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Spermophilus adocetustropical ground squirrel

By Melody Weber

Geographic Range

Tropical ground squirrels (Spermophilus adocetus) are endemic to the mountainous Balsas Basin region in Mexico, including the states of Jalisco, Michoacan, Mexico City, and Guerrero. Smaller populations of this species have also been identified outside of these areas. These isolated cases have been attributed to the tendency for the tropical ground squirrels to be kept as pets by humans outside of the Balsas Basin region. Thus, the expanded distribution of tropical ground squirrels can be attributed to the release of such pets (Ceballos, 2014). (Ceballos, 2014)

Habitat

Tropical ground squirrels tend to stay underneath shelter such as rocks, shrubs, or crops that are close to or enveloped by deciduous jungle, farmland, or xeric scrubland (Ceballos, 2014). Tropical ground squirrels scavenge for fruits, plant sprouts, and seeds throughout their environment. They thrive in habitats ranging from 200 to 1,200 m above sea level (Ceballos, 2014). (Ceballos, 2014)

  • Range elevation
    200 to 1200 m
    656.17 to 3937.01 ft

Physical Description

Tropical ground squirrels are generally buffish-grey in color and range in size from 131.9 to 168.3 mm for females and 150.2 to 175.5 mm for males (Thorington et. al 2012). They are distinguishable from closely-related species by their ear size. They are also a slightly paler shade of grey than other similar species. Tropical ground squirrels have bronze pelage on either side of their heads in addition to closed supraorbital foramina (Thorington et. al 2012). Their abdomens are most commonly light yellow. This color extends ventrally to the inside of their legs. Tropical ground squirrels weigh from 163 to 250 g (Ceballos, 2014). (Ceballos, 2014; Thorington, et al., 2012)

  • Sexual Dimorphism
  • male larger
  • Range mass
    163 to 250 g
    5.74 to 8.81 oz
  • Range length
    131.9 to 175.5 mm
    5.19 to 6.91 in

Reproduction

The mating system of tropical ground squirrels is unknown. In another Spermophilus species, Ictidomys parvidens, females compete with other females for space and resources to provide for prospective offspring. Male reproductive success has been cited to favor a polygynous system, where males mate with multiple females throughout their breeding season (Schwanz et al., 2016). (Schwanz, et al., 2016)

No reproductive data has been acquired for tropical ground squirrels. However, species closely related to tropical ground squirrels reproduce several times throughout the year, with those times depending mostly upon climate, the presence of predators, and available food sources. Males of these species reach sexual maturity at around eight months and females reach sexual maturity at ten months. The interestrous interval, or time between viable egg production, spans from 76.5 to 146 days. Gestation lasts an average of 48 days and, after young are born, mothers lactate for approximately 52 days. Tropical ground squirrels will yield anywhere from one to three litters per year with one to two young per litter (Waterman, 1996). (de Grammont and Cuaron, 2016; Waterman, 1996)

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • Average gestation period
    48 days
  • Average age at sexual or reproductive maturity (female)
    6 months
  • Average age at sexual or reproductive maturity (male)
    8 months

Female tropical ground squirrels aggregate in burrow clusters of one to three individuals, which are dispersed with males intermediating the clusters. Females almost exclusively care for juveniles, which involves providing food and shelter to young as they develop (Waterman, 1996). (Waterman, 1996)

Lifespan/Longevity

Lifespan and longevity information for tropical ground squirrels is currently unreported.

Behavior

Tropical ground squirrels have been reported to damage agricultural areas by eating crops. This behavior has given them a reputation as a pest species, but this reputation has not significantly impacted population sizes. Tropical ground squirrels are often most active during the mid-morning hours - from 9:00 to 11:00 am. They are reported to enter periods of aestivation and hibernation (Ceballos, 2014).

Home Range

There is no information regarding the average home range of tropical ground squirrels.

