Riverine rabbit
Species of mammal From Wikipedia, the free encyclopedia
The riverine rabbit (Bunolagus monticularis), also known as the bushman rabbit or bushman hare, is a species of mammal in the family Leporidae found in patches of thick vegetation in the Karoo Desert of South Africa's Western and Northern Cape provinces. It is the only member of the genus Bunolagus. The most recent estimates of the species' population range from 157 to 207 mature individuals, and 224 to 380 total.
| Riverine rabbit[1] | |
|---|---|
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| Bunolagus monticularis in Western Cape, South Africa | |
| Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Lagomorpha |
| Family: | Leporidae |
| Genus: | Bunolagus Thomas, 1929 |
| Species: | B. monticularis |
| Binomial name | |
| Bunolagus monticularis (Thomas, 1903) | |
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| IUCN distribution of the Riverine rabbit
Extant (resident) | |
First identified in 1903 as a member of the hares, the riverine rabbit is a medium-sized (33.7 to 47.0 centimetres (13.3 to 18.5 in) long) rabbit. Its fur has a unique dark brown-coloured stripe from the edge of its mouth up towards the base of its ears, and a white- to grey-coloured ring around each eye. It is nocturnal and herbivorous, and its diet consists of grasses, flowers and leaves, most of which are dicotyledons. The riverine rabbit will dig burrows in the soft alluvial soils of its habitat near seasonal rivers, using them for protection from the heat and for females to nest and protect the young. Though they live alone throughout the year, riverine rabbits are polygamous.
Unlike most rabbits, female riverine rabbits produce only one to two offspring per year. This, along with habitat loss from agricultural development, soil erosion, and predators contributes to its classification as critically endangered, the most severe classification used by the International Union for Conservation of Nature. Of the factors impacting the species' survival, anthropogenic effects including climate change and land development have the greatest impact. Currently, there are conservation plans being enacted to help with its decreasing population and habitat.
Taxonomy and evolution
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The riverine rabbit's scientific name is Bunolagus monticularis.[3] It was first described by Oldfield Thomas in 1903 as Lepus monticularis with the type locality of Deelfontein, Cape Colony, South Africa. The species name monticularis was derived from the Latin monticulus, meaning "little mountain", referring to the kopjes (diminutive word for "mountain", kop, in Afrikaans) where it was found.[4] It was separated into its own species in 1929.[5] Some common names referring to it are the bushman hare and the bushman rabbit.[6] This rabbit also has several common names in Afrikaans, such as boshaas and vleihaas, referring to the rabbit's habitats being moist and dense - bos meaning "forest" or "thicket", vlei meaning "swamp", and haas meaning "hare".[7] Other names it has are pondhaas and oewerkonyn.[5]
Phylogeny
Genetically, the closest relations of Bunolagus monticularis are to the Amami rabbit, the hispid hare, and the European rabbit.[7] A cladogram showing this is from Matthee et al., 2004, based on nuclear and mitochondrial gene analysis.[8]
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Bunolagus is not well known in the fossil record. It may date back to the middle Pleistocene, 0.4 million years ago in South Africa. Its distribution has likely always been very restricted. The only known fossils of the genus have as of 2007 been reconsidered as small specimens of Lepus.[9] No subspecies are recognized,[1] but there are significant genetic differences between isolated populations above and below the Great Escarpment.[5]
Characteristics
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Riverine rabbit in the Klein Karoo from two angles, showing the rufous nuchal patch and brown tail
The riverine rabbit is native to the Karoo desert in South Africa.[10] It has a similar appearance to hares (lagomorphs in the genus Lepus), particularly in the characteristics of the skull; it most closely resembles the Cape hare (Lepus capensis) in its morphology, but not in its fur patterns. It is distinct from the red rock hares,[5] some of which overlap it in distribution;[11][2] in its first description, it was noted as being about the same size as the Natal red rock hare (Pronolagus crassicaudatus),[4] though it has been later described as smaller than all red rock hares besides Smith's red rock hare (P. rupestris).[12]
Bunolagus monticularis has an adult head and body length of 33.7 to 47.0 centimetres (13.3 to 18.5 in). It typically has a dark brown stripe running from the lower jaw over the cheek and upwards towards the base of the ears and a white ring around each eye.[5] The nuchal patch, as well as the limbs and lower flanks, are rufous in colour.[13] It has a brown woolly tail, and cream to greyish-coloured fur on its undersides. The hind feet are broad and club-shaped.[14] Its dental formula is 2.0.3.31.0.2.3 × 2 = 28, as is the case with all rabbits.[15] Its tail is pale brown with a tinge of black toward the tip. Its coat is soft and silky, more so than that of hares, and is of a reddish-brown to black shade. Its limbs are short and heavily furred, with the hind foot measuring 9–12 centimetres (3.5–4.7 in).[5] The ears measure 11–12 centimetres (4.3–4.7 in)[16] and are rounded at the tips.[13] The species displays sexual dimorphism in the size of individual rabbits, with males weighing approximately 1.5 kilograms (3.3 lb) and females weighing about 1.8 kilograms (4.0 lb).[14]
Habitat
