ORIGINAL
ARTICLE
Mammals of Borneo ? small size on a
large island
Shai Meiri1,*, Erik Meijaard2,3, Serge A. Wich4, Colin P. Groves3 and Kristofer
M. Helgen5
1NERC Centre for Population Biology,
Imperial College London, Silwood Park
Campus, Ascot, UK, 2Tropical Forest Initiative,
The Nature Conservancy, Balikpapan,
Indonesia, 3School of Archaeology and
Anthropology, Australian National University,
Canberra, Australia, 4Great Ape Trust of Iowa,
Des Moines, IA, USA, 5Division of Mammals,
National Museum of Natural History,
Smithsonian Institution, Washington, DC,
USA
*Correspondence: Shai Meiri, NERC Centre for
Population Biology, Imperial College London,
Silwood Park Campus, Ascot, UK.
E-mail: s.meiri@imperial.ac.uk
ABSTRACT
Aim Island mammals have featured prominently in models of the evolution of
body size. Most of these models examine size evolution across a wide range of
islands in order to test which island characteristics influence evolutionary
pathways. Here, we examine the mammalian fauna of a single island, Borneo,
where previous work has detected that some mammal species have evolved a
relatively small size. We test whether Borneo is characterized by smaller mammals
than adjacent areas, and examine possible causes for the different trajectories of
size evolution between different Bornean species.
Location Sundaland: Borneo, Sumatra, Java and the Malay/Thai Peninsula.
Methods We compared the mammalian body size frequency distributions in the
four areas to examine whether the large mammal fauna of Borneo is more
depauperate than elsewhere. We measured specimens belonging to 54 mammal
species that are shared between Borneo and any of the other areas in order to
determine whether there is an intraspecific tendency for Bornean mammals to
evolve small body size. Using data on diet, body size and geographical ranges we
examine factors that are thought to influence body size.
Results Borneo has fewer large mammals than the other areas, but this is not
statistically significant. Large Bornean mammals are significantly smaller than their
conspecifics in the other regions, while there are no differences between the body
sizes of mammals on Sumatra, Java and theMalay/Thai Peninsula. The finding that
large mammals show the greatest size difference between Borneo and elsewhere
contrasts with somemodels of size evolution on islands of different areas. Diet does
not correlate with the degree of size reduction. Sunda region endemics show a
weaker tendency to be small on Borneo than do widespread species.
Main conclusions We suggest that soil quality may drive size evolution by
affecting primary productivity. On Borneo, where soils are generally poor in
nutrients, this may both limit biomass and cause mammals to be reduced in body
size. We hypothesize that widespread species respond to low resource abundance
by reducing in size, while endemic elements of the fauna have had longer to adjust
to local conditions by altering their behaviour, physiology and/or ecology, and are
thus similar in size across the region.
Keywords
Body size, Borneo, distribution, dwarfism, island rule, Java, Malay Peninsula,
productivity, Sumatra.
Journal of Biogeography (J. Biogeogr.) (2008) 35, 1087?1094
? 2008 The Authors www.blackwellpublishing.com/jbi 1087
Journal compilation ? 2008 Blackwell Publishing Ltd doi:10.1111/j.1365-2699.2008.01897.x
INTRODUCTION
Island mammals often differ strikingly in size from their
mainland relatives (Hooijer, 1949; Kurten, 1953). Much
research effort has concentrated on quantifying size evolution
over a large array of islands to examine whether attributes of
the colonizing species (e.g. phylogenetic affinity, body size,
diet) result in predictable patterns of size evolution (Foster,
1964; Lomolino, 1985; Raia & Meiri, 2006; Meiri et al., 2008).
Island attributes such as area, isolation and latitude have been
widely studied (Heaney, 1978; Clegg & Owens, 2002; Lomo-
lino, 2005; Meiri et al., 2005a; Meiri, 2007).
