RICHNESS, ABUNDANCE, AND HABITAT RELATIONS OF
RODENTS IN THE LANG BIAN MOUNTAINS
OF SOUTHERN VIET NAM
GREGORY
H.
ADLER, SCOlI
A.
MANGAN, AND VICTOR SUNTSOV
University of Wisconsin-Oshkosh, Department of Biology and Microbiology,
Oshkosh, W154901 (CHA, SAM)
Tropical Center, Number 3 Street 3/2, 10 District, Ho Chi Minh City, Viet Nam (VS)
We sampled rodents in the Lang Bian Mountains of southern Viet Nam in June 1997 (rainy
season) and January 1998 (dry season) by live-trapping. Eight transects in pine (Pinus)
savanna and primary forest were sampled for 10 consecutive nights. We captured 11 species
of rodents, including 10 murids and one sciurid. Niviventer fulvescens was the most frequently-captured species and apparently was a habitat generalist. That species was captured
in both pine savanna and primary forest, but a distinct shift in habitat use occurred between
the t",'o seasons. During the rainy season, individuals were captured frequently in both
habitats, but during the dry season, N. fulvescens was restricted mostly to forest. Fluctuation
in resource abundance was the most likely explanation for that habitat shift; enormous
quantities of acorns were present in the dry season, but few resources were available in
the rainy season. Other species of rodents were captured less frequently, and several species
appeared to be more restricted in their habitat distributions than N. fulvescens.
Key words:
Niviventer fulvescens, rodents, murids, species richness, abundance, Viet Nam
Tropical regions of southeastern Asia are
among the richest mammalian faunas in the
world. About 250 species of mammals, excluding cetaceans, have been recorded from
Thailand alone (Lekagul and McNeely,
1988), and the list of nonmarine mammals
from Viet Nam numbers over 230 species
(Sokolov et aI., 1986). Rodents contribute
a substantial fraction to overall mammalian
richness in southeast Asia, with most species belonging to the families Sciuridae and
Muridae.
Viet Nam harbors a rich rodent fauna of
2::63 species (Sokolov et aI., 1986), including 20 sciurids and 35 murids. Much of this
fauna occurs within the topographically diverse Central Highlands. Several species
are confined to these highlands and similar
areas of Cambodia, Laos, and Thailand, and
one species (Rattus osgoodi) is endemic to
the slopes of Nui Lang Bian and nearby
Gou Gah (Musser and Newcomb, 1985).
Despite the richness of this rodent fauna,
JOIlYl/a/ ,,( Mal//l//{//oKY. 80(3):891-898. 1999
little is known of the ecology of the species
comprising the fauna. Accordingly, we
present an analysis of richness, abundance,
and habitat relations of rodents in the Lang
Bian Mountains of southern Viet Nam. This
region is of particular interest because it has
been designated a southeastern Asian biodiversity "hotspot" (Schmid, 1993).
MATERIALS AND METHODS
Study area.-The Lang Bian Mountains of
the Central Highlands in southern Viet Nam
consist of low-lying mountains with steep ridges
separated by valleys containing swift-flowing
streams, with the highest point at Bi Doup
(2,287 m above mean sea level). The area was
formerly largely covered with broad leaf evergreen hill forest. Much of this forest has been
cut or burned and replaced with pine (Pin liS) savanna, but vast undisturbed tracts still occur in
some areas. Intact forest contains high diversity
of tree species numerically and structurally dominated by the following families (P. Jelinek, in
litt.): Pinaceae (including P. krempjii), Podocarpaceae (including Dacrycarplls imbricatlls), Fa891
JOURNAL OF MAMMALOGY
892
350.,----------------,.25
300
20
E
i
250
E
-15
200
"a.. 150
10
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100
50
t... Precipitation -*" Temperature
I
O~.~--r-~~~~~~~~_,~
Jan
Feb
Mar
Apr
May Jun
Jul
Aug
Sep
Oct
Nov Dec
FIG. I.-Monthly mean precipitation and temperature at Da Lat, Viet Nam.
gaceae (including Lithocarpus leucotrichus,
Quercus haianensis, Q. langbianensis, Q. truncata, Q. echinifera, Castanopsis javanica, Pasania [Lithocarpus] cerifera), Elaeocarpaceae
(including Elaeocarpus), Lauraceae, Aceraceae
(including Acer campbellii), Betulaceae (including Carpinus), Arecaceae (including Phoenix),
and Moraceae (including many species of Ficus). Canopy heights often exceeded 30 m, with
emergent trees such as broad-needled pines (P.
krempfii) reaching ca. 50 m in height. Forest understory consisted primarily of small shrubs and
understory trees, with less coverage by herbaceous dicots and ferns. Pine savanna generally
contained only one species of tree (P. kesyia)
and had a dense cover of grass and scattered
small bushes and. herbs.
