A number of biological characteristics may predispose a species or population to decline or extinction. These are rarity, population dynamics, spatial dynamics, and life history parameters.
Rarity refers to the static qualities of a population—geographic range, abundance and habitat specificity (Rabinowitz 1981). Species or populations most predisposed to extinction are those which have small geographic ranges, low abundance and narrow habitat specificity.
Population dynamics are the dynamic qualities of a population, that is, whether it is increasing, stable or decreasing in size (Caughley 1994).
Spatial dynamics, or metapopulation dynamics, is the interaction between colonisation and extinction of sub-populations that make up a population (Hanski and Gilpin 1991). The parameters that contribute to the potential risk of extinction of a species through metapopulation collapse are the variability in abundance of individual populations and dispersal ability (Turin and den Boer 1988).
Life history parameters are aspects of biology that may predispose a species to the threat of extinction under particular circumstances. The two most important parameters identified are reproductive output and longevity (Pimm et al. 1988).
6.2.1 Assessment methods
Each species listed in Table 6.1 was assigned a rating for the parameters associated with rarity, population dynamics, spatial dynamics, and life history, based on the scores for the contributing factors. A full explanation of the derivation of the parameters is contained in Dexter (1996). Each rating indicates the relative magnitude of the contribution of each parameter to the probability of extinction, as described below.
For the parameters associated with rarity, geographic range within the Central Highlands was classified for each species as large, medium or small, based on a measure or estimate of range size, and the proportion of the Central Highlands in which the species is found (large >30%, medium 10 to 30%, small <10% of Central Highlands). Range size was calculated by summing the area of each Atlas of Victoria grid cell containing a record for each species. This is likely to overestimate geographic range as the area of a grid cell is usually larger than the home range of a particular species. As an additional check, the amount of potentially suitable habitat for each species was calculated by summing the area of each EVC in which a species is likely to occur. Abundance within the Central Highlands was classified as high, medium or low, based the number of records on the Atlas of Victorian Wildlife and on expert opinion. Habitat specificity was classified as narrow or wide, based on expert opinion of the proportion of habitats used or likely to be used within the region.
When considering the parameters associated with rarity, species or populations with small geographic range, low abundance and narrow habitat specificity are considered more predisposed to the threat of extinction than species with large geographic ranges, high abundance and broad habitat specificity.
Population dynamics were assessed by identifying those species whose numbers have been relatively stable or increased, and those which have declined over a recent time period (the last 10 years). Past population dynamics (from discovery by Europeans until 10 years ago) were also classified for all species as either having increased, declined or remained stable.
Stable species and populations are considered to be at a lower risk of extinction than species and populations that are declining. Species whose status is stable but dependent on active management intervention (such as predator control), are assumed to be more likely to be at risk of extinction, than those that do not depend on management intervention. It is also assumed that species that have declined in abundance since their discovery by Europeans, but have had stable abundance in the last 10 years, would have a higher risk of extinction than species who have maintained a stable abundance since their discovery by Europeans. Population trends since European settlement were classified by experts, and were generally based on the change in the amount of each species’ habitat within the Central Highlands.
Spatial dynamics is the interaction between colonisation and extinction of sub-populations, and can be assessed using estimates of population variability and dispersal ability. Species were classified as having high or low population variability, based on measures or estimates of changes in abundance over time. Species that have high population variability are more likely to be under threat of extinction than species that have low population variability. Species were classified as having high or low dispersal ability, based on measured dispersal distances or inferences from anatomy (e.g. wings developed for flying long distances). Species with high mobility are more likely to colonise new patches of habitat and are less likely to be threatened by extinction than species that have low mobility.
The two life history parameters considered in this assessment are reproductive output and longevity. Species were classified as having high, medium or low reproductive output, based on measures or estimates of litter or clutch sizes or rates of increase, and as being long- or short-lived based on measures or estimates of longevity or inferred from body size.
Species that have high reproductive outputs are more likely to recover quickly from major declines in abundance than species with low reproductive outputs and so minimise the threat of extinction due to accidents.
Species that are long-lived tend to be less susceptible to accidental extinction when abundance is low because of their low adult mortality (compared to species with high adult mortality).
For some species the biological information available for a number of parameters was limited and classifications could not be made. Parameters with no information were either classified as unknown, or a classification assigned by experts, based on the most likely estimate.
6.2.2 Results and discussion
Detailed information on the life history and population dynamics for each species is included in Appendix G. The available life history and population dynamics information for the species reviewed is summarised in Table 6.2. The intention of this assessment is to provide a basis for prioritising those species requiring management action to improve the prospects for their long-term survival. This assessment should also be considered in conjunction with the information relating to threatening processes.
