Placental Carnivores Research Articles

Redescription of Physaloptera sarcophili Johnston & Mawson, 1940 and the description of Physaloptera dasyuri sp. nov. (Nematoda: Spirurida) parasitic in Australasian dasyurid marsupials

ABSTRACT Physaloptera sarcophili Johnston & Mawson, 1940 (Nematoda: Spirurida), originally described from the Tasmania devil, Sarcophilus harrisii (Boitard), is redescribed based on additional material from this host species. Physaloptera dasyuri sp. nov. is described from quolls, Dasyurus maculatus (Kerr) from Tasmania, Dasyurus hallucatus Gould from the Northern Territory and the Kimberly District of Western Australia and Dasyurus albopunctatus Schlegel from New Guinea. The two nematode species are distinguished by measurements, with values of those of P. sarcophili being approximately twice as large as those of P. dasyuri sp. nov. and by differences in the ratio of right to left spicule lengths. Limited morphological variation in the distribution of the papillae on the caudal bursa is described. Both species are differentiated from congeners in Australian mammals by the presence of four sessile post-cloacal papillae arranged in a single row, the arrangement of the three pairs of post-cloacal sessile papillae and spicule measurements. The differentiation of both species from congeners in South American marsupials and eutherian carnivores is also discussed.

The osteology of Triisodon crassicuspis (Cope, 1882): New insights into the enigmatic "archaic" placental mammal group "Triisodontidae".

Following the end-Cretaceous mass extinction, mammals underwent an increase in body size, taxonomic diversity and ecological specialization throughout the Paleocene, exemplifying their adaptability. One especially enigmatic group is the "Triisodontidae", medium- to large-sized ungulate-like placentals from the Paleocene which are best known from their teeth that exhibit adaptations towards carnivory. The "triisodontids" were the first large carnivorous mammals and pre-date, and may have given rise to, Mesonychia, a group of more specialized placental carnivores. The "triisodontids" have been well-described from dental material, although very little is known about their postcrania. Here, we describe the postcrania of Triisodon crassicuspis-the most completely represented species of the genus to date-from a specimen (NMMNH P-72096) recovered from basal Torrejonian strata of the Nacimiento Formation in the San Juan Basin, New Mexico. Anatomical comparisons reveal that the forelimb long bones of Tri. crassicuspis are robust relative to its size, more so than other "triisodontids". Attachment sites on the ulna are evidence of well-developed muscles involved in powerful extension and flexion of the manus. In Tri. crassicuspis, the range of pronation-supination was limited as evident from the humeroradial morphology. Qualitative functional assessment of osteological features of the forelimb of Tri. crassicuspis is suggestive of terrestrial locomotion with at least moderate digging ability. Re-analyses of the dentition confirmed that Tri. crassicuspis had specializations for carnivory, and provide a body mass estimate of ca. 32-44 kg based on dental proxies. In summary, Tri. crassicuspis was a relatively large and powerful terrestrial animal, and one of the first known placentals to fill a largely carnivorous niche.

The rise and fall of notoungulates: How Andean uplift, available land area, competition, and depredation driven its diversification dynamics

Unraveling the biotic and abiotic drivers likely influencing clades’ diversification dynamics (differential speciation and extinction rates) is crucial for understanding life on Earth. Here, we present a comprehensive analysis of the diversification dynamics of notoungulates (Mammalia: Notoungulata), the most diverse and widespread Cenozoic herbivore mammals that evolved in South America (SA) but are now entirely extinct. Employing fossil occurrences restricted to the southern part of the SA and a Bayesian framework, we examined the historical speciation and extinction rates across all notoungulates, suborders, and three body size categories and tested whether these dynamics could be driven by biotic (e.g., diversity dependence, competition) and abiotic (e.g., Andean uplift and temperature changes) factors. Our findings reveal significant variability in diversification rates over time and groups driven by biotic and abiotic factors. We observed an increase in notoungulate speciation rates correlated with lower group self-diversity, likely related to limited environmental productivity and more extensive emerged continental areas that can provide increased environmental and ecological heterogeneity. In contrast, elevated extinction rates were correlated with intensified Andean uplift events, which can trigger landscape modifications and the arrival of placental carnivores after the Great American Biotic Interchange, probably due to notoungulate vulnerability to novel predation pressures. Furthermore, sparassodont diversity appears to increase speciation and extinction rates of notoungulates, although the direct mechanism relating them remains uncertain. The heterogeneity in the observed patterns of speciation and extinction across distinct size categories and taxonomic clades provides valuable perspectives on how ancient global and regional changes impacted the diversification dynamics of mammals and underscores the intricate interplay between environmental changes and biological interactions in shaping the evolution of life on Earth.