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Bunolagus monticularis is found in only a few places in the Karoo Desert. The riverine rabbit prefers to occupy areas of dense vegetation in river basins and shrubland. It feeds on the dense shrubland, and the soft soil allows for it to create burrows and dens for protection, brooding young, and thermoregulation. The riverine rabbit lives in very dense growth along seasonal rivers in the central semi-arid Karoo region of South Africa. Its habitat regions are tropical and terrestrial while its terrestrial biomes are desert or dune and scrub forest.[14] Two of the most common plants in its habitat are Salsola glabrescens, Amaranthaceae (34·8%) and Lycium spp. Solanaceae (11·2%).[16]
They appear and live specifically in riverine vegetation on alluvial soils adjacent to seasonal rivers,[17] though studies have found this habitat to be sixty-seven per cent fragmented in certain areas. As of 2016, it was estimated that the riverine rabbit occupied a region spanning only 86 square kilometres (33 sq mi).[18] The riverine rabbit requires particular vegetation and soil to construct its burrows,[6] and is sensitive to changes in habitat; thus, it is considered an indicator species within its distribution.[19] From the early 20th century up until 2008, over two-thirds of their habitat has been lost. Removal of the natural vegetation along the rivers and streams causes loss of soft allvial soils and prevents rabbits from being able to construct stable breeding burrows. Overgrazing of domestic herbivores also causes degradation and fragmentation of the land. Without suitable habitat, the riverine rabbit has a lower rate of survival.[6] A 1990 study put forth that the remaining habitat was only able to support 1,435 rabbits.[20]
Behaviour and ecology
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Riverine rabbits are solitary and nocturnal.[16] At night, they feed on flowers, grasses, and leaves. During the day, they rest in forms. The rabbit practices cecotrophy, producing two types of droppings—hard droppings during the night, and soft droppings during the day, which are taken directly from the anus and swallowed. These soft droppings provide the rabbit with nutrients produced by bacteria in the hindgut and recycled minerals.[10]
The riverine rabbit is polygamous, but lives and browses for food alone. It has intra-sexually exclusive home ranges: the males' home ranges overlap slightly with those of various females, with males having an average home range size roughly 60% larger than females (20.9 hectares (52 acres) compared to 12.9 hectares (32 acres)).[21] This home range size is the largest of all rabbits, though it is smaller than those of most hares.[22] The breeding season takes place between August and May, wherein females will make a grass- and fur-lined nest in a burrow, blocking the entrance with soil and twigs to keep out predators. The average length of a generation is 2 years; in captivity, individuals have been recorded as living up to 5 years.[21]
Diet
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The riverine rabbit mainly feeds through browsing.[14] When grasses are available during the wet season, they are the rabbit's preferred food, but most of the time the diet of Bunolagus monticularis is restricted to the flowers and leaves of dicotyledons in the Karoo Desert. These include species in the families Asteraceae, Amaranthaceae, and Aizoaceae,[23] particularly salt-loving plants such as the salsola and lycium that grow along seasonal rivers in the desert. Aside from their conventional food intake, they also consume soft day-time droppings that come directly from the anus in the process known as cecotrophy. Their faeces contain vitamins, such as various B vitamins, produced by the bacteria in the hindgut, as well as recycled nutrients, such as calcium and phosphorus.[14]
Populations in the more northern areas of the species' distribution are more strongly associated with the vegetation that grows narrowly along seasonal rivers; those in the southern parts of its distribution are not as closely tied to this type of vegetation and have been observed feeding on newly grown plants in fallow land.[5]
Reproduction
The riverine rabbit has a polygamous mating system, wherein males will mate with multiple females. Based on limited observations, the breeding season takes place from August through May, and gestation takes 35 to 36 days. It bears its young underground for protection, relying on soft soil in the flood plains of its habitat to construct its breeding burrows. These burrows are lined with fur and grass, and the entrance is closed off with dirt and twigs for camouflage from predators. This burrow is 20–30 centimetres (7.9–11.8 in) long, and the nesting chamber within is 12–17 centimetres (4.7–6.7 in) wide.[16] The riverine rabbit has 44 diploid chromosomes,[5] as do several closely related rabbits, the European rabbit (Oryctolagus cuniculus)[24] and hispid hare (Caprolagus hispidus).[25]
The offspring that the rabbit produces, one to two per litter, are born altricial, or bald, blind, and helpless, and weighs from 40 to 50 grams. The helpless offspring stays with the mother until it is capable of living on its own and fending for itself.[5] The low breeding rate of only one to two offspring per year is unlike most other rabbits and has led to attempts to increase numbers of this endangered species.[14] A breeding colony has been established at the De Wildt Cheetah and Wildlife Centre near Pretoria.[26]
Predators and competitors
