RELATIVE POPULATION DENSITY OF Tarsius dianae IN MAN-INFLUENCED HABITATS OF LORE LINDU NATIONAL PARK, CENTRAL SULAWESI, INDONESIA

Abstract

The aim of this study was to know the impact of human activities on population density of Tarsius dianae by estimating the relative population density in four habitat types differently influenced by man. The study was conducted in the vicinity of Kamarora, at the northeastern boundary of Lore Lindu National Park, Central Sulawesi. Four different habitats were chosen: (H1) primary or old secondary forest; (H2) secondary forest ± 30 years after clearance with small-scale selective logging; (H3) forest with interspersed small coffee and cocoa plantations; and (H4) forest with selective logging and plantations. The tarsiers' sleeping sites were determined using triangulation. Relative population density was estimated by measuring the average distances between three nearest neighbors. The results suggest that different human-influenced habitat have different effects on tarsier's density. The smallest distances (116.2 ± 18 m) between sleeping sites, which represent the highest estimated population density (57.1 groups in one square km), were found in habitat type H1, the least disturbed habitat. Estimated population density in habitat type H3 or "forest plantations" was 38 groups/km 2 , followed by habitat type H2 or secondary forest with selective logging 36.4 groups/km 2 , and the smallest population density was estimated at 32.9 groups/km 2 in habitat type H4 or forest with selective logging and plantations.

Full text

Asian Primates Journal 1(1), 200810
RELATIVE POPULATION DENSITY OF Tarsius dianae IN MAN-INFLUENCED HABITATS
OF LORE LINDU NATIONAL PARK, CENTRAL SULAWESI, INDONESIA
Indra Yustian1, Stefan Merker2, Jatna Supriatna3, and Noviar Andayani4
1 Dept. of Biology, Faculty of Mathematics and Natural Sciences, University of Sriwijaya, Indonesia.
2 Institute of Anthropology, University of Mainz, Germany.
3 Conservation International Indonesia and Department of Biology, University of Indonesia.
4 Wildlife Conservation Society-Indonesia Program and Department of Biology, University of Indonesia, Indonesia.
ABSTRACT
The aim of this study was to know the impact of human activities on population density of Tarsius dianae by
estimating the relative population density in four habitat types differently influenced by man. The study was
conducted in the vicinity of Kamarora, at the northeastern boundary of Lore Lindu National Park, Central Sulawesi.
Four different habitats were chosen: (H1) primary or old secondary forest; (H2) secondary forest ± 30 years after
clearance with small-scale selective logging; (H3) forest with interspersed small coffee and cocoa plantations; and
(H4) forest with selective logging and plantations. The tarsiers’ sleeping sites were determined using triangulation.
Relative population density was estimated by measuring the average distances between three nearest neighbors.
The results suggest that different human-influenced habitat have different effects on tarsier’s density. The smallest
distances (116.2 ± 18 m) between sleeping sites, which represent the highest estimated population density (57.1
groups in one square km), were found in habitat type H1, the least disturbed habitat. Estimated population density
in habitat type H3 or “forest plantations” was 38 groups/km2, followed by habitat type H2 or secondary forest with
selective logging 36.4 groups/km2, and the smallest population density was estimated at 32.9 groups/km2 in habitat
type H4 or forest with selective logging and plantations.
Keywords: population density, Tarsius dianae, sleeping trees, Ficus spp., Sulawesi.
INTRODUCTION
Eight species of tarsiers are currently
recognized, six of which are endemic to
Sulawesi and surrounding islands. These are:
Dian’s tarsier Tarsius dianae Niemitz et al., 1991
(or perhaps synonymous T. dentatus Miller &
Hollister, 1921 according to Brandon-Jones et al.,
2004), endemic to lower mountains of Central
Sulawesi; the Pygmy tarsier T. pumilus Miller &
Hollister, 1921, which is found in the high
mountains in Central Sulawesi; Spectral Tarsier
T. spectrum Pallas, 1778 (or perhaps the correct
name for this species is T. tarsier Erxleben 1777
as mentioned by Brandon-Jones et al., 2004 and
Merker & Groves, 2006), endemic to lowlands,
with the type locality in northern Sulawesi;
Sangihe Island tarsier T. sangirensis Meyer, 1896,
endemic to the Sangir-Talaud; Peleng Island
tarsier T. pelengensis Sody, 1949; and the last
described Lariang tarsier T. lariang Merker &
Groves, 2006. The two species not found in
Sulawesi are Philippine Tarsier T. syrichta
Linnaeus, 1758 which live in the southern islands
of the Philippines, and Western Tarsier T.
bancanus Horsfield, 1821 in Borneo, Bangka,
Belitung, and southern parts of Sumatra. (Musser
& Dagosto, 1987; Niemitz et al., 1991; Tremble
et al., 1993; Groves, 1998; Supriatna & Wahyono,
2000).
T. dianae was described as distinct from other
tarsier species morphologically, anatomically, and
in vocalizations, by Niemitz et al. (1991). This
species might be the predominant species in
Central Sulawesi, based on vocalizations
(Nietsch, 1999).
Like many other primates, tarsiers are arboreal
and use trees and plants as feeding sites or for
sleeping sites. The sleeping sites of tarsiers vary
with habitat type. In primary forest, tarsiers are
often found to sleep in tree cavities, especially
of strangler figs (Ficus spp.). In secondary
vegetation, tarsiers can sleep in tree cavities,
bamboo stands, or shrubs (MacKinnon &
MacKinnon, 1980; Tremble et al., 1993; Leksono
et al., 1997). Gursky (1998) found Ficus
caulocarpa was often used by Spectral tarsier
as a sleeping tree in Tangkoko-Batuangus Nature
Reserve.

