The mesoscavenger release hypothesis and implications for ecosystem and human well‐being

O’Bryan, Christopher J.; Holden, Matthew; Watson, James

doi:10.1111/ele.13288

Cited by 38 publications

(44 citation statements)

References 58 publications

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“…For some facultative scavengers, carrion is a resource consumed primarily when other food is scarce, which may further influence seasonal dynamics of road kill scavenging (Hill et al 2018a). When vulture (families Accipitridae and Cathartidae) populations decline, carrion can become increasingly available to mammalian scavengers (O'Bryan et al 2019), which has the potential to increase mammal consumption of road kill.…”

Section: Resultsmentioning

confidence: 99%

A review of ecological factors promoting road use by mammals

2020

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Roads have numerous negative impacts for mammals, but may also serve as attractants due to altered vegetation or provisioning of resources. We reviewed the use of roads and their associated features by mammals, in order to understand the ecological factors contributing to road use. We documented 129 studies that recorded road use by 116 mammalian species, spanning 15 orders and 35 families, in six continents. Carnivora was the most common order (40 species, 34% of all 116 species), followed by Artiodactyla (24 species, 20%) and Rodentia (21 species, 18%). The species were placed in the IUCN categories Least Concern (88 species, 76% of all 116 species), Vulnerable (11 species, 9%), Near Threatened (9 species, 8%), Endangered (6 species, 5%), and Critically Endangered (2 species, 2%). We assigned road use to five ecological categories, reflecting the reason for it, with subcategories where appropriate: (1) communication; (2) foraging (subcategories: anthropogenic food, herbivory, predation, salt, scavenging, water); (3) movement (subcategories: bridges, environmental alterations, habitat connectivity); (4) refuge (subcategories: avoidance, burrowing and denning, cover, roosting); and (5) thermoregulation. Foraging, movement, and refuge were the most common uses. Roads provide a variety of resources to mammals, but road use is highly dynamic in time and space. We suggest that the use of roads by mammals is extensive, both geographically and taxonomically. Road use is likely to influence mammalian ecology while contributing to the risk of collisions with vehicles.

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Section: Resultsmentioning

confidence: 99%

A review of ecological factors promoting road use by mammals

2020

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“…Increased scavenging opportunities opened by the loss of apex predators may lead to an increased abundance of the surviving scavengers, affecting ecosystem structure and function (Allen et al 2014; O’Bryan et al 2019) In south-eastern Spain, red foxes ( Vulpes vulpes ) were observed to be in higher abundance in areas where the absence of vultures ( Gyps spp.) increased carrion availability (Morales-Reyes et al 2017).…”

Section: Discussionmentioning

confidence: 99%

“…Scavenging is an essential ecological function for maintaining stability in the ecosystem, via the control of community composition and carrion availability (Wilson & Wolkovich 2011; Barton et al 2013; Buechley & Şekercioğlu 2016). As most carnivores are facultative scavengers, their loss can influence herbivore density and prompt mesopredator release (O’Bryan et al 2019). For example, in north-east Tasmania, where Tasmanian devils ( Sarcophilus harrisii ) have declined due to devil-facial-tumour disease, feral cats ( Felis catus ) and forest ravens ( Corvus tasmanicus ) have increased in abundance due to increased access to carrion (Cunningham et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Roadkill islands: carnivore extinction shifts seasonal use of roadside carrion by generalist avian scavenger

