Lethal interactions among vertebrate top predators: a review of concepts, assumptions and terminology

Predator becomes prey: Martial eagle predation of lion cubs in the greater Mara region, Kenya

In many intact African savannah ecosystems, martial eagles are the top avian predator, while lions are the top terrestrial predator. Here, we report seven records of martial eagle predation or attempted predation of lion cubs in the greater Mara region, Kenya. These events resulted in the death of nine lion cubs, most of which were at least partially consumed, and are the first detailed records of this behaviour to be published. While these observations represent intraguild interactions, we suggest that they reflect neither intraguild predation nor interspecific killing. Rather, the ecology of both species coupled with the details of our records suggest that martial eagles opportunistically kill lion cubs purely to eat them. We hope that by publishing these records we will encourage others to share their observations of raptors predating on large mammalian carnivores, thus improving our understanding of a behaviour that we suspect may be more widespread than the current lack of evidence suggests.

Interspecific killing of wolverines by one wolf pack

Interactions between different species of predators are not uncommon, yet they are generally understudied in North America. Across their range, gray wolves (Canis lupus) and wolverines (Gulo gulo) occupy similar habitats and dietary niches. However, due to the elusiveness and relatively low density of these two species, interactions between them are not well documented. Here, we describe three instances of a single wolf pack killing a wolverine in the span of 13 months. None of the wolverines killed by wolves were consumed, suggesting that food was not the primary motivation behind the killings. Alternatively, defense of a food resource, territoriality, interspecific competitive killing, or some combination of those behaviors appear to be the cause of these actions. Documentation of these occurrences improves our understanding of wolf and wolverine ecology, interspecific predator interactions, and potential future changes to this aspect of community ecology.

Behaviour of mesopredatory coral reef fishes in response to threats from sharks and humans

Both sharks and humans present a potentially lethal threat to mesopredatory fishes in coral reef systems, with implications for both population dynamics and the role of mesopredatory fishes in reef ecosystems. This study quantifies the antipredator behaviours mesopredatory fishes exhibit towards the presence of large coral reef carnivores and compares these behavioural responses to those elicited by the presence of snorkelers. Here, we used snorkelers and animated life-size models of the blacktip reef shark (Carcharhinus melanopterus) to simulate potential predatory threats to mesopredatory reef fishes (lethrinids, lutjanids, haemulids and serranids). The responses of these reef fishes to the models and the snorkelers were compared to those generated by three non-threatening controls (life-size models of a green turtle [Chelonia mydas], a PVC-pipe [an object control] and a Perspex shape [a second object control]). A Remote Underwater Stereo-Video System (Stereo-RUV) recorded the approach of the different treatments and controls and allowed accurate measurement of Flight Initiation Distance (FID) and categorization of the type of flight response by fishes. We found that mesopredatory reef fishes had greater FIDs in response to the approach of threatening models (1402 ± 402-1533 ± 171 mm; mean ± SE) compared to the controls (706 ± 151-896 ± 8963 mm). There was no significant difference in FID of mesopredatory fishes between the shark model and the snorkeler, suggesting that these treatments provoked similar levels of predator avoidance behaviour. This has implications for researchers monitoring behaviour in situ or using underwater census as a technique to estimate the abundance of reef fishes. Our study suggests that, irrespective of the degree to which sharks actually consume these mesopredatory reef fishes, they still elicit a predictable and consistent antipredator response that has the potential to create risk effects.

Wolf Is Back: A Novel Sensitive Sentinel Rejoins the Trichinella Cycle in the Western Alps

Trichinella is a foodborne parasite whose wildlife reservoirs are represented by carnivores and omnivores with predatory and scavenger behavior. The aim of the present study was to investigate the occurrence of Trichinella infection in grey wolves (Canis lupus) that recolonized the Western Alps from the end of the past century, and discuss the epidemiological role played by this apex predator in the early phases of its return. During the period 2017–2022, diaphragm samples were obtained from 130 individuals collected in the frame of a wolf mortality survey. Trichinella larvae were found in 15 wolves (11.53%) with a parasite intensity of 11.74 larvae per gram. Trichinella britovi was the only species identified. This is the first prevalence survey of Trichinella in wolves recolonizing the Alps. Results suggest that, in this particular biotope, the wolf has rejoined the Trichinella cycle and has the potential to play an increasingly important role as maintenance host. Arguments in favor and against this perspective are discussed and knowledge gaps highlighted. The calculated Trichinella larval biomass in the estimated wolf population roaming in Northwest Italy will serve as baseline value to explore possible shifts in the relative importance of wolves as Trichinella reservoir within the regional carnivore community. Finally, wolves re-colonizing the Alps already appear as sensitive sentinels to monitor the risk of Trichinella zoonotic transmission by infected wild boar meat.

