Leporid Species Research Articles

Digestive strategies in two sympatrically occurring lagomorphs

AbstractSeparation of low digestible fibres and fermentation of the digestible part of the food in the caecum is an adaptation of some small herbivores to cope with low‐quality forage. The caecum content is later re‐ingested as soft faeces so that the herbivore can benefit from this protein‐rich material. This is known as caecotrophy and is a common phenomenon in species of leporids, although differences exist between hares and rabbits. Hares have amorphous soft faeces and the amount of soft faeces produced is smaller compared to that of rabbits. Both factors suggest that hares have smaller benefits from re‐ingestion of the caecal contents compared with rabbits and, as a consequence, have a less efficient digestion (mainly of nitrogen) compared to rabbits. The assertion was tested whether digestive efficiency is different between the two herbivores and how this affects the choice of food plants in a natural situation. A feeding trial was conducted using hares and rabbits fed with diets with a range of fibre contents. Dry matter digestibility was not different, but nitrogen digestibility was lower in hares than in rabbits, indicating a less efficient digestion of protein. Both taxa showed a different response to increased fibre content in the diet. Rabbits maximized digestibility by increasing retention time of the food, hares maximized digestion rate by increasing the passage rate of the food through the digestive tract. The daily digestible nitrogen intake was higher in hares Lepus europaeus than that in rabbits Oryctolagus cuniculus, indicating that hares compensated for their lower nitrogen digestibility. Hares were predicted to select for higher quality plant species in a natural situation, but they had, on average, a lower nitrogen and higher total fibre content in their diet compared to sympatrically occurring rabbits. This indicated that hares did not compensate for their lower digestive efficiency by selecting higher quality food plants. The present experiment shows that hares and rabbits have different digestive strategies to cope with low quality forage. Rabbits had a higher N‐digestibility by increasing the retention time, whereas hares appeared to compensate for their lower N‐digestibility by increasing the processing rate, when food quality deteriorated.

Habitat Characteristics of 3 Leporid Species in Southeastern Arizona

Antelope jackrabbits (Lepus alleni), black-tailed jackrabbits (Lepus californicus), and desert cottontails (Sylvilagus audubonii) are sympatric in the southwestern United States. However, how each species uses resources has not been examined. We quantified vegetation characteristics and patterns of habitat use by these 3 species of leporids in the Picacho Mountains, Arizona, USA, May-August 1999 and 2000. All leporids used similar diameters of overhead vegetation cover for above-ground resting sites. Desert cottontails used dense vegetation that was closer to the ground more often thanjackrabbits. Desert cottontails typically built forms in areas with triangle-leaf bursage (Ambrosia deltoidea) and tall plants (>1.5 m) that provided thermal cover but rarely built in areas dominated by mesquite (Prosopis spp.) or creosote bush (Larrea tridentata). Jackrabbits built forms predominantly in mesquite-and creosote-dominated areas. Landscape managers should consider how altered vegetation (i.e., through livestock allotment management plans) can favor 1 leporid species over others.

Multiple substitutions affect the phylogenetic utility of cytochrome b and 12S rDNA data: examining a rapid radiation in leporid (Lagomorpha) evolution.

Partial sequences of two mitochondrial genes, the 12S ribosomal gene (739 bp) and the cytochrome b gene (672 bp), were analyzed in hopes of reconstructing the evolutionary relationships of 11 leporid species, representative of seven genera. However, partial cytochrome b sequences were of little phylogenetic value in this study. A suite of pairwise comparisons between taxa revealed that at the intergeneric level, the cytochrome b gene is saturated at synonymous coding positions due to multiple substitution events. Furthermore, variation at the nonsynonymous positions is limited, rendering the cytochrome b gene of little phylogenetic value for assessing the relationships between leporid genera. If the cytochrome b data are analyzed without accounting for these two classes of nucleotides (i.e., synonymous and nonsynonymous sites), one may incorrectly conclude that signal exists in the cytochrome b data. The mitochondrial 12S rRNA gene, on the other hand, has not experienced excessive saturation at either stem or loop positions. Phylogenies reconstructed from the 12S rDNA data support hypotheses based on fossil evidence that African rock rabbits (Pronolagus) are outside of the main leporid stock and that leporids experienced a rapid radiation. However, the molecular data suggest that this radiation event occurred in the mid-Miocene several millions of years earlier than the Pleistocene dates suggested by paleontological evidence.

