Probability of Competition between Introduced and Native Rodents in Madagascar: An Estimation Based on Morphological Traits/sissetoodud Ja Aborigeensete Nariliste Vahelise Konkurentsi Toenaolisus Madagaskaril: Morfoloogilistel Tunnustel Pohinev Hinnang

Article excerpt

INTRODUCTION

To avoid competition, coexisting species use various resources that usually require different morphological adaptations (reviewed by Begon et al., 1990; Dayan & Simberloff, 1998; Moulton et al., 2001). For example, arboreal mammals need curved and sharp claws, while fossorial mammals require claws that are straight and blunt. Two animal species with a similar body form but different body sizes may avoid competition by using food items (Gittleman, 1985; Dayan & Simberloff, 1994) and shelters (burrows, rock crevices, tree hollows etc.) of different dimensions.

Several authors (Grant, 1972; Strong et al., 1979; Simberloff & Boecklen, 1981; Duncan & Blackburn, 2002) criticized the importance of interspecific competition. Begon et al. (1990, p. 738) concluded that even when interspecific competition is important, it affects only interactions between members of the same guild and even within a guild only those species closest together are likely to compete. Therefore, it is not always certain that the morphological overlap between two coexisting species leads to interspecific competition, but we can assume that morphologically different species are very unlikely to compete. These considerations were taken into account here to estimate the probability of interspecific competition between introduced and native rodents in Madagascar.

There are 9 genera and 24 species of native rodents in Madagascar (Goodman & Soarimalala, 2005; Goodman et al., 2005; Musser & Carleton, 2005), all belonging to the same endemic subfamily of morid rodents: the Nesomyinae. Their monophyletic origin, however, is a matter for discussion and was neither clearly confirmed nor rejected (Jansa et al., 1999; Jansa & Carleton, 2003a; Musser & Carleton, 2005).

The number of introduced species of rodents in Madagascar is three: the black rat Rattus rattus, the brown rat R. norvegicus, and the house mouse Mus musculus (Garbutt, 1999); all three are synanthropic species with worldwide distribution. The brown rat in Madagascar is restricted to urban environments, while the black rat is found throughout the island, occupying a variety of habitats from human dwellings to pristine rainforests (Goodman, 1995). However, the abundance of R. rattus increases with the level of habitat disturbance (Lehtonen et al., 2001). The oldest record of R. rattus in Madagascar is from an 11th-14th century Islamic archaeological site in the northern part of the island (Rakotozafy, 1996; Radimilahy, 1997). An allozymic study demonstrated that specimens of R. rattus collected in different habitats and altitudes in Madagascar all belong to the same species and present the same diploid number (2n = 38) (Duplantier et al., 2003).

The house mouse is found in houses, rice fields, savannas, and marshes, but never in closed forests (Langrand & Goodman, 1997; Rakotondravony & Randrianjafy, 1998; Lehtonen et al., 2001). A mitochondrial study showed that the house mouse in Madagascar originated from the Arabian Peninsula in a single colonization (Duplantier et al., 2002).

The introduction of alien rodents may threaten native rodent species of Madagascar (Goodman, 1995). The more so as in certain intact areas of primary forest 96% of the rodents captured were R. rattus (Goodman et a1., 1997). It was suggested that R. rattus competes with nesomyine rodents as a result of overlap in their food preferences (Goodman & Sterling, 1996). However, more detailed field studies are needed to clear up this competition hypothesis. Steps in this direction were taken by Ramanamanjato & Ganzhorn (2001) and Ganzhorn (2003). Ganzhorn (2003) stated that for the time being it is impossible to evaluate the effects of introduced rats on the native mammal fauna of Madagascar.

The main goal of this work is to provide a preliminary estimation of the potential for interspecific competition between introduced and native rodents in Madagascar. Regarding the scarcity of data on the ecology of Nesomyinae, this estimation would hardly be done on the basis of ecological data. Thus, we use the degree of ecomorphological similarity between introduced and native Malagasy rodents as a measure of the probability of competition between them. In doing so, we proceeded from the suggestion that the more similar these species are, the more strongly they may compete for living resources.

MATERIAL AND METHODS

Specimens examined

A total of 87 introduced and 62 nesomyine rodent specimens were measured, including representatives of all genera of the Nesomyinae except Hypogeomys, Monticolomys, and Yoalavo (Tables I-III of the Appendix). In total, data on 11 species of native Malagasy rodents are used here. Other nesomyine species were excluded because of insufficiency of data (Monticolomys, Yoalavo, Brachytarsomys villosa, Brachyuromys ramirohitra, Macrotarsomys petteri, Nesomys lambertoni, Hypogeomys antimena, and some Eliurus species). However, data on the length of the head and body (HB) for most of these excluded species were obtained from the literature and used for comparison of size.

Specimens of R. rattus were collected by J. T. Lehtonen in Ranomafana National Park in the eastern humid forest of Madagascar between September and November 2000. Unfortunately, we did not have access to any Madagascar specimens of R. norvegicus and M. musculus, that is why our data on these species belong to the European specimens collected from Estonia. We assumed that the external and cranial proportions did not differ significantly between European and Malagasy populations of the same species.

The deficiency of the available material and our intention to use samples that were as homogeneous as possible (in terms of sex, age, and geography) resulted in a small sample size for some species. We believe that these small homogeneous samples reveal general tendencies better than large but heterogeneous ones. The results may be verified later using more representative data.

The specimens of Nesomynae used in this study are from the collections of the Museum of Natural History, London; Museum National d'Histoire Naturelle, Paris; and the Finnish Museum of Natural History, Helsinki (collected by J. T. Lehtonen). The specimens of R. norvegicus and M. musculus are from the Zoological Museum of the University of Tartu, Estonia.

Measurements, abbreviations, and estimation of qualitative characters

A total of 19 measurements were used in this study: 8 external, 4 skeletal, and 7 craniodental. All characters used are ecology-dependent. They were selected from a larger number of characters in the course of a previous study by comparison of morphological traits and ecology in different species of rodents (see Miljutin, 1997, 1999 for details). These characters, as well as certain qualitative characters, may serve as morphological indicators of ecological strategies. The measurements were taken using a ruler and dial callipers graduated to tenths of millimetres through a lens. The angles were measured with a protractor. Standard external measurements (W, HB, T, E, and HF) were mostly obtained from specimen labels. The symbols of measurements and their meanings are explained below.

External measurements:

W--weight

HB--head and body length: the distance from the tip of the nose to the base of the tail

T--length of tail: the distance from the base of the tail to its tip without terminal hairs

E--ear length: the distance from the basal notch to the tip without terminal hairs (standard measurement)

HF--length of hind foot: the distance from the heel to the tip of the longest digit without claw (standard measurement)

FF--length of forefoot: the distance from the notch between the radius and corpus to the tip of the longest digit without claw. The notch may be located in dead animals or study skins by touching the area with a finger. In the birch mice it more or less coincides with the most proximal end of the inner metacarpal pad

Vib--length of vibrissae: the length of the longest vibrissa from base to tip in natural position

UM--length of forefoot claw: the distance from the base of the longest claw at its inferior surface to the tip.

Skeletal measurements:

Fe--length of femur: the distance from the most proximal surface of the caput to the distal surfaces of the condylae, parallel to the femur's axis

Ti--length of tibia: the greatest length of the tibia parallel to its axis

Hu--length of humerus: the greatest length of the humerus parallel to its axis

Ra--length of radius: the greatest length of the radius without the styloid process. Craniodental measurements:

CBL--condylo-basal length: the distance from the border between the anterior surface of the upper incisors and intermaxilla to the posterior surfaces of the occipital condyles measured parallel to the cranial axis

LR--length of rostrum: the distance from the tip of the nasal bones to the anterior edge of the zygomatic arch, measured level with the nasals and parallel to the cranial axis

ZB--zygomatic breadth: the greatest breadth across the zygomatic arches

BIT--breadth across incisor tips: the distance across the tips of the incisors

LMT--alveolar length of maxillary toothrow: the distance from the anterior edge of the alveolus of the maxillary toothrow's first tooth to the posterior edge of the alveolus of the third molar

HMd--height of mandibular corpus: measured perpendicular to the masticatory surface of the mandibular toothrow from the anterio-dorsal part of the first molar to the ventral surface of the mandibular corpus

ACP--angle of condylar process: the angle between the tangent to the ventral surface of the mandibular corpus parallel to the masticatory surface of the mandibular toothrow and the line connecting the tangent's contact point with the axis of the mandibular condyle.