Other attributes of islands are often harder to quantify, and
are thus more seldom studied. Some attributes, however, may
have important and island-specific consequences for size
evolution. Recent work suggests that Borneo, the world?s third
largest island (743,000 km2), may be an island where evolution
usually favours small size: Meijaard (2004a) found that
Bornean sun bears (Helarctos malayanus) were significantly
smaller than mainland Asian and Sumatran specimens. Similar
size trends were found for the greater chevrotain (Tragulus
napu) (Meijaard & Groves, 2004b) and sambar (Cervus
unicolor) (Meijaard & Groves, 2004a), with Bornean specimens
being much smaller than their conspecifics on Sumatra. Meiri
et al. (2004) found that among carnivores in general, Bornean
forms were smaller than their mainland conspecifics (six
species). Still, these size relationships are not consistent across
all taxa; for instance the lesser chevrotain (Tragulus kanchil) is
larger on Borneo than elsewhere (Meijaard & Groves, 2004b).
Available data suggest that Borneo has lower primary
productivity and soil nutrient levels than Java and Sumatra
(Payne, 1990;Meijaard et al., 2005;Marshall et al., in press; S. A.
Wich, A.J. Marshall, G. Fredriksson, N. Ghaffar, M. Leighton,
C.P. Yeager, F.Q. Brearley, J. Proctor, M. Heydon & C.P. Van
Schaik, unpublished data). Between Borneo and Peninsular
Malaysia, which share a similar geological history (Hall, 1998),
the differences in productivity are less clear, but may still be
substantial, with soils on Peninsular Malaysia being more fertile
than those on Borneo and leaf digestibility likewise being greater
on the mainland (Waterman et al., 1988).
Perhaps because of these differences in soil quality, Borneo
seems to support generally lower population densities and lower
biomass per unit area than the adjacent mainland, Sumatra and
Java, in diverse vertebrate groups (Waterman et al., 1988; Payne,
1990; Meijaard, 2004b; Wong et al., 2005). Lower population
densities may reflect, in part, greater hunting pressure (e.g.
Marshall et al., 2006), but comparative resource limitation on
Borneo could also limit population densities and body size
relative to areas with higher productivity more typical of Java
and Sumatra. Although PeninsularMalaysia is similar to Borneo
in some geological attributes (Hall & Holloway, 1998), it is
connected to the Asian mainland and generally supports higher
population densities (Payne, 1990; Meijaard, 2004b).
Here, we test whether Borneo is characterized not only by
low population densities but also by smaller numbers of large
mammal species, and if body sizes of Bornean mammals are
lower than those on the other large landmasses of the Sunda
area. We start by comparing interspecific body size frequency
distributions to examine whether Borneo has fewer large
species than its near neighbours. We also compare body sizes
within species (or species-groups, since some Bornean mam-
mals have recently been classified as distinct species from their
closest relatives elsewhere) to see whether Bornean mammals
are generally smaller than their conspecifics on the adjacent
mainland and nearby large islands (Java and Sumatra).
Specifically, we examine predictions regarding size evolution
that will arise if primary production is indeed lower on
Borneo. We then test the following predictions regarding the
roles of body size and diet in driving the observed patterns of
size variation:
(1) Larger-bodied species may suffer less from resource
scarcity since their lower mass-specific metabolic requirements
and higher energy reserves allow them to survive periods of
reduced food availability (Wheatley, 1982; Lindstedt & Boyce,
1985). Thus, we hypothesize that larger-bodied species will be
less affected by the relatively low productivity of Borneo than
smaller-bodied species, and therefore that small species will
differ more in size between Borneo and adjacent areas whereas
large species will be more similar in size. This is consistent with
models of size evolution in relation to island area (Heaney,
1978; Lomolino, 1985) that would predict that the largest
mammals on Borneo will be larger than those on the smaller
islands of Java and Sumatra, and that small-bodied species will
be smaller there (the Malay Peninsula may function either as
an island or a mainland, and hence predictions are more
difficult).
(2) We hypothesize that body size of species with higher-
quality diets would be most affected by resource scarcity and
therefore show a more drastic reduction in size on Borneo
compared with species with lower-quality diets.
METHODS
We compared the body size frequency distribution of mammal
faunas from Borneo, the Malay Peninsula (south of the
Isthmus of Kra), Sumatra and Java, using distribution data
from Corbet & Hill (1992), Wilson & Reeder (2005), other
literature sources and data from museum specimens. We
omitted species that probably represent human introductions
(Lepus nigricollis, Mus caroli, Mus musculus, Mus terricolor,
Rattus exulans, Rattus rattus, Rattus norvegicus and Bandicota
spp.; Wilson & Reeder, 2005). We used body masses from the
literature (mostly from Smith et al., 2003; see Appendix S1 in
Supplementary Material). For some species, we were unable to
obtain body mass data. For these, we use the average of the log-
transformed body masses of all species of a known mass in
their genus.
