The comparative effects of large carnivores on the acquisition of carrion by scavengers

Lion lords and sharing hyaenas: Carnivore guild dynamics around elephant carcasses

Megaherbivore carcasses represent sporadic but energetically rewarding resources for carnivores, offering a unique opportunity to study coexistence dynamics between facultative scavengers. South African fenced protected areas, such as Madikwe Game Reserve (Madikwe hereafter), host viable populations of large carnivores and high densities of elephants, Loxodonta africana. However, high carnivore densities can lead to potentially fatal interspecific encounters and increased competition, particularly around high-quality trophic resources. This study explores the temporal partitioning and co-detection strategies of carnivores at six elephant carcasses in Madikwe, aiming to understand how the increased carrion biomass available at elephant carcasses influences coexistence dynamics. Camera traps were deployed to monitor carcasses during two periods (2019 and 2020), revealing occurrences of six carnivore species. Carnivores, particularly black-backed jackals, Lupulella mesomelas, (hereafter jackal), lions, Panthera leo, and spotted hyaenas, Crocuta crocuta, comprised 56.7% of carcass observations, highlighting their pivotal roles in scavenging dynamics. Pairwise co-detection analysis demonstrated consistent association and shared peak activity periods between jackals and spotted hyaenas, indicating potential resource sharing. However, the minimal co-detection rates between lions and other carnivores highlight their resource domination. There was some evidence of temporal partitioning between carnivores, with most species exhibiting earlier peaks in nocturnal activity to avoid temporal overlap with lions. This study emphasises the importance of elephant carcasses in the diet of multiple species and coexistence techniques utilised to exploit this ephemeral resource. As fenced protected areas become crucial for conserving intact carnivore guilds globally, further research into carnivore behavioural adaptations at carcasses is recommended to shed light on their coexistence strategies.

Influence of tree cover on carcass detection and consumption by facultative vertebrate scavengers

Scavenging mammals and vultures can exploit and deplete carcasses much faster than other birds and invertebrates. Vultures are strongly influenced by habitat type, e.g. tree cover, since they rely on their eyesight to detect carcasses. It remains unclear whether and how facultative scavengers - both other birds and mammals - are influenced by tree cover and how that affect carcass decomposition time, which in turn affects biodiversity and ecological processes, including the cycle of energy and nutrients. We studied whether the carcass detection and consumption, hence carcass decomposition speed, by facultative avian and mammalian scavengers varies with tree cover in areas without vultures. Fresh mammal carcasses were placed in different landscapes across the Netherlands at locations that widely varied in tree cover. Camera traps were used to record carcass exploitation by facultative avian and mammalian scavengers and to estimate carcass decomposition time. We found that carcass detection and consumption by birds, wild boar, and other mammals varied between locations. Carcass decomposition speed indeed increased with carcass detection and exploitation by mammals, especially by wild boar. However, this variation was not related to tree cover. We conclude that tree cover is not a major determinant of carcass exploitation by facultative scavengers in areas without obligate scavengers and large carnivores.

Mesocarnivores vary in their spatiotemporal avoidance strategies at communications hubs of an apex carnivore

Mesocarnivores face interspecific competition and risk intraguild predation when sharing resources with apex carnivores. Within a landscape, carnivores across trophic levels may use the same communication hubs, which provide a mix of risks (injury/death) and rewards (gaining information) for subordinate species. We predicted that mesocarnivores would employ different strategies to avoid apex carnivores at shared communication hubs, depending on their trophic position. To test our prediction, we examined how different subordinate carnivore species in the Santa Cruz Mountains of California, USA, manage spatial overlap with pumas (Puma concolor), both at communication hubs and across a landscape-level camera trap array. We estimated species-specific occurrence, visitation rates, temporal overlap, and Avoidance-Attraction Ratios from camera traps and tested for differences between the two types of sites. We found that mesocarnivores generally avoided pumas at communication hubs, and this became more pronounced when pumas scent-marked during their most recent visit. Coyotes (Canis latrans), the pumas' closest subordinate competitor in our system, exhibited the strongest avoidance at communication hubs. Gray foxes (Urocyon cinereoargenteus) avoided pumas the least, which may suggest possible benefits from pumas suppressing coyotes. Overall, mesocarnivores exhibited various spatiotemporal avoidance strategies at communication hubs rather than outright avoidance, likely because they benefit from information gained while 'eavesdropping' on puma activity. Variability in avoidance strategies may be due to differential predation risks, as apex carnivores often interact more aggressively with their closest competitors. Combined, our results show how apex carnivores trigger complex species interactions across the entire carnivore guild and how trophic position determines behavioral responses and subsequent space use of subordinate mesocarnivores across the landscape.