One qualitative feature was used in this work: the development degree of the tail cover. The different states of this character were provided with the following values: 0 = tapering tail without elongated hairs; 2 = tail with terminal tuft of elongated hairs, and 4 = bushy tail (not found in Malagasy rodents). We estimated the development of the tail cover in species of Eliurus and Macrotarsomys as 2. In all other Malagasy rodents it is 0.

Data processing

Conversion of raw data to ratios

To enable comparisons of species of different size, absolute values were converted to ratios. For this the absolute value of each external and skeletal character was divided by HB and the absolute value of the craniodental character was divided by CBL. The result was multiplied by 100 to express it as a percentage. To distinguish an absolute value from its ratio, an apostrophe (') was used for the ratio. For example, E is the absolute length of the ear in millimetres, while E' is its percentage of the length of the head and body (HB).

Estimation of similarity

For the estimation of similarity between species we used cluster analysis (described in Sneath & Sokal (1973) and statistical manuals). Two procedures were made: (1) ranging of character values and (2) calculation of the distances between species. Ranging is necessary for equalizing the raw data in gross size and variability. Otherwise characters with larger size and higher variability (e.g. length of tail) would obtain a greater statistical weight than the smaller and less variable characters (e.g. length of ear). For ranging, the ratios from Tables I-III were processed using the formula: Xr = [(X' - [X'.sub.min])/([X'.sub.max] - [X'.sub.min])] X 4, where X' is the ratio and Xr its ranged value. This formula differs from those usually used (Sneath & Sokal, 1973) having two peculiarities. Firstly, the maximum and minimum values here are not those of the sample but of the majority of rodents (Table 1). Namely, the minimum values are for rodents in general, and the maximum values reflect a specialized condition of characters. As a specialized condition of a character we accepted the value about 75% of its actual maximum in rodents. The value 75% was arbitrarily selected, just because it is exactly between 50% (medial development of a character) and 100% (maximal development of a character). The actual maximum values are the means for species, not individual records. They were obtained from our data base on rodent morphology. Secondly, the results of ranging division were multiplied not by 100 as usual, but by 4, which is why the results normally range from 0 to 4 (or may exceed 4 in the case of an extraordinarily large value of a character) (Table 2). The first modification makes the results more meaningful in an ecological sense and comparable with data on other rodents. Indeed, if we considered the values of a few species with extreme morphology as maximum, we would conceal the important differences between hundreds of rodent species and might draw wrong ecological conclusions. For example, the ecological differences between animals with the relative tail length equal to 150% and 200% (both are highly specialized) are very small if any, while animals with the tails 50% and 100% have a completely different ecology. In both cases the tail length difference is 50%. If we take 200% as a maximum value, then the medial or unspecialized condition would be 100%. It is a completely wrong interpretation, because the rodents with such a long tail are certainly specialized. If we take 150% (75% of 200) as a maximum value, then the medial (unspecialized) condition would be 75% - the value we find in the brown rat, a classical example of an unspecialized rodent. The second modification, multiplying by 4, enables using both quantitative and coded qualitative data in the common data matrix. In the case of qualitative traits, it is usually easy to estimate the minimal (0), medial (2), and maximal (4) condition of the trait. We may use 1 when we hesitate between 0 and 2, and 3 when we hesitate between 2 and 4. To represent quantitative data in comparable size we should consider their maximal values as equal to 4.

The Manhattan (city-block) distances between species were calculated using unweighted pair-group average linkage (UPGA) (Sneath & Sokal, 1973). For this, the ranged values of 12 morphological characters: 6 external and 6 craniodental ones (from Table 2) were used. The forefoot length and the skeletal measurements were omitted from calculations because of insufficiency of data. The distances were calculated separately for external characters and for craniodental ones. Because the value of Manhattan distances depends on the number of characters concerned, the distances are expressed here in a more comparable way--as a percentage of the maximally possible distance. Since the maximum possible distance for a single character is equal to 4, the maximum possible distance for all characters used is obtained by multiplying the number of characters by 4. In our case it is 24 (6 x 4 = 24) both for external and craniodental characters. For a verbal interpretation of distances we recognized five degrees of similarity (external or craniodental): (1) no similarity (dissimilarity is 50% or more - species are more dissimilar than similar), (2) very low similarity (49.9-37.5%), (3) moderately low similarity (37.4-25.0%), (4) moderately high similarity (24.9-12.5%), and (5) very high similarity (12.4-0%). The number of similarity degrees is just arbitrary, and the interval between them (12.5%) is dictated by the number of degrees (50% : 4 = 12.5%).

RESULTS AND DISCUSSION

The initial data are presented in Tables I-III of the Appendix, ranged data in Table 2, the size differences in Table 3, and dissimilarity distances in Table 4. Ecological interpretations of morphological characters are based on the ecological meaning of characters used (see Miljutin, 1997 for details). Ecological data are from Garbutt (1999), if not indicated otherwise.

Potential competitors with introduced rodents

Hutchinson (1959) stated that in order to coexist, two species need a minimum size ratio of approximately 1.3 in the linear dimension. Bowers & Brown (1982) in their study of interspecific competition in desert rodents regarded species as being of similar size if their body mass ratios were less than 1.5. We used here the length of the head and body for comparison of size, because it has smaller intraspecific variability than mass. We did not use the criterion of Hutchinson because (1) it is not universal (Ganeshaiah, 1999) and (2) we do not have empirical data, and so is safer to use an arbitrary criterion than an empirical one based on completely different taxa.

Based on the size differences (Table 3) and distances (external and craniodental) between species (Table 4), we compiled preliminary lists of potential competitors by selecting pairs of species with the degree of similarity more than very low (with at least one distance or size difference less than 37.5%). Doing so we obtained the following groups of species for further comparison:

(1)Rattus rattus-R. norvegicus, Brachytarsomys albicauda, B. villosa, Brachyuromys betsileoensis, B. ramirohitra, Eliurus ellermani, E. grandidieri, E. majori, E. myoxinus, E. petteri, E. tanala, E. webbi, Gymnuromys roberti, Macrotarsomys ingens, Nesomys audeberti, N. lambertoni, N. rufos

(2)Ratius norvegicus -R. rattus, Brachytarsomys albicauda, B. villosa, Nesomys audeberti, N. lambertoni, N. rufos

(3)Mus musculus--Eliurus minor, Macrotarsomys bastardi, Monticolomys koopmani, Yoalavo gymnocaudatus.

Rattus rattus as a potential competitor with other Malagasy rodents

Rattus rattus and R. norvegicus

Comparison. Rattus norvegicus (European) averages about 34% larger than R. rattus. In Europe, however, this difference is smaller (19% in Estonia). The degree of external and craniodental similarity is very high.

Discussion. The competition between synanthropic rats is outside the scope of this study, but the morphological differences between them may serve as a scale for comparison of other species. Laboratory experiments and field observations of synanthropic populations demonstrated that these two species compete for territory and that R. norvegicus, which is on average larger, is competitively dominant over the smaller R. rattus (Barnett, 1958; Miljutin et a1., 1991). In addition, these species successfully coexist under natural conditions due to spatial niche segregation, e.g. in the Transcaucasus (Bernstein, 1959; Kalinin, 1995) and in Australia (Williams et a1., 2003). Therefore, the differences in ecology, behaviour, and morphology between these two species of synanthropic rats allow them to avoid competition under normal conditions but to switch a mechanism of competition in particular situations.

