Small mammals, habitat patches and PVA models: a field test of model predictive ability

• Published in: Biological Conservation
• Main Authors: Lacy, Robert, Lindenmayer, David B
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier
• Subjects: Keywords: habitat fragmentation; minimum viable population; population modeling; prediction; small mammal; species conservation; Australia; Animalia; Antechinus; Antechinus agilis; Mammalia; Pinus radiata; Potato virus A; Rattus; Rattus fuscipes Antechinus; Fragmentation; VORTEX; Rattus rattus
• Online Access: http://hdl.handle.net/1885/92744; https://doi.org/10.1016/S0006-3207(01)00134-3; https://openresearch-repository.anu.edu.au/bitstream/1885/92744/5/MigratedxPub25949_RSD_2002.pdf.jpg; https://openresearch-repository.anu.edu.au/bitstream/1885/92744/7/01_Lindenmayer_Small_mammals%2c_habitat_patches_2001.pdf.jpg

The results are described of comparisons between actual values for patch occupancy for two species of Australian small mammals (Bush Rat Rattus fuscipes and Agile Antechinus Antechinus agilis) determined from field sampling and predictions of patch occupancy made using VORTEX, a generic simulation model for Population Viability Analysis (PVA). The work focussed on a fragmented forest in south-eastern Australia comprised of a network of 39 patches of native eucalypt forest surrounded by extensive stands of exotic softwood Radiata Pine (Pinus radiata) plantation. A range of modelling scenarios were completed in which four broad factors were varied: (1) inter-patch variation in habitat quality; (2) the pattern of inter-patch dispersal; (3) the rate of inter-patch dispersal; and (4) the population sink effects of the Radiata Pine matrix that surrounded the eucalypt patches. Model predictions were made for the total number of animals, the distribution of animal density among patches, the total number of occupied patches, and the probability of patch occupancy. Predictions were then compared with observed values for these same measures based on extensive field surveys of small mammals in the patch system. For most models for the Bush Rat, the predicted relative density of animals per patch correlated well with the values estimated from field surveys. Predictions of patch occupancy were not significantly different from the actual value for the number of occupied patches in half the models tested. The better models explained 10-16% of the log-likelihood of the probability of patch occupancy. While some of the models gave reasonable forecasts of the number of occupied patches, even in these cases, they had only moderate ability to predict which patches were occupied. Field surveys revealed there was no relationship between patch area and population density for the Agile Antechinus - an outcome correctly predicted by only a few models. Five of the 18 scenarios completed for the Agile Antechinus gave predicted numbers of ...