Rowena Hamer | University of Tasmania (original) (raw)

Papers by Rowena Hamer

Journal of Animal Ecology, May 23, 2023

Understanding the spatial dynamics and drivers of wildlife pathogens is constrained by sampling l... more Understanding the spatial dynamics and drivers of wildlife pathogens is constrained by sampling logistics, with implications for advancing the field of landscape epidemiology and targeted allocation of management resources. However, visually apparent wildlife diseases, when combined with remote‐surveillance and distribution modelling technologies, present an opportunity to overcome this landscape‐scale problem. Here, we investigated dynamics and drivers of landscape‐scale wildlife disease, using clinical signs of sarcoptic mange (caused by Sarcoptes scabiei) in its bare‐nosed wombat (BNW; Vombatus ursinus) host. We used 53,089 camera‐trap observations from over 3261 locations across the 68,401 km2 area of Tasmania, Australia, combined with landscape data and ensemble species distribution modelling (SDM). We investigated: (1) landscape variables predicted to drive habitat suitability of the host; (2) host and landscape variables associated with clinical signs of disease in the host; and (3) predicted locations and environmental conditions at greatest risk of disease occurrence, including some Bass Strait islands where BNW translocations are proposed. We showed that the Tasmanian landscape, and ecosystems therein, are nearly ubiquitously suited to BNWs. Only high mean annual precipitation reduced habitat suitability for the host. In contrast, clinical signs of sarcoptic mange disease in BNWs were widespread, but heterogeneously distributed across the landscape. Mange (which is environmentally transmitted in BNWs) was most likely to be observed in areas of increased host habitat suitability, lower annual precipitation, near sources of freshwater and where topographic roughness was minimal (e.g. human modified landscapes, such as farmland and intensive land‐use areas, shrub and grass lands). Thus, a confluence of host, environmental and anthropogenic variables appear to influence the risk of environmental transmission of S. scabiei. We identified that the Bass Strait Islands are highly suitable for BNWs and predicted a mix of high and low suitability for the pathogen. This study is the largest spatial assessment of sarcoptic mange in any host species, and advances understanding of the landscape epidemiology of environmentally transmitted S. scabiei. This research illustrates how host‐pathogen co‐suitability can be useful for allocating management resources in the landscape.

Australian Mammalogy, Sep 20, 2022

Like many other Australian mammals, eastern quolls (Dasyurus viverrinus) were widespread in the s... more Like many other Australian mammals, eastern quolls (Dasyurus viverrinus) were widespread in the south-east of mainland Australia but went extinct there during the 20th century. The species remained abundant in Tasmania until it rapidly declined from 2001 to 2003, coinciding with a period of unsuitable weather. We provide an updated analysis of eastern quoll population trends in Tasmania using a time series of annual spotlight counts (1985–2019) collected across most of the species’ range. Eastern quolls were widespread and abundant in Tasmania until the early 2000s. In addition to the previously documented severe decline in the early 2000s in the east and northeast, we present new evidence of an earlier decline in the north (mid-1990s) and a more recent decline in the south (~2009). Declines have continued unabated during the last decade, resulting in a ~67% decline since the late 1990s in the area with high quoll abundance. Although the major decline in the early 2000s coincided with unfavourable weather, the continuing and more recent declines suggest other undetermined causes are also involved. We can no longer assume the presence of eastern quolls in Tasmania ensures the species’ long-term survival, highlighting the urgent need to conserve the remaining populations in Tasmania.

Science, Sep 9, 2016

Edited by Jennifer Sills LETTERS A Tokyo Electric Power Co. (TEPCO) employee walks in front of th... more Edited by Jennifer Sills LETTERS A Tokyo Electric Power Co. (TEPCO) employee walks in front of the No. 1 reactor building at TEPCO's tsunami-crippled Fukushima Daiichi nuclear power plant in the town of Okuma, Japan. After the Fukushima disaster, support among Chinese citizens for China's nuclear energy program plummeted.

Australian Mammalogy

Like many other Australian mammals, eastern quolls (Dasyurus viverrinus) were widespread in the s... more Like many other Australian mammals, eastern quolls (Dasyurus viverrinus) were widespread in the south-east of mainland Australia but went extinct there during the 20th century. The species remained abundant in Tasmania until it rapidly declined from 2001 to 2003, coinciding with a period of unsuitable weather. We provide an updated analysis of eastern quoll population trends in Tasmania using a time series of annual spotlight counts (1985–2019) collected across most of the species’ range. Eastern quolls were widespread and abundant in Tasmania until the early 2000s. In addition to the previously documented severe decline in the early 2000s in the east and northeast, we present new evidence of an earlier decline in the north (mid-1990s) and a more recent decline in the south (~2009). Declines have continued unabated during the last decade, resulting in a ~67% decline since the late 1990s in the area with high quoll abundance. Although the major decline in the early 2000s coincided wi...

