Ontogenetic differences in the spatial ecology of immature Komodo dragons

Abstract

The early life-history stages of reptiles are extremely important to an individual's fitness, but in an ecological sense, among the most difficult to observe. Here, we used radio-tracking techniques to describe the differences in movement patterns, habitat use and home range between hatchling and juvenile Komodo dragons Varanus komodoensis on Komodo Island, Indonesia. The movement of hatchlings from their nests was largely linear and suggested a natal dispersal event. The movement patterns of juvenile Komodo dragons exhibited a greater spatial overlap than hatchlings, indicating greater site fidelity and thus use of a more defined activity area. The rates of daily movement were significantly less for hatchlings compared with juvenile dragons. The activity areas of hatchlings were significantly smaller than juvenile dragons. Both age classes preferred utilizing dry monsoon forest compared with other habitat types. Hatchlings were predominantly arboreal compared with juveniles and the degree of arboreal activity was strongly correlated with an individual's size. These distinct differences in spatial ecology between immature life-history stages suggest that different selection pressures may affect different size classes of Komodo dragons.

Full text

Ontogenetic differences in the spatial ecology of immature
Komodo dragons
M. J. Imansyah
1,2
, T. S. Jessop
1,3
, C. Ciofi
4
& Z. Akbar
2
1 Conservation and Research for Endangered Species, Zoological Society of San Diego, Escondido, CA, USA
2 School of Environmental and Natural Resource Science, University of Kebangsaan Malaysia, UKM, Bangi, Malaysia
3 Department of Wildlife Conservation and Science, Zoos Victoria, Parkville Vic., Australia
4 Department of Animal Biology and Genetics, University of Florence, Florence, Italy
Keywords
spatial ecology; ontogenetic differences;
movement; activity; habitat use; Varanus
komodoensis.
Correspondence
Tim S. Jessop, Department of Wildlife
Conservation and Research, Zoos Victoria,
PO Box 72 Parkville Vic., 3052, Australia.
Email: tjessop@zoo.org.au
Received 24 April 2007; accepted
5 July 2007
doi:10.1111/j.1469-7998.2007.00368.x
Abstract
The early life-history stages of reptiles are extremely important to an individual’s
fitness, but in an ecological sense, among the most difficult to observe. Here, we
used radio-tracking techniques to describe the differences in movement patterns,
habitat use and home range between hatchling and juvenile Komodo dragons
Varanus komodoensis on Komodo Island, Indonesia. The movement of hatchlings
from their nests was largely linear and suggested a natal dispersal event. The
movement patterns of juvenile Komodo dragons exhibited a greater spatial
overlap than hatchlings, indicating greater site fidelity and thus use of a more
defined activity area. The rates of daily movement were significantly less for
hatchlings compared with juvenile dragons. The activity areas of hatchlings were
significantly smaller than juvenile dragons. Both age classes preferred utilizing dry
monsoon forest compared with other habitat types. Hatchlings were predomi-
nantly arboreal compared with juveniles and the degree of arboreal activity was
strongly correlated with an individual’s size. These distinct differences in spatial
ecology between immature life-history stages suggest that different selection
pressures may affect different size classes of Komodo dragons.
Introduction
Ontogenetic transitions through an animal’s life history are
often associated with large changes in their ecology (Stamps,
1983; Calder, 1984; Polis, 1984). This is particularly evident
in reptiles that may vary in mass by several orders of
magnitude over their lifespan and coincide with large
transitions in diet, habitat use and home range (Stamps,
1983; Shine, 2005; Herrel et al., 2006). The most dynamic
changes within an individual’s life history often occur in the
early life phases (e.g. post-natal and juvenile), often reflect-
ing greater selection pressures on survival. For example,
early post-natal movement, generally associated with peri-
ods of dispersal in reptiles, can range from relatively passive
movements, resulting in high natal fidelity (e.g. Prickly
forest skink, Gnypetoscincus queenslandiae, Sumner, 2006),
to highly irruptive movements (e.g. marine turtles) that
disperse offspring a considerable distance from their natal
site (Wyneken & Salmon, 1992). Similarly, shifts in habitat
use (e.g. terrestrial vs. arboreal) are often pronounced in
early periods of development and again may result from
multiple selection pressures acting on an individual, includ-
ing food availability, morphological constraints, microcli-
mate, predator avoidance and intraspecific aggression
(Stamps, 1983; Huey, 1991).
