Invasive cane toads might initiate cascades of direct and indirect effects in a terrestrial ecosystem

Understanding the impacts that invasive vertebrates have on terrestrial ecosystems extends primarily to invaders’ impacts on species with which they interact directly through mechanisms such as predation, competition and habitat modification. In addition to direct effects, invaders can also initiate ecological cascades via indirect population level effects on species with which they do not directly interact. However, evidence that invasive vertebrates initiate ecological cascades in terrestrial ecosystems remains scarce. Here, we ask whether the invasion of the cane toad, a vertebrate invader that is toxic to many of Australia’s vertebrate predators, has induced ecological cascades in a semi-arid rangeland. We compared activity of a large predatory lizard, the sand-goanna, and abundances of smaller lizards preyed upon by goannas in areas of high toad activity near toads’ dry season refuges and areas of low toad activity distant from toads’ dry season refuges. Consistent with the hypothesis that toad invasion has led to declines of native predators susceptible to poisoning, goanna activity was lower in areas of high toad activity. Consistent with the hypothesis that toad-induced goanna decline lead to increases in abundance the prey of goannas, smaller lizards were more abundant in areas of high toad activity. Structural equation modelling showed a positive correlation between goanna activity and distance from dry season refuge habitats used by toads. The abundances of small lizards was correlated negatively with goanna activity and distance from dry season refuges of toads. Our findings provide support for the notion that invasions by terrestrial vertebrates can trigger ecological cascades.     

School for Skinks: Can Conditioned Taste Aversion Enable Bluetongue Lizards (Tiliqua scincoides) to Avoid Toxic Cane Toads (Rhinella marina) as Prey?

The invasion of cane toads (Rhinella marina) through Australia imperils native predators that are killed if they consume these toxic anurans. The magnitude of impact depends upon the predators’ capacity for aversion learning: toad impact is lower if predators can learn not to attack toads. In laboratory trials, we assessed whether bluetongue lizards (Tiliqua scincoides) – a species under severe threat from toads – are capable of learned taste aversion and whether we can facilitate that learning by exposing lizards to toad tissue combined with a nausea‐inducing chemical (lithium chloride). Captive bluetongues rapidly learned to avoid the ‘unpalatable’ food. Taste aversion also developed (albeit less strongly) in response to meals of minced cane toad alone. Our data suggest that taste aversion learning may help bluetongue lizards survive the onslaught of cane toads, but that many encounters will be fatal because the toxin content of toads is so high relative to lizard tolerance of those toxins. Thus, baiting with nausea‐inducing (but non‐lethal) toad products might provide a feasible management option to reduce the impact of cane toad invasion on these native predators.     

Indirect facilitation of a native mesopredator by an invasive species: are cane toads re-shaping tropical riparian communities?

Top predators can suppress mesopredators both by killing them and by motivating changes in their behavior, and there are numerous examples of mesopredator release caused by declines in top predator populations. Demonstrated cases of invasive species triggering such releases among vertebrate trophic linkages (indirect facilitation), however, are rare. The invasive cane toad, Bufo marinus, has caused severe population-level declines in some Australian predators via lethal toxic ingestion. During a long-term study of the direct impacts of cane toads on predatory monitor lizards in tropical Australia, we documented significant, marked increases in annual counts of a mesopredator, the common tree snake (Dendrelaphis punctulatus). Mean snake counts during surveys of 70-km river transects at two sites increased from <1 individual per survey during 2001–2006, to 8–18 per survey in 2007. These increases occurred approximately 3 years following the arrival of cane toads, and 1–3 years after 71–96 % population declines in three species of predatory monitor lizards (Varanus panoptes, V. mertensi, and V. mitchelli). These data suggest a mesopredator release: the dramatic reduction of predatory monitor lizards caused increases in the tree snake by decreasing predation risk. The increases in tree snake counts were not attributable to either abiotic factors, or a trophic subsidy. The severe declines of predatory monitor lizards, coupled with recent evidence of cascading effects on their prey, suggest that cane toads are re-shaping riparian communities in tropical Australia through both direct negative effects and indirect facilitation.     

