Hypercarnivorous Species Research Articles

Different, but the same: Inferring the hunting behaviour of the hypercarnivorous bush dog (Speothos venaticus) through finite element analysis.

Cerdocyonina is a clade composed by the South-American canids in which the bush dog (Speothos venaticus) is one of the most elusive species. Known for its unique morphology within the group, this small, bear-like faced canid is the only member of the clade adapted to hypercarnivory, an almost exclusively meat-based diet currently present only in usually large, pack-hunting canids such as the grey wolf (Canis lupus). However, much of the biology of the bush dog is poorly understood, and inferences about its ecology, hunting strategies and diet are usually based on observation of captive individuals and anecdotal records, with reduced quantitative data to offer support. Here, we investigated the craniomandibular functional morphology of the bush dog through finite element analysis (FEA). FEA was employed to model the biting behaviour and to create extrinsic and intrinsic functional scenarios with different loads, corresponding to different bites used to subdue and process the prey. For comparison, the same modelling was applied to the skull of a grey wolf and a grey fox (Urocyon cinereoargenteus). Our analysis showed that the bush dog's responses to loading are more similar to the wolf's than to the fox's in most scenarios, suggesting a convergent craniomandibular functional morphology between these two hypercarnivorous species, despite their distinct phylogenetic positions and body sizes. Differences between the three taxa are noteworthy and suggested to be related to the size of the usual prey. The modelled bite force for the bush dog is relatively strong, about half of that estimated for the wolf and about 40% stronger than the fox's bite. The results strengthen with quantitative data the inferences of the bush dog as a pack-hunting predator with prey size similar to its own, such as large rodents and armadillos, being specialised in subduing and killing its prey using multiple bites. Its similarity to the wolf also confirms anecdotal accounts of predation on mammals that are much larger than itself, such as peccaries and tapirs. These data highlight the ecological specialisation of this small canid in a continent where large, pack-hunting canids are absent.

Changes in canid cranial morphology induced by captivity and conservation implications

Hypercarnivorous mammal species are among the most vulnerable to population losses and endangerment. Among species belonging to Family Canidae, hypercarnivores are frequently subject to intense conservation efforts including captive breeding and reintroduction attempts. However, hypercarnivorous species may be most vulnerable to morphological changes in captivity, potentially altering their cranial functionality and limiting their reintroduction success. Other canid species with varying dietary preferences are also maintained in captivity, although it is unknown if morphological changes are prevalent across all captive canid populations or if these changes are concentrated primarily within hypercarnivores. To examine whether canids display morphological changes in captivity regardless of dietary preference, we assessed cranial and mandibular shape of 1621 specimens representing 15 canid species using geometric morphometric techniques. All hypercarnivores (4 species) and many hypocarnivores (5 of 7 species) differed between captive and wild populations in at least one shape variable. None of the mesocarnivores (4 species) differed in any shape variable. Among the carnivory types, hypercarnivorous species had the most pronounced differences in shape, particularly associated with a widening and shortening of the cranium within captive populations. Changes in cranial shape may impact an animal's ability to successfully capture and consume prey, therefore differences in cranial shape in captive populations may represent an obstacle to future reintroduction success. By examining cranial and mandibular shape differences between captive and wild populations, we explore the long-term impacts of captivity in canids in an effort to mitigate these negative effects in the future and increase the potential for reintroduction success.

Adaptations to prey base in the hypercarnivorous leopard cat Prionailurus bengalensis

Investigating biogeographical variations in diet composition can help understand the adaptability and generalism of species. Although the dietary adaptability of omnivorous mesocarnivores is well established, far less work has explored how more specialist hypercarnivores optimise their diets. By reviewing 11 studies of the leopard cat (Prionailurus bengalensis), we quantitatively examined how dietary composition varies over the wide range of biomes they occupy in Asia. Specifically, we contrasted the diet of the Iriomote Island sub-species (south-western Japan), where native rodents are absent, with that of the mainland. Leopard cat diet typically comprised mammals, birds, amphibians, reptiles, and invertebrates. In Iriomote Island, however, the low relative frequency of occurrence of small mammals (only introduced rats) was compensated by higher frequencies of reptiles and amphibians compared to the mainland. Consequently, trophic diversity and dietary niche breadth were higher for leopard cats in Iriomote Island than for the mainland. This shows that even hypercarnivorous species can use trophic plasticity to adapt to local prey availability. Given that rodent numbers often fluctuate substantially over time, the availability of alternative prey, such as herptiles, may be vital for the conservation of the leopard cat, and especially the critically endangered Iriomote cat. More generally, the trophic versatility of hypercarnivores must be considered when assessing their vulnerability to environmental change.