Cats and dogs: A mesopredator navigating risk and reward provisioned by an apex predator

Successfully perceiving risk and reward is fundamental to the fitness of an animal, and can be achieved through a variety of perception tactics. For example, mesopredators may "directly" perceive risk by visually observing apex predators, or may "indirectly" perceive risk by observing habitats used by predators. Direct assessments should more accurately characterize the arrangement of risk and reward; however, indirect assessments are used more frequently in studies concerning the response of GPS-marked animals to spatiotemporally variable sources of risk and reward. We investigated the response of a mesopredator to the presence of risk and reward created by an apex predator, where risk and reward likely vary in relative perceptibility (i.e., degree of being perceptible). First, we tested whether coyotes (Canis latrans) use direct or indirect assessments to navigate the presence of mountain lions (Puma concolor; risk) and kills made by mountain lions (reward) in an area where coyotes were a common prey item for mountain lions. Second, we assessed the behavioral response of coyotes to direct encounters with mountain lions. Third, we evaluated spatiotemporal use of carrion by coyotes at kills made by mountain lions. Indirect assessments generally outperformed direct assessments when integrating analyses into a unified framework; nevertheless, our ability to detect direct perception in navigating to mountain lion kills was likely restricted by scale and sampling limitations (e.g., collar fix rates, unsampled kill sites). Rather than responding to the risk of direct encounters with mountain lions, coyotes facilitated encounters by increasing their movement rate, and engaged in risky behavior by scavenging at mountain lion kills. Coyotes appear to mitigate risk by using indirect perception to avoid mountain lions. Our predator-predator interactions and insights are nuanced and counter to the conventional predator-prey systems that have generated much of the predation risk literature.

Red foxes at their northern edge: competition with the Arctic fox and winter movements

Rapid range expansion of boreal forest predators onto the tundra may disrupt local ecological processes, notably through competition with ecologically similar species. Red foxes (Vulpes vulpes) have expanded their range northwards throughout the Canadian Arctic, inducing competition with endemic Arctic foxes (V. lagopus). We studied competition between Arctic and red foxes, with a focus on interference competition, and winter movements of red foxes using satellite telemetry and den occupancy data from both species. We worked at Bylot Island (Nunavut) and Herschel Island (northern Yukon), two sites at the northern limit of the red fox’s range. As expected, red fox home ranges were 56% larger on average than Arctic fox home ranges. However, red foxes did not exclude Arctic foxes regionally nor did they prevent them from breeding successfully in their vicinity. On Bylot Island, Arctic foxes did not spatially avoid red foxes more than their conspecifics, as evidenced by similar intra- and interspecific home-range overlaps. On Herschel Island, the red fox pair’s home range extensively overlapped the home range of their Arctic fox neighbors. While red foxes tracked on Bylot Island survived several winters without expanding or leaving their home ranges, those on Herschel Island moved onto the sea ice and died. Overall, our results demonstrate low levels of interference competition between the two species in the High Canadian Arctic. When red fox density is low, as in our study areas where land protection prevents predator subsidization by anthropogenic food sources, Arctic and red foxes may be able to co-exist with limited antagonistic interactions. Our sample sizes were limited by the naturally low density of red foxes at their northernmost edge. Replication therefore is needed to fully understand winter space use and intraguild interactions in this species at its northern range limit.

Niche partitioning between sympatric wild canids: the case of the golden jackal (Canis aureus) and the red fox (Vulpes vulpes) in north-eastern Italy

BACKGROUND

Two coexisting species with similar ecological requirements avoid or reduce competition by changing the extent of their use of a given resource. Numerous coexistence mechanisms have been proposed, but species interactions can also be aggressive; thus, generally a subordinate species modifies its realized niche to limit the probability of direct encounters with the dominant species. We studied niche partitioning between two sympatric wild canids in north-eastern Italy: the golden jackal and the red fox, which, based on competition theories, have a high potential for competition. We considered four main niche dimensions: space, habitat, time, and diet.