Influence of heterospecifics on mesocarnivore behaviour at shared scavenging opportunities in the Canadian Rocky Mountains

In seasonal environments, the ability of mustelid species to acquire carrion-a dietary resource heavily depended upon-is driven by a collection local habitat characteristics and competition dynamics. In resource-scarce winter, sympatric mesocarnivores must balance energetic rewards of carrion with avoiding antagonistic interactions with conspecifics. We examined scavenging interactions among three mustelid species in the northern Canadian Rocky Mountains. Camera traps (n = 59) were baited with carrion during winter between 2006 to 2008. Spatial and temporal dimensions of scavenger behaviour (i.e., carcass use) were evaluated using a multi-model approach, which enabled us to recognize potentially adaptive behavioural mechanisms for mitigating competition at carcass sites. Best performing models indicated that carrion site use is governed by a combination of competition threats and environmental factors. A decrease in scavenging with increasing snow depth was observed across all species. Mustelids adopted a host of adaptive behavioural strategies to access shared scavenging opportunities. We found evidence that wolverine (Gulo gulo) and American marten (Martes americana) segregate in space but temporally tracked one another. Short-tailed weasel (Mustela erminea) scavenging decreased with greater site use by marten. Carcass availability across a spatially complex environment, as well as spatial-temporal avoidance strategies, can facilitate carrion resource partitioning.

Interactions between carnivore species: limited spatiotemporal partitioning between apex predator and smaller carnivores in a Mediterranean protected area

BACKGROUND

There is need of information on ecological interactions that keystone species such as apex predators establish in ecosystems recently recolonised. Interactions among carnivore species have the potential to influence community-level processes, with consequences for ecosystem dynamics. Although avoidance of apex predators by smaller carnivores has been reported, there is increasing evidence that the potential for competitive-to-facilitative interactions is context-dependent. In a protected area recently recolonised by the wolf Canis lupus and hosting abundant wild prey (3 ungulate species, 20-30 individuals/km², together), we used 5-year food habit analyses and 3-year camera trapping to (i) investigate the role of mesocarnivores (4 species) in the wolf diet; (ii) test for temporal, spatial, and fine-scale spatiotemporal association between mesocarnivores and the wolf.

RESULTS

Wolf diet was dominated by large herbivores (86% occurrences, N = 2201 scats), with mesocarnivores occurring in 2% scats. We collected 12,808 carnivore detections over > 19,000 camera trapping days. We found substantial (i.e., generally ≥ 0.75, 0-1 scale) temporal overlap between mesocarnivores-in particular red fox-and the wolf, with no support for negative temporal or spatial associations between mesocarnivore and wolf detection rates. All the species were nocturnal/crepuscular and results suggested a minor role of human activity in modifying interspecific spatiotemporal partitioning.

CONCLUSIONS

Results suggest that the local great availability of large prey to wolves limited negative interactions towards smaller carnivores, thus reducing the potential for spatiotemporal avoidance. Our study emphasises that avoidance patterns leading to substantial spatiotemporal partitioning are not ubiquitous in carnivore guilds.

Increased abundance of a common scavenger affects allocation of carrion but not efficiency of carcass removal in the Fukushima Exclusion Zone

The 2011 nuclear accident in Fukushima, Japan caused the evacuation of > 100,000 people and prompted studies on environmental impacts of radiological contamination. However, few researchers have explored how the human evacuation has affected ecosystem processes. Despite contamination, one common scavenger (wild boar, Sus scrofa) is 2–3× more abundant inside the Fukushima Exclusion Zone (FEZ). Shifts in abundance of some scavenger species can have cascading effects on ecosystems, so our objective was to investigate impacts of the evacuation and the resulting increase in wild boar on vertebrate scavenger communities. We deployed cameras at 300 carcasses in the FEZ and a nearby inhabited area, and quantified carcass fate, scavenger species, and detection/persistence times. We also tested effects of carcass size and habitat on scavenger community composition and efficiency by balancing trials across two carcass sizes and habitats in each zone. Overall scavenger richness and carcass removal rates (73%) were similar in the FEZ and inhabited area, but species-specific carcass removal rates and occurrence differed between zones. Wild boar removed substantially more carcasses inside the FEZ, with implications for nutrient and contaminant distribution. Our results suggest carcass size affects scavenging dynamics more than human activity or habitat, and abundance changes of common scavengers can influence carrion resource allocation.

