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The Journal of Animal Ecology has now released my latest paper in the ‘accepted unedited articles section’. Below is a copy of the abstract.
Paper title: A continental scale trophic cascade from wolves through coyotes to foxes
By: Thomas M Newsome and William J Ripple
- Top-down processes, via the direct and indirect effects of interspecific competitive killing (no consumption of the kill) or intraguild predation (consumption of the kill), can potentially influence the spatial distribution of terrestrial predators, but few studies have demonstrated the phenomenon at a continental scale.
- For example, in North America, grey wolves (Canis lupus) are known to kill coyotes (Canis latrans), and coyotes, in turn, may kill foxes (Vulpes spp.), but the spatial effects of these competitive interactions at large scales are unknown.
- Here, we analyse fur return data across eight jurisdictions in North America to test whether the presence or absence of wolves has caused a continent-wide shift in coyote and red fox (Vulpes vulpes) density.
- Our results support the existence of a continental scale cascade whereby coyotes outnumber red foxes in areas where wolves have been extirpated by humans, whereas red foxes outnumber coyotes in areas where wolves are present. However, for a distance of up to 200 km on the edge of wolf distribution, there is a transition zone where the effects of top-down control are weakened, possibly due to the rapid dispersal and reinvasion capabilities of coyotes into areas where wolves are sporadically distributed or at low densities.
- Our results have implications for understanding how the restoration of wolf populations across North America could potentially affect co-occurring predators and prey. We conclude that large carnivores may need to occupy large continuous areas to facilitate among-carnivore cascades and that studies of small areas may not be indicative of the effects of top-down mesopredator control.
Oregon State University Press Release
This story is also available here
CORVALLIS, Ore. — Scientists have used coyote and red fox fur trapping records across North America to show how the presence of wolves influences the balance of smaller predators further down the food chain. From Alaska and Yukon to Nova Scotia and Maine, the researchers have demonstrated that a “wolf effect” exists, favoring red foxes where wolves are present and coyotes where wolves are absent.
This effect requires that enough wolves be present to suppress coyotes over a wide area. Fur trapping records from Saskatchewan and Manitoba reveal that, where wolves are absent in the southern agricultural regions of each province, coyotes outnumber foxes on average by 3 to 1. However, where wolves are abundant in the north, the balance swings dramatically in favor of foxes on average by 4 to 1 and at an extreme of 500 to 1 at one site. In between is a 200-kilometer (124-mile) transition zone where too few wolves are present to tip the balance between coyotes and foxes.
The results of the study by Thomas Newsome and William Ripple in the Oregon State University Department of Forest Ecosystems and Society were published today in the Journal of Animal Ecology by the British Ecological Society.
“As wolves were extirpated across the southern half of North America, coyotes dramatically expanded their range,” said Newsome, a post-doctoral researcher. “They were historically located in the middle and western United States, but they dispersed all the way to Alaska in the early 1900’s and to New Brunswick and Maine by the 1970s. So essentially coyotes have been dispersing into wolf and red-fox range in the north but also into areas where wolves are absent but red fox are present in the east.”
Newsome came to the United States on a Fulbright scholarship from Australia where he earned a Ph.D. from the University of Sydney and specialized in the study of dingoes, that continent’s top predator. There’s a debate among Australians, he said, about the potential role of dingoes in suppressing introduced pests that have already decimated wildlife there. “Over the last 200 years, Australia has had the highest extinction rate in the world,” Newsome said. “The debate is about whether the dingo can provide positive ecological benefits,” he added. “Where dingoes have been removed, the impacts of introduced red foxes and feral cats have been quite severe on native fauna.”
Dingoes are managed as a pest in New South Wales, the country’s most populous state. To reduce dingo predation in the livestock industry, Australia also maintains the world’s longest fence, which runs for 5,500 kilometers (3,400 miles) in an attempt to exclude dingoes from almost a quarter of the continent.
In North America, the effect of wolves on coyotes and red foxes provides a natural case study that can be instructive for Australians. “Australians can learn a lot from how wolves are managed in North America, and Americans can learn from the ecological role of the dingo,” Newsome said.
As coyotes have expanded in North America, they have become a major cause of concern for the livestock industry. In the United States in 2004, researchers estimated annual losses due to coyote predation on sheep and cattle at $40 million. To reduce those damages, the Wildlife Service of the U.S. Department of Agriculture has a program to reduce coyote numbers, an effort that has drawn criticism from conservation groups.
In reviewing the fur trapping data from two U.S. and six Canadian jurisdictions, Newsome and Ripple eliminated potential sources of bias such as records from fur farms that raise foxes. The fur prices of coyotes and red foxes are also strongly correlated, and the two species occupy much of the same types of habitat, so they are equally likely to be targeted and caught in hunters’ traps.