RESULTS

We investigated three study areas monitoring target species populations from March 2017 to November 2018 using non-invasive monitoring techniques. Red fox presence was ascertained in every study area, while golden jackal presence was not ascertained in one study area, where we collected data regarding wolf presence. Considering the two target species, we observed partial diet partitioning based on prey size, with the golden jackal mainly feeding on wild ungulates and the red fox mainly feeding on small mammals. The two canids had an extensive temporal overlap along the diel cycle, having both predominant crepuscular and nocturnal activity patterns, but marked spatial partitioning and differential use of habitats. The golden jackal proved to be specialist concerning the habitat dimension, while the red fox resulted completely generalist: the former selected less human-modified habitats and avoided intensively cultivated lands, while the latter was present in all habitats, including intensively cultivated lands.

CONCLUSIONS

The observed partitioning might be due partially to some ecological adaptations (e.g. specialist vs. generalist use of resources) and specific behaviours (e.g. cooperative vs. solitary hunting) and partially to the avoidance response of the red fox aimed at reducing the probability of direct encounters with the golden jackal.

The effect of competing carnivores on the feeding behaviour of leopards (Panthera pardus) in an African savanna

Knowledge of competition dynamics among Africa's large carnivores is important for conservation. However, investigating carnivore behaviour in the field can be challenging especially for species that are difficult to access. Methods that enable remote collection of data provide a means of recording natural behaviour and are therefore useful for studying elusive species such as leopards (Panthera pardus). Camera traps and Global Positioning System (GPS) collars are powerful tools often used independently to study animal behaviour but where their data are combined, the interpretation of a species' behaviours is improved. In this study we used data from baited camera trap stations to investigate the feeding habits of leopards at Malilangwe Wildlife Reserve, Zimbabwe. We investigated the influence of spotted hyenas, lions and other competing leopards on the feeding duration of leopards using Generalized Linear Mixed Effects Modelling. To test the influence of competing predators on resting distances from bait sites, eight leopards were fitted with GPS collars. Results showed that leopards spent the shortest time feeding on the baits in the presence of competing male leopards compared to other predators while lion presence caused animals to rest farthest from bait sites. Interaction analysis indicated that small-bodied leopards spent significantly shorter durations feeding when spotted hyenas were present. Our findings demonstrate that competition from guild carnivores has negative impacts on the food intake of leopards, which may have implications for fitness and survival. This study provides a snapshot of the competition dynamics at bait sites which may give insight to ecosystem level interactions among large carnivores in savanna 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.

Skunks and gray foxes in a tropical dry region: casual or positive interactions?

Previous studies have shown that skunks present negative interactions with foxes. However, recently published observations have demonstrated that southern spotted skunk (Spilogale angustifrons) individuals follow gray foxes (Urocyon cinereoargenteus) in the Tehuacán-Cuicatlán Biosphere Reserve (TCBR) in Mexico. In this paper, we reported the same interaction in other locations in the TCBR and evaluated whether this interaction is casual or statistically positive. In this analysis, we included data pertaining to three skunk species (S. angustifrons, Conepatus leuconotus, and Mephitis macroura) and U. cinereoargenteus. We sampled 172 sites using camera traps from 2011 to 2018 for a total effort of 49,764 trap-days. The four studied species were nocturnal; the overlap coefficient between foxes and skunks varied from 0.70 to 0.83. Of the 32 consecutive records between S. angustifrons and U. cinereoargenteus, 11 showed that individuals of this skunk species closely followed U. cinereoargenteus and that these encounters were not random (time interval <1 min). We did not find evidence of a behavioral association of U. cinereoargenteus with C. leuconotus and M. macroura.

Restriction of anthropogenic foods alters a top predator’s diet and intraspecific interactions

Anthropogenic foods are utilized by many animals around the world, and these resources could impact dietary preferences and intra- and interspecific interactions. Under a quasi-Before-After-Control-Impact experimental design, we assessed how dingoes (Canis dingo) responded to a decline in anthropogenic foods in the Tanami Desert, central Australia. We did so by assessing dingo diets close to and away from human influence during a period when food waste was available at two rubbish tips, and then during a period when food waste was restricted at one of the tips. Our results demonstrate that access to anthropogenic foods can alter a top predator’s diet. Namely, dingoes showed a preference for eating the desert mouse (Pseudomys desertor) in areas where food waste was restricted, whereas dingo diets did not reflect ambient prey availability at areas where food waste was constantly available. Reduced availability of food waste also affected interactions between dingoes, with cannibalism decreasing where food waste was removed, and it may have increased consumption of a subordinate mesopredator, the feral cat (Felis catus). By implication, efforts to manage food waste could reestablish or strengthen interactions between predators and their wild prey with possible cascading consequences for ecosystems.

