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Echimys semivillosusspeckled tree rat

By Rebecca Adams

Geographic Range

Echimys semivillosus is found across much of northern South America and on Margarita Island. The species occurs from about 10 to 2 degrees N latitude. (Mares and Ojeda, 1982; "Echimys semivillosus - Speckled tree rat", 2004; Nowak, 2004)

Habitat

Echimys semivillosus inhabits thorn, gallery, and dry deciduous forests as well as trees in the South American llanos. The species is relatively rare in the rainforest. It occurs at up to 600 m above sea level. Though it is known to replace Echimys armatus in drier regions, the species also thrives near rivers. In areas where they are common, speckled tree rats can occur at densities of up to 1 individual per 4 hectares. (Eisenberg, 1989; Emmons, 1990; Nowak, 2004)

  • Range elevation
    600 (high) m
    1968.50 (high) ft

Physical Description

Speckled tree rats are comparable in size to other arboreal spiny rats. Head and body length ranges from 200 to 268 mm. Tail length is 210 to 261 mm, or 80 to 120% of head and body length. Ears are 17 to 22 mm long. Height is 36 to 43 mm. Speckled tree rats can weigh anywhere from 194 to 407 g. (Emmons, 1990; Nowak, 1983)

The head, neck, and shoulders of E. semivillosus are usually gray streaked with black. Specimens from Columbia may have a white muzzle and black crown. The back is a uniform gray, flecked with numerous spines. These spines are white-tipped, and may continue down onto the gray-brown rump. Sides are light black or gray. Flatter, more flexible spines run down the shoulder and mid-back and are often completely white. The underbelly of speckled tree rats is white or pale orange in color, and may become gray across the abdomen. Young are gray or yellow-brown. They have soft fur and lack spines. (Emmons, 1990; Nowak, 1983)

Echimys semivillosus has small ears with pale patches behind and below. Whiskers are long, dense, and black. The tail has a thin covering of light brown hairs, but otherwise appears naked and scaly. It is rare to find a speckled tree rat with an intact tail. The vertebrae are unusually brittle – the fifth breaks particularly easily. Cheek-teeth are rooted and flat-crowned. Broad gray or gray-yellow feet have slightly elongated digits and prominent claws adapted to an arboreal lifestyle. (Eisenberg, 1989; Emmons, 1990; Nowak, 1983)

  • Range mass
    0.190 to 0.410 kg
    0.42 to 0.90 lb
  • Range length
    200 to 268 mm
    7.87 to 10.55 in

Reproduction

The mating systems of E. semivillosus have been insufficiently studied. The basic mating pattern of this species remains unknown. (Mares and Ojeda, 1982; "Echimys semivillosus - Speckled tree rat", 2004)

Details on the reproduction of E. semivillosus are lacking. Other hystricognath rodents have extended gestation periods and long estrus cycles. In these animals, a delay of up to 40 days may occur between an infertile estrus and the initiation of a new pregnancy. Speckled tree rats have not been specifically studied in this regard, but it is reasonable to assume they follow the general family pattern. Average number of offspring for E. semivillosus is 2. (Nowak, 2004; Woods, 1982)

  • Breeding interval
    The breeding interval of these animals is not known.
  • Breeding season
    The breeding season for E. semivillosus has not been documented.
  • Range number of offspring
    1 to 7
  • Average number of offspring
    2

Female speckled tree rats birth their young in arboreal dens. The pups are protected in these dens prior to weaning. It is reasonable to assume that in this species, as in other mammals, mothers provide the offspring with food, protection, and grooming. The role of males in parental care is not known. (Nowak, 1983; Nowak, 2004)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

The lifespan of E. semivillosus is unknown. (Mares and Ojeda, 1982)

Behavior

Speckled tree rats are an arboreal species. They create nests by lining hollow trunks or tree cavities with dry leaves. Two nests are often built vertically into one tree, one above the other. The nocturnal rats hide in the upper hole during the day, then come out to forage at night. Echimys semivillosus is said to slink, rather than scamper, along branches.