Rattus rattus and Brachytarsomys species

Size and body form. Brachytarsomys species are about 30% larger than R. rattus. The degree of external similarity is very high. Brachytarsomys albicauda differs from R. rattus in having a broader head, shorter ears, and shorter hind feet. Both the forefeet and hind feet of B. albicauda are very broad and they are supplied with large pads. The functional digits terminate in curved claws that are strong and sharp. All these characters indicate a high degree of specialization for arboreal life that parallels the way it nests in tree holes. The feet of R. rattus are slenderer with smaller pads and weaker claws. Both species exhibit specialization for arboreal locomotion, but B. albicauda is more specialized than R. rattus.

Craniodental characters. The degree of craniodental similarity is moderately high. The skull construction of B. albicauda betrays its specialization for a herbivorous (folivorous) diet. It has a short rostrum, broad zygomatic arches, relatively wide incisors, and a long row of molars that have ridged masticatory surfaces with an arvicolinelike enamel pattern. The skull of R. rattus has, in contrast, an elongated shape and bunodont molars. Both features are typical of frugivorous (granivorous) rodents.

Concluding remarks. The craniodental features described above enable us to conclude that Rattus rattus and Brachytarsomys species have rather different diets. The degree of their external similarity suggests that spatial niches of these species may overlap somewhat, but due to larger sizes and higher levels of specialization Brachytarsomys species are probably not threatened by R. rattus.

Rattus rattus and Brachyuromys species

Size and body form. Brachyuromys betsileoensis and B. ramirohitra average about 9% and 10% smaller than R. rattus. The degree of external similarity is moderately high. The two Brachyuromys species are very similar and differ from R. rattus in having a shorter tail, shorter vibrissae, and longer forefoot claws. The proportions of limb segments in B. betsileoensis are similar to those of R. rattus. The forefoot of Brachyuromys, compared with that of R. rattus, is shorter and broader with smaller interdigital pads. The claws are longer and less curved. The relative length and width of the hind foot of Brachyuromys are more or less equal to those of R. rattus, but in Brachyuromys the two proximal interdigital pads and the thenar pad are smaller. The peculiarities of Brachyuromys external morphology reveal its moderate specialization for subterranean (fossorial) life, while R. rattus is a semiarboreal species. As far as we know, Brachyuromys species have never been captured above ground.

Craniodental characters. The degree of Craniodental similarity is moderately high. The Craniodental characters of B. betsileoensis are more dissimilar to those of R. rattus than to those of any other native Malagasy rodent. The skull and dentition of B. betsileoensis differ from those of R. rattus in having a short rostrum, broad zygomatic arches, a more vertical condylar process, wide incisors, and long molar rows. The molars have rather high crowns and their masticatory surface is flat with oblique ridges.

Concluding remarks. The morphology of Brachyuromys demonstrates specialization for a herbivorous diet and a semifossorial locomotion, while R. rattus is a semiarboreal frugivore. Thus, R. rattus and Brachyuromys species show differing ecological specialization, which makes competition between them unlikely. Nevertheless, J. Ryan (unpublished data, cited in Jansa & Carleton, 2003b) suggested that R. rattus may displace B. betsileoensis in rice fields.

Rattus rattus and Eliurus species

Size and body form. All Eliurus species average 8~4% smaller than R. rattus. The degree of external similarity is moderately high in all four species studied. Eliurus species differ from R. rattus in having a tufted tail, longer ears, longer vibrissae, and longer limb segments. Eliurus webbi and E. tanala also have tails that are much longer than those in R. rattus. The forefoot of Eliurus, compared with that of R. rattus, is broader and the forefoot claws are stronger (larger and with a wider base). The forefoot interdigital pads are relatively larger than in R. rattus (E. majori) or about the same size (E. tanala and E. webbi). The hind foot of E. myoxinus (and small E. minor) is broad with large plantar pads, while E. tanala and E. webbi have hind feet that resemble the hind feet of R. rattus and are slenderer than those of E. myoxinus and with smaller pads. Both R. rattus and Eliurus species demonstrate specialization for arboreal locomotion, but Eliurus species are more specialized. It should be noted that Eliurus species vary in their level of specialization. Among the species studied, the morphological characters of E. tanala and E. webbi indicate that they are more terrestrial than the others.

Craniodental characters. The degree of Craniodental similarity is very high. Based on their ecology-dependent Craniodental characters, Eliurus species differ from R. rattus most significantly in their dentition. Eliurus species have short molar rows with low-crowned lophodont teeth. This unusual combination of traits suggests a predominantly frugivorous diet.

Concluding remarks. Both R. rattus and Eliurus species are semiarboreal or arboreal frugivores (in the broad sense) but the latter appear less granivorous and are more specialized for arboreal life. In addition, some Eliurus species are apparently more terrestrial than others. It is likely that the trophic and spatial niches of R. rattus and the larger Eliurus species (especially E. tanala and E. webbi) may overlap, which may lead to interspecific competition.

Rattus rattus and Gymnuromys roberti

Size and body form. Gymnuromys roberti averages only 6% smaller than R. rattus. The degree of external similarity is especially high. The difference in size and external dissimilarity between R. rattus and G. roberti are less than those between R. rattus and any other Malagasy rodents including R. norvegicus. Gymnuromys roberti differs from R. rattus in having relatively longer hind feet, while the differences in the other external characters studied are insignificant. The forefoot of G. roberti is similar in proportion to that of R. rattus, but the claws are less curved and the palmar pads are smaller. The hind feet of these two species are similar in relative broadness, but G. roberti has smaller pads and a slightly shorter fifth digit. These peculiarities of the foot structure of G. roberti indicate that it is more terrestrial than R. rattus. It was suggested that G. roberti do not climb trees (Goodman & Carleton, 1996, 1998; Carleton & Goodman, 2000).

Craniodental characters. The degree of craniodental similarity is very high. The skull of G. roberti has a longer rostrum, while the differences in other proportions are insignificant. Its relatively short molar rows consist of low-crowned molars with a plane masticatory surface and numerous perpendicular ridges. The molars may functionally correspond to the molar teeth of Eliurus and the Myoxidae, thus connecting them with a frugivorous diet.

Concluding remarks. The close morphological resemblance between the generalist frugivore G. roberti and the semiarboreal frugivore R. rattus indicates a close ecological resemblance between them. This makes competition between the two species highly probable, the more so as they are more or less equal in size.

Rattus rattus and Macrotarsomys ingens

Size and body form. Macrotarsomys ingens is about 25% smaller than R. rattus. The degree of external similarity is moderately high. The external dissimilarity between R. rattus and M. ingens is greater than that between R. rattus and any other Malagasy rodent, except M. bastardi. Macrotarsomys ingens differs from R. rattus in having a longer tail, ears, vibrissae, and all limb segments, especially those of the hind limbs. The relative length of the forelimb is 34.6% in R. rattus and 40.2% in M. ingens. The relative length of the hind limb is 57.6% and 72.9%, respectively. The tail of M. ingens has a tuft of elongated hairs on its distal part. The forefeet of M. ingens have relatively longer digits and smaller pads than those of R. rattus. The hind feet of M. ingens are significantly elongated and have small pads. These peculiarities of the foot structure of M. ingens indicate its terrestrial habits and saltatorial locomotion. In addition, the long forefoot digits enable the animal to climb bushes and grasses.

Craniodental characters. The degree of Craniodental similarity is moderately high. The skull of M. ingens has a longer rostrum and wider zygomatic arches than in R. rattus. The molar rows of M. ingens are quite short and consist of low-crowned bunodont molars, which are generally connected with a predominantly granivorous diet.

Concluding remarks. The body structure of M. ingens indicates a high level of specialization for terrestrial locomotion. Despite the possibility of partial overlap of the trophic niches of M. ingens and the black rat, the obvious differences in their locomotor specialization and size make competition between these two species unlikely.

