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IGUANA  •  VOLUME 13, NUMBER 2  •  JUNE 2006 163CONSERVATION RESEARCH REPORTS

Dietary Shifts of Turtles in Pristine
and Oil-polluted Habitats of the
Niger Delta in Southern Nigeria

LUISELLI ET AL. (2004. Herpetological
Journal 14: 57–64) examined the diets of
sympatric freshwater turtles at two study
areas in the Niger Delta (southern
Nigeria). One site was unpolluted and the
other was polluted by an oil spill, but
both areas were otherwise similar. Four
species of turtle (Trionyx triunguis, Pelusios
castaneus, Pelusios niger, and Pelomedusa
subrufa) were captured in the unpolluted
area, whereas only two species (Pelusios
castaneus and Pelusios niger) were captured
in the polluted area. In the unpolluted
area, the taxonomic composition of the
diets of Pelusios castaneus and Pelusios niger
was similar, whereas the diets of
Pelomedusa subrufa and Trionyx triunguis
were very different from the other two
species and one another. In the polluted
area, the taxonomic composition of the
diet of Pelusios castaneus was significantly
different from that of conspecifics in the
unpolluted area, and consisted mainly of
plant matter, annelids (earthworms and
leeches), and gastropods. The taxonomic
composition of the diet of Pelusios niger
was also significantly different from that
of conspecifics at the unpolluted area, and
consisted mainly of annelids and gas-
tropods, and secondarily of plant matter.
Amphibian prey (eggs, tadpoles, and
adults), which were one of the main food
types for all turtles in the unpolluted area,

practically disappeared from the diet of
turtles at the polluted area. The two
species that survived the oil spill obviously
shifted their dietary preferences. In both
species, an obvious reduction in the
breadth of the trophic niche was appar-
ent. Such a reduction in trophic niche
breadth may reflect the reduced availabil-
ity of most food sources (particularly
amphibians, fish, and environmentally-
sensitive invertebrates) in the polluted
area, despite over 10 years of restoration
operations at the site. The reduction in
trophic niche breadth also may reflect
shifts in habitat use by the surviving tur-
tles, which tended to concentrate into sin-
gle habitat types in the polluted area,
compared to the unpolluted area where
they were more habitat generalists.

Biology of Endangered 
Ploughshare Tortoises

Successful conservation requires a good
understanding of both the direct and
indirect causes of any decline in popula-
tion size. Harvests of wild populations
often target the largest, oldest individuals
that have the greatest economic value. If
these individuals contribute dispropor-
tionately more to recruitment than con-
specifics, the harvest will cause a greater
reduction in population viability than ini-
tially anticipated. The Ploughshare
Tortoise (Geochelone yniphora), endemic
to Madagascar, has been reduced to <600

individuals due to exploitation and habi-
tat loss. A trial release of captive-bred
juveniles has been carried out but the rel-
ative suitability of individuals for release,
in terms of body size, was not considered.
Using data from a long-term mark-recap-
ture study of an unharvested wild popu-
lation of ploughshare tortoises, O’BRIEN

ET AL. (2005. Biological Conservation 126:
141–145) found that larger juveniles were
significantly more likely to survive their
first year of life than smaller tortoises.
Juveniles that survived beyond their first
year of life generally grew at the same rate,
but had a significantly larger hatch size
(mean = 41.7 mm), compared with juve-
niles that did not survive (mean = 39.3
mm). The conservation implications of
these results are that release of captive-
bred Ploughshare Tortoises is likely to be
more successful if larger individuals are
released. Previous studies have reported
larger female Ploughshare Tortoises laying
larger eggs which hatch larger juveniles.
This study shows individuals with a larger
hatch size retain their size advantage over
smaller conspecifics and are more likely to
survive their first year of life. This suggests
a harvest that targets the largest females in
the Ploughshare Tortoises population
could be highly detrimental to population
viability.