Nothing is known about the social behavior of these animals. (Eisenberg, 1989; Emmons, 1990; Nowak, 1983; Nowak, 2004)

Home Range

The home ranges of these animals is not known.

Communication and Perception

Speckled tree rats are vocal at night. Their loud nocturnal calls sound similar to cries of "cró, cró" or "tró, tró". (Nowak, 2004)

Although information on communication in E. semivillosus is scant, it is reasonable to assume that they are like other mammals in many regards. They likely have some forms of chemical communication, as scents are commonly used in mammals as a means of individual identification, marking of territories, and part of reproductive behavior. Tactile communication is likely to occur between mothers and their offspring as well as between mates. Visual signals, such as body posture may also be used in social communication.

Food Habits

Echimys semivillosus is primarily frugivorous. Little is known about the species' specific food preferences, but bananas, other fruits, grass, sugar cane, and nuts all make up part of the general diet of Echimyidae. Speckled tree rats feed mainly in the treetops but may also forage on the forest floor. They drink often. (Eisenberg, 1989; Nowak, 1983)

  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit

Predation

Speckled tree rats are visibly spined, which may act as a deterrent to predators. They also have easily fractured tails. These tails are likely to snap in a predator's grip and help the rats avoid capture. Gray, gray-yellow, or gray-brown pelage suggests camouflage within their arboreal habitat. (Emmons, 1990; Nowak, 1983)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Speckled tree rats have never been the subject of a satisfying ecological study. Various predators certainly exploit their presence, and these rats may aid in the dispersal of certain types of seeds. (Mares and Ojeda, 1982; Nowak, 1983; Nowak, 2004)

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

Speckled tree rats are of no known benefit to humanity. (Mares and Ojeda, 1982; "Echimys semivillosus - Speckled tree rat", 2004)

Economic Importance for Humans: Negative

Echimys semivillosus is not known to adversely affect humans. (Mares and Ojeda, 1982; "Echimys semivillosus - Speckled tree rat", 2004)

Conservation Status

Speckled tree rats are currently of Least Concern on the IUCN Red List. CITES does not list the species.

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Rebecca Adams (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

arboreal

Referring to an animal that lives in trees; tree-climbing.

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.

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

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.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

frugivore

an animal that mainly eats fruit

herbivore

An animal that eats mainly plants or parts of plants.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

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.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scrub forest

scrub forests develop in areas that experience dry seasons.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Nature Serve. 2004. "Echimys semivillosus - Speckled tree rat" (On-line). InfoNatura: Birds, mammals, and amphibians of Latin America. Accessed March 24, 2004 at http://www.natureserve.org/infonatura.

Eisenberg, J. 1989. Mammals of the Neotropics: The Northern Neotropics. Chicago & London: The University of Chicago Press.

Emmons, L. 1990. Neotropical Rainforest Mammals: A Field Guide. Chicago: The University of Chicago Press.

Mares, M., R. Ojeda. 1982. Patterns of Diversity and Adaptations in South American Hystricognath Rodents. Mammalian Biology in South America, 6: 393-394.

Nowak, R. 2004. "Arboreal Spiny Rats" (On-line). Walker's Mammals of the World. Accessed March 24, 2004 at http://www.press.jhu.edu/books/walkers_mammals_of_the_world/rodentia/rodentia.echimyidae.echimys.html.

Nowak, R. 1983. Rodentia; Family Echimyidae - Spiny Rats. Pp. 837 in Walker's Mammals of the World, Vol. 2, 4th Edition. Baltimore & London: The Johns Hopkins University Press.

Woods, C. 1982. The History and Classification of South American Hystricognath Rodents: Reflections on the Far Away and Long Ago. Mammalian Biology in South America, 6: 377-392.

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