Simultaneous GPS tracking reveals male associations in a solitary carnivore

In hypercarnivorous species, females have large spatial requirements to meet their nutritional needs, and food competition among females is intense. As a result, females are typically solitary and territorial, and solitary males compete for access to dispersed females. Yet, largely anecdotal reports indicate that facultative male sociality may be more common in solitary carnivores than previously thought. We studied spatial interactions among fossas (Cryptoprocta ferox), Madagascar's largest carnivore, using simultaneous GPS tracking of 13 adult individuals to determine patterns of sex-specific spatial distribution and sociality. Male home ranges were larger than those of females, male home ranges overlapped more with those of other males than those of females with other females. Whereas some males were solitary, a subset of adult males was found to have very high home range overlap, high rates of co-location within <50 m, low minimum inter-individual distances, and significantly positive “dynamic interaction”. These associated dyads sometimes, but not always, were close relatives. The fact that solitary and associated males coexist in this population raises interesting questions concerning constraints and flexibility of social tolerance. This study yielded preliminary indications that female distribution appears to be primarily structured by resource competition, whereas male sociality seems to depend on demographic chance events, yet unknown proximate determinants of social tolerance, and it is associated with somatic and reproductive advantages. Male associations among carnivores are therefore more widespread and appear to be based on a wider range of factors than previously thought.

First record of immigrantPhoberogale(Mammalia, Ursidae, Carnivora) from Southern California

ABSTRACT Phoberogale Ginsburg & Morales, 1995, is a primitive ursid named to separate hypercarnivorous species from a rather heterogeneous group formerly included in the genus Cephalogale Jourdan, 1862. The presence of Cephalogale (s.l.) in the Great Plains of the United States has been documented since the late 1980s, often in the context of immigrant taxa and Neogene biochronology. However, no formal description or illustration of the respective specimens was published. Recently, an associated skull and left dentary were recovered from an early Miocene terrestrial deposit in southern California. We take this opportunity to describe the California specimen, which represents a new species, Phoberogale shareri n. sp. This new species belongs to the Phoberogale-Phoberocyon lineage and is distinguished from species of Cephalogale (s.s.) by its larger size, less-reduced pre-carnassial premolars, and less-elongated M2. Within the genus Phoberogale, P. shareri n. sp. is more derived than Europeans species (P. b...

Chapter 7

Borophaginae is the largest of the three subfamilies of the dog family Canidae, with some 66 species, spanning approximately 34 m.y. (Orellan to Blancan). Not surprisingly, this extensive radiation of canids includes a diverse array of dietary types, ranging from hypocarnivorous to hypercarnivorous and durophagous. The last 16 m.y. of borophagine history is dominated by hypercarnivorous forms that were the dominant doglike predators within their faunas. Because of their relatively robust skeletons and their resemblance to extant hyenas in craniodental morphology, many or most of these hypercarnivorous species, particularly those of the late Miocene and Pliocene, have been assumed as primarily scavengers rather than hunters. The classification of most hypercarnivorous borophagines as scavengers relegates them to much less important roles in the ecology and evolution of their respective communities than does a classification as hunters. Unlike hunters, scavengers are unlikely to influence the evolution of the animals they eat, and are expected to exist at relatively low densities as do the only extant scavenging carnivorans, brown (Parahyaena brunnea) and striped hyenas (Hyaena hyaena). Given the substantial fossil record of the Borophaginae, it seems unlikely that all or most of the hypercarnivorous forms were primarily scavengers. Moreover, if some hunted, the larger species might be expected to have done so in groups, as large canids hunt in packs today.Here we examine possible foraging modes within the Borophaginae using morphometrics and two new approaches to estimating the typical prey size of extinct carnivores. The craniodental morphology of the Borophaginae is compared with that of the living Caninae and Hyaeninae (hyaenids exclusive of Proteles cristata, the aardwolf) based on measurements that reflect relative tooth size, jaw muscle leverage, rigidity of the dentary, and grinding versus slicing function of the teeth. The Borophaginae are found to be intermediate in morphology between the Caninae and Hyaeninae. Unlike hyaenids and like canines, they retain substantial postcarnassial molars. However, like hyaenids, the borophagines had significantly stronger jaws and enhanced jaw muscle leverage compared to other canids. Prey size is estimated for borophagines based on correlation between dentary height and typical prey size in living canids. These results are compared with those produced using a recently published energetic model that predicts that all carnivores larger than about 21 kg feed on prey as large or larger than themselves. The methods provide similar predictions, resulting in a list of 11 borophagines (all subtribes Aelurodontina and Borophagina) that probably consumed large prey.Comparisons with extant hyaenids reveal that the sole hunter of large prey, the spotted hyena (Crocuta), differs from the two mainly scavenging species, the brown and striped hyenas, in being significantly larger, more abundant, and widespread. Moreover, morphometric comparisons indicate that spotted hyenas have a more hypercarnivorous dentition. Given this, it is expected that the largest, most common borophagines with the most reduced dental grinding areas hunted most of their food. Based on their craniodental morphology and abundance in the record, Epicyon saevus, E. haydeni, Borophagus secundus, Aelurodon ferox, and A. taxoides were hunters. Although it is clear that Aelurodon and Borophagus were more capable of grasping prey than are extant canids, no borophagine evolved sharp, curved claws as in felids. Consequently, their ability to grapple with prey seems to have been limited, and packs were probably more successful at making a kill than individuals. Previous workers have argued against hunting in borophagines based on heavy dental wear, robust skeletal morphology, and external brain features. None of these precludes either hunting or hunting in packs in our view, and sharp teeth are not required for making a kill. While li

