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).
- Biogeographic Regions
- neotropical
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).
- Habitat Regions
- tropical
- Terrestrial Biomes
- rainforest
- Other Habitat Features
- agricultural
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).
- Other Physical Features
- endothermic
- bilateral symmetry
- Sexual Dimorphism
- male larger
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).
- Mating System
- polygynous
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).
- Key Reproductive Features
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
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).
- Parental Investment
- female parental care
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).
- Key Behaviors
- terricolous
- diurnal
- motile
- hibernation
- aestivation
- territorial
- social
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 (
Marmosa 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.
- Communication Channels
- acoustic
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).
- Primary Diet
- omnivore
- Animal Foods
- birds
- reptiles
- Plant Foods
- seeds, grains, and nuts
- fruit
Predation
No predators of tropical ground squirrels have been identified.
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).
- 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.
- 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).
Additional Links
Contributors
Melody Weber (author), Colorado State University, Kate Gloeckner (editor), Colorado State University.
- Neotropical
-
living in the southern part of the New World. In other words, Central and South America.
- introduced
-
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- 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.
- agricultural
-
living in landscapes dominated by human agriculture.
- polygynous
-
having more than one female as a mate at one time
- female parental care
-
parental care is carried out by females
- diurnal
-
- active during the day, 2. lasting for one day.
- motile
-
having the capacity to move from one place to another.
- 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.
- 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
- social
-
associates with others of its species; forms social groups.
- acoustic
-
uses sound to communicate
- omnivore
-
an animal that mainly eats all kinds of things, including plants and animals
- 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.
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
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 .