Australia has a bad mammal extinction record – and it’s probably worse than we think!

AUSTRALIA HAS A BAD MAMMAL EXTINCTION RECORD – AND IT’S PROBABLY WORSE THAN WE THINK!

by Matt McDowell, 27th March at 8:34 AM

Since European settlement in 1788, Australia has had the highest mammal extinction rate in the world. At least one third of Australia’s original or pre-European terrestrial mammal fauna is now extinct or threatened with extinction (Fusco et al. 2017). However, the ongoing recognition of new taxa (e.g., Start et al. 2012, who report the discovery of three new species of rodents that were probably extant when Europeans colonised the Kimberley region of north Western Australia) suggests the extent of Australia’s biodiversity loss is underestimated (Abbott 2000; Woinarski et al. 2014; Abbott & Wills 2016; Burbidge & Abbott 2017). European-settlement-related impacts pose many challenges for the conservation and restoration of Australia’s ecosystems. Landscape modification, associated habitat loss and the introduction of exotic species caused the rapid extinction of numerous taxa and mainland extirpation of at least nine mammals that now survive on land-bridge islands only (Woinarski et al. 2014; Burbidge et al. 2018).

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Fig. 1: The former (blue) and present (labelled Islands) range of the Burrowing bettong (Bettongia lesueur). Red dots are managed populations (after van Dyck and Strahan 2008

Local extinctions are still happening at an alarming rate, with at least 39 extant mammal species vanishing from >75% of the bioregions they are known to have occupied before European settlement. Some species were deliberately persecuted (e.g., the Thylacine – Thylacinus cynocephalus), some were lost through neglect or apathy (e.g., the recently extinct Bramble Cay Melomys – Melomys rubicola) and others appear to have simply been in the wrong place at the wrong time (e.g., Gilbert’s Potoroo – Potorous gilbertii, though not extinct, Gilbert’s Potoroo is the most endangered marsupial in the world and recently lost 90 per cent of its natural habitat to bushfires).

Our appreciation of diversity loss is further masked by poor documentation of species biogeography by colonists. The distributions of many species were not recorded before they were extirpated or extinguished. The result –– shifting baselines. A baseline in this context is a snapshot of the ecology from a given area at a given time against which biodiversity loss can be measured. Australian conservation managers essentially have a choice between four basic timeframes from which to establish baselines:

  • employment date of the current park manager;
  • park proclamation date;
  • shortly before European arrival (late 18th century);
  • pre-human arrival (ca. 50,000 years ago) (Hayward 2009).

If timeframes 1 or 2 are adopted, it is almost certain that ‘baseline shift’ will occur. Baseline shift (or ‘shifting baseline syndrome’) transpires when an arbitrary baseline is accepted and used to evaluate change with no consideration of prior human-induced ecological modification (Miller 2005). A growing body of research on Holocene fossil accumulations (Fig. 2) is providing insights into the composition and biogeography of Australian ecosystems prior to European settlement; data that can be used to establish appropriate baselines, measure biodiversity loss and establish the potential for species translocations and reintroductions, particularly to islands (McDowell 2014).

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Fig. 2: A close look at a particularly rich Holocene fossil assemblage from Bat Cave, Kangaroo Island Scale bar 10 mm. Photo: M.C. MCDOWELL

Examples of the differences between pre- and post-European mammal diversity (Table 1) show that if a modern (i.e. post-European) diversity is accepted as the baseline, as much as 80% of a region’s pre-European mammal community may be overlooked. I argue that late Holocene species records, where available, constitute the most appropriate baseline for management and restoration planning. Even if a species has been extirpated from a region, maintenance or restoration of its ecosystem to the highest possible standard could facilitate future reintroduction and may even provide potential for natural repopulation (Falk et al. 2006; Lunt et al. 2013).

Table 1: Summary of Modern and Holocene fossil mammals recorded in various geographic regions of Australia including three Kimberley rainfall zones. NSW = New South Wales; NT = Northern Territory; SA = South Australia; Vic. = Victoria; WA = Western Australia.