Pacific Conservation Biology

Proceedings of the Royal Society B: Biological Sciences

Correction to: 'A triple threat: high population density, high foraging intensity and flexible ha... more Correction to: 'A triple threat: high population density, high foraging intensity and flexible habitat preferences explain high impact of feral cats on prey' (2021) by Hamer et al.

Tasmanian populations of the eastern quoll Dasyurus viverrinus, which represent the last wild str... more Tasmanian populations of the eastern quoll Dasyurus viverrinus, which represent the last wild stronghold of this species after its extirpation from the Australian mainland, have experienced declines of more than 50% over the past three decades. In this pilot study, we investigate the feasibility of supplementing wild populations with captive-bred individuals to attempt to reverse observed declines. Our results are encouraging, in that we recorded high initial survival and low initial dispersal of captive-bred individuals relative to previous release attempts in mainland Australia. Further work is ongoing to determine long-term survival of released individuals and the genetic and population-level impacts on local populations. Our preliminary results support the use of population supplementation as an effective conservation action, which allows for early intervention to address species declines while simultaneously testing hypotheses about their underlying causes.

Ecological Management & Restoration, 2021

Article type : Feature Article Research supporting restoration aiming to make a frag e ted la dsc... more Article type : Feature Article Research supporting restoration aiming to make a frag e ted la dscape fu ctio al for native wildlife Summary Temperate woodlands are among the most threatened ecosystems in Australia because the land on which they occur is highly suited to agriculture. Two hundred years of habitat loss and fragmentation in the Midlands agricultural region in Tasmania have led to widespread declines in native vertebrates and landscapes with populations of predators including feral Cat (Felis catus) and the native-invasive Noisy Miner (Manorina melanocephala). Ecologists at the University of Tasmania co-designed mechanistic animal-centric research on mammals and birds in the Midlands to inform vegetation restoration carried out by Greening Australia that would support the recovery of wildlife species. We used species-appropriate technologies to assess the decisions made by individual animals to find food and shelter and to disperse across this fragmented landscape, and linked these, together with patterns of occupancy, across multiple spatial and temporal scales. We focussed on a native (Spottedtailed Quoll, Dasyurus maculatus) and an invasive (Cat) carnivore, a woodland-specialist herbivore (Eastern Bettong, Bettongia gaimardi) and woodland birds including the nativeinvasive Noisy Miner. Our results, which show intense predatory and competitive pressure of Cat and Noisy Miners on native fauna, highlight how grounding restoration in the context of ecological

Landscape Ecology, 2018

Context The classical theory of island biogeography explains loss of species in fragmented landsc... more Context The classical theory of island biogeography explains loss of species in fragmented landscapes as an effect of remnant patch size and isolation. Recently this has been challenged by the habitat amount and habitat continuum hypotheses, according to which persistence in modified landscapes is related to total habitat amount rather than habitat configuration or the ability of species to use all habitats to varying degrees. Distinguishing between these theories is essential for effective conservation planning in modified landscapes. Objective Identify which factors of habitat type, amount and configuration predict the persistence of a keystone woodland specialist, the eastern bettong Bettongia gaimardi, in a fragmented landscape. Method In the Midlands region of Tasmania we carried out camera surveys at 62 sites in summer and winter. We included habitat and landscape features to model whether habitat amount or patch size and isolation influenced the presence of the eastern bettong, and to measure effects of habitat quality. Results Habitat amount within a 1 km buffer was a better predictor of occupancy than patch size and isolation. Occupancy was also affected by habitat quality, indicated by density of regenerating stems. Conclusion Our results support the habitat amount hypothesis as a better predictor of presence. For a species that is able to cross the matrix between remnant patches and utilise multiple patches, the island biogeography concept does not explain habitat use in fragmented landscapes. Our results emphasize the value of small remnant patches for conservation of the eastern bettong, provided those patches are in good condition.

Ecological Management & Restoration, 2021

This is the author manuscript accepted for publication and has undergone full peer review but has... more This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Like many other Australian mammals, the eastern quoll (Dasyurus viverrinus) was widespread on the... more Like many other Australian mammals, the eastern quoll (Dasyurus viverrinus) was widespread on the Australian mainland but went extinct there during the 20th century. The species remained abundant in Tasmania until a rapid decline occurred from 2001 to 2003, coinciding with a period of unsuitable weather. We provide an updated analysis of eastern quoll population trends in Tasmania by analysing a Tasmania-wide time series of annual spotlight counts (1985-2019). Eastern quolls were widespread and abundant in Tasmania until the early 2000s. A distinct change occurred in the early 2000s in the east and northeast, which led to severe population reductions. However, we present new evidence of an earlier decline in the north (mid-1990s) and a more recent decline around 2009 in the south. Range-wide declines have continued unabated during the last decade, resulting in a ∼67% decline (since the late 1990s) in the area with high quoll abundance. Although the timing of the major decline in the...