Kill rates and associated ecological factors for an apex predator

Kill rates and functional responses are fundamental to the study of predator ecology and the understanding of predatory-prey dynamics. As the most widely distributed apex predator in the western hemisphere, pumas (Puma concolor) have been well studied, yet a synthesis of their kill rates is currently lacking. We reviewed the literature and compiled data on sex- and age-specific kill rate estimates of pumas on ungulates, and conducted analyses aimed at understanding ecological factors explaining the observed spatial variation. Kill rate studies on pumas, while numerous, were primarily conducted in Temperate Conifer Forests (< 10% of puma range), revealing a dearth of knowledge across much of their range, especially from tropical and subtropical habitats. Across studies, kill rates in ungulates/week were highest for adult females with kitten(s) (1.24 ± 0.41 ungulates/week) but did not vary significantly between adult males (0.84 ± 0.18) and solitary adult females (0.99 ± 0.26). Kill rates in kg/day differed only marginally among reproductive classes. Kill rates of adult pumas increased with ungulate density, particularly for males. Ungulate species richness had a weak negative association with adult male kill rates. Neither scavenger richness, puma density, the proportion of non-ungulate prey in the diet, nor regional human population density had a significant effect on ungulate kill rates, but additional studies and standardization would provide further insights. Our results had a strong temperate-ecosystem bias highlighting the need for further research across the diverse biomes pumas occupy to fully interpret kill rates for the species. Data from more populations would also allow for multivariate analyses providing deeper inference into the ecological and behavioural factors driving kill rates and functional responses of pumas, and apex predators in general.

Assessing carnivore spatial co-occurrence and temporal overlap in the face of human interference in a semiarid forest

Apex predators drive top-down effects in ecosystems and the loss of such species can trigger mesopredator release. This ecological process has been well documented in human-modified small areas, but for management and conservation of ecological communities, it is important to know which human factors affect apex predator occurrence and which mediate mesopredators release at large scales. We hypothesized that mesopredators would avoid spatial and temporal overlap with the apex predator, the puma; but that human perturbations (i.e., cattle raising and trophy hunting) would dampen top-down effects and mediate habitat use. We installed 16 camera traps in each of 45, 10 × 10 km grid cells in the Caldén forest region of central Argentina resulting in 706 total stations covering 61,611 km² . We used single-season occupancy and two-species co-occurrence models and calculated the species interaction factor (SIF) to explore the contributions of habitat, biotic, and anthropic variables in explaining co-occurrence between carnivore pairs. We also used kernel density estimation techniques to analyze temporal overlap in activity patterns of the carnivore guild. We found that puma habitat use increased with abundance of large prey and with proximity to protected areas. Geoffroy's cats and skunks spatially avoided pumas and this effect was strong and mediated by distance to protected areas and game reserves, but pumas did not influence pampas fox and pampas cat space use. At medium and low levels of puma occupancy, we found evidence of spatial avoidance between three pairs of mesocarnivores. All predators were mostly nocturnal and crepuscular across seasons and mesopredators showed little consistent evidence of changing activity patterns with varying levels of puma occupancy or human interference. We found potential for mesopredator release at large scale, especially on the spatial niche axis. Our results suggest that a combination of interacting factors, in conjunction with habitat features and intervening human activities, may make mesopredator release unlikely or difficult to discern at broad scales. Overall, we believe that promoting the creation of new protected areas linked by small forest patches would likely lead to increased predator and prey abundances, as well as the interactions among carnivores inside and outside of protected areas.