Our study area (l2°05'N, 108°25'E) was located at an elevation of 1,700 m in Lam Dong
Province 10 Ian NW of the provincial capital of
Da Lat and 7 Ian W of the peak Nui Lang Bian
Vol. 80, No.3
(2,167 m). The study area contained both pine
savanna and a tract of several hundred thousand
hectares of primary forest. The interior of the
primary forest had been subjected to only modest disturbance by indigenous people living in
small villages surrounding the forest. That disturbance was in the form of a few small clearings, each of several hundred square meters, occupied on an itinerant basis by hunters and subsequently abandoned. Based on our observations, the area still harbored a virtually intact
fauna of large mammals, including Hylobates
gabriellae (golden-cheeked gibbon), Panthera
tigris (tiger), Cervus unicolor (sambar), and Sus
scrofa (wild boar).
Mean annual rainfall in Da Lat is 1,820 mm!
year, and mean annual temperature is 18.3°C
(Pham and Phan, 1978). Temperature varies little
throughout the year, but precipitation is strongly
seasonal (Fig. 1). An 8-month rainy season is
punctuated by a shorter but severe dry season
from December through March. Although only
6% of annual precipitation falls during the dry
season, fog is frequent in the morning.
Sampling procedures.-We established eight
sampling transects within primary and disturbed
forest and pine savanna (Table 1). Transects
ranged from 250-1,000 m in length, with sampling stations within each transect located at 10m intervals. Transects were sampled once by
live-trapping for 10 consecutive nights. A single
wire mesh live-trap (26.5 by 17 by 13 cm, manufactured in Ho Chi Minh City, Viet Nam) was
set on the ground at each sampling station.
TABLE I.-Descriptions of the eight sampling transects. Transects 1-4 were sampled in May-June
1997, and transects 7-10 were sampled in January 1998. Transects 5 and 6 were sampled for only
3 nights and were not included in the analysis.
Number Number of
Tran- of ground arboreal
traps
sect
traps
50
0
2
3
50
25
25
0
4
50
0
7
8
9
10
100
100
10
10
50
50
10
0
Description
Mostly along the edge of a small tract (ca. 20 ha) of primary forest; traps were
set both within forest and in adjacent grassland
Within the large tract of primary forest
First five stations were located within grassland, with the remainder located
within a 100-ha tract of primary forest
Within grassland and the edge of a disturbed patch (ca. 10 ha) of broad-leaved
evergreen forest
Along a small stream I km inside the large tract of primary forest
Along the ridge adjacent to transect 7
Within dense cane and grass beside a small spring
Within grassland in pine savanna
ADLER ET AL.-ECOLOGY OF RODENTS IN VIET NAM
August 1999
TABLE
2.-Descriptions of the 21 habitat variables measured at each trap station.
Description
Name
I.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Small shrubs
Large shrubs
Shrub species
Understory trees
Understory species
Overs tory trees
Overstory species
Small logs
Medium logs
Large logs
Vines
Gradient
13. Forb cover
14.
IS.
16.
17.
18.
19.
20.
21.
893
Grass cover
Shrub cover
Hollow tree base
Tree distance
Tree size
Lianas
Liana size
Canopy height
Number of shrubs <I m in height within a IS-m 2 circle
Number of shrubs 21 m in height within a IS-m2 circle
Number of shrub species within a IS-m 2 circle
Number of understory trees within a I5-m 2 circle
Number of understory species within a IS-m 2 circle
Number of overs tory trees within a IS-m2 circle
Number of overstory trees within a I5-m 2 circle
Number of logs 5-10 cm in diameter within a 15-m2 circle
Number of logs 10-20 cm in diameter within a I5-m 2 circle
Number of logs >20 cm in diameter within a IS-m 2 circle
Number of vines and lianas within a IS-m 2 circle
Degree of development of the overstory, including grassland (numerical value of
3), edge between forest and grassland (2), gap within primary forest (1), and
primary forest (0)
An index of coverage by herbaceous vegetation excluding grass (0 = no herbaceous cover, I = 1-25% cover, 2 = 2S-50% cover, 3 = 50-75% cover, 4 =
75-100% cover)
An index of coverage by grasses; values similar to those for forb cover
An index of coverage by shrubs; values similar to those for forb cover
Presence or absence of a tree with holes or hollows at the base
Mean distance to the trap of the four measured trees
Mean dbh of the four measured trees
Mean number of lianas supported by the four measured trees
Mean diameter of the largest liana supported by each of the four measured trees
Height of the canopy directly above the trap
Along three transects within primary forest
(transects 2, 7, and 8), we also set a trap in trees
or lianas 1-2 m above ground at alternate stations. Along one transect within dense grassland
and cane (transect 9), we attached traps above
ground to cane stems because no trees were
present. Each trap was baited with cassava tubers (Manihot esculenta) covered with vegetable
oil. Traps were checked every morning and rebaited every 3rd day or immediately following
a capture.
