An experimental manipulation of the intensity of interspecific competition: effects on a small marsupial

Contrasting population manipulations reveal resource competition between two large marsupials: bare-nosed wombats and eastern grey kangaroos

Resource competition is an important interaction that can structure ecological communities, but is difficult to demonstrate in nature, and rarely demonstrated for large mammals including marsupials. We analysed 10 years of population survey data to investigate resource competition between bare-nosed wombats (Vombatus ursinus) and eastern grey kangaroos (Macropus giganteus) at two sites to assess whether resource competition is occurring. At one site, wombat abundance was reduced by increased mortality from mange disease, whereas at the other site, kangaroo abundance was reduced primarily by culling. We used the modified Lotka-Volterra competition (LVC) models to describe the mechanism of resource competition and fitted those models to the empirical data by maximum likelihood estimation. We found strong negative relationships between the abundance of wombats and kangaroos at each site, and resource competition was also mechanistically supported by the modified LVC models. The estimated competition coefficients indicate that bare-nosed wombats are a slightly superior competitor of eastern grey kangaroos than vice versa, and that intraspecific competition is almost twice as strong as interspecific competition. In addition, this study facilitated the calculation of the transmission rate associated with mange disease at one site (0.011), and the removal rate owing to culling, the introduction of a predator species, and drought at the other site (0.0006). Collectively, this research represents a rare empirical demonstration of resource competition between large mammals and contributes new insight into the ecology of two of Australia's largest grazing marsupials.

Observations of arboreal behaviour in the mainland dusky antechinus (Antechinus mimetes)

During camera-trapping surveys for arboreal mammals within Yellingbo Nature Conservation Reserve we recorded arboreal behaviour in the mainland dusky antechinus, which is typically regarded as a strictly terrestrial species. The species was detected visiting baits positioned ~3.5m high on trees on 29 occasions, providing additional evidence of arboreal behaviour in the species and further demonstrating the value of camera traps in providing novel insights into animal behaviour.

Determining the efficacy of camera traps, live capture traps, and detection dogs for locating cryptic small mammal species

Metal box (e.g., Elliott, Sherman) traps and remote cameras are two of the most commonly employed methods presently used to survey terrestrial mammals. However, their relative efficacy at accurately detecting cryptic small mammals has not been adequately assessed. The present study therefore compared the effectiveness of metal box (Elliott) traps and vertically oriented, close range, white flash camera traps in detecting small mammals occurring in the Scenic Rim of eastern Australia. We also conducted a preliminary survey to determine effectiveness of a conservation detection dog (CDD) for identifying presence of a threatened carnivorous marsupial, Antechinus arktos, in present-day and historical locations, using camera traps to corroborate detections. 200 Elliott traps and 20 white flash camera traps were set for four deployments per method, across a site where the target small mammals, including A. arktos, are known to occur. Camera traps produced higher detection probabilities than Elliott traps for all four species. Thus, vertically mounted white flash cameras were preferable for detecting the presence of cryptic small mammals in our survey. The CDD, which had been trained to detect A. arktos scat, indicated in total 31 times when deployed in the field survey area, with subsequent camera trap deployments specifically corroborating A. arktos presence at 100% (3) indication locations. Importantly, the dog indicated twice within Border Ranges National Park, where historical (1980s-1990s) specimen-based records indicate the species was present, but extensive Elliott and camera trapping over the last 5-10 years have resulted in zero A. arktos captures. Camera traps subsequently corroborated A. arktos presence at these sites. This demonstrates that detection dogs can be a highly effective means of locating threatened, cryptic species, especially when traditional methods are unable to detect low-density mammal populations.

Space use by female agile antechinus: are teat number and home-range size linked?