Asian Primates Journal 1(1), 2008 11
Tarsius dianae suffers the risk of population
decline as primary rain forest in the island is
converted into plantations and transmigration
settlements. Sulawesi has lost over 20% of its
forest cover during 1985–1997, which is 1,890
km2 per year (Holmes, 2002). Forest clearance
even occurs inside conservation areas, including
Lore Lindu National Park in Central Sulawesi.
Besides coffee and cocoa plantations, exploitation
of woods, bamboo and rattan, are one of the
most common human activities in Sulawesi.
Bynum (1999) identified some variables to
detect and monitor the influence of human
activities on lowland rain forest in Lore Lindu
NP. Those variables, i.e. the number of stumps,
exotic trees, large trees and rattan, are very
useful to determine and monitor disturbances
in lowland forest in Lore Lindu NP.
Although extinction risk of Tarsius dianae is
not high at the moment (IUCN category Lower
Risk/conservation-dependent), increased human
activities in Lore Lindu National Park may
present a serious threat to this endemic species.
While there have been many field studies
about tarsiers (e.g. MacKinnon & MacKinnon,
1980; Crompton & Andau, 1986, 1987; Musser &
Dagosto, 1987; Niemitz et al., 1991; Tremble et
al., 1993; Gursky, 1998; Nietsch, 1999; Merker &
Muehlenberg, 2000; Merker et al., 2004 &
2005; Merker, 2006), information on the possible
impacts of human activities on tarsier density
is needed for a conservation program to be
effective. Only MacKinnon & MacKinnon (1980),
Merker & Muehlenberg (2000), and Merker et
al. (2004 & 2005) showed that there can be a
different population density in different
habitats.
The main objectives in this study were to
estimate the relative population density of
Tarsius dianae in four habitat types with
different levels of human activities in Lore Lindu
National Park. This information is needed to
assess the conservation status and conservation
action of the genus Tarsius.
MATERIALS AND METHODS
The study was conducted in the Kamarora
field station, situated at approximately 700–
900 m above sea level (asl) at the northeastern
boundary of Lore Lindu National Park, Central
Sulawesi, about 70 km southeast of Palu (Figure
1). Kamarora is the type locality of T. dianae. Data
collection was carried out from February to
June 2001. Four forest patches, each 10-20 ha,
were selected as sampling sites. Those sites
were: (H1) pristine forest or the “least disturbed
forest”; (H2) secondary forest with small-scale
selective logging, or “slightly disturbed forest”;
(H3) secondary forest interspersed with several
small (0.2–0.5 ha) old coffee and cocoa
plantations, or “moderately disturbed forest”;
and (H4) forest with either logging and intensive
plantations still occurring or “heavily disturbed
forest”.
To localize tarsier sleeping trees in a given
area, we recorded all audible duet songs the
animals performed every morning around
dawn. By triangulating (Kenward, 1987;
Muehlenberg, 1993) the positions of the call
sources and multiple repetition of this procedure,
tarsiers could be traced to their sleeping sites.
Once all the sleeping sites in each habitat were
known, mapping all sleeping sites in the
investigated areas and measuring the distances
between the groups resulted in relative
population density estimates (Brockelman & Ali,
1987). To ensure their confinement to one
specific habitat, only groups living in the center
of each forest patch were considered. We
assumed that one sleeping site represent one
groups. The average distance of three nearest
neighbors was used to estimate the range size
of one group and then to estimate the population
density in a given area (detail method in Merker,
2003 and Merker et al., 2004).
Sixteen randomly-selected point samples
were evaluated to assess the level of human
disturbance in each habitat (Bynum, 1999;
Merker et al., 2004 & 2005). At each point, a 10
m x 10 m quadrate was made, and we measured
the number of stumps, exotic trees, and trees
of diameter at breast height > 50 cm. The
disturbance parameters were determined in
each and then integrated into a disturbance
index (described in Merker, 2003 and Merker et
al., 2004) to compare the relative intensities of
anthropogenic influence.
To determine the extent to which food
abundance and locomotor support affect the
distribution of tarsier, the availability of insects

