Invasive mesopredators should be controlled at the same time

Molsher, R., Newsome, A. E., Newsome, T. M., & Dickman, C. R. (2017). Mesopredator Management: Effects of Red Fox Control on the Abundance, Diet and Use of Space by Feral Cats. PloS one, 12(1), e0168460.

Apex predators are subject to lethal control in many parts of the world to minimize their impacts on human industries and livelihoods. Diverse communities of smaller predators—mesopredators—often remain after apex predator removal. Despite concern that these mesopredators may be 'released' in the absence of the apex predator and exert negative effects on each other and on co-occurring prey, these interactions have been little studied. Here, we investigate the potential effects of competition and intraguild predation between red foxes (Vulpes vulpes) and feral cats (Felis catus) in south-eastern Australia where the apex predator, the dingo (Canis dingo), has been extirpated by humans. We predicted that the larger fox would dominate the cat in encounters, and used a fox-removal experiment to assess whether foxes affect cat abundance, diet, home-range and habitat use. Our results provide little indication that intraguild predation occurred or 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. Fox control takes place over large areas of Australia to protect threatened native species and agricultural interests. Our results suggest that fox control programmes 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. Moreover, with intensive and more sustained fox control it is possible that cats could respond numerically and alter their behaviour in different ways to those documented herein. Such outcomes need to be considered when estimating the indirect impacts of fox control. We conclude that novel approaches are urgently required to control invasive mesopredators at the same time, especially in areas where apex predators are absent.

Use of camera traps to examine the mesopredator release hypothesis in a fragmented landscape

Cove, M. V., Jones, B. M., Bossert, A. J., Clever Jr, D. R., Dunwoody, R. K., White, B. C., & Jackson, V. L. (2012). Use of camera traps to examine the mesopredator release hypothesis in a fragmented Midwestern landscape. The American Midland Naturalist, 168(2), 456-465.

The mesopredator release hypothesis (MRH) has been suggested as a reason why many mammalian generalist mesopredators flourish and become abundant. However, the MRH has only been examined in a limited number of field studies. Some studies have argued that coyotes (Canis latrans) act as top predators in fragmented forest systems and coyote presence has a positive effect on song bird diversity and abundance by controlling mesopredator abundance. We integrated camera trap data and occupancy modeling to determine the factors that affect coyote detection probability and habitat use in a fragmented suburban landscape in central Missouri. We then examined the influence of coyote presence and other habitat variables on mesopredator detection probability and habitat use in the same system. Coyote detection was negatively related to increasing forest cover, whereas red fox (Vulpes vulpes) detection was positively related to increasing urbanization. Coyote occurrence models suggested little habitat selection, while the mesopredator occurrence models suggested an affinity for urbanization. Although there was a slight negative effect of coyote presence on site use by other mesopredators, we suggest that the smaller species are better adapted to coexisting with humans and thus have increased in abundance.

Coyotes and houses, the best predictors of domestic cat presence

Kays, R., Costello, R., Forrester, T., Baker, M. C., Parsons, A. W., Kalies, E. L., ... & McShea, W. (2015). Cats are rare where coyotes roam. Journal of Mammalogy, gyv100.

Domestic cats (Felis catus) have caused the extinction of many island species and are thought to kill many billions of birds and mammals in the continental United States each year. However, the spatial distribution and abundance of cats and their risk to our protected areas remains unknown. We worked with citizen scientists to survey the mammals at 2,117 sites in 32 protected areas and one urban area across 6 states in the eastern United States using camera traps. We found that most protected areas had high levels of coyote (Canis latrans) activity, but few or no domestic cats. The relative abundance of domestic cats in residential yards, where coyotes were rare, was 300 times higher than in the protected areas. Our spatial models of cat distribution show the amount of coyote activity and housing density are the best predictors of cat activity, and that coyotes and cats overlap the most in small urban forests. Coyotes were nocturnal at all sites, while cats were nocturnal in protected areas, but significantly more diurnal in urban sites. We suggest that the ecological impact of free-ranging cats in the region is concentrated in urban areas or other sites, such as islands, with few coyotes. Our study also shows the value of citizen science for conducting broadscale mammal surveys using photo-vouchered locations that ensure high data quality.

Optimal multispecies eradication schedules for a commonly encountered invaded island ecosystem

Bode, M., Baker, C. M., & Plein, M. (2015). Eradicating down the food chain: optimal multispecies eradication schedules for a commonly encountered invaded island ecosystem. Journal of Applied Ecology, 52(3), 571-579.