Over-eruption in marsupial carnivore teeth: compensation for a constraint

Pronounced over-eruption of the canine teeth, causing the cervical enamel margin to extend beyond the alveolar bone and exposing the root, occurs with age and growth in Australian marsupial carnivores, much more than in eco-morphologically equivalent placental carnivores. Suppression of functional tooth replacement is characteristic of marsupials, where most placentals have the primitive diphyodont pattern of two generations of incisor, canine and premolar teeth. Canine and molar tooth dimensions of four species of marsupial carnivores (thylacine Thylacinus cynocephalus , Tasmanian devil Sarcophilus harrisii and two quolls Dasyurus spp . ) and canine dimensions of seven eco-morphologically equivalent placental carnivore species were measured from museum specimens. Canine dimensions were measured in a time series on live wild-living individual devils and quolls. The canine teeth and to a lesser extent the molar teeth of marsupial carnivores continue to erupt through life, resulting in a net increase in tooth height and diameter, a phenomenon not evident in placental carnivores. Potential mechanisms causing over-eruption include tooth wear and gradual release of occlusal pressure as the individual grows. Over-eruption in marsupial carnivores may be a compensatory response for tooth size limits imposed by monophyodont tooth replacement, ensuring that animal's teeth are scaled to jaw size from juvenile to adulthood.

What drives the abundance of marsupial carnivores in production forest landscapes?

Production forest landscapes provide important habitat for wildlife but expose them to disturbances from forestry practices. Understanding how threatened carnivores use production forests can inform management practices to improve their conservation. While there have been many studies of eutherian carnivores in production forests, the use of these landscapes by marsupial carnivores is poorly understood. Using a network of remote cameras, we investigated the use of forestry landscape features by two endangered marsupial carnivores, Tasmanian devils (Sarcophilus harrisii) and eastern quolls (Dasyurus viverrinus). Devil and quoll abundance increased with the extent of timber plantations within production forest landscapes. Overall, devils were positively associated with higher tree density and eastern quolls with indicators of open habitat such as less understorey, fewer trees and more grassland. Within plantations, devil abundance increased with the volume of windrows (piles of woody debris from harvesting arranged in rows), as did eastern quoll abundance in pine plantations. Eastern quoll abundance was higher in pine plantations established on pasture than those established on cleared native forest land, and in eucalypt plantations, higher with windrows comprised of plantation debris. Neither species showed a strong response to logging-related features in native forest such as time since harvest, though eastern quolls were positively associated with log cover. Our results demonstrate that plantations provide valuable habitat for marsupial carnivores and that they can persist in harvested native forests. Windrows likely benefit devils and eastern quolls by providing denning, shelter and foraging opportunities, and should be managed as important habitat features for carnivores. These findings can be used by forest managers to guide decisions and help maintain threatened carnivore populations in human-modified landscapes.

Orientation pinwheels in primary visual cortex of a highly visual marsupial.

Primary visual cortices in many mammalian species exhibit modular and periodic orientation preference maps arranged in pinwheel-like layouts. The role of inherited traits as opposed to environmental influences in determining this organization remains unclear. Here, we characterize the cortical organization of an Australian marsupial, revealing pinwheel organization resembling that of eutherian carnivores and primates but distinctly different from the simpler salt-and-pepper arrangement of eutherian rodents and rabbits. The divergence of marsupials from eutherians 160 million years ago and the later emergence of rodents and rabbits suggest that the salt-and-pepper structure is not the primitive ancestral form. Rather, the genetic code that enables complex pinwheel formation is likely widespread, perhaps extending back to the common therian ancestors of modern mammals.