Context The number of teats that a female agile antechinus (Antechinus agilis) possesses effectively determines her initial litter size. In the Otway Ranges, south-eastern Australia, numerous separate populations in which all females have either six or 10 teats occur fairly close together in similar, contiguous forest at comparable altitudes and latitudes. Six-teat and 10-teat females have a similar mean mass, but the latter have a 1.7 × greater reproductive potential and so should have a greater nutritional requirement while raising young than do six-teat females. Theoretically, they could meet this requirement by occupying larger and/or more exclusive home ranges during breeding than do six-teat females do (provided that their food-resource abundance is comparable), albeit at a greater energetic cost. Aims The aim of the study was to determine whether 10-teat A. agilis females occupied larger and less overlapping home ranges than did six-teat females. To interpret the findings more meaningfully, it was necessary to compare food abundance and habitat characteristics in areas occupied by the two phenotypes. Methods The investigation was conducted in six-teat and 10-teat A. agilis areas in cool temperate forest over 22 months. Population density was determined by mark–recapture methods and arthropod prey biomass and abundance by pitfall trapping. Vegetation structure and plant-taxa abundance and diversity were determined by standard plant-survey methods. Female home-range estimates determined by radio-tracking were based on 95% minimal convex polygons (MCP) and kernel analysis. Home-range overlap was based on 80% MCP range determinations and core areas were calculated from utilisation plots. Key results Female population density was 2.5 × lower in exclusively 10-teat than in exclusively six-teat populations. Radio-tracked 10-teat females’ home ranges less commonly overlapped those of identified female neighbours and, on average, were 1.5 × larger than ranges of six-teat females. Food abundance and composition was similar in six-teat and 10-teat areas, but ground cover was denser and more complex in the latter areas. Conclusions Food-resource availability was similar in the six-teat and 10-teat phenotype areas, so the larger, and probably more exclusive, home ranges of 10-teat females could reflect greater nutritional requirements resulting from having larger litters, and account for their lower population density. Implications The A. agilis teat-number variation pattern in the Otways may be a rare, visible example of ongoing incipient speciation. This makes it of great scientific and conservation value and it is important to document how the phenomenon operates.

Camera trapping: a contemporary approach to monitoring invasive rodents in high conservation priority ecosystems

Invasive rodent species have established on 80% of the world's islands causing significant damage to island environments. Insular ecosystems support proportionally more biodiversity than comparative mainland areas, highlighting them as critical for global biodiversity conservation. Few techniques currently exist to adequately detect, with high confidence, species that are trap-adverse such as the black rat, Rattus rattus, in high conservation priority areas where multiple non-target species persist. This study investigates the effectiveness of camera trapping for monitoring invasive rodents in high conservation areas, and the influence of habitat features and density of colonial-nesting seabirds on rodent relative activity levels to provide insights into their potential impacts. A total of 276 camera sites were established and left in situ for 8 days. Identified species were recorded in discrete 15 min intervals, referred to as ‘events’. In total, 19 804 events were recorded. From these, 31 species were identified comprising 25 native species and six introduced. Two introduced rodent species were detected: the black rat (90% of sites), and house mouse Mus musculus (56% of sites). Rodent activity of both black rats and house mice were positively associated with the structural density of habitats. Density of seabird burrows was not strongly associated with relative activity levels of rodents, yet rodents were still present in these areas. Camera trapping enabled a large number of rodents to be detected with confidence in site-specific absences and high resolution to quantify relative activity levels. This method enables detection of multiple species simultaneously with low impact (for both target and non-target individuals); an ideal strategy for monitoring trap-adverse invasive rodents in high conservation areas.

Interspecific dominance via vocal interactions mediates altitudinal zonation in neotropical singing mice

Interspecific aggression between ecologically similar species may influence geographic limits by mediating competitive exclusion at the range edge. Advertisement signals that mediate competitive interactions within species may also provide social information that contributes to behavioral dominance and spatial segregation among species. We studied the mechanisms underlying altitudinal range limits in Neotropical singing mice (Scotinomys), a genus of muroid rodent in which males vocalize to repel rivals and attract mates. We first delineated replacement zones and described temperature regimes on three mountains in Costa Rica and Panama where Chiriquí singing mice (S. xerampelinus) abruptly replace Alston's singing mice (S. teguina). Next, we conducted interspecific behavioral trials and reciprocal removal experiments to examine if interspecific aggression mediated species replacement. Finally, we performed reciprocal playback experiments to investigate whether response to song matched competitive interactions. Behavioral trials and removal experiments suggest that S. xerampelinus is behaviorally dominant and excludes S. teguina from higher, cooler altitudes. Playback experiments indicate that subordinate S. teguina is silenced and repelled by heterospecific song, whereas S. xerampelinus responded to heterospecifics with approach and song rates comparable to responses to conspecifics. Thus, interspecific communication reflects underlying dominance and suggests that acoustic signaling contributes to altitudinal zonation of ecologically similar congeners. Our findings implicate the use of social information in structuring spatial distributions of animal communities across landscapes and provide insight into how large-scale patterns are generated by individual interactions.