Despite being among the most dynamic phases in the life
history of reptiles, documentation of the ecological aspects
of these early life stages is often constrained by a reduced
capture probability (i.e. linked to small size, cryptic beha-
vior, arboreality, wariness or reduced survival) that limits
the collection of detailed ecological information at least via
mark–recapture methods (Fitzgerald, Shine & Lemckert,
2002). However, squamate reptiles such as boid snakes and
many varanid lizards, with their large offspring, are amen-
able for use with radio-telemetry techniques, allowing gath-
ering of more detailed information on the ecological habits
of early life stages (Wilson, Heinsohn & Legge, 2006). In this
study, we investigated both hatchling and juvenile Komodo
dragons Varanus komodoensis with respect to aspects of
their spatial ecology and habitat requirements, which, un-
like their older conspecifics, are poorly documented (Ciofi
et al., 2007). The Komodo dragon, a large monitor lizard
(up to 87 kg), is endemic to five islands in Eastern Indonesia,
where it occupies a niche as a top carnivore (Auffenberg,
1981). Previous research on the spatial ecology on Komodo
dragons has focused on preliminary descriptions of move-
ments and activity area of individuals using footprint
locations and sighting records Auffenberg (1981). More
recently, Ciofi et al. (2007) estimated activity areas and
the movements on five adult Komodo dragons with a
Journal of Zoology ]] (2007) 1–9 c2007 The Authors. Journal compilation c2007 The Zoological Society of London 1
Journal of Zoology. Print ISSN 0952-8369

snout–vent length (SVL) of 116–154 cm. Similar studies on
other varanid species have also described aspects of spatial
ecology (e.g. King & Green, 1999; Thompson, De Boer &
Pianka, 1999; Guarino, 2002; Ibrahim, 2002) and interac-
tions with physiology, reproduction and demography (see
Christian & Weavers, 1994; Phillips, 1995; James, 1996). In
this study, we conducted research by way of radio-telemetry
to understand three aspects of the spatial ecology of im-
mature Komodo dragons:
(1) Describing movement patterns of hatchlings following
emergence from their nest as a basis to gain an insight into
the initial natal dispersal tendencies in this species.
(2) Estimating differences in the movement capacity and
activity areas (i.e. a subset of home ranges used during a
defined time period; see Thompson et al., 1999) of hatchling
and juvenile Komodo dragons.
(3) Determining basic patterns of habitat use in hatchling
and juvenile Komodo dragons.
These three facets of study are considered to be important
in acquiring fundamental ecological information about this
species and are likely to contribute considerably to improv-
ing its management by increasing an understanding of its
habitat requirements. For Komodo dragons, which occupy
a limited geographical range and whose populations are
fragmented across islands, knowledge of hatchling and
juvenile dispersal could potentially be important in influen-
cing metapopulation dynamics. Similarly, habitat require-
ments throughout ontogeny are essential to understanding
those resources (e.g. food or habitat), which, if disturbed by
humans, could perturb population processes of Komodo
dragons, a priority conservation species in Indonesia.
Materials and methods
Study site
The study was conducted in the Loh Liang valley (9.4 km
2
)
on Komodo Island, (813304000 Sand119129 05100 E) in Komodo
National Park (KNP) (Fig. 1), East Nusa Tenggara,
Indonesia. Vegetation cover of KNP has been described
elsewhere (e.g. Auffenberg, 1981). Komodo Island is a
rugged, mountainous island covered predominantly by
savannah grassland. Deciduous monsoon forests dominated
by Tamarind tree Tamarindus indica are found in coastal
valleys, while closed evergreen forest persists on hills above
500 m altitude. The mean daily field temperatures (sourced
from a data logger located at sea level in Loh Liang valley)
during the period of this study averaged 29.5 0.1 1C and
varied within 1.5 1C between months and 0.2 1C between
years.
Study animals
Five hatchling Komodo dragons with a mean SVL of
20.16 0.85 cm (SEM) (range 18.25–22.6 cm) and a body
mass of 0.11 0.01 kg (range 0.095–0.135 kg) were captured
following emergence from their nest. Hatchlings were cap-
tured by hand or in PVC pipe traps (10 cm diameter and
100 cm in length) on emergence from their nests. Seven
juvenile Komodo dragons (mean and SEM of SVL 55.81
2.97 cm and body mass of 3.03 0.56, range 1.4–5.7 kg)
were captured by hand or in baited box traps. We could not
determine the sex (i.e. a potential covariate underpinning
differences in spatial ecology) of these 12 individuals, as this
requires the use of genetic sexing techniques (Halverson &
Spelman, 2002), which currently have not been tested on our
sample set (C. Ciofi, unpubl. data).
Radio-telemetry techniques
This study was conducted between March and June over 2
years (2004–2005). In 2004, two hatchlings and four juve-
niles were radio-tracked, and in 2005 three hatchlings and
four juveniles were followed. Telemetry equipment con-
sisted of activity-sensitive AVM G31 V transmitters (AVM
Instruments Co. Ltd., Colfax, CA, USA), an AVM LA12Q
receiver and a three-element Yagi antenna. Transmitters
were attached to the dragon’s tail using duct tape.
Komodo
Loh Liang Valley
N
N
0 500 1000 m
0 10 20 km
Figure 1 Location of the study site in the Loh
Liang valley on Komodo Island, the largest
island in Komodo National Park (inset). Con-
tours are at intervals of 100 m.
Journal of Zoology ]] (2007) 1–9 c2007 The Authors. Journal compilation c2007 The Zoological Society of London2
Spatial ecology of immature Komodo dragons M. J. Imansyah et al.

After the transmitters were attached, hatchlings and
juveniles were released immediately. Each animal was
radio-tracked for 7–56 days (mean 31.42 5.05 days). Initial
observations showed that radio-tracked Komodo dragons
never moved during the night. To increase independence of
the data, individual daily observations were made in four
sessions, separated by a minimum daily time interval of
2–3 h. Daily positions and habitat-use observations were
made from 06:00 to 18:00 h across four time periods of
06:00–09:00, 09:00–12:00, 12:00–15:00 and 15:00–18:00 h.
