Is the loss of Australian digging mammals contributing to a deterioration in ecosystem function?

Abstract

Despite once being described as common, digging mammal species have been lost from the Australian landscape over the last 200 years. Around half of digging mammal species are now extinct or under conservation threat, and the majority of extant species have undergone marked range contractions. Our aim is to identify the role of digging mammals in ecosystem processes throughout Australia. We highlight how the actions of digging mammals are vital for maintaining ecosystem functioning and how their extirpation has led to loss of ecosystem functions. A review of the literature indicates that many aspects of the influence of bioturbation on ecosystem functioning have been studied. The role of digging mammals in arid and semi‐arid zones has been previously established. We collate and review a broader scope of studies, including those carried out in the mesic woodlands and forests of Australia. We identify roles of digging mammals in the context of ecosystem functioning and conservation management. Bioturbation significantly alters soil processes, increasing soil turnover and altering the chemical and structural properties of soil. Greater water infiltration and decreased surface run‐off and erosion alter soil hydrophobicity and increase soil moisture. Diggings capture organic matter, provide habitat for a diversity of microscopic and macroscopic organisms, and increase nutrient cycling. Mycophagous mammals disperse fungi (e.g. mycorrhizae), while all diggings can create suitable sites for fungal growth. Diggings also capture plant seeds, increasing seedling germination, recruitment and plant growth. The overall effect of mammal diggings is therefore increased plant vigour and resilience, increased biodiversity and consequently improved ecosystem functioning. We propose that the loss of digging mammals has contributed to the deterioration of ecosystems in Australia. Recognising the roles of digging mammals will inform potential management options such as species translocations or reintroductions.

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“…Fauna affect the flow of energy through ecosystems via trophic cascades and networks (Terborgh and Estes 2010, Sandom et al 2013b, Fleming et al 2014. In addition to the importance of trophic cascades in determining ecosystem composition (see previous section), trophic network theory highlights the importance of key species in ensuring a functioning ecosystem.…”

The private life of echidnas: using accelerometry and GPS to examine field biomechanics and assess the ecological impact of a widespread, semi-fossorial monotreme

“…Bioturbation is a mechanical form of ecosystem engineering that can alter soil physical and biotic properties (James et al, 2009;Reichman and Seabloom, 2002), resulting in increased soil mixing (Zhang et al, 2003) and species diversity (Ceballos et al, 1999;Davidson and Lightfoot, 2008). Although most mammals associated with bioturbation in Australia have suffered considerable reductions in density and distribution post-European settlement (Fleming et al, 2014;McKenzie et al, 2007) the shortbeaked echidna is the Australian mammalian species least impacted; it has the widest geographical range of any Australian species and is listed as 'least concern' by the International Union for Conservation of Nature red list (Nicol, 2015). Therefore, it may be one of Australia's most important living bioturbators, yet the extent and time it spends digging has not been accurately recorded.…”

Invasive predators and global biodiversity loss

“…The decline and extinction of native species due to invasive predators can have impacts that cascade throughout entire ecosystems (9). For example, predation by feral cats and red foxes (Vulpes vulpes) has led to the decline or extinction of two thirds of Australia's digging mammal species over the past 200 y (10,11). Reduced disturbance to topsoil in the absence of digging mammals has led to impoverished landscapes where little organic matter accumulates and rates of seed germination are low (10).…”

“…For example, predation by feral cats and red foxes (Vulpes vulpes) has led to the decline or extinction of two thirds of Australia's digging mammal species over the past 200 y (10,11). Reduced disturbance to topsoil in the absence of digging mammals has led to impoverished landscapes where little organic matter accumulates and rates of seed germination are low (10). In the Aleutian archipelago, predation of seabirds by introduced Arctic foxes (Alopex lagopus) has lowered nutrient input and soil fertility, ultimately causing vegetation to transform from grasslands to dwarf shrub/forb-dominated systems (12).…”