Identifying biodiversity surrogates and management indicator species for tall, wet Forests: A case study of Australian arboreal marsupials

Halting the loss of biodiversity is a major challenge for humanity given the number of species at risk, the limited resources dedicated to conservation relative to levels of investment that are needed, and the impossibility of monitoring all threatened species, even in wealthy nations. Some of these challenges might be possibly addressed, in part, if conservation shortcuts could be found. These include the use of surrogates, proxies, and indicators in which easy to measure entities can accurately reflect the remainder of, for example, a particular assemblage of species. In the work reported here, we explored the indicator potential of particular species of arboreal marsupials in the tall, wet forests of south-eastern Australia. We did this through an empirical exploration of co-occurrence patterns using an analysis of a long-term dataset on arboreal marsupials that we gathered between 1997 and 2022 at 178 permanent field sites. Our analyses contained evidence of positive co-occurrence relationships between some pairs of species, but negative ones between others. In addition, relatively high levels of overall species richness in the arboreal marsupial assemblage were associated with four of the six species we analysed. We then tested the idea that these co-occurrence patterns were context-dependent. Although context dependence is a familiar issue in ecology, its importance for recognizing and understanding the limitations of surrogates like indicator species is often not well recognised. Indeed, we present evidence that some co-occurrence patterns varied across time and in response to key aspects of forest condition including the availability of nest sites in hollow-bearing trees, forest type, and stand age. We discuss these findings in relation to how context dependence can help us understand the applicability and limitations of ecological indicators. Our findings, based on long-term data, suggest that focused management efforts for a particular species as a “management indicator species” will not necessarily ensure positive outcomes for other species across all contexts. Therefore, targeted conservation efforts may be required for individual species, particularly species of conservation concern.