The ratings for each species in relation to geographic range, abundance, and habitat specificity are presented in Table 6.2. Most of the species assessed had small geographic ranges in the Central Highlands. The geographic range size of the Regent Honeyeater and White-bellied Sea-Eagle are unknown but were classified as large due to the widely scattered nature of records contained on the Atlas of Victorian Wildlife and because both these species are highly mobile and known to range widely. Atlas of Victorian Wildlife records for both the Sooty Owl and Powerful Owl indicate both species have large geographic ranges within the Central Highlands; the Central Highlands is a stronghold of the Sooty Owl. Although there are only 12 Atlas of Victorian Wildlife records of the Square-tailed Kite within the Central Highlands, the records indicate the species occupies a large geographic range. Most Atlas of Victorian Wildlife records of Dingoes are not distinguishable from records of feral domestic dogs and their hybrids and as a result its geographic range is unknown.
As expected for a group of species selected because there is some documented concern for their status, most had low abundance. Only Leadbeater’s Possum was classified as having a medium abundance. This species is mainly confined to the montane ash forests of the Central Highlands, where its distribution is patchy. In areas of suitable habitat, Leadbeater’s Possum can be locally common (Macfarlane et al. 1995). Most of the species were rated as habitat specific with the exception of the Spot-tailed Quoll, Dingo, Regent Honeyeater, Square-tailed Kite, Grey Goshawk, White-bellied Sea-Eagle, and Powerful Owl. Most of these species are highly mobile and occupy large home ranges.
Five species of mammal (Squirrel Glider, Swamp Antechinus, Common Dunnart, Eastern Horseshoe Bat and Grey-headed Flying Fox), five species of bird (Swift Parrot, Helmeted Honeyeater, Painted Honeyeater, Grey Crowned Babbler and Bush Stone-curlew), the three reptile species (Alpine Bog Skink, Swamp Skink and Glossy Grass Skink), and three of the four amphibian species assessed (Spotted Tree Frog, Alpine Tree Frog and Baw Baw Frog) have small geographic range sizes, a low abundance and are habitat specific. Consequently, of the species assessed, these are more predisposed to the threat of decline or extinction within the Central Highlands. Based on the rarity parameter, these species should be given particular consideration in developing priorities for management action. Of these species, the Squirrel Glider, Grey-headed Flying-fox, Swift Parrot, Painted Honeyeater and Bush Stone-curlew are on the edge of a more extensive distribution outside the Central Highlands region. The Grey-crowned Babbler and Swamp Antechinus are known from only single populations within the Central Highlands; no individuals of either species have been recorded since 1983 and both populations may now be extinct. The Broad-toothed Rat, while rated as having a ‘medium’ geographic range size, has a restricted distribution and a recent study (Jelinek et al, 1997) failed to locate it in wet sub-alpine heathlands (a favoured habitat) in the Lake Mountain area, despite intensive trapping and searching.
The ratings for species according to population variability, mobility, reproductive output and longevity are shown in Table 6.2. Species such as Leadbeater’s Possum, Spot-tailed Quoll, Dingo, Common Bent-wing Bat, Barking Owl, Powerful Owl, and Sooty Owl have favourable spatial dynamic attributes that reduce the threat of extinction due to metapopulation collapse. Species such as the Smoky Mouse, Swamp Antechinus, Common Dunnart and Spotted Tree Frog, have high population variability and low powers of dispersal which render them more vulnerable to the threat of extinction through metapopulation collapse. The population variability of several species including Squirrel Glider, Square-tailed Kite, Grey Goshawk, Masked Owl, Giant Burrowing Frog and Alpine Tree Frog is unknown and the powers of dispersal of the Large-footed Myotis, Bush Stone-curlew and Baw Baw Frog are also unknown. For these species, there is no indication of vulnerability to metapopulation collapse based on the spatial dynamics parameter and highlights the need for basic biological information for a number of species. Similarly, the longevity of the Spot-tailed Quoll, Painted Honeyeater, Regent Honeyeater, Grey Goshawk, Alpine Bog Skink, Glossy Grass Skink, Giant Burrowing Frog, Alpine Tree Frog is unknown. The longevity of the Broad-toothed Rat, Swift Parrot, Barking Owl and Swamp Skink is also unknown but a classification was assigned based on the most likely estimate.