Fixes were collected by either direct observation or by
triangulation (Samuel & Fuller, 1996; Fitzgerald et al., 2002;
Ciofi et al., 2007). Fixes were recorded using a Global
Positioning System (GPS; Garmin Etrex, Olathe, KS, USA),
and then recorded into an excel spreadsheet and visualized
onto digital topographic maps using ArcView 3.1 (Environ-
mental System Research Institute, Redlands, CA, USA).
Habitat use
To quantify, and compare, the habitat use of juvenile and
hatchling lizards, we collected data on habitat and shelter
site parameters concurrently with their positions obtained
during radio-tracking (Olupot & Waser, 2001). Four para-
meters were measured and defined as follows:
(1) Habitat strata defined as the use of either terrestrial or
arboreal strata.
(2) Habitat type defined as the presence of lizards in one of
three key habitat types including open deciduous forest,
closed dense forest and savannah grassland. These habitat
types were readily distinguished by canopy closure and
floristic composition.
(3) Shelter site included a description of resting or sleeping
location based on the use of vegetation (identified to species)
or substrate type. Further, with relation to vegetation,
particularly trees, tree diameter at breast height (Dbh) and
tree height were also recorded. Tree height and the Komodo
dragons’ height above ground were calculated using a
Suunto clinometer PM5 (Suunto, Finland).
(4) Elevation the elevation at which a lizard was located was
recorded alongside every positional fix.
Habitat selection
To identify broad-scale patterns of habitat selection in
Komodo dragons, we scored both the vegetation type
(closed forest, open forest and savannah grassland) and
elevation occupied by the dragon at each position as a
measure of habitat selection. These observed habitat char-
acteristics were then compared with a dataset of similar
measures drawn from 209 randomly generated locations
(each scored for habitat type and elevation) within the study
valley. We selected the number of random points based on
the average number of habitat fixes collected from both
hatchling and juvenile Komodo dragons to ensure a ba-
lanced design for statistical purposes. Comparisons between
the observed and random habitat positions were used as a
basis to determine whether dragons utilized habitat in a non-
random manner.
Data analysis
Movement and orientation
Patterns of path movement (linearity) of Komodo dragons
were estimated using directionality and tortuousity analysis
(Nams & Bourgeois, 2004). Directionality was analyzed by
measuring the turning angle of movement on each point in a
compass direction (Claussen, Finkler & Smith, 1997). The
turning angles indicate the movement angles between two
consecutive points (Higham, Davenport & Jayne, 2001).
Tortuosity was measured by analyzing the fractal dimension
(D), whose values range between 1 and 2; at D=1, the
animal’s path of movement is straight. In contrast, when
D=2 (i.e. maximum), the animal’s path of movement is so
tortuous as to cover a plane completely (Nams & Bourgeois,
2004). To describe site fidelity, we ran the Site Fidelity Test
(with 1000 replications) to obtain the r
2
value; the lower the
r
2
value, the higher the site fidelity of an animal. Direction-
ality and site fidelity were computed using the Movement
Program extension (Hooge, Eichenlaub & Solomon, 1999)
and X Tools of ArcVIew 3.1 (ESRI), while fractal dimen-
sions were computed using the computer program Fractal
(Nams, 2004).
Komodo dragon movement distances were calculated as
the distance moved between two consecutive points (Samuel
& Fuller, 1996). The mean daily movement distance was
obtained by dividing the total distance of recorded move-
ments by the total number of radio-tracking days (Phillips,
1995; Fitzgerald et al., 2002; Ibrahim, 2002). These calcula-
tions were made using the Animal Movement Program
(Hooge et al., 1999) and X Tools extension of ArcView 3.1
(ESRI).
Activity area
Activity areas were calculated using two methods: the 100%
minimum convex polygon (MCP) and the adaptive kernell
analysis (AKA) representing 95 and 50% of the probability
distribution of animal locations (Samuel & Fuller, 1996).
The 95% AKA is believed to be a very effective method
for estimating the internal structure of activity areas, and
provides one of the least biased estimates of home range
size (Samuel & Fuller, 1996). The 50% AKA has
been widely used to determine the core area or habitat use
in other reptiles (Kernohan et al., 1998; Fitzgerald et al.,
2002). In this study, the estimate from the 50%
AKA method was used to determine core areas within the
activity area of hatchling and juvenile Komodo dragons.
Activity area estimations were calculated using the
Animal Movement Program (Hooge et al., 1999) in Arc-
View 3.1 (ESRI). Individuals with o10 fixes (i.e. hatchling
64CDC09 and juvenile 6EDB3B7) were not included in this
analysis.
Journal of Zoology ]] (2007) 1–9 c2007 The Authors. Journal compilation c2007 The Zoological Society of London 3
Spatial ecology of immature Komodo dragonsM. J. Imansyah et al.

Statistical analysis
Pre-analysis, all continuous data were log transformed to
meet assumptions of parametric statistical tests (Zar, 1999).
Log-transformed data failing these assumptions were ana-
lyzed using non-parametric statistical procedures. Categori-
cal data were analyzed using w
2
statistical procedures.
