Geographic Range
Gymnuromys roberti
, or the voalavoanala, is found in Eastern Madagascar, where it ranges from the Northern
Highlands to the southern limits of the Anosyenne Mountains.
- Other Geographic Terms
- island endemic
Habitat
Gymnuromys roberti
occupies lowland and montane humid forests. Its also commonly found in the Reserve
Naturelle Integrale d'Andohahela, the Reserve Speciale d'Anjanaharibe-Sud, and the
Parc National de Marojejy of Madagascar.
Gymnuromys roberti
can be found at elevations ranging from 500 m to 1,625 m, but usually resides between
900 m and 1,625 m. It lives in burrows near fallen trees, which can be up to one
meter deep and terminate in a food storage chamber.
- Habitat Regions
- tropical
- terrestrial
- Terrestrial Biomes
- forest
- rainforest
- mountains
Physical Description
Gymnuromys roberti
is a medium-sized rodent with rat-like features. Head-body length ranges from 149
to 175 mm, and its tail ranges from 176 to 197 mm (approximately 110 to 115% of the
head/body length). This species also has long, wide hind feet. Dorsal pelage is
typically slate grey, and ventral pelage is greyish white with a slight silvery sheen.
The vibrissae are long and dark, ranging in length from 50 to 60 mm. Its tail has
little hair on it and is grey on top and lighter grey or white underneath and the
tip can be completely white. The ears are ovular and project out from the head.
Gymnuromys roberti
shows moderate variation in mass, ranging from 100 to 155 g. Sexual dimorphism has
not been reported in this species.
The skull of
Gymnuromys roberti
(
dorsal view
,
ventral view
,
lataral view
) has a smooth braincase, reduced auditory bullae, a narrow hourglass-shaped interorbital
region, short incisive foramina, and no sub-squamosal foramen. They have
hypsodont
or high crowned
molars
, and the upper and lower molars increase in size from the front to the posterior
of the mouth, unlike most
Muroidea
. The skull of
Gymnuromys roberti
is similar to those in the genus
Eliurus
, except for the lack of a sub-squamosal foramen.
Gymnuromys roberti
most closely resembles
Eliurus majori
with respect to size, tail length, and greyish pelt. These two species can be distinguished
by the tuft of hair at the end of
E. majori
's tail, which is not present in
G. roberti
. The tail of
E. majori
(120% of the head/body length) is also significantly longer that that of
G. roberti
(110 to 115% of the head/body length).
- Other Physical Features
- endothermic
- homoiothermic
- bilateral symmetry
- Sexual Dimorphism
- sexes alike
Reproduction
There is no information available concerning the mating system of
Gymnuromys roberti
.
Other than anecdotal accounts of captive animals, relatively little is known about
the breeding behavior of
Gymnuromys roberti
. Females are thought to produce very small litters. Two separate accounts have
found female specimens pregnant with two embryos each, and in both accounts the females
were discovered between June and July. Males are thought to be sexually active between
October and December.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- viviparous
There is no information available concerning parental investment in
Gymnuromys roberti
. As a with all mammals, however, mothers nurse their young until weaning.
- Parental Investment
- female parental care
-
pre-fertilization
- provisioning
-
protecting
- female
-
pre-hatching/birth
-
provisioning
- female
-
protecting
- female
-
provisioning
-
pre-weaning/fledging
-
provisioning
- female
-
protecting
- female
-
provisioning
Lifespan/Longevity
No information is available on the lifespan of Gymnuromys roberti .
Behavior
Perhaps due to its nocturnal lifestyle, there is little information concerning the
behavior of
Gymnuromys roberti
. It lives in burrows near fallen trees, which can be up to one meter deep and terminate
in a food storage chamber.
Home Range
There is no information available concerning the home range of Gymnuromys roberti .
Communication and Perception
There is no information available concerning communication and perception in
Gymnuromys roberti
. It is nocturnal, which may indicate an increased dependence on its auditory, olfactory,
and haptic senses. In addition to these, its closest relatives rely on their sense
of sight as well.
Food Habits
Gymnuromys roberti
forages for food in the leaf litter at the base of trees, where it eats fallen seeds
and fruits. Also, it stores seeds and fruits in an underground chamber at the end
of its burrow.
