Testing the effects of ecologically extinct mammals on vegetation in arid Australia: A long-term experimental approach

The loss of species from ecosystems can have cascading impacts on species interactions and ecosystem function. Australia has experienced the greatest loss of mammals globally in the past 200 years, but we know little of how the loss of this suite of ecosystem engineers and herbivores has affected vegetation. We used a threatened mammal reintroduction sanctuary to investigate effects of ecologically extinct mammals on plant assemblages. First, we tested the net effects of mammals using a long-term exclusion experiment within the sanctuary. Second, we used a three-year disturbance experiment to determine the relative roles of herbivory and physical disturbance in driving changes in plant assemblages. Third, we compared outcomes inside and outside the sanctuary to determine how effects of reintroduced mammals differed from contemporary mammal assemblages. Plant species richness was greatest in mammal exclusion plots and declined across all treatments from 2011 to 2018, probably due to drought. Plant composition changed in response to mammal exclusion, with six species increasing significantly, shrubs and myrmecochorous plants becoming more common and large-seeded species less common. Responses to experimental disturbance were less clear. Grass and resprouters were more common, and palatable and large-seeded plants were less common outside the sanctuary (exposed to contemporary mammal assemblage). Our study shows that reintroductions of ecologically extinct mammals have substantial impacts on plant assemblages, both through ecosystem engineering and herbivory, and these impacts differ from those of contemporary mammal faunas, suggesting that pre-European Australian ecosystems were markedly different from contemporary ecosystems.