Occurrence and Abundance of an Apex Predator and a Sympatric Mesopredator in Rural Areas of the Coastal Range of Southern Chile

The two mammalian carnivores, puma (Puma concolor) and South American grey fox (Lycalopex griseus) were studied, in a remote area located in the humid temperate forest of the coastal range of southern Chile. A total of six locations were selected in three landscapes: pre-mountain range, mountain range, and coast. The chosen study locations are relevant because they correspond to threatened areas with different levels of human intervention., so they offer the ideal setting for studying how different species of carnivores respond to both human presence and activities. A dataset was collected for 24 months during 2016–2018 through photo-trapping (13 camera traps placed along 50 photo-trap stations). Wes estimated the apparent occurrence and relative abundance index (RAI) of the fauna registered, by means of generalized linear models to contrast those of an apex predator, such as the puma and a sympatric mesopredator, the South American grey fox, across the three landscapes. The ecological variables assessed were the RAI of the other carnivore considered, exotic carnivores such as dogs and cats, human intervention, farmland effect, prey availability, and habitat quality. The primary hypothesis was that the apparent occurrence and RAI of puma and fox would be positively associated with the RAI of prey and livestock and negatively with human intervention. On the other hand, the secondary hypothesis dealt with the interactions between puma and fox faced with different degrees of human intervention. The results showed that the apparent occurrence of the puma was statistically explained by location only, and it was highest at the mountain range. The apparent occurrence of foxes was explained by both puma apparent occurrence and relative integrated anthropization index (INRA), being highest in the pre-mountain range. Concerning the RAI of pumas, high values were yielded by location and fox RAI. For the RAI of foxes, they were location, puma RAI, and INRA. It can be suggested that eucalyptus plantations from the pre-mountain range could offer an adequate habitat for the puma and the fox, but not the coastal range, as the mountain range could be acting as a biological barrier. Due to the nature of the data, it was not possible to detect any relevant effect between the two carnivores’ considered, between their respective preys, or the very abundant presence of dogs.

Smart carnivores think twice: Red fox delays scavenging on conspecific carcasses to reduce parasite risk

The recent SARS-CoV-2 epidemic has highlighted the need to prevent emerging and re-emerging diseases, which means that we must approach the study of diseases from a One Health perspective. The study of pathogen transmission in wildlife is challenging, but it is unquestionably key to understand how epidemiological interactions occur at the wildlife-domestic-human interface. In this context, studying parasite avoidance behaviours may provide essential insights on parasite transmission, host-parasite coevolution, and energy flow through food-webs. However, the strategies of avoiding trophically transmitted parasites in mammalian carnivores have received little scientific attention. Here, we explore the behaviour of red foxes (Vulpes vulpes) and other mammalian carnivores at conspecific and heterospecific carnivore carcasses using videos recorded by camera traps. We aim to determine 1) the factors influencing the probability of foxes to practice cannibalism, and 2) whether the scavenging behaviour of foxes differ when facing conspecific vs. heterospecific carcasses. We found that red foxes were generally reluctant to consume mesocarnivore carrion, especially of conspecifics. When recorded, consumption by foxes was delayed several days (heterospecific carcasses) or weeks (conspecific carcasses) after carcass detection. Other mammalian scavengers showed a similar pattern. Also, meat-borne parasite transmission from wild carnivore carcasses to domestic dogs and cats was highly unlikely. Our findings challenge the widespread assumption that cannibalistic or intra-specific scavenging is a major transmission route for Trichinella spp. and other meat-borne parasites, especially for the red fox. Overall, our results suggest that the feeding decisions of scavengers are probably shaped by two main contrasting forces, namely the nutritional reward provided by carrion of phylogenetically similar species and the risk of acquiring meat-borne parasites shared with these species. This study illustrates how the detailed monitoring of carnivore behaviour is essential to assess the epidemiological role of these hosts in the maintenance and dispersion of parasites of public and animal health relevance.

Variable strategies to solve risk-reward tradeoffs in carnivore communities

Mesopredator release theory suggests that dominant predators suppress subordinate carnivores and ultimately shape community dynamics, but the assumption that subordinate species are only negatively affected ignores the possibility of facilitation through scavenging. We examined the interplay within a carnivore community consisting of cougars, coyotes, black bears, and bobcats using contemporaneous Global Positioning System telemetry data from 51 individuals; diet analysis from 972 DNA-metabarcoded scats; and data from 128 physical investigations of cougar kill sites, 28 of which were monitored with remote cameras. Resource provisioning from competitively dominant cougars to coyotes through scavenging was so prolific as to be an overwhelming determinant of coyote behavior, space use, and resource acquisition. This was evident via the strong attraction of coyotes to cougar kill sites, frequent scavenging of cougar-killed prey, and coyote diets that nearly matched cougars in the magnitude of ungulate consumption. Yet coyotes were often killed by cougars and used space to minimize encounters, complicating the fitness benefits gained from scavenging. We estimated that 23% (95% CI: 8 to 55%) of the coyote population in our study area was killed by cougars annually, suggesting that coyote interactions with cougars are a complex behavioral game of risk and reward. In contrast, we found no indication that bobcat space use or diet was influenced by cougars. Black bears avoided cougars, but there was no evidence of attraction to cougar kill sites and much lower levels of ungulate consumption and carcass visitation than for coyotes. Interspecific interactions among carnivores are multifaceted, encompassing both suppression and facilitation.