Geographic Region No. modern

mammals

No. fossil

mammals

Species

loss (%)

Source
Kimberley, WA (700–900 mm) 18 26 30.8 Start et al. 2010
Kimberley, WA (600–800 mm) 14 26 46.2 Start et al. 2010
Kimberley, WA (500–600 mm) 8 16 50.0 Start et al. 2010
Pilbara, WA 25 37 32.4 Baynes & McDowell 2010
Uluru National Park, NT 23 34 32.4 Baynes & Baird 1992
Jenolan, NSW 17 26 34.6 Morris et al. 1997
Gippsland, Vic. 10 28 64.3 Bilney et al. 2010
Naracoorte, SA 19 30 36.7 Macken & Reed 2013
Yorke Peninsula, SA 8 27 70.4 McDowell et al. 2012
Eyre Peninsula, SA 5 25 80.0 McDowell & Medlin 2010

Whilst I advocate the use of pre-European faunas as baselines for ecological management, it is important to remember that ecosystems are dynamic and naturally variable. In fact, many Australian ecosystems are characterised by natural variability, which provides long-term resilience to disturbances such as fire, drought and climate change (Walker et al. 2004). However, fossil assemblages indicate that most native mammals persist over thousands of years. Therefore, Holocene fossil accumulations can make significant contributions to management programmes by providing long-term perspectives on ecological systems (Lyman 2006; Froyd & Willis 2008).

When a species is lost from a community the processes and functions they performed are also lost. All mammal species contribute to the maintenance of their community ecology, but few would contribute more than fossorial (digging) species such as bettongs, potoroos and bandicoots. Bettongs are particularly important because most species mainly eat hypogeal fungi (truffles). Consequently, they spread fungal spores wherever they dig. As all Eucalypts form a symbiotic relationship with hypogeal fungus for at least some part of their life, by spreading spores, bettongs perform a fundamental ecosystem service. They also facilitate seedling germination and establishment, soil aeration, incorporation of organic matter and improvement moisture infiltration.

What about rabbits I hear you say? Rabbits are also fossorial but don’t dig anywhere as deeply or widely, and therefore do not appear to contribute to soil improvement anywhere near as effectively as native mammals (Eldridge and James 2009). The almost total loss of native “ecosystem engineers” from mainland Australia has far-reaching implications that may ultimately lead to vegetation succession. I recently described a Bettong (Bettongia anhydra; McDowell et al. 2015; Fig. 3) that was collected alive near the NT-SA border in 1933. Until now it was considered synonymous with its morphologically similar cousin Bettongia lesueur. While its capture by Europeans may be considered unlucky for the individual, it was lucky for us because the species has never been encountered alive since. How many other native mammals have been lost without being recognised or rest in museum cabinets just waiting for the right person to look at them?

Recent breakthroughs in DNA analyses have shown that what were once considered wide ranging species are in many cases species complexes, revealing even more hidden biodiversity. For example, recent molecular research on Antechinus swainsonii has demonstrated it to be a complex of five species. Following this realisation, morphological differences began to emerge from what were previously considered highly variable physical characteristics. So the good news is Australia’s biodiversity is richer than we thought. The bad news is we’re still losing species at an alarming rate. So what can we do to reduce further loss of our unique mammals?

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Fig. 3: The skull of the Bettongia anhydra showing its short nose, long flexed premolar, highly reduced 4th molar and inflated (damaged) ear chambers. Photo: M.C. MCDOWELL

Obviously we need to protect pristine areas that retain most of their pre-European biodiversity, but before attempting any ecological restoration we need to consult the Holocene fossil record to find out which species that area supported in the recent past. Only then can we formulate management strategies that reflect species’ biogeography and ecological preferences, and with a bit of luck some species may recolonise their former range without help from us, like the Plains mouse (Pseudomys australis) did to Arid Recovery, a 123 square km wildlife reserve in the arid north of South Australia. (http://www.aridrecovery.org.au/arid-recovery-news/build-it-and-they-will-come).

References

Abbott, I. (2000) Improving the conservation of threatened and rare mammal species through translocation to islands: case study Western Australia. Biological Conservation 93, 195–201.

Abbott, I. and Wills, A. (2016) Review and synthesis of knowledge of insular ecology, with emphasis on the islands of Western Australia. Conservation Science Western Australia 11 [online]. https://www.dpaw.wa.gov.au/CSWAjournal

Baynes, A. and Baird R. (1992) The original mammal fauna and some information on the original bird fauna of Uluru National Park, Northern Territory. Rangeland Journal 14, 92–106.