After the crash: How do predators adjust following the invasion of a novel toxic prey type?

The ability of a native predator to adjust to a dangerously toxic invasive species is key to avoiding an ongoing suppression of the predator's population and the trophic cascade of effects that can result. Many species of anurophagous predators have suffered population declines due to the cane toad's (Rhinella marina: Bufonidae) invasion of Australia; these predators can be fatally poisoned from attempting to consume the toxic toad. We studied one such toad‐vulnerable predator, the yellow‐spotted monitor (Varanus panoptes: Varanidae), testing whether changes to the predator's feeding behaviour could explain how the species persists following toad invasion. Wild, free‐roaming lizards from (1) toad‐naïve and (2) toad‐exposed populations were offered non‐toxic native frogs and slightly toxic cane toads (with parotoid glands removed) in standardized feeding trials. Toad‐naïve lizards readily consumed both frogs and toads, with some lizards displaying overt signs of illness after consuming toads. In contrast, lizards from toad‐exposed populations consumed frogs but avoided toads. Repeated encounters with toads did not modify feeding responses by lizards from the toad‐naïve populations, suggesting that aversion learning is limited (but may nonetheless occur). Our results suggest that this vulnerable predator can adjust to toad invasion by developing an aversion to feeding on the toxic invader, but it remains unclear as to whether the lizard's toad‐aversion arises via adaptation or learning.     

The impact of invasive cane toads on native wildlife in southern Australia

Commonly, invaders have different impacts in different places. The spread of cane toads (Rhinella marina: Bufonidae) has been devastating for native fauna in tropical Australia, but the toads' impact remains unstudied in temperate‐zone Australia. We surveyed habitat characteristics and fauna in campgrounds along the central eastern coast of Australia, in eight sites that have been colonized by cane toads and another eight that have not. The presence of cane toads was associated with lower faunal abundance and species richness, and a difference in species composition. Populations of three species of large lizards (land mullets Bellatorias major, eastern water dragons Intellagama lesueurii, and lace monitors Varanus varius) and a snake (red‐bellied blacksnake Pseudechis porphyriacus) were lower (by 84 to 100%) in areas with toads. The scarcity of scavenging lace monitors in toad‐invaded areas translated into a 52% decrease in rates of carrion removal (based on camera traps at bait stations) and an increase (by 61%) in numbers of brush turkeys (Alectura lathami). The invasion of cane toads through temperate‐zone Australia appears to have reduced populations of at least four anurophagous predators, facilitated other taxa, and decreased rates of scavenging. Our data identify a paradox: The impacts of cane toads are at least as devastating in southern Australia as in the tropics, yet we know far more about toad invasion in the sparsely populated wilderness areas of tropical Australia than in the densely populated southeastern seaboard.     

Sampling skinks and geckos in artificial cover objects in a dry mixed grassland-shrubland with mammalian predator control

Introduced mammalian predators threaten populations of endemic New Zealand lizards but their effects on lizard populations have not been quantified on the mainland. We trialled the use of artificial cover objects (ACOs) for sampling small terrestrial lizards (the skinks Oligosoma maccanni, O. nigriplantare polychroma and O. inconspicuum, and gecko Hoplodactylus maculatus) in three experimental mammal-management treatments: a mammal-proof fence, two sites in an intensive mammal-removal area, and an experimental control site with no mammal removal. These predator control regimes were established in 2005-2006 to protect endangered grand skinks (O. grande) and Otago skinks (O. otagense) at Macraes Flat, North Otago. We (1) counted skinks and geckos found under ACOs on a single day and compared these counts between treatments, and (2) estimated lizard population sizes (N) based on capture-mark-recapture (CMR) of lizards under ACOs in daily and weekly sampling sessions. Our results provide baseline data of the abundance of the small lizard species shortly after implementation of predator management. Single-day counts of skinks were significantly higher inside the mammal fence compared with the experimental control. No consistent differences were found between the other treatments. Significantly more skinks were counted in gully habitats than in ridge habitats. N?, counts of skinks from the first day of CMR, and the total number of individuals caught were correlated, but these relationships must be validated with independent data. Few geckos were caught unless ACOs were placed near rock outcrops. Only two skinks but 25% of geckos moved between adjacent ACOs (5-m spacing). The recapture rate of skinks was low; captures declined when ACOs were checked daily but not when they were checked weekly. Because of potential biases of these methods, we propose to compare counts in ACOs and N? based on CMR in ACOs with N? based on CMR in pitfall traps with 3-m spacing.     