Eomakhaira molossus, A New Saber-Toothed Sparassodont (Metatheria: Thylacosmilinae) from the Early Oligocene (?Tinguirirican) Cachapoal Locality, Andean Main Range, Chile

Thylacosmiline sparassodonts (previously recognized as thylacosmilids) are among the most iconic groups of endemic South American Cenozoic mammals due to their distinctive morphology and convergent resemblance to saber-toothed placental carnivores. However, the early evolution of this group and its relationship to other sparassodonts remains poorly understood, primarily because only highly specialized Neogene taxa such as Thylacosmilus, Anachlysictis, and Patagosmilus are well known. Here, we describe a new Paleogene sparassodont, Eomakhaira molossus, from the Cachapoal locality of central Chile, the first sparassodont reported from early Oligocene strata of the Abanico Formation. Eomakhaira shares features with both Neogene thylacosmilines and Paleogene “proborhyaenids,” and phylogenetic analyses recover this taxon as sister to the clade of Patagosmilus + Thylacosmilus. This broader clade, in turn, is nested within the group conventionally termed Proborhyaenidae. Our analyses support prior hypotheses of a close relationship between thylacosmilines and traditionally recognized proborhyaenids and provide the strongest evidence to date that thylacosmilines are proborhyaenids (i.e, the latter name as conventionally used refers to a paraphyletic group). To reflect the internestedness of these taxa, we propose use of Riggs' (1933) original name Thylacosmilinae for the less inclusive grouping and Proborhyaenidae for the more inclusive one. Saber teeth arose just once among metatherians (among thylacosmilines), perhaps reflecting a developmental constraint related to nonreplacement of canines in metatherians; hypselodonty may have relaxed this potential constraint in thylacosmilines. The occurrence of Eomakhaira in strata of early Oligocene age from the Chilean Andes demonstrates that the stratigraphic range of thylacosmilines spanned almost 30 million years, far surpassing those of saber-toothed placental lineages.

Trophic ecology of marsupial predators in arid Australia following reshaping of predator assemblages

The extirpation of marsupial predators and their replacement by eutherian carnivores are likely to have cascading ecological impacts on the trophic structure of arid Australia. Here, we assessed the diet and characterized the trophic role of the 3 largest remaining carnivorous marsupials (< 200 g body mass) in arid Australia: cresttailed mulgaras (Dasycercus cristicauda), kowaris (Dasyuroides byrnei), and brush-tailed mulgaras (Dasycercusblythi). The species show a high level of trophic connectivity; each is highly interactive, being predator or prey of numerous species across multiple phyla. The prey base of each of the predator species was broad and included vertebrates, invertebrates, and plants. Crest-tailed mulgaras consumed the most vertebrates including prey up to the size of the southern marsupial mole (Notoryctes typhlops). Kowaris consumed prey up to the size of the European rabbit (Oryctolagus cuniculus). Although capable of capturing or scavenging vertebrates, the diet of each species was dominated by arthropods < 2 g in body mass.

Diversity and disparity of sparassodonts (Metatheria) reveal non-analogue nature of ancient South American mammalian carnivore guilds.

This study investigates whether terrestrial mammalian carnivore guilds of ancient South America, which developed in relative isolation, were similar to those of other continents. We do so through analyses of clade diversification, ecomorphology and guild structure in the Sparassodonta, metatherians that were the predominant mammalian carnivores of pre-Pleistocene South America. Body mass and 16 characters of the dentition are used to quantify morphological diversity (disparity) in sparassodonts and to compare them to extant marsupial and placental carnivores and extinct North American carnivoramorphans. We also compare trophic diversity of the Early Miocene terrestrial carnivore guild of Santa Cruz, Argentina to that of 14 modern and fossil guilds from other continents. We find that sparassodonts had comparatively low ecomorphological disparity throughout their history and that South American carnivore palaeoguilds, as represented by that of Santa Cruz, Argentina, were unlike modern or fossil carnivore guilds of other continents in their lack of mesocarnivores and hypocarnivores. Our results add to a growing body of evidence highlighting non-analogue aspects of extinct South American mammals and illustrate the dramatic effects that historical contingency can have on the evolution of mammalian palaeocommunities.