Biology Letters, 2011

Olfaction is a common sensory mode of communication in much of the Vertebrata, although its use b... more Olfaction is a common sensory mode of communication in much of the Vertebrata, although its use by adult frogs remains poorly studied. Being part of an open signalling system, odour cues can be exploited by ‘eavesdropping’ predators that hunt by smell, making association with odour a high-risk behaviour for prey. Here, we show that adult great barred frogs ( Mixophes fasciolatus ) are highly attracted to odour cues of conspecifics and those of sympatric striped marsh frogs ( Limnodynastes peronii ). This attraction decreased significantly with the addition of odours of a scent-hunting predator, the red-bellied black snake ( Pseudechis porphyriacus ), indicating that frogs perceived predation risks from associating with frog odours. Male frogs, however, maintained some attraction to unfamiliar conspecific scents even with predator odours present, suggesting that they perceived benefits of odour communication despite the risk. Our results indicate that adult frogs can identify species...

Ecological Management & Restoration

Sleeper populations of non-native species can remain at low abundance for decades before irruptin... more Sleeper populations of non-native species can remain at low abundance for decades before irrupting. For over a century, fallow deer ( Dama dama ) in the island state of Tasmania, Australia, remained at low abundance and close to the region in which they were released. Recently, there are indications the population has increased in abundance and distribution. Here, we spatially quantify the population change using a time series of annual spotlight counts from 1985 to 2019 (total of 5,761 counts). Next, we predict the potential for further range expansion, using global occurrences to characterise the species’ climatic niche, and remote-camera surveys (n = 3,225) to model fine-grained habitat suitability. Spotlight counts of fallow deer increased by 11.5% annually, resulting in a 40-fold increase from 1985 to 2019. The core distribution increased 2.9-fold during this 35-year period, and now spans c. 27% of Tasmania’s land area. Satellite populations have established in locations where ...

Journal of Animal Ecology, May 23, 2023

Understanding the spatial dynamics and drivers of wildlife pathogens is constrained by sampling l... more Understanding the spatial dynamics and drivers of wildlife pathogens is constrained by sampling logistics, with implications for advancing the field of landscape epidemiology and targeted allocation of management resources. However, visually apparent wildlife diseases, when combined with remote‐surveillance and distribution modelling technologies, present an opportunity to overcome this landscape‐scale problem. Here, we investigated dynamics and drivers of landscape‐scale wildlife disease, using clinical signs of sarcoptic mange (caused by Sarcoptes scabiei) in its bare‐nosed wombat (BNW; Vombatus ursinus) host. We used 53,089 camera‐trap observations from over 3261 locations across the 68,401 km2 area of Tasmania, Australia, combined with landscape data and ensemble species distribution modelling (SDM). We investigated: (1) landscape variables predicted to drive habitat suitability of the host; (2) host and landscape variables associated with clinical signs of disease in the host; and (3) predicted locations and environmental conditions at greatest risk of disease occurrence, including some Bass Strait islands where BNW translocations are proposed. We showed that the Tasmanian landscape, and ecosystems therein, are nearly ubiquitously suited to BNWs. Only high mean annual precipitation reduced habitat suitability for the host. In contrast, clinical signs of sarcoptic mange disease in BNWs were widespread, but heterogeneously distributed across the landscape. Mange (which is environmentally transmitted in BNWs) was most likely to be observed in areas of increased host habitat suitability, lower annual precipitation, near sources of freshwater and where topographic roughness was minimal (e.g. human modified landscapes, such as farmland and intensive land‐use areas, shrub and grass lands). Thus, a confluence of host, environmental and anthropogenic variables appear to influence the risk of environmental transmission of S. scabiei. We identified that the Bass Strait Islands are highly suitable for BNWs and predicted a mix of high and low suitability for the pathogen. This study is the largest spatial assessment of sarcoptic mange in any host species, and advances understanding of the landscape epidemiology of environmentally transmitted S. scabiei. This research illustrates how host‐pathogen co‐suitability can be useful for allocating management resources in the landscape.