The Swift Parrot, Helmeted Honeyeater, and Grey-crowned Babbler have a high reproductive output and longevity, making them less predisposed to extinction. In contrast, Leadbeater’s Possum, the only species known to have a low reproductive output and longevity, is particularly vulnerable in this regard. The Regent Honeyeater, Grey Goshawk, Alpine Bog Skink, Glossy Grass Skink and Alpine Tree Frog have a low reproductive output but an unknown longevity and no assessment of vulnerability to extinction based on life history parameters could be made.
The population trend since European settlement for each species is detailed in Appendix G. The majority of species are thought to have declined in abundance since European settlement, usually as a result of loss of habitat through clearing for agriculture and urban development. In contrast, the Common Bent-wing Bat and Eastern Horseshoe Bat are thought to have increased since European settlement. Both species have narrow roost requirements and are dependent on a limited number of suitable sites. Since European settlement and the construction of mineshafts, the number of suitable sites has increased and may have led to an increase in these two species (L. Lumsden pers. comm.). The Grey-headed Flying-fox and Dingo are also thought to have increased since European settlement. The Grey-headed Flying Fox has most likely increased as a result of an increase in food sources. In the Central Highlands the species mostly feeds on the fruit of cultivated fruit trees (Menkhorst 1995, L. Lumsden pers. comm.). Nothing is known of the diet of the Dingo in the Central Highlands. However, a study of the diet of wild dogs in East Gippsland indicated non-native species (mainly rabbit) made up only a small proportion of the diet (Brown and Triggs 1990). However, rabbits may provide an alternative food source, particularly when native prey is scarce (Corbett 1995). Although the Dingo has been the subject of control measures since European settlement, such measures may have led to an increase in numbers by disrupting the social organisation of packs resulting in an increase in the number of breeding females (Corbett 1995).
Population trends are the clearest indicators of a species likelihood of extinction. However, for a range of species, the population trend in the past 10 years could not be determined (Table 6.2 ). This highlights the need for further biological information on a large number of the species assessed. Of the species whose population trend in the past 10 years could be determined, the majority have decreased. The Helmeted Honeyeater has increased over this time period, mainly as a result of an intensive recovery program. Although the Powerful Owl, Swamp Skink and Glossy Grass Skink populations have decreased since European settlement, they are thought to have stabilised over the past 10 years. Within the Central Highlands, reported sightings of the Powerful Owl have remained relatively constant, and the number of known pairs on the outskirts of Melbourne have not decreased and it is likely the population is relatively stable (R. Loyn pers. comm.). The stable status of the Powerful Owl population is considered to be partly dependent on management, particularly the protection of known and potential nest sites. Although very little is known of the population trend of the Swamp Skink and Glossy Grass Skink over the past 10 years, processes which most likely caused population declines in the past (including clearing and draining of favoured swampland and heathland habitats) are now much less widespread. As a result, populations of both species are now in a relatively stable state which is unlikely to be dependent on management (P. Robertson pers. comm.).
Table 6.2 : Summary of life history and population dynamics information.
The following taxa, which are either wholly confined to the Region or significantly represented there, are listed under the Endangered Species Protection Act and are noteworthy both in terms of conservation concern and their high public profile.
Leadbeater’s Possum is a small possum found only in the Central Highlands of Victoria. Previously thought to be extinct, it was rediscovered in 1961 and is considered nationally endangered. It is currently found mainly in mountain forests dominated by Mountain Ash, Alpine Ash and Shining Gum and has recently been recorded in Snow Gum woodland at Lake Mountain. A small population also exists in Yellingbo State Nature Reserve, in lowland swamp forest.
Wildfires in 1939 burnt approximately 84% of the Central Highlands ash-eucalypt forests. A wattle understorey provides important feeding habit for Leadbeater’s Possum and the fire-killed remnants of mature forest and resultant regrowth from the 1939 fires has provided abundant feeding and nesting habitat for the species during the past 30 years. However, as the fire-killed nest trees decay and fall, the extent of this type of habitat is diminishing.
Even if timber harvesting were excluded from the regrowth ash forests, they will not be capable of providing suitable nest sites for a further 150 years - assuming that Ash trees must be about 200 years old before they can provide suitable nest sites. It therefore follows that the existing older-aged forest must continue to provide habitat for at least another 150 years.
More details on this species are provided in Box 2 (Section 6.4.2).
