (
B
= 6.211) and females (
B
= 6.897) was
very similar (
P
> 0.7, Mantel linear test), and the
same was true for
C. cristatus
({
B
= 5.618, }
B
= 4.310; inter–sexual differences:
P
= 0.372 at
Mantel linear test).
At a inter–specific level, the four species proved
to be arranged along a continuum in terms of
taxonomical food niche width, from the less
generalist (
C. cristatus B
= 4.964, after pooling
data for the two sexes) to the more generalist (
C.
gracilis B =
7.708), with the other two species at
intermediate places of this continuum (
R. spectrum
B =
6.481, and
C. owenii B
= 6.554). Trophic niche
overlap estimates (in terms of taxonomical dietary
composition) among species indicated that the
highest similarity occurred between
C. owenii
and
C. gracilis,
whereas a general low similarity
occurred between
R. spectrum
and each of the
three
Chamaeleo
species (table 2).
In terms of prey size, there were significant
differences among the four species (fig. 2;
Kruskal–Wallis ANOVA
F
3,74
= 14.456,
P
< 0.001),
and a Tukey’s HSD post–hoc test indicated that
R.
spectrum
preyed on significantly smaller preys
than the other three species, and
C. cristatus
preyed on significantly larger preys than the
other three species.
Daily and foraging patterns
As observed in other agamids from Africa
(ANIBALDI et al., 1998), the chameleon’s foraging
strategy consisted of frequent predatory
attempts, also at very short time intervals
between two consecutive trials.
C. cristatus
ingested 276 insects of which 53.6% were taken
between 09.00 and 11.00 h local time (fig. 3);
C.
gracilis
ingested 247 insects with 53.4% at the
activity peak of 09.00–11.00 a.m. (fig. 3), and
C.
owenii
ingested 232 insects with 50.4% gulped
at the same peak period (fig. 3). Daily patterns
of foraging activity were not significantly
different among individuals (at least
P
> 0.572 in
all comparisons at Mann–Whitney U–test). The
feeding strategy pattern exhibited by the three
chameleon species indicates that, although these
lizards begin hunting very early in the morning,
fewer insects are caught at this time. As the sun
rises, insect hunting is intensified and the highest
number is caught between 09.00 and 11.00 h.
During this period the lizards assumed their
brightest colour as they also basked in the
morning sun. By midday, the hunting propensity,
and consequently the number of prey ingested,
has dropped, probably as a result of the intense
heat from the sun. By 15.00–17.00 h however,
hunting ressumes, but not at the same rates as
in the morning hours. They appear to be least
successful towards dusk, and hunt more or less
on the lower branches and undergrowth of the
forest, as they return from the higher branches.
No feeding attempt was recorded during the
night hours, which suggests that Nigerian
chameleons are strictly diurnal, at least as far as
predatory activity is concerned.
Diet of thread–trailed chameleons (fig. 4) was
composed of orthopterans, coleopterans and
other pterygotes (winged insects), namely
Odonata, Hemiptera and Lepidoptera. Green–
type insects (grasshoppers, praying mantis and
stick insects) are preferred in relation to brown
or multicoloured forms (e.g., Z
onocerus
variegatus
). Prey items identified included:
Gryllotalpa africana, Locusta migratoria
migratorioides, Zonocerus variegatus, Podagrica
sjostedti, Empoasca
sp
., Rhyncophorus phoenicis,
Lagria villosa, Heteroligus
sp
., Diacrinia
(Spilosoma) maculosa, Acraea eponina,
and
A.
terpsicore.
Furthermore, all the species exhibit
similar basking habits. At night and early morning
hours, chameleons tended to rest climbed on the
lower branches, approximately at 30–70 cm from
Animal Biodiversity and Conservation 24.2 (2001) 7
the ground. As the day advances, especially by
midday, they tended to migrate towards the
higher branches of the trees. Skin colour begins
to change until it becomes fully brightened.
After basking for about 15–25 minutes, they often
withdraw and hide behind broad leaves, branches
of epiphytes, or twigs, to avoid excessive heating.
Hiding behind broad leaves is also the typical
antipredatory behaviour exhibited by these
animals during daylight hours.
Structure of the population and abundance
Densities were very similar at all study sites
(table 3), but highest in the area of mature
secondary forest (area A) and lowest in the area
of bush–grassland mosaic (area C) (fig. 5). The
species diversity was different in the three study
areas, with four species (i.e.