Islands are global hotspots of both biodiversity and extinction. Invasive species are a primary threat, and the majority of islands have been invaded by more than one. Multispecies eradications are essential for conserving the biodiversity of these islands, but experience has shown that eradicating species at the wrong time can be disastrous for endemic species.
Managers not only have to decide how to eradicate each invasive species, they need to determine when to target each species, and how to control multiple species with a limited budget. We use dynamic control theory to show that, when resources are limited, species should be eradicated in a particular order (an eradication schedule). We focus on a common invaded island ecosystem motif, where one invasive predator consumes two prey species (one endemic, one invasive), and managers wish to eradicate both invasives while ensuring the persistence of the endemic species. We identify the optimal eradication schedule for this entire class of problem. To illustrate the application of our solution, we also analyse a particular case study from California's Channel Islands.
For any island ecosystem that shares this motif, managers should begin by allocating all of their resources towards invasive predator control. Only later should resources be shifted towards controlling the invasive prey. This shift should ideally be gradual, but an abrupt shift is very close to optimal. The Channel Islands case study confirms these findings. Targeting both species simultaneously is substantially suboptimal.
We reach the robust conclusion that the same eradication schedule should be applied to any island with this ecosystem motif, even if the ecosystem contains different species to the Channel Islands case study.
Synthesis and applications. Although very numerous, the world's invaded island ecosystems could be described by a limited range of invaded ecosystem motifs. By calculating robust optimal eradication schedules for each motif, the approach defined in this study could offer rapid decision-support for a large number of future conservation projects where specific data are scarce.

Rats, cats and seabirds: hyperpredation and mesopredator release

Ringler, D., Russell, J., & Le Corre, M. (2015). Trophic roles of black rats and seabird impacts on tropical islands: Mesopredator release or hyperpredation?.Biological Conservation.

Rats contribute to the decline of tropical seabird populations by affecting their breeding success through direct predation of eggs and chicks. When they coexist with other predators, invasive rats may also generate indirect interactions via the changes they impose on the structure of communities and trophic interactions following invasion (‘hyperpredation process’), or when apex predators are eradicated from the ecosystem (‘mesopredator release effect’). Understanding these effects is necessary to implement restoration operations that actually benefit threatened seabird populations. We investigated these processes on two French tropical seabird islands of the western Indian Ocean, Europa and Juan de Nova, where black rats coexist with two different apex predator species (introduced cats and potentially native barn owls). The parallel use of several methods (diet analysis, stable isotopes, seabird monitoring) to identify trophic roles of rats revealed that the direct impact of rats on seabirds was particularly high on Europa where only rats and owls occur, with high consumption of chicks resulting in low breeding success for several seabird species. We also suggested that hyperpredation associated with top-down regulation of cats is occurring on Juan de Nova, although territoriality of cats may buffer this process. Conversely we found evidence that mesopredator release effect is unlikely, irrespective of the apex predator identity. Considering the most likely effects on both islands we provided recommendations on eradication priorities to mitigate the risk of local extinction that seabirds are currently facing.

Lack of mesopredator release after top-predator control

Allen, B. L., Allen, L. R., Engeman, R. M., & Leung, L. K. (2013). Intraguild relationships between sympatric predators exposed to lethal control: predator manipulation experiments. Frontiers in zoology, 10(1), 39.

Introduction
Terrestrial top-predators are expected to regulate and stabilise food webs through their consumptive and non-consumptive effects on sympatric mesopredators and prey. The lethal control of top-predators has therefore been predicted to inhibit top-predator function, generate the release of mesopredators and indirectly harm native fauna through trophic cascade effects. Understanding the outcomes of lethal control on interactions within terrestrial predator guilds is important for zoologists, conservation biologists and wildlife managers. However, few studies have the capacity to test these predictions experimentally, and no such studies have previously been conducted on the eclectic suite of native and exotic, mammalian and reptilian taxa we simultaneously assess. We conducted a series of landscape-scale, multi-year, manipulative experiments at nine sites spanning five ecosystem types across the Australian continental rangelands to investigate the responses of mesopredators (red foxes, feral cats and goannas) to contemporary poison-baiting programs intended to control top-predators (dingoes) for livestock protection.

Result
Short-term behavioural releases of mesopredators were not apparent, and in almost all cases, the three mesopredators we assessed were in similar or greater abundance in unbaited areas relative to baited areas, with mesopredator abundance trends typically either uncorrelated or positively correlated with top-predator abundance trends over time. The exotic mammals and native reptile we assessed responded similarly (poorly) to top-predator population manipulation. This is because poison baits were taken by multiple target and non-target predators and top-predator populations quickly recovered to pre-control levels, thus reducing the overall impact of baiting on top-predators and averting a trophic cascade.