Similar Winter Energy Strategies of Grouse, Hares and Rabbits in Northern Biomes

Neutral fat and protein reserves were measured in three species of grouse, cottontail rabbits, snowshoe hares and European hares collected during the mid to late winter period in their natural habitats. Neutral fat levels were measured in arctic hares from the Canadian high arctic during late summer. Sharp-tailed grouse, spruce grouse and ruffed grouse contained, respectively, 2.2, 2.3 and 1.0 g of fat per 100 g fat-free body weight, regardless of sex, year or location. Cottontail rabbits, arctic hares, snowshoe hares and European hares had, respectively, 4.1, 2.5, 2.3-4.1 and 6.9 g of fat per 100 g fat-free body weight. The low values for fat and protein reserves are similar to those reported for other grouse and leporid species in different parts of North America and Scandinavia. Collectively they indicate that species in both taxa have little metabolic resistance to winter fasting and must feed regularly to maintain energy balance. Grouse, hares and rabbits in winter habitats share similar energetic tactics of acquiring small energy reserves, feeding regularly for short periods and emphasize energy conservation rather than energy acquisition. A theoretical model relates the size of energy reserves in these species to the probability and duration of fasts due to severe winter weather, the changing quality of diets, and the probability of predation while amassing reserves prior to winter and using them during winter.

Zależność wielkości areału od ciężaru ciała u zajęcy i królików (Leporidae)

Data for 12 species of leporids (rabbits and hares) indicates that home range size scales allometrically with body mass and is considerably influenced by the positive association between body mass and S, and index of home range overlap. Futhermore, the average area available per conspecific appears to be related to its energy requirements. Becouse behavioral ecology is a key determinant of home range size in many mammals, comparative studies must consider effects of patterns and home range size.

Seasonal Foods of Blacktail Jackrabbits and Nuttall Cottontails in Southeastern Idaho

The diets of blacktail jackrabbits (Lepus californicus) and nuttall cottontails (Sylvilagus nuttalli) were estimated by examination of fecal pellet botanical composition. The deficiencies of fecal analysis are noted, but dietary trends and relative importance of forage plants are accurate. Cluster analysis combined leporid pellets into 2 distinct groups based on botanical composition, representing feeding during spring-summer and fall-winter periods. Seven variables (plant species) accounted for significant differences (P<O.05) within and among the leporids studied in seasonal food selection. Generally, grasses and forbs were most abundant in blacktail jackrabbit and nuttall cottontail pellets during the spring-summer period, whereas shrubs were most abundant during the fall-winter period. Diet similarity was greatest between blacktail jackrabbits and nuttall cottontails during the same season. Diversity of forage consumed was greatest for both leporids during spring-summer periods. Habitat segregation minimizes competition for forage between the leporids studied. Livestock grazing appears to limit leporid population density rather than alter leporid food habits. During the period of research, authors were graduate research assistant and professor, respectively, Department of Range Science, Colorado State University, Fort Collins 80523. MacCracken's present address is P.O. Box 3145, Palmer, AK 99645. The authors thank O.D. Markham, W.J. Arthur, D.K. Halford, M.K. Johnson, G.C. Lucich, R.L. Potter, E.R. Johnson, and D. Simonson for their participation in this study. M.E. Voorhees did the microhistological work. This project was supported in part through grant DE-A507-761D-1526, MOD 006 from the U.S. Department of Energy, Idaho National Engineering Laboratory Ecology Program to Colorado State University. Manuscript received September 28, 1982. Leporids play a major role in the ecology of the Great Basin area of the western USA. They compete with livestock and other wildlife for forage, cause extensive crop damage, and are a major food source for coyotes (Clark 1972, MacCracken and Hansen 1982a) and other predators which in turn kill livestock and game animals. Leporids are primarily herbivorous, but have been reported to consume carrion (Hansen and Flinders 1969, DeCalesta 1971). When jackrabbits (Lepus spp.) become overly abundant, about every 10 years, their impact on the ecosystem is tremendous. In January 1982 such a situation existed, and it was estimated that local people killed about 64,000 jackrabbits during 6 different roundups at Mud Lake, Ida., bordering our study area. Information on food selection by jackrabbits during low and high population levels helps to determine if such controversial management procedures are justified. The foods of most species of leporids have been documented in the literature (Hansen and Flinders 1969, DeCalesta 1971). Feeding by blacktail jackrabbits (Lepus californicus) may have been the most thoroughly examined (Uresk 1978, Westoby 1980). Even though studies dealing with leporid food habits have been published, few have investigated seasonal food selection by sympatric leporids. The purpose of this paper is to present the results of a study which examined seasonal food habits of sympatric blacktail jackrabbits, and nuttall cottontail (Sylvilagus nuttalli) in southeastern Idaho when the jackrabbit population was at low levels. 256 JOURNAL OF RANGE MANAGEMENT 37(3), May 1984 This content downloaded from 40.77.167.54 on Wed, 06 Jul 2016 04:25:14 UTC All use subject to http://about.jstor.org/terms