“This study gives us a whole other avenue to understand the ecological effects of wolves on landscapes and animal communities,” said Ripple. He has studied the influence of carnivores on their prey — such as deer and elk — and on vegetation from aspen trees to willows. He and his colleagues have shown that the removal of top predators can cause dramatic shifts within ecosystems.
Wolves are naturally recolonizing many areas of the United States following their reintroduction into Yellowstone National Park and surrounding areas in 1995. Scientists are studying wolf interactions with other species, and in particular, there is interest in determining whether recolonizing wolves will suppress coyote populations and have cascading effects on red foxes and other species.
Newsome received funding from the Australian-American Fulbright Commission and from the government and universities of New South Wales in Australia.
In case you missed it, here is my interview on the proposed dingo fence extension in western Queensland:
ABC Webpage Links:
“Farmers lobby for longer dog fence”
The dog fence stretching from south-eastern Queensland to the Eyre Peninsula in South Australia is the world’s longest fence.
But sheep producers in central western Queensland are lobbying for it to be lengthened by 1400 kilometres.
They’re warning the sheep industry’s very survival is under threat from wild dogs and governments need to step in to save it.
Over the last two centuries, widespread predator control resulted in wolves being largely extirpated from the conterminous United States. In more recent decades, wolf population declines have been arrested because of enhanced legal protections, reintroduction programs, and natural recolonisations. From a scientific point of view, the return of wolves to the United States after a 70 year absence has provided unprecedented opportunities to explore how wolves interact with other predators and prey. In particular, the reintroduction of wolves into Yellowstone National Park in 1995-1996 has yielded significant insights into the ecology and behaviour of wolves and how they interact with other species.
According to the ecological theory of a “trophic cascade”, wolves should assert strong effects on ecosystems by regulating the abundance and/or activity of their main prey, such as elk. Wolves should also suppress lower order competitors, such as coyotes. If these interactions across different trophic levels result in decreased grazing pressure by elk on plants, as well as decreased predation pressure by coyotes on their preferred prey, then many other species should benefit.
The key question then is what has happened in Yellowstone?
In a recent paper published by Ripple et al. (2014) the authors illustrate that wolves have directly affected elk and coyote populations in Yellowstone. This, in turn, has indirectly benefited pronghorn, small mammals, woody plants, stream morphology, beavers, birds, berry production, scavengers and bears. For example, a reduction in coyote predation has benefited pronghorn and small mammals. Decreased grazing pressure by elk has resulted in the regeneration of trees and shrubs, which has improved stream morphology and provided more suitable habitat for beavers and birds. With an increase in berry production on shrubs, bears have been provided with an improved food source. Many scavengers, such as crows and ravens, have also benefited from an increased availability of wolf-killed carcasses to scavenge on.
Taken as a whole, the research in Yellowstone provides support for the theory that top-predators, like wolves, are integral to maintaining healthy ecosystems. But, there is some debate about the exact ways in which wolves influence their main prey and other competitors in Yellowstone. For example, there is a debate about whether wolves influence elk by (a) reducing their abundance (causing a density-mediated trophic cascade) or (b) by changing their behaviour (causing a behaviourally-mediated trophic cascade). Of course, no ecological system is so simple that wolves will either do (a) or (b), and it is likely that the “wolf effect” in Yellowstone varies depending on seasonal conditions, pack structures and the availability of alternate prey. However, it appears that there are also other factors to consider in this debate, such as the impact of harvesting the elk population and drought, which have arguably played a role in influencing elk numbers (which are declining). On top of this, the response of the vegetation to the decline in elk numbers is patchy, leading to variable results between studies.
The high profile nature of the debate about the ecological role of wolves in Yellowstone provides for an excellent case study from which to learn. In fact, the debate is very similar to the one in Australia associated with the ecological role of the dingo. Perhaps the key difference is that the research on wolves in the United States is related to the reintroduction of wolves, whereas no reintroduction of the dingo has been trialled in Australia over a large area. Therefore, Australians can learn much from the successes and failures of wolf reintroduction in the United States. This is one of the main aims of my current research and earlier this year I had the opportunity to travel to Yellowstone with researchers from the University of Washington. This was an ideal way to see Yellowstone for the first time, with events organised each day with park staff and other researchers. Some highlights included: seeing wolves stalking elk, snow-shoeing into a wolf den site, inspecting a wolf-kill site and learning how to perform autopsies on the carcass, speaking with ranchers who run cattle on the edge of Yellowstone, and capturing and releasing eagles at a nearby location.