Conclusions
These results are in accord with other predator manipulation experiments conducted worldwide, and suggest that Australian populations of native prey fauna at lower trophic levels are unlikely to be negatively affected by contemporary dingo control practices through the release of mesopredators. We conclude that contemporary lethal control practices used on some top-predator populations do not produce the conditions required to generate positive responses from mesopredators. Functional relationships between sympatric terrestrial predators may not be altered by exposure to spatially and temporally sporadic application of non-selective lethal control.

Allen, B. L., Allen, L. R., Engeman, R. M., & Leung, L. K. (2014). Sympatric prey responses to lethal top-predator control: predator manipulation experiments. Frontiers in Zoology, 11(1), 56.

Introduction: Many prey species around the world are suffering declines due to a variety of interacting causes such as land use change, climate change, invasive species and novel disease. Recent studies on the ecological roles of top-predators have suggested that lethal top-predator control by humans (typically undertaken to protect livestock or managed game from predation) is an indirect additional cause of prey declines through trophic cascade effects. Such studies have prompted calls to prohibit lethal top-predator control with the expectation that doing so will result in widespread benefits for biodiversity at all trophic levels. However, applied experiments investigating in situ responses of prey populations to contemporary top-predator management practices are few and none have previously been conducted on the eclectic suite of native and exotic mammalian, reptilian, avian and amphibian predator and prey taxa we simultaneously assess. We conducted a series of landscape-scale, multi-year, manipulative experiments at nine sites spanning five ecosystem types across the Australian continental rangelands to investigate the responses of sympatric prey populations to contemporary poison-baiting programs intended to control top-predators (dingoes) for livestock protection.
Results: Prey populations were almost always in similar or greater abundances in baited areas. Short-term prey responses to baiting were seldom apparent. Longer-term prey population trends fluctuated independently of baiting for every prey species at all sites, and divergence or convergence of prey population trends occurred rarely. Top-predator population trends fluctuated independently of baiting in all cases, and never did diverge or converge. Mesopredator population trends likewise fluctuated independently of baiting in almost all cases, but did diverge or converge in a few instances.
Conclusions: These results demonstrate that Australian populations of prey fauna at lower trophic levels are typically unaffected by top-predator control because top-predator populations are not substantially affected by contemporary control practices, thus averting a trophic cascade. We conclude that alteration of current top-predator management practices is probably unnecessary for enhancing fauna recovery in the Australian rangelands. More generally, our results suggest that theoretical and observational studies advancing the idea that lethal control of top-predators induces trophic cascades may not be as universal as previously supposed.

Questioning mesopredator release in Australia

Allen, B. L., Lundie‐Jenkins, G., Burrows, N. D., Engeman, R. M., Fleming, P. J., & Leung, L. K. P. (2014). Does lethal control of top‐predators release mesopredators? A re‐evaluation of three Australian case studies. Ecological Management & Restoration.

Top-predators can sometimes be important for structuring fauna assemblages in terrestrial ecosystems. Through a complex trophic cascade, the lethal control of top-predators has been predicted to elicit positive population responses from mesopredators that may in turn increase predation pressure on prey species of concern. In support of this hypothesis, many relevant research papers, opinion pieces and literature reviews identify three particular case studies as supporting evidence for top-predator control-induced release of mesopredators in Australia. However, many fundamental details essential for supporting this hypothesis are missing from these case studies, which were each designed to investigate alternative aims. Here, we re-evaluate the strength of evidence for top-predator control-induced mesopredator release from these three studies after comprehensive analyses of associated unpublished correlative and experimental data. Circumstantial evidence alluded to mesopredator releases of either the European Red Fox (Vulpes vulpes) or feral Cat (Felis catus) coinciding with Dingo (Canis lupus dingo) control in each case. Importantly, however, substantial limitations in predator population sampling techniques and/or experimental designs preclude strong assertions about the effect of lethal control on mesopredator populations from these studies. In all cases, multiple confounding factors and plausible alternative explanations for observed changes in predator populations exist. In accord with several critical reviews and a growing body of demonstrated experimental evidence on the subject, we conclude that there is an absence of reliable evidence for top-predator control-induced mesopredator release from these three case studies. Well-designed and executed studies are critical for investigating potential top-predator control-induced mesopredator release.

Little evidence of top-predators biocontrol on invasive mesopredators

Allen, B. L., Allen, L. R., & Leung, L. K. P. 2014. Interactions between two naturalised invasive predators in Australia: are feral cats suppressed by dingoes?.Biological Invasions, 1-16.