Detecting the impact of invasive species on native fauna: Cane toads (Bufo marinus), frillneck lizards (Chlamydosaurus kingii) and the importance of spatial replication

An understanding of which native species are severely impacted by an anthropogenic change (such as the arrival of an invasive species) and which are not is critical to prioritizing conservation efforts. However, it is difficult to detect such impacts if the native taxa exhibit strong stochastic variations in abundance; a ‘natural’ population decline might be wrongly interpreted as an impact of the invader. Frillneck lizards (Chlamydosaurus kingii) are large iconic Australian agamids, and have been reported to decline following the invasion of toxic cane toads. We monitored three populations of the species in the savanna woodland of tropical Australia over a 7‐year period bracketing toad arrival. One population crashed, one remained stable and one increased. Hence, studies on any single population might have inferred that cane toads have negative, negligible or positive effects on frillneck lizards. With the benefit of spatial replication, and in combination with observations of prey choice by captive lizards, our data suggest that invasive cane toads have had little or no effect on frillneck abundance.     

No signs of Na+/K+‐ATPase adaptations to an invasive exotic toxic prey in native squamate predators

Invasions by exotic toxic prey, like the release of the South American cane toad (Bufo (Rhinella) marinus) to the toad‐free Australian continent in 1935, have been shown to result in massive declines in native predator numbers. Due to minor nucleotide mutations of the Na⁺/K⁺‐ATPase gene most Australian squamate predators are highly susceptible to cane toad toxin. However, in spite of this, predators like yellow‐spotted goannas (Varanus panoptes) and red‐bellied black snakes (Pseudechis porhyriacus) still persist in parts of Queensland where they, in some areas, have co‐existed with cane toads for more than 70 years. Here, we show that the amino acids of the Na⁺/K⁺‐ATPase enzyme in the two species do not provide toad toxin resistance, and hence the two Queensland predators are still highly susceptible to cane toad toxin. Both yellow‐spotted goannas and lace monitors (Varanus varius) have, however, been recorded avoiding feeding on cane toads in areas where they co‐exist with this toxic amphibian. Moreover, both varanids have also been shown to learn to avoid feeding on toads when first subjected to conditioned taste aversion. Such behavioural shifts may therefore explain why yellow‐spotted goannas and red‐bellied black snakes still exist in cane toad infested areas of Queensland. The process appears, however, to be unable to rapidly restore varanid populations to pre‐toad population numbers as even after 10 years of co‐existence with cane toads in the Northern Territory, we see no signs of an increase in yellow‐spotted goanna numbers.     

