In a paper published last week in Nature Communications we explored relationships between top predators and lower order predators (mesopredators) across three separate continents. We found that top predators can suppress the abundances of mesopredators, but only when top predators occur at high densities over large areas. The results have important implications for understanding the ecological role of top predators, like dingoes and wolves, and for the conservation of ecosystems more broadly.
The results have been summarised in The Conversation.
See below for links to some of the media generated and for a copy of the abstract.
Reintroducing dingoes can help manage feral foxes and cats, study suggests (SMH)
Dingoes could be used to control fox numbers and prevent ecological decline (ABC)
Dingoes need more space to fight off pests, study finds (Australian Geographic)
Dingoes to the rescue? (Deakin University)
Wolves need space to roam to control expanding coyote population (University of Washington)
Study: to mitigate problem predators, give wolves more space, tolerance (KUOW)
Top predators can suppress mesopredators by killing them, competing for resources and instilling fear, but it is unclear how suppression of mesopredators varies with the distribution and abundance of top predators at large spatial scales and among different ecological contexts. We suggest that suppression of mesopredators will be strongest where top predators occur at high densities over large areas. These conditions are more likely to occur in the core than on the margins of top predator ranges. We propose the Enemy Constraint Hypothesis, which predicts weakened top-down effects on mesopredators towards the edge of top predators’ ranges. Using bounty data from North America, Europe and Australia we show that the effects of top predators on mesopredators increase from the margin towards the core of their ranges, as predicted. Continuing global contraction of top predator ranges could promote further release of mesopredator populations, altering ecosystem structure and contributing to biodiversity loss.
In a recent paper we explored the global impacts of domestic dogs on wildlife.
For a summary see our opinion piece published in The Conversation.
Below is a copy of the abstract and you can view the paper HERE.
Domestic dogs (Canis familiaris) have a near-global distribution. They range from being feral and free-ranging to owned and completely dependent on humans. All types of domestic dogs can interact with wildlife and have severe negative impacts on biodiversity. Here, we use IUCN Red List data to quantify the number of threatened species negatively impacted by dogs, assess the prevalence of different types of dog impact, and identify regional hotspots containing high numbers of impacted species. Using this information, we highlight key research and management gaps and priorities. Domestic dogs have contributed to 11 vertebrate extinctions and are a known or potential threat to at least 188 threatened species worldwide. These estimates are greater than those reported by previous assessments, but are probably conservative due to biases in the species, regions and types of impacts studied and/or reported. Predation is the most frequently reported impact, followed by disturbance, disease transmission, competition, and hybridisation. Regions with the most species impacted are: South-east Asia, Central America and the Caribbean, South America, Asia (excluding SE), Micro/Mela/Polynesia, and Australia. We propose that the impacts of domestic dogs can be better understood and managed through: taxonomic and spatial prioritisation of research and management; examining potential synergisms between dogs and other threatening processes; strategic engagement with animal welfare and human health campaigns; community engagement and education; and mitigating anthropogenic effects such as resource subsidies. Such actions are essential for threatened species persistence, especially given that human and dog populations are expected to increase both numerically and geographically in the coming decades.
Below is a copy of the press release prepared by BioScience.
Press Release by BioScience:
On landscapes around the world, environmental change is bringing people and large carnivores together—but the union is not without its problems. Human–wildlife conflict is on the rise as development continues unabated and apex predators begin to reoccupy their former ranges. Further complicating matters, many of these species are now reliant on anthropogenic, or human foods, including livestock, livestock and other ungulate carcasses, and garbage.
Writing in BioScience, Thomas Newsome, of Deakin University and the University of Sydney, and his colleagues use gray wolves and other large predators as case studies to explore the effects of anthropogenic foods. They find numerous instances of species’ changing their social structures, movements, and behavior to acquire human-provisioned resources. For instance, in central Iran, gray wolves’ diets consist almost entirely of farmed chickens, domestic goats, and garbage.
Other instances of these phenomena abound. In a similar case in Australia, dingoes gained access to anthropogenic foods from a waste facility. The result, according to the authors, was “decreased home-range areas and movements, larger group sizes, and altered dietary preferences to the extent that they filled a similar dietary niche to domestic dogs.” Moreover, wrote the authors, “the population of subsidized dingoes was a genetically distinct cluster,” which may portend future speciation events. Hybridization among similar predator species may also contribute to evolutionary divergence: “Anthropogenic resources in human-modified environments could increase the probability of non-aggressive contact” between species. According to the authors, “If extant wolves continue to increase their reliance on anthropogenic foods, we should expect to observe evidence of dietary niche differentiation and, over time, the development of genetic structure that could signal incipient speciation.”