Abiotic conditions mediate intraguild interactions between mammalian carnivores

Intraguild (IG) interactions are common among mammalian carnivores, can include intraguild predation (IGP) and interspecific killing (IK), and are often asymmetrical, where a larger more dominant species (IG_predator ) kills a smaller one (IG_prey ). According to ecological theory, the potential for an IG_predator and IG_prey to coexist depends on whether the direct consumptive benefits for the IG_predator are substantial (IGP) or insignificant (IK), the extent to which the IG_prey is the superior exploitative competitor on shared prey resources, and overall ecosystem productivity. We used resource selection models and spatially explicit age and harvest data for two closely related mesopredators that engage in IG interactions, American martens (Martes americana; IG_prey ) and fishers (Pekania pennanti; IG_predator ), to identify drivers of distributions, delineate areas of sympatry and allopatry, and explore the role of an apex predator (coyote; Canis latrans) on these interactions. Model selection revealed that fisher use of this landscape was strongly influenced by late winter abiotic conditions, but other bottom-up (forest composition) and top-down (coyote abundance) factors also influenced their distribution. Overall, fisher probability of use was higher where late winter temperatures were warmer, snowpack was deeper, and measures of productivity were greater. Martens were constrained to areas of the landscape where the probability of fisher use, coyote abundance, and productivity were low and selected for forest conditions that presumably maximized prey availability. Marten age data indicated an increased proportion of juveniles outside of the predicted area of sympatry, suggesting that few animals survived >1.5 years in this area that supported higher densities of fishers and coyotes. Consistent with asymmetrical IG interaction theory, the IG_predator (fishers and, to a lesser degree, coyotes) competitively excluded the IG_prey (martens) from more productive, milder temperature habitats, whereas IG_predators and IG_prey coexisted in low productivity environments, where a combination of abiotic and biotic conditions enabled the IG_prey to be the superior exploitative competitor.

Lynx eats cat: disease risk assessment during an Iberian lynx intraguild predation

Lethal interactions between members of the carnivore guild are well represented in literature. In the Iberian lynx, interspecific killing (without prey consumption) of some mesocarnivores, such as the Egyptian mongoose, genet, and red fox, has been reported. Although vaguely documented, evidence suggests feral cats fall victim to interactions with this apex predator. Here, we describe the first documented case of interspecific killing and partial consumption of a feral cat by an adult male Iberian lynx reintroduced in Southwestern Spain. Ulterior analyses demonstrated that the victim was viremic to feline leukemia virus. To prevent the dissemination of the virus and a potential outbreak in the Iberian lynx population, control measures, including the clinical evaluation of the male Iberian lynx, and intensive monitoring were implemented in order to detect intraspecific interactions. After 3 weeks, the lynx was evaluated, presented good condition and resulted negative to both ELISA and RT-PCR. Thanks to the long-term monitoring, this case could be detected and measures to prevent an outbreak could be implemented.

Interference competition pressure predicts the number of avian predators that shifted their timing of activity

Being active at different times facilitates the coexistence of functionally similar species. Hence, time partitioning might be induced by competition. However, the relative importance of direct interference and indirect exploitation competition on time partitioning remains unclear. The aim of this study was to investigate the relative importance of these two forms of competition on the occurrence of time-shifting among avian predator species. As a measure of interference competition pressure, we used the species richness of day-active avian predator species or of night-active avian predator species (i.e. species of Accipitriformes, Falconiformes and Strigiformes) in a particular geographical area (assemblage). As an estimate of exploitation competition pressure, we used the total species richness of avian predators in each assemblage. Estimates of the intensity of interference competition robustly predicted the number of Accipitriformes species that became crepuscular and the number of Strigiformes species that became day-active or strictly crepuscular. Interference competition pressure may depend on body size and on the total duration of the typical active period (day or night length). Our results support-to some extent-that smaller species are more likely to become time-shifters. Day length did not have an effect on the number of time-shifter species in the Accipitriformes. Among the large Strigiformes, more time-shifter species occur in areas where nights are shorter (i.e. where less of the typical time resource is available). However, in the small Strigiformes, we found the opposite, counterintuitive effect: more time-shifters where nights are longer. Exploitation competition may have had an additional positive effect on the number of time-shifters, but only in Accipitriformes, and the effect was not as robust. Our results thus support the interference competition hypothesis, suggesting that animals may have shifted their time of activity, despite phylogenetic constraints on the ability to do so, to reduce the costs of direct interactions. Our findings also highlight the influence of body size as a surrogate of competitive ability during encounters on time partitioning, at least among avian predators.