Top-predators can play important roles in terrestrial food webs, fuelling speculation that top-predators might be used as biocontrol tools against invasive mesopredators. Feral cats are believed to be largely responsible for the current declines of native fauna across tropical northern Australia, where substantial beef cattle production occurs. Dingoes are known to impact cattle production there and are predicted to impact native fauna also. However, dingoes are forecasted to curtail the impacts of cats and reverse native fauna declines. We review (1) empirical studies investigating the relationships between dingoes and cats, and dingo control and cats, (2) records of cat remains in dingo diets, and (3) historical records of lethal dingo control using 1080-poisoned baits across Australia between 1999 and 2008 to show how two naturalised invasive species can interact in dynamic agro-ecological landscapes. From the 35 studies assessed, most reported no detectable relationship between dingoes and cats; negative or positive relationships were seldom detected. Dingoes do not appear to exclude cats beyond fine scales, but may alter cat activity periods under certain conditions. Cat remains were found in only 0.63 % of over 31,000 dingo diet records. Lethal dingo control occurs (in varying degrees) across about two-thirds of Australia and does not appear to substantially influence dingo-cat relationships. We conclude that the presently available data provides little evidence that bolstering dingo populations will reduce the impacts of cats. Much more work is needed to identify situations where top-predators might be used as effective biocontrol tools against invasive mesopredators in agro-ecological systems.

Bottom-up and top-down processes interact to modify intraguild interactions in resource-pulse environments

Greenville, A. C., Wardle, G. M., Tamayo, B., & Dickman, C. R. (2014). Bottom-up and top-down processes interact to modify intraguild interactions in resource-pulse environments. Oecologia, 1-10.

Top predators are declining globally, in turn allowing populations of smaller predators, or mesopredators, to increase and potentially have negative effects on biodiversity. However, detection of interactions among sympatric predators can be complicated by fluctuations in the background availability of resources in the environment, which may modify both the numbers of predators and the strengths of their interactions. Here, we first present a conceptual framework that predicts how top-down and bottom-up interactions may regulate sympatric predator populations in environments that experience resource pulses. We then test it using 2 years of remote-camera trapping data to uncover spatial and temporal interactions between a top predator, the dingo Canis dingo, and the mesopredatory European red fox Vulpes vulpes and feral cat Felis catus, during population booms, declines and busts in numbers of their prey in a model desert system. We found that dingoes predictably suppress abundances of the mesopredators and that the effects are strongest during declines and busts in prey numbers. Given that resource pulses are usually driven by large yet infrequent rains, we conclude that top predators like the dingo provide net benefits to prey populations by suppressing mesopredators during prolonged bust periods when prey populations are low and potentially vulnerable.

Top‐predator control on islands boosts endemic prey but not mesopredator

Bonnaud, E., Zarzoso‐Lacoste, D., Bourgeois, K., Ruffino, L., Legrand, J., & Vidal, E. (2010). Top‐predator control on islands boosts endemic prey but not mesopredator. Animal conservation, 13(6), 556-567.

Introduced predators on islands are responsible for numerous native species extirpations and extinctions. Predation by cats is particularly detrimental to seabirds and cat control or eradication is generally the best option to reduce their negative impacts on native fauna. However, potential cascading effects, such as mesopredator release effect, need to be monitored after cat removal. In Port-Cros Island, a cat control campaign was undertaken to eliminate the strong and recurrent threat from feral cat predation to the small yelkouan shearwater Puffinus yelkouan population, without harming a neutered domestic cat population. To evaluate the conservation value of this campaign for an island endemic and endangered species, the diet and impact of the remaining domestic cats were studied through scat analysis and trap success. Moreover, to evaluate the recovery of the seabird population and detect any potential mesopredator release effect, shearwater and rat populations were monitored before, alongside and after the cat control. Only live traps were used, and most cats were trapped in the first year of cat eradication. The last incidence of cat predation on the yelkouan shearwater occurred the following year. The recovery of the shearwater population, occurring the first year of cat control, was mainly attributable to the settlement of new breeders in the colony. Rat population dynamics fluctuated widely but, even though the interactions between rats and shearwaters at breeding cavities increased, no evidence of rat predation on shearwaters was recorded. Thus, cat control on Port-Cros Island was a success for native species conservation, proving that such management strategy can induce an increase in the population of the endemic species, here the yelkouan shearwater, without any evidence of a mesopredator release effect.

Apex predator control and mesopredator release in Australia

Brook, L. A., Johnson, C. N., & Ritchie, E. G. (2012). Effects of predator control on behaviour of an apex predator and indirect consequences for mesopredator suppression. Journal of applied ecology, 49(6), 1278-1286.