Herpetofaunal Diversity in
Southeastern National Parks

The southeastern United States supports
about half of the nations species of
amphibians and reptiles, of which about
20% are endemic to the region. Because
few areas have been formally inventoried,

C O N S E R V A T I O N  R E S E A R C H  R E P O R T S

Pelomedusa subrufa was restricted to unpolluted areas in the Niger Delta (Nigeria).

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The Ploughshare Tortoise (Geochelone
yniphora), endemic to Madagascar, has been
reduced to fewer than 600 individuals due to
exploitation and habitat loss.

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164 IGUANA  •  VOLUME 13, NUMBER 2  •  JUNE 2006 CONSERVATION RESEARCH REPORTS

TURBERVILLE ET AL. (2005. Southeastern
Naturalist 4:537–569) conducted biolog-
ical inventories at 16 parks in the
National Park Service’s Southeast Coast
Network. Using a variety of standard field
techniques and surveys of museum collec-
tions, the authors documented the pres-
ence of 123 native species of amphibians
and reptiles in the 16 parks, with num-
bers of species ranging from 6–64 per
park.

Increasing Leatherback 
Numbers Linked to 

Long-term Nest Protection
The Leatherback Turtle (Dermochelys cori-
acea) is considered to be at serious risk of
global extinction, despite ongoing conser-
vation efforts. Intensive long-term moni-
toring of a Leatherback nesting popula-
tion on Sandy Point (St. Croix, US
Virgin Islands) offers a unique opportu-
nity to quantify basic population param-
eters and evaluate effectiveness of nesting
beach conservation practices. DUTTON ET

AL. (2005. Biological Conservation 126:
186–194) reported a significant increase
in the number of females nesting annu-

ally from ca. 18–30 in the 1980s to 186
in 2001, with a corresponding increase in
annual hatchling production from ca.
2000 to over 49,000. They then analyzed
resighting data from 1991 to 2001 with
an open robust-design capture-mark-
recapture model to estimate annual nester
survival and adult abundance for this
population. The expected annual survival
probability was estimated at ca. 0.893
(95% CI: 0.87–0.92) and the population
was estimated to be increasing ca. 13% pa
since the early 1990s. Taken together with
DNA fingerprinting that identify
mother-daughter relations, their findings
suggest that the increase in the size of the
nesting population since 1991 was prob-
ably due to an aggressive program of

beach protection and egg relocation initi-
ated more than 20 years ago. Beach pro-
tection and egg relocation provide a sim-
ple and effective conservation strategy for
this Northern Caribbean nesting popula-
tion as long as adult survival at sea
remains relatively high.

Impact of Deforestation on Lizards,
Small Mammals, and Birds in

Southern Madagascar
Madagascar is a global biodiversity
hotspot threatened by forest loss, degra-
dation, and fragmentation, all of which
are detrimental to the future survival of
forest-dwelling organisms. For conserva-
tion purposes, determining how species
respond to habitat disturbance, specifi-
cally deforestation, is essential. SCOTT ET

AL. (2006. Biological Conservation 127:
72–87) investigated the impacts of defor-
estation on three vertebrate communities,
lizards, small mammals, and birds, in an
area of spiny forest subjected to anthro-
pogenic forest clearance. Spiny forest has
high levels of endemism, but conservation
in this unique ecosystem is hindered by
the lack of research. The authors assessed
species richness, species abundance, and
community composition of lizards, small
mammals, and birds in six areas of ‘forest’
and six ‘cleared’ areas. From surveys and
opportunistic sightings, they recorded a
total of 70 species of birds, 14 species of

Leatherbacks (Dermochelys coriacea) are criti-
cally endangered. Beach protection and egg
relocation provide a simple and effective con-
servation strategy for nesting populations as
long as adult survival at sea remains relatively
high.

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Oustalet’s Chameleon (Furcifer oustaleti) is one of the world’s largest chameleons and is one of
the many unique species of lizards that inhabit the spiny forests of Madagascar.