Rattus rattus and Nesomys species

Size and body form. Nesomys species average 5-17% larger than R. rattus. The degree of external similarity is very high. Nesomys species differ from R. rattus in having a slightly shorter tail, longer forefoot claws, and greater length of all limb segments. The last difference is especially striking. The relative lengths of the forelimb and hind limb in N. audeberti are 41% and 73.3%, respectively. Thus, the proportion of limb segments of Nesomys is comparable to that of Macrotarsomys. The feet of Nesomys are slenderer than those of R. rattus. The claws are longer and straighter, the pads are smaller, and the fifth digit is relatively shorter than in R. rattus. These peculiarities of the foot structure of Nesomys testify to a greater degree of terrestriality than in R. rattus and even G. roberti. The radiotracking study of Ryan et al. (1993) showed that the Nesomys species are strictly terrestrial and only rarely move along the tops of fallen logs. In our preliminary cage experiment (Lehtonen et al., unpublished) N. audeberti and N. rufos regularly but awkwardly climbed a metal net wall and a trunk at an angle of 45 degrees, but we have never captured them in trees.

Craniodental characters. The degree of Craniodental similarity is very high or moderately high. The skull of Nesomys has a remarkably long rostrum and slightly broader zygomatic arches than R. rattus. The molar rows are of medium length and the molars are brachyobunodont. Thus, the dentition of Nesomys probably is functionally equivalent to that of R. rattus.

Concluding remarks. The close morphological similarity in size and body proportions between Nesomys species and R. rattus suggests that interspecific competition between them is highly probable, despite the greater terrestriality of Nesomys.

Rattus norvegicus and Mus musculus as potential competitors with other Malagasy rodents

The size of R. norvegicus may make it a potential competitor for R. rattus and Brachytarsomys and Nesomys species. Its relationships with R. rattus were discussed above. Competition with such specialized arboreal rodents as Brachytarsomys, despite their superficial resemblance to the brown rat (external dissimilarity is 7%), is highly improbable. Encounters of R. norvegicus with the forest-dwelling Nesomys are also improbable. Thus, R. rattus is apparently the only rodent that may be threatened by R. norvegicus in Madagascar.

Mus musculus is one of the smallest rodents in Madagascar. The probability of its competition with such highly specialized native small rodents as E. minor and M. bastardi is low. Attention should be focused on its relationships with the relatively recently described M. koopmani and Yoalavo species. It is noteworthy that M. musculus in Madagascar averages 7.4 mm shorter (HB) and 4.0 g lighter (Duplantier et al., 2002) than our specimens from Estonia used in this study.

CONCLUSIONS

The ecomorphological comparison given above supports the probability of interspecific competition between introduced and native rodents in Madagascar. The black rat is not only the most widespread introduced rodent on the island but also the most universally potential competitor.

Based on the degree of dimensional and ecomorphological similarity, we estimate the probability of interspecific competition as (1) very high between R. rattus and G. roberti, (2) high between R. rattus and Nesomys species and between R. rattus and the larger semiarboreal species of Eliurus (E. tanala, E. webbi), (3) moderately low between R. rattus and Brachytarsomys species and between R. rattus and the larger arboreal species of Eliurus (e.g. E. myoxinus), and (4) low between R. rattus and Brachyuromys species and between R. rattus and M. ingens.

Interspecific competition between R. rattus and native Malagasy rodents other than those mentioned above is unlikely. Interspecific competition of R. norvegieus and M. musculus with native Malagasy rodents is also improbable, except possibly for M. musculus and the recently described Monticolomys koopmani and Yoalavo species.

Rattus rattus may not be the stronger competitor with all native rodent species. Among the potential competitors with R. rattus, four species--B. albicauda, B. villosa, N. audeberti, and N. lambertoni--are on average larger than the black rat, which may help them to predominate over R. rattus. All other potential competitors with R. rattus have smaller or equal sizes and may be threatened by the black rat.

We recommend that in further studies special attention be directed to the relationships between R. rattus and two Malagasy rodents: G. roberti and N. rufos. Especially because in Madagascar R. rattus is largely terrestrial and uses the same burrow types as G. roberti and N. rufos (Laakkonen et al., 2003).

ACKNOWLEDGEMENTS

We express our deepest gratitude to the staff of the Laboratoire de Zoologie, Mammiferes et Oiseaux, Museum National d'Histoire Naturelle in Paris, and to the staff of the Vertebrate Department of the British Museum (Natural History) in London for allowing us to study their collections and for the sincere help we received there. Volatiana Rasataharilala and Frangois Zakamanana assisted in the field and Jari Niemela provided constructive advice on drafts of this article. The Association National pour la Gestion des Aires Protegees (ANGAP) allowed J.T.L. to work in Madagascar and the Madagascar Institut pour la Conservation des Environments Tropicaux (MICET) helped with the logistics. A.M.'s visit to the British Museum in 1994 was made possible with the support of the George Soros Foundation. The Finnish Cultural Foundation granted support to J.T.L.'s work in Madagascar. All the above-mentioned persons and organizations are highly appreciated.

APPENDIX

Received 17 December 2007, in revised form 22 Apri12008

REFERENCES

Barnett, S. A. 1958. An analysis of social behaviour in wild rats. Proc. Zool. Soc. London, 130, 107-152.

Begon, M., Harper, J. L. & Townsend, C. R 1990. Ecology: Individuals, Populations and Communities. 2nd edn. Blackwell Science, London.

Bernstein, A. D. 1959. Some peculiarities of the black rat biology in Abkhazia. Bull. MOIP, Otd. biol., 64(1), 5-14 (in Russian).

Bowers, M. A. & Brown, J. H. 1982. Body size and coexistence in desert rodents: Chance or community stmcture? Ecology, 63(2), 39100.

Carleton, M. D. & Goodman, S. M. 1996. Systematic studies of Madagascar's endemic rodents (Muroidea: Nesomyinae): A new genus and species from the Central Highlands. Field. Zool., New Ser., 85, 231-256.

Carleton, M. D. & Goodman, S. M. 1998. New taxa of nesomyinae rodents (Muroidea: Muridae) from Madagascar's northern highlands, with taxonomic comments on previously described forms. Field. Zool., New Ser.,139, 161-200.

Carleton, M. D. & Goodman, S. M. 2000. Rodents of the Parc National de Marojejy, Madagascar. Field. Zool., New Ser., 97, 231-263.

Carleton, M. D. & Goodman, S. M. 2003. Rodentia: Brachytarsomys, white-tailed tree rats. In The Natural History of Madagascar (Goodman, S. M. & Benstead, J. P., eds), pp. 1368-1370. Univ. Chicago Press, Chicago and London.

Dayan, T. & Simberloff, D. 1994. Morphological relationships among coexisting heteromyids: An incisive dental character. Am. Nat., 143, 46277.

Dayan, T. & Simberloff, D. 1998. Size patterns among competitors: Ecological character displacement and character release in mammals, with special reference to island populations. Mammal Rev., 28, 99-124.

Duncan, R. P. & Blackburn, T. M. 2002. Morphological over-dispersion in game birds (Ayes: Galliformes) successfully introduced to New Zealand was not caused by interspecific competition. Evol. Ecol. Res., 4, 551-561.

Duplantier, J. M., Orth, A., Catalan, J. & Bonhomme, F. 2002. Evidence for a mitochondrial lineage originating from the Arabian Peninsula in the Madagascar house mouse (Mus musculus). Heredity, 89, 154-158.

Duplantier, J. M., Catalan, J., Orth, A., Grolleau, B. & Britton-Davidian, J. 2003. Systematics of the black rat in Madagascar: Consequences for the transmission and distribution of plague. Biol. J. Linn. Soc., 78, 335-341.

Ganeshaiah, K N. 1999. How much should the Hutchinson ratio be and why? Oikos, 87, 201-203.

Ganzhorn, J. U. 2003. Effects of introduced Rattus rattus on endemic small mammals in dry deciduous forest fragments of western Madagascar. Anim. Conserv. , 6, 147-157.

