Tiny desert mice could help save Australia\u27s grasslands from invasion

You should stop skylarking about with those bloody desert mice and try and stop those woody weeds. I could see clear through that paddock in the \u2760s. Now look at it. That scrub costs us tens of thousands of dollars in lost fodder and it\u27s almost impossible to muster the livestock. That blunt assessment of our research, first offered by a local farmer in Australia\u27s arid rangelands almost seven years ago, raised an irresistible question for us as field ecologists. Why are Australia\u27s (and many others around the world) grasslands becoming woodier

Behavioural flexibility allows an invasive vertebrate to survive in a semi-arid environment

Plasticity or evolution in behavioural responses are key attributes of successful animal invasions. In northern Australia, the invasive cane toad (Rhinella marina) recently invaded semi-arid regions. Here, cane toads endure repeated daily bouts of severe desiccation and thermal stress during the long dry season (April-October).We investigated whether cane toads have shifted their ancestral nocturnal rehydration behaviour to one that exploits water resources during the day. Such a shift in hydration behaviour could increase the fitness of individual toads by reducing exposure to desiccation and thermal stress suffered during the day even within terrestrial shelters.We used a novel method (acoustic tags) to monitor the daily hydration behaviour of 20 toads at two artificial reservoirs on Camfield station, Northern Territory. Remarkably, cane toads visited reservoirs to rehydrate during daylight hours, with peaks in activity between 9.00 and 17.00. This diurnal pattern of rehydration activity contrasts with nocturnal rehydration behaviour exhibited by adult toads in their native geographical range and more mesic parts of Australia. Our results demonstrate that cane toads phase shift a key behaviour to survive in a harsh semi-arid landscape. Behavioural phase shifts have rarely been reported in invasive species but could facilitate ongoing invasion success. © 2014 The Author(s) Published by the Royal Society

Carrion subsidies provided by fishermen increase predation of beach-nesting bird nests by facultative scavengers

© 2014 The Zoological Society of London. Many predators are also scavengers that feed on carrion and human refuse. Therefore, the availability of carrion can elevate the abundance or activity of facultative scavengers, amplifying predation pressure on prey. On Australian beaches, fishermen often discard fish carcasses that could attract facultative scavengers, both native, such as Australian ravens Corvus coronoides, and invasive, such as European red foxes Vulpes vulpes, and result in elevated rates of predation on wildlife. We tested whether the presence of fish carcasses increased the risk of depredation for nearby nests of beach-nesting birds by deploying artificial nests in 12 subsidized and 12 control patches, spaced 1 km apart, on a beach. We placed a fish carcass in each subsidized patch, but not at control patches. In each patch, we placed two artificial nests, which resembled red-capped plover Charadrius ruficapillus nests, 80 m apart and 40m from carcasses at subsidized patches. Nest predators were identified from tracks and predator activity near subsidized and control nests was measured by counting tracks crossing a straight transect (220m). The activity of a native predator, the Australian raven, was 17 times higher near (<80m) nests with fish carcasses than nests without carcasses. After 72h, 96% of nests near carcasses were depredated compared with 30% of nests without carcasses. Ravens were identified as the culprit for 80% of depredated nests. Although other predators were present in the study area, they did not depredate artificial nests in this experiment. Previous studies have highlighted the effects of permanent and/or large-scale food resources on scavenger abundance and impact. A key management implication of our study is that even small, sparsely distributed, temporally irregular food subsidies, provided by humans, can elevate the activity and predatory impacts of facultative scavengers

Negative frequency dependent prey selection by two canid predators and its implications for the conservation of a threatened rodent in arid Australia

Unprecedented anthropogenic changes to biodiversity and biogeography demand a greater understanding of the consequences of altered faunal composition for ecosystem functioning. Selective predation has important, yet poorly understood effects on ecosystem stability, and can be strongly influenced by the relative frequencies of different prey types in the environment. Yet, how predators adjust their selection for prey according to their environmental frequency is often overlooked. Here, we assessed frequency dependent selection of prey by dingoes and foxes in the Australian desert, biannually, across a nine-year period (2007-2016). Both predators exhibited potentially destabilizing, negative frequency dependent selection for prey. Foxes persisted to preferentially consume a threatened, native rodent (Notomys fuscus) when it was environmentally scarce. Bolstered by the observation that N.fuscus occurs at low densities in areas where foxes are common, our results suggest that N.fuscus is particularly vulnerable to predation by this predator; possibly because it is naive and/or lacks adaptations to avoid or escape predation by the relatively recently introduced fox. Dingoes tended to consume reptiles when they were scarce; potentially constituting a conservation concern if selected reptilian taxa are threatened. Foxes avoided, thus were unlikely to control populations of overabundant kangaroos, while both foxes and dingoes showed a preference for, and may therefore control populations of invasive rabbits. The integration of our results into the relative suites of (de)stabilizing influences exerted by dingoes and foxes is important to provide a more dynamic insight into how each predator impacts their naturally fluctuating ecosystems

Artificial water points facilitate the spread of an invasive vertebrate in arid Australia

Summary: The spread of invasive species after their initial introduction is often facilitated by human actions. In some cases, invaders only become established in habitats where dominant native species have been displaced as a result of human actions or where humans inadvertently provide essential resources such as food, water or shelter. We investigated if dams that provide water for livestock have facilitated the cane toad's (Rhinella marina) invasion of a hot semi-arid landscape by providing toads with a resource subsidy and hence refuge from extreme heat and aridity. To determine the relationship between the presence of surface water and habitat occupancy by toads, we surveyed natural and artificial water features for cane toads during the annual dry season. We used radiotracking and acoustic tags to determine whether movement patterns and shelter use of cane toads were focussed around dams. To determine whether dams provide toads with refuge from extreme heat and aridity, we deployed plaster models with internal thermometers to estimate ambient temperatures and toad desiccation rates in shelter sites. To determine whether dams alleviate the stress experienced by toads, we measured plasma corticosterone levels of toads that sheltered in and away from dams. Toads were present in sites with standing water and absent from waterless sites. Most radiotracked toads sheltered within 1 m of water. Toad movements were focussed around water. Toads tracked with passive acoustic telemetry over a 6-month dry season were highly resident at dams. Plaster models placed in toad shelter sites away from the water lost 27% more mass and experienced higher temperatures than models placed near the water's edge. Toads that sheltered in terrestrial shelters exhibited higher plasma corticosterone levels compared to toads that sheltered near dams. Dams provide toads with refuge habitats where they are less at risk from overheating and dehydration. Synthesis and applications. Artificial water points can facilitate biological invasions in arid regions by providing a resource subsidy for water-dependent invasive species. Our study suggests that there is scope to control populations of water-dependent invasive vertebrates in arid regions by restricting their access to artificial water points. © 2014 British Ecological Society

A trophic cascade initiated by an invasive vertebrate alters the structure of native reptile communities.

Invasive vertebrates are frequently reported to have catastrophic effects on the populations of species which they directly impact. It follows then, that if invaders exert strong suppressive effects on some species then other species will indirectly benefit due to ecological release from interactions with directly impacted species. However, evidence that invasive vertebrates trigger such trophic cascades and alter community structure in terrestrial ecosystems remains rare. Here, we ask how the cane toad, a vertebrate invader that is toxic to many of Australia's vertebrate predators, influences lizard assemblages in a semi-arid rangeland. In our study area, the density of cane toads is influenced by the availability of water accessible to toads. We compared an index of the abundance of sand goannas, a large predatory lizard that is susceptible to poisoning by cane toads and the abundances of four lizard families preyed upon by goannas (skinks, pygopods, agamid lizards and geckos) in areas where cane toads were common or rare. Consistent with the idea that suppression of sand goannas by cane toads initiates a trophic cascade, goanna activity was lower and small lizards were more abundant where toads were common. The hypothesis that suppression of sand goannas by cane toads triggers a trophic cascade was further supported by our findings that small terrestrial lizards that are frequently preyed upon by goannas were more affected by toad abundance than arboreal geckos, which are rarely consumed by goannas. Furthermore, the abundance of at least one genus of terrestrial skinks benefitted from allogenic ecosystem engineering by goannas where toads were rare. Overall, our study provides evidence that the invasion of ecosystems by non-native species can have important effects on the structure and integrity of native communities extending beyond their often most obvious and frequently documented direct ecological effects

Interactions between corticosterone phenotype, environmental stressor pervasiveness and irruptive movement-related survival in the cane toad

© 2018. Published by The Company of Biologists Ltd Animals use irruptive movement to avoid exposure to stochastic and pervasive environmental stressors that impact fitness. Beneficial irruptive movements transfer individuals from high-stress areas (conferring low fitness) to alternative localities that may improve survival or reproduction. However, being stochastic, environmental stressors can limit an animal’s preparatory capacity to enhance irruptive movement performance. Thus individuals must rely on pre-existing, or rapidly induced, physiological and behavioural responses. Rapid elevation of glucocorticoid hormones in response to environmental stressors are widely implicated in adjusting physiological and behaviour processes that could influence irruptive movement capacity. However, there remains little direct evidence demonstrating that corticosterone-regulated movement performance or interaction with pervasiveness of environmental stress, confers adaptive movement outcomes. Here, we compared how movement-related survival of cane toads (Rhinella marina) varied with three different experimental corticosterone phenotypes across four increments of increasing environmental stressor pervasiveness (i.e. distance from water in a semi-arid landscape). Our results indicated that toads with phenotypically increased corticosterone levels attained higher movement-related survival compared with individuals with control or lowered corticosterone phenotypes. However, the effects of corticosterone