Communication and Perception

Tropical ground squirrels frequently interact with other species in their habitats; they have known sympatric relationships with grayish mouse opossums (Tlacuatzin canescens), Michoacan deer mice (Osgoodomys banderanus), painted spiny pocket mice (Liomys pictus), and Allen's wood rats (Hodomys alleni) (Ceballos, 2014). Tropical ground squirrels are known to vocalize using high pitched calls when near humans (Thorington et. al 2012). They perceive their environment through sight, smell, touch, taste, and hearing. (Thorington, et al., 2012)

Food Habits

Tropical ground squirrels are omnivorous. Their primary diet consists seeds and fruits of the genera Prunus, Prosopis, Acacia, and Crescentia in addition to corn, beans, and sorghum crops, often retrieved from prominent agricultural areas. Tropical ground squirrels rely on their naturally occurring food sources when crops they typically utilize are not growing (Thorington et. al 2012). No research on the predation tactics of tropical ground squirrels has been conducted. However, a study assessing the predation tactics of related species of ground squirrels, Spermophilus citellus and Spermophilus beecheyi, found that they consume prey such as snakes, lizards, and birds (Callahan, 1993). (Callahan, 1993; Thorington, et al., 2012)

  • Animal Foods
  • birds
  • reptiles
  • Plant Foods
  • seeds, grains, and nuts
  • fruit

Predation

No predators of tropical ground squirrels have been identified.

  • Known Predators
    • No known predators

Ecosystem Roles

Tropical ground squirrels are one of eleven mammal species cited to live in the Transvolcanic Belt of Mexico. As consumers of seeds, tropical ground squirrels have the potential to spread small clumps of uneaten seeds throughout their habitat, thereby acting as seed dispersers for several plants.

Ectoparasites have been theorized to use tropical ground squirrels as a host species; in these theoretical parasitic relationships, tropical ground squirrels are vital to sustaining the vitality of their ectoparasites (Thorington et. al 2012). Through burrowing, tropical ground squirrels alter the topography of their environment and aerate the soil (Thorington et. al 2012). As predators, tropical ground squirrels play a role in controlling the population sizes of potential prey items (Callahan, 1993). (Callahan, 1993; Thorington, et al., 2012)

Commensal/Parasitic Species
  • Ectoparasites

Economic Importance for Humans: Positive

Tropical ground squirrels have predatory habits that likely ensure the populations of their prey sources do not grow to unstable levels. As a result, humans are less likely to encounter such species in their communities. Furthermore, information about tropical ground squirrels has been used along with other information about their habitats for educational purposes. (Thorington, et al., 2012)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

Tropical ground squirrels can have unfavorable impacts on local economies due to the fact that they routinely invade agricultural areas, destroying crops and reducing agricultural yields. In order to reduce the amount of tropical ground squirrels infiltrating their land, farmers spend money to repel them, further harming profit margins (Thorington et. al 2012).

  • Negative Impacts
  • crop pest

Conservation Status

Tropical ground squirrels are abundant in their respective habitats and thus the official status provided by the IUCN Red List is “least concern". Their populations are currently stable. In regards to conservation, tropical ground squirrels are considered to be a “key species” for conservation in the Transvolcanic Belt of Mexico (Thorington et. al 2012). (de Grammont and Cuaron, 2016)

Contributors

Melody Weber (author), Colorado State University, Kate Gloeckner (editor), Colorado State University.

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

agricultural

living in landscapes dominated by human agriculture.

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

diurnal
  1. active during the day, 2. lasting for one day.
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.

female parental care

parental care is carried out by females

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

motile

having the capacity to move from one place to another.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

polygynous

having more than one female as a mate at one time

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.

sexual

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

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

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

References

Callahan, J. 1993. Squirrels as Predators. Great Basin Naturalist, Vol. 53: No. 2: 138-141. Accessed March 26, 2019 at https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=2835&context=gbn.

Ceballos, G. 2014. Mammals of Mexico. Baltimore, Maryland: The Johns Hopkins University Press. Accessed February 26, 2019 at https://books.google.com/books?id=UrvxBQAAQBAJ&pg=PA163#v=onepage&q&f=false.