Garbutt, N. 1999. Mammals of Madagascar. Pica Press, Sussex.

Gittleman, J. L. 1985. Carnivore body size: Ecological and taxonomical correlates. Oecologia, 67, 540-554.

Goodman, S. M. 1995. Rattus on Madagascar and the dilemma of protecting the endemic rodent fauna. Conserv. Biol., 9(2), 45053.

Goodman, S. M. & Carleton, M. D. 1996. The rodents of the Reserve Naturelle Integrale d'Andringitra, Madagascar. Field. Zool., 85, 257-283.

Goodman, S. M. & Carleton, M. D. 1998. The rodents of the Reserve Speciale d'Anjanaharibe-Sud, Madagascar. Field. Zool., 90, 201-221.

Goodman, S. M. & Schutz, H. 2003. Specimen evidence of the continued existence of the Malagasy rodent Nesomys lambertoni (Muridae: Nesomyinae). Mammalia, 67(3), 44549.

Goodman, S. M. & Soarimalala, V. 2005. A new species of Macrotarsomys (Rodentia: Muridae: Nesomyinae) from southwestern Madagascar. Proc. Biol. Soc. Wash., 118(2), 45064.

Goodman, S. M. & Sterling, E. J. 1996. The utilization of Canarium (Burseraceae) seeds by vertebrates in the RNI d'Andringitra, Madagascar. Field. Zool., 85, 83-89.

Goodman, S. M., Ganzhorn, J. U., Olson, L. E., Pidgeon, M. & Soarimalala, V. 1997. Annual variation in species diversity and relative density of rodents and insectivores in the Parc National de la Montagne d'Ambre, Madagascar. Ecotropica, 3, 109-118.

Goodman, S. M., Rakotondravony, D., Randriamanantsoa, H. N. & Rakotomalala-Razanahoera, M. 2005. A new species of rodent from the montane forest of central eastern Madagascar (Muridae: Nesomyinae: Voalavo). Proc. Biol. Soc. Wash.,118(4), 863-873.

Grant, P. R. 1972. Convergent and divergent character displacement. Biol. J. Linn. Soc., 4, 398. Hutchinson, G. E. 1959. Homage to Santa Rosalia, or why are there so many kinds of animals? Am. Nat., 93, 145-159.

Jansa, S. A. & Carleton, M. D. 2003a. Systematics and phylogenetics of Madagascar's rodents. In The Natural History of Madagascar (Goodman, S. M. & Benstead, J. P., eds), pp. 1257-1265. Univ. Chicago Press, Chicago and London.

Jansa, S. A. & Carleton, M. D. 2003b. Brachyuromys, short-tailed rats or Malagasy voles. In The Natural History of Madagascar (Goodman, S. M. & Benstead, J. P., eds), pp. 1370-1373. Univ. Chicago Press, Chicago and London.

Jansa, S. A., Goodman, S. M. & Tucker, P. K. 1999. Molecular phylogeny and biogeography of the native rodents of Madagascar (Muridae: Nesomyinae): A test of the single-origin hypothesis. Cladistics, 15, 253-270.

Kalinin, A. A. 1995. Interspec~c Relationships Between the Norway and Black Rats. Nauka, Moscow (in Russian).

Laakkonen, J., Goodman, S. M., Duchemin, J.-B. & Duplantier, J.-M. 2003. Trypomastigotes and potential flea vectors of the endemic rodents and the introduced Rattus rattus in the rain- forests of Madagascar. Biodiv. Conserv., 12, 1775-1783.

Langrand, O. & Goodman, S. M. 1997. Inventaire des oiseaux et des micromammiferes des zones sommitales de la Reserve Naturelle Integrale d'Andringitra. Akon'ny Ala, 20, 39-54.

Lehtonen, J. T., Mustonen, O., Ramiarinjanahary, H., Niemela, J. & Rita, H. 2001. Habitat use by endemic and introduced rodents along a gradient of forest disturbance in Madagascar. Biodiv. Conserv., 10, 1185-1202.

Miljutin, A. 1997. Ecomorphology of the Baltic rodents: Body form, ecological strategies and adaptive evolution. Folia Theriol. Est., 3, 1-111.

Miljutin, A. 1999. Trends of specialization in rodents: The birch mice, genus Sicista (Dipodoidea, Rodentia). Folia Theriol. Est., 4, 91-128.

Miljutin, A., Maran, T. & Ohnan, V. 1991. Experimental research of the relationships between the black rat, Rattus rattus, and the Norway rat, R. norvegicus. Folia Theriol. Est., 2, 18-30.

Moulton, P. M., Sanderson, J. G. & Labisky, R F. 2001. Patterns of success in game bird (Ayes: Galliformes) introductions to the Hawaiian islands and New Zealand. Evol. Ecol. Res., 3, 507-519.

Musser, G. G. & Carleton, M. D. 2005. Superfamily Muroidea. In Mammal Species of the World: A Taxonomic and Geographic Reference (Wilson, D. E. & Reeder, D. M., eds), 3rd edn, vol. 2, pp. 894-1531. The Johns Hopkins University Press, Baltimore.

Radimilahy, C. 1997. Mahilaka, an eleventh to fourteenth century Islamic port: The first impact of urbanism in Madagascar. In Natural Change and Human Impact in Madagascar (Goodman, S. M. & Patterson, B. D., eds), pp. 342-377. Smithsonian Institution Press, Washington, DC.

Rakotondravony, A. D. S. & Randrianjafy, R. V. 1998. Especes introduites et endemiques de Madagascar: description, repartition, biologie et ecologie. In Rongeurs et lutte antimurine a Madagascar. Proceedings, pp. 51-76. Tamatave, 6-9 Decembre 1994. DPV/ GTZ (Direction de la Protection dex Vegetaux / Deutche Gesellschaft fiir Technische Zusammenarbeit).

Rakotozafy, L. M. A. 1996. Etude de la constitution du regime alimentaire des habitants du site de Mahilika du XI au XIV siecle a partir des produits de fouilles archeologiques. PhD thesis, University d'Antananarivo.

Ramanamanjato, J.-B. & Ganzhorn, J. U. 2001. Effects of forest fragmentation, introduced Rattus rattus and the role of exotic tree plantations and secondary vegetation for the conservation of an endemic rodent and a small lemur in littoral forest of southeastern Madagascar. Animal Conserv., 4, 175-183.

Ryan, J. M., Creighton, G. K. & Emmons, L. H. 1993. Activity patterns of two species of Nesomys (Muridae: Nesomyinae) in a Madagascar rain forest. J. Trop. Ecol., 9, 101-107.

Simberloff, D. & Boecklen, W. 1981. Santa Rosalia reconsidered: Size ratios and competition. Evolution, 35, 1206-1228.

Sneath, P. H. A. & Sokal, R. R 1973. Numerical Taxonomy. The Principles and Practice of Numerical Classification. W.H. Freeman, San Francisco.

Strong, D. R, Szyska, L. A. & Simberloff, D. 1979. Tests of community-wide character displacement against null hypotheses. Evolution, 33, 897-913.

Williams, R. L., Singleton, G. R. & Dickman, C. R. 2003. The role of interspeciflc competition in determining macrohabitat use by the black rat and brown rat at Bradley's Head, NSW. In Rats, Mice and People: Rodent Biology and Management (Singleton, G. R., Hinds, L. A., Krebs, C. J., Spratt, D. M., eds), pp. 366-369. ACIAR Monograph, 96. Australian Centre for International Agricultural Research, Canberra.