We compared body sizes using the condylobasal lengths
(CBL) of skulls from all species that we measured in natural
history museums and that were represented both on Borneo
and on Sumatra, Java or the Malay Peninsula. Condylobasal
length is commonly employed as an index of mammalian body
S. Meiri et al.
1088 Journal of Biogeography 35, 1087?1094
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size, and is known to be measured with little error (Dayan
et al., 2002; Meiri et al., 2005b). Because sexual size dimor-
phism is substantial in some species, we calculated the mean
CBL for each gender and then averaged these values, regardless
of within-gender sample size. For sexually dimorphic species
for which we had measurements for only one gender from a
particular region we restricted our inter-regional comparisons
to data for that gender only. Sample sizes for different species
range from 3 to 170 (mean 39).
We used two methods to test for size differences between
Borneo and other regions. First, for each species (or sister-
species pair) we averaged CBL values for all populations
outside of Borneo (Java, the Malay Peninsula and Sumatra)
from which we had measurements, and then compared these
averages with the average CBL on Borneo using a paired t-test.
In a separate analysis, we calculated the ratio of each
population relative to the one with the largest CBL for each
species (so where a species was largest the index is 100%). We
then compared the relative sizes across all species using a one-
way anova.
To explore the role of different biological attributes in
promoting size change on Borneo, we used the ratio of CBL on
Borneo to CBL where a species is largest as the response
variable, and examined whether the degree of size reduction is
related to body mass and feeding habits. Body-mass data were
taken from the literature (see Appendix S2). We used quan-
titative data on diets (Payne & Francis 1985; Meijaard et al.,
2008) to score, for each species, a ?dietary quality? index as
follows:
quality = proportion of leaves in the diet + 2 ? proportion of
fruit in the diet + 3.5 ? proportion of animal food in the diet
(Sailer et al., 1985; Leonard & Robertson, 1994). All analyses
were conducted using R (R Development Core Team, 2006).
RESULTS
Our data set included 218 species from Borneo, 218 from the
Malay Peninsula, 196 from Sumatra and 132 from Java (see
Appendix S1). Average (log-transformed) body mass was
lower on Borneo (108 g), than on the Malay Peninsula
(144 g) and Sumatra (184 g) but no lower than on Java
(106 g). However, these differences were not statistically
significant (one-way anova, F3,760 = 1.42, P = 0.23). Results
were qualitatively similar when we omitted bats from the
analysis (Borneo, 124 species, 551 g; Malay Peninsula, 119
species, 1120 g; Sumatra, 120 species, 885 g; Java, 66 species,
799 g: F3,425 = 1.39, P = 0.24). Examining only the highest
quartile of body masses (excluding bats) to see whether Borneo
has fewer large mammals yielded no significant results
(F3,105 = 1.43, P = 0.24), although Borneo had the lowest mass
for this subset (16,600 g vs. 28,300 g on Sumatra, 32,200 g on
Java and 42,400 g on the Malay Peninsula). Comparing the
body size frequency distribution of mammal species on Borneo
with other regions similarly revealed no significant differences
(Kolmogorov?Smirnov tests; all mammals: Sumatra, d = 0.08,
P = 0.48; Java, d = 0.06, P = 0.94; Malay Peninsula, d = 0.06,
P = 0.83; terrestrial mammals only: Sumatra, d = 0.09,
P = 0.66; Java, d = 0.09, P = 0.85; Malay Peninsula,
d = 0.13, P = 0.23; Fig. 1).
Intraspecific comparisons
Borneo shares 87 mammal species with Java, 142 with Sumatra
and 154 with the Malay Peninsula (Appendix S1). Skull
measurements of 54 species that are shared between Borneo
and at least one of these regions are presented in Appendix S2.