C. owenii, C. cristatus,
C. gracilis
and
R. spectrum
) recorded in the
mature secondary forest (area A), two species
Table 1. Dietary data recorded from faecal pellets of four species of chameleons recorded at a
study plot in southern Nigeria (Eket, Akwa–Ibom State). Dietary composition is assessed by: N.
Numbers of items; (n). Numbers of pellets containing that prey type. In addition, one frog was
eaten by a male
C. cristatus
. (See text for more details.)
Tabla 1. Datos sobre la dieta registrados a partir de bolas fecales de cuatro especies de camaleones
registrados en el área de estudio en el sur de Nigeria (Eket, estado de Akwa–Obom). La
composición de la dieta se calcula por: N. Número de unidades; (n). Número de bolas fecales
conteniendo este tipo de presa. Además, una rana fue devorada por un macho de C. cristatus. (Ver
el texto para más detalles.)
R. spectrum C. owenii C. crstatus C. gracilis
Prey type { } { } { } { }
Miriapoda 1(1) 3(3) 1(1) 0 1(1) 0 1(1) 1(1)
Chilopoda 0 0 0 1(1) 0 0 1(1) 0
Isopoda 1(1) 4(3) 0 1(1) 0 0 1(1) 0
Scorpiones 0 1 (1) 0 0 0 1(1) 0 0
Araneae 6(6) 15(10) 2(2) 3(2) 1(1) 5(2) 4(4) 5(4)
Opilionidae 1(1) 2(2) 0 1(1) 0 0 1(1) 1(1)
Dermaptera 1(1) 5(4) 1(1) 1(1) 1(1) 0 0 1(1)
Isoptera 23(5) 12(4) 0 0 1(1) 0 0 5(1)
Orthoptera 10(6) 15(8) 21(7) 6(4) 10(5) 8(3) 18(9) 13(8)
Diptera 1(1) 2(2) 8(6) 1(1) 0 0 4(1) 4(2)
Hemiptera 3(2) 3(2) 4(3) 0 8(3) 7(2) 1(1) 8(5)
Lepidoptera
adults 2(2) 2(2) 4(4) 0 0 0 2 (2) 7(4)
larvae 2(2) 5(5) 1(1) 0 0 0 2 (2) 6(4)
Odonata 0 0 3(2) 1(1) 12(6) 0 6 (4) 2(2)
Coleoptera (indet.) 0 3(2) 2(2) 1(1) 2(2) 0 1 (1) 3(3)
Carabidae 1(1) 0 0 0 0 0 0 0
Tenebrionide 0 1(1) 0 0 0 0 0 0
Formicoidea 7(3) 21(6) 11(1) 0 0 0 0 6(2)
Vespoidea 0 0 1(1) 1(1) 1(1) 0 1 (1) 1(1)
Apoidea 0 0 2(2) 0 1(1) 1 (1) 1 (1) 0
Blattoidea 0 0 3(3) 1(1) 1(1) 1 (1) 1 (1) 2(2)
Mantodea 0 0 2 (2) 4 (3) 3 (3) 2 (1) 3 (3) 3(3)
8Akani et al.
(i.e.
C. owenii
and
R. spectrum
) in the riparian
woodland (area B), and one species (i.e.
C. gracilis
)
in the bush–grassland mosaic (area C).
Concerning area A where logging was
undertaken, this manipulation did not substantially
reduce the abundance of chameleons (fig. 5), but
had dramatic effects on the specific diversity. In
fact, three of the four species became extinct after
the changes on the initial habitat (i.e.
C. owenii, C.
cristatus,
and
R. spectrum
), while one substantially
increased its abundance (i.e.
C. gracilis
) (fig. 5).
Discussion
Distribution and habitat
All the species of chameleons found in our study
had been already reported for Nigeria (e.g., TALBOT,
1912; PASQUAL, 1937; ROMER, 1953; DUNGER, 1967a,
1967b; BUTLER, 1986; REID, 1986; AKANI et al
.,
1999),
but information was in most cases anecdotal.
Other species which are known to occur in western
Cameroon and south–eastern Nigeria (cf. BÖHME,
1975; JOGER, 1982; KLAVER & BÖHME, 1997; LEBRETON,
1999; WILD, 1993, 1994) were not observed on any
occasion during the present study.