1. Apex predators can benefit ecosystems through top–down control of mesopredators and herbivores. However, apex predators are often subject to lethal control aimed at minimizing attacks on livestock. Lethal control can affect both the abundance and behaviour of apex predators. These changes could in turn influence the abundance and behaviour of mesopredators.
2. We used remote camera surveys at nine pairs of large Australian rangeland properties, comparing properties that controlled dingoes Canis lupus dingo with properties that did not, to test the effects of predator control on dingo activity and to evaluate the responses of a mesopredator, the feral cat Felis catus.
3. Indices of dingo abundance were generally reduced on properties that practiced dingo control, in comparison with paired properties that did not, although the effect size of control was variable. Dingoes in uncontrolled populations were crepuscular, similar to major prey. In populations subject to control, dingoes became less active around dusk, and activity was concentrated in the period shortly before dawn.
4. Shifts in feral cat abundance indices between properties with and without dingo control were inversely related to corresponding shifts in indices of dingo abundance. There was also a negative relationship between predator visitation rates at individual camera stations, suggesting cats avoided areas where dingoes were locally common. Reduced activity by dingoes at dusk was associated with higher activity of cats at dusk.
5. Our results suggest that effective dingo control not only leads to higher abundance of feral cats, but allows them to optimize hunting behaviour when dingoes are less active. This double effect could amplify the impacts of dingo control on prey species selected by cats. In areas managed for conservation, stable dingo populations may thus contribute to management objectives by restricting feral cat access to prey populations.
6. Synthesis and applications. Predator control not only reduces indices of apex predator abundance but can also modify their behaviour. Hence, indicators other than abundance, such as behavioural patterns, should be considered when estimating a predator's capacity to effectively interact with lower trophic guilds. Changes to apex predator behaviour may relax limitations on the behaviour of mesopredators, providing enhanced access to resources and prey.

Urban coyotes and cats

Webster, J.C. (2007). Missing cats, stray coyotes: one citizen’s perspective. Wildlife Damage Management Conferences -- Proceedings.Paper 78.

Comments

Originally published in Proceedings of the 12th Wildlife Damage Management Conference (D.L. Nolte, W.M. Arjo, D.H. Stalman, Eds). 2007. This is the revised version that appears in Urban Coyote Management: A collection of papers pre-sented at the Urban Coyote Symposium within the 12th Wildlife Damage Management Conference Corpus Christi, Texas, April 11, 2007, Robert M. Timm, Editor (Collierville, TN, 2008). ISBN 978-1-60458-362-5 Copyright © 2007 by the Wildlife Damage Management Working Group of The Wildlife Society. Used by permission.


Abstract

The author explores the issue of urban coyotes and coyote management from a cat owner’s perspective, with specific examples from Vancouver, B.C., Canada. Following a personal encounter with two coyotes in July 2005 that led to the death of a cat, the author has delved into the history of Vancouver’s “Co-existing with Coyotes”, a government-funded program run by a nonprofit ecological society. The policy’s roots in conservation biology, the environmental movement, and the human dimensions branch of wildlife management are documented. The author contends that “Co-existing with Coyotes” puts people and pets at greater risk of attack by its inadequate response to habituated coyotes, and by an educational component that misrepresents real dangers and offers unworkable advice. The environmental impact of domestic cats is addressed. The author makes the case that generalized opinions about the negative effects of cats on songbird populations and other wildlife, and assertions that urban coyotes are beneficial, are unsupported by objective experimental data. When environmentalists, who predominantly hold these views, also research, promote, and oversee urban wildlife policy, there is a consequent lack of interest in restricting coyote populations in cities, along with little concern for the fate of outdoor cats and even a desire for their depredation.

Mesopredator release and toxoplasmosis

Hollings, T., Jones, M., Mooney, N., & McCallum, H. (2013). Wildlife disease ecology in changing landscapes: Mesopredator release and toxoplasmosis.International Journal for Parasitology: Parasites and Wildlife, 2, 110-118.

Changing ecosystem dynamics are increasing the threat of disease epidemics arising in wildlife populations. Several recent disease outbreaks have highlighted the critical need for understanding pathogen dynamics, including the role host densities play in disease transmission. In Australia, introduced feral cats are of immense concern because of the risk they pose to native wildlife through predation and competition. They are also the only known definitive host of the coccidian parasite, Toxoplasma gondii, the population-level impacts of which are unknown in any species. Australia’s native wildlife have not evolved in the presence of cats or their parasites, and feral cats may be linked with several native mammal declines and extinctions. In Tasmania there is emerging evidence that feral cat populations are increasing following wide-ranging and extensive declines in the apex predator, the Tasmanian devil, from a consistently fatal transmissible cancer.

We assess whether feral cat density is associated with the seroprevalence of T. gondii in native wildlife to determine whether an increasing population of feral cats may correspond to an increased level of risk to naive native intermediate hosts. We found evidence that seroprevalence of T. gondii in Tasmanian pademelons was lower in the north-west of Tasmania than in the north-east and central regions where cat density was higher. Also, samples obtained from road-killed animals had significantly higher seroprevalence of T. gondii than those from culled individuals, suggesting there may be behavioural differences associated with infection. In addition, seroprevalence in different trophic levels was assessed to determine whether position in the food-web influences exposure risk. Higher order carnivores had significantly higher seroprevalence than medium-sized browser species. The highest seroprevalence observed in an intermediate host was 71% in spotted-tailed quolls (Dasyurus maculatus), the largest mammalian mesopredator, in areas of low cat density. Mesopredator release of cats may be a significant issue for native species conservation, potentially affecting the population viability of many endangered species.