Bornean mammals were significantly smaller than their
conspecifics elsewhere, both when we averaged the skull
lengths of non-Bornean species (paired t-test, n = 53 pairs;
(a)
(b)
0.3
0.25
0.2
0.15
0.1
0.05
Log body mass
Pr
op
or
tio
n 
of
 s
pe
cie
s
Pr
op
or
tio
n 
of
 s
pe
cie
s
Log body mass
0
0?0.5 0.5?1 1?1.5 1.5?2 2?2.5 2.5?3 3?3.5 3.5?4 4?4.5 4.5?5 5?5.5 5.5?6 6?7
0?0.5 0.5?1 1?1.5 1.5?2 2?2.5 2.5?3 3?3.5 3.5?4 4?4.5 4.5?5 5?5.5 5.5?6 6?7
0.25
0.2
0.15
0.1
0.05
0
Figure 1 Body size distribution of mammalian masses on Bor-
neo, Java, Sumatra and the Malay Peninsula: (a) all mammals,
(b) non-volant mammals (excluding bats). The x-axis on a base-10
logarithmic scale (0?0.5 = < 3.1 g; 0.5?1 = 3.1?10 g; 1?1.5 = 10?
31 g; 1.5?2 = 32?100 g etc.). The y-axis is the proportion of
species in each size class of the total mammalian species in an area
(i.e. the number of species in the size class divided by the total
number of species). Filled bars, Borneo; squares, Java; grey, Malay
Peninsula; stripes, Sumatra. Sample sizes: all mammals, Borneo,
n = 218; Java, n = 132; Sumatra, n = 196; Malay Peninsula,
n = 218. Terrestrial mammals, Borneo, n = 123; Java, n = 66;
Sumatra, n = 120; Malay Peninsula, n = 119.
Small size on a large island
Journal of Biogeography 35, 1087?1094 1089
? 2008 The Authors. Journal compilation ? 2008 Blackwell Publishing Ltd
mean difference = 4.97 mm, t = 2.84, P = 0.006) and when
we divided the CBL of each population by the value of the
largest population of their species (one-way anova,
F3,158 = 4.58, P = 0.004). A post hoc Tukey honestly significant
difference (HSD) test revealed significant differences between
Borneo and Java, and between Borneo and the Malay
Peninsula, but not in other comparisons (Table 1).
Correlates of size differences
We examined several predictors of body size in Bornean
mammals relative to the size of the largest-bodied population
on the Sunda Shelf. Body mass was negatively correlated with
relative size on Borneo, i.e. larger taxa tend to be relatively
smaller there (n = 54, r = )0.40, P = 0.003; Fig. 2), con-
tradicting our first prediction. In fact, small (< 1 kg) mammals
are not, on average, smaller on Borneo than elsewhere
(controlling for species identity, F3,31 = 0.26, P = 0.86).
Correlations between body mass and relative size for the
other regions are all positive but non-significant (Malay
Peninsula, n = 43, r = 0.14, P = 0.368; Sumatra, n = 45,
r = 0.07, P = 0.631; Java, n = 20, r = 0.32, P = 0.16). Diet is
unrelated to the degree of size reduction on Borneo
(F2,51 = 1.20, P = 0.31), and dietary index does not correlate
with the degree of size reduction (n = 51, r2 = 0.006,
P = 0.59), contradicting our second prediction.
We note an additional pattern that emerged from our
analyses: mammals endemic to the Sundaic region are, on
average, 97.7% of the maximum size in the region (n = 27).
However, Bornean populations of mammals with wider
distribution in the Oriental Realm are on average relatively
smaller: 93.5% of the maximum size (n = 27, t = 3.96,
P = 0.0003). When we compare relative sizes of wide-ranging
species, we find significant differences between the four areas
(F3,81 = 9.21, P < 0.0001, mean relative size = 93.5% on
Borneo vs. 96.0% on Sumatra, 98.2% on the mainland and
98.3% on Java). A Tukey HSD test found no significant
differences between Sumatra, Java and the mainland, but
comparisons involving Borneo are nearly (vs. Sumatra,
P = 0.083) or highly significantly (Borneo vs. the mainland,
P = 0.0001, vs. Java, P = 0.0004) different. Comparing en-
demic Sundaic species in the four areas, however, no
significant differences between relative sizes were found
(F3,73 = 0.07, P = 0.98, mean relative sizes all between 97.3%
and 97.8%).
DISCUSSION
There is strong evidence that large terrestrial mammals on
Borneo are, in general, smaller than their closest relatives on
Java, Sumatra and the Malay Peninsula. These latter three
areas, on the other hand, show few consistent patterns of size
differences between them. Borneo also has fewer species of
large mammals than these other regions (Fig. 1), although this
is not statistically significant, and its largest mammals are
smaller. Neither of the hypotheses we set out to explain this
pattern are supported by our data: size reduction is most
prominent in large, not small, mammals, and diet does not
seem to influence the degree of size difference between Borneo
and adjacent regions.