Results
Patterns of movement
During our study, hatchlings moved in a predominantly
linear fashion with little movement over previously occupied
areas (Fig. 2, animals a and b). In contrast, juvenile dragons
exhibited much more tortuous movement paths, reflecting
increased activity over the same area (Fig. 2 animals c and
d). Fractal analysis indicated that the movement paths
undertaken by hatchlings D= 1.11 0.009 were signifi-
cantly more linearly directed (i.e. strait) than that of juvenile
dragons (D= 1.39 0.05; Mann–Whitney Utest; Z=
2.56, P=0.011). Moreover, the degree of site fidelity in
hatchling (r
2
= 729 502.68) was significantly less than that of
juveniles (r
2
= 2 729 220.96; t-test; t
1,9
=39.12, P0.001).
Hatchlings were significantly less active than juvenile
dragons and, on average, moved 32.62 12.67 m day
1
compared with 129.14 41.71 m day
1
(t-test; t
1,9
=3.014,
P=0.015). Furthermore, the longest daily movements
recorded by hatchlings (163.99 22.96 m day
1
) were
significantly less than those of juvenile dragons
(509.87 73.32 m day
1
)(t-test; t
1,9
=5.24, P=0.001).
The daily activity of hatchlings was significantly less than
juvenile dragons (w
2
test; w
2
=51.68, P0.001) based on the
relative proportion of movement fixes compared with the
proportion of stationary fixes.
Activity area size
The activity areas of hatchling and juveniles ranged between
1.72–4.83 ha and 4.03–61.77 ha for MCP, 12.14–20.12 ha
and 5.49–33.23 for 95% AKA and 2.51–4.74 and
0.56–10.48 ha for 50% AKA, respectively (see Table 1 and
Fig. 3). Hatchlings used significantly smaller activity areas:
approximately eight times less than juveniles for the 100%
MCP (t-test; t
1,9
=3.658, P=0.006). However, there were
no significant differences in 95% AKA (t-test; t
1,9
=0.018,
P=0.177) and neither for 50% AKA (t-test; t
1,9
=0.396,
P=0.702). In five of six cases, the activity areas of juvenile
dragons overlapped with one (n= 4) or two (n= 1) conspe-
cifics and the extent of this overlap ranged from 4.84 to
91.00% or from 2.55 to 6.65 ha.
Habitat preferences
Hatchling and juvenile Komodo dragons significantly dif-
fered in the parameters of habitat use. Hatchlings were
predominantly arboreal (97.7% arboreal vs. 2.30% terres-
trial), while juveniles were predominantly terrestrial
(28.96% arboreal vs. 71.04% terrestrial) (w
2
test;
w
2
=239.22, P0.001; Fig. 4a). On average, hatchlings
remained on the same tree for 9.5 days (SEM= 3.17)
before moving to the next tree. Hatchlings were rarely
observed on the ground, except during long-distance move-
ments between trees (430 m). We observed an occasional
arboreal movement whereby hatchlings were able to move
between trees with overlapping canopy. Juveniles, on the
other hand, spent significantly less time on trees (average of
3.17 days SEM = 0.75) (t-test; t
1,8
=2.257, P=0.038).
Body size was a better indicator of habitat use, as there was
a highly significant negative linear relationship between
body size and amount of arboreal habitat use (%arboreal
119°29'50" 119°30'00" 119°30'10"
8°33'00"
8°33'10"
119°30'10"119°30'00"
0 50 100 m
N
119°29'50"
(a)
(b)
(c)
(d)
8°33'10"
8°33'00"
Figure 2 Examples of the movement pattern
of hatchling (a and b) and juvenile (c and d)
Komodo dragons Varanus komodoensis. The
arrows indicate the direction of movements,
and circles represent nocturnal shelter sites.
Journal of Zoology ]] (2007) 1–9 c2007 The Authors. Journal compilation c2007 The Zoological Society of London4
Spatial ecology of immature Komodo dragons M. J. Imansyah et al.

activity=2.070 SVL+139.244, r=0.965; ANOVA,
F
1,9
=108.423, P=0.001; Fig. 4b).
Both hatchling (w
2
test; w
2
=45.86, P0.001) and juve-
nile Komodo dragons (w
2
test; w
2
=85.04, P0.001) were
observed most frequently in open deciduous forest, com-
pared with either closed dense forest or savannah. There was
no significant difference in the frequency of observed habitat
preference use between hatchlings and juveniles (w
2
test;
w
2
=1.89, P=0.389; Fig. 4c). However, immature Komodo
dragons were observed to occupy habitat types significantly
different from a randomly assigned distribution of habitat
locations (w
2
test; w
2
=25.45, P0.001; Fig. 4c). Relative
to the occupancy distribution of random locations among
habitat types, Komodo dragons were observed more preva-
lently to occupy open deciduous forest and less likely to
occupy either closed forest or savannah habitats.