Killer whales redistribute white shark foraging pressure on seals

Predatory behavior and top-down effects in marine ecosystems are well-described, however, intraguild interactions among co-occurring marine top predators remain less understood, but can have far reaching ecological implications. Killer whales and white sharks are prominent upper trophic level predators with highly-overlapping niches, yet their ecological interactions and subsequent effects have remained obscure. Using long-term electronic tagging and survey data we reveal rare and cryptic interactions between these predators at a shared foraging site, Southeast Farallon Island (SEFI). In multiple instances, brief visits from killer whales displaced white sharks from SEFI, disrupting shark feeding behavior for extended periods at this aggregation site. As a result, annual predations of pinnipeds by white sharks at SEFI were negatively correlated with close encounters with killer whales. Tagged white sharks relocated to other aggregation sites, creating detectable increases in white shark density at Ano Nuevo Island. This work highlights the importance of risk effects and intraguild relationships among top ocean predators and the value of long-term data sets revealing these consequential, albeit infrequent, ecological interactions.

Fear, foraging and olfaction: how mesopredators avoid costly interactions with apex predators

Where direct killing is rare and niche overlap low, sympatric carnivores may appear to coexist without conflict. Interference interactions, harassment and injury from larger carnivores may still pose a risk to smaller mesopredators. Foraging theory suggests that animals should adjust their behaviour accordingly to optimise foraging efficiency and overall fitness, trading off harvest rate with costs to fitness. The foraging behaviour of red foxes, Vulpes vulpes, was studied with automated cameras and a repeated measures giving-up density (GUD) experiment where olfactory risk cues were manipulated. In Plitvice Lakes National Park, Croatia, red foxes increased GUDs by 34% and quitting harvest rates by 29% in response to wolf urine. In addition to leaving more food behind, foxes also responded to wolf urine by spending less time visiting food patches each day and altering their behaviour in order to compensate for the increased risk when foraging from patches. Thus, red foxes utilised olfaction to assess risk and experienced foraging costs due to the presence of a cue from gray wolves, Canis lupus. This study identifies behavioural mechanisms which may enable competing predators to coexist, and highlights the potential for additional ecosystem service pathways arising from the behaviour of large carnivores. Given the vulnerability of large carnivores to anthropogenic disturbance, a growing human population and intensifying resource consumption, it becomes increasingly important to understand ecological processes so that land can be managed appropriately.

Resource partitioning between kit foxes (Vulpes macrotis) and coyotes (Canis latrans): a comparison of historical and contemporary dietary overlap

Range expansions by generalists can alter communities and introduce competitive pressures on native species. In the Great Basin Desert, USA, coyotes (Canis latrans Say, 1823) have colonized and are now sympatric with native kit foxes (Vulpes macrotis Merriam, 1888). Since both species have similar diets, dietary partitioning may facilitate coexistence. We analyzed coyote and kit fox diets, then compared our results to an earlier study. Because populations are dynamic, we expected that decreases in prey or increases in predator abundance could alter dietary patterns. We found no significant changes in population-level prey diversity for kit foxes or coyotes, but found high levels of dietary overlap between species. We did detect a significant decrease in the relative importance of leporids (family Leporidae) in the diets of both canids, but they remained important for coyotes. The relative importance of small mammals was greater for kit foxes than coyotes, but their importance had not changed significantly over time. We detected significant declines in prey diversity per sample (scat-level dietary diversity) for both canids, suggesting that during a foraging event, individuals may encounter less diverse prey now than historically. These findings suggested that kit foxes and coyotes were not limited by prey, despite high dietary overlap.

Colour polymorphism in owls is linked to light variability

Owls show an astonishing variation in their degree of colour polymorphism, although the exact mechanisms driving such variation remain controversial. Here we address this fundamental question by considering information on all extant owls and recent advances in comparative methods in the frame of three mutually non-exclusive evolutionary scenarios. In addition, we study for the first time whether the evolution of influential ecological characters facilitated the evolution of colour polymorphism (or vice versa). In agreement with the niche divergence hypothesis, we found that species living under more variable luminal conditions, i.e., species with diurnal and crepuscular habits and those inhabiting in a mixture of open and closed habitats, were more likely to show colour polymorphism. Correlated evolution analyses revealed that a change in the luminal niche might be a fundamental requisite for the evolution of colour polymorphism. Moreover, polymorphism was more frequent among owl species occupying lower trophic levels, which could be explained by a particularly high selection for crypsis on small predator owls. Our results, thus, provide support for the idea that colour polymorphism in owls is an adaptive character likely maintained by the selective advantage of morphs under different environmental conditions via disruptive selection mechanisms.

