PRIMERA GENERACIÓN

In the following sections a brief summary is given of the ecology of the four herbivore species that are considered to damage eucalypt seedlings in Tasmanian forestry plantations.

2.1.1 The Bennett's

_{wallaby (Macropus rufogriseus rufogriseus)}

The Bennett's wallaby is a medium sized, native marsupial belonging to the family Macropodidae. On average, adult males weigh around 20 kg (Calaby 1 983). As is typical of the sexually dimorphic macropod species, females tend to be

considerably lighter than males, having an average adult body weight of 14 kg (Calaby 1983). Bennett's wallabies occur throughout Tasmania and many of its offshore islands. The range of its closely related subspecies, the red-necked wallaby (Macropus rufogriseus banksianus), extends along the coast from the

south-east of South Australia through eastern New South Wales to the south-east of Queensland (Calaby 1983). The species is abundantthroughout its range and it

is believed to be one of the few marsupial species to have benefited from land­ clearing (Calaby and Grigg 1 989� Johnson et a/. 1 989). It occurs in many habitat

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types but typically prefers eucalypt forests with a recognisable shrub stratum or tall

coastal heath communities (Calaby 1 983).

As with other macropod species, M rufogriseus gives birth to only one young at a time. It can achieve a continuous breeding cycle through post partum ovulation and embryonic diapause (Tyndale-Biscoe 1989). However, in the Tasmanian

subspecies, breeding tends to be seasonal, with a peak in births occurring in February and March (Merchant and Calaby 1981� Curlewis 1 989). Like most other marsupial species, the young spend the majority oftheir early development in a pouch, leaving at approximately 270 days of age and continuing to suckle to

around 360 days (Lee and Ward 1989). Females reach sexual maturity between 1 1

and 21 months of age and males at around 12 months (Lee and Ward 1989).

J\tfacropus nifogriseus is essentially nocturnal and spends the majority of the day sheltering in bushland areas. In those areas where bushland abuts cleared areas, the Bennett's wallaby will typically move from shelter into the open where it will feed throughout the night (Mooney and Johnson 1979). It is essentially a grazer,

preferring to feed on monocotyledons such as grasses and soft leaved dicotyledons (Calaby 1983; Statham 1983; Jarman and Phillips 1989; Sprent 1997). In

Tasmania, home ranges have been found to average around 1 00 ha (Mooney and Johnson 1979); while on the mainland, median home ranges of 16.3 ha have been recorded (Johnson 1987).

2.1.2 The Tasmanian pademelon ( Thylogale billardierii}

The Tasmanian pademelon is another native marsupial belonging to the

Macropodidae family. Adult male pademelons on average weigh 7 kg (Johnson and Rose 1983). Females have an average weight of 4 kg. Pademelons occur throughout Tasmania and the larger islands of Bass Straight (Johnson and Rose 1983). Its distribution once extended into the south of Victoria and South

Australia (Wood-Jones 1925) but it is now thought to be extinct on the mainland (Calaby 1971). In Tasmania, it is considered abundant and land clearing is thought to have lead to a general increase in numbers (Frith 1973; Driessen and Hocking 1992). Throughout its present range the pademelon occurs in a variety of habitats, though it generally prefers densely vegetated areas such as wet sclerophyll forest and rainforest, which afford it protection during daylight hours (Green 1973; Johnson and Rose 1983; Tasmanian Conservation Trust 1987).

Breeding occurs throughout the year but peaks from April to June. Gestation takes around 30 days, after which the young spend approximately 200 days in the pouch (Rose and McCartney 1982; Johnson and Rose 1983). Sexual maturity is reached at around 14 months (Rose and McCartney 1982).

The pademelon is essentially nocturnal and forages predominantly at night

(Johnson and Rose 1983). There is limited information regarding the home range of pademelons in Tasmania. One radio-tracking study carried out by Johnson

(1978) found that the home ranges of five male pademelons varied from 148 ha to

169 ha. Where forest adjoins cleared areas, pademelons may move into the open to feed (Johnson 1978), though they are thought to rarely venture far from shelter

(Johnson and Rose 1983). Pademelons feed on a wide range of plant species, preferring soft leaved dicotyledons and grasses (Statham 1983; Sprent 1997).

2.1.3 The common brushtail possum ( Trichosurus vulpecu/a)

The brush tail possum is an abundant, medium sized, arboreal marsupial. Adult males weigh between 2 and 4.5 kg (How 1983). Adult females weigh between 1.5 and 3.5 kg (How 1983). Three subspecies are described (How 1983) : T. v.

johnstoni, extending from northern Queensland through to southern Victoria; T. v. vulpecula, extending from southern Victoria through central Australia to south­ western West Australia; and T. v. fuliginosus which is distributed throughout Tasmania. The combined range of these three subspecies is one of the largest for any Australian marsupial (Kerle 1984). It lives in a wide variety of treed habitats, ranging from the arid zone in central Australia through to the rainforests of

Tasmania. The brushtail possum is also well adapted for survival in the urban environment (Fitzgerald 1975).

Longevity is typically less than 11 years (Flannery 1994). It is a continuous ...

breeder but there is a peak in births during autumn (Green 1984 ). Sexual maturity is reached after around one year in females (How 1983). Females give birth to only one young at a time, with one to two young being produced each year. Following a gestation period of around 18 days, the young spends 4-5 months in the pouch (Flannery 1994). Another 1-2 months are spent suckling and riding on the mother's back (Flannery 1994).

The brushtail possum is essentially a nocturnal animal. During the day it nests in tree hollows and logs which it defends from other possums (Flannery 1994 ). At night it forages for food both in the tree tops and on the ground (MacLennan

1984). It is typically a browser, feeding predominantly on soft and hard leaved dicotyledons (Statham 1983; Fitzgerald 1984; Green 1984; Kerle 1984; Evans

1992; Owen and Norton 1995). However, a wide range of other foodstuffs are more occasionally eaten including fruit, buds, bark, insects and meat (Flannery

1994 ). Home range size for the brushtail possum varies between habitat types. Ranges determined from Australian studies have varied in size from 3.0 ha to 7.4

ha for males and 1.0 ha to 4.7 ha for females (see review by Green 1984).

Plate 3 : The brushtail possum

(Trichosurus vulpecula,

2.1.4 The introduced European rabbit (Oryctolagus cuniculus)

The European rabbit, a placental mammal, was introduced into south-eastern Australia in the 1800s (Rolls 1969). Since then, the rabbit has spread over much of mainland Australia, Tasmania and several offshore islands. Throughout Australia, the rabbit occurs in a wide range of habitat types and is apparently limited only by the availability of water and soil suitable for burrows in which to shelter (Myers 1983; Parer and Libke 1985). For both sexes, average adult body weight is around 1 .6 kg (Myers 1983).

Longevity is typically short (approximately 3 years) and mortality of juveniles high (Cooke 1982, 1983). The rabbit is a prolific breeder. Sexual maturity is reached after 4 months in some areas (Myers et al. 1994 ). On average, around four or five young are born in each litter (Myers et al. 1994). In favourable areas up to five litters can be born in a year (Myers 1983).

Rabbits have a diet typical of grazers, though they are known to be remarkably adaptable where preferred vegetation is scarce (Cooke 1982; Myers et al. 1994). In Tasmania the rabbit has been observed to feed primarily on soft leaved

dicotyledons and grasses (Statham 1 983). Home ranges vary markedly between environments (Myers et al. 1994), measuring up to 4.7 ha in dJy sparsely vegetated areas (Fullagar 1981, as cited in Myers et al. 1994).