Current theory regarding change in size on islands (e.g.
Lomolino, 2005) would not identify Borneo as an island where
considerable size evolution would be expected. One of the
largest islands in the world, Borneo lies on the Asian
continental shelf, maintained a continuous land-bridge con-
nection with the Asian mainland until the Middle Pliocene and
Table 1 Results of a post hoc Tukey honestly significant difference (HSD) test for intraspecific differences in condylobasal length (CBL)
between mammals on Borneo, Java, the Malay Peninsula and Sumatra.
Comparison Difference Lower 95% confidence limit Upper 95% confidence limit P
Java?Borneo 0.025 0.001 0.048 0.034
Malaya?Borneo 0.023 0.005 0.042 0.007
Sumatra?Borneo 0.014 )0.004 0.032 0.198
Malaya?Java )0.002 )0.026 0.023 0.998
Sumatra?Java )0.011 )0.035 0.013 0.639
Sumatra?Malaya )0.009 )0.028 0.010 0.585
2 3 4 5 6
0.
85
0.
90
0.
95
1.
00
Log body mass
R
el
at
iv
e 
si
ze
 o
n 
Bo
rn
eo
Figure 2 The relative skull size of Bornean mammals (Borneo
condylobasal lengths (CBL)/largest CBL in the region) vs. the base-
10 logarithm of their body mass (in grams, species-specific data
from the literature). Sample sizes: Borneo, n = 53 species; Java,
n = 20 species; Sumatra, n = 44 species; Malay Peninsula, n = 43
species.
S. Meiri et al.
1090 Journal of Biogeography 35, 1087?1094
? 2008 The Authors. Journal compilation ? 2008 Blackwell Publishing Ltd
an intermittent connection that subsequently did not disap-
pear until the Late Pleistocene (Meijaard, 2003), and supports
a rich and diverse mammalian fauna. It is thus reasonable to
expect that similar trophic structuring and competition
regimes should characterize the mammalian faunas of Borneo
and the mainland. However, one major difference between the
two areas is the lack of large predators on Borneo today, which
probably means that large mammals on Borneo face lower
rates of predation than on Sumatra, Java and Peninsular
Malaysia. These latter regions are all inhabited today, or were
until recent centuries, by tigers, leopards (absent from
Sumatra) and Asian wild dogs ? all of which are missing from
Borneo (Meijaard, 2004b). Past land connections to Java,
Sumatra and the Asian mainland would have provided access
to Borneo for any of the large predator species that existed in
the region during the Pleistocene (e.g. Panthera tigris, Panthera
pardus, Hyaena brevirostris, Merriam?s dog Megacyon merri-
ami, the dirk-toothed cat Megantereon sp., the sabre-toothed
cat Hemimachairodus zwierzyckii and the scimitar-toothed cat
Homotherium ultimum). Tigers inhabited Borneo until the
Holocene (Piper et al., 2007), but because of Borneo?s poor
fossil record, it is unclear whether and when other large
predators existed there. The evidence suggests that none of the
other large predators have survived on Borneo since the Last
Glacial Maximum. Release from predation could thus be one
factor implicated in dimensional size reduction in Borneo,
especially for large species (Heaney, 1978; Raia & Meiri, 2006).
The largest carnivore on Borneo is the 20 kg clouded leopard
Neofelis nebulosa (the sun bear feeds mostly on fruit and
insects: Fitzgerald & Krausman, 2002; Fredriksson et al., 2006).
Nevertheless, emerging evidence suggests that until the late
Pleistocene and, to a lesser extent, until at least the mid
Holocene, Borneo?s large mammal fauna was considerably
richer than it is today (Cranbrook & Piper, 2007; Louys et al.,
2007; Piper et al., 2007). To what extent palaeoenvironmental
changes, or over-hunting and habitat modification by humans
played a role in the extinctions of Borneo?s mammals remains
unclear. Firmer understanding of ecological mechanisms
underlying the relatively small size of mammals in Borneo
may help to explain why extinctions of large mammals during
the Holocene have been more severe on Borneo relative to
smaller landmasses such as Sumatra and Java (Louys et al.,
2007).