The Population Origins and Expansion of Feral Cats in Australia

The historical literature suggests that in Australia, the domestic cat (Felis catus) had a European origin [~200 years before present (ybp)], but it is unclear if cats arrived from across the Asian land bridge contemporaneously with the dingo (4000 ybp), or perhaps immigrated ~40000 ybp in association with Aboriginal settlement from Asia. The origin of cats in Australia is important because the continent has a complex and ancient faunal assemblage that is dominated by endemic rodents and marsupials and lacks the large placental carnivores found on other large continents. Cats are now ubiquitous across the entire Australian continent and have been implicit in the range contraction or extinction of its small to medium sized (<3.5kg) mammals. We analyzed the population structure of 830 cats using 15 short tandem repeat (STR) genomic markers. Their origin appears to come exclusively from European founders. Feral cats in continental Australia exhibit high genetic diversity in comparison with the low diversity found in populations of feral cats living on islands. The genetic structure is consistent with a rapid westerly expansion from eastern Australia and a limited expansion in coastal Western Australia. Australian cats show modest if any population structure and a close genetic alignment with European feral cats as compared to cats from Asia, the Christmas and Cocos (Keeling) Islands (Indian Ocean), and European wildcats (F. silvestris silvestris).

Mandible morphology and diet of the South American extinct metatherian predators (Mammalia, Metatheria, Sparassodonta)

ABSTRACTSparassodonta is a diverse group of extinct metatherian predators that include forms with diets ranging from omnivores to hypercarnivores, including potential bone-crushers and sabre-tooth specialised species. Most of the previous dietary studies on the group were based on qualitative approaches or dental morphometric indexes and/or bite force estimations. In this study, we explore the evolution of mandible shape and diet of Sparassodonta in a comparative phylogenetic framework, using geometric morphometric tools and allometric and discriminant analyses. We analysed the mandible shape of 142 extant species of marsupials and placental carnivores, and 15 fossil sparassodont species. We found that the relationship between shape and size of the mandible is strongly structured by phylogeny, where the more derived borhyaenoids tend to possess stronger and larger mandibles. Derived borhyaenoid sparassodonts and basal borhyaenoids were classified as hypercarnivores (with short and robust mandibular body). Hathliacynid were classified as mesocarnivores or as hypercarnivores, but with lower probabilities and less specialised morphologies (with a long and slender mandible). Although dental morphology suggests that most of the species of Sparassodonta would have been hypercarnivores, the robustness of the mandible seems to be informative regarding the prey size and degree of specialisation. The relationship between mandibular size and shape, and talonid/trigonid relative size, is strongly influenced by the phylogenetic legacy, suggesting that ecological factors could have influenced the evolution of the sparassodonts.

Random Wiring, Ganglion Cell Mosaics, and the Functional Architecture of the Visual Cortex.

The architecture of iso-orientation domains in the primary visual cortex (V1) of placental carnivores and primates apparently follows species invariant quantitative laws. Dynamical optimization models assuming that neurons coordinate their stimulus preferences throughout cortical circuits linking millions of cells specifically predict these invariants. This might indicate that V1’s intrinsic connectome and its functional architecture adhere to a single optimization principle with high precision and robustness. To validate this hypothesis, it is critical to closely examine the quantitative predictions of alternative candidate theories. Random feedforward wiring within the retino-cortical pathway represents a conceptually appealing alternative to dynamical circuit optimization because random dimension-expanding projections are believed to generically exhibit computationally favorable properties for stimulus representations. Here, we ask whether the quantitative invariants of V1 architecture can be explained as a generic emergent property of random wiring. We generalize and examine the stochastic wiring model proposed by Ringach and coworkers, in which iso-orientation domains in the visual cortex arise through random feedforward connections between semi-regular mosaics of retinal ganglion cells (RGCs) and visual cortical neurons. We derive closed-form expressions for cortical receptive fields and domain layouts predicted by the model for perfectly hexagonal RGC mosaics. Including spatial disorder in the RGC positions considerably changes the domain layout properties as a function of disorder parameters such as position scatter and its correlations across the retina. However, independent of parameter choice, we find that the model predictions substantially deviate from the layout laws of iso-orientation domains observed experimentally. Considering random wiring with the currently most realistic model of RGC mosaic layouts, a pairwise interacting point process, the predicted layouts remain distinct from experimental observations and resemble Gaussian random fields. We conclude that V1 layout invariants are specific quantitative signatures of visual cortical optimization, which cannot be explained by generic random feedforward-wiring models.

