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

The population viability analysis (PVA) program VORTEX was used to examine the viability of different sized populations of the Mahogany Glider Petaurus gracilis, and to examine the impact of a one in a hundred year catastrophe (each requiring a different reserve size) of different severities on different sized populations. The PVA showed that populations up to 300 individuals (1 500 ha) have a negative population growth rate, high losses of genetic diversity and a greater than 5% chance of extinction within 100 years. Populations of 400?700 individuals (2 000?3 500 ha) showed a decreasing trend in population size suggesting they are likely to become extinct after 100 years. A population of 800 individuals (4 000 ha) was needed for the population size to stabilize. Sensitivity analysis showed adult mortality of greater than 25% to be important in decreasing the viability of populations. Populations of 400 were resistant to a one in 100 year catastrophe which had a 20% mortality and 20% decrease in reproduction. When the mortality was 70%, with 70% decrease in reproduction, a population of 1 000 still had a 12% chance of extinction. As only approximately 50% of the available habitat appears to be occupied, an area up to 8 000 ha (800 individuals) is suggested to be required to maintain viable populations of Mahogany Gliders. A number of management options are recommended including the retention of habitat, establishing corridors between key populations, and using fire to minimize rainforest expansion.

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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.

Wildlife Research ◽

10.1071/wr9930067 ◽

1993 ◽

Vol 20 (1) ◽

pp. 67 ◽

Cited By ~ 37

Author(s):

DB Lindenmayer ◽

RC Lacy ◽

VC Thomas ◽

TW Clark

Keyword(s):

Computer Program ◽

Population Size ◽

Carrying Capacity ◽

Population Viability Analysis ◽

Population Viability ◽

Suitable Habitat ◽

Viability Analysis ◽

Nest Sites ◽

Leadbeater's Possum

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.

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