Invasive species removal in whole ecosystem context

Zavaleta, E. S., Hobbs, R. J., & Mooney, H. A. (2001). Viewing invasive species removal in a whole-ecosystem context. Trends in Ecology & Evolution, 16(8), 454-459.

Eradications of invasive species often have striking positive effects on native biota. However, recent research has shown that species removal in isolation can also result in unexpected changes to other ecosystem components. These secondary effects will become more likely as numbers of interacting invaders increase in ecosystems, and as exotics in late stages of invasion eliminate native species and replace their functional roles. Food web and functional role frameworks can be used to identify ecological conditions that forecast the potential for unwanted secondary impacts. Integration of eradication into a holistic process of assessment and restoration will help safeguard against accidental, adverse effects on native ecosystems.

Feral cat vs. dingo perception: a gender-cultural bias or a real ecological difference?

Smith, N. (1999). The howl and the pussy: feral cats and wild dogs in the Australian imagination. The Australian journal of anthropology, 10(3): 288-305.

This paper looks at recent attention given to feral cats in Australia, particularly focusing on their symbolic status in eco-nationalist discourses. Australian eco-nationalism is a specific blend of environmentalist and patriotic sentiments which, in an exaggerated way, positions the feral cat as a rapacious European invader predating on native wild life. This vilification of the cat can be related to much earlier forms of (mainly European) symbolism associating the creature with femininity and evil, which I illustrate by looking at the manner in which the feral cat is opposed to the masculinised Australian wild dog—the dingo. I argue that the recent surfacing of this totemic opposition between ‘the howl and the pussycat’ is related to an eco-nationalist sense of place which simultaneously recognises and denies that the human colonisation of Australia was (and is) a form of feral invasion.

Hytten, K. F. (2009). Dingo dualisms: Exploring the ambiguous identity of Australian dingoes. Australian Zoologist, 35(1), 18-27.

How wildlife is defined, and which wildlife is accorded protection, emerges from competing constructions of nature and culture. Few species of Australian wildlife have as ambiguous an identity as dingoes. This paper identifies three dualisms that characterise discourses relating to Australian dingoes Canis lupus dingo. They are at once classified as both a pest and protected species, perceived to be feral and native, and most recently categorised as either pure or hybrid. It is argued that these dualisms are underpinned by different versions of the nature-culture dichotomy. Portrayals and perceptions of dingoes around Australia are explored to reveal how different aspects of the dualisms identified are drawn upon within different contexts. Illustrations of the contradictory constructions of dingoes highlight the need to critically deconstruct discourses relating to wildlife, particularly when they inform actions. As such, this paper demonstrates the important contribution a discourse-sensitive approach can make to understanding human perceptions of wildlife.



Letnic, M., Ritchie, E. G., & Dickman, C. R. (2012). Top predators as biodiversity regulators: the dingo Canis lupus dingo as a case study. Biological reviews, 87(2), 390-413.

Top-order predators often have positive effects on biological diversity owing to their key functional roles in regulating trophic cascades and other ecological processes. Their loss has been identified as a major factor contributing to the decline of biodiversity in both aquatic and terrestrial systems. Consequently, restoring and maintaining the ecological function of top predators is a critical global imperative. Here we review studies of the ecological effects of the dingo Canis lupus dingo, Australia's largest land predator, using this as a case study to explore the influence of a top predator on biodiversity at a continental scale. The dingo was introduced to Australia by people at least 3500 years ago and has an ambiguous status owing to its brief history on the continent, its adverse impacts on livestock production and its role as an ecosystem architect. A large body of research now indicates that dingoes regulate ecological cascades, particularly in arid Australia, and that the removal of dingoes results in an increase in the abundances and impacts of herbivores and invasive mesopredators, most notably the red fox Vulpes vulpes. The loss of dingoes has been linked to widespread losses of small and medium-sized native mammals, the depletion of plant biomass due to the effects of irrupting herbivore populations and increased predation rates by red foxes. We outline a suite of conceptual models to describe the effects of dingoes on vertebrate populations across different Australian environments. Finally, we discuss key issues that require consideration or warrant research before the ecological effects of dingoes can be incorporated formally into biodiversity conservation programs.

Eradication and control of feral dogs in Galápagos

Barnett, B. D. (1986). Eradication and control of feral and free-ranging dogs in the Galápagos Islands. In Proceedings of the Twelfth Vertebrate Pest Conference (1986) (8 pp.).

