# The Ecological Separation of Deer and Domestic, Feral and Native Mammals in Tropical Northern Australia—A Review

## TL;DR

This paper reviews how introduced herbivores have replaced native ones in northern Australia and highlights the lack of knowledge about the ecological impact of deer expansion.

## Contribution

The paper identifies critical knowledge gaps regarding the ecological impact of deer species dispersal in northern Australia.

## Key findings

- Native large herbivores disappeared 46,000 years ago and were replaced by introduced species in the last 200 years.
- The current herbivore guild ecologically differentiates between native and introduced species.
- There is insufficient evidence to assess the impact of deer range expansion on the ecosystem.

## Abstract

Simple Summary: In northern Australia, large native herbivorous mammals (weighing over 1000 kg) disappeared about 46 kya, and they have been replaced in the last 200 years by a range of introduced mammalian herbivores up to 1000 kg in bodyweight. Only one native herbivore has an adult bodyweight approaching 100 kg, and for the past 200 years, the total biomass of introduced domestic and wild vertebrate herbivores has massively exceeded that of native herbivorous species. Following a comprehensive review, we conclude that the current guild of native and introduced mammalian herbivores differentially utilises the landscape ecologically. However, climate- and anthropogenically related changes due to fire, drought, flooding, predation and introduced weeds are likely to have significant impacts on the trajectory of their relative ecological roles and populations. Given their differing ecological and dietary characteristics, against this backdrop, it is unclear what the potential impact of the dispersal of deer species could have in northern Australia. There is a dearth of supporting evidence to inform appropriate sustainable management should deer range expansion occur. We identify suitable research required to fill the identified knowledge gaps.

We explored the ecological and historical factors that led to formation of the unique guild of native and introduced mammalian herbivores between 5 and 1000 kg in northern Australia. Following the disappearance of large native herbivores about 46 kya, and until the arrival of Europeans and their livestock, the only herbivorous mammals were mid-sized endemic marsupial macropods, which continued to utilise the same vegetation as their much larger former neighbours. Only one species of contemporary native herbivore has an adult bodyweight approaching 100 kg, and for the past 150–200 years, the total biomass of introduced domestic and wild vertebrate herbivores has massively exceeded that of native herbivorous species. We conclude that the current guild of native and introduced mammalian herbivores differentially utilises the landscape ecologically. However, climate- and anthropogenically related changes due to fire, drought, flooding, predation and introduced weeds are likely to have significant impacts on the trajectory of their relative ecological roles and populations. Given their differing ecological and dietary characteristics, against this backdrop, it is unclear what the potential impact of the dispersal of deer species could have in northern Australia. We hence focus on whether sufficient knowledge exists against which the potential impacts of the range expansion of three deer species can be adequately assessed and have found a dearth of supporting evidence to inform appropriate sustainable management. We identify suitable research required to fill the identified knowledge gaps.