Andrei Miljutin (a[email]) and Jukka T. Lehtonen (b)

(a) Zoological Museum, University of Tartu, Vanemuise 46, 51014 Tartu, Estonia

(b) Faculty of Biosciences, PO Box 56, FIN-00014 University of Helsinki, Finland

([email]) Corresponding author, amiljutin@hot.ee

Table 1. Limits of quantitative character variability (in the
majority of rodents) used for data ranging (in % except for ACP)

                                             Limits of variability

Character                                    Minimum   Maximum

Tail length (T')                                0       150
Ear length (E')                                 0        35
Vibrissae length (Vib')                         5        60
Forefoot claw length (UM')                      0         5
Hind foot length (HF')                         10        40
Forefoot length (FF')                           5        20
Rostrum length (LR')                           15        40
Zigomatic breadth (ZB')                        40        70
Breadth across incisor tips (BIT')              3        10
Length of maxillary toothrow (LMT')             5        25
Height of mandibular corpus (HMd')             10        25
Angle of condylar process (ACP, [degrees])     10        60

Table 2. Ranged data matrix (based on data from Tables I-III of the
Appendix). The abbreviations for the measurements are explained in
Table 1

Species               T'     E'    Vib'   UM'    HF'    Tuft

Rattus rattus        3.0    1.5    2.1    0.6    1.3     0
R. norvegicus        2.1    1.0    1.4    0.6    1.2     0
Mus musculus         2.3    1.8    1.6    0.7    1.3     0
Brachytarsomys       2.8    0.9    1.8    0.6    0.7     0
  albicauda
Brachyuromys         1.4    1.5    0.9    1.2    1.1     0
  betsileoensis
Eliurus minor        2.7    1.9    3.0    0.7    1.5     2
E. myoxinus          2.9    1.8    2.8    0.6    1.3     2
E. tanala            3.5    1.7    2.9    0.8    1.6     2
E. webbi             3.6    1.7    2.8    0.8    1.7     2
Gymnuromys roberti   2.9    1.6    2.4    0.6    1.7     0
Macrotarsomys        3.9    2.8    3.3    1.0    2.6     2
  bastardi
M. ingens            4.2    2.1    2.8    0.8    2.3     2
Nesomys audeberti    2.5    1.4    1.8    1.0    2.1     0
N. rufus             2.5    1.5    1.6    1.0    2.0     0

Species              LR'    ZB'    BIT'   LMT'   HMd'   ACP'

Rattus rattus        1.8    1.5    1.4    2.7    2.2    1.5
R. norvegicus        2.0    1.5    2.1    2.1    2.4    1.5
Mus musculus         1.6    2.1    2.0    2.3    1.8    1.6
Brachytarsomys       0.9    2.8    2.6    2.8    2.9    2.0
  albicauda
Brachyuromys         1.4    3.0    3.4    3.1    2.6    2.2
  betsileoensis
Eliurus minor        2.2    2.1    1.8    2.1    2.0    1.8
E. myoxinus          2.0    1.7    1.7    1.9    1.9    1.7
E. tanala            2.5    1.4    1.7    2.0    1.9    1.7
E. webbi             2.8    1.8    1.5    2.0    1.8    1.7
Gymnuromys roberti   2.6    2.0    1.8    2.2    2.1    1.8
Macrotarsomys        2.8    2.0    1.5    2.1    1.8    1.7
  bastardi
M. ingens            3.5    2.1    1.7    1.8    2.2    1.8
Nesomys audeberti    3.2    2.4    1.7    2.4    2.0    1.5
N. rufus             3.0    2.5    1.5    2.5    1.9    1.6

Table 3. Mean body length of Malagasy rodents and their length
differences

                                      Head and body length
                                         differences, %
                                   [([X.sub.max] - [X.sub.min])/
                                        [X.sub.min]] x 100
                      Mean head
                       and body    Rattus     Rattus       Mus
Species               length, mm   rattus   norvegicus   musculus

Rattus rattus         170.9             0           34        119
R. norvegicus         229.2            34            0        193
Mus musculus           78.1 (a)       119          193          0
Brachytarsomys        221.6            30            3        184
 albicauda
B. villosa              228 (b)        33            1        192
Brachyuromys          157.5             9           46        107
 betsileoensis
B. ramirohitra        155.0 (c)        10           48         98
Eliurus ellermani     152.0 (d)        12           51         95
E. grandidieri        127.3 (d)        34           80         63
E. majori             157.9 (c)         8           45        102
E. minor              102.6            67          123         31
E. myoxinus           140.0            22           64         79
E. petteri            133.0 (d)        28           72         70
E. tanala             146.2            17           57         87
E. webbi              137.3            24           67         76
Gymnuromys roberti    161.0             6           42        106
Hypogeomys antimena   332.1            94           45        325
Macrotarsomys          91.8            86          150         18
 bastardi
M. ingens             136.5            25           68         75
Monticolomys           95.7 (e)        79          139         23
 koopmani
Nesomys audeberti     199.0            16           15        155
N. lambertoni           200 (f)        17           15        156
N. rufus              179.0             5           28        129
Voalavo                87.7 (d)        95          161         12
 gymnocaudatus

(a) Duplantier et al., 2002.

(b) Carleton & Goodman, 2003.

(c) Goodman & Carleton, 1996.

(d) Carleton & Goodman, 1998.

(e) Carleton & Goodman, 1996.

(f) Goodman & Schutz, 2003.

Table 4. Distances between introduced and native species of Malagasy
rodents: E - based on the external characters, C - based on the
craniodental characters (in % of the maximum possible  difference)

                              Rattus       Rattus        Mus
Species                       rattus     norvegicus    musculus

                              E     C      E     C      E     C

Rattus rattus                 0     0      9     7      7    10
R. norvegicus                 9     7      0     0      6     8
Mus musculus                  7    10      6     8      0     0
Brachytarsomys albicauda      7    20      7    19     10    17
Brachyuromys betsileoensis   15    22     10    22     11    20
Eliurus minor                16    10     23     8     17     6
E. myoxinus                  13     8     21     6     16     7
E. tanala                    17    10     26     8     21    10
E. webbi                     17    11     26    11     21    10
Gymnuromys roberti            4    11     12     9      9     8
Macrotarsomys bastardi       30    12     39    11     33     9
M. ingens                    24    16     33    14     27    14
Nesomys audeberti             9    13     10    13      8    11
N. rufus                      9    12     10    15      6    11

Table I. Body weight (W), head and body length (HB), relative
length of the tail (T'), ear (E'),  vibrissae (Vib'), and forefoot
claw (UM') of rodents (in % of HB except W and HB) (mean, standard
deviation, and number and sex of specimens: m - males, f - females,
? - sex unknown)

Species                         W, g                 HB, mm

Rattus rattus            119.0 [+ or -] 19.1   170.9 [+ or -] 9.2
                                (9 m)                 (9 m)
R. norvegicus            343.0 [+ or -] 52.2   229.2 [+ or -] 13.8
                                (5 m)                (57 m)
Mus musculus              16.9 [+ or -] 2.9     85.5 [+ or -] 4.7
                               (16 m)                (21 m)
Brachytarsomys                    -            221.6 [+ or -] 20.3
  albicauda                                          (5 mf)
Brachyuromys                      -            157.5 [+ or -] 6.1
  betsileoensis                                      (6 mf)
Eliurus minor                     -            102.6 [+ or -] 4.3
                                                     (7 mf)
E. myoxinus                       -            140.0 [+ or -] 5.0
                                                     (3 mf)
E. tanala                104.8 [+ or -] 15.2   146.2 [+ or -] 10.2
                               (4 mf)                (6 mf)
E. webbi                          -            137.3 [+ or -] 2.5
                                                     (3 f?)
Gymnuromys roberti                -                161.0 (1 f)
Macrotarsomys bastardi            -             91.8 [+ or -] 4.4
                                                     (14 m)
M. ingens                    60.0 (1 m)        136.5 [+ or -] 19.1
                                                     (2 mf)
Nesomys audeberti            216.0 (1 m)       199.0 [+ or -] 11.2
                                                     (11 mf)
N. rufus                     174.0 (1 m)       179.0 [+ or -] 8.6
                                                     (4 mf)

Species                          T'                   E'