The history of canid introduction in Galápagos, their impact on biodiversity and the control and eradication by different methods, mainly poisoning with 1080 and chemical sterilisation.

After eradication in some areas, some mesopredator release effect was detected and cats further threatened iguanas populations. Sea lions became free of this danger, but cattle invaded areas previously occupied by dogs.

Mammal extinctions and mesopredator release

Hanna, E. & M. Cardillo (2013). Island mammal extinctions are determined by interactive effects of life history, island biogeography and mesopredator suppression. Global Ecology and Biogeography, in press. doi: 10.1111/geb.12103

Abstract:
Aim Understanding extinction on islands is critical for biodiversity conservation. Introduced predators are a major cause of island extinctions, but there have been few large-scale studies of the complexity of the effects of predators on island faunas, or how predation interacts with other factors. Using a large database of island mammal populations, we describe and explain patterns of island mammal extinctions as a function of introduced predators, life history and geography.

Location:

Three hundred and twenty-three Australian islands.

Methods 

We built a database of 934 island mammal populations, extinct and extant, including life history and ecology, island geography and the presence of introduced predators. To test predictors of extinction probability, we used generalized linear mixed models to control partially for phylogenetic non-independence, and decision trees to more fully explore interactive effects.

Results

The decision trees identified large mammals (> 2.7 kg) as having higher extinction probabilities than small species (< 2.7 kg). In large species, extinction patterns are consistent with island biogeography theory, with distance from the mainland being the primary predictor of extinction. For small species, the presence of introduced black rats is the primary predictor of extinction. As predicted by mesopredator suppression theory, extinction probabilities are lower on islands with both black rats and a larger introduced predator (cats, foxes or dingoes), compared with islands with rats but no larger predator. Similarly, extinction probabilities are lower on islands with both a mid-sized (cats or foxes) and a larger (dingoes) predator, compared with islands with cats or foxes only.

Main conclusions 

Island mammal extinctions result from complex interactions of introduced predators, island geography and prey biology. One conservation implication of our results is that eradication of introduced apex predators (cats, foxes or dingoes) from islands could precipitate the expansion of black rat populations, potentially leading to extinction of native mammal species whose remaining populations are confined to islands.

Mesopredator release within an oceanic island

Rayner, M. J., Hauber, M. E., Imber, M. J., Stamp, R. K., & Clout, M. N. (2007). Spatial heterogeneity of mesopredator release within an oceanic island system. Proceedings of the National Academy of Sciences, 104(52), 20862-20865.

Predator–prey communities are ubiquitous in ecology, but introduced predators can drive native species to extinction within island systems, prompting the eradication of such exotics. Ecological theory predicts that elimination of top-introduced predators from islands can lead to the counterintuitive decline of native prey populations through the ecological release of smaller introduced species in a process termed “mesopredator release”.

 We show, in accordance with mesopredator release theory and counter to conservation goals for a New Zealand island reserve, that initial eradication of cats on Little Barrier Island led to reduced breeding success of Cook's petrels, which also are vulnerable to predation by a mesopredator, the Pacific rat. The rat's impact on prey productivity varied with elevation within the island. Rat eradication was followed by a rise in petrel productivity, in support of both ecological theory and practical conservation management goals. It appears that interactions among introduced predators, native prey, and environmental gradients can drive counterintuitive and spatially heterogeneous responses to predator eradications from islands. Location-specific, ecosystem-level understanding is essential for predicting the outcomes of such restoration management techniques.


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Bird and rat numbers on Little Barrier after cat eradication

Girardet, S. A. B., Veitch, C. R., & Craig, J. L. (2001). Bird and rat numbers on Little Barrier Island, New Zealand, over the period of cat eradication 1976–80. New Zealand Journal of Zoology, 28(1), 13-29.

Passerines were monitored on Little Barrier Island over 15 years (1975–89) spanning the period (1976–80) when feral cats were eradicated from the island. All birds seen and heard were recorded while walking three transects representing an altitudinal range from near sea level to approximately 550 m above sea level. Analysis of variance statistics were used to test for differences in bird numbers between transects and between years. Bird species were examined by transect to test for changes in numbers over time. Three species had increased on some transects, and two species had decreased on some transects, but it was difficult to attribute changes in bird numbers to the one cause which we were able to study: reduced cat numbers. Examination of numbers of individuals of 14 species recorded between transects showed significant differences for some individual species, but not for all species grouped together. Four species did not show any significant differences between transects. This study demonstrates different patterns in bird distributions on Little Barrier Island which cannot be understood from these data.

