Learn about the main results of the Threatened Mammal Index from the TSX Team:
Threatened Mammal Index for Australia 2019 for all sites
Interpreting the index graphs
The index shows the average change in populations compared to a base year. It shows a relative change and not population numbers themselves. The base year of this index is 1995, which gets an index score of one. A score of 1.2 would mean a 20% increase compared to numbers in 1995 on average, while a score of 0.8 would mean a 20% decrease compared to 1995 on average.
The Living Planet Index team has produced a blog which illustrates how the numbers are typically crunched to produce an index. This is the same for the calculation of the Threatened Species Index.
Threatened Species Index for Australian Mammals 2019
The 2019 index for threatened and near-threatened mammals in Australia shows us that between 1995 and 2016 there was a 38% decrease on average in Australian mammal populations across all sites for which we have data.
For mammals, we can also look at how mammals are doing at sites with and without conservation management such as invasive predator control, fire management and feral predator-free havens like islands and fenced areas. At sites where conservation actions have occurred, like feral animal control and/or ecological fire management on average populations have increased by 46%. While at sites where no conservation actions have occurred populations have decreased by over 60% on average. The separation of mammal sites into sites with and without conservation management is based on information communicated by our data custodians.
The overall index is based upon data for many species and subspecies. The mammal index developed throughout 2019 includes data for 57 threatened and near-threatened mammals from 1,186 sites. As more data is added these numbers will grow.
Within this, some species have decreased a bit more and others a bit less. The grey cloud around the index trend represents some of the variability in the trends of individual species that make up the overall multi-species index. It is created by randomly sampling species trends from all possible trends in the dataset 100 times, and dropping the 5 trends that are furthest from the average, resulting in a 95% “confidence limit”.
In addition to the Australian index, our web visualisation tool allows you to generate indices individual Australian states and territories and for a range of species groups, such as marine and terrestrial mammals. The mammal index has also the option to show sub-indices based on mammal weight categories e.g. <50g, 50-5000g, and >5000g.
More details on the Australian index and all state and territory indices can be found in our research findings factsheets. This project and the factsheets were developed in collaboration with the Commonwealth Department of the Agriculture, Water and the Environment, and all of our major data contributors, including all state and territory governments, and the Australian Wildlife Conservancy and Arid Recovery.