The Sunda Shelf, of which Borneo, Java and Sumatra are a
part, is geologically very active. The land areas of Sumatra and
Java on the region?s volcanic arc are relatively new, but Borneo
is part of the old geological core of the Sunda Shelf, which once
connected it to the Thai/Malay Peninsula (Meijaard, 2003).
Bornean soils are generally much less fertile than the rich
volcanic soils of large parts of neighbouring Java and Sumatra
(MacKinnon et al., 1996). Deep complete weathering, com-
bined with leaching, results in soils of low fertility in many of
the lowland areas surrounding the central mountain chain in
Borneo. The more frequent soil renewal around the active
volcanoes of Java and Sumatra results in more productive soils.
This is indicated in the predominant agricultural systems. On
Borneo, low soil fertility has predominantly resulted in shifting
cultivation with short cropping regimes and long fallows,
nomadic hunter?gatherer systems and permanent agriculture
in only a few of the most fertile areas, while these permanent
systems are much more common in Sumatra, and are the
norm on Java. The general productivity of Kalimantan (the
Indonesian part of Borneo), Sumatra and Java is reflected in
the percentage of total land area suitable for agricultural
development, which is respectively 45%, 55% and 93% (Land
Resources Department/Bina Program, 1990). It may also affect
human population densities which, historically, were much
lower on Borneo than on either Sumatra or Java (Mohr, 1938).
Clearly, there is within-island variation in the overall produc-
tivity patterns, with areas of low productivity on Java and
Sumatra, such as the south-eastern limestone of the former
and the extensive coastal peat swamps in the latter. Locally
poor soils may reduce productivity even in well-watered high-
energy regions. It has been hypothesized that overall forest
productivity in Borneo is lower than on the mainland
(Waterman et al., 1988), and lower than typical of Sumatra
and Java, because extensive tectonic activity and volcanism
generated more fertile soils on Sumatra and Java (MacKinnon
et al., 1996; Delgado & van Schaik, 2000). Although a detailed
analysis of overall forest productivity across the Sunda Shelf
remains to be conducted, recent multi-site comparisons
indicate that forest fruit production is higher on Sumatra
than on Borneo (Marshall et al., in press; S. A. Wich et al.,
unpublished data). The biomass of leaf-eating monkeys
(Presbytis) is lower on Borneo than on Sumatra, Java and
Peninsular Malaysia (Waterman et al., 1988), even though
their diversity is higher (Meijaard & Groves, 2004c), further
supporting a hypothesis of lower productivity on Borneo
(Waterman et al., 1988; Payne, 1990). Furthermore, Borneo
lacks three species of common and widespread fruit bats that
otherwise occur widely on the Sunda Shelf (Rousettus lesche-
naultii, Cynopterus titthaecheilus and Macroglossus sobrinus),
perhaps indicating lower fruit production. Waterman et al.
(1988) reported lower digestibility of leaves on Borneo relative
to that on Peninsular Malaysia, which again may promote size
differences. If these findings are indicative of overall forest
productivity, this could be an important factor explaining
smaller body sizes on Borneo. Overall poor soil productivity
may have resulted in low prey biomass (Waterman et al., 1988;
Wong et al., 2005), in turn affecting the diversity and
abundance of large predators (Meijaard, 2004a,b). This may
have resulted in herbivores growing smaller in the face of
reduced mortality, causing the remaining predators to grow
smaller in turn (Raia & Meiri, 2006, and see Appendix S2 for,
e.g., Neofelis).
Wong et al. (2005) hypothesized that frequent starvation of
large Bornean mammals, and overall low large mammal
densities on the island may result from high inter-annual
variation in fruit abundance. High intra-annual variation in
productivity (i.e. high seasonality) has been thought to
promote size increase (Lindsey, 1966; Calder, 1974; cf. Meiri
et al., 2005c), because large size is associated with a longer time
Small size on a large island
Journal of Biogeography 35, 1087?1094 1091
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to starvation. It may be, however, that this mechanism leads to
large size where food availability varies between seasons, but
that when food availability varies over a longer time-scale
(between years) large mammals are at a disadvantage, because
of their high overall food requirements (McNab, 1971). Thus,
the fact that Java is more seasonal than Borneo (Regional
Physical Planning Programme for Transmigration, 1991) but
inter-annual variability is higher on Borneo (Wong et al.,
2005) may explain why Javan mammals are larger.