Fig. 1. Plot showing numbers of chameleons from which faeces were examined against cumulative
number of prey categories identified from their faeces. Note that an obvious plateau phase was
obtained for
Rhampholeon spectrum
and
Chamaeleo gracilis
, whereas the same curve stability
was not reached in the other two species.
Fig. 1. Diagrama del número de camaleones cuyas heces se examinaron y según el número
acumulado de categorías de presas identificadas a partir de las heces. Nótese que se obtuvo una
meseta para Rhampholeon spectrum
y
Chamaeleo gracilis
mientras que la misma estabilidad de
la curva no se encontró en las otras dos especies.
Table 2. Food niche overlap estimates
(calculated by PIANKA’s (1986) symmetric
equation) of taxonomical dietary composition
among sympatric species of chameleons from
the study area: Rs.
Rhampholeon spectrum
; Co.
Chamaeleo owenii
; Cc.
Chamaeleo cristatus
; Cg.
Chamaeleo gracilis
.
Tabla 2. Estimación del solapamiento del
nicho alimentario (calculado mediante la
ecuación simétrica de PIANKA (1986) de la
composición alimentaria taxonómica entre
especies simpátricas de camaleones del área
de estudio: Rs. Rhampholeon spectrum; Co.
Chamaeleo owenii; Cc. Chamaeleo cristatus;
Cg. Chamaeleo gracilis.
Rs Co Cc Cg
Rs – 0.513 0.583 0.596
Co – – 0.645 0.778
Cc – – – 0.639
Cg – – – –
R. spectrumR. spectrum
R. spectrumR. spectrum
R. spectrum
C. oweniiC. owenii
C. oweniiC. owenii
C. owenii
C. cristatusC. cristatus
C. cristatusC. cristatus
C. cristatus
C. gracilisC. gracilis
C. gracilisC. gracilis
C. gracilis
22
22
200
00
0
1818
1818
18
1616
1616
16
1414
1414
14
1212
1212
12
1010
1010
10
88
88
8
66
66
6
44
44
4
22
22
2
00
00
0
Cumulated number of prey categoriesCumulated number of prey categories
Cumulated number of prey categoriesCumulated number of prey categories
Cumulated number of prey categories
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46
Number of specimens Number of specimens
Number of specimens Number of specimens
Number of specimens
Animal Biodiversity and Conservation 24.2 (2001) 9
Fig. 2. Prey size distributions for the four species of sympatric chameleons studied in this paper,
inferred from faecal pellets. Symbols for prey size categories: 1. 0–3 mm; 2. 3–6 mm; 3. 6–9 mm;
4. 9–12 mm; 5. 12–15 mm; 6. 15–18 mm; 7. 18–21mm; 8. > 21 mm.
Fig. 2. Distribución del tamaño de las presas de cuatro especies simpátricas de camaleones
estudiadas en este trabajo, obtenidas a partir de las bolas fecales. Símbolos para cada categoría
de presa: 1. 0–3 mm; 2. 3–6 mm; 3. 6–9 mm; 4. 9–12 mm; 5. 12–15 mm; 6. 15–18 mm; 7. 18–21mm;
8. > 21 mm.
Fig. 3. Diet feeding patterns of three “thread-trailed” chameleons at the Niger Delta (
n
= 1 for all species).
Fig. 3. Patrones alimentarios de la dieta de tres camaleones “thread–trailed” en el delta del Níger
(n = 1 para todas las especies).