With respect to elevation, there was a significant pre-
ference for hatchlings to be located in the lowest elevation
class (54.55% o25 m above sea level) (w
2
test; w
2
=20.98,
P0.001). Juvenile dragons (w
2
test; w
2
=9.26, P=0.002)
exhibited a significant preference for elevations between 25
and 50 m (36.17%) above sea level. Elevation use for
hatchlings and juvenile dragons was significantly different
(w
2
test; w
2
=25.127, P=0.0001). Furthermore, elevation
preferences between hatchlings (w
2
test; w
2
=53.707,
P0.001) and juveniles (w
2
test; w
2
=29.736, P0.001)
differed significantly from a random selection of elevations
within their environment.
Shelter sites
Shelter sites were defined as those places used by hatchlings
and juveniles for resting (also as sites between movements –
for juveniles only) or as overnight refuges. Hatchlings used
trees exclusively for shelter. They significantly used live
(84.71%) over dead trees (15.29%) (w
2
test; w
2
=122.859,
P0.0001). Among live trees (15 spp. recorded), there was
a significant tendency for hatchlings to occupy Tamarind
trees Tamarindus indica (45.37%) (w
2
test; w
2
=122.859,
P0.001). Juveniles used predominantly crevices under or
among rocks (51.77 5.72%) as shelters. These shelters
were found in forested area with significant granitic exfolia-
tion (i.e. rocky fields). Juvenile Komodo dragons, albeit
infrequent, used nine tree species for resting or basking.
Discussion
Distinct ontogenetic differences in movement, activity area
and habitat use were evident between hatchling and juvenile
Komodo dragons in the Loh Liang valley on Komodo
Island. In particular, movements of hatchling dragons were
largely linear compared with those of juveniles that occupied
a defined activity area (i.e. a component of their home
range). The rate and distance moved by hatchlings within
their natal valley was up to 75% less than juveniles. Limited
spatial overlap (i.e. tortuosity) of movement and the re-
duced rates of daily movements would explain the much-
reduced activity areas estimated for hatchlings compared
with juveniles. Combined, these attributes of the post-natal
spatial ecology of hatchling V. komodoensis are evidence for
dispersal resulting in hatchlings moving as far as possible
away from their nests relative to the actual distance tra-
velled. Over the month-long period of radio-tracking,
hatchlings had moved up to 500 m from their nests. Other
studies in lizards have detected differences in natal dispersal
tendencies, with some species being relatively sedentary (i.e.
remain in close proximity to natal hatching/birth sites)
(Olsson & Shine, 2003; Sumner, 2006) to others being more
irruptive and moving away from their hatching/birth sites
(Doughty & Sinervo, 1994). Two major hypotheses are
suggested to explain the differences in natal dispersal ten-
dencies including avoidance of inbreeding and a reduction in
resource competition among conspecifics (Olsson & Shine,
2003). From our results, given the relatively small time
Table 1 Summary of results on the movements and activity areas of hatchling and juvenile Komodo dragons Varanus komodoensis
Animal ID (PIT tag) SVL
Total
movement
(m)
Mean daily
movement
(m)
Longest daily
movement
(m)
Activity area
100% MCP
(ha)
Activity
area 95%
AK (ha)
Activity
area 50%
AK (ha)
Tracking
duration
(days)
Number
of fixes
Hatchlings
64E4218 22.6 983.39 70.24 191.19 4.82 20.12 4.73 14 50
63DFB2A 18.25 571.60 15.04 195.08 1.71 13.06 3.60 38 66
64D4C0E 18.30 692.91 23.09 96.62 1.95 13.47 2.51 30 51
63C1383 20.35 949.37 22.07 173.08 3.58 12.14 2.70 43 67
Mean 20.16 0.85 799.32 99.82 32.61 12.67 163.99 22.96 3.02 0.73 14.70 1.83 3.39 0.51 31.25 6.34 58.50 4.63
Juveniles
64CF2AO 61.85 2286.24 326.60 397.86 12.53 33.23 10.477 7 18
639E332 68.35 6308.95 143.38 791.58 32.37 16.34 2.327 44 39
643761C 58.05 350.71 43.84 334.34 4.02 5.49 0.558 8 18
64E2E95 55.45 2879.15 89.97 427.53 17.41 32.55 2.451 32 14
63DE6F1 51.15 5556.63 99.22 672.06 61.77 30.51 4.301 56 57
63D9C4B 44.45 3445.53 71.78 435.83 17.75 21.56 2.650 48 44
Mean 55.81 2.97 3471.20 892.46 129.13 41.71 509.87 73.32 24.31 8.38 23.28 4.49 3.79 1.42 32.5 8.52 31.67 7.15
SVL, snout–vent length; MCP, minimum convex polygon; AK, adaptive kernell.
Journal of Zoology ]] (2007) 1–9 c2007 The Authors. Journal compilation c2007 The Zoological Society of London 5
Spatial ecology of immature Komodo dragonsM. J. Imansyah et al.

frame (1–2 months) used to follo w the animals, we were unable
to determine the termination of natal dispersal (i.e. the point at
which a hatchling begins to use a defined home range) and thus
cannot comment on what may be the predominant selection
pressure associated with these movements.