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Alligator Snapping Turtles (Macroclemys tem-
minckii) and American Alligators (Alligator
mississippiensis) are but two of 123 native
species of amphibians and reptiles found in
16 national parks in the southeastern United
States.

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Where Gopher Tortoises (Gopherus polyphe-
mus) are present, their burrows are used for
shelter by many other animals.

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mammals, and 38 species of reptiles and
amphibians. They found forest clearing to
have a negative effect on species richness
and community structure of all groups
and identified loss of canopy cover as a
driving factor. However, the response and
sensitivity to clearing varied between
groups and species. Lizards (50%) and
small mammals (40%) had the greatest
decline in species richness in response to
clearing as compared to birds (26%),
although birds showed the greatest shift
in community structure. The community
in cleared areas contained more generalist
and introduced species than species
unique to the spiny forest. The first
species to suffer from forest clearance were
those of high conservation priority due to
their restricted geographic range.

Roads and Snake Movements
Roads affect survivorship and behavior
and can act as barriers to movement,
which exacerbates habitat fragmentation
and disrupts landscape permeability.
ANDREWS AND GIBBONS (2005. Copeia
2005: 772–782) conducted field experi-
ments that demonstrated interspecific dif-
ferences in snakes of the southeastern
United States that encountered roads.
Smaller species exhibited higher levels of
road avoidance, venomous species crossed
more slowly than nonvenomous forms,
and three species responded to traffic by
becoming immobile, which prolonged
crossing times and magnified susceptibil-
ity to road mortality. All species crossed
roads at perpendicular angles. Models
using crossing speeds indicated that some
species couldn’t successfully cross roads
with high traffic densities.

Conservation and Reptilian 
Diversity on the Guiana Shield

The Guiana Shield region is a biologically
rich area that includes much of northeast-
ern South America. It is strictly defined
by the underlying geological formation of
the same name. Total area is approxi-
mately 1,520,000 km2 and portions or all
of five nations are included. In their intro-
duction to the “Checklist of the terrestrial
vertebrates of the Guiana Shield,” editors
HOLLOWELL AND REYNOLDS (2005.
Bulletin of the Biological Society of
Washington (13): x + 98 pp.) addressed
conservation:

With the exception of a few populated
localities, the environment of the Guiana
Shield has benefited from limited access
and low population densities, although
this same isolation has hindered biodiver-
sity research. Estimates vary, but much of
the vegetation is still relatively undis-
turbed by human activities. Recently,

however, the pace of disturbance has
greatly increased. Current threats include
large-scale logging, large- and small-scale
gold and diamond mining, oil prospect-
ing, bauxite mining, hydroelectric dams,
wildlife trade, and population-related
pressures such as burning, grazing, agri-
culture, and the expansion of Amerindian
villages. Taken together, these impacts
have begun to take their toll, with vast
areas vulnerable to increasing disturbance.

The status of conservation efforts
varies by country. Throughout the
Guiana Shield, many areas that are desig-
nated as protected are often only “paper”
parks, because a lack of infrastructure and
funds fails to protect the areas. Over the
last four decades, Venezuela has estab-
lished seven national parks, 29 natural
monuments, and two biosphere reserves
covering about 142,280 km2, more than
30% of its share of the Guiana Shield. In
Guyana, the progress of conservation
efforts has been slower, with only one

IGUANA  •  VOLUME 13, NUMBER 2  •  JUNE 2006 165CONSERVATION RESEARCH REPORTS

Larger individuals of Timber Rattlesnakes
(Crotalus horridus) were more likely than
smaller snakes to avoid roads. However, 50%
of snakes on the road froze for up to a minute
even before vehicles passed, prolonging cross-
ing times and magnifying susceptibility to
road mortality.

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Number of reptilian species known to occur on the Guiana Shield: Total numbers of species
listed by family, species with broadly endemic distributions within the area, and species with site-
specific endemic distributions.