Importantly though, the trip provided a great overview of how the restoration of wolves in Yellowstone is progressing and the challenges that lie ahead. According to the most recent annual report, there were at least 83 wolves in 10 packs occupying Yellowstone National Park at the end of 2012. This represents a 15% decline in numbers from the previous three years, and a 50% decline since 2007. The decline in wolf numbers is mostly because the elk population has also declined, and elk are the main food for wolves. However, during the first years of the reintroduction program the wolf population expanded from 20 individuals in 1995 to 174 by 2003, a fairly remarkable rate of increase. Indeed, some wolf packs contained as many as 20 individuals in 2003, so it is unsurprising that when food supplies (elk) declined, that wolf numbers, along with pack sizes, have also declined (in 2012 the largest wolf pack had only 11 individuals). Interestingly, intraspecific killing (wolves killing each other) has been one of the biggest causes of wolf mortality. This behaviour is common among canids, particularly during periods of food shortage when there is an advantage to having fewer individuals within a pack. That said, it will be interesting to see how wolves respond to a decline in elk numbers and whether wolf numbers and pack sizes will ever reach those obtained in 2003.
Some preliminary data suggests that one response by the wolves to a declining elk herd is to predate more on bison. For example, in 2012 13% of kills made by wolves were on bison, whereas in 1995-1996 no bison were killed by wolves. Bison present a formidable opponent to wolves because of their size and strength and the fact that bison tend to stand their ground when being challenged by wolves. Therefore, it will be interesting to see if the number of wolf kills on bison continues to increase and whether wolves adopt new hunting strategies to target bison, while elk numbers are low. In systems elsewhere, such as in Wood Buffalo National Park in Canada, bison comprise over 30% of wolf diet, so there is no underlying reason why bison cannot become a primary source of prey for wolves in Yellowstone. Given that the bison herd has to be actively managed (harvested) in Yellowstone, additional predation pressure by wolves could actually be beneficial. For example, there were certainly areas that appeared to be heavily grazed by bison, and Painter and Ripple (2012) found that plants have been increasing in size, except where intensively browsed by bison. This suggests that bison may be playing an important role in mediating trophic cascades in Yellowstone. With such a high profile debate about whether wolves changed the behaviour of elk and whether this resulted in cascading effects on vegetation, perhaps there is an opportunity now to see if the “wolf effect” extends to other species such as bison.
Outside of Yellowstone, there is another related development worthy of mention. In January 2012, the grey wolf was delisted from the Endangered Species Act in the west and upper midwest of the United States where viable populations had been established. This resulted in legal harvesting (hunting) of wolf populations for the first time in decades (the below map shows the status of grey wolves in the conterminous U.S. as of October 2012).
Following this decision, in June 2013, the U.S. Fish and Wildlife Service proposed that grey wolves (excluding the Mexican wolf subspecies) should be delisted from the Endangered Species Act throughout the entire lower 48 States. This was a controversial move because the delisting was based on a definition of endangerment that is inconsistent with legislative history and the historical implementation of the Endangered Species Act (Bruskotter et al. 2013). For example, Bruskotter et al. (2013) point out that the U.S. Fish and Wildlife Service have not met their obligations to conserve grey wolves because these wolves only reoccupied about 15% of their historic range. Indeed, the authors also state that the decision could set a dangerous precedent and have far-reaching implications for the recovery and listing of other endangered species. More recently, an independent review of the delisting also concluded that the proposal is not supported by the best available science.
It is yet to be seen if the proposal to delist wolves across the entire lower 48 States will be taken off the table, but perhaps it reflects the political nature of wolf management in the United States and the level of intolerance for wolves by some sectors of the community. That said, it is important to recognise that wolves can impact on human enterprises, particularly the livestock industry, and that much of the areas once utilised by wolves are probably unsuitable now due to human disturbances. But, even in the face of these challenges, the key question here is whether or not the decision to entirely delist wolves is a premature reaction to a highly politicised debate about how to manage wolves in the United States. If the proposal goes ahead, at least the rest of the world can learn from whether or not delisting wolves from the Endangered Species Act is truly a mistake with irreversible consequences.
This short video was filmed while I was out working on the Washington Wolf-Deer project. It features members I am collaborating with from the Predator Ecology Lab at The University of Washington:
For more information on the Washington Wolf-Deer project see my previous posts:
Paper title: Dietary niche overlap of free-roaming dingoes and domestic dogs: the role of human-provided food
Abstract: As both companion animals and opportunistic predators, dogs (Canis lupus spp.) have had a long and complex relationship with humans. In Australia, the dingo (C. l. dingo) was introduced 4,000 years ago and, other than humans, is now the continent’s top mammalian predator. Domestic dogs (C. l. familiaris) were introduced by Europeans more recently and they interbreed with dingoes. This hybridization has caused growing concern about the roles that domestic dogs and dingoes play in shaping ecosystem processes. There is also considerable debate about whether anthropogenic environmental changes can alter the ecological roles of dingoes. We used scat analysis to test whether the dingo, as the longer-established predator, occupies a different dietary niche from that of free-roaming domestic dogs, irrespective of human influence. Our results demonstrate considerable dietary overlap between dingoes and domestic dogs in areas where humans provide supplementary food, providing evidence against our hypothesis. However, the consumption by dingoes of a greater diversity of prey, in association with historical differences in the interactions between dingoes and humans, suggests a partial separation of their dietary niche from that of domestic dogs. We conclude that anthropogenic changes in resource availability could prevent dingoes from fulfilling their trophic regulatory or pre-European roles. Effective management of human-provided food is therefore required urgently to minimize the potential for subsidized populations of dingoes and domestic dogs to negatively affect co-occurring prey.