The highly arboreal nature of hatchling Komodo dragons
compared with the much more terrestrial-based activity of
juveniles is a clear indication of an ontogenetic habitat shift
between these two immature life phases. Arboreal habitat use
by hatchling Komodo dragons is considered to be of a
response to some of the selection pressures that trigger
ontogenetic habitat shifts observed in other lizards and snakes
(Stamps, 1983; Irschick, 2002; Keren-Rotem, Bouskila &
Geffen, 2006). In particular avoidance of larger conspecifics,
well known for intraspecfic predation (Auffenberg, 1981),
would seem an intuitive reason for Komodo dragon hatchl-
ings to remain predominantly arboreal. Similarly, prey avail-
ability which is likely to be determined by the relatively small
jaw gape of hatchlings could predispose arboreal activity to
obtain suitable sized prey such as geckoes (observed in this
study), skinks and large insects (Auffenberg, 1981). Other
than predation and food availability, intraspecific competi-
tion, thermoregulation, morphological constraints and shelter
sites are additional hypotheses that could necessitate arboreal
activity in hatchling Komodo dragons (Stamps, 1983; Huey,
1991; Keren-Rotem et al., 2006). Experimental manipulation
119°29'30" 119°30'30"119°30'00" 119°31'00"
8°33'30"
8°33'00"
8°34'00"
8°33'30"
8°33'00"
8°34'00"
119°31'00"119°30'00" 119°30'30"
0
6
5
3
3
4
4
5
6
5
1
1
2
2
500 1000 m
N
0 500 1000 m
N
119°29'30"
119°31'00"119°30'00" 119°30'30"119°29'30"
119°31'00"119°30'00" 119°30'30"119°29'30"
(a)
(b)
8°33'30"
8°34'00"
8°33'00"
8°33'30"
8°34'00"
8°33'00"
Figure 3 Activity area overlap of six juvenile
Komodo dragons Varanus komodoensis as cal-
culated by minimum convex polygon (a) and
adaptive kernell (50% hatched areas & 95%
outer line) (b). Numbers refer to juvenile ID as
follows: (1) 64CF2A0, (2) 639E332, (3)
64E761C, (4) 64E2E95, (5) 63DE6F1, (6)
63D9C4B.
Journal of Zoology ]] (2007) 1–9 c2007 The Authors. Journal compilation c2007 The Zoological Society of London6
Spatial ecology of immature Komodo dragons M. J. Imansyah et al.

of these factors, although logistically difficult, could quantify
the relative importance of specific mechanisms to explaining
arboreality in hatchling Komodo dragons.
The ontogenetic transition to a more terrestrial based
activity appeared largely size dependent (Fig. 4b) and thus
individual Komodo dragons underwent a gradual shift
towards terrestrial activity rather than any discreet transi-
tion. Presumably, with increased body size, relaxation of
some selection pressures that necessitate arboreality (e.g.
conspecific avoidance) and the increasing need to acquire
larger terrestrial prey could underpin habitat use transitions
in juvenile Komodo dragons. As terrestrial activity in-
creased juvenile dragons occupied discreet areas of habitat
underpinning an activity area (i.e. a subset of their home-
range). The size of juvenile activity areas was estimated
(using MCP) at 24.31 8.38 ha, an area 800% larger than
hatchlings but only 5% of the activity area estimated for
adult Komodo dragons (Ciofi et al., 2007). Size related
differences in an individuals space use are well recognized
in reptiles and often linked with increased utilization
of resources (Christian & Waldschmidt, 1984; Perry &
Garland, 2002; Pearson, Shine & Williams, 2005). In most
instances there were some degrees of overlap in the esti-
mated activity areas of juvenile Komodo dragons. However,
within their activity areas, the 50% kernell analysis identi-
fied smaller more frequently used areas that were exclusively
occupied by a single individual. While we have not tracked
all individuals that could overlap with our focal animals, on
closer examination of their core movement areas, there was
often the presence of an individual’s overnight shelter area.
In an ontogenetic context, core areas, while frequently used
at particular points in time, are subject to change with age/
size or even seasonally, again depending on resource avail-
ability (e.g. King & Green, 1999). The individual’s sex
appears to be another important covariate underpinning
spatial ecology in adult reptiles (Perry & Garland, 2002). In
this study, however, sex could not be determined from either
external examination or on probing the cloaca for the
presence of hemipenes. Thus, we are unable to ascertain
whether sex was a significant covariate linked to spatial use
in immature Komodo dragons.
With respect to patterns of broad-scale habitat use, both
hatchlings and juveniles were found to significantly utilize
open deciduous forest compared with either closed forest or
the more xeric savannah grassland. Among these different
habitat types, it is suspected that immature Komodo dra-
gons could encounter highly different regimes of prey,
shelter, predators, competition, parasites and temperature
(Dunham, Grant & Overall, 1989; Huey, 1991). These
differences are likely to strongly influence an individual’s
fitness (Huey, 1991). For example, aversion of savannah
grassland by immature Komodo dragons could be envi-
saged due to low densities of small prey but also that the
thermal environment is uniformly hot with little shade,
which might limit the capacity of small dragons to thermo-
regulate effectively. In contrast, the open deciduous forest
provides a mosaic of thermal conditions, higher prey pro-
ductivity and shelter, which are likely to be important
habitat elements influencing habitat use in small Komodo
dragons. The low-frequency use of closed forest by imma-
ture dragons is suspected of being negatively biased due to
the relatively low proportion of its availability (17.6%)
relative to the other two predominant habitat types (60.4
and 22.0% for open forest and savannah, respectively).
