Predictions of the impacts of changes in population size and environmental variablitity on Leadbeater's possum, Gymnobelideus leadbeateri McCoy (Marsupialia: Petauridae) using population viability analysis: an application of the computer program VORTEX.

Abstract

Population Viability Analysis (PVA) uses computer modelling to simulate interacting deterministic and stochastic factors (e.g. demographic, genetic, spatial, environmental and catastrophic processes) that act on small populations and assess their long-term vulnerability to extinction. The computer program VORTEX was used in a PVA of Leadbeater's possum, Gymnobelideus leadbeateri McCoy, an endangered arboreal marsupial that is restricted to the montane ash forests of the central highlands of Victoria. PVA was used to examine the impacts of changes in the size of subpopulations and the effects of environmental variation. Our analyses demonstrated that an annual linear decline in the carrying capacity in all or parts of the habitat will lead to the extinction of G. leadbeateri in those areas. Mean time to extinction was related to the rate of annual decrease. This conclusion is of practical and management importance as there is presently a decline in suitable habitat because of an annual loss of more than 3.5% of trees with hollows, which provide nest sites for G. leadbeateri. Because nest sites are a factor that limits populations of G. leadbeateri, the species could be lost from large areas within the next 50 years. PVA was also used to determine the viability of populations in areas, such as oldgrowth forest, where there is not likely to be a steady decline in habitat carrying capacity resulting from the loss of trees with hollows. This allowed an analysis of the cumulative impacts of small population size, environmental variation and genetic factors, which showed that, for a 100-year projection, simulated populations of 200 animals or more remained demographically stable and experienced a less than 10% decline in predicted genetic variability. However, the relatively simplified nature of population modelling and the suite of assumptions that underpin VORTEX mean that the probability of extinction of populations of this size may be greater than determined in this study. As a result, it is possible that only populations of more than 200 animals may persist in the long term where suitable habitat can be conserved or established and subsequently maintained without a reduction in carrying capacity.

Ranking Conservation and Timber Management Options for Leadbeater’s Possum in Southeastern Australia Using Population Viability Analysis

“…In the case of G. leadbeateri, for example, the program VORTEX was used in studies of the interactions between genetic and demographic factors and population persistence (Lindenmayer et al 1993c;Lindenmayer & Lacy 1995). Burgman et al (1994) the RAMAS package to examine aspects of the reintroduction biology of the species.…”

“…Several detailed studies of the biology and ecology of G. leadbeateri have been completed (Smith 1980(Smith , 1984a(Smith , 1984bSmith & Lindenmayer 1988Lindenmayer 1989;Thomas 1989;Lindenmayer et al 1990aLindenmayer et al -1990bLindenmayer et al , 1991aLindenmayer et al -1991f, 1993aLindenmayer et al -1993cLindenmayer et al , 1994aLindenmayer et al -1994b. Information from these investigations has been used to calculate key parameters for input to ALEX, such as age at sexual maturity and age-specific rates of mortality ( Table 1).…”

The conservation of arboreal marsupials in the montane ash forests of the central highlands of Victoria, south-eastern Australia — VII. Modelling the persistence of Leadbeater's possum in response to modified timber harvesting practices

“…They were based on the results of a wide range of field studies of the species (Smith, 1980(Smith, , 1982(Smith, , 1984aLindenmayer, 1989;Thomas, 1989;Lindenmayer et al 1991aLindenmayer et al ,b,c,d, 1993a. The rationale for these values has been outlined in a previous study (see Lindenmayer et al, 1993a) and it is only briefly summarised here. G. leadbeateri has a matriarchal social structure in which colonies of animals are typically comprised of a monogamously-mated breeding pair, pre-dispersal aged subadult offspring, and unrelated non-breeding adult males.…”

“…Value Reference a a 1, Smith (1980);3, Smith (1982);3, Smith (1984a);4, Lindenmayer et al (unpublished data) derived from mark-recapture and radio-telemetry studies at Cambarville in the central highlands of Victoria (see also Meggs et al, 1991); 5, Derived from the application of a subprogram within ALEX called BIRTHS (see Possingham & Davies, 1995) where the probability of a certain number of young is calculated using data on sex ratio at birth and the number and size of litters; 6, Values based on data summarised in Lindenmayer et al (1993a) that have, in turn, been synthesised from studies by Smith (1980Smith ( , 1982Smith ( , 1984a as well as records from captive animals and a recent recapture investigation (Lindenmayer et al, unpublished data); 7, Calculated by ALEX from a synthesis of other input data; 8, Quasi-extinction threshold (sensu Ginzburg et al, 1982) defined as two specifically for the purposes of this study; 9, Derived from radio-telemetry studies (Lindenmayer et al, unpublished data); 10, Estimates calculated from a synthesis of field studies by Smith (1980Smith ( , 1982Smith ( , 1984a and Lindenmayer et al (unpublished data).…”

Ecological-Economic Analysis and Valuation of Biodiversity

“…the geographic area of suitable habitat required as to support the minimum viable population. Recent published studies on the leadbeaster's possum (Lindenmayer et al 1993), the eastern barred bandicoot (Lacy and Clark 1990), the Puerto Rico parrot (Howels and Edward-Jones 1997), and the giant panda (Zhou and Pan 1997) confirm the use of the population viability analysis in the policy decision circles and help conservation decisions. Another example of the application of computer system for ecological evaluation refers to the System for Evaluating Rivers for Conservation (SERCON) recently undertaken by the Scottish Natural Heritage, the nature conservation agency in Scotland (Boon et al 1997).…”