Limitations of current knowledge about the ecology of Grey Foxes hamper conservation efforts

Species-specific conservation is important for maintaining the integrity of ecological communities but is dependent on sufficiently understanding multiple aspects of a species’ ecology. Species-specific data are commonly lacking for species in geographic areas with little research and species perceived to have insufficient charisma or economic importance. Despite their widespread distribution across central and North America and status as a furbearing mammal, little is known about the ecology of Grey Foxes Urocyon cinereoargenteus compared to other species of furbearing mammals. To understand what is known about this species, especially factors affecting population dynamics, we performed a systematic review of the scientific literature. We found 234 studies about Grey Foxes, with studies increasing substantially over time but with geographic gaps in the Great Plains and most of Mexico and central America. Most studies we reviewed examined relative abundance or occupancy (n= 35), habitat associations (n= 30), primarily as part of larger mammalian community studies, or spatiotemporal effects of other mammalian carnivores (n= 19), predominately Coyote Canis latrans. Grey Foxes were primarily forest-associated although associations with specific forest communities or anthropogenically disturbed habitats varied among studies. Multiple studies across ecoregions reported this fox as among both the most- and least-abundant mammalian carnivore. The inter-specific effects of Coyote were often, but not exclusively, negative and were likely mediated by landscape composition and human development. Importantly, very few studies examined population-effects of coyotes on Grey Foxes. Studies of population trends, demographics, and space use of Grey Foxes were comparatively rare and small inter- and intra-study sample sizes limited our ability to infer broader patterns. We suggest multiple avenues for future research to better understand the population status of this species throughout their range. 

Effect of scavenging on predation in a food web

Scavenging can have important consequences for food web dynamics, for example, it may support additional consumer species and affect predation on live prey. Still, few food web models include scavenging. We develop a dynamic model that includes two facultative scavenger species, which we refer to as the predator or scavenger species according to their natural scavenging propensity, as well as live prey, and a carrion pool to show ramifications of scavenging for predation in simple food webs. Our modeling suggests that the presence of scavengers can both increase and decrease predator kill rates and overall predation in model food webs and the impact varies (in magnitude and direction) with context. In particular, we explore the impact of the amount of dynamics (exploitative competition) allowed in the predator, scavenger, and prey populations as well as the direction and magnitude of interference competition between predators and scavengers. One fundamental prediction is that scavengers most likely increase predator kill rates, especially if there are exploitative feedback effects on the prey or carrion resources like is normally observed in natural systems. Scavengers only have minimal effects on predator kill rate when predator, scavenger, and prey abundances are kept constant by management. In such controlled systems, interference competition can greatly affect the interactions in contrast to more natural systems, with an increase in interference competition leading to a decrease in predator kill rate. Our study adds to studies that show that the presence of predators affects scavenger behavior, vital rates, and food web structure, by showing that scavengers impact predator kill rates through multiple mechanisms, and therefore indicating that scavenging and predation patterns are tightly intertwined. We provide a road map to the different theoretical outcomes and their support from different empirical studies on vertebrate guilds to provide guidance in wildlife management.

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

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 used 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 lack of 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.

Living on the edge: spatial response of coyotes (Canis latrans) to wolves (Canis lupus) in the subarctic

Understanding how mesopredators manage the risks associated with apex predators is key to explaining impacts of apex predators on mesopredator populations and patterns of mesopredator space use. Here we examine the spatial response of coyotes (Canis latrans Say, 1823) to risk posed by wolves (Canis lupus Linnaeus, 1758) using data from sympatric individuals fitted with GPS collars in subarctic Alaska, USA, near the northern range limit for coyotes. We show that coyotes do not universally avoid wolves, but instead demonstrate season-specific responses to both wolf proximity and long-term use of the landscape by wolves. Specifically, coyotes switched from avoiding wolves in summer to preferring areas with wolves in winter, and this selection was consistent across short-term and longer term temporal scales. In the summer, coyotes responded less strongly to risk of wolves when in open areas than when in closed vegetation. We also demonstrate that coyotes maintain extremely large territories averaging 291 km2, and experience low annual survival (0.50) with large carnivores being the largest source of mortality. This combination of attraction and avoidance predicated on season and landcover suggests that mesopredators use complex behavioral strategies to mediate the effects of apex predators.