Just Out – Opinion Piece on Dingoes in The Conversation:
Paper title: Experiments in no-impact control of dingoes: comment on Allen et al. 2013
Abstract: There has been much recent debate in Australia over whether lethal control of dingoes incurs environmental costs, particularly by allowing increase of populations of mesopredators such as red foxes and feral cats. Allen et al. FIZ 10:39, 2013 claim to show in their recent study that suppression of dingo activity by poison baiting does not lead to mesopredator release, because mesopredators are also suppressed by poisoning. We show that this claim is not supported by the data and analysis reported in Allen et al.’s paper.
In December last year I spent two weeks out on the Washington Wolf-Deer project. The biggest eye opener was the diversity of large predators in the system. On top of wolves, there are bears, cougars, coyotes and bobcats.
For an Australian who is used to studying the interactions between three small-medium sized predators (the dingo, red fox and feral cat) the idea of having all these large predators within a study site is a new challenge.
For example, there is debate in Australia about the ecological role of dingoes. Indeed, we struggle to unravel the complex relationships between dingoes, red foxes and feral cats. So attempting to understand how wolves, bears, cougars, coyotes and bobcats interact with each other is a whole new ball game.
Because wolves have recently recolonised Washington State it is possible to study interactions between predators in two different scenarios being with and without wolves.
As mentioned in a previous post (https://thomasnewsome.com/2013/11/26/from-desert-dingoes-to-alpine-wolves/), the research group from the University of Washington are putting camera and GPS collars on two deer species to look at behavioural changes in response to recolonising wolves.
During my first two weeks on the Washington Wolf-Deer project we set out traps to catch the deer each night. Unfortunately the lack of snow made it difficult to lure deer into the traps using alfalfa, old apples and molasses (deer are much easier to catch when there is snow because the grass is covered and inaccessible to eat).
In early January I made the trip back to the field site hoping that with more snow there would be a higher chance of catching deer. Fortunately, success!
The additional impetus for heading back out in the field was the company of a fellow Australian researcher, Prof. Chris Dickman, who had a few days to spare after we attended the Gordon Research Conference on Predator-Prey interactions in California.
Chris has spent his career working in the arid deserts of Australia. Fortunately, I found enough warm clothes to see him through a North American winter field experience.
Working in a complex multi-predator system raises a plethora of ecological questions for consideration.
For example, with wolves in the system, is the “top-dog” canine or feline?
Cougars and wolves will both be competing for resources (deer) so there is the question of whether or not wolves will out-compete cougars. Wolves are also known to suppress coyotes so there is the question of whether or not coyote density will decline in areas where wolves are present.
Some of these questions were addressed after wolves were reintroduced into Yellowstone National Park in 1995-1996. However, in Washington State, wolves have recolonised managed lands where there are hunting seasons, logging and cattle ranching. Therefore, the future persistence of wolves in managed lands depends on minimising negative interactions between people and wildlife.
It also depends on the ecological role of wolves in managed lands i.e. how they interact with other predators and prey.
The results from the Washington Wolf-Deer project therefore have important implications for understanding how people, wolves and other wildlife might be able to coexist in managed lands.
When results from the project become available I will be sure to share them here.
Paper title: Human-resource subsidies alter the dietary preferences of a mammalian top predator
Abstract: Resource subsidies to opportunistic predators may alter natural predator–prey relationships and, in turn, have implications for how these predators affect co-occurring prey. To explore this idea, we compared the prey available to and eaten by a top canid predator, the Australian dingo (Canis lupus dingo), in areas with and without human-provided food. Overall, small mammals formed the majority of dingo prey, followed by reptiles and then invertebrates. Where human-provided food resources were available, dingoes ate them; 17 % of their diet comprised kitchen waste from a refuse facility. There was evidence of dietary preference for small mammals in areas where human-provided food was available. In more distant areas, by contrast, reptiles were the primary prey. The level of seasonal switching between small mammals and reptiles was also more pronounced in areas away from human-provided food. This reaffirmed concepts of prey switching but within a short, seasonal time frame. It also confirmed that the diet of dingoes is altered where human-provided food is available. We suggest that the availability of anthropogenic food to this species and other apex predators therefore has the potential to alter trophic cascades.