Demography and competition in Hyrax : A 17 years study

This study investigates the demography and interspecific interactions of 6 Heterohyrax brucei and 4 Procavia johnstoni populations, which inhabited 6 kopjes (rock outcrops) in the Serengeti National Park, Tanzania over a period of 17 years. On three kopjes (H1, O2 and PH2) both species lived sympatrically, while on the other three (H2, H3 and P1) either one or the other species occurred allopatrically. The rainfall pattern between 1971/1972 and 1981/1982 had undergone major changes. There was significantly less precipitation in the wet season and the dry season had become extremer and longer. The kopje vegetation, recorded as percentage crown cover of browse from bushes and trees, had changed also, decreasing between 1971/72 and 1982 on 5 kopjes. In three kopjes (H1, O2 and PH2), which were shared by both hyrax species, an increase in the number of P. johnstoni, a decrease (H1 and O2) and extinction (PH2) of H. brucei took place between the time periods 1971-1976 ("good browse years") and 1982-1984 ("poor browse years"). These changes are probably the result of indirect interspecific competition (exploitative competition) for browse material, which is the main food source for both species during the dry season. When the browsing resources are abundant coexistence on sympatric kopjes between both species is possible, but when browse is scarce the result is competitive exclusion of H. brucei by P. johnstoni. It is also argued, that P. johnstoni by being the larger species and by also being a grazer had several ecological advantages over H. brucei. In kopjes H2, H3 and P1 where H. brucei occurred allopatrically the population increased (H2, P1) or decreased (H3) during the same time period. Natural extinction was observed in kopje P1 in the allopatrically living P. johnstoni group through mange. Dispersal of 7 females and 7 males H. brucei as well as 1 female and 4 male P. johnstoni were recorded in kopjes H1, H2 and P1. One female H. brucei that immigrated successfully into kopje H2 reached an age of over 11 years. One H. brucei family group (H2) shifted its birth season from December-January to May-August. Successful natural colonization was recorded for H. brucei in kopje P1 and for P. johnstoni in H1. Two kopjes (PH2 and H3), which had no hyrax and are located far away from other hyrax populations, were experimentally colonized in 1971 and 1972 respectively. The P. Johnstoni on PH2 and the H. brucei group on H3 had been under breeding isolation for 16 years. Under such conditions P. johnstoni males can reach an age of over 8.5 years. These long-term observations have shown that the occupancy of the kopjes by both species is a dynamic process depending on the combination of several abiotic (rainfall and availability of holes and hiding places) and biotic factors (interspecific and intraspecific competition for food, interspecific cooperation, predation and parasites) as well as the degree of inbreeding dependent on the geographic isolation of the kopje.

Two new species of Antechinus Macleay (Dasyuridae:Marsupialia) from mid-Pleistocene cave deposits in eastern central Queensland

The dasyurid genus Antechinus occurs in numerous Cainozoic fossil sites but until now only one extinct species has been described, Antechinus puteus Van Dyck. Antechinus yammal sp. nov. and A. yuna sp. nov. are described here on the basis of dental remains recovered from middle Pleistocene (between >500 and 205–170 thousand years ago) cave deposits at Mount Etna, eastern central Queensland. Most of these sites are interpreted as closed rainforest palaeoenvironments, and this is the likely habitat of both species. Both taxa are morphologically variable. A. yammal is characterised by complete anterior cingula and well developed posterior cingula on the upper molars; a relatively unreduced, robust P3; and small entoconids. A. yuna is a relatively large species, typified by poorly developed or absent posterior cingula on M1–3, lack of a metacone on M4, and large entoconids on M1–3. Dental morphology suggests that A. yuna was a near relative of the extant A. leo. The dentition of A. yammal shows some similarities to that of A. flavipes, but its exact phylogenetic position is unclear. A. yammal became extinct coincident with the loss of its rainforest habitat some time between 280 and 205–170 thousand years ago. A. yuna survived somewhat longer, but by the late Pleistocene had been replaced by A. flavipes.