Rattus rattus            113.9 [+ or -] 3.3    13.0 [+ or -] 0.6
                                (8 m)                (9 m)
R. norvegicus             77.8 [+ or -] 4.1    8.9 [+ or -] 0.6
                               (57 m)               (57 m)
Mus musculus              85.6 [+ or -] 6.8    15.6 [+ or -] 0.9
                               (21 m)               (21 m)
Brachytarsomys           103.8 [+ or -] 10.1   7.8 [+ or -] 0.8
  albicauda                    (5 mf)               (5 mf)
Brachyuromys              52.9 [+ or -] 4.2    12.7 [+ or -] 0.8
  betsileoensis                (5 mf)               (6 mf)
Eliurus minor            103.0 [+ or -] 10.2   16.4 [+ or -] 1.1
                               (5 mf)               (6 mf)
E. myoxinus              109.2 [+ or -] 13.1   16.0 [+ or -] 0.4
                               (2 mf)               (3 mf)
E. tanala                132.8 [+ or -] 7.6    14.7 [+ or -] 1.2
                               (4 mf)               (6 mf)
E. webbi                 136.0 [+ or -] 6.9    14.8 [+ or -] 1.4
                               (3 f?)               (3 f?)
Gymnuromys roberti           108.7 (1 f)          13.7 (1 f)
Macrotarsomys bastardi   145.0 [+ or -] 8.8    24.8 [+ or -] 1.4
                               (14 m)               (14 m)
M. ingens                158.4 [+ or -] 2.2    18.0 [+ or -] 1.0
                               (2 mf)               (2 mf)
Nesomys audeberti         94.6 [+ or -] 6.7    12.5 [+ or -] 0.9
                               (11 mf)              (11 mf)
N. rufus                  93.3 [+ or -] 3.9    12.8 [+ or -] 0.8
                               (4 mf)               (4 mf)

Species                        Vib'                UM'

Rattus rattus            33.5 [+ or -] 2.6   0.8 [+ or -] 0.1
                               (9 m)              (9 m)
R. norvegicus            24.0 [+ or -] 2.2   0.8 [+ or -] 0.1
                               (8 m)              (8 m)
Mus musculus             26.6 [+ or -] 2.8   0.9 [+ or -] 0.1
                              (21 m)              (21 m)
Brachytarsomys           30.4 [+ or -] 2.5   0.8 [+ or -] 0.04
  albicauda                   (5 mf)              (5 mf)
Brachyuromys             17.2 [+ or -] 2.1   1.8 [+ or -] 0.2
  betsileoensis               (6 mf)              (6 mf)
Eliurus minor            46.8 [+ or -] 3.0   0.9 [+ or -] 0.1
                              (7 mf)              (7 mf)
E. myoxinus              43.8 [+ or -] 2.7   0.7 [+ or -] 0.0
                              (3 mf)              (2 m)
E. tanala                45.3 [+ or -] 4.4   1.0 [+ or -] 0.2
                              (6 mf)              (6 mf)
E. webbi                 43.7 [+ or -] 0.1   1.0 [+ or -] 0.2
                              (3 f?)              (3 f?)
Gymnuromys roberti          37.9 (1 f)          0.7 (1 f)
Macrotarsomys bastardi   47.2 [+ or -] 6.2   1.3 [+ or -] 0.3
                              (14 m)              (14 m)
M. ingens                43.8 [+ or -] 2.5   1.0 [+ or -] 0.3
                              (2 mf)              (2 mf)
Nesomys audeberti        30.4 [+ or -] 2.0   1.3 [+ or -] 0.2
                              (10 mf)            (11 mf)
N. rufus                 27.5 [+ or -] 2.3   1.2 [+ or -] 0.0
                              (4 mf)              (4 mf)

- No data.

Table II. Relative length of the limb segments of rodents (in % of HB)
(mean, standard deviation, d number and sex of specimens: m - males,
f - females, ? - sex unknown)

                           Femur               Tibia
Species                    (Fe')               (Ti')

Rattus rattus        17.5 [+ or -] 0.5   20.3 [+ or -] 0.6
                           (7 m)               (8 m)
R. norvegicus        15.0 [+ or -] 0.9   17.7 [+ or -] 0.6
                           (8 m)               (7 m)
Mus musculus            16.0 (1 m)          18.9 (1 m)

Brachytarsomys               -                   -
  albicauda
Brachyuromys         16.5 [+ or -] 0.7   19.2 [+ or -] 1.0
  betsileoensis           (5 mf)              (5 mf)
Eliurus minor           18.4 (1 f)          21.7 (1 f)

E. myoxinus          18.3 [+ or -] 0.7   20.3 [+ or -] 0.3
                          (3 mf)              (3 mf)
E. tanala            20.0 [+ or -] 2.4   23.6 [+ or -] 2.1
                          (4 mf)              (4 mf)
E. webbi             20.0 [+ or -] 0.0   23.3 [+ or -] 0.6
                          (2 f?)              (2 f?)
Gymnuromys roberti           -                   -
Macrotarsomys        21.1 [+ or -] 1.2   27.0 [+ or -] 1.3
  bastardi                 (5 m)               (5 m)
M. ingens            20.8 [+ or -] 1.1   25.2 [+ or -] 1.2
                          (2 mf)              (2 mf)
Nesomys audeberti    21.4 [+ or -] 1.3   26.0 [+ or -] 0.4
                           (2 f)               (2 f)
N. rufus             19.6 [+ or -] 1.1   24.6 [+ or -] 1.9
                          (3 mf)              (3 mf)

                         Hind foot            Humerus
Species                    (HF')               (Hu')

Rattus rattus        19.8 [+ or -] 0.9   12.8 [+ or -] 0.5
                           (9 m)               (8 m)
R. norvegicus        18.7 [+ or -] 1.2   12.3 [+ or -] 0.6
                          (57 m)               (6 m)
Mus musculus         19.7 [+ or -] 0.8      12.7 (1 m)
                          (21 m)
Brachytarsomys       14.9 [+ or -] 0.9           -
  albicauda               (5 mf)
Brachyuromys         18.5 [+ or -] 0.7   12.9 [+ or -] 0.7
  betsileoensis           (6 mf)              (5 mf)
Eliurus minor        21.0 [+ or -] 0.9      14.6 (1 f)
                          (7 mf)
E. myoxinus          20.0 [+ or -] 1.3   14.4 [+ or -] 0.7
                          (3 mf)              (3 mf)
E. tanala            22.0 [+ or -] 1.7   15.6 [+ or -] 1.8
                          (6 mf)              (4 mf)
E. webbi             22.6 [+ or -] 0.5   15.1 [+ or -] 0.7
                          (3 f?)              (2 f?)
Gymnuromys roberti      22.4 (1 f)               -
Macrotarsomys        29.3 [+ or -] 1.8   13.9 [+ or -] 1.0
  bastardi                (14 m)               (5 m)
M. ingens            26.9 [+ or -] 2.3   14.8 [+ or -] 0.8
                          (2 mf)              (2 mf)
Nesomys audeberti    25.9 [+ or -] 1.6   15.8 [+ or -] 1.2
                          (11 mf)              (2 f)
N. rufus             25.2 [+ or -] 1.9   14.7 [+ or -] 1.0
                          (4 mf)              (3 mf)

                          Radius             Forefoot
Species                    (Ra')               (FF')

Rattus rattus        12.3 [+ or -] 0.5   9.5 [+ or -] 0.5
                           (8 m)               (9 m)
R. norvegicus        10.7 [+ or -] 0.4   9.0 [+ or -] 0.6
                           (6 m)               (5 m)
Mus musculus            12.0 (1 m)       8.7 [+ or -] 0.7
                                               (7 m)
Brachytarsomys               -                   -
  albicauda
Brachyuromys         12.2 [+ or -] 0.6   8.4 [+ or -] 0.6
  betsileoensis            (3 m)              (2 mf)
Eliurus minor           15.0 (1 f)       10.8 [+ or -] 0.2
                                              (5 mf)
E. myoxinus          13.7 [+ or -] 0.6           -
                          (3 mf)
E. tanala            15.3 [+ or -] 1.7   9.8 [+ or -] 0.6
                          (4 mf)              (4 mf)
E. webbi             15.3 [+ or -] 0.4   10.5 [+ or -] 0.1
                          (2 f?)              (2 f?)
Gymnuromys roberti           -                   -
Macrotarsomys        14.9 [+ or -] 0.6   10.6 [+ or -] 0.5
  bastardi                 (5 m)               (2 m)
M. ingens            14.8 [+ or -] 0.8   10.6 [+ or -] 0.9
                          (2 mf)              (2 mf)
Nesomys audeberti    14.9 [+ or -] 0.7   10.3 [+ or -] 0.4
                           (2 f)              (7 mf)
N. rufus             14.5 [+ or -] 1.0   9.6 [+ or -] 0.3
                          (3 mf)              (2 mf)

- No data.