Australian Mammalogy, Sep 20, 2022

Like many other Australian mammals, eastern quolls (Dasyurus viverrinus) were widespread in the s... more Like many other Australian mammals, eastern quolls (Dasyurus viverrinus) were widespread in the south-east of mainland Australia but went extinct there during the 20th century. The species remained abundant in Tasmania until it rapidly declined from 2001 to 2003, coinciding with a period of unsuitable weather. We provide an updated analysis of eastern quoll population trends in Tasmania using a time series of annual spotlight counts (1985–2019) collected across most of the species’ range. Eastern quolls were widespread and abundant in Tasmania until the early 2000s. In addition to the previously documented severe decline in the early 2000s in the east and northeast, we present new evidence of an earlier decline in the north (mid-1990s) and a more recent decline in the south (~2009). Declines have continued unabated during the last decade, resulting in a ~67% decline since the late 1990s in the area with high quoll abundance. Although the major decline in the early 2000s coincided with unfavourable weather, the continuing and more recent declines suggest other undetermined causes are also involved. We can no longer assume the presence of eastern quolls in Tasmania ensures the species’ long-term survival, highlighting the urgent need to conserve the remaining populations in Tasmania.

Science, Sep 9, 2016

Edited by Jennifer Sills LETTERS A Tokyo Electric Power Co. (TEPCO) employee walks in front of th... more Edited by Jennifer Sills LETTERS A Tokyo Electric Power Co. (TEPCO) employee walks in front of the No. 1 reactor building at TEPCO's tsunami-crippled Fukushima Daiichi nuclear power plant in the town of Okuma, Japan. After the Fukushima disaster, support among Chinese citizens for China's nuclear energy program plummeted.

Australian Mammalogy

Like many other Australian mammals, eastern quolls (Dasyurus viverrinus) were widespread in the s... more Like many other Australian mammals, eastern quolls (Dasyurus viverrinus) were widespread in the south-east of mainland Australia but went extinct there during the 20th century. The species remained abundant in Tasmania until it rapidly declined from 2001 to 2003, coinciding with a period of unsuitable weather. We provide an updated analysis of eastern quoll population trends in Tasmania using a time series of annual spotlight counts (1985–2019) collected across most of the species’ range. Eastern quolls were widespread and abundant in Tasmania until the early 2000s. In addition to the previously documented severe decline in the early 2000s in the east and northeast, we present new evidence of an earlier decline in the north (mid-1990s) and a more recent decline in the south (~2009). Declines have continued unabated during the last decade, resulting in a ~67% decline since the late 1990s in the area with high quoll abundance. Although the major decline in the early 2000s coincided wi...

Pacific Conservation Biology

Proceedings of the Royal Society B: Biological Sciences

Correction to: 'A triple threat: high population density, high foraging intensity and flexible ha... more Correction to: 'A triple threat: high population density, high foraging intensity and flexible habitat preferences explain high impact of feral cats on prey' (2021) by Hamer et al.

Tasmanian populations of the eastern quoll Dasyurus viverrinus, which represent the last wild str... more Tasmanian populations of the eastern quoll Dasyurus viverrinus, which represent the last wild stronghold of this species after its extirpation from the Australian mainland, have experienced declines of more than 50% over the past three decades. In this pilot study, we investigate the feasibility of supplementing wild populations with captive-bred individuals to attempt to reverse observed declines. Our results are encouraging, in that we recorded high initial survival and low initial dispersal of captive-bred individuals relative to previous release attempts in mainland Australia. Further work is ongoing to determine long-term survival of released individuals and the genetic and population-level impacts on local populations. Our preliminary results support the use of population supplementation as an effective conservation action, which allows for early intervention to address species declines while simultaneously testing hypotheses about their underlying causes.

Ecological Management & Restoration, 2021

Article type : Feature Article Research supporting restoration aiming to make a frag e ted la dsc... more Article type : Feature Article Research supporting restoration aiming to make a frag e ted la dscape fu ctio al for native wildlife Summary Temperate woodlands are among the most threatened ecosystems in Australia because the land on which they occur is highly suited to agriculture. Two hundred years of habitat loss and fragmentation in the Midlands agricultural region in Tasmania have led to widespread declines in native vertebrates and landscapes with populations of predators including feral Cat (Felis catus) and the native-invasive Noisy Miner (Manorina melanocephala). Ecologists at the University of Tasmania co-designed mechanistic animal-centric research on mammals and birds in the Midlands to inform vegetation restoration carried out by Greening Australia that would support the recovery of wildlife species. We used species-appropriate technologies to assess the decisions made by individual animals to find food and shelter and to disperse across this fragmented landscape, and linked these, together with patterns of occupancy, across multiple spatial and temporal scales. We focussed on a native (Spottedtailed Quoll, Dasyurus maculatus) and an invasive (Cat) carnivore, a woodland-specialist herbivore (Eastern Bettong, Bettongia gaimardi) and woodland birds including the nativeinvasive Noisy Miner. Our results, which show intense predatory and competitive pressure of Cat and Noisy Miners on native fauna, highlight how grounding restoration in the context of ecological

