Category Archives: Research

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

Authors: Rebecca C Cherubin, Susanna E Venn, Don A Driscoll, Tim S Doherty, and Euan G Ritchie

Published in: Ecological Management & Restoration

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.

Cherubin RC, Venn SE, Driscoll DA, Doherty TS, Ritchie EG (2019) Feral horse impacts on threatened plants and animals in sub-alpine and montane environments in Victoria, Australia. Ecological Management & Restoration PDF DOI

Impacts of feral horses in the Australian Alps and evidence-based solutions

Authors: Don A Driscoll, Graeme L Worboys, Hugh Allan, Sam C Banks, Nicholas J Beeton, Rebecca C Cherubin, Tim S Doherty, C Max Finlayson, Ken Green, Renée Hartley, Geoffrey Hope, Chris N Johnson, Mark Lintermans, Brendan Mackey, David J Paull, Jamie Pittock, Luciana L Porfirio, Euan G Ritchie, Chloe F Sato, Ben C Scheele, Deirdre A Slattery, Susanna Venn, David Watson, Maggie Watson, and Richard M Williams

Published in: Ecological Management & Restoration

Summary

New evidence of impacts by feral horses in Australia’s alpine parks systems confirms they endanger threatened species and extensively damage critically endangered bog communities that could take millennia to recover. These impacts are not confounded by effects of deer and accumulate over time, even when only a small number of feral horses (∼100) are present.

With protected areas representing only a small proportion of the area of the Australian states of New South Wales (9.3%) and Victoria (17%), allowing feral horses to degrade reserves is not a reasonable management compromise, is contrary to the purpose of the protected area system and conflicts with international obligations.

Modelling and decades of management experience indicate that trapping alone does not control feral horse numbers. Trapping and fertility control can work in small populations, but not when there are several thousand horses in remote areas. Aerial culling is needed to cost‐effectively and humanely control feral horse populations.

The relatively small amount of suffering feral horses experience during a cull is outweighed by

  1. avoiding suffering and death of horses from starvation and thirst,
  2. avoiding the suffering of native animals displaced by horses, and
  3. avoiding the ethical concerns of driving threatened species towards extinction.

Objections to aerial culling on welfare and cultural grounds are contradicted by evidence.

Improving knowledge in the general community about what is at stake is long overdue because without this knowledge, small groups with vested interests and unfounded claims have been able to dominate debate and dictate management actions.

As a result of ineffective management, horse populations are now expanding and causing well‐documented damage to Australia’s alpine parks, placing at risk almost $10M spent on restoration after livestock grazing ended. The costs of horse control and restoration escalate the longer large horse populations remain in the alpine parks.

It is crucial that feral horse numbers are rapidly reduced to levels where ecosystems begin to recover. Aerial culling is needed as part of the toolbox to achieve that reduction.

Driscoll DA, Worboys GL, Allan H, Banks SC, Beeton NJ, Cherubin RC, Doherty TS, Finlayson CM, Green K, Hartley R, Hope G, Johnson CN, Lintermans M, Mackey B, Paull DJ, Pittock J, Porfirio LL, Ritchie EG, Sato CF, Scheele BC, Slattery DA, Venn S, Watson D, Watson M, Williams RM (2019) Impacts of feral horses in the Australian Alps and evidence-based solutions. Ecological Management & Restoration PDF DOI 

ABC Science: If extinct animals could be brought back from the dead, should we do it?

We’re living in the middle of an extinction crisis, on par with what wiped out the dinosaurs 65 million years ago. But an asteroid isn’t responsible this time; we are.

Imagine walking into the most beautiful museum, taking all the artworks off the shelves and burning them or throwing them in the bin. That’s what we’re doing. We’re losing species every day all over the world.

De-extinction science can never replicate the wonder of evolution, nor how long it takes for species to evolve…

Read the full article on the ABC website

The secret life of possums: data loggers reveal the movement ecology of an arboreal mammal

Authors: Blake M Allan, Dale G Nimmo, John P Y Arnould, Jennifer K Martin, and Euan G Ritchie

Published in: Journal of Mammalogy

Abstract

Understanding animal movement patterns is fundamental to ecology, as it allows inference about species’ habitat preferences and their niches. Such knowledge also underpins our ability to predict how animals may respond to environmental change, including habitat loss and modification. Data-logging devices such as GPS trackers and accelerometers are rapidly becoming cheaper and smaller, allowing movement at fine scales to be recorded on a broad range of animal species.

We examined movement patterns of an arboreal mammal (bobuck, Trichosurus cunninghami) in a highly fragmented forest ecosystem.

The GPS data showed males travelled greater distances than females in linear roadside strip habitats, but not in forest fragments. The accelerometer data showed that both sexes exhibited higher activity levels in roadside habitats compared to forest fragments. By coupling GPS and accelerometer data, we uncovered for this species an ecological pattern similar to other mammals: that male bobucks had higher activity levels than females for a given distance travelled.

Our findings also suggest that habitat fragmentation changes the amount and type of activity bobucks perform while moving, and that linear forest strips could be considered “energetically challenging” habitats, which informs how we should manage the spatial distribution of key supplementary resources for this species such as nest sites and minimum fragment sizes.