Are single odorous components of a predator sufficient to elicit defensive behaviors in prey species?

When exposed to the odor of a sympatric predator, prey animals typically display escape or defensive responses. These phenomena have been well-documented, especially in rodents, when exposed to the odor of a cat, ferret, or fox. As a result of these experiments new discussions center on the following questions: (1) is a single volatile compound such as a major or a minor mixture constituent in urine or feces, emitted by the predator sufficient to cause defensive reactions in a potential prey species or (2) is a whole array of odors required to elicit a response and (3) will the relative size or escapability of the prey as compared to the predator influence responsiveness. Most predator-prey studies on this topic have been performed in the laboratory or under semi-natural conditions. Field studies could help to find answers to these questions. Australian mammals are completely naïve toward the introduced placental carnivores. That offers ideal opportunities to analyze in the field the responses of potential prey species to unknown predator odors. During the last decades researchers have accumulated an enormous amount of data exploring the effects of eutherian predator odors on native marsupial mammals. In this review, we will give a survey about the development of olfactory research, chemical signals and their influence on the behavior and—in some cases—physiology of prey species. In addition, we report on the effects of predator odor experiments performed under natural conditions in Australia. When studying all these literature we learned that data gained under controlled laboratory conditions elucidate the role of individual odors on brain structures and ultimately on a comparatively narrow range behaviors. In contrast to single odors odor arrays mimic much more the situation prey animals are confronted to in nature. Therefore, a broad range of methodology—from chemistry to ecology including anatomy, physiology, and behavior—is needed to understand all the different (relevant) stimuli that govern and guide the interactions between a predator and its potential prey.

Using Geometric Morphometrics to Examine Cranial Disparity in Extinct and Extant Marsupial and Placental Carnivores

Carnivory evolved independently in multiple mammalian lineages including Carnivora, Dasyuramorphia, and extinct Borhyaenidae, Oxyaenida and Hyaenodontida. Each lineage combines expanded attachment sites for mandibular adductors with specialized shearing dentition. Three‐dimensional geometric morphometrics were used to characterize cranial disparity in each carnivorous lineage to test for a correlation between developmental constraint in the marsupial carnivore skull and the limited morphological diversity of the group. When only extant Carnivora is included in the analysis, marsupial carnivores do occupy a separate, limited region of morphospace. When a large sample of extinct placental carnivores are included, placental morphospace and marsupial morphospace overlap. Placental Hyaenodontida, which shares with marsupial carnivores the presence of multiple carnassialized molars, unreduced dentition, long rostra, and distal temporomandibular joints, overlap extensively with marsupial carnivores. Hyaenodontidans dominated carnivore niches during early Paleogene, but were replaced by carnivorans. This analysis demonstrates the anatomical similarities between hyaenodontidans and marsupial mammals may be more significant factors in the extinction of both carnivorous lineages rather than developmental constraints affecting the cranial and functional diversity of marsupials.

Diets of sympatric native and introduced carnivores in the Barrington Tops, eastern Australia

AbstractInvasive predators have severe impacts on global biodiversity, and their effects in Australia have been more extreme than on any other continent. The spotted‐tailed quoll (Dasyurus maculatus), an endangered marsupial carnivore, coexists with three eutherian carnivores, the red fox (Vulpes vulpes), feral cat (Felis catus) and wild dog (Canis lupus ssp.) with which it did not coevolve. No previous study has investigated dietary overlap between quolls and the suite of three eutherian carnivores. By analysing scats, we aimed to quantify dietary overlap within this carnivore assemblage in eastern Australia, and to detect any differences that may facilitate coexistence. We also sought evidence of intraguild predation. Dietary overlap between predators was extensive, with the greatest similarity occurring between foxes and cats. However, some differences were apparent. For example, cats mainly consumed smaller prey, and wild dogs larger prey. Quolls showed greater dietary overlap with foxes and cats than with dogs. Intraguild predation was evident, with fox remains occurring in 3% of wild dog scats. Our results suggest wild dogs competitively dominate invasive foxes, which in turn are likely to compete with the endangered quoll.