Effects of drought on weight, survival and breeding success of agile antechinus (Antechinus agilis), dusky antechinus (A. swainsonii) and bush rats (Rattus fuscipes)

Extreme weather conditions, such as drought, significantly decrease the survival and breeding success of numerous species. Despite the frequent occurrence of such conditions in Australia, little is known about the effects of changing environmental conditions on the native small mammals. This study, conducted from 2002 to 2004, focussed on sympatric wild populations of the agile antechinus (Antechinus agilis), with more limited information on the dusky antechinus (A. swainsonii) and the bush rat (Rattus fuscipes). Bodyweights of agile antechinus before and during the breeding season were significantly lower in 2003 (drought) than in 2002 or 2004. Survival of female agile antechinus and the number of young per litter also decreased significantly during drought. In contrast, the dusky antechinus showed no difference in mean bodyweights between years, high survival rates of females and similar litter sizes in 2002 and 2003. There was also no difference in bodyweight of bush rats between years. Low rainfall was recorded during pregnancy and lactation in the agile antechinus, but rainfall was higher during pregnancy and lactation in the dusky antechinus. The survival and breeding success of the agile antechinus may have been adversely affected by a combination of interspecific competition, timing of the breeding season and severity of the drought.

Space invaders? A search for patterns underlying the coexistence of alien black rats and Galápagos rice rats

The introduction and spread of the black rat Rattus rattus is believed to have caused the worst decline of any vertebrate taxon in Galápagos. However, the "extinct" Santiago rice rat Nesoryzomys swarthi has recently been rediscovered in sympatry with R. rattus providing the first exception to this general pattern of displacement. We carried out an exploratory investigation of this novel system with the aim of identifying patterns that may facilitate the apparent coexistence of the two species. We carried out an extensive survey of Santiago Island to map the current distribution of the endemic rice rat and to explore broad scale distribution-habitat associations. We then used live-trapping, radio-tracking, and spool-and-line tracking to quantify abundance-habitat correlations and to test for evidence of interspecific spatial segregation, alteration of N. swarthi activity patterns (spatial and temporal), and microhabitat partitioning. We found that N. swarthi has disappeared from part of its historical range and appears to be restricted to a 14 km stretch of the north-central coast, characterised by high density of the cactus Opuntia galapageia. In contrast, the generalist R. rattus was found at all survey sites. We found no evidence of spatial segregation, and home range size, temporal activity and density of N. swarthi did not vary with local density of R. rattus. However, pre-dawn and post-dusk N. swarthi activity levels increased with R. rattus density perhaps reflecting an increase in foraging effort necessary to compensate for the costs of interspecific exploitation or interference competition. The distribution, microhabitat selection, and abundance-habitat relations of N. swarthi suggest that the endemic cactus O. galapageia may facilitate interspecific coexistence. Further research should include a comparison of inter-seasonal resource preference and foraging activity of the two species coupled with replicated field experiments to confirm and quantify competition and to elucidate the mechanism of competitive coexistence.

Floristic and structural components of habitat use by the eastern pygmy-possum (Cercartetus nanus) in burnt and unburnt habitats

The eastern pygmy-possum (Cercartetus nanus) occurs broadly but patchily in south-eastern Australia. It is a small, difficult-to-trap marsupial with poorly known resource and habitat preferences. This study investigated the structural and floristic habitat resources used and selected by C. nanus in Royal National Park (which was heavily burnt by bushfire in 1994) and Heathcote National Park (most of which had remained unburnt for over two decades at the time of study), in central-coastal New South Wales. Three different sampling methods were used – pitfall traps, Elliott traps and hair tubes – with pitfall trapping being by far the most effective method for detecting C. nanus. Live-trapping in different habitats revealed higher numbers of C. nanus in unburnt and burnt woodland, burnt heathland and burnt coastal complex than in unburnt coastal complex and burnt and unburnt rainforest. To identify the components of habitat contributing to this pattern, we first scored floristic and structural features of vegetation around trap stations and then quantified habitat components further by using spool- and radio-tracking. We found little evidence that C. nanus responded to any structural components of habitat, although arboreal activity was greater, not surprisingly, in wooded than in burnt heathland habitats. C. nanus was associated most strongly with the abundance of certain plants in the Proteaceae and Myrtaceae. In particular, the species prefers Banksia spp. (probably for food) and Eucalyptus and Xanthorrhoea spp. (probably for shelter).