All captured rodents were identified to species
and sex, uniquely toe-clipped for individual
identification, and weighed. Reproductive data
(testes position in males and vaginal patency and
development of lactation tissue in females) also
were recorded. All individuals were released at
their station of capture immediately following
data collection, except one or two individuals of
each species of uncertain identity that were collected as vouchers and identified later.
To characterize habitat structure, we measured
21 variables at every trap station (Table 2). The
first 16 variables were measured within a 1S-m2
circle centered on the trap. To measure variables
17-20, we selected the first tree encountered in
each of the four cardinal compass directions
from the trap. For each of these four trees, we
measured diameter at breast height (dbh, 1.3 m
above ground), number of lianas supported by
the tree, and diameter of the largest liana. For
sampling stations located within grassland, we
measured distance to the edge of the forest and
set tree diameters and liana numbers and sizes
at zero. Canopy height was measured to the
highest point of the forest directly above each
trap with a range-finder, and canopy heights
within grassland were recorded as zero. All sampling was conducted during the rainy season in
May-June 1997 (transects 1-4) and the dry season in January 1998 (transects 7-10).
Data analysis.-We tabulated numbers of individuals and captures for each species and transect to examine patterns of richness and abundance. Our goal in analyzing habitat data was to
quantify gradients in habitat structure across all
sampling sites by explaining as much variation
in structure as possible while using the fewest
variables (Seamon and Adler, 1996). We used
factor analysis for this purpose rather than prin-
894
JOURNAL OF MAMMALOGY
cipal components analysis (PCA) because the
fonner technique included only common variance of a variable when calculating factors. PCA
included both common and unique variances,
and principal components were therefore more
complex functions of raw variables (Cureton and
D' Agostino, 1983). The first principal component had high factor loadings for each raw variable, and principal components were consequently more difficult to interpret than rotated
factors (Seamon and Adler, 1996). We used principal axes factoring, and we inserted initial communalities as diagonals in an initial factor analysis (Cureton and D' Agostino, 1983). Resulting
factors were retained for oblique promax rotation if the scree plot and critical minimum eigenvalues were consistent. The critical minimum eigenvalue was detennined as Acrit = NO.6/
15 (Cureton and D' Agostino, 1983), where N is
the number of raw habitat variables. Thus, Acrit
= 0.41 in our analysis.
All captures of each species were then plotted
in the resulting multivariate space of the first
two factors to portray patterns of habitat occupancy (Adler, 1995). Thus, rodents were distributed within habitat space that was represented
by composite gradients of habitat structure. Resulting patterns of habitat occupancy did not assess directly features of habitat that were related
to capture probability. We used multiple logistic
regression to relate probability of capture at a
trap station to features of the habitat as determined by factor analysis. We included in this
analysis only the first capture of an individual to
eliminate problems of dependence, and we included only the most abundant species to ensure
that statistically meaningful regressions were
constructed. The dichotomous dependent variable was represented as either presence or absence of a species at a trap station. We perfonned separate regressions for the two seasonal
samples (1997 rainy season and 1998 dry season) and for all samples combined. We constructed both stepwise models and full models
that included all retained factors.
We examined arboreal use of habitat by comparing numbers of captures per ground and arboreal trap. In this analysis, we included only
those transects that contained arboreal traps. For
the most abundant species, we compared counts
of captures in traps set on the ground and in
trees by constructing linear models for the analysis of categorical data (Kleinbaum and Kupper,
Vol. 80. No.3
1978), which were appropriate for count rather
than frequency data (Lindsey, 1995).