Asian Primates Journal 1(1), 200812
and substrate density were also assessed. At
eight sample points in each habitat type, the
abundance of insects eaten by Sulawesi tarsiers
(Nietsch, 1993; Tremble et al., 1993) was estimated
using two methods (Merker, 2003; Merker et al.,
2004): (1) to count moths, winged termites and
mantids, a Petromax kerosene pressure lantern
was fastened at 1.5 m in a small tree, and during
the subsequent 5 min all visible insects with
body length >1 cm attracted by the light were
counted; by differentiating the animals by
species, size and location it was possible to
avoid repeat counts of single specimens. (2) to
count grasshoppers, crickets and cicadas,
insects vocalizing within a 10 m radius around
the sample point within 5 min were
counted; repeated counts were avoided by
noting specific vocalization patterns and the
locations of individuals. At each of the eight
sample points three replicate counts, each on
a different evening, were made over 19.00-
21.00.
Based on the results of the habitat-use
analysis by Crompton & Andau (1986 & 1987)
and Merker (1999 & 2003), the branch/trunk/
sapling trees with a diameter between 1-4 cm
were measured, in vertical and horizontal
orientation, to analyse the substrate for locomotion
abundance. The sampling method used PCQ,
with 16 randomly placed points in each habitat.
All data sets were tested for normality using
the Kolmogorov-Smirnov test. For normally
distributed data, ANOVA and the Least Significant
Difference Post Hoc Test were used, and the non-
parametric Median Test was used to detect
significant differences between habitats.
Spearman’s rs was used to test correlations
between parameters. All tests are two-tailed.
(Sokal and Rohlf, 1995)
RESULTS
Observed groups of Tarsius dianae always
came back to their initial sleeping site each
morning. However, there is a tendency that
tarsier moved to alternate sleeping sites when
disturbed. Average distance to three nearest
neighbors and estimated population densities
are shown in Table 1. The smallest distances to
nearest neighbors (116.2 ± 18.0 m, n = 9 groups),
which is calculated and estimated to the
highest density 57.1 groups/km2, were found
in H1, the least disturbed habitat. Meanwhile,
in habitat where both logging and plantations
still occurred (H4), distances between sleeping
sites was the greatest (152.9 ± 7.1 m, n = 9
groups), giving the estimated tarsier population
Figure 1. Map of Sulawesi and location of the study plots along the northeastern boundary of Lore Lindu National Park
(after Merker, 2006).