Allan BM, Nimmo DG, Arnould JPY, Martin JK, Ritchie EG (2018) The secret life of possums: data loggers reveal the movement ecology of an arboreal mammal. Journal of Mammalogy PDF DOI

Diversity in Australia’s tropical savannas: An integrative taxonomic revision of agamid lizards from the genera Amphibolurus and Lophognathus (Lacertilia: Agamidae)

Authors: Jane Melville, Euan G Ritchie, Stephanie N J Chapple, Richard E Glor And James A Schulte II

Published in: Memoirs of Museum Victoria, volume 77

Abstract

The taxonomy of many of Australia’s agamid lizard genera remains unresolved because morphological characters have proved to be unreliable across numerous lineages. We undertook a morphological study and integrated this with a recent genetic study to resolve long-standing taxonomic problems in three genera of large-bodied Australian agamid lizards: Amphibolurus, Gowidon and Lophognathus. We had broad geographic sampling across genera, including all currently recognised species and subspecies.

Using an integrative taxonomic approach, incorporating mitochondrial (ND2) and nuclear (RAG1) genetic data, and our morphological review, we found that both generic and species-level taxonomic revisions were required. We revise generic designations, creating one new genus (Tropicagama gen. nov.) and confirming the validity of Gowidon, giving a total of four genera. In addition, we describe a new species (Lophognathus horneri sp. nov.) and reclassify two other species.

Our results provide a significant step forward in the taxonomy of some of Australia’s most iconic and well-known lizards and provide a clearer understanding of biogeographic patterns across Australia’s monsoonal and arid landscapes.

Melville J, Ritchie EG, Chapple SNJ, Glor RE Schulte II JA (2018) Diversity in Australia’s tropical savannas: An integrative taxonomic revision of agamid lizards from the genera Amphibolurus and Lophognathus (Lacertilia: Agamidae). Memoirs of Museum Victoria PDF DOI

Towards meaningful monitoring: A case study of a threatened rodent

Authors: Hayley M Geyle, Gurutzeta Guillera‐Arroita, Hugh F Davies, Ronald S C Firth, Brett P Murphy, Dale G Nimmo, Euan G Ritchie, John C Z Woinarski, and Emily Nicholson

Published in: Austral Ecology

Abstract

Detecting trends in species’ distribution and abundance are essential for conserving threatened species, and depend upon effective monitoring programmes. Despite this, monitoring programmes are often designed without explicit consideration of their ability to deliver the information required by managers, such as their power to detect population changes.

Here, we demonstrate the use of existing data to support the design of monitoring programmes aimed at detecting declines in species occupancy. We used single‐season occupancy models and baseline data to gain information on variables affecting the occupancy and detectability of the threatened brush‐tailed rabbit‐rat Conilurus penicillatus (Gould 1842) on the Tiwi Islands, Australia. This information was then used to estimate the survey effort required to achieve sufficient power to detect changes in occupancy of different magnitudes.

We found that occupancy varied spatially, driven primarily by habitat (canopy height and cover, distance to water) and fire history across the landscape. Detectability varied strongly among seasons, and was three times higher in the late dry season (July–September), compared to the early dry season (April–June). Evaluation of three monitoring scenarios showed that conducting surveys at times when detectability is highest can lead to a substantial improvement in our ability to detect declines, thus reducing the survey effort and costs.

Our study highlights the need for careful consideration of survey design related to the ecology of a species, as it can lead to substantial cost savings and improved insight into species population change via monitoring.

Geyle HM, Guillera-Arroita G, Davies HF, Firth RSC, Murphy BP, Nimmo DG, Ritchie EG, Woinarski JCZ, Nicholson E (2018) Towards meaningful monitoring: A case study of a threatened rodent. Austral Ecology, PDF DOI

Eradicating abundant invasive prey could cause unexpected and varied biodiversity outcomes: The importance of multispecies interactions

Authors: Miguel Lurgi, Euan G Ritchie, and Damien A Fordham

Published in: Journal of Applied Ecology

Abstract

Abundant and widely distributed invasive prey can negatively affect co‐occurring native species by competing for food and/or shelter, removing vegetation cover and reducing habitat complexity (changing predation risk), and by sustaining elevated abundances of invasive mesopredators. However, information regarding the community and trophic consequences of controlling invasive prey and their temporal dynamics remain poorly understood.

We used multispecies ecological network models to simulate the consequences of changing European rabbit Oryctolagus cuniculus abundance in an arid mammalian community. We quantified how changes in the dominant prey (rabbits) affected multiple trophic levels, examining changes in predator–prey interactions through time and how they affected native prey persistence.

Our results suggest that removal of rabbits can benefit native biodiversity immediately at removal rates between 30% and 40%. However, beyond these levels, densities of small native mammals will decline in the short term. The processes underpinning these declines are: (a) increased competition for resources (vegetation) with kangaroos Macropus spp., whose numbers increase due to their release from competition with rabbits and (b) increased predation (prey switching) by feral cats Felis catus. Both effects are mediated by dingoes Canis dingo, a native apex predator.

Importantly, native mammal abundance recovers after a time delay, which is prolonged when high rates of rabbit control are applied. This is likely due to a reduction in hyperpredation by invasive feral cats and red foxes Vulpes vulpes following rabbit removal.

Continued eradication of rabbits in arid Australia will benefit native species due to a decrease in apparent competition for resources and by alleviating hyperpredation from invasive mesopredators. Furthermore, ecosystem‐level conservation benefits of reducing invasive prey abundance are as important as direct control of invasive mesopredators.

Synthesis and applications: Multispecies ecological network models provide wildlife managers with tools to better understand and predict the complex effects of species removal and control on both intact and modified ecosystems. Our results show that management of the Australian arid zone can benefit from controlling invasive prey as well as invasive predators. However, invasive species control can cause unexpected outcomes on native biodiversity. This extends to other systems where dominant prey may play fundamental roles in ecosystem structure and function.

Lurgi M, Ritchie EG, Fordham DA (2018) Eradicating abundant invasive prey could cause unexpected and varied biodiversity outcomes: The importance of multispecies interactions, Journal of Applied Ecology, PDF DOI