RESULTS
Richness and abundance.-In 5,225 trap
nights, we captured 11 species of rodents
represented by 295 captures of 135 individuals (Table 3). We also captured two species
of insectivores, including two Suncus murinus (house shrew) and one HyIomys suilIus (lesser gymnure). The transect along a
stream within primary forest recorded the
most species of rodents (six). We also observed the sciurids Tamiops macclellandi
(Burmese striped tree squirrel), Callosciurus erythraeus (red-bellied squirrel), and
Dremomys rufigenis (red-cheeked squirrel)
along this transect, but those species were
not captured. We captured five species in
transects 2 (primary forest) and 4 (largely
edge between grassland and disturbed forest). The least rich site was transect 10
(pine savanna), with only two species.
Overall rodent abundance (measured as
number of individualsllOO trap nights) was
greater in June (3.9) than in January (1.8).
Overall abundance was greatest in transect
2 and least in transect 8, both of which were
in primary forest.
Niviventer fuIvescens (chestnut spiny rat)
was by far the most abundant species, comprising 67% of all individuals. That species
was numerically dominant in all sampled
sites except the two short, exclusively
grassland transects (9 and 10). Mus caroli
(Ryukyu mouse) and Maxomys moi (softfurred rajah rat) were relatively common in
grassland and forest sites, respectively. All
other species were captured only rarely.
However, T. macclellandi commonly was
observed around each transect within primary forest, indicating that that species was
underrepresented by our sampling.
Habitat structure and occupancy.-Initial principal-axes factoring indicated that
the common-factor space had eight primary
dimensions based on the two retention criteria (scree plot and eigenvalues). After rotation, those eight factors were interpreted
August
1999
August 1999
ADLER ET AL.-ECOLOGY
AL._ECOLOGY OF RODENTS IN VIET NAM
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based on factor structure (in descending order of eigenvalues) as representing a gradient from grassland to forest and gradients
in shrubs, overstory vegetation, understory
vegetation, lianas, shrub species, small and
medium-sized logs, and large logs. The first
two factors accounted for more than onedata..
half of the variation in the raw habitat data
Rodent species were distributed differently within habitat space defined by the
first two factors. Niviventer fulvescens was
distributed throughout multivariate habitat
space from forest edge to primary forest
and from sparse to dense shrubs and therefore utilized most available habitat (Fig. 2)
2)..
However, we captured that species in grassland only during the rainy season. Mus
Mus carcarMus pahari
pahari (Gardner's shrew-mouse),
oli,
oli, Mus
and Vandeleuria
Vandeleuria oleracea
oleracea (long-tailed cane
mouse) were captured exclusively in grassland (Fig. 2). Within grassland, M. caroli
was distributed in multivariate space along
the shrub gradient. Tamiops macclellandi,
macclellandi.
Chiropodomys gliroides (common penciltailed tree mouse), M. moi, Rattus sikkisildcimensis
mens
is (Sladen's rat), and Rattus nitidus
(Himalayan rat) were captured exclusively
in primary forest. Niviventer langbianis
(Lang Bian spiny rat) was distributed from
forest edge to primary forest (Fig. 2). Berylmys bowersi (Bower's white-toothed rat)
was distributed from grassland to primary
forest but was not distributed similarly
along the shrub gradient (Fig. 2).
Niviventer fulvescens was the only species with sufficient captures to include in
logistic regression analysis. Full models
with all factors included and stepwise models differed only slightly in intercepts and
slopes, and we therefore present results
only from the full models. With all samples
included, probability of capture at a trap
station was related positively to the gradient
(X 22 =
= 5.05,
from grassland to primary forest (X
d.f =
= 1, P =
= 0.025). Thus, there was a
d.!
higher capture probability in forest than in
grassland. A similar relationship prevailed
in the dry-season sample (Xl
(X 2 = 6.51, d.f.
d.f =
=
1, P =
= 0.011), but capture probability was
896
JOURNAL OF MAMMALOGY
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FIG. 2.--Distributions of all sampling stations and of 11 species of rodents within multivariate
habitat space of the first two factors derived from factor analysis. Polygons define limits of habitat
sampled in this study. Note that many sampling points were obscured by other sampling points,
particularly in the plot with all sampling points included.
unrelated to any of the factors in the rainyseason sample.
All species except C. gliroides were captured in traps set on the ground. Tamiops
macclellandi, V. oleracea, N. fulvescens, N.
langbianis, and R. sikkimensis also were
captured in arboreal traps. Only N. fulvescens had a sufficient number of captures to
compare capture counts in ground (n = 109
captures of 260 traps) and arboreal traps (n
= 15 captures of 135 traps). That species
was captured more frequently in traps set
on the ground (X 2 = 33.86, d.t = 1, P <
0.001), but the same individuals were often
captured in ground and arboreal traps.