R. spectrumR. spectrum
R. spectrumR. spectrum
R. spectrum
C. oweniiC. owenii
C. oweniiC. owenii
C. owenii
C. cristatusC. cristatus
C. cristatusC. cristatus
C. cristatus
C. gracilisC. gracilis
C. gracilisC. gracilis
C. gracilis
C. cristatusC. cristatus
C. cristatusC. cristatus
C. cristatus
C. oweniiC. owenii
C. oweniiC. owenii
C. owenii
C. gracilisC. gracilis
C. gracilisC. gracilis
C. gracilis
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
Prey size categories Prey size categories
Prey size categories Prey size categories
Prey size categories
6–9 9–12 12–15 15–18 18–21 6–9 9–12 12–15 15–18 18–21
6–9 9–12 12–15 15–18 18–21 6–9 9–12 12–15 15–18 18–21
6–9 9–12 12–15 15–18 18–21
Hours (Lagos time) Hours (Lagos time)
Hours (Lagos time) Hours (Lagos time)
Hours (Lagos time)
180180
180180
180
160160
160160
160
140140
140140
140
120120
120120
120
100100
100100
100
8080
8080
80
6060
6060
60
4040
4040
40
2020
2020
20
00
00
0
Number of insectes ingestedNumber of insectes ingested
Number of insectes ingestedNumber of insectes ingested
Number of insectes ingested
9090
9090
90
8080
8080
80
7070
7070
70
6060
6060
60
5050
5050
50
4040
4040
40
3030
3030
30
2020
2020
20
1010
1010
10
00
00
0
% prey items% prey items
% prey items% prey items
% prey items
10 Akani et al.
Fig. 4. Dietary spectrum of three specimens of chameleons at the Niger Delta, based on “thread–
trailing” continuous monitoring.
Fig. 4. Espectro alimentario de tres especímenes de camaleones en el delta del Níger, basada en
controles continuos en "thread–trailing".
Rhampholeon spectrum
The distribution is well known in the extreme
south–eastern region of Nigeria (e.g., TALBOT,
1912; REID, 1986),
R. spectrum
is apparently
more common in forests east of the Cross River,
although the records from Eket and Stubbs
Creek Forest Reserve demonstrate it is not a
species for which the Cross River course may
represent a geographical barrier (as is the case
for numerous other small vertebrates, e.g. see
KINGDON, 1990). It is described as euryzonal,
and abundant in premontane, submontane,
and montane forests (500–1,700 m a.s.l.) of
western Cameroon, but much more rare in
lowland forest (LAWSON, 1993; WILD, 1994). It
is unknown whether the same distributional
pattern may occur also in Nigeria, but
according to several experienced hunters
interviewed, this species is very common in
the montane forests of the northern Cross
River State. Its presence was reportedly
influenced by other ecological factors, i.e. co–
occurrence of food competitors: WILD (1994)
claimed that it may suffer from competition
with forest toads (
Bufo camerunensis
), which
may have a very similar dietary spectrum.
Chamaeleo cristatus
Well known to occur in south–eastern Nigeria,
this species was captured probably around Oban
(Cross River State) by TALBOT (1912), and much
more recently both east (at Osomba, see REID,
1986), and west (at Eket, see AKANI et al
.,
1999)
of Cross River. Original records of this study also
indicate that it is also found in the western
portion of the Nigerian forest zone (i.e. at Oredo,
western axis of the Niger Delta). Altitude is
likely not an important factor in the distribution
of
C. cristatus
, which was in fact observed both
in lowland moist forests and in hilly–montane
sites. However, micro–habitat characteristics seem
to be important, as both our observations and
those of WILD (1994) indicate a strong preference
for specific micro–habitats (low, thick, flowering
bushes in our case, and “the shrub layer in
primary forest” in Wild’s case), and thus a
restricted habitat selection.
Chamaeleo owenii
Its presence in the forests of south–eastern
Nigeria is well documented (see ROMER, 1953, for
Port Harcourt (Rivers State, eastern axis of the
Niger Delta, and AKANI et al.,
1999, for additional
localities of the eastern Niger Delta). Records
given here suggest that it is found in lowland
moist forests and in forest–plantation mosaics.
SCHMIDT (1919) reported similar habitats for
conspecifics from the former Belgian Congo.
Chamaeleo wiedersheimi
The less common of the five species of
chameleons observed in the present study in
C. cristatusC. cristatus
C. cristatusC. cristatus
C. cristatus
C. gracilisC. gracilis
C. gracilisC. gracilis
C. gracilis
C. oweniiC. owenii
C. oweniiC. owenii
C. owenii
6060
6060
60
5050
5050
50
4040
4040
40
3030
3030
30
2020
2020
20
1010
1010
10
00
00
0
%%
%%
%
Orthoptera Coleoptera Odonata Hemiptera Lepidoptera OthersOrthoptera Coleoptera Odonata Hemiptera Lepidoptera Others
Orthoptera Coleoptera Odonata Hemiptera Lepidoptera OthersOrthoptera Coleoptera Odonata Hemiptera Lepidoptera Others
Orthoptera Coleoptera Odonata Hemiptera Lepidoptera Others
Prey categories Prey categories
Prey categories Prey categories
Prey categories
Animal Biodiversity and Conservation 24.2 (2001) 11
Fig. 5. Abundance of chameleons (number of specimens observed in relation to the number of
hours spent in the field) in three study areas of south–easthern Nigeria. Study areas: A. Mature
secondary forest before treatment; A'. Mature secondary forest after treatment; B. Riparian
woodland; C. Bush–grasland mosaic.