Wolves’ use of anthropogenic food could have serious implications for wider conservation efforts, as well. In particular, Newsome and his colleagues raise concerns about whether wolf reintroduction and recolonisation programs will meet ecosystem-restoration goals in human-modified systems. Managers will need to consider “how broadly insights into the role played by wolves gleaned from protected areas such as Yellowstone can be applied in areas that have been greatly modified by humans,” say the authors.
Newsome and his colleagues call for further research—in particular, “studies showing the niche characteristics and population structure of wolves in areas where human influence is pervasive and heavy reliance on human foods has been documented.” Through such studies, they argue that “we might be able to ask whether heavy reliance of anthropogenic subsidies can act as a driver of evolutionary divergence and, potentially, provide the makings of a new dog.”
Rob Wallis from the Office of the Deputy Vice-Chancellor (Research & Innovation), the Federation University Australia, recently reviewed our book “The Red Kangaroo in Central Australia; an early account by A.E. Newsome”.
The review was published in the February 2017 issue of The Victorian Naturalist.
A copy of the review is provided below:
“Alan Newsome was one of Australia’s great naturalists and also a leading scientist whose early work focused on the biology of the Red Kangaroo Osphranter rufus. His work on the species began in 1957 and, unbeknown to his family, he had been preparing a book on his research which the publisher (Collins) was expecting to be completed in 1975. However, like so many things in people’s busy lives, it got put aside; why it was never completed remains a mystery. In 2010 his son Thomas discovered the manuscript in a box of materials his father had left behind in his son’s Canberra garage and, after a thorough read of it, Thomas decided to edit it for publication. I suspect Alan intended this book to be primarily an account of the biology of the Red Kangaroo, elucidated by his field work. If readers treat it as such, they will be somewhat disappointed as there have been many more accounts of kangaroo biology published recently that are much more up-to-date and complete. Indeed, this journal has published reviews of such books.
What makes this book a fascinating read, however, is the description of how this pioneer of ecological research went about his work. As the preface notes:
It is rare for an ecologist to write reflectively and personally about the experience of discovery, especially during the early stages of a career … I suspect it is also because few early career scientists have a journey that results in the kind of pioneering discoveries that Alan’s did (p. xx).
Alan Newsome’s research dispelled many myths and incorrect claims about Red Kangaroos. His blend of acute observational skills of a naturalist combined with rigorous scientific examination helped answer these questions:
…why were red kangaroos so abundant on open plains and creeks during droughts, and more so on some than others? Where did they disappear to after rain? Why did they sometimes congregate to form large mobs? What did they eat and did they compete severely or at all with cattle and sheep? How did kangaroos foul pastures as claimed? How could 5 to 10 shooters work one 500 km2 plain 50 km north of Alice Springs night after night in the 1950s without making an impression on numbers? Their breeding would seem to be prodigious for such to happen. So what were the reproductive processes, and what ensured reproductive success?…..Why did kangaroos appear to be more numerous on cattle country than land never stocked? Was it due to stock waters man has made? If so, why were kangaroos so rarely seen at water? Had kangaroos always been so numerous? (pp. 9–10).
For so many questions to be answered in such a slim book is remarkable, especially when they are explained so clearly and logically!
Explorers’ accounts of Central Australia suggest the Red Kangaroo was quite rare before European exploitation of the environment. Yet Newsome observed huge mobs—one of about 1500 animals south of Alice Springs. These massive changes in numbers reflect significant environmental change—change that Newsome also noted had deleterious effects on small to medium sized fauna, which was facing extirpation. His observations and suggested explanations make interesting reading.
Thomas Newsome notes his father rated his paper ‘The Eco-Mythology of the Red Kangaroo in Central Australia’ published in 1980 as his favourite, yet the manuscript proved very difficult to get accepted and remains infrequently cited. Fortunately it is reproduced in full in the book. I found it fascinating in demonstrating Indigenous myths that turned out to be based on sound ecological knowledge. Newsome’s work was prescient—today we should recognise the value of Indigenous knowledge as a sound basis for ecological research and that proper management of our natural assets are best achieved by a blend of Indigenous wisdom with scientific work.
During Newsome’s 16 field trips to the centre between 1959 and 1962 he shot 2000 Red Kangaroos! That was the way in those days—even small mammals were usually caught using break-back traps! I wonder how such research propositions would have fared in today’s environment where work must be approved by independent animal ethic committees?
This is an important book which needs to be read in the context of when it was written and when the research was carried out. In his foreword, Hugh Tyndale-Biscoe believes this book rates with other natural history classics such as Ratcliffe’s Flying Fox and Drifting Sand, Frith’s The Mallee Fowl: the bird that makes an incubator and Rolls’ They All Ran Wild. This may be an exaggeration (it is a slim volume) but certainly field naturalists will enjoy reading about the early journey Newsome took in his field work career.
Frith HJ (1962) The Mallee Fowl: the bird that makes an incubator. (Angus and Robertson: Sydney)
Ratcliffe F (1938) Flying Fox and drifting sand. (Chatto and Windus: London)
Rolls EC (1969) They all ran wild: the story of pests on the land in Australia. (Angus and Robertson: Sydney)”
Thanks Rob for the review.