Index traplines were set for Pacific rats or kiore (Rattus exulans) between 1977 and 1984, before and after cat eradication. Rat numbers fluctuated widely, and there were no significant differences that could be attributed to the changes in cat numbers.

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Two classics in ecology: Mesopredator release

Soulé, M. E., Bolger, D. T., Alberts, A. C., Wrights, J., Sorice, M., & Hill, S. (1988). Reconstructed dynamics of rapid extinctions of chaparral‐requiring birds in urban habitat islands. Conservation Biology, 2(1), 75-92.

The distribution of native, chaparral-requiring bird species was determined for 37 isolated fragments of canyon habitat ranging in size from 0.4 to 104 hectares in coastal, urban San Diego County, California. The area of chaparral habitat and canyon age (time since isolation of the habitat fragment) explains most of the variation in the number of chaparral-requiring bird species. In addition, the distribution of native predators may influence species number. There is statistical evidence that coyotes control the populations of smaller predators such as foxes and domestic cats. The absence of coyotes may lead to higher levels of predation by a process of mesopredator release. The distance of canyons from other patches of chaparral habitat does not add significantly to the explained variance in chaparral-requiring species number–probably because of the virtual inability of most chaparral-requiring species to disperse through developed areas and nonscrub habitats. These results and other lines of evidence suggest that chaparral-requiring birds in isolated canyons have very high rates of extinction, in part because of their low vagility. The best predictors of vulnerability of the individual species are their abundances (densities) in undisturbed habitat and their body sizes; together these two variables account for 95 percent of the variation in canyon occupancy. A hypothesis is proposed to account for the similarity between the steep slopes of species-area curves for chaparral-requiring birds and the slopes for some forest birds on small islands or in habitat fragments. The provision of corridors appears to be the most effective design and planning feature for preventing the elimination of chaparral-requiring species in a fragmented landscape.

En el condado urbano de San Diego, California 37 fragmentos de hábitat de cañón que varían de tamaño de 0.4 a 104 hectáreas fueron examinados para determinar la distribución de especies de aves nativas que requieren de chaparral. El tamaño del área de hábitat de chaparral y la edad del cañón (tiempo transcurrido desde que ocurrió el aislamiento del fragmento de hábitat explican la mayor parte de la variación en el número de especies de aves que requieren de este hábitat Así mismo, la distribución de depredadores nativos puede influenciar el número de especies. Existen evidencias estadísticas de que los coyotes controlan las poblaciones de depredadores menores tales como los zorros y los gatos domésticos. La ausencia de coyotes puede conducir a niveles de depredación mas altos mediante un proceso de liberación de mesodepredadores. El aislamiento de cañones con respecto a otros pedazos de hábitat de chaparral no incrementa significativamente la varianza en el número de especies que requieren chaparral – probablemente debido a la virtual inhabilitad de la mayoría de las especies que requieren chaparral para dispersarse en áreas desarrolladas y en hábitats no—arbustivos. Estos resultados y otras evidencias sugieren que las aves que requieren chaparral en los cañones aislados tienen muy altas tasas de extinción, en parte debido a su baja dispersabilidad. Los mejores pronosticadores de la vulnerabilidad de una especie en particular son su abundancia (densidad) en habitats no perturbados y el tamaño de sus cuerpos; juntas, estas dos variables explican el 95% de la variación de su residencia en el cañón. Una hipótesis es propuesta para explicar la similaridad entre las fuertes pendientes de la curves de especies-área para las aves que requieren chaparral y las pendientes para algunas aves de bosque en pequeñas islas o en hábitats fragmentados. La provisión de corredores parece ser el diseño y el rasgo de la planificación más efectivo para prevenir la eliminación de especies que requieren chaparral en un paisaje fragmentado.

Crooks, K. R., & Soulé, M. E. (1999). Mesopredator release and avifaunal extinctions in a fragmented system. Nature, 400(6744), 563-566.

Mammalian carnivores are particularly vulnerable to extinction in fragmented landscapes, and their disappearance may lead to increased numbers of smaller carnivores that are principle predators of birds and other small vertebrates. Such 'mesopredator release' has been implicated in the decline and extinction of prey species. Because experimental manipulation of carnivores is logistically, financially and ethically problematic, however, few studies have evaluated how trophic cascades generated by the decline of dominant predators combine with other fragmentation effects to influence species diversity in terrestrial systems. Although the mesopredator release hypothesis has received only limited critical evaluation and remains controversial, it has become the basis for conservation programmes justifying the protection of carnivores. Here we describe a study that exploits spatial and temporal variation in the distribution and abundance of an apex predator, the coyote, in a landscape fragmented by development. It appears that the decline and disappearance of the coyote, in conjunction with the effects of habitat fragmentation, affect the distribution and abundance of smaller carnivores and the persistence of their avian prey.