Fig. 5. Abundancia de camaleones (número de especímenes observados con relación al número
de horas empleadas en el campo) en tres áreas de estudio del sudeste de Nigeria. Áreas de
estudio: A. Bosque secundario maduro antes de ser sometido a explotación; A'. Bosque secundario
maduro después de ser sometido a explotación; B. Bosque maduro; C. Mosaico de bosque y
pradera.
Table 3. Numbers of chameleons observed in three study plots in southern Nigeria.
Tabla 3. Número de camaleones observados en tres áreas estudiadas en el sur de Nigeria.
Area A
Before timbering After timbering Area B Area C
Chamaeleo owenii
4(3{ 1}) 0 3{ 0
Chamaeleo cristatus
1{ 0 0 0
Chamaeleo gracilis
1} 7(3{ 4}) 0 4{
Rhampholeon spectrum
2(1{ 1}) 0 4(2{ 2}) 0
C. oweniiC. owenii
C. oweniiC. owenii
C. owenii
C. cristatusC. cristatus
C. cristatusC. cristatus
C. cristatus
C. gracilisC. gracilis
C. gracilisC. gracilis
C. gracilis
R.R.
R.R.
R.
spectrumspectrum
spectrumspectrum
spectrum
A A' B C A A' B C
A A' B C A A' B C
A A' B C
Study areas Study areas
Study areas Study areas
Study areas
0.180.18
0.180.18
0.18
0.160.16
0.160.16
0.16
0.140.14
0.140.14
0.14
0.120.12
0.120.12
0.12
0.10.1
0.10.1
0.1
0.080.08
0.080.08
0.08
0.060.06
0.060.06
0.06
0.040.04
0.040.04
0.04
0.020.02
0.020.02
0.02
00
00
0
Abundance (Nº specimens / h field efAbundance (Nº specimens / h field ef
Abundance (Nº specimens / h field efAbundance (Nº specimens / h field ef
Abundance (Nº specimens / h field effort)fort)
fort)fort)
fort)
southern Nigeria. Their distribution is linked
specifically to hilly and montane sites, and
montane savannas / grasslands in Cameroon
(WILD, 1993; JOGER, 1981; DUNGER, 1967b).
According to WILD (1994),
C. wiedersheimi
is
restricted to the shrub layer in primary forest, the
same as
C. cristatus
and
Chamaeleo camerunensis
Müller, 1909.
12 Akani et al.
Chamaeleo gracilis
This a typical and common forest species of
south–eastern Nigeria (e.g., DUNGER, 1967a;
BUTLER, 1986; AKANI et al.,
1999), but is certainly
found also in the savannas (e.g., see DUNGER,
1967b). As in other countries (e.g., in Cameroon
and Liberia, see SCHMIDT, 1919; WITTE, 1965), it is
a habitat generalist.
Reproductive biology
Data on reproduction timing of female
R. spectrum
are fully consistent with data from conspecifics at
Mt. Kupe (western Cameroon, cf. WILD, 1994),
and our data on
C. cristatus
are also in agreement
with the single record available on the
reproduction of a Nigerian conspecific (REID, 1986).
DUNGER (1967b) recorded seven newly–hatched
C.