Baw Baw Frog
Until recently the Baw Baw Frog was believed to be confined to the Baw Baw Plateau, within an area of 80 km2, which is primarily within the Baw Baw National Park. The species has recently been recorded at lower elevations (1100-1300 m) in forest areas available for timber harvesting. A continued decline in Baw Baw Frog numbers on the Plateau has meant that conservation of these lower-elevation populations is now very important to the survival of the species. Ongoing monitoring of these lower altitude populations are being conducted. Adults of this species are known to use habitat adjacent to and some distance from breeding sites. Very little is known of movements of juveniles and sub-adults.
Spotted Tree Frog
The Spotted Tree Frog is known to occur in only thirteen discrete populations - eleven in Victoria and two in New South Wales. These are mainly on the north-west side of the Great Dividing Range between the Central Highlands in Victoria and Mt Kosciusko in New South Wales. Survey results suggest the species has suffered a significant decline during the past 20 years. Tadpole development occurs in upland streams, with adjacent stream-side vegetation being used by adults for sheltering and basking.
6.2.4 Other important vertebrate species
There are a number of other vertebrate fauna species which, while not formally listed as threatened, are considered by some researchers to require monitoring and possible management intervention because of perceived population declines in the Central Highlands. These include:
Yellow-bellied Glider (Petaurus australis)
Greater Glider (Petauroides volans)
Mountain Brushtail Possum (Trichosurus caninus)
Dusky Antechinus (Antechinus swainsonii)
Peregrine Falcon (Falco peregrinus)
Gang Gang Cockatoo (Callocephalon fimbriatum)
Yellow-tailed Black Cockatoo (Calyptorhynchus funereus)
Wonga Pigeon (Leucosarcia melanolcuca)
Azure Kingfisher (Alcedo azurea)
Tree Goanna (Varanus varius)
Some of these species, for example the Yellow-bellied Glider, are dependent on large tree hollows for shelter and breeding. A shortage of large, old trees with hollows in the Central Highlands regrowth forests is likely to have implications for the conservation of the Yellow-bellied Glider and other hollow-dependent fauna (Lindenmayer, D.B. et al, in press). Other threatening processes such as predation, and water quality might be implicated in the concern over some of these species, however for most of them, insufficient information is available to assign probable threats.
6.2.5 Terrestrial invertebrates
Terrestrial invertebrates, which actually comprise the vast majority of faunal species in the region, have not been systematically surveyed. This lack is a constraint on the formulation of comprehensive management designed to conserve species-level biodiversity. Experience elsewhere suggests that many invertebrate species are likely to have localised distributions and/or be vulnerable to a range of disturbances. Many rely on the maintenance of microclimates which are readily disrupted. Old-growth forests with an abundance of ground litter and rotting logs are often a rich source of moisture-loving species.
Little is known of the appropriateness of management techniques designed for vertebrates—such as the provision of wildlife corridors—on invertebrates, particularly those species having low vagility. Planned fire regimes of a frequency and intensity believed to be tolerated by vertebrates may be incompatible with the reproductive and mobility capacities of invertebrates (and their resultant ability to recolonise areas). It is an area deserving of further research, particularly given the acknowledged importance of invertebrates in sustaining the ecological processes of forests.
In the short term, the representative conservation of Ecological Vegetation Classes and protection of old growth provided by the existing conservation estate and as outlined in the Proposed Central Highlands Forest Management Plan (NRE 1996b) is expected to be important for the protection of terrestrial invertebrate diversity in the absence of detailed information on this group. This technique has limitations because of the widespread phenomenon of local endemism and a generally poor correlation between vegetation communities and the distribution of invertebrates the medium and longer-term, directed research offers the only means of delivering the data necessary to make informed decisions affecting this important component of the fauna.
A list of all insects recorded at the Australian National Insect Collection (ANIC) from the region is at Appendix H. A number of these species are known only from the region. In such cases, this status may represent a real geographic restriction or be an artefact of incomplete sampling.
Among notable non-insect invertebrates are at least 2 species of Onycophora (velvet-worms). Ooperipatus centunculus is known only from the Mt Donna Buang-Warburton area and O. pulchellus appears to be restricted to Mt Baw Baw (Reid, 1996).
Land-snails known to have distributions largely restricted to the study area include Discocharopa inexpectata ,Rhopodon problematica,Pillomena marysvillensis (all from litter and under decaying timber in wet sclerophyll forest) and Victaphanta atramentaria (deep litter in temperate rainforest). The conservation status of these species is uncertain.
A number of earthworm species (many from the genus Diporochaeta s. lat.) are also recorded from the area. Some, originally described by W Baldwin Spencer last century, have not been recorded since.