The Biogeography of Volcano Rabbit (Romerolagus diazi )
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One of the world’s endangered species, the volcano rabbit (see Figure 1) or Romerolagus diazi, is a little known creature that resides on only four volcanoes in Mexico. I chose this rabbit because of my combined interest in lagomorphs and endangered species. Hopefully this paper will inform the reader about the volcano rabbit and bring realization about the greater problem of possible extinction. R. diazi may not have a huge presence, such as the panda or tiger, but it does deserve the right to live.
Figure 1, http://www.animalinfo.org/image/romediaz2%20j%2014.jpg Kingdom: Animalia SPECIES DESCRIPTION/NATURAL HISTORY Romerolagus diazi, or the volcano rabbit, is a small rabbit, with only the pygmy rabbit being smaller. Short, round ears and short legs characterize the volcano rabbit (see Figure 2). The fur is short and dense with the top and sides of the rabbit being dark brown to black (Chapman and Flux, 1990 and Davis and Demello, 2003).
Figure 2, http://www.animalinfo.org/image/romediaz1%20j%2012.jpg The volcano rabbit lives in a distinct habitat in central Mexico. They are "found between 2,800 and 4250m in elevation inhabiting pine forests (Pinus) with dense undergrowth of bunch grass ("zacaton") and rocky substrates" (Chapman and Flux, 1990). Generally the location experiences winter drought and summer rain. The most important feature of R. diazi's habitat seems to be the bunch grass. Distribution of the volcano rabbit appears to correlate with the density of the bunch grass, perhaps providing the rabbit with safety and nesting sites (Hoth et al. 1987). Feeding habits are mostly unknown. However research finds that R. diazi eat the "zacaton" grasses. They "select the green and tender young leaves of grasses, biting the base and lower edges of the clump" (Chapman and Flux, 1990). The social organization of R. diazi is in need of research. However groups of two to five rabbits have been reported (Chapman and Flux, 1990). In captivity groups of six comprised of two males and four females formed, with only one male and one or two females breeding in each group (Chapman and Flux, 1990). Also in captivity the females were found to be aggressive towards both males and females (Chapman and Flux, 1990). Males never incited aggression against a female and the dominant member of the group was always a female (Chapman and Flux, 1990). Volcano rabbits can breed throughout the year, but there is a distinct reproductive peak in the warm, rainy summer (Cervantes, 1990). The gestation period lasts an average of 38-40 days and "compared to other lagomorphs is longer than most Sylvilagus and Ochotona, but shorter than in most Lepus" (Cervantes, 1990). The average litter size for R. diazi is 2.1 (Cervantes, 1990). Newborn rabbits are born completely covered with fur, but with their eyes closed (Cervantes, 1990). Their eyes open in about 4-8 days but they stay in the nest for 14 days after birth (Cervantes, 1990). A unique behavior of the volcano rabbit is the tendency to utter high-pitched, penetrating calls (Cervantes, 1990). Two calls have been reported, "one a squeaking noise like someone rubbing a wet thumb over a balloon and a short, high-pitched bark" (Cervantes, 1990). If alarmed the volcano rabbit gives a sharp call and hurries to a burrow. No other member of the family Leporidae is vocal (Cervantes, 1990). The volcano rabbit, Romerolagus diazi, is endemic to and located only on the slopes of four volcanoes (see Figure 3) in central Mexico (Chapman and Flux, 1990 and Hoth et al. 1987). These volcanoes (Pelado, Tlaloc, Popocatepetl, Iztacohuat) are part of the transverse neovolcanic belt (TNB), which is south of Mexico City (Chapman and Flux, 1990 and Hoth et al. 1987). The total area of distribution is about 386 km2 (Velàzquez, 1994). This geographic distribution is discontinuous with Volcan Tlaloc situated 40 km west of Popocatepetl and V. Pelado being 20 km west of V. Tlaloc (Hoth et al. 1987).
