Megafauna Habitat Modification and Pleistocene Capybaras in Southeastern North America

Since 1970, dry tropical forests in the Grand Chaco region of Paraguay have rapidly been transformed into pasture for cattle.  Though this change has been detrimental for many species of wildlife, it has benefited capybaras (Hydrochoerus hydrachaeris).  According to Juan Krauer who wrote his PHD dissertation about capybara range expansion in the Grand Chaco, ranchers provide capybaras with food by planting nutritious grasses, and the rodents utilize the artificial ponds that help water cattle.  Ranchers also suppress the population of predators that would otherwise reduce capybara numbers.  It occurred to me that this manmade landscape mirrors the situation extinct species of capybaras enjoyed in southeastern North America during the Pleistocene.  Mammoths and mastodons killed trees while foraging, allowing grass and herbs to grow free of shade; they dug down to the water table during droughts, creating standing bodies of water; and they chased away predators.  Some paleoecologists have suggested the extinction of the Pleistocene megafauna had a negative cascading effect on many smaller organisms.  This may be true for the extinct species of North American capybaras.  Without the presence of mammoths, mastodons, and ground sloths the habitat preferred by capybaras was replaced by closed canopy forests in many areas.  The remaining available habitat became more limited in extant, perhaps making capybaras more vulnerable to human hunting pressure.

Capybara (Hydrochoerus hydrochaeris), Corrientes, Argentina. Is the largest living rodent in the world. Capybara are semi-aquatic mammals found wild in much of South America. Capybaras are herbivores, grazing mainly on grasses and aquatic plants. Image by Andres Morya

 

http://www.gettyimages.com/detail/news-photo/capybara-is-the-largest-rodent-in-the-world-grazing-next-to-news-photo/460612790

http://www.gettyimages.com/detail/news-photo/capybara-is-the-largest-rodent-in-the-world-grazing-next-to-news-photo/460612790

http://www.gettyimages.com/detail/news-photo/capybara-is-the-largest-rodent-in-the-world-grazing-next-to-news-photo/460612790

Photo of capybaras grazing with cattle in the 3 links. (All 3 links are the same photo…I can’t delete the other 2 links and the photo won’t directly show up on  my blog.) The transformation of dry tropical forest to pastureland has allowed capybaras to expand their range in South America.  This suggests the likelihood that capybaras benefited from megafaunal habitat modification in southeastern North America during the Pleistocene.

There were 2 species of capybaras living in southeastern North America during the Pleistocene.  Holmes’s capybara (Hydrochoerus holmesi) and Pinckney’s capybara (Neochoerus pinckneyi) were likely common in suitable habitat in Florida and the coastal plain of South Carolina, Georgia, and Texas.  Fossil specimens of both species have been found at numerous sites in all 4 states, ranging temporally from the late Pliocene to the late Pleistocene.  Capybaras colonized the region after a land bridge formed connecting North America with South America.  Capybaras descend from rodents that rafted to the latter continent from Africa well over 10 million years ago.  Because both species survived for over 2 million years in southeastern North America, I think climate change was not a factor in their extinction.  Capybaras survived dozens of dramatic shifts in climate but became extinct when man appeared in the archaeological record.

Fossil Capybara Maxilla

Cheek teeth and jaw bone of Neochoerus pinckneyi

In his classic book Pleistocene Mammals of North America Bjorn Kurten wrongly states “the present distribution of Hydrochoerus suggests that the extinct species must have lived in North America when winters, even in Florida, were warmer than they are now…” The present day range of the extant species of South American capybara includes regions that have a climate similar to Florida and the coastal plain of Georgia, South Carolina, and Texas.  Freezing temperatures regularly occur in northern Argentina and Ecuador during winter.  Capybaras live in regions where winter lows have reached below 20 degrees F, so they could potentially live in Florida today.  However, northern Argentina is the southern limit of their range– prolonged cold spells seem to be a limiting factor on their distribution.  North American capybaras probably had the capability of enduring colder weather than their modern cousins.  Neochoerus pinckneyi was significantly larger than the present day South American species.  The former averaged 200-250 lbs compared to an average of 100 lbs for the present day species.  The larger size may have helped them retain body heat better than their South American relatives.  Moreover, both North American species lived for over 2 million years in the southeast where they surely evolved adaptations to the long term vicissitudes of the local climate.

Capybaras graze in meadows, bed down in the woods, and spend much of their time in water.  They require habitat that offers all 3 of these environments.  They use water to escape from predators and to cool down during the heat of the day.  They are not as helpless as they look for they are fast runners and swimmers, and they have thick hides.  Nevertheless, jaguars were likely their most dangerous enemy in North America during the Pleistocene.  The extinction of capybaras here probably contributed to the extirpation of jaguars in this region.

https://www.youtube.com/watch?v=n1iCxqXaVJE

This could have been a scene along the Altamaha River in Georgia 13,000 years ago.  Jaguars hunted capybaras for hundreds of thousands of years here.

Abundant rivers, oxbow lakes, creeks, and beaver ponds offered plenty of aquatic habitats for capybaras in Georgia, South Carolina, and Texas; and in Florida the many lakes and springs there were the perfect refugia for them.  North American capybaras were well adapted to the mosaic of habitats that existed during the Pleistocene.  During stadials braided river channels surrounded by wet meadows or dry prairies occurred all along river valleys from the lower piedmont to the ocean.  The many creeks in Georgia consisted of long chains of beaver ponds, some of which filled with sediment to become grassy marshes–another capybara-friendly habitat.  Capybaras grazed with long-horned bison and horses in wet pine savannahs, an ancient environment created by lightning-ignited wild fires.  And there were the aforementioned natural pastures resulting from megafauna foraging.  Capybaras themselves transformed their own environments into closely cropped lawns.  This attracted many species of birds such as robins, blackbirds, and cowbirds.  Capybaras are considered the ecological equivalents of hippos.

Did capybaras ever colonize the piedmont region of the south?  The fossil record of this region is too meager to know for sure (there is only 1 site). During the warmest of climate phases they may well have.  The exact northern limits of their range fluctuated with changing climate cycles.

References:

Krauer, Juan

“Landscape Ecology of the Capybara”

PHD Dissertation Kansas State 2009

Kurten, Bjorn; and Elaine Anderson

Pleistocene Mammals of North America

Columbia University Press 1980

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