Santa Catarina’s guinea pig is one of the rarest species on the planet because of its very small population size (approximately 42 individuals). It also has one of the smallest geographic distributions of any mammal – less than 10 ha. Its ancestors diverged from the mainland guinea pigs following the isolation of Moleques do Sul Island as a result of rising sea levels some 8,000 years ago. Over this time period the species has evolved a number of characteristics that distinguish it from other guinea pigs: individuals show several adaptations to island life, such as high population density, stable age structure and small home range size. With such a small population size and range the species is particularly vulnerable to threats such as hunting and natural disasters.
Santa Catarina’s guinea pig is regarded as phylogenetically closest to the mainland greater guinea pig, C. magna, from which it supposedly derived after Moleques do Sul Island was isolated by rising sea levels about 8,000 years ago. The two species share many similar morphologic, morphometric, and genetic traits, and are estimated to have diverged from other mammal species in the late Miocene.
The reproduction and growth rates of C. intermedia are reduced, even by caviomorph standards. Reproductive rates are low (78% of pregnant females with a single offspring), young are born quite large (19% of adult females’ weight), and sexual maturity is reached quite late (at around 59 days). The home-range size for C. intermedia (0.17 ha) is small in relation to home-range size for C. magna. These characteristics are consistent with the island syndrome whereby insular rodent populations display a suite of characteristics distinct from continental populations, regarding density (high and stable), age structure (stable and mostly composed of adults), survival rate (high), and home range size (reduced). These characteristics may contribute to the persistence of this species.
Caviids are usually diurnal or crepuscular and do not hibernate. They shelter in burrows that they dig or that are left by other animals. They are generally social, occurring in pairs or in groups. The population density is estimated to be 6.6 individuals/ha. Mammalian predators are absent from Moleques do Sul Island and raptors are the only potential predators.
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