Are pumas subordinate carnivores, and does it matter?

BACKGROUND

Interspecific competition affects species fitness, community assemblages and structure, and the geographic distributions of species. Established dominance hierarchies among species mitigate the need for fighting and contribute to the realized niche for subordinate species. This is especially important for apex predators, many of which simultaneous contend with the costs of competition with more dominant species and the costs associated with human hunting and lethal management.

METHODS

Pumas are a widespread solitary felid heavily regulated through hunting to reduce conflicts with livestock and people. Across their range, pumas overlap with six apex predators (gray wolf, grizzly bear, American black bear, jaguar, coyote, maned wolf), two of which (gray wolf, grizzly bear) are currently expanding in North America following recovery efforts. We conducted a literature search to assess whether pumas were subordinate or dominant with sympatric apex predators, as well as with three felid mesocarnivores with similar ecology (ocelot, bobcat, Canada lynx). We also conducted an analysis of the spatial distributions of pumas and their dominant sympatric competitors to estimate in what part of their range, pumas are dominant versus subordinate.

RESULTS

We used 64 sources to assess dominance among pumas and other apex predators, and 13 sources to assess their relationships with felid mesocarnivores. Evidence suggested that wolves, grizzly bears, black bears, and jaguars are dominant over pumas, but that pumas are dominant over coyotes and maned wolves. Evidence suggested that pumas are also dominant over all three felid mesocarnivores with which they share range. More broadly, pumas are subordinate to at least one other apex carnivore in 10,799,252 (47.5%) of their 22,735,268 km2 range across North and South America.

DISCUSSION

Subordinate pumas change their habitat use, suffer displacement at food sources, likely experience increased energetic demands from harassment, exhibit increased starvation, and are sometimes directly killed in competitive interactions with dominant competitors. Nevertheless, we lack research clearly linking the costs of competition to puma fitness. Further, we lack research that assesses the influence of human effects simultaneous with the negative effects of competition with other sympatric carnivores. Until the time that we understand whether competitive effects are additive with human management, or even potentially synergistic, we encourage caution among managers responsible for determining harvest limits for pumas and other subordinate, apex carnivores in areas where they are sympatric with dominant species. This may be especially important information for managers working in regions where wolves and brown bears are recolonizing and recovering, and historic competition scenarios among multiple apex predators are being realized.

Carnivore carcasses are avoided by carnivores

Ecologists have traditionally focused on herbivore carcasses as study models in scavenging research. However, some observations of scavengers avoiding feeding on carnivore carrion suggest that different types of carrion may lead to differential pressures. Untested assumptions about carrion produced at different trophic levels could therefore lead ecologists to overlook important evolutionary processes and their ecological consequences. Our general goal was to investigate the use of mammalian carnivore carrion by vertebrate scavengers. In particular, we aimed to test the hypothesis that carnivore carcasses are avoided by other carnivores, especially at the intraspecific level, most likely to reduce exposure to parasitism. We take a three-pronged approach to study this principle by: (i) providing data from field experiments, (ii) carrying out evolutionary simulations of carnivore scavenging strategies under risks of parasitic infection, and (iii) conducting a literature-review to test two predictions regarding parasite life-history strategies. First, our field experiments showed that the mean number of species observed feeding at carcasses and the percentage of consumed carrion biomass were substantially higher at herbivore carcasses than at carnivore carcasses. This occurred even though the number of scavenger species visiting carcasses and the time needed by scavengers to detect carcasses were similar between both types of carcasses. In addition, we did not observe cannibalism. Second, our evolutionary simulations demonstrated that a risk of parasite transmission leads to the evolution of scavengers with generally low cannibalistic tendencies, and that the emergence of cannibalism-avoidance behaviour depends strongly on assumptions about parasite-based mortality rates. Third, our literature review indicated that parasite species potentially able to follow a carnivore-carnivore indirect cycle, as well as those transmitted via meat consumption, are rare in our study system. Our findings support the existence of a novel coevolutionary relation between carnivores and their parasites, and suggest that carnivore and herbivore carcasses play very different roles in food webs and ecosystems.

Guardian or threat: does golden eagle predation risk have cascading effects on forest grouse?