Gifts of an enemy: scavenging dynamics in the presence of wolves (Canis lupus)

Carrion represents an important resource for carnivores. Examining competition for carrion in a risk–reward framework allows for a better understanding of how predator guilds compete for and benefit from carrion. We used trail camera data to compare wintertime carrion use and vigilance behavior of four carnivores in Denali National Park and Preserve. We found that carrion use was dominated by wolves (Canis lupus) and wolverines (Gulo gulo), followed by red foxes (Vulpes vulpes) and coyotes (Canis latrans). Wolves and wolverines were twice as likely to visit a carcass as foxes and coyotes, and their visits were longer and more numerous. Our results suggest scavenging animals reduced their risk exposure primarily by reducing their use of carrion, with some evidence of increased vigilance at busy sites. We found that carrion use and behavior at carcass sites were influenced by the mortality type of the carcass, the age of the carcass, and the long-term intensity of wolf use in the area. Our results also suggest that wolves are the “top scavenger,” and indicate that intraguild competition for carrion strongly affects which species benefit from carrion, with larger and more aggressive species dominating.

Scavenging Effects of Large Canids

Many large predators are also facultative scavengers that may compete with and depredate other species at carcasses. Yet, the ecological impacts of facultative scavenging by large predators, or their "scavenging effects," still receive relatively little attention in comparison to their predation effects. To address this knowledge gap, we comprehensively examine the roles played by, and impacts of, facultative scavengers, with a focus on large canids: the African wild dog (Lycaon pictus), dhole (Cuon alpinus), dingo (Canis dingo), Ethiopian wolf (Canis simensis), gray wolf (Canis lupus), maned wolf (Chrysocyon brachyurus), and red wolf (Canis rufus). Specifically, after defining facultative scavenging as use or usurpation of a carcass that a consumer has not killed, we (1) provide a conceptual overview of the community interactions around carcasses that can be initiated by facultative scavengers, (2) review the extent of scavenging by and the evidence for scavenging effects of large canids, (3) discuss external factors that may diminish or enhance the effects of large canids as scavengers, and (4) identify aspects of this phenomenon that require additional research attention as a guide for future work.

Spatiotemporal patterns of wolf, mesocarnivores and prey in a Mediterranean area

Abstract

Spatial and temporal occurrence can mediate behavioural interactions between apex predators, mesocarnivores and herbivores. Predators should adapt their activity to that of prey, whereas predator avoidance would be expected to influence activity patterns and space use of prey and smaller competitors. We evaluated interspecific spatiotemporal relationships in a prey-rich community including an apex predator (the wolf), three wild ungulates and several smaller herbivores/mesocarnivores, through camera trapping. All considered species (i.e. wolves and potential prey/smaller competitors: wild boar, fallow deer, roe deer, crested porcupine, red fox and European badger) were active especially at night and/or twilight. Among wild ungulates, the wolf showed the greatest temporal overlap with the wild boar and the lowest one with the least abundant and used of them, i.e. the roe deer. The main prey (i.e. the fallow deer) showed more diurnal activity and a lower temporal overlap with the predator in sites with high wolf activity than in low-activity ones. Among mesocarnivores, the red fox showed extensive temporal overlap with the wolf: the overlap between the two canids was greater in sites intensively used by this apex predator than in sites with low wolf activity, supporting a concurrent study which suggested a potential for facilitative—rather than competitive—interactions. Spatiotemporal relationships suggest complex interactions between the apex predator, prey and smaller carnivores, for which a substantial temporal or spatial association was often supported.

Significance statement

There is a growing interest in the influence of apex predators on ecosystems through their effects on the behaviour of prey and smaller carnivores, especially in the light of the ongoing recovery of large carnivores in temperate areas. Predators should synchronise their activity to that of prey; conversely, prey and smaller carnivores would be expected to avoid predators. In a rich community including the wolf, three wild ungulates and several mesomammals, we detected (i) a substantial temporal overlap between wolves and wild boar, porcupines and mesocarnivores; (ii) a negative temporal association between the predator and its main prey (i.e. the fallow deer) and (iii) a great temporal overlap between the wolf and the red fox. We provide a baseline to evaluate temporal changes of predator-prey-mesocarnivore behavioural interactions along with variations of carnivore-prey densities.