Invertebrate prey of the bark-foraging insectivore Phascogale tapoatafa: distribution of biomass amongst alternative foraging substrates within south-western Australian woodlands

The bark of trees is an important foraging substrate for a range of vertebrate insectivores. This study aimed to investigate the distribution of food resources available to the bark-foraging insectivore Phascogale tapoatafa, and to compare prey biomass on bark versus the litter layer. We conducted nocturnal sampling for arthropods on tree trunks and litter in a forest in south-western Australia. The bark fauna biomass was dominated by spiders, with cockroaches, beetles and ants also well represented. In contrast, the litter was dominated by orthopterans. Invertebrate biomass was much greater in the litter layer than on tree trunks. Prey items in bark were more plentiful in Melaleuca swamps than in the surrounding dry sclerophyll woodland. Within swamps, trees with the highest invertebrate densities had thin trunks or loose bark, whilst in woodland it was trees with thick bark. Water availability may increase the prey resource used by bark-foraging insectivores.

Complex interactions among mammalian carnivores in Australia, and their implications for wildlife management

Mammalian carnivore populations are often intensively managed, either because the carnivore in question is endangered, or because it is viewed as a pest and is subjected to control measures, or both. Most management programmes treat carnivore species in isolation. However, there is a large and emerging body of evidence to demonstrate that populations of different carnivores interact with each other in a variety of complex ways. Thus, the removal or introduction of predators to or from a system can often affect other species in ways that are difficult to predict. Wildlife managers must consider such interactions when planning predator control programmes. Integrated predator control will require a greater understanding of the complex relationships between species. In many parts of the world, sympatric species of carnivores have coexisted over an evolutionary time scale so that niche differentiation has occurred, and competition is difficult to observe. Australia has experienced numerous introductions during the past 200 years, including those of the red fox (Vulpes vulpes) and the feral cat (Felis catus). These species now exist in sympatry with native mammalian predators, providing ecologists with the opportunity to study their interactions without the confounding effects of coevolution. Despite an increasing body of observational evidence for complex interactions among native and introduced predators in Australia, few studies have attempted to clarify these relationships experimentally, and the interactions remain largely unacknowledged. A greater understanding of these interactions would provide ecologists and wildlife managers world-wide with the ability to construct robust predictive models of carnivore communities, and to identify their broader effects on ecosystem functioning. We suggest that future research should focus on controlled and replicated predator removal or addition experiments. The dingo (Canis lupus dingo), as a likely keystone species, should be a particular focus of attention.

Diet quality differentially affects breeding effort of Mastomys coucha and M. natalensis: Implications for rodent pests

In this study we compare the reproductive ability of Mastomys natalensis, an agricultural rodent pest and that of the closely related species M. coucha, which has not been ascribed as a pest. We suggest that the ability of M. natalensis to plague, as well as dominate, resource-limited habitats, may in part be related to its differential breeding response to variation in diet quality. Thus, we examined the reproductive response of M. coucha and M. natalensis mothers to variation in dietary protein intake. Our results demonstrated that typical levels of reproduction extended over a narrower range of dietary protein content for M. coucha than M. natalensis females. Only M. natalensis females bred on 6% protein diets, while on 20% protein diets the reproductive output of M. coucha was lower than on diets containing 10- and 15% protein. M. natalensis responded to low protein diets by reducing litter size and litter mass but not individual pup mass. Thus, providing diet quality improves before parturition, conception under sub-optimal conditions may not compromise individual pup growth. Furthermore, the ability of M. natalensis to breed under conditions of low diet quality may advance their breeding season compared to species that cannot breed until diet quality improves, allowing M. natalensis to produce additional litters through the season, while more daughters could reproduce during the season of their birth, both factors that are known to contribute to the plaguing tendency of M. natalensis.