Our finding that mammals endemic to the Sundaic region
differ less in size between Borneo and other areas, but that
mammals with wider distribution in Southeast Asia are
smaller on Borneo, provides a possible hint towards a role for
resource limitation in size evolution. Most species widely
distributed in the Southeast Asian region arrived later on
Borneo compared with Sundaic endemics (some of which
may have evolved on Borneo; Meijaard, 2003). These widely
distributed species also tend to be more ecologically versatile
than regionally endemic taxa, usually occurring across a
greater range of habitats than Sundaic endemics, which tend
to be closely associated with forests (Meijaard et al., 2008).
We suggest that this relative ecological flexibility coincides
with a tendency towards greater morphological lability (Meiri
et al., 2007), and that widespread taxa quickly adapt to the
resource-poor local environment of Borneo by reducing their
size. Longer-established Sundaic endemics may have adapted
to Bornean environmental conditions through trenchant
changes in ecology and behaviour (such as diet, physiology
or habitat specialization), not just via size change. In other
words, size change might be a first step in the adaptation
process, followed and tempered by ecological or behavioural
change. This suggests that time since isolation should be
taken into account when predicting patterns of body size
evolution on islands.
In conclusion, while we have shown that large Bornean
mammals are smaller than conspecifics elsewhere, the actual
mechanism or mechanisms underlying this phenomenon
remain speculative. It is also not yet clear whether relatively
small body size characterizes other groups of Bornean verte-
brates (e.g. birds, reptiles), though sufficient resources to
evaluate this point are probably available in museum collec-
tions. Continuing examinations of such patterns have a high
potential to further our understanding of the reasons for
change in mammal size on Borneo, and the mechanisms that
promote body size evolution in general.
ACKNOWLEDGEMENTS
We thank Tamar Dayan and Daniel Simberloff for their
support, help and advice. We thank Robert Asher (Museum
fu?r Naturkunde, Humboldt Universita?t zu Berlin), Yang
Chang Man and Norman Lim (Raffles Museum of Biodiver-
sity Research), Judith Chupasko (Museum of Comparative
Zoology), Judith Eger (Royal Ontario Museum), Thor Holmes
(Museum of Natural History, University of Kansas), Paula
Jenkins and Daphne Hills (Natural History Museum,
London), Richard Kraft (Zoologische Staatsamlung Mu?n-
chen), Georges Lenglet (Institut Royal des Sciences Naturelles
de Belgique), Suzanne McLaren (Carnegie Museum of Natural
History), Adri Rol (University of Amsterdam Zoological
Museum), Byrdena Shepherd, Linda Gordon, Don Wilson,
and Lauren Helgen (National Museum of Natural History,
Smithsonian Institution), Chris Smeenk (National Museum of
Natural History ?Naturalis?), William Stanley (Field Museum),
Clara Stefen (Staatliche Naturhistorische Sammlungen, Dres-
den), Ray Symonds (Zoology Museum, Cambridge Univer-
sity), Ge?raldine Veron (Mus?eum National d?Histoire
Naturelle, Paris) and Darrin Lunde, Nancy Simmons and
Eileen Westwig (American Museum of Natural History) for
their invaluable help during data collection. We thank Gavin
Thomas and Ally Phillimore for advice and discussion. We are
grateful to Alison Boyer, Joaqu??n Hortal and an anonymous
referee for important comments on an earlier version of this
paper.
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SUPPLEMENTARY MATERIAL
The following supplementary material is available for this
article:
Appendix S1 Body masses and mammal distribution.
Appendix S2 Mammal measurements, dietary data and
geographical distributions.
This material is available as part of the online article from:
http://www.blackwellsynergy.com/10.1111/j.1365-2699.2008.
01897.x (This link will take you to the article abstract).
Please note: Blackwell Publishing is not responsible for the
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the article.
BIOSKETCH
Shai Meiri is interested in the evolution of body size and its
implications, biogeographical correlates of morphology and
the morphological signatures of speciation and community
composition.
Editor: Lawrence Heaney
S. Meiri et al.
1094 Journal of Biogeography 35, 1087?1094
? 2008 The Authors. Journal compilation ? 2008 Blackwell Publishing Ltd