Conclusions
Radio-tracking of immature life stages of the Komodo
dragon revealed several key features of their spatial ecology.
(a)
(b)
(c)
Habitat strata
Terrestrial Arboreal
Frequency of use (%)
0
20
40
60
80
100
Hatchling
Juvenile
SVL (cm)
20 40 60 80
Frequency of arboreal activity (%)
0
20
40
60
80
100
Vegetation type
Closed forest Open forest Savannah
Frequency of habitat occupancy (%)
0
20
40
60
80
100
Hatchlings
Juveniles
Random positions
Figure 4 Differences between hatchling and juvenile Komodo dra-
gons Varanus komodoensis with respect to terrestrial versus arboreal
habitat use (a), the relationship between their body size and arboreal
activity (b) and differences in habitat use (c).
Journal of Zoology ]] (2007) 1–9 c2007 The Authors. Journal compilation c2007 The Zoological Society of London 7
Spatial ecology of immature Komodo dragonsM. J. Imansyah et al.

On emergence, hatchling Komodo dragons became arboreal
and moved in a largely linear fashion away from their nest.
The lack of overlap in their movements suggests that this
early life stage is associated with a period of natal dispersal.
At this stage, we have very limited direct evidence for how
far hatchlings might disperse. For example, from the hun-
dreds of marked hatchlings we have released to date as part
of a long-term population ecology study, only a single
individual has been recaptured and in this case the juvenile
had remained within its natal valley one year after its birth.
However, indirect information from population genetics has
indicated significant sub-structuring among valley popula-
tions, perhaps indicating that there may be limited dispersal
across all size classes over evolutionary time frames (Ciofi &
Bruford, 1999). With respect to the management and con-
servation of this species, given the strong reliance of im-
mature animals on open deciduous forest for food and
shelter, clearing of this habitat for agriculture or timber
would represent a major threat that would severely impact
the survival of immature Komodo dragons. At present,
within KNP, enforcement of habitat protection appears to
be adequate to prevent major changes in habitat structure.
Acknowledgements
We thank the KNP staff and volunteers (particularly Aris,
Dimas and Niken) for field assistance. Approval for re-
search was conducted under a collaborative program be-
tween the Zoological Society of San Diego, The Nature
Conservancy (Indonesia program) and the Indonesian De-
partment of Forest Protection and Nature Conservation
(PHKA). Financial support for this research was provided
by the Zoological Society of San Diego, National Geo-
graphic Society (7211-04) and the American Zoo Associa-
tion Komodo Dragon Conservation fund.
References
Auffenberg, W. (1981). Behavioral ecology of the Komodo
monitor. Gainesville: University Presses of Florida.
Calder, W.A. (1984). Size, function, and life history. Harvard:
Harvard University Press.
Christian, K. & Weavers, B. (1994). Analysis of the activity
and energetics of the lizard Varanus rosenbergi.Copeia
1994, 289–295.
Christian, K.A. & Waldschmidt, S. (1984). The relationship
between lizard activity area and body size: reanalysis of the
data. Herpetologica 40, 68–75.
Ciofi, C. & Bruford, M.W. (1999). Genetic structure and gene
flow among Komodo dragon populations inferred by
microsatellite loci analysis. Mol. Ecol. 8, S17–S30.
Ciofi, C., Puswati, J., Winana, D., De Boer, M.E., Chelazzi,
G. & Sastrawan, P. (2007). Preliminary analysis of home
range structure of the Komodo monitor Varanus komo-
doensis.Copeia 2007, 462–470.
Claussen, D.L., Finkler, M.S. & Smith, M.M. (1997). Thread
trailing of turtles: methods for evaluating spatial move-
ments and pathway structure. Can. J. Zool. 75, 2120–
2128.
Doughty, P. & Sinervo, B. (1994). The effects of habitat, time
of hatching, and body size on the dispersal of hatchling Uta
stansburiana.J. Herpetol. 28, 485–490.
Dunham, A.E., Grant, B.W. & Overall, K.L. (1989). Inter-
faces between biophysical and physiological ecology and
the population biology of terrestrial vertebrate ectotherms.
Physiol. Zool. 62, 335–355.
Fitzgerald, M., Shine, R. & Lemckert, F. (2002). Spatial
ecology of arboreal snakes (Hoplocephalus stephensii Ela-
pidae) in an Eastern Australian forest. Aust. Ecol. 27,
527–545.
Guarino, F. (2002). Spatial ecology of a large carnivorous
lizard, Varanus varius (Squamata: Varanidae). J. Zool.
(Lond.) 258, 449–457.
Halverson, J. & Spelman, L.H. (2002). Sex determination and
its role in management. In Komodo dragons: biology and
conservation: 165–177. Murphy, J.B., Ciofi, C., de La
Panouse, C. & Walsh, T. (Eds). Washington, DC: Smith-
sonian Institution Press.
Herrel, A., Joachim, R., Vanhooydonck, B. & Irschick,
D.J. (2006). Ecological consequences of ontogenetic
changes in head shape and bite performance in the
Jamaican lizard Anolis lineatopus.Biol. J. Linn. Soc. 89,
443–454.