Numbers of captures within transects that
contained traps set on the ground and in
trees was too small (n = 1-3 captures) for
most species to draw conclusions about
their relative use of arboreal versus terrestrial habitats. However, all nine captures of
M. moi were on the ground, and all 10 captures of C. gliroides were in arboreal traps.
DISCUSSION
The Lang Bian Mountains contained a
moderately rich rodent fauna of :2: 10 species of murids and one sciurid that were
captured with relatively little sampling effort. Two additional sciurids also were
August 1999
ADLER ET AL.-ECOLOGY OF RODENTS IN VIET NAM
sighted. The rodent fauna was dominated
numerically by N. fulvescens. That species
used a variety of habitats ranging from open
grassland to pristine primary forest. Jones
(1983) also captured that species in both
forest and grassland in Viet N am. Marshall
(1988) found N. fulvescens in a variety of
primary and secondary forests in Thailand.
A distinct habitat shift by that species occurred between rainy and dry seasons in our
study. N. fulvescens was virtually absent
from grassland in the dry season. We captured no individuals in the grassland transects in our study and only two individuals
in a grassland that we trapped for only 3
nights near our study area. We suggest that
this habitat shift was due to changes in resource abundance in the forest. During the
dry season, Quercus were producing enormous crops of fruit throughout the forested
study sites. Small groups of indigenous
people foraging at the edge of the forest in
January 1998 could collect several hundred
kilograms of acorns in a few hours. By contrast, we found no Quercus fruiting in June
1997. Trappability of N.fulvescens also was
much greater in the rainy season. We caught
each individual an average of 3.5 times in
June 1997 and only 1.2 times in January
1998. That difference in trappability was
consistent with previous observations that
tropical frugivorous and granivorous rodents were more trappable when food resources were scarce (Adler and Lambert,
1997; Rudd, 1979).
We suggest that N. fulvescens is primarily a forest species but exploits secondary
habitats, including grasslands, in times of
low resource abundance in the forest. This
species also is able to use vertical habitat,
as evidenced by captures in trees and on
vines. Although arboreal traps were set near
the ground, many individuals adeptly
sought refuge high in trees following their
release. This species is therefore a habitat
generalist, not unlike the widely distributed
terrestrial echimyids such as Proechimys
semispinosus (Central American spiny rat)
in the Neotropics (Adler, 1996).
897
Capture frequencies were too low to statistically assess habitat use by other species
in this rodent fauna. However, Berylmys
bowersi also was distributed from grassland
to primary forest but, in contrast to N. fulvescens, was not distributed along the entire
length of the shrub gradient. We captured
three individuals in small gaps several kilometers inside primary forest, and two individuals were captured repeatedly in grassland at the edge of disturbed forest. We suggest that B. bowersi may be a gap specialist
that also can exploit forest edges and grasslands. All 22 captures of M. caroli were
within grassland, consistent with previous
reports (Adler, 1995; Marshall, 1988). Chiropodomys gliroides was highly arboreal,
and all 10 captures in our study were made
in primary forest. That species has been
found in both primary and secondary forests (Marshall, 1988), but because we did
not set traps above the forest floor in the
smaller tracts of disturbed forest, we do not
know if C. gliroides was present in such
forest in our study area. All 16 captures of
M. moi were within primary forest. Van
Peenen (1969) and Van Peenen et al. (1971)
found M. moi in lowland second-growth
forest in southern Viet Nam, but Jones
(1983) captured this species within secondgrowth forest, scrubby habitats, and grassland with bushes. Although M. moi has
been found in secondary habitats, it may be
more abundant in less disturbed forests.
Within primary forest in our study area, M.
moi was distributed throughout available
habitat. Additional study of the natural history and ecology of this poorly-known fauna is needed to assess status and distribution of species comprising the fauna.
ACKNOWLEDGMENTS
We thank Huyn Q., N. Suntsova, Nguyen M.
T., Vu X. K., Nguyen V. v., Tran V. T., and Nu
V. M. for logistical and field support and Ph am
T. P. for expert interpreting assistance. We are
also indebted to G. Musser for identifying rodent
specimens, P. Jelinek for supplying information
on trees, and an anonymous reviewer for helpful
898
JOURNAL OF MAMMALOGY
comments. This study was supported in part by
a grant from the National Science Foundation
(DEB9628943) to G. H. Adler.
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Submitted 3 June 1998. Accepted 19 November 1998.
Associate Editor was Edward J. Heske.