An endemic Taenia from South America: validation of T. talicei Dollfus, 1960 (Cestoda: Taeniidae) with characterization of metacestodes and adults

Taenia talicei is redescribed based on new data from polycephalic, fimbriocercus and cysticercus metacestodes found in Ctenomys spp. (Rodentia: Ctenomyidae) from Argentina. Strobilate adult specimens, derived from experimental infections in domestic dogs, are described for the first time. Identity of the adult and metacestodes stages is based on the number of rostellar hooks (44–50 hooks in 2 rows), their dimensions (large hooks= 232–242; small= 150–187) and shape. Taenia talicei is distinguished from those species that occur naturally in Neotropical Felidae and from those cosmopolitan species that circulate in synanthropic cycles with rodents (or lagomorphs) and domestic hosts such as cats and dogs in South America based on the structure of the metacestode, dimensions and numbers of rostellar hooks and a suite of specific characters of the genital system in strobilate adults. This species is the first that can be considered endemic to South America. Origins of an endemic Taenia species or taeniid assemblages in South America would have relationships to either North American or Eurasian placental carnivores. In these instances, the expansion of Taenia may have resulted from geographic colonization of South America, radiation in both felids (and canids), and host switching by tapeworms to caviomorphs, prior to the emergence of the Panamanian Isthmus. Taenia talicei is capable of development in domestic dogs, and metacestodes in species of Ctenomys were found in urban or semi-urban environments. These factors may establish a role for synanthropic cycles linked to definitive hosts including dogs and cats as a route for exposure of humans to infection by this taeniid.

First description of milk teeth of fossil South American procyonid from the lower Chapadmalalan (Late Miocene–Early Pliocene) of “Farola Monte Hermoso,” Argentina: paleoecological considerations

The first record of milk teeth of South American fossil procyonids comes from the Late Miocene–Early Pliocene at “Farola Monte Hermoso,” Buenos Aires Province, Argentina. Five extant genera of Procyonidae inhabit South America (Bassaricyon Allen, Nasuella Hollister, Potos Geoffroy Saint-Hilaire and Cuvier, Procyon Storr, and Nasua Storr). Of these only Procyon and Nasua are present in the fossil record (Late Pleistocene–Holocene), in several localities in Brazil, Uruguay, and Bolivia. In addition, six other fossil genera were named, but only two are considered valid: Cyonasua and Chapadmalania. Thus, Cyonasua encompasses ten formally named species and Chapadmalania two. The new specimen, MLP 09-X-5-1, is assigned to cf. Cyonasua. In addition, anatomical evidence implies a much more carnivorous diet in Late Miocene–Early Pleistocene procyonids than that of extant South American taxa. Finally, I examine and discuss the “competitive displacement” hypothesis regarding the extinction of native marsupial carnivores after the arrival of immigrant placental carnivores in South America.