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The riverine rabbit is hunted by Verreaux's eagles,[14] African wildcats, and caracals, the latter two of which have seen population increases due to the decline of the black-backed jackal in the region.[16] To escape predation, the riverine rabbit makes use of forms during the day to stay hidden—shallow depressions in the soil made under vegetation. It can also jump over one meter high while being pursued.[7]
Relationship with humans
The riverine rabbit provides benefits for farmers. It causes the riverine vegetation that it eats to bind to the soil and prevent soil erosion through flooding. Through this process, the vegetation allows for filtration of rainwater into groundwater. This benefits farmers, who rely on windmills to draw up water from the ground for their livestock. Without the riverine rabbit or other animals that browse upon the same plants in the same manner, these benefits are lost.[14] The species is suspected to be hunted for bushmeat by farm workers and for sport.[21]
Endangerment
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Extent
The riverine rabbit is in extreme danger of extinction. In 1981, it was first labelled as an endangered species. The International Union for Conservation of Nature (IUCN) classified it under the most severe category of endangerment (aside from extinction), critically endangered, in 2002.[7] The National Red List of South Africa maintained by the South African National Biodiversity Institute (SANBI) uses this same classification. Both organizations maintain this position as of their most recent evaluations from 2016.[21] It has a population of 157 to 207 mature rabbits[19] and up to 380 overall, which continues to decline. This species' population is divided into several isolated groups, about 12 in total, all with less than 50 rabbits in each. These isolated populations are protected by jackal-proof fencing and separated by major agricultural projects.[2]
Causes
The decline in the riverine rabbit population is largely due to the alteration of its historically limited[9] habitat. Over half of the rabbit's range has been rendered unable to support the species due to agricultural development since 1970. The range of habitable area continues to decline, and in 2008 it was predicted that over the next 100 years, one fifth of habitable area will be lost. Commercial agricultural development has contributed significantly to habitat loss, with much of the rabbit's former habitat rendered inhabitable or closed off. These developments additionally isolate rabbit populations due to the construction of impermeable barriers designed to protect against jackals.[6] The remaining land left to support the species is being damaged by climate change. Populations are further reduced through anthropogenic means.[27] Hunting and accidental trapping by farmers is a direct cause of population decline,[28] while removal and exploitation of trees limits the rabbit's opportunities for shelter from heat and predators. Structures on rivers like dams isolate subpopulations from each other, discouraging population regeneration. Soil erosion caused by other animals grazing and feeding on local vegetation can also impact the availability of food for the rabbit.[7] Relatively recent threats to the riverine rabbit are fracking and wind farm developments in the Nama Karoo, the former of which could alter the region's hydrology, and both of which will further fragment the available habitat.[5]
Conservation
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Relative to other similar species, known information about key aspects of the riverine rabbit, such as behaviour and diet, is deficient. Conservation efforts are better informed by researching this species and involving local communities, particularly farmers.[7] Plans to protect the remaining members of the population have been criticized, with experts claiming that a large part of the remaining land that can support the rabbit is outside the area being preserved for it.[20] Additionally, studies are susceptible to sampling bias, and failure to account for climactic and biological variables can lead to error, which can impact conservation recommendations.[19] Efforts have been made to form agreements with and educate landowners to ensure that certain measures are taken to help and reduce harm to the rabbit population.[7]
The IUCN recommends further conservation measures in addition to those already planned and advised according to SANBI. They recommend capturing the animal as to safely allow it to reproduce without danger of predators or starvation. They also recommend different methods of managing the habitat and the population in the wild. The IUCN also notes that further research is needed into its ecology and into the conservation actions that would be most effective.[2] Conservation of the rabbit's habitat and maintaining interconnection between populations is important to the preservation of the species, as its complex genetic structure makes breeding with groups outside of the species difficult, if not impossible.[5][27] Thorough monitoring of rabbit populations is needed to accurately estimate needed conservation efforts, a task that has been carried out in part by the Endangered Wildlife Trust.[28] One location being monitored is Sanbona Wildlife Reserve, a protected wilderness area with a successful breeding population where the species is being researched.[14]
A 2016 assessment by SANBI noted that there were increased sightings of the species within its extent of occurrence, and that camera traps and further observations were needed to confirm the spread of subpopulations in regions south and eastward of the rabbit's native range.[21] The species' extent as of 2024 is being evaluated through analysis of droppings across the Karoo region.[29]
References
External links
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