A comparison of the plains viscacha (Lagostomus maximus) and the black-tailed prairie dog (Cynomys ludovicianus)

(writing in progress)

Two rodents invite comparison, viz.

The former is a hystricomorph (https://en.wikipedia.org/wiki/Hystricomorpha) belonging to the Chinchillidae (https://en.wikipedia.org/wiki/Chinchillidae), whereas the latter is a sciuromorph (https://en.wikipedia.org/wiki/Sciuromorpha) belonging to the Sciuridae (https://en.wikipedia.org/wiki/Squirrel).

The two species are comparable because both are

  • the largest rodents in their habitats (which are mainly mesic and treeless in both cases),
  • herbivorous (with green grass as a staple), to the degree of being regarded as unwelcome competitors for domestic livestock,
  • burrowing (mainly for the excavation of permanent living quarters)
  • colonial (with several family groups sharing a single system of burrows),
  • sexually dimorphic (with males more massive than females),
  • precocial (with large, well-developed newborns), and
  • unusually vocal for rodents (with various calls used socially and in reaction to predators),

However, the plains viscacha is the more specialised species in its role as a herbivore, and the more aberrant w.r.t. rodents in general.

This is because the plains viscacha

  • has about five-fold the body mass of the black-tailed prairie dog, as well as being the more sexually dimorphic of the two,
  • has a diet more strictly herbivorous (and graminivorous) than that of the black-tailed prairie dog,
  • forms and maintains lawns,
  • is caecotrophic (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8208658/), as opposed to having hindgut fermentation without caecotrophy in the case of the black-tailed prairie dog, and
  • forages throughout the year, as opposed to spending the winter partly in torpor in the case of the black-tailed prairie dog.

with caecotrophic digestion

Nocturnal vs diurnal

Unlike the black-tailed prairie dog, the plains viscacha forages gregariously.

Publicado el septiembre 4, 2023 12:32 MAÑANA por milewski milewski

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Two points to note re skeleton of plains vizcacha https://www.alamy.com/stock-photo-skeleton-of-viscacha-77314951.html:

a) skull is large relative to rest of body, suggesting chewing power, perhaps analogous with Equidae
b) tail is fragile at fourth caudal vertebra (Jackson et al. 1996, Mammalian Species no. 543), allowing something approaching autotomy (https://en.wikipedia.org/wiki/Autotomy) as an anti-predator adaptation.

Publicado por milewski hace 11 meses

I find it notable for the plains viscachas to form and maintain lawns, what an interesting rodent.

Publicado por paradoxornithidae hace 10 meses

@paradoxornithidae

...which leads me to wonder: is there any other species of rodent or lagomorph, worldwide, that forms and maintains lawns? Or is it the case that, although some rodents/lagomorphs forage for grass on lawns, the lawns concerned are in every case formed by other animals (potentially including geese)?

The following spp. of Chloephaga, which are potentially lawn-formers, occur in Buenos Aires province, making them at least partly sympatric with the plains viscacha:
https://www.inaturalist.org/taxa/7117-Chloephaga-picta
https://www.inaturalist.org/taxa/7114-Chloephaga-poliocephala
https://www.inaturalist.org/taxa/7116-Chloephaga-rubidiceps

I wonder what the relationship is/was, between Chloephaga and the plains viscacha, in forming and maintaining the lawns around viscacheras. Perhaps the rodent grazes on these lawns by night, whereas the birds graze on the same lawns by day? Or is it the case that Chloephaga tends to graze on poorly-drained parts of the Pampas, while the plains viscacha is restricted to the well-drained parts of the Pampas?

I think it is safe to assume that Chloephaga and Lagostomus beling to the same guild (grazers of short grass), but it would be interesting to know a) the degree of original sympatry, b) the degree of co-occurrence at a fine scale, c) the degree of dietary overlap, and d) if there is significant co-foraging, which species is the more causal in terms of forming lawns in the first place.

Publicado por milewski hace 10 meses

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