Declining trajectories characterise arboreal marsupial assemblages in eastern Australia

Abstract

Understanding species responses to global change requires robust information on species trajectories across their distributions. However, few studies have documented long-term trajectories in different populations of the same taxon in multiple parts of its distribution. We quantified temporal trajectories in arboreal marsupial detection across 671 field sites within four independent large-scale, long-term studies, located in three major bioregions spanning ∼ 1000 km of latitude in eastern Australia. Using Bayesian generalized linear mixed models, we analysed the trajectories of nine arboreal marsupial species across our four studies, yielding 11 response curves overall for temporal change in the probability of detection. There was evidence of declines in detection probability in seven cases. We identified several places where most species were declining, indicating the potential for homogenisation in arboreal marsupial assemblages. There were increases in detections in four cases across our four studies; two of these were for the Common Brushtail Possum (Trichosurus vulpecula). We found between-study differences in temporal trajectories of the Common Ringtail Possum (Pseudocheirus peregrinus) and Krefft's Glider (Petaurus notatus) (also known as the Inland Sugar Glider), highlighting the existence of non-stationarity (i.e. spatial variation in temporal trajectories) in those taxa. The declines we documented encompassed taxa with a range of life history attributes and included rare species (e.g. the Southern Greater Glider (Petauroides volans)) as well as some previously relatively common species in particular areas (e.g. the Common Ringtail Possum). This underscores the importance of avoiding complacency in conservation and cautions against assuming security of currently common species.