Interacting impacts of invasive plants and invasive toads on native lizards

The ecological impacts of an invasive species may be reduced by prior invasions if selective pressures imposed by earlier events preadapt the native biota to deal with the newer arrival. In northwestern Australia, invasion of the cane toad (Rhinella marina) kills many native predators if they ingest the highly toxic toads. Remarkably, the toads' defensive toxins (bufadienolides) are chemically similar to those of another invasive species: an ornamental plant from Madagascar, Bryophyllum spp. (Crassulaceae, mother-of-millions). Omnivorous lizards (bluetongue skinks, Tiliqua scincoides) are imperiled by the invasion of toads in northwestern Australia, but conspecifics from other areas of the continent (those where exotic plants were introduced and including areas where toads have yet to invade) are less affected because they exhibit higher physiological tolerance of toad toxins (and also of plant toxins). The willingness of captive bluetongues to consume both toads and these plants and the high correlation in the lizards' sensitivity to toad toxins versus plant toxins suggest that exotic plants may have imposed strong selection on the lizards' physiological tolerance of bufadienolides. As a result, populations of lizards from areas previously exposed to these alien plants may be preadapted to deal with the toxins of the more recent anuran invader.     

Population-level declines in Australian predators caused by an invasive species

The cane toad Bufo marinus has been migrating westward across northern Australia since its introduction as a biological control agent in 1935. It has been implicated in the widespread decline of many native frog-eating predators. To investigate the impacts of this invasive species on native predatory reptiles, annual surveys were conducted from 2001 to 2007 to document variation in the relative abundances of three varanid lizards ( Varanus mertensi, Varanus mitchelli and Varanus panoptes ) and one crocodile Crocodylus johnstoni species known to consume toads. In addition, the indirect effects of this variation on one agamid lizard Amphibolurus gilberti , a known prey item of V. panoptes , were also examined. Surveys were performed at two sites in northern Australia before and after the arrival of B. marinus . Significant declines in the relative abundances of all three species of varanid lizard were observed following toad arrival. Declines in the abundance of V. panoptes, V. mitchelli and V. mertensi at the two sites ranged 83–96, 71–97 and 87–93%, respectively. In contrast, A. gilberti increased by 23–26%; whereas there were no significant population-level declines in C. johnstoni despite observations of individual effects (i.e. several dead crocodiles with B. marinus in their stomachs). These findings suggest population-level changes in Australian lizards caused by an invasive species.     

Not such silly sausages: Evidence suggests northern quolls exhibit aversion to toads after training with toad sausages

The invasion of toxic cane toads (Rhinella marina) is a major threat to northern quolls (Dasyurus hallucatus) which are poisoned when they attack this novel prey item. Quolls are now endangered as a consequence of the toad invasion. Conditioned taste aversion can be used to train individual quolls to avoid toads, but we currently lack a training technique that can be used at a landscape scale to buffer entire populations from toad impact. Broad‐scale deployment requires a bait that can be used for training, but there is no guarantee that such a bait will ultimately elicit aversion to toads. Here, we test a manufactured bait – a ‘toad sausage’ – in a small captive trial, for its ability to elicit aversion to toads in northern quolls. To do this, we exposed one group of quolls to a toad sausage and another to a control sausage and compared the quolls' predatory responses when presented with a dead adult toad. Captive quolls that consumed a single toad sausage showed a reduced interest in cane toads, interacting with them for less than half the time of their untrained counterparts and showing reduced Attack behaviour. We also quantified bait uptake in the field, by both quolls and non‐target species. These field trials showed that wild quolls were the most frequent species attracted to the baits, and that approx. 61% of quolls consumed toad‐aversion baits when first encountered. Between 40% and 68% of these animals developed aversion to further bait consumption. Our results suggest that toad‐aversion sausages may be used to train wild quolls to avoid cane toads. This opens the possibility for broad‐scale quoll training with toad aversion sausages: a technique that may allow wildlife managers to prevent quoll extinctions at a landscape scale.     