Table III. Cranial size and proportions of rodents (in % of CBL,
except CBL and ACP) (mean, standard deviation, and number and sex of
specimens: m - males, f - females, ? - sex unknown). Abbreviations of
measurements are explained in Table 1 and Material and Methods

Species               CBL (mm)               LR'

Rattus rattus     38.1 [+ or -] 1.0   31.6 [+ or -] 0.8
                        (8 m)               (8 m)
R. norvegicus     46.3 [+ or -] 2.8   32.4 [+ or -] 0.7
                       (20 m)              (20 m)
Mus musculus      20.3 [+ or -] 0.5   29.9 [+ or -] 1.4
                       (10 m)              (10 m)
Brachytarsomys    43.4 [+ or -] 1.5   25.9 [+ or -] 0.6
  albicauda            (5 mf)              (5 mf)
Brachyuromys      34.3 [+ or -] 1.0   28.9 [+ or -] 1.0
  betsileoensis        (6 mf)              (6 mf)
Eliurus minor     27.3 [+ or -] 0.9   33.7 [+ or -] 1.6
                       (6 mf)              (6 mf)
E. myoxinus       34.5 [+ or -] 1.1   32.2 [+ or -] 1.1
                       (3 mf)              (3 mf)
E. tanala         38.8 [+ or -] 0.7   35.9 [+ or -] 0.8
                       (3 mf)              (3 mf)
E. webbi          35.6 [+ or -] 1.0   37.5 [+ or -] 1.9
                       (3 f?)              (3 f?)
Gymnuromys        36.4 [+ or -] 1.9   36.1 [+ or -] 1.8
  roberti              (5 m?)              (5 m?)
Macrotarsomys     26.4 [+ or -] 0.7   37.7 [+ or -] 2.1
  bastardi             (12 m)              (12 m)
M. ingens         35.4 [+ or -] 1.7   41.6 [+ or -] 0.6
                       (2 mf)              (2 mf)
Nesomys           43.4 [+ or -] 0.9   40.2 [+ or -] 1.6
  audeberti            (5 mf)              (5 mf)
N. rufus          39.9 [+ or -] 0.7   38.6 [+ or -] 0.9
                       (8 mf)              (8 mf)

Species                  ZB'                BIT'

Rattus rattus     51.2 [+ or -] 1.0   5.5 [+ or -] 0.4
                        (8 m)               (8 m)
R. norvegicus     51.2 [+ or -] 2.0   6.6 [+ or -] 0.4
                       (19 m)              (20 m)
Mus musculus      55.5 [+ or -] 1.4   6.5 [+ or -] 0.5
                       (10 m)              (10 m)
Brachytarsomys    61.2 [+ or -] 2.6   7.6 [+ or -] 0.3
  albicauda            (5 mf)              (5 mf)
Brachyuromys      62.4 [+ or -] 1.4   8.9 [+ or -] 0.3
  betsileoensis        (6 mf)              (5 mf)
Eliurus minor     55.9 [+ or -] 2.6   6.1 [+ or -] 0.2
                       (4 mf)              (6 mf)
E. myoxinus       53.0 [+ or -] 1.1   5.9 [+ or -] 0.0
                       (3 mf)               (2 m)
E. tanala         50.6 [+ or -] 1.1   5.9 [+ or -] 0.3
                       (3 mf)              (3 mf)
E. webbi             53.6 (1 f)       5.6 [+ or -] 0.2
                                           (3 f?)
Gymnuromys        55.3 [+ or -] 3.8   6.2 [+ or -] 0.3
  roberti              (4 m?)              (4 m?)
Macrotarsomys     55.3 [+ or -] 1.0   5.6 [+ or -] 0.5
  bastardi             (10 m)              (11 m)
M. ingens         56.1 [+ or -] 0.8   5.9 [+ or -] 0.1
                       (2 mf)              (2 mf)
Nesomys           57.9 [+ or -] 1.1   5.9 [+ or -] 0.4
  audeberti            (4 mf)              (5 mf)
N. rufus          58.8 [+ or -] 1.3   5.6 [+ or -] 0.4
                       (8 mf)              (7 mf)

Species                 LMT'                HMd'

Rattus rattus     18.7 [+ or -] 0.4   18.4 [+ or -] 0.3
                        (8 m)               (8 m)
R. norvegicus     15.5 [+ or -] 0.8   19.0 [+ or -] 1.0
                       (20 m)              (20 m)
Mus musculus      16.5 [+ or -] 0.5   17.0 [+ or -] 0.7
                       (10 m)              (10 m)
Brachytarsomys    19.2 [+ or -] 1.3   20.8 [+ or -] 0.9
  albicauda            (5 mf)              (5 mf)
Brachyuromys      20.5 [+ or -] 1.2   19.7 [+ or -] 0.7
  betsileoensis        (6 mf)              (6 mf)
Eliurus minor     15.3 [+ or -] 0.7   17.6 [+ or -] 0.7
                       (6 mf)              (6 mf)
E. myoxinus       14.5 [+ or -] 0.4   17.3 [+ or -] 0.8
                       (3 mf)              (3 mf)
E. tanala         14.9 [+ or -] 0.7   17.3 [+ or -] 0.3
                       (3 mf)              (3 mf)
E. webbi          14.8 [+ or -] 0.3   16.6 [+ or -] 0.7
                       (3 f?)              (3 f?)
Gymnuromys        15.8 [+ or -] 1.0   17.7 [+ or -] 0.7
  roberti              (5 m?)              (5 m?)
Macrotarsomys     15.7 [+ or -] 0.4   16.7 [+ or -] 0.4
  bastardi             (11 m)              (12 m)
M. ingens         14.2 [+ or -] 1.1   18.2 [+ or -] 1.9
                       (2 mf)              (2 mf)
Nesomys           17.0 [+ or -] 0.7   17.5 [+ or -] 0.5
  audeberti            (5 mf)              (5 mf)
N. rufus          17.7 [+ or -] 0.5   17.2 [+ or -] 0.4
                       (8 mf)              (8 mf)

Species            ACP, [degrees]

Rattus rattus     29.2 [+ or -] 1.8
                        (8 m)
R. norvegicus     29.3 [+ or -] 3.0
                       (20 m)
Mus musculus      30.1 [+ or -] 1.8
                       (10 m)
Brachytarsomys    34.5 [+ or -] 1.3
  albicauda            (5 mf)
Brachyuromys      37.0 [+ or -] 1.9
  betsileoensis        (6 mf)
Eliurus minor     32.0 [+ or -] 2.4
                       (6 mf)
E. myoxinus       30.7 [+ or -] 1.2
                       (3 mf)
E. tanala         31.0 [+ or -] 1.0
                       (3 mf)
E. webbi          30.7 [+ or -] 1.2
                       (3 f?)
Gymnuromys        32.0 [+ or -] 1.4
  roberti              (5 m?)
Macrotarsomys     30.7 [+ or -] 2.0
  bastardi             (11 m)
M. ingens         32.5 [+ or -] 0.7
                       (2 mf)
Nesomys           29.0 [+ or -] 1.7
  audeberti             (5 f)
N. rufus          30.0 [+ or -] 2.5
                       (8 mf)

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