The Antelope Jack Rabbit (Lepus alleni) Lived in Southeastern North America During the Pleistocene

Today, the antelope jack rabbit is restricted to desert grassland habitat in western Mexico and southern Arizona, but during the Pleistocene it occurred as far east as Florida.  Fossils of this species have been found at 2 sites in Florida, dating to the middle Pleistocene.  Over 50 fossils of unidentified hare species (Lepus sp.) that probably also were antelope jack rabbits have been found at many sites in Florida, dating to the early Pleistocene and the Pliocene.  The early Pleistocene/late Pliocene climate was much drier than it is today, and desert grassland habitat was more prevalent.  Several species of pronghorns lived in the southeast as well.  Antelope jack rabbits gradually declined in abundance and may have disappeared from the southeast completely by the late Pleistocene, but the fossil record is so incomplete that there is no way of knowing exactly when they became extirpated from the region.

The antelope jack rabbit prefers arid habitat and does not need water.  It gets enough moisture from the plants it eats.

 

Modern day range of the antelope jack rabbit.  During the Pliocene and early to mid Pleistocene, it lived as far east as Florida.  It now is relegated to relic status.

 

The antelope jack rabbit’s favorite present day habitat looks like this.  They are most abundant in mesa type vegetation.

 

There are probably several factors explaining the decline of this once more widespread species.  About 300,000 years ago, a prolonged interglacial climate phase occurred.  During interglacials, precipitation increases, causing forests, woodlands, and wet meadows to predominate over arid grasslands.  Antelope jack rabbits are absent from fossil sites in Florida that date to after this prolonged interglacial.  However, this doesn’t mean they became completely extirpated in the region. Antelope jack rabbits may have persisted in relic populations in sandhill areas where the conditions allowed the continued existence of dry scrub habitat.  But these isolated populations would have been more susceptible to diseases.  Tularemia, also known as rabbit fever, is caused by the bacterium, Francisella tularensis.  It is spread through ticks, deer flies and other insects.  This plague causes a high fatality rate among all species of lagomorphs, and there are some regions of the antelope jack rabbit’s present day range where the disease has completely eliminated local populations.  Incidentally, hunters should wear gloves and surgical masks when cleaning rabbits.  If untreated, tularemia has a 7% fatality rate among humans.

 

Climate change combined with disease may have wiped out antelope jack rabbits in the southeast, but if there were still any surviving populations here during the late Pleistocene, the extinction of the megafauna would have been the final blow.  Jack rabbits favor overgrazed habitat. The trampling, feeding, and defecating of large mammals increases the types of forbs and other plants that jack rabbits like to eat.  Herds of mammoth, bison, and horses certainly overgrazed the landscape.  Without the presence of these species, jack rabbit habit was further degraded.

 

Though there were similarities between the modern day arid grasslands of the southwest and the early Pleistocene environment of the southeast, they were not exactly the same.  In the southeast the range of the cottontail rabbit and the antelope jack rabbit overlapped.  Today, the ranges of these 2 species do not overlap at all.  Antelope jack rabbits can live without ever drinking water.  They can get all the moisture they need from their diet which includes green grass, mesquite, and cactus.  (Insects are ingested accidentally.)  Therefore, they can live in areas where water was scarce.  But water holes did exist in Florida during the early Pleistocene, though they were less abundant than they are today.  Alligators, raccoons, and river otters all occur in the early Pleistocene fossil record of Florida.  So antelope jack rabbits did formerly occur in areas where water sources were more available.  This is evidence that some Pleistocene environments just have no modern analogue.

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Tags: antelope jack rabbits in the Florida Pleistocene, Lepus alleni, tularemia