The ecological impact of invasive cane toads (Bufo marinus) in Australia

Although invasive species are viewed as major threats to ecosystems worldwide, few such species have been studied in enough detail to identify the pathways, magnitudes, and timescales of their impact on native fauna. One of the most intensively studied invasive taxa in this respect is the cane toad (Bufo marinus), which was introduced to Australia in 1935. A review of these studies suggests that a single pathway-lethal toxic ingestion of toads by frog-eating predators-is the major mechanism of impact, but that the magnitude of impact varies dramatically among predator taxa, as well as through space and time. Populations of large predators (e.g., varanid and scincid lizards, elapid snakes, freshwater crocodiles, and dasyurid marsupials) may be imperilled by toad invasion, but impacts vary spatially even within the same predator species. Some of the taxa severely impacted by toad invasion recover within a few decades, via aversion learning and longer-term adaptive changes. No native species have gone extinct as a result of toad invasion, and many native taxa widely imagined to be at risk are not affected, largely as a result of their physiological ability to tolerate toad toxins (e.g., as found in many birds and rodents), as well as the reluctance of many native anuran-eating predators to consume toads, either innately or as a learned response. Indirect effects of cane toads as mediated through trophic webs are likely as important as direct effects, but they are more difficult to study. Overall, some Australian native species (mostly large predators) have declined due to cane toads; others, especially species formerly consumed by those predators, have benefited. For yet others, effects have been minor or have been mediated indirectly rather than through direct interactions with the invasive toads. Factors that increase a predator's vulnerability to toad invasion include habitat overlap with toads, anurophagy, large body size, inability to develop rapid behavioral aversion to toads as prey items, and physiological vulnerability to bufotoxins as a result of a lack of coevolutionary history of exposure to other bufonid taxa.     

Behavioural tactics used by invasive cane toads (Rhinella marina) to exploit apiaries in Australia

Behavioural flexibility plays a key role in facilitating the ability of invasive species to exploit anthropogenically‐created resources. In Australia, invasive cane toads (Rhinella marina) often gather around commercial beehives (apiaries), whereas native frogs do not. To document how toads use this resource, we spool‐tracked cane toads in areas containing beehives and in adjacent natural habitat without beehives, conducted standardized observations of toad feeding behaviour, and ran prey‐manipulation trials to compare the responses of cane toads versus native frogs to honeybees as potential prey. Toads feeding around beehives travelled shorter distances per night, and hence used different microhabitats, than did toads from nearby control sites without beehives. The toads consumed live bees from the hive entrance (rather than dead bees from the ground), often climbing on top of one another to gain access to the hive entrance. Prey manipulation trials confirm that bee movement is the critical stimulus that elicits the toads’ feeding response; and in standardized trials, native frogs consumed bees less frequently than did toads. In summary, cane toads flexibly modify their movements, foraging behaviour and dietary composition to exploit the nutritional opportunities created by commercial beehives, whereas native anurans do not.     

Behavioural responses of reptile predators to invasive cane toads in tropical Australia

The ecological impact of an invasive species can depend on the behavioural responses of native fauna to the invader. For example, the greatest risk posed by invasive cane toads (Rhinella marina Bufonidae) in tropical Australia is lethal poisoning of predators that attempt to eat a toad; and thus, a predator's response to a toad determines its vulnerability. We conducted standardized laboratory trials on recently captured (toad‐naïve) predatory snakes and lizards, in advance of the toad invasion front as it progressed through tropical Australia. Responses to a live edible‐sized toad differed strongly among squamate species. We recorded attacks (and hence, predator mortality) in scincid, agamid and varanid lizards, and in elapid, colubrid and pythonid snakes. Larger‐bodied predators were at greater risk, and some groups (elapid snakes and varanid lizards) were especially vulnerable. However, feeding responses differed among species within families and within genera. Some taxa (notably, many scincid and agamid lizards) do not attack toads; and many colubrid snakes either do not consume toads, or are physiologically resistant to the toad's toxins. Intraspecific variation in responses means that even in taxa that apparently are unaffected by toad invasion at the population level, some individual predators nonetheless may be fatally poisoned by invasive cane toads.     