GEOGRAPHIC AND TEMPORAL RANGES OF MIDDLE AND LATE MIOCENE CARNIVORES

Carnivores are ecologically diverse mammals. Dietary adaptations vary from strict herbivory to pure carnivory. These adaptations have evolved independently several times within families, so evolution within the order is iterative. I used 2 databases to examine whether ecological adaptations have an effect on longevity or spatial distributions of fossil carnivores. Miocene hypercarnivorous species had, on average, the widest spatial distributions. Their temporal distributions were not significantly longer than those of other carnivores. Body size also had a significant interaction with maximum spatial distribution. Large-bodied carnivores, regardless of feeding adaptations, had larger geographical ranges, but did not have greater longevity. However, when all the data were pooled, temporal distribution had a significant correlation with spatial distribution. The position of hypercarnivores at the top of the food chain and their specialized adaptations for meat eating probably increased their extinction risk to the same level of more narrowly distributed, less specialized carnivores.

Iterative evolution of hypercarnivory in canids (Mammalia: Carnivora): evolutionary interactions among sympatric predators

Convergent evolution of hypercarnivorous adaptations in canids has occurred a number of times in the last 40 m.y. among distantly related taxa. The adaptations include an increase in carnassial blade length, reduction or loss of post-carnassial molars, and transformation of the talonid of the lower first molar from a basinlike depression into a trenchant, bladelike cusp. Although the diversity of these specialized canids is typically low in past and present communities, it was unusually high during the Late Oligocene of North America and the Pleistocene of South America. These two comparable events provide an opportunity for exploring possible causes of the evolution of hypercarnivory in canids. Plots of generic diversity against time for North American predators reveal a roughly inverse relationship between the number of hypercarnivorous canid taxa and the numbers of other hypercarnivores, such as creodonts, nimravids, mustelids, and amphicyonids. Similarly, the radiation of hypercarnivorous canids in South America occurred at a time of relatively low diversity of other hypercarnivores. Analysis of trophic diversity within the North American carnivore paleoguild before, during, and after the Late Oligocene reveals considerable taxonomic turnover among carnivores because of immigration and speciation. Late Oligocene hypercarnivorous canids appear to have been replaced first by amphicyonids and large mustelids, and then by felids.Despite the repeated tendency of canids to evolve adaptations for hypercarnivory, a canid has yet to appear that is completely catlike, that is, without any post-carnassial molars. This possible constraint on morphological evolution in canids is argued to have resulted, paradoxically, in increased flexibility over evolutionary time and a great potential for rapid diversification and clade survivorship. Finally, it is suggested that the iterative pattern of specialization of the lower molars for meat-slicing that is seen in all families of carnivores, past and present, is probably a result of intraspecific competition for food, perhaps among littermates. This intraspecific selective force is countered by competition among species, since there are limits on the number of sympatric hypercarnivorous species within a single community.