Baynes, A. and McDowell, M.C. (2010) The original mammal fauna of the Pilbara biogeographic region of north-western Australia. Records of the Western Australian Museum Supplement 78, 285–298.

Bilney, R.J., Cooke R. and White J.G. (2010) Underestimated and severe: small mammal decline from the forests of south-eastern Australia since European settlement, as revealed by a top-order predator. Biological Conservation 143, 52–59.

Burbidge, A.A. and Abbott, I. (2017) Mammals on Western Australian islands: occurrence and preliminary analysis. Australian Journal of Zoology 65, 183–195.

Burbidge, A.A., Legge, S. and Woinarski, J.C. (2018) Australian islands as ‘arks’ for biodiversity. Pp. 99–113 in: Moro, D., Ball, D. and Bryant, S. (Eds) Australian Island Arks: Conservation, Management and Opportunities. (CSIRO publidhing)

Eldridge, D.J. and James, A.I. (2009) Soil-disturbance by native animals plays a critical role in maintaining healthy Australian landscapes. Ecological Management & Restoration 10 (S1). S27–S34.

Falk, D.A., Palmer, M.A. and Zedler, J. (2006) Foundations of Restoration Ecology. (Island Press, Washington, DC.)

Froyd, C. and Willis, K. (2008) Emerging issues in biodiversity and conservation management: the need for a palaeoecological perspective. Quaternary Science Reviews 27, 1723–1732.

Fusco, D.A., McDowell, M.C., Medlin, G. and Prideaux, G.J. (2017) Fossils reveal late Holocene diversity and post-European decline of the terrestrial mammals of the Murray–Darling Depression. Wildlife Research 44, 60–71.

Hayward, M.W. (2009) Conservation management for the past, present and future. Biodiversity and Conservation 18, 765–775.

Lunt, I. D., Byrne, M., Hellmann J. J. et al. (2013) Using assisted colonisation to conserve biodiversity and restore ecosystem function under climate change. Biological Conservation 157, 172–177.

Lyman, R.L. (2006) Paleozoology in the service of conservation biology. Evolutionary Anthropology 15, 11–19.

Macken, A.C. and Reed, E.H. (2013) Late Quaternary small mammal faunas of the Naracoorte  Caves World Heritage Area. Transactions of the Royal Society of South Australia 137, 53–67.

McDowell, M.C. (2014) Holocene vertebrate fossils aid the management and restoration of Australian ecosystems. Ecological Management & Restoration 15, 58–63.

McDowell, M.C. and Medlin, G.C. (2010) Natural Resource Management implications of the pre-European non-volant mammal fauna of the southern tip of Eyre Peninsula, South Australia. Australian Mammalogy 32, 87–93.

McDowell, M.C., Baynes, A., Medlin, G.C. and Prideaux, G.J. (2012) The impact of European colonization on the late-Holocene non-volant mammals of Yorke Peninsula, South Australia. The Holocene 22, 1441–1450.

McDowell, M.C., Haouchar, D., Aplin, K.P., Bunce, M., Baynes, A. and Prideaux, G.J., 2015. Morphological and molecular evidence supports specific recognition of the recently extinct Bettongia anhydra (Marsupialia: Macropodidae). Journal of Mammalogy,96, 287–296.

Morris, D., Augee, M., Gilleson, D. and Head, J. (1997) Analysis of a Late Quaternary deposit and small mammal fauna from Nettle Cave, Jenolan, New South Wales. Proceedings of the Linnean Society of New South Wales 117, 135–162.

Start, A.N., Burbidge, A.A., McDowell, M.C. and McKenzie, N.L. (2012) The status of nonvolant mammals along a rainfall gradient in the south-west Kimberley, Western Australia. Australian Mammalogy 34, 36–48.

Van Dyck, S. and Strahan, R. Editors. (2008) The mammals of Australia. Third ed. (Reed New Holland: Sydney)

Walker, B., Holling, C.S., Carpenter, S. and Kinzig, A. (2004) Resilience, adaptability and transformability in social–ecological systems. Ecology and society 9(2).

Woinarski, J.C., Burbidge, A.A. and Harrison, P.L. (2014) The action plan for Australian mammals 2012. (CSIRO Publishing: Canberra.)

 

*All posts are personal reflections of the blog-post author and do not necessarily reflect the views of other DEEP members

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