Landscape Ecology, 2018

Context The classical theory of island biogeography explains loss of species in fragmented landsc... more Context The classical theory of island biogeography explains loss of species in fragmented landscapes as an effect of remnant patch size and isolation. Recently this has been challenged by the habitat amount and habitat continuum hypotheses, according to which persistence in modified landscapes is related to total habitat amount rather than habitat configuration or the ability of species to use all habitats to varying degrees. Distinguishing between these theories is essential for effective conservation planning in modified landscapes. Objective Identify which factors of habitat type, amount and configuration predict the persistence of a keystone woodland specialist, the eastern bettong Bettongia gaimardi, in a fragmented landscape. Method In the Midlands region of Tasmania we carried out camera surveys at 62 sites in summer and winter. We included habitat and landscape features to model whether habitat amount or patch size and isolation influenced the presence of the eastern bettong, and to measure effects of habitat quality. Results Habitat amount within a 1 km buffer was a better predictor of occupancy than patch size and isolation. Occupancy was also affected by habitat quality, indicated by density of regenerating stems. Conclusion Our results support the habitat amount hypothesis as a better predictor of presence. For a species that is able to cross the matrix between remnant patches and utilise multiple patches, the island biogeography concept does not explain habitat use in fragmented landscapes. Our results emphasize the value of small remnant patches for conservation of the eastern bettong, provided those patches are in good condition.

Ecological Management & Restoration, 2021

This is the author manuscript accepted for publication and has undergone full peer review but has... more This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Like many other Australian mammals, the eastern quoll (Dasyurus viverrinus) was widespread on the... more Like many other Australian mammals, the eastern quoll (Dasyurus viverrinus) was widespread on the Australian mainland but went extinct there during the 20th century. The species remained abundant in Tasmania until a rapid decline occurred from 2001 to 2003, coinciding with a period of unsuitable weather. We provide an updated analysis of eastern quoll population trends in Tasmania by analysing a Tasmania-wide time series of annual spotlight counts (1985-2019). Eastern quolls were widespread and abundant in Tasmania until the early 2000s. A distinct change occurred in the early 2000s in the east and northeast, which led to severe population reductions. However, we present new evidence of an earlier decline in the north (mid-1990s) and a more recent decline around 2009 in the south. Range-wide declines have continued unabated during the last decade, resulting in a ∼67% decline (since the late 1990s) in the area with high quoll abundance. Although the timing of the major decline in the...

Biology Letters, 2011

Olfaction is a common sensory mode of communication in much of the Vertebrata, although its use b... more Olfaction is a common sensory mode of communication in much of the Vertebrata, although its use by adult frogs remains poorly studied. Being part of an open signalling system, odour cues can be exploited by ‘eavesdropping’ predators that hunt by smell, making association with odour a high-risk behaviour for prey. Here, we show that adult great barred frogs ( Mixophes fasciolatus ) are highly attracted to odour cues of conspecifics and those of sympatric striped marsh frogs ( Limnodynastes peronii ). This attraction decreased significantly with the addition of odours of a scent-hunting predator, the red-bellied black snake ( Pseudechis porphyriacus ), indicating that frogs perceived predation risks from associating with frog odours. Male frogs, however, maintained some attraction to unfamiliar conspecific scents even with predator odours present, suggesting that they perceived benefits of odour communication despite the risk. Our results indicate that adult frogs can identify species...

Ecological Management & Restoration

Sleeper populations of non-native species can remain at low abundance for decades before irruptin... more Sleeper populations of non-native species can remain at low abundance for decades before irrupting. For over a century, fallow deer ( Dama dama ) in the island state of Tasmania, Australia, remained at low abundance and close to the region in which they were released. Recently, there are indications the population has increased in abundance and distribution. Here, we spatially quantify the population change using a time series of annual spotlight counts from 1985 to 2019 (total of 5,761 counts). Next, we predict the potential for further range expansion, using global occurrences to characterise the species’ climatic niche, and remote-camera surveys (n = 3,225) to model fine-grained habitat suitability. Spotlight counts of fallow deer increased by 11.5% annually, resulting in a 40-fold increase from 1985 to 2019. The core distribution increased 2.9-fold during this 35-year period, and now spans c. 27% of Tasmania’s land area. Satellite populations have established in locations where ...