Composition and Degradation of Jackrabbit and Cottontail Fecal Pellets, Texas High Plains

Highlight: Fecal pellets were taken from black-tailed jacktabbits and desert cottontail rabbits for studies of rates of natural degradation. Microscopic analyses of fecal samples showed a significant difference in the proportion of grasses, forbs, and woody plants ingested by the two leporid species sampled. Jackrabbits had ingested greater proportions of grasses and woody plants while cottontails had ingested greater proportions of forb material. Degradation of fecal pellets was observed at regular intervals from 1972 to 1974. Time required for complete disappearance of pellets was estimated at 4.4 years for jackrabbits and 9.5 years for cottontails. Relative humidity and precipitation were strongly correlated (r = -0.98 and -0.95 for jackrabbits and cottontails, respectively) with disappearance of pellets.

Chromosome banding pattern relationships of hares, rabbits, and pikas (order Lagomorpha)

The chromosome banding patterns of the domestic rabbit, Oryctolagus cuniculus, the brush rabbit, Sylvilagus bachmani, and the snowshoe hare, Lepus americanus, are nearly identical except for minor differences in the amount of constitutive heterochromatin present. The major mechanisms of chromosome evolution in leporid lagomorphs are centric fusion and addition of heterochromatin. The G- and C-banding patterns of the pika, Ochotona princeps, revealed little easily recognized structural homology with the leporid species. Several tentative banding pattern matches were found for segments of some chromosomes of Ochotona, indicating that tandem fusions may have been responsible for structural modification of the early lagomorph genome. Chromosome evolution in the lagomorphs and the use of chromosomal data in studies of mammalian systematics are discussed.

Spring Population Responses of Cottontails and Jackrabbits to Cattle Grazing Shortgrass Prairie

Highlight: Spring population densities of black-tailed jackrabbits, white-tailed jackrabbits, and desert cottontail rabbits were estimated on pastures under four different grazing treatments by cattle on the shortgrass prairie of northeastern Colorado. Black-tailed jackrabbits were most abundant on pastures with light-summer and moderate-summer grazing treatments. White-tailed jackrabbits showed no strict preference for any grazing treatments but preferred all upland pastures. Desert cottontail rabbits were most abundant in pastures under moderate-summer and moderate-winter grazing treatment. The ratio of abundance between the three species of leporids is, in part, a function of the different levels of grazing intensity. A ny future long-term changes in vegetational management in the area could be expected to affect populational ratios.

Experimental vector and wildlife host ranges of buttonwillow virus in Kern County, California.

Selected species of wild vertebrates and hematophagous arthropods indigenous to Kern County, California, were evaluated as experimental hosts and vectors of Buttonwillow (BUT) virus. Vertebrate hosts were inoculated subcutaneously with approximately 1,000 plaque-forming units (PFU) of virus and arthropods were fed on pledgets soaked with high concentrations of virus in defibrinated blood or on viremic Sylvilagus auduboni. Two species of leporids, Lepus californicus and S. auduboni, were readily infected with BUT virus and developed high level but transient viremias. Some individual squirrels of two species, Ammospermophilus nelsoni and Citellus beecheyi, were partially susceptible to infection, whereas two other species of rodents, Dipodomys nitratoides and Peromyscus maniculatus, were refractory. Low titers of hemagglutination-inhibiting antibodies to BUT virus were demonstrated in most infected mammals and usually persisted for at least 12 weeks. Five species of wild birds were refractory to experimental infection. BUT virus multiplied in Culicoides variipennis and reached peak titers of 104.0 PFU per midge within 3 days after feeding on virus. Infection rates of BUT virus in C. variipennis were always low. A transmission cycle from viremic S. auduboni to C. variipennis to susceptible S. auduboni was completed on three occasions. Five species of mosquitoes (Aedes melanimon, Aedes nigromaculis, Anopheles free-borni, Culex tarsalis, and Culiseta inornata) and two species of ticks (Dermacentor parumapertus and Ornithodorus parkeri) were unable to serve as experimental vectors of BUT virus. High concentrations of blood from viremic S. auduboni contained a dissociable substance that partially inhibited the plaquing of virus on vero cells.