In a recent paper we explored whether the expansion of golden jackal populations in Europe is linked to the widespread extirpation of the grey wolf.
Below is a copy of the abstract and you can view the open access paper HERE
Top-down suppression by apex predators can limit the abundance and spatial distribution of mesopredators. However, this phenomenon has not been studied over long time periods in human-dominated landscapes, where the strength of this process might be limited. Here, we used a multi-scale approach to analyse interactions between two canids in the human-dominated landscapes of Europe. We tested the hypothesis that the range expansion of golden jackals (Canis aureus) was triggered by intensive persecution and resulting decline of the apex predator, the grey wolf (Canis lupus). To do so, we (1) reviewed literature to reconstruct the historic changes in the distribution and abundance of the two canid species on the continental scale, (2) analysed hunting data patterns for both species in Bulgaria and Serbia, and (3) surveyed jackal persistence in eight study areas that became re-colonized by territorial wolves. The observed trends were generally consistent with the predictions of the mesopredator release hypothesis and supported the existence of top-down suppression by wolves on jackals. We observed inverse patterns of relative abundance and distribution for both canid species at various spatial scales. In most (seven out of eight) cases of wolf re-colonization of jackal territories, jackals disappeared or were displaced out or to the periphery of the newly established wolf home-ranges. We suggest that wolf extermination could be the key driver that enabled the expansion of jackals throughout Europe. Our results also indicate that top-down suppression may be weakened where wolves are intensively persecuted by humans or occur at reduced densities in human-dominated landscapes, which has important management implications and warrants further research.
The arguments focused on two key points:
- That dingo reintroduction proposals have been inspired largely by the reintroduction of wolves into Yellowstone National Park.
- That unstable climates in Australia will make if difficult for dingoes to exert strong effects on ecosystems via trophic cascades.
(see here for a definition of a trophic cascade, and below for an example of a dingo-induced trophic cascade).
In a paper published in the journal Food Webs, we responded to these criticisms and argued that (1) the case for dingo reintroduction has never been solely based on the reintroduction of wolves into Yellowstone National Park, and (2) that the climatic circumstances under which dingoes can provide net positive effects on ecosystems via trophic cascades are those that typically prevail in Australia.
We concluded that the case for dingo reintroduction in Australia remains strong, and urge managers and decision makers to consider the mounting evidence that dingoes can have positive effects on ecosystems before deciding whether or not to reintroduce dingoes into ecosystems where they have been extirpated by humans.
A dingo-induced trophic cascade (solid arrows).
If dingoes suppress large herbivores (e.g. kangaroos and emus), then grass and herb biomass is expected to increase. If dingoes suppress lower order predators (e.g. foxes and cats), then numbers of small mammals (e.g. mice), reptiles (e.g. goannas), and birds (e.g. parrots) are expected to increase. Invertebrates also may respond to improved vegetation conditions and contribute to soil quality. However, the strength of all interactions may be influenced by the extent of rainfall and fires (hashed arrows). Numbers represent the predicted sequence of events based on trophic cascade theory.
Since my last post I have been a co-author on two research papers on feral cats.
1. Legge S, et al (including Newsome TM) (2017) Enumerating a continental-scale threat: how many feral cats are in Australia? (Biological Conservation)
In this paper we found that feral cats cover over 99.8% of Australia’s land area, including almost 80% of the area of our islands.
“Australia’s total feral cat population fluctuates between 2.1 million when times are lean, up to 6.3 million when widespread rain results in plenty of available prey,” explains the lead author Dr Sarah Legge from The University of Queensland.
Furthermore, cat densities were found to be the same both inside and outside conservation reserves, such as National Parks, showing that declaring protected areas alone is not enough to safeguard our native wildlife.
This paper has now become the most heavily ‘e-cited’ paper in the journal Biological Conservation.
A full summary of the media generated can be found HERE
2. Molsher R, Newsome AE, Newsome TM, Dickman CR (2017) Mesopredator management: effects of red fox control on the abundance, diet and use of space by feral cats (PLOS ONE)
In this paper we investigated interactions between red foxes and feral cats in south-eastern Australia.
We used a fox-removal experiment to assess whether foxes affect cat abundance, diet, home-range and habitat use.
The results provide little indication that cats responded numerically to the fox removal, but suggest that the fox affects some aspects of cat resource use. In particular, where foxes were removed cats increased their consumption of invertebrates and carrion, decreased their home range size and foraged more in open habitats.
The results suggest that fox control programs could lead to changes in the way that cats interact with co-occurring prey, and that some prey may become more vulnerable to cat predation in open habitats after foxes have been removed.
The paper was featured in the NRM Research and Innovation Network weekly updates.