A review of ecological interactions between native frogs and invasive cane toads in Australia

Translocated from their native range in the Americas in 1935, cane toads (Rhinella marina, Bufonidae) have now spread through much of tropical and subtropical Australia. The toad's invasion and impact have attracted detailed study. In this paper, I review information on ecological interactions between cane toads and Australian anurans. The phylogenetic relatedness and ecological similarity between frogs and toads creates opportunities for diverse interactions, ranging from predation to competition to parasite transfer, plus a host of indirect effects mediated via impacts of toads on other species, and by people's attempts to control toads. The most clear‐cut effect of toads on frogs is a positive one: reducing predator pressure by fatally poisoning anuran‐eating varanid lizards. However, toads also have a wide range of other effects on frogs, some positive (e.g. taking up parasites that would otherwise infect native frogs) and others negative (e.g. eating frogs, poisoning frogs, competing with tadpoles). Although information on such mechanisms predicts intense interactions between toads and frogs, field surveys show that cane toad invasion has negligible overall impacts on frog abundance. That counter‐intuitive result is because of a broad balancing of negative and positive impacts, coupled with stochastic (weather‐induced) fluctuations in anuran abundance that overwhelm any impacts of toads. Also, the impacts of toads on frogs differ among frog species and life‐history stages, and depend upon local environmental conditions. The impacts of native frogs on cane toads have attracted much less study, but may well be important: frogs may impose biotic resistance to cane toad colonization, especially via competition in the larval phase. Overall, the interactions between native frogs and invasive toads illustrate the diverse ways in which an invader's arrival can perturb the native fauna by both direct and indirect mechanisms, and by which the native species can curtail an invader's success. These studies also offer a cautionary tale about the difficulty of predicting the impact of an invasive species, even with a clear understanding of mechanisms of direct interaction.     

The herpetofauna of Timor-Leste: a first report

Fieldwork conducted throughout Timor-Leste in September 2004 and July 2009 resulted in a collection or recording of 263 herpetological specimens (100 amphibians, 163 reptiles), comprising at least seven species of frogs and toads, 20 species of lizards, seven species of snakes, two species of turtles, and one species of crocodile. Among the amphibians, the most frequently encountered species were toads (Duttaphrynus melanostictus), rice paddy frogs (genus Fejervarya), and rhacophorid treefrogs (Polypedates cf. leucomystax). All three variants of rice paddy frogs encountered represent undescribed species similar to Fejervarya verruculosa from neighboring Wetar Island. Records of Fejervarya cancrivora and Fejervarya limnocharis for Timor Island are apparently errors based on misidentification. We obtained voucher specimens for a total of 147 lizards and voucher photographs only for four specimens of Varanus timorensis. Aside from geckos frequently associated with human habitations (e.g., Gehyra mutilata, Gekko gecko, Hemidactylus frenatus, Hemidactylus platyurus), we discovered an as yet undescribed species of bent-toed gecko, genus Cyrtodactylus, in the Same valley. Our specimens of Hemidactylus platyurus are the first record of this species from Timor-Leste. Commonly encountered skinks included four-fingered skinks (genus Carlia), wedge skinks (genus Sphenomorphus), and night skinks (genus Eremiascincus). Notable among the 15 snakes collected was the frequency of pitvipers (Cryptelytrops insularis), which amounted to over 25% of all snakes. Our specimen of the wolfsnake Lycodon subcinctus is the first record of this species for Timor-Leste. Based on these findings, it appears that the biodiversity of amphibians and reptiles in this remote corner of Wallacea is much greater than previously thought, particularly with respect to scincid lizards. The detail we provide in the species accounts is designed to allow the use of this report as a preliminary field guide to the amphibians and reptiles of Timor-Leste. However, survey work is ongoing.     

Does intraspecific niche partitioning in a native predator influence its response to an invasion by a toxic prey species?