- Plant Foods
- seeds, grains, and nuts
- fruit
- Foraging Behavior
- stores or caches food
Predation
There is no information available concerning the major predators of
Gymnuromys roberti
.
Ecosystem Roles
Gymnuromys roberti
is an herbivore that primarily consumes seeds and fruit, which they store in their
burrows. Thus, is likely that they play an important role in their local ecosystem
as seed dispersers. Food caches may be forgotten, or a cache owner may die before
it is depleted. It is also possible that many seeds are lost while individuals are
en route to their cache site. There is no information available concerning parasites
specific to this species. The burrows of
Gymnuromys roberti
may help aerate soil and increase water penetration throughout their geographic range.
- Ecosystem Impact
- disperses seeds
- soil aeration
Economic Importance for Humans: Positive
There are no known positive effects of Gymnuromys roberti on humans. However, local economies that depend on forest resources may yield indirect economic benefits from seed dispersal and burrowing by G. roberti .
Economic Importance for Humans: Negative
There are no known adverse effects of Gymnuromys roberti on humans. However, as seed predators this species may create a problem for grain farmers throughout its native range.
Conservation Status
Based on trapping efforts throughout its range in Madagascar,
Gymnuromys roberti
has never been particularly common. Previously,
G. roberti
was listed as vulnerable on the IUCN's Red List of Threatened Species. In 2008,
this species was downgraded from vulnerable to least concern and it appears to be
somewhat tolerant of habitat change. At present, population trends of
G. roberti
are unknown. Potential threats include habitat loss due to agricultural expansion
and contraction of diseases (e.g.,
plague
) from introduced species such as
Rattus rattus
.
Gymnuromys roberti
may also be suffering from increased resource competition with
R. rattus
.
Additional Links
Contributors
Stephanie Boyle (author), University of Michigan-Ann Arbor, Phil Myers (editor), University of Michigan-Ann Arbor, John Berini (editor), Animal Diversity Web Staff.
- Ethiopian
-
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- island endemic
-
animals that live only on an island or set of islands.
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- terrestrial
-
Living on the ground.
- forest
-
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
- rainforest
-
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
- mountains
-
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
- endothermic
-
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
- bilateral symmetry
-
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- iteroparous
-
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- female parental care
-
parental care is carried out by females
- fossorial
-
Referring to a burrowing life-style or behavior, specialized for digging or burrowing.
- nocturnal
-
active during the night
- motile
-
having the capacity to move from one place to another.
- stores or caches food
-
places a food item in a special place to be eaten later. Also called "hoarding"
- soil aeration
-
digs and breaks up soil so air and water can get in
- herbivore
-
An animal that eats mainly plants or parts of plants.
- frugivore
-
an animal that mainly eats fruit
- granivore
-
an animal that mainly eats seeds
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
References
Carleton, M., S. Goodman. 2004. The Natural History of Madagascar . Chicago: The University of Chicago Press.
Carleton, M., S. Goodman. 2000. Rodents of the Parc National de Marojejy, Madagascar. Fieldiana, Zoology , 97: 231-263.
Garbutt, N. 2007. Mammals of Madagascar: A Complete Guide . United States: Yale University Press.
Goodman, S., M. Carleton, M. Pidgeon. 1999. Rodents of the Reserve Naturelle Integrale d'Andohahela, Madagascar. Fieldiana, Zoology , 94: 217-250.
Goodman, S., M. Carleton. 1998. The Rodents of the Reserve Speciale d'Anjanaharibe-Sud, Madagascar. Fieldiana, Zoology , 90: 201-221.
Gunther, A., W. Carruthers, W. Francis. 1896. The Annals and Magazine of Natural History, including Zoology, Botany, and Geology . London: Taylor and Francis.
Musser, G., M. Carleton. 2005. Mammal Species of the World: A Taxonomic and Geographic References . Baltimore: The Johns Hopkins University Press.
Nowak, R. 1999. Walker's Mammals of the World . Baltimore and London: The Johns Hopkins University Press.
Vaughan, T., J. Ryan, N. Czaplewski. 2011. Mammalogy . Sudbury, MA: Jones and Bartlett Publishers, LLC.
2010. "The IUCN Red List of Threatened Species" (On-line). Accessed March 12, 2011 at http://www.iucnredlist.org/apps/redlist/details/9581/0 .