Not avian but mammalian scavengers efficiently consume carcasses under heavy snowfall conditions: a case from northern Japan

Interest in trophic interactions and ecosystem functions derived from carcass consumption by scavengers has been increasing. Here, we conducted the first evaluation of scavenging processes in an ecosystem with heavy snow, located in northern Japan, which is characterized by the limitations of visual and odor cues to detect carcasses. In this study, we verified the behavioral traits and assemblage compositions of avian and mammalian scavengers, which consumed six different carcass types buried in snow. We measured the visits of scavengers using camera traps between 2010 and 2020. The total scavenger richness observed was relatively low (only 12 species) compared to warmer biomes. We observed seven avian scavenger species, but their visit frequencies were extremely low compared with those of nocturnal mammalian scavengers, such as raccoon dogs (Nyctereutes procyonoides) and martens (Martes melampus), which were able to detect carcasses more rapidly and frequently. Our findings imply that large snow piles significantly prevent avian scavengers from detecting carcasses. In contrast, the snow piles could protect carcasses from the freezing air and ensure the occurrence of a basal level of microbial decomposition, possibly leading to carcass decomposition. This probably results in carcasses still providing odor cues for mammalian scavengers with heightened sense of smell. Moreover, considering the high carcass consumption rate (91.3% of full-body carcass; n = 23) and short carcass detection times (approximately 90 h) observed, it is possible that scavenging in heavy snowfall conditions has become systematically integrated into the foraging tactics of many mammalian scavengers.

The Role of Carrion in the Landscapes of Fear and Disgust: A Review and Prospects

Animal behavior is greatly shaped by the ‘landscape of fear’, induced by predation risk, and the equivalent ‘landscape of disgust’, induced by parasitism or infection risk. However, the role that carrion may play in these landscapes of peril has been largely overlooked. Here, we aim to emphasize that animal carcasses likely represent ubiquitous hotspots for both predation and infection risk, thus being an outstanding paradigm of how predation and parasitism pressures can concur in space and time. By conducting a literature review, we highlight the manifold inter- and intra-specific interactions linked to carrion via predation and parasitism risks, which may affect not only scavengers, but also non-scavengers. However, we identified major knowledge gaps, as reviewed articles were highly biased towards fear, terrestrial environments, vertebrates, and behavioral responses. Based on the reviewed literature, we provide a conceptual framework on the main fear- and disgust-based interaction pathways associated with carrion resources. This framework may be used to formulate predictions about how the landscape of fear and disgust around carcasses might influence animals’ individual behavior and ecological processes, from population to ecosystem functioning. We encourage ecologists, evolutionary biologists, epidemiologists, forensic scientists, and conservation biologists to explore the promising research avenues associated with the scary and disgusting facets of carrion. Acknowledging the multiple trophic and non-trophic interactions among dead and live animals, including both herbivores and carnivores, will notably improve our understanding of the overlapping pressures that shape the landscape of fear and disgust.

Habitat complexity and lifetime predation risk influence mesopredator survival in a multi-predator system

Variability in habitat selection can lead to differences in fitness; however limited research exists on how habitat selection of mid-ranking predators can influence population-level processes in multi-predator systems. For mid-ranking, or mesopredators, differences in habitat use might have strong demographic effects because mesopredators need to simultaneously avoid apex predators and acquire prey. We studied spatially-explicit survival of cheetahs (Acinonyx jubatus) in the Mun-Ya-Wana Conservancy, South Africa, to test hypotheses related to spatial influences of predation risk, prey availability, and vegetation complexity, on mesopredator survival. For each monitored cheetah, we estimated lion encounter risk, prey density, and vegetation complexity within their home range, on short-term (seasonal) and long-term (lifetime) scales and estimated survival based on these covariates. Survival was lowest for adult cheetahs and cubs in areas with high vegetation complexity on both seasonal and lifetime scales. Additionally, cub survival was negatively related to the long-term risk of encountering a lion. We suggest that complex habitats are only beneficial to mesopredators when they are able to effectively find and hunt prey, and show that spatial drivers of survival for mesopredators can vary temporally. Collectively, our research illustrates that individual variation in mesopredator habitat use can scale-up and have population-level effects.