Previous studies on intraguild predation have mainly focused on within-class assemblages, even though avian top predators may also influence mammalian mesopredator prey. By using nation-wide long-term data from Finland, northern Europe, we examined the impacts of golden eagles (Aquila chrysaetos) together with red foxes (Vulpes vulpes) and pine martens (Martes martes) on forest-dwelling herbivores, black grouse (Tetrao tetrix) and hazel grouse (Tetrastes bonasia). We hypothesized that eagles may alleviate the overall predation pressure on grouse by imposing intraguild predation risk on mesopredators. The predation impact of eagle was modelled using eagle density estimates and distance to eagle nest. Wildlife triangle counts were used as predation impact proxies of mammalian mesopredators and as measures of response in grouse. Our results show that eagle density correlated negatively with black grouse abundance indices while being positively associated with the proportion of juveniles in both grouse species, irrespective of the abundance of mesopredators. Yet, foxes and martens alone had a negative effect on the abundance indices and the proportion of young in the two grouse species. This suggests that the possible cascading effects of eagles are not mediated by decreased mesopredator numbers, but instead by fear effects. Alternatively, they may be mediated by other species than fox or marten studied here. In conclusion, we found support for the hypothesis that eagles provide protection for juvenile black and hazel grouse, whereas they are a threat for adult grouse. This important information helps us to better understand the role of avian top predators in terrestrial ecosystems.

Context Dependent Effect of Landscape on the Occurrence of an Apex Predator across Different Climate Regions

In studies of habitat suitability at landscape scales, transferability of species-landscape associations among sites are likely to be critical because it is often impractical to collect datasets across various regions. However, limiting factors, such as prey availability, are not likely to be constant across scales because of the differences in species pools. This is particularly true for top predators that are often the target for conservation concern. Here we focus on gray-faced buzzards, apex predators of farmland-dominated landscapes in East Asia. We investigated context dependency of "buzzard-landscape relationship", using nest location datasets from five sites, each differing in landscape composition. Based on the similarities of prey items and landscape compositions across the sites, we determined several alternative ways of grouping the sites, and then examined whether buzzard-landscape relationship change among groups, which was conducted separately for each way of grouping. As a result, the model of study-sites grouping based on similarities in prey items showed the smallest ΔAICc. Because the terms of interaction between group IDs and areas of broad-leaved forests and grasslands were selected, buzzard-landscape relationship showed a context dependency, i.e., these two landscape elements strengthen the relationship in southern region. The difference in prey fauna, which is associated with the difference in climate, might generate regional differences in the buzzard-landscape associations.

Intraguild predation leads to cascading effects on habitat choice, behaviour and reproductive performance

Intraguild predation (IGP) is a commonly recognized mechanism influencing the community structure of predators, but the complex interactions are notoriously difficult to disentangle. The mesopredator suppression hypothesis predicts that a superpredator may either simultaneously repress two mesopredators, restrain the dominant one and thereby release the subdominant mesopredator, or elicit different responses by both mesopredators. We show the outcome arising from such conditions in a three-level predator assemblage (Eurasian eagle owl Bubo bubo L., northern goshawk Accipiter gentilis L. and common buzzard Buteo buteo L.) studied over 25 years. In the second half of the study period, the eagle owl re-colonized the study area, thereby providing a natural experiment of superpredator introduction. We combined this set-up with detailed GIS analysis of habitat use and a field experiment simulating intrusion by the superpredator into territories of the subdominant mesopredator, the buzzard. Although population trends were positive for all three species in the assemblage, the proportion of failed breeding attempts increased significantly in both mesopredators after the superpredator re-colonized the area. We predicted that superpredator-induced niche shifts in the dominant mesopredator may facilitate mesopredator coexistence in superpredator-free refugia. We found significant changes in nesting habitat choice in goshawk, but not in buzzard. Since competition for enemy-free refugia and the rapid increase in population density may have constrained niche shifts of the subdominant mesopredator, we further predicted behavioural changes in response to the superpredator. The field experiment indeed showed a significant increase in aggressive response of buzzards towards eagle owl territory intrusion over the course of 10 years, probably due to phenotypic plasticity in the response towards superpredation risk. Overall, our results show that intraguild predation can be a powerful force of behavioural change, simultaneously influencing habitat use and aggressiveness in predator communities. These changes might help to buffer mesopredator populations against the negative effects of intraguild predation.

Differential Habitat Use or Intraguild Interactions: What Structures a Carnivore Community?