gracilis
on 20th May on a low bush in Jos (09°55'
N, 08°53' E), and thus suggested that hatching
occurs during the early rains. It is quite consistent
with a period of oviposition at the peak of the
dry season, as indicated by the original data
presented in this study. Concerning
R. spectrum,
an invariable clutch size of two eggs was also
detected by WILD (1994) in western Cameroon,
which suggests that it is a general pattern for this
species (but a clutch size of 2–5 eggs is reported
for this species by KAIWI (2000), 1–3 eggs in the
closely related
Rhampholeon boulengeri
from the
former Belgian Congo [SCHMIDT, 1919], and 3 eggs
in a Tanzanian
Rhampholeon uluguruensis
[TILBURY
& EMMRICH, 1996]). Clutch sizes of 15 and 17 eggs
were reported in two
C. owenii
from the former
Belgian Congo (SCHMIDT, 1919), which is very
consistent with the original data reported in this
study. However, clutch sizes of free–ranging
females from Nigeria were considerably smaller
than those reported in the layman’s literature for
either
C. cristatus
(16–37 eggs, see KAIWI, 2000) or
C. gracilis
(20–40 eggs, see KAIWI, 2000), and also
a free–ranging female
C. gracilis
from Belgian
Congo had 60 eggs (SCHMIDT, 1919).
Feeding ecology
The four studied chameleon species of tropical
Nigeria fed almost exclusively upon arthropods. It
is consistent with data on
R. spectrum
from south–
eastern Nigeria (REID, 1986) and Cameroon (WILD,
1994), with data on
C. owenii
from the former
Belgian Congo (SCHMIDT, 1919), and in general
with dietary data on chameleons elsewhere (e.g.,
PLEGUEZUELOS et al.,
1999). It is noteworthy
however, that a single case of vertebrate–eating
(a froglet) by a
C. cristatus
was recorded. Although
this predation event appears exceptionally unusual
in the wild (at least considering data presented in
table 1), Nigerian
C. cristatus
are known to readily
eat frogs and newly metamorphosed toads in
captivity (REID, 1986), which suggests that they
have a natural “attitude” for preying upon small
amphibians. In any case, it is certainly premature
to stress that amphibian–eating is a trophic niche
difference between
C. cristatus
and the other
three sympatric species.
In the two better studied species (i.e.
R. spectrum
and
C. gracilis
), there were significant inter–sexual
differences in dietary habits, with the females
exhibiting a wider food niche width than males.
The reasons for this inter–sexual difference are
unknown, and are likely not correlated with any
sexual size dimorphism (SSD) as SSD is certainly not
big enough to justify such an assumption in both
Table 4. Data on chameleon trade in local markets of the Niger Delta Basin during the year,
2000: N. Number of chameleons on display; P. Unit selling price (in "Nairas"); $. US dollar
equivalent (all of them used for traditional medicine).
Tabla 4. Datos sobre el comercio en mercados locales de la cuenca del delta del Níger a lo largo
del año 2000: N. Número de camaleones observados; P. Precio por unidad (en "Nairas"); $.
Equivalente en dólares americanos (todos ellos utilizados en la medicina tradicional).
Date Location of market N Suppliers P ($)
17 V 2000 Mile 1, market P. H. 1 Hunter from Bayelsa 2,500 23.0
19 V 2000 Mile 3, market P. H. 3 Hunters from Omoku and Biseni 2,700 25.0
4 VII 2000 Otari 4 Farmers / hunters from Ogbema Abua 3,000 27.0
23 VIII 2000 Yenagoa 2 Farmers / hunters from Zarana Epie 2,800 26.5
27 X 2000 Benin City 6 Hunters from Mosoga, Oredo and Aghara 3,200 29.0
Total 16
Animal Biodiversity and Conservation 24.2 (2001) 13
species (WILD, 1994). At the inter–specific level, the
apparent continuum of dietary specialisation from
the less generalist species (
C. cristatus
) to the more
generalist species (
C. gracilis
) may suggest that a
true phenomenon of food resource partitioning
occurs between sympatric forest chameleons. In
this regard, an obvious pattern of resource
partitioning among species was also seen with
regard to prey size, with
R. spectrum
and
C. cristatus
at the two extremes of the continuum, and
C.
gracilis
being the most generalist species. In general
terms,
C. gracilis
appears thus not only the most
generalist species in terms of habitat, but also in
terms of prey type and prey size. The lesser
interspecific overlap was observed between
R.
spectrum
and
C. owenii.
It is likely that it depended
on the combined effect of size and habits (
R.
spectrum
is mostly terrestrial–dwelling, whereas
C.
owenii
is mainly arboreal).
Despite these interspecific differences found
in diet composition, our data should be
considered as a “snapshot” of the chameleon
diet. A considerably higher variation is likely.