Higham, T.E., Davenport, M.S. & Jayne, B.C. (2001). Man-
oeuvring in an arboreal habitat: the effects of turning angle
on the locomotion of three sympatric ecomorphs of Anolis
lizards. J. Exp. Biol. 204, 4141–4155.
Hooge, P.N., Eichenlaub, W. & Solomon, E. (1999) The
Animal Movement Program. USGS, Alaska Biological
Science Center. (Online) http://www.absc.usgs.gov/glba/
gistools/index.htm (December 20, 2003).
Huey, R.B. (1991). Physiological consequences of habitat
selection. Am. Nat. 137, S91–S115.
Ibrahim, A.A. (2002). Activity area, movement patterns, and
habitat use of the desert monitor, Varabus griseus, in the
Zaranik Protected Area, North Sinai, Egypt. Afr. J. Her-
petol. 5, 35–45.
Irschick, D.J. (2002). Evolutionary approaches for studying
functional morphology: examples from studies of perfor-
mance capacity. Integ. Comp. Biol. 42, 278–290.
James, C.D. (1996). Ecology of the pygmy goanna (Varanus
brevicauda) in Spinifex Grasslands of Central Australia.
Aust. J. Zool. 44, 177–192.
Keren-Rotem, T., Bouskila, A. & Geffen, E. (2006). Ontoge-
netic habitat shift and risk of cannibalism in the common
chameleon (Chamaeleo chamaeleon). Behav. Ecol. Socio-
biol. 59, 723–731.
Kernohan, B.J., Millspaugh, J.J, Jenks, J.A. & Naugle, D.E.
(1998). Use of an adaptive kernel home-range estimator in
a GIS environment to calculate habitat use. J. Environ.
Mgmt. 53, 83–89.
Journal of Zoology ]] (2007) 1–9 c2007 The Authors. Journal compilation c2007 The Zoological Society of London8
Spatial ecology of immature Komodo dragons M. J. Imansyah et al.

King, D. & Green, B. (1999). Goannas: the biology of Varanid
Lizards. Kensington, NSW: New South Wales University
Press.
Nams, V.O. (2004). Fractal version 4.08. Canada: Department
of Environmental Science, NSAC.
Nams, V.O. & Bourgeois, M. (2004). Fractal analysis
measures habitat use at different spatial scales: an
example with American marten. Can. J. Zool. 82,
1738–1747.
Olsson, M. & Shine, R. (2003). Female-biased natal and
breeding dispersal in an alpine lizard, Niveoscincus micro-
lepidotus.Biol. J. Linn. Soc. 79, 277–283.
Olupot, W. & Waser, P.M. (2001). Activity patterns, habitat
use and mortality risks of mangabey males living outside
social groups. Anim. Behav. 61, 1227–1235.
Pearson, D., Shine, R. & Williams, A. (2005). Spatial ecology
of a threatened python (Morelia spilota imbricata) and the
effects of anthropogenic habitat change. Aust. Ecol. 30,
261–274.
Perry, G. & Garland Jr., T. (2002). Lizard home ranges
revisited: effects of sex, body size, diet, habitat and phylo-
geny. Ecology 83, 1870–1885.
Phillips, J.A. (1995). Movement patterns and density of
Varanus albigularis.J. Herpetol. 29, 407–416.
Polis, G.A. (1984). Age structure component of niche
width and intraspecific resource partitioning – can age-
groups function as ecological species. Am. Nat. 123,
541–564.
Samuel, M.D. & Fuller, M.R. (1996). Wildlife radio-teleme-
try. In Research and management techniques for wildlife and
habitats: 370–418. Bookhout, T.A. (Ed.) Bethesda, MD:
The Wildlife Society.
Shine, R. (2005). Life-history evolution in reptiles. Invited
review. Annu. Rev. Ecol. Evol. Syst. 36, 23–46.
Stamps, J.A. (1983). The relationship between ontogenetic habi-
tat shifts, competition and predator avoidance in a juvenile
lizard (Anolis aeneus). Behav. Ecol. Sociobiol. 12, 19–33.
Sumner, J. (2006). Higher relatedness within groups due to
deferred natal dispersal in a rainforest skink, Gnypetoscin-
cus queenslandiae.Aust. Ecol. 31, 441–448.
Thompson, G., De Boer, M. & Pianka, E.R. (1999). Activity
areas and daily movements of an arboreal monitor lizard,
Varanus tristis (Squamata: Varanidae) during the breeding
season. Aust. Ecol. 24, 117–122.
Wilson, D., Heinsohn, R. & Legge, S. (2006). Age- and sex-
related differences in the spatial ecology of a dichromatic
tropical python (Morelia viridis). Aust. Ecol. 31, 577–587.
Wyneken, J. & Salmon, M. (1992). Frenzy and post-frenzy
swimming activity in loggerhead, green, and leatherback
hatchling sea turtles. Copeia 1992, 478–484.
Zar, J.H. (1999). Biostatistical analysis. Upper Saddle River,
NJ: Prentice-Hall International.
Journal of Zoology ]] (2007) 1–9 c2007 The Authors. Journal compilation c2007 The Zoological Society of London 9
Spatial ecology of immature Komodo dragonsM. J. Imansyah et al.