Enemies with benefits: integrating positive and negative interactions among terrestrial carnivores

Interactions among terrestrial carnivores involve a complex interplay of competition, predation and facilitation via carrion provisioning, and these negative and positive pathways may be closely linked. Here, we developed an integrative framework and synthesized data from 256 studies of intraguild predation, scavenging, kleptoparisitism and resource availability to examine global patterns of suppression and facilitation. Large carnivores were responsible for one third of mesocarnivore mortality (n = 1,581 individuals), and intraguild mortality rates were superadditive, increasing from 10.6% to 25.5% in systems with two vs. three large carnivores. Scavenged ungulates comprised 30% of mesocarnivore diets, with larger mesocarnivores relying most heavily on carrion. Large carnivores provided 1,351 kg of carrion per individual per year to scavengers, and this subsidy decreased at higher latitudes. However, reliance on carrion by mesocarnivores remained high, and abundance correlations among sympatric carnivores were more negative in these stressful, high-latitude systems. Carrion provisioning by large carnivores may therefore enhance suppression rather than benefiting mesocarnivores. These findings highlight the synergistic effects of scavenging and predation risk in structuring carnivore communities, suggesting that the ecosystem service of mesocarnivore suppression provided by large carnivores is strong and not easily replaced by humans.

Vertebrate scavenger guild composition and utilization of carrion in an East Asian temperate forest

Scavenging is a common feeding behavior by many species that plays an important role in ecosystem stability and function while also providing ecosystem services. Despite its importance, facultative scavenging on large animal carcasses has generally been overlooked in Asian temperate forest ecosystems. The aim of this study was to determine the composition and feeding behavior of the facultative scavenger guild as it relates to sika deer (Cervus nippon) carcasses in Japanese forests. There are no obligate scavengers or large predators that kill adult ungulates, but humans fill the role of large predators by culling deer for population management. We documented nine vertebrate species scavenging on deer carcasses and found that mammals were more frequent scavengers than birds and also fed for longer durations. This result suggests that there is a facultative scavenger guild composed mainly of mammals in our forest ecosystem and that carcass utilization by birds was restricted to only forest species. Raccoon dogs (Nyctereutes procyonoides) and Asian black bears (Ursus thibetanus) were the most frequent scavenger species and also fed for longer durations than other scavengers. There were significant seasonal differences in scavenging by Asian black bear, Japanese marten (Martes melampus), and mountain hawk-eagle (Nisaetus nipalensis), suggesting the availability of other food resources may alter facultative scavenging by each species. Our results support that scavenging is widespread in this system and likely has important functions including building links in the food web.

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

Many apex scavenger species, including nearly all obligate scavengers, are in a state of rapid decline and there is growing evidence these declines can drastically alter ecological food webs. Our understanding of how apex scavengers regulate populations of mesoscavengers, those less-efficient scavengers occupying mid-trophic levels, is improving; yet, there has been no comprehensive evaluation of the evidence around the competitive release of these species by the loss of apex scavengers. Here we present current evidence that supports the mesoscavenger release hypothesis, the increase in mesoscavengers and increase in carrion in the face of declining apex scavengers. We provide two models of scavenger dynamics to demonstrate that the mesoscavenger release hypothesis is consistent with ecological theory. We further examine the ecological and human well-being implications of apex scavenger decline, including carrion removal and disease regulation services.

Resource limitations and competitive interactions affect carnivore community composition at different ecological scales in a temperate island system

Selective pressures (i.e. resource limitation and competitive interaction) that drive the composition of ecological communities vary, and often operate on different ecological scales (ecological variables across varying spatial scales) than observed patterns. We studied the drivers of distribution and abundance of the American marten (Martes americana) and the carnivore community at three ecological scales on a Great Lakes island archipelago using camera traps. We found different drivers appeared important at each ecological scale and studying any of the three scales alone would give a biased understanding of the process driving the system. Island biogeography (resource limitation) was most important for carnivore richness, with higher richness on larger islands and lower richness as distance from the mainland increased. Marten presence on individual islands appeared to be driven by island size (resource limitation) and human avoidance (competitive interaction). Marten abundance at camera trap sites was driven by the cascading effect of coyotes (Canis latrans) on fishers (Pekania pennanti) (competitive interaction). Incorporating three ecological scales gave novel insights into the varying effects of resource limitation and competitive interaction processes. Our data suggests that ecological communities are structured through multiple competing ecological forces, and effective management and conservation relies on our ability to understand ecological forces operating at multiple ecological scales.