Asian Primates Journal 1(1), 2008 13
density as small as 32.9 groups/km2. An
intermediate number of groups were found
where both secondary forest with small-scale
logging (H2) and secondary forest with old
plantations (H3) were present. Table 1 also shows
the disturbances (represented by average
number of stumps per 100 m2 - while the other
disturbance parameters is shown in Figure 2),
Habitat type
H1 (primary H2 (second H3 (second H4 (second
forest) forest with forest with forest with
small scale small-scale logging and
logging) interspersed pl;antations)
plantations)
Average distances to three nearest 116.2 ± 18.0 145.5 ± 13.7 142.4 ± 11.2 152.9 ± 7.1
neighbors ± SD (m)
No. of groups observed (n) 9 10 10 9
Population density ± SD 57.1 ± 21.5 36.4 ± 6.8 38.0 ± 5.8 32.9 ± 3.1
(groups/km2)
Average stumps density per 100 m22.5 ± 4.4 3.5 ± 4.3 9.2 ± 10.3 11.5 ± 3.1
Average insects density ± SD 11.6 ± 1.7 12.1 ± 1.9 13.5 ± 2.6 10.3 ± 2.4
(ind./5 min./point)
Locomotor support abundance ± SD 32.7 ± 4.2 115.0 ± 14.6 67.2 ± 8.5 77.8 ± 9.9
(substrates per 100 m2)
Table 1. The average distances between three nearest neighbors, relative population density of Tarsius dianae, number of
stumps, insects density and locomotor support abundance in four different habitats at Lore Lindu National Park, Central
Sulawesi.
Figure 2. The average of some human activities variables in four habitat types at Lore Lindu National Park, Central
Sulawesi.
Legend explanation: H1 = least disturbed forest; H2 = slightly disturbed forest; H3 = moderately disturbed forest;
H4 = heavily disturbed forest.
insect abundance (individuals/5 minute/
sampling-point), and locomotors supports
density (substrates per 100 m2) in each habitat.
The average distance between the sleeping
site of a group and the sleeping sites of its three
nearest neighbouring groups differed significantly
between studied habitat type (ANOVA,
F3,19=3.76, P<0.05).
0
2
4
6
8
10
12
14
Stumps Exotic Trees Treedbh>50cm
Variables of dis turbance
Averages in 10 x 10m plot
H1 H2 H3 H4