Fielding¹,

Buettel²,

Brook³

et al. 2021

Preprint

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Global road networks facilitate habitat modification and are integral to human expansion. Many animals, particularly scavengers, use roads as they provide a reliable source of food, such as carrion left after vehicle collisions. Tasmania is often cited as the 'roadkill capital of Australia', with the isolated offshore islands in the Bass Strait experiencing similar, if not higher, levels of roadkill. However, native mammalian predators on the islands are extirpated, meaning the remaining scavengers are likely to experience lower interference competition. In this study, we use a naturally occurring experiment to examine how the loss of mammalian carnivores within a community impacts roadside foraging behaviour by avian scavengers. We monitored the locations of roadkill and forest ravens (Corvus tasmanicus), an abundant scavenger species, on eight road transects across the Tasmanian mainland (high scavenging competition) and the Bass Strait islands (low scavenging competition). We represented raven observations as one-dimensional point patterns, using hierarchical Bayesian models to investigate the dependence of raven spatial intensity on habitat, season, distance to roadkill and route location. We found that roadkill carcasses were a strong predictor of raven presence along road networks. The effect of roadkill was amplified on roads on the Bass Strait islands, where roadside carrion was a predictor of raven presence across the entire year. In contrast, ravens were more often associated with roadkill on Tasmanian mainland roads in the autumn, when other resources were low. This suggests that in the absence of competing mammalian scavengers, ravens choose to feed on roadside carrion throughout the year, even in seasons when other resources are available. This low interference competition could be disproportionately benefiting forest ravens, leading to augmented raven populations and changes to the vertebrate community structure. Our study provides evidence that scavengers modify their behaviour in response to reduced scavenger species diversity, potentially triggering trophic shifts and highlighting the importance of conserving or reintroducing carnivores within ecosystems.

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“…Altered distributions may induce shifts within species communities and in predator–prey dynamics (Krebs & Elwood, 2008; Tylianakis, Didham, Bascompte, & Wardle, 2008), potentially leading to cascading effects (Ripple & Beschta, 2012). A well‐known ecological cascade is extirpation of apex predators causing increased mesopredator abundance with subsequent decline in the abundance of prey species (O'Bryan, Holden, & Watson, 2019; Prugh et al., 2009).…”

Section: Introductionmentioning

confidence: 99%

Highways associated with expansion of boreal scavengers into the alpine tundra of Fennoscandia

Rød‐Eriksen

Skrutvold

Herfindal

et al. 2020

Journal of Applied Ecology

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Habitat fragmentation may affect species distributions through, for example, altered resource availability and shifts in species interactions. Fragmentation by roads has had negative impacts on Fennoscandian alpine ecosystems, with reduction of habitats and connectivity for alpine species. Concurrently, infrastructure development causes influx of subsidies through roadkills and litter, which may facilitate expansion of boreal scavenging species, such as the red fox Vulpes vulpes, which may intensify negative interactions with alpine species. Hence, understanding the impact of subsidies within marginal alpine areas is imperative for successful conservation and management of particularly vulnerable alpine species. We used snow tracking and camera traps in three alpine tundra areas in Norway to investigate whether the presence of boreal scavengers was positively associated with highways during winter, and if this contrasted the pattern of a critically endangered alpine species, the Arctic fox Vulpes lagopus. In summer, artificial nests were used to assess whether predation risk was related to proximity to highways. During winter, the occurrence of red foxes was higher close to highways and decreased with increasing distance to highways, while the arctic fox showed no discernible pattern. Red fox occurrence increased with the number of edible items of anthropogenic origin located along highways, whereas arctic fox occurrence decreased. The overall predation risk of artificial nests during summer was high (>31.2%) and increased with proximity to the highway in the area with highest traffic volume. Synthesis and applications. Highways crossing alpine areas may attract boreal scavengers, possibly connected to increased access to subsidies of anthropogenic origin. Litter and food waste dominated available subsidies along highways in our study, and prevailing mitigating measures directed at reducing roadkill and movement restrictions may not be applicable to reduce negative effects of littering. We recommend actions focusing on informational campaigns, improved garbage disposal facilities and routines, and imposing fines for littering, to reduce negative impacts on vulnerable species. This is likely needed to achieve goals of ‘no impact’ from the physical loss of habitats due to road development.

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The mesoscavenger release hypothesis and implications for ecosystem and human well‐being

Cited by 38 publications

References 58 publications

A review of ecological factors promoting road use by mammals

A review of ecological factors promoting road use by mammals

Roadkill islands: carnivore extinction shifts seasonal use of roadside carrion by generalist avian scavenger

Highways associated with expansion of boreal scavengers into the alpine tundra of Fennoscandia

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