Feral horse impacts on threatened plants and animals in sub‐alpine and montane environments in Victoria, Australia

Abstract

Summary Feral herbivores are a major driver of biodiversity loss globally and can alter the structure, composition and functioning of ecosystems. The direct impacts of feral herbivores on plant communities are well studied, but the direct and indirect effect they have on wildlife is not well understood. In Victoria (south‐eastern Australia), a large feral Horse (Equus caballus) population coincides with highly sensitive and nationally endangered Alpine Sphagnum Bogs and Associated Fens communities, and several threatened animal species. We assessed the impact of feral horses on this ecological community and the Alpine Water Skink (Eulamprus kosciuskoi) and the Broad‐toothed Rat (Mastacomys fuscus) at 20 sites with varying levels of horse disturbance. We used scat counts to determine an index of feral horse abundance and quantified impacts associated with their presence in the landscape. Active searches were used for Alpine Water Skink and scat and runway surveys for Broad‐toothed Rat. We also measured the vegetation structure and the abundance of different vegetation types (life forms). Our results suggest that feral horses are associated with vegetation types and characteristics that negatively influence the presence or abundance of Alpine Water Skink and Broad‐toothed Rat. Sites with high horse activity had more low‐growing forbs, and the abundance of Alpine Water Skink was negatively related to this vegetation type. Grasses, sedges, rushes and shrubs were also less dense and lower in height in high horse activity sites, and Broad‐toothed Rat was less likely to be present in areas with these habitat attributes. We recommend that feral horses are controlled to protect these threatened vertebrate species and their Sphagnum bog habitat.

Sage‐Grouse Population Dynamics are Adversely Affected by Overabundant Feral Horses

“…Previous research on ecological effects of horses has largely focused on vegetation and soils (Davies and Boyd 2019), but few studies have addressed effects on wildlife (Eldridge et al 2020). Although interactions between horses and other ungulates have been investigated (Berger 1985, Ostermann‐Kelm et al 2008, Perry et al 2015, Gooch et al 2017, Hall et al 2018), the effects to sensitive species are not well‐understood (Cherubin et al 2019). Our study corroborates hypothesized links between horses and sage‐grouse populations (Beever and Aldridge 2011) by demonstrating reductions in sage‐grouse population λ in response to increases in horse abundances relative to AML max settings.…”

Modelling the factors influencing Sambar Deer (Rusa unicolor) occurrence in the wet eucalypt forests of south-eastern Australia

“…The Australian environment and Australian biodiversity have been affected by a wide range of exotic animals (Woinarski et al 2015). These include large introduced herbivores (Braysher 2017; West 2018) such as horses (Equus caballus) (Cherubin et al 2019;Driscoll et al 2019), camels (Camelus dromedaries) (Hart and Edwards 2016), goats (Capra hircus) (Masters et al 2018), and buffalo (Bubalus bubalis). Six species of deer also have become established in Australia (Braysher 2017).…”

Untangling the influence of biotic and abiotic factors on habitat selection by a tropical rodent

“…Kutt and Gordon 31 found differences in small mammal diversity and abundance between grazed and ungrazed areas, and Legge et al 32 noted trampling and soil compaction as a potential effect on populations of small mammals in tropical Australia. In montane regions, overgrazing by feral horses changes habitat composition and structural complexity, exposing broad toothed rats ( Mastocomys fuscus ) to higher rates of predation and leading to their extirpation from areas with high abundance of horses 33 , 34 . In keeping with this broader background, previous studies have speculated that hoofed ungulates can impact populations of Rattus tunneyi via refuge destruction 16 , 35 , 36 .…”