Taking into account that the diet composition of
thread–trailed specimens and the composition
of faeces was very similar, it is concluded that
“thread–trailing” is a very good experimental
procedure to study chameleon ecology in sites
where these lizards are rare or endangered, and
when it is particularly difficult to establish an
experimental protocol involving the capture of
many specimens.
Structure of the population and abundance
Density of chameleons in the forest habitats of
southern Nigeria was low and certainly much
less than that observed in other African regions
(e.g. Madagascar, cf. KAUFFMANN et al., 1997).
Moreover, the species diversity at single sites
clearly appears much less than that observed in
the forests of the adjacent Cameroon (WILD,
1993, 1994). For instance,
R. spectrum
sympatric
was observed in this study with up to three
Chamaeleo
species in southern Nigeria, whereas
WILD (1994) found up to ten different species in
Cameroon forests. However, the diversity of
sympatric chameleon species of the Biafran
forests is certainly influenced by the the relative
elevation: WILD (1994) found seven sympatric
species of
Chamaeleo
in montane areas around
Mt. Manenguba, but only four species in lowland
Cameroon forests.
Despite the differences in the structure of the
vegetation among sites, the overall abundance of
chameleons was similar, although densities were
higher at mature secondary forests. After logging,
the overall abundance of chameleons declined
only slightly, whereas the species diversity declined
drastically. These findings support the hypothesis
that the population of free–ranging chameleons
declines in rainforest habitats where rapid changes
in the environment are occurring.
Implications for conservation
Results of this study provide new insights with
important implications for the conservation of
chameleons in Nigeria (and probably, West
Central Africa). All chameleons in the Niger Delta
and in south–eastern Nigeria inhabit very fragile
ecosystems such as mature secondary forests and
riparian forests. Human alteration of the remnant
forest is likely to further destroy this habitat
type in the next decades (OLAJIDE & ENIANG, 2000),
especially due to the continuing exploration of
unaltered biota for oil industry development,
which is the main economic income for the
country. In addition, hundreds of
C. gracilis
are
captured and later desecated
every year from
the forests around Lagos and Ibadan, and sent
to public markets in Calabar, Uyo (and probably
other towns) where they are traded for local
medicine or juju practices at a low price (Naira
150–400, i.e. approximately 2–4 US dollars, on
March 2001) (Akani et al.,
unpublished). Both
factors are likely to have a tremendous influence
on species conservation in the near future.
Species diversity changed dramatically in one
of our study sites after human impact. Moreover,
the only surviving species (
C. gracilis
, i.e. the
ecologically most versatile species of the forest
region of Nigeria), which was rare before
timbering, became much more common (i.e.
largely dominant in the chameleon community)
after logging. The present results fully agree
those of GRAY (1989) who suggested that rare
and more specialised species tend to disappear
with habitat loss, whereas moderately common
species (more habitat generalist) would increase
in abundance. Accordingly,
C. owenii, C. cristatus,
and
R. spectrum
may be dramatically affected by
habitat loss and forest fragmentation, whereas
C. gracilis
might even benefit from this situation,
possibly also because of less inter–specific
competition with the other chameleon species.
The broad similarity in activity patterns and
feeding habits among two “fragile” species (
C.
owenii
and
C. cristatus
) versus one “versatile”
species (
C. gracilis
) indicate that these life–history
attributes cannot influence differently the
species–specific persistence in altered habitats,
and so it is likely that prey resource availability
does not play an important role in determining
the scarcity of some particular species in altered
habitats. The rarity of chameleons in the study
area is attributed to: 1. Habitat destruction /
modification through lumbering and cultivation;
2. Local fires in bush areas, especially at the end
of the dry season (March–April), for agricultural
purposes; 3. Illegal trade because of the great
demand for chameleons following the increasing
market values (N 2,500–N3,000; approx. 23–29 US
dollar (see table 4); 4. Capture and desiccation
for traditional medicinal purposes. The authors
wish to encourage State and Local Governments
to establish some forest reserves specifically
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Acknowledgements
We are grateful to “Prime Energy Resources
PLC” (Port Harcourt) for logistic support and
financial assistance throughout this project. Data
were also collected during environmental projects
supported by E. N. I. S. p. A. and by “T. S. K. J.
Nigeria Ltd.”. F. M. Angelici, D. Capizzi, E. A.
Eniang, and E. Politano contributed with many
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original draft version, and our referees, M.
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