Differential habitat use and intraguild competition are both thought to be important drivers of animal population sizes and distributions. Habitat associations for individual species are well-established, and interactions between particular pairs of species have been highlighted in many focal studies. However, community-wide assessments of the relative strengths of these two factors have not been conducted. We built multi-scale habitat occupancy models for five carnivore taxa of New York's Adirondack landscape and assessed the relative performance of these models against ones in which co-occurrences of potentially competing carnivore species were also incorporated. Distribution models based on habitat performed well for all species. Black bear (Ursus americanus) and fisher (Martes pennanti) distribution was similar in that occupancy of both species was negatively associated with paved roads. However, black bears were also associated with larger forest fragments and fishers with smaller forest fragments. No models with habitat features were more supported than the null habitat model for raccoons (Procyon lotor). Martens (Martes americana) were most associated with increased terrain ruggedness and elevation. Weasel (Mustela spp.) occupancy increased with the cover of deciduous forest. For most species dyads habitat-only models were more supported than those models with potential competitors incorporated. The exception to this finding was for the smallest carnivore taxa (marten and weasel) where habitat plus coyote abundance models typically performed better than habitat-only models. Assessing this carnivore community as whole, we conclude that differential habitat use is more important than species interactions in maintaining the distribution and structure of this carnivore guild.

Recolonizing wolves influence the realized niche of resident cougars

BACKGROUND

Niche differentiation may betray current, ongoing competition between two sympatric species or reflect evolutionary responses to historic competition that drove species apart. The best opportunity to test whether ongoing competition contributes to niche differentiation is to test for behavioral shifts by the subordinate competitor in controlled experiments in which the abundance of the dominant competitor is manipulated. Because these circumstances are difficult to coordinate in natural settings for wide-ranging species, researchers seize opportunities presented by species reintroductions. We tested for new competition between reintroduced wolves and resident cougars in the Southern Yellowstone Ecosystem to assess whether wolves might be impacting the realized niche of sympatric cougars.

RESULTS

Between2002 and 2012, a period during which wolves increased from 15 to as high as 91 in the study area, cougars significantly increased the percentage of deer and decreased the percentage of elk in their diet in summer. Our top models explaining these changes identified elk availability, defined as the number of elk per wolf each year, as the strongest predictor of changing cougar prey selection. Both elk and deer were simultaneously declining in the system, though deer more quickly than elk, and wolf numbers increased exponentially during the same time frame. Therefore,we concluded that prey availability did not explain prey switching and that competition with wolves at least partially explained cougar prey switching from elk to deer. We also recorded 5 marked cougar kittens killed by wolves and 2 more that were killed by an undetermined predator. In addition, between 2005 and 2012, 9 adult cougars and 10 cougar kittens died of starvation, which may also be in part explained by competition with wolves.

CONCLUSIONS

Direct interspecific predation and shifting cougar prey selection as wolves increased in the system provided evidence for competition between recolonizing wolves and resident cougars. Through competition, recolonizing wolves have impacted the realized niche of resident cougars in the Southern Yellowstone Ecosystem (SYE), and current resident cougars may now exhibit a realized niche more reflective of an era when these species were previously sympatric in the Yellowstone Ecosystem.

Avian top predator and the landscape of fear: responses of mammalian mesopredators to risk imposed by the golden eagle

Top predators may induce extensive cascading effects on lower trophic levels, for example, through intraguild predation (IGP). The impacts of both mammalian and avian top predators on species of the same class have been extensively studied, but the effects of the latter upon mammalian mesopredators are not yet as well known. We examined the impact of the predation risk imposed by a large avian predator, the golden eagle (Aquila chrysaetos, L.), on its potential mammalian mesopredator prey, the red fox (Vulpes vulpes, L.), and the pine marten (Martes martes, L.). The study combined 23 years of countrywide data from nesting records of eagles and wildlife track counts of mesopredators in Finland, northern Europe. The predation risk of the golden eagle was modeled as a function of territory density, density of fledglings produced, and distance to nearest active eagle territory, with the expectation that a high predation risk would reduce the abundances of smaller sized pine martens in particular. Red foxes appeared not to suffer from eagle predation, being in fact most numerous close to eagle nests and in areas with more eagle territories. This is likely due to similar prey preferences of the two predators and the larger size of foxes enabling them to escape eagle predation risk. Somewhat contrary to our prediction, the abundance of pine martens increased from low to intermediate territory density and at close proximity to eagle nests, possibly because of similar habitat preferences of martens and eagles. We found a slightly decreasing trend of marten abundance at high territory density, which could indicate that the response in marten populations is dependent on eagle density. However, more research is needed to better establish whether mesopredators are intimidated or predated by golden eagles, and whether such effects could in turn cascade to lower trophic levels, benefitting herbivorous species.