Abstract The introduced and highly toxic cane toad (Bufo marinus) is rapidly spreading across northern Australia where it may affect populations of large terrestrial vertebrate predators. The ecological impact of cane toads will depend upon the diets, foraging modes and habitat use of native predators, and their feeding responses to cane toads. However, intraspecific niche partitioning may influence the degree of vulnerability of predators to toxic prey, as well as the time course of the impact of alien invaders on native species. We studied the diet of the northern death adder Acanthophis praelongus and their feeding responses to cane toads. In the laboratory, death adders from all size classes and sexes readily consumed frogs and cane toads. Diets of free ranging A. praelongus from the Adelaide River floodplain were more heterogeneous. Juvenile snakes ate mainly frogs (39% of prey items) and small scincid lizards (43%). Both sexes displayed an ontogenetic dietary shift from lizards to mammals, but adult males fed on frogs (49%) and mammals (39%) whereas adult females (which grew larger than males) fed mainly on mammals (91%) and occasionally, frogs (9%). Feeding rates and body condition of adult snakes varied temporally and tracked fluctuations in prey availability. These results suggest that cane toads may negatively affect populations of northern death adders in the Darwin region. However, we predict that different size and sex classes of A. praelongus will experience differential mortality rates over different timescales. The initial invasion of large toads may affect adult males, but juveniles may be unaffected until juvenile toads appear the following year, and major affects on adult female death adders may be delayed until annual rainfall fluctuations reduce the availability of alternative (rodent) prey.     

Why are some mitochondria more powerful than others: insights from comparisons of muscle mitochondria from three terrestrial vertebrates

We studied the molecular composition of muscle mitochondria to evaluate whether the contents of cytochromes or adenine nucleotide translocase (ANT) or phospholipid acyl compositions reflect differences in mitochondrial oxidative capacities. We isolated mitochondria from three vertebrates of similar size and preferred temperature, the rat (Rattus norvegicus), the cane toad (Bufo marinus) and the bearded dragon lizard (Pogona vitticeps). Mitochondrial oxidative capacities were higher in rats and cane toads than in bearded dragon, whether rates were expressed relative to protein, cytochromes or ANT. Inter-specific differences were least pronounced when rates were expressed relative to cytochrome A, a component of cytochrome C oxidase (CCO), or ANT. In mitochondria from rat and cane toad, cytochrome A was more abundant than C followed by B and then C(1), while in bearded dragon mitochondria, the cytochromes were present in roughly equal levels. Analysis of correlations between mitochondrial oxidative capacities and macromolecular components revealed that cytochrome A explained at least half of the intra- and inter-specific variability in substrate oxidation rates. ANT levels were an excellent correlate of state 3 rates while phospholipid contents were correlated with state 4 rates. As the % poly-unsaturation and the % 20:4n-6 in mitochondrial phospholipids were equivalent in toads and rats, and exceeded the levels in lizards, they may contribute to the inter-specific differences in oxidative capacities. We suggest that the numbers of CCO and ANT together with the poly-unsaturation of phospholipids explain the higher oxidative capacities in muscle mitochondria from rats and cane toads.     

Responses of Australian wading birds to a novel toxic prey type, the invasive cane toad Rhinella marina

The impact of invasive predators on native prey has attracted considerable scientific attention, whereas the reverse situation (invasive species being eaten by native predators) has been less frequently studied. Such interactions might affect invasion success; an invader that is readily consumed by native species may be less likely to flourish in its new range than one that is ignored by those taxa. Invasive cane toads (Rhinella marina) in Australia have fatally poisoned many native predators (e.g., marsupials, crocodiles, lizards) that attempt to ingest the toxic anurans, but birds are more resistant to toad toxins. We quantified prey preferences of four species of wading birds (Nankeen night heron, purple swamphen, pied heron, little egret) in the wild, by offering cane toads and alternative native prey items (total of 279 trays offered, 14 different combinations of prey types). All bird species tested preferred the native prey, avoiding both tadpole and metamorph cane toads. Avoidance of toads was strong enough to reduce foraging on native prey presented in combination with the toads, suggesting that the presence of cane toads could affect predator foraging tactics, and reduce the intensity of predation on native prey species found in association with toads.