Figure 3, Present distribution of the volcano rabbit, Chapman and Flux, 1990 In terms of biogeography, Romerolagus diazi occurs within these core areas due to the "density of zacaton grass ground cover" (Hoth et al. 1987). Because the volcanoes act as "islands" it makes plants and animals, like R. diazi, endemic to these specific locations (Hoth et al. 1987). However, human activity is currently the dominating force determining the volcano rabbit’s distribution. Habitat destruction and hunting continue to be major threats to its survival (Hoth et al. 1987). Hoth et al. (1987) states clearly, "The restricted areas of zacaton/forest habitat are being continually eroded by a combination of encroaching agriculture, sprawling urbanization, the uncontrolled burning of ‘zacaton’ grasses to promote new growth of grazing pasture for cattle and sheep, plus the exploitation of zacaton for the manufacture of household brushes" (Hoth et al. 1987). The result of research by Hoth et al. (1987) shows that R. diazi has vanished from locations within the TNB where it had been previously found, such as the eastern slopes of Iztaccihuatl and the Nevado de Toluca. Residents from Nevado de Toluca say that the rabbits have been absent for 15-20 years (Hoth et al. 1987). However, small scattered populations have been found outside of the core areas (Hoth et al. 1987). These groups are separated from core populations by barriers of freeways and contrasting habitat (Hoth et al. 1987). Because these populations are so small and scattered, it makes them extremely vulnerable (Hoth et al. 1987). According to Chapman and Flux (1990) volcano rabbits
are in captivity at three facilities: Jersey Wildlife Preservation
Trust, Chapultepec Zoo, and Central Institute for Experimental Animals,
Japan. "The Chapultepec colony, where the animals are grouped
in outdoor enclosures planted with clumps of "zacaton"
grasses, bred particularly well for the first couple of years but
infant mortality has been very high" (Chapman and Flux, 1990). The volcano rabbit, Romerolagus diazi, is a member of the order Lagomorpha and family Leporidae. Originally lagomorphs were classified as rodents and it wasn’t until 1912 that the distinction was made between lagomorphs and Rodentia (Chapman and Flux, 1990). Lagomorphs are different from other rodent-like mammals because they have a second set of incisors, known as "peg" teeth, directly behind the front upper incisors (Chapman and Flux, 1990). Compared to rodents there are relatively few lagomorph species and the question is why (Chapman and Flux, 1990). Most likely lagomorphs diversified slowly and conservatively in early geological time which led to "bounding locomotion in the rabbits and hares" (Chapman and Flux, 1990). All the Leporidae, including rabbits and hares, are designed for speed to evade predators. The long hind legs are adapted to cursorial or bounding locomotion (Chapman and Flux, 1990). Lagomorphs and, more specifically, Leporidae are known for their large ears and acute hearing. The ears can rotate and move to sense danger (Chapman and Flux, 1990). According to research done in Eurasia the species diversity of lagomorphs slowly increased during the Pleistocene (Averianov, 2001). During the early Pleistocene some relict genera went extinct (see Figure 4), such as Pliopentalagus and Alilepus, and in the Middle Pleistocene Sericolagus became extinct (Averianov, 2001). The Holocene is one of thriving growth and biological advancement in phylogenetically young lagomorphs, such as Leporinae " a subfamily of Leporidae (Averianov, 2001).
Figure 4 Evolutionary Tree, Chapman and Flux, 1990 Specifically, for the genus Romerolagus, no
fossil records have been found (Cervantes et al. 1990).
As Figure 4 shows, R. diazi, along with most rabbits and
hares, descended from Alilepus. By some scholars R. diazi
is considered to be "the most primitive of living rabbits and
hares" (Chapman and Flux, 1990). As mentioned above, the volcano rabbit is considered an endangered species due to human causes such as habitat destruction and urban sprawl. Hunting also continues to be a threat, despite new hunting laws making it illegal (Chapman and Flux, 1990). Conservation recommendations to facilitate survival include more research, more awareness, and preservation. Several scholars realize the immediate need to preserve and research the zacaton-forest vegetation that R. diazi is so dependant on (Ceballos et al. 1998; Chapman and Flux, 1990; Hoth et al. 1987). This vegetation region is important not only for R. diazi, but for other endemic species (Chapman and Flux, 1990). A balance between wildlife protection and use of resources needs to be made (Chapman and Flux, 1990). Once protected areas have been set up good management practices must be implicated; often supervision and enforcement is minimal (Ceballos et al. 1998 and Chapman and Flux, 1990). Suggested management includes prohibiting hunting and controlled burning to coincide with other areas (Chapman and Flux, 1990). Planning and management go hand in hand with education and public awareness. Majority of locals are unaware that the volcano rabbit is a protected species (Chapman and Flux, 1990). People in or near core areas of zacaton need to be informed about "the impact of land use methods" (Chapman and Flux, 1990). Awareness at the national and international level is essential as well (Chapman and Flux, 1990). The populations of R. diazi are captivity are also of tremendous value. They help to promote public awareness and offer educational opportunities (Chapman and Flux, 1990). Further research of R. diazi should include the dynamics
of the zacaton-forest and its relationship with the volcano rabbit
(Hoth et al. 1987). Also more study is needed on the population
and social organization, the evolutionary history, its history of
restricted distribution, and the fossil history via pollen analysis
(Hoth et al. 1987). Ceballos, Gerardo, Pilar Rodriguez, and Rodrigo A. Medellin, 1998. "Assessing Conservation Priorities in Megadiverse Mexico: Mammalian Diversity, Endemicity, and Endangerment." Ecological Applications vol.8: pp. 8-17. Averianov, Alexander, 2001. Pleistocene lagomorphs of Eurasia.
Deinsea Cervantes, Fernando A., Consuelo Lorenzo, and Robert S. Hoffmann, 1990. "Romerolagus diazi." Mammalian Species vol. 360: pp. 1-7. Chapman, Joseph A., and John E. C. Flux, 1990. Rabbits, Hares and Pikas: Status Survey and Conservation Plan. ICUN/SSC Lagomorph Specialist Group. Davis, Susan E., and Margo Demello, 2003. Stories Rabbits Tell. New York, Lantern Books. Hoth, J., A. Velazquez, F. J. Romero, L. Leon, M. Aranda, and D. J. Bell, 1987. "The Volcano Rabbit-A Shrinking Distribution and A Threatened Habitat." Oryx vol. 21: pp. 85-91. Massicot, Paul. (2003, September, 3). Animal Info " Volcano Rabbit." http://www.animalinfo.org/species/romediaz.htm. September 15, 2003. Velàzquez, Alejandro, 1994. "Distribution and Population
Size of Romerolagus Diazi on El Pelado Volcano, Mexico." Journal
of Mammalogy vol. 75: pp. 743-749.
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