Asian Primates Journal 1(1), 200814
There was no significant difference between
habitat types in the number of insects (ANOVA,
P>0.05). The results indicate relative population
density was lower where stump density was
higher (Spearman rank correlation rs-0.8).
Population density was positively related to the
abundance of insects but the relations were
weak (Spearman rank correlation rs = 0.4).
DISCUSSION
Different habitat types, with different human
activities, had different relative population
densities of T. dianae, although no replicates
were performed in each type so the differences
recorded cannot be firmly attributed to habitat
type. Primary forest, the least disturbed habitat,
had the highest relative population density
(Table 1). The relative population density of
tarsier in primary forest (57.1 groups/km2) was
significantly greater compare to each other
habitat types that are influenced by human
land-use (ANOVA, P<0.05). There are no significant
differences between tarsier population densities
in the secondary forest with small-scale logging
(H2) or secondary forest with small-scale
interspersed plantations (H3) and secondary
forest with both logging and plantations (H4).
Some studies mentioned that Tarsius
bancanus was commonly found in secondary
forest (i.e. Fogden, 1974; Niemitz, 1984).
MacKinnon & MacKinnon (1980) also found that
in Tangkoko-Batuangus, the population density
at sea level of Tarsius spectrum in shrubby
forest (10 indiv./ha) was greater than in primary
forest at 1,000 m asl (only 5 indiv./ha). However,
Gursky (1998) reported that T. spectrum were
more abundant in the conservation area in
Tangkoko-Batuangus (lowland rainforest, sea
level).
Merker & Muehlenberg (2000) also found
that forest with small-scale interspersed
plantations had higher estimated population
density of tarsier than other habitat types.
Ganzhorn (1987) reported that population
density of lemur species in Madagascar tended
to be higher in old plantations than other
habitat types, but not as high as in primary
forest. Our research found that relative population
density of Tarsius dianae in primary forest was
higher than other habitat types. Unfortunately,
considering the differences in methodology and
specific site, it was not possible to make a
direct comparison between this study and the
other studies.
If we compare to the results in the year 1998
(Merker and Muehlenberg, 2000), there are a
decreasing tendency on population density of
T. dianae in Lore Lindu National Park. Merker and
Muehlenberg (2000) reported that the lowest
population density was 5.6 groups/10 ha, which
is similar to the highest number in our results
57.1 groups/km2. Indeed, there is no information
about forest loss or change to other human land-
use especially between years 1998 to 2001.
Merker et al. (2004) showed a subsequent decline
in T. dianae population densities and suggested
that human activities affect the population and
survival of T. dianae in Lore Lindu NP. Merker et
al. (2005) mentioned that population density
decreased with increasing anthropogenic
influences. They also stated that focusing solely
on population density, primary forest is the most
important habitat for tarsier conservation. As
mentioned by Merker et al.(2005), it is not clear
what causes the lower abundance of tarsiers in
the slightly disturbed habitats (H2) even
though resources are plentiful. One possible
reason may be the high susceptibility of these
animals to visual and acoustic disturbance in
their environment (Merker & Mühlenberg,
2000).
Conservation strategy for this unique and
endemic species should consider the differences
of human activities. Tarsiers can adapt to
traditional land uses such as small-scale
plantations or selective logging (Merker &
Muehlenberg, 2000; Yustian, 2007). Slight
disturbance may open up the forest canopy and
result in a greater heterogeneity of the forest
and subsequently a higher arthropod diversity
and density. Insect abundance was found to be
highest in the slightly disturbed habitats, H2
and H3, and lowest in the mixed-species
plantation H4. The increased prey density in H2
and H3 may balance the adverse effects of
selective logging and acoustic disturbance at
these sites (Merker & Mühlenberg, 2000). More
research is needed to study the role of small-scale
plantations as the support habitat for tarsiers.

Asian Primates Journal 1(1), 2008 15
CONCLUSIONS
Different habitats with different level of
human activities were found to have different
relative population densities of T. dianae. The
highest relative density was in primary forest,
the least disturbed habitat (57.1 ± 21.5 groups/
km2), followed by relatively more disturbed
habitats: forest with small-scale old plantations
(38.0 ± 5.8 groups/km2), secondary forest (36.4
± 6.8 groups/km2), and forest with both logging
and plantations (32.9 ± 3.1 groups/km2).
ACKNOWLEDGMENTS
The research has been supported by grants
from the German Academic Exchange Service
(HSP III) and the German National Merit
Foundation (to S.M.). We would to thank Banjar
Y. Laban, the Head of Balai Taman Nasional Lore
Lindu, Central Sulawesi and his Staff, especially
the Head of Kamarora Sub-section Yulisan, the
rangers in Tongoa and Kamarora Resort: Sapri,
Toni, Idris, Mulyani, and their families. We greatly
acknowledge the help of Ecil and Tamalagi's
family in Palu.
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