Schwanz, L., W. Sherwin, K. Ognenovska, E. Lacey. 2016. Paternity and male mating strategies of a ground squirrel (Ictidomys parvidens) with an extended mating season. Journal of Mammology. Accessed May 06, 2019 at https://watermark.silverchair.com/gyv204.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAAkMwggI_BgkqhkiG9w0BBwagggIwMIICLAIBADCCAiUGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMkFw5AXLfbELYt0XcAgEQgIIB9nLn3lHcl9gJJfa_zbR7qFXigTfw0hOGFwC7DrprO_j5VSzR2bE_W1SOAhI_hEYuHtdiRaIQbc-5IUU8J00GJB0bl28bAIoI3Vs2PLl_CBjRLJ72CnTYbJeO6HPHEQkraWy9jgKjEkjdmRB0nFFOUrIWO9JPyRTeWvMSWgjVudrwCeiagZKJTWwL4BUI0zmSiYQnw8NZ7ZbuQjpsUCR-LETOBSkAbxGia1Mle4-seJ5bZIsSoDfOuaUrlpA131AI5aSC81BuIx4Hqi942_AbMzjBhdccFIj237KhA5KpN_xoZKQIFCUbyZoYHvJtznep9dMxyf8yoMTAiLrybkG0KrotThkiWNi-ju2788qMs1-YMafhbWf2QZJq0RQtRYORTFH9suOphAVZaUBKHbaRGn8gUYY3n6PPdJDVcFKH3fM8qTwz7GuNzwC-V7KXaG9sN16XgCddZA30F1Np4G_wIN1xyorgXDlbssoWfLKE3odJyD0T-Ia7sSAlGVElnKYvsn4cT0-x11ObruHlnRCmFTKzdCPWJ5qcsmP8SoV2SAalM65wmH-GeZEEbPaFEQ_o428oGJ5ktLUHQSvtPM0FImWUaDRGJp9JjBjyz_AceglPR268GCvZVLtMFgznaHVHfhP8XoTcvEz2kB-vpf2mbg68lcXsJ5E.

Thorington, R., J. Koprowski, M. Steele, J. Whatton. 2012. Squirrels of the World. Baltimore, Maryland: The Johns Hopkins University Press. Accessed February 26, 2019 at https://books.google.com/books?id=7PeYX8PwBxUC&pg=PT301#v=onepage&q&f=false.

Waterman, J. 1996. Reproductive Biology of a Tropical, Non-Hibernating Ground Squirrel. Journal of Mammology, Vol. 77: Issue 1: 134-140. Accessed March 26, 2019 at https://watermark.silverchair.com/77-1-134.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAAlgwggJUBgkqhkiG9w0BBwagggJFMIICQQIBADCCAjoGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMSOQxhM2RD6tchxKLAgEQgIICC1oI3un0nyDkE58gzYUL2EYpg4aitUKBbwqWf1NCYuCfnm1HNsMSBI0vNFYyPYNQQ0bgj2fHNjKobS9rxFgiKF29BqsyGCIGG-lfRdm9Sd5Gtxv2JU30IZqgVH-ZZ68wEnAET0vAb9jJ5jTZcM2curHqnO2upzwi1PUdShLOGysP_WqxjBL4cY2y86xte0hIPyUhQzH_2jTNgajRWNWHHkVxgfKE612oZHBfHqZ-KQ1lGBoLdFLbLK2aCIS3QMp9_Z8T7dpoggzMP37myrAZZtWYK8YTsMhhTc03hsHue84S989ZW-RpVUOgXutu7kf108hK9KKydTb7EvwJsKs6eekDwaVAIvCtXqomjYFlh499EWAu_e_B3U27d5SfEtheJoVmlCvEonOKbVvtHXe1E-SWsksvzDaPSH3bHPUT3EMTD7lHLW9joj63H5m_9UtBUGXCoj6MpNgRZTXyQRX5bzqDAxyOxEgbLEC9mB-FA_9XTFOzUTsboCDRFCTbOkAOI4EPfT2RLCZJ8RqB67nbfzaGTqPpn1Taaykp8r9M28VdjkdeEAoAqDRSBjEOMtClyi6uROjuoZmMVU4b8GZkGvcHx7KMp46PgjOf90b91lX3-z9z2X2RXU_kNfcX_PB7LzNMyQw4q8HX7nMU26t6fqvPlBnQHYut_HNLpHhlt2_Ztssl7KbEhkEQIQM.

de Grammont, P., A. Cuaron. 2016. "Notocitellus adocetus" (On-line). IUCN Red List. Accessed March 05, 2019 at https://www.iucnredlist.org/species/20477/22265744.

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