Encephalization of Australian and New Guinean Marsupials

Encephalization of Australian marsupials was analyzed using the endocranial volume (ECV) of 52 species of Dasyuromorphia and Notoryctemorphia, 14 species of Peramelemorphia and 116 species of Diprotodontia from Australia and New Guinea and compared with 16 species of Ameridelphian marsupials and 3 species of native and recently introduced Australian eutherian carnivores (dingo, feral cat and feral fox). Linear regression analysis of the relationship between ECV and body weight for marsupials revealed that allometric parameters for these groups are different from those previously derived for samples of (mainly eutherian) mammals, with higher slopes for Dasyuromorphia and Diprotodontia and lower slopes for Ameridelphians and Peramelemorphia. Absolute ECV for small Australian and New Guinea marsupial carnivores (Antechinus and Sminthopsis) were found to be comparable to eutherians of similar body weight, but large marsupial carnivores such as the Tasmanian devil and thylacine had substantially smaller ECVs than eutherian carnivores of similar body weight. Similarly, members of some superfamilies within Diprotodontia (Burramyoidea, Petauroidea, Tarsipedoidea) had ECVs comparable to prosimians, whereas bandicoots, bilbies and many macropods were found to be poorly encephalized. When both encephalization quotient (EQ) and residuals from regression analysis were used to compare relative ECV of extinct/threatened species with common species there were no significant differences for any of the orders of Australian marsupials, suggesting that encephalization is not a major factor in the current extinction crisis for Australian marsupials. Similarly there were no consistent differences in relative ECV between marsupials from New Guinea and associated islands compared to Australia or between arid and non-arid Australian regions for any of the marsupial orders. The results indicate that marsupials are not uniformly poorly encephalized and that small marsupial carnivores and some members of Diprotodontia are of comparable encephalization to eutherians of similar body weight. In particular, honey possums and some gliders show an encephalization level comparable to prosimians, perhaps reflecting convergence in adaptation to similar arboreal niches.

Niche overlap between marsupial and eutherian carnivores: does competition threaten the endangered spotted‐tailed quoll?

Summary The significance of top‐down regulation by carnivores is receiving increasing global recognition. As a consequence, key objectives in many programmes that seek to maintain ecosystem function now include conserving carnivores and understanding their interactions. This study examined overlap in resource use (space and diet) of introduced eutherian carnivores and an endangered marsupial carnivore, the spotted‐tailed quoll Dasyurus maculatus, in eastern Australia. We also investigated mechanisms of niche partitioning and evidence for interspecific aggression. Dietary overlap between quolls, red foxes Vulpes vulpes and wild dogs Canis lupus ssp. was assessed by analysis of scats. Trapping, radio‐tracking and direct observations were used to quantify spatial overlap between quolls, foxes, wild dogs and feral cats Felis catus. Dietary overlap among the carnivores was extensive. Medium‐sized mammals were the most important prey for all three predators, indicating potential for exploitative interactions. However, hunting of different size classes of secondary prey and consumption by quolls of more arboreal prey than their counterparts may assist coexistence. Remains of quoll were found in two dog scats, and cat hair in another, possibly indicating intraguild predation. We observed extensive spatial overlap between quolls and eutherian carnivores. However, we inferred from dietary data that quolls foraged primarily in forested habitat, while canids foraged mainly in cleared habitat. Synthesis and applications. Our results indicate strong potential for competition between spotted‐tailed quolls and eutherian carnivores, and thus a situation where control of introduced predators may be desirable, not only for the conservation of prey species but also for the protection of native carnivores. Concern over potential non‐target mortality of quolls has hindered efforts to control foxes in eastern Australia using poison baits. We contend that, rather than harming quoll populations, baiting for foxes should aid the conservation of quolls and should be implemented in areas of sympatry where fox numbers are high.

The energetics of reproduction in endotherms and its implication for their conservation

The energy expenditure of endotherms, through its impact on the rate of reproduction, affects their ability to withstand competition, to tolerate environmental disturbances, and to endure predation. The fecundity of eutherian mammals increases with rate of metabolism because the post-natal growth rate increases and the gestation and conception-to-weaning periods decrease with a mass-independent increase in basal rate of metabolism. These correlations account for the observation that species that have large population fluctuations have high rates of metabolism and reproduction. Species with high rates of metabolism out-compete species with low rates when using resources that permit consumers to have high rates of metabolism, which explains why eutherian carnivores replace marsupial carnivores, none of which have high basal rates as a result of their form of reproduction. Fecundity in birds also appears to correlate with energy expenditure, which may account for the huge die-off of birds endemic to oceanic islands after the invasion of humans: island endemics, many of which have low rates of metabolism, are unable to increase fecundity in response to a human-based increase in mortality. The long-term protection for endotherms characterized by low rates of energy expenditure requires their isolation from high levels of predation and competition, conditions that are likely to occur only on islands free from eutherian predators and with low species diversity. Such endotherms may survive on continents if they are ecologically isolated from the general fauna.