Shield-wide Site-specific
Family Species Endemics Endemics

Colubridae 104 6 15

Gymnophthalmidae 45 7 18

Iguanidae (sensu lato) 32 2 9

Gekkonidae 16 4 1

Elapidae 13 4 1

Teiidae 12 1 1

Amphisbaenidae 10 3 5

Leptotyphlopidae 8 2 1

Boidae 8 1 -

Viperidae 8 - 1

Chelidae 8 1 -

Podocnemididae 6 1 -

Crocodylidae 5 1 -

Anomalepididae 4 - 1

Cheloniidae 4 - -

Scincidae 3 1 -

Typhlopidae 3 - -

Testudinidae 2 - -

Dermochelyidae 1 - -

Kinosternidae 1 - -

Bataguridae 1 - -

Aniliidae 1 - -

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national park of 627 km2, about 3% of
the country’s area, although additional
reserves are under consideration. Guyana’s
3,710 km2 Iwokrama Forest is dedicated
to sustainable use. Surinam’s protected
areas system includes one national park
and a network of 11 reserves, totaling
almost 20,000 km2, over 12% of its total
area. This includes the recently created
16,000 km2 Central Surinam Nature
Reserve, a UNESCO World Heritage
Site that joined and expanded three exist-
ing reserves. French Guiana has no offi-
cially designated protected areas, but 18
proposed sites total 6,710 km2, about
7.5% of it area. The natural areas of
Venezuela and Guyana are currently
under the most anthropogenic pressure,
while those of French Guiana are proba-
bly less threatened.

Cooperation among the nations
with areas on the Guiana Shield is some-
times hampered by border disputes and
illegal cross-border transportation of gold
and wildlife. The implementation of con-
servation practices is further complicated
by many issues concerning the indige-
nous peoples of the region. All of these
challenges will have to be overcome on
the way to designing and maintaining a
viable reserve system.

ÁVILA PIRES (2005. Reptiles, pp. 24–40.
In: Bulletin of the Biological Society of
Washington (13): x + 98 pp.) listed 295
species of reptiles currently known from
the Guiana Shield (see Table). When only
species endemic to the region are consid-
ered, the proportion of lizards and
amphisbaenians increases, whereas the
proportion of snakes decreases. These dif-
ferences may be real or sampling artifacts.
Amphisbaenians are difficult to sample

and ranges of several species could be
wider than presently known, decreasing
the number of species considered to be
Guiana Shield endemics. In contrast,
ranges of widely distributed species of
snakes are well-known and probably real,
unless most currently recognized species
turn out to be species complexes. Many
new species remain to be discovered,
especially in the highlands.

Variability in Brachylophus
Most iguanas are found in the Americas,
but the genus Brachylophus occurs in Fiji
and Tonga in the South Pacific. Effective
conservation relies on understanding the
relationships among the populations on

various islands, which have previously
been poorly understood. BURNS ET AL.
(2006. Pacific Conservation Biology
12:64–77) analyzed DNA samples from
35 individuals from 10 islands. They
identified three forms, of which the
Tonga animals were the most genetically
distinct. Fijian and Tongan populations
have each evolved following their separa-
tion at least 7 million years ago. The
authors suggest a need to reassess conser-
vation strategies to better reflect the
greater degree of differentiation identified
by this study. Most populations are small
and vulnerable to introduced predators,
especially cats and mongooses. Both on-
site and zoo-based measures are urgently
recommended.

166 IGUANA  •  VOLUME 13, NUMBER 2  •  JUNE 2006 CONSERVATION RESEARCH REPORTS

Fijian iguanas in the genus Brachylophus, like this B. vitiensis, may include more genetically dis-
tinct entities than previously thought.

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Three species from the Guiana Shield: Phimophis guianensis (left) and Siphlophis compressus (center) are colubrid snakes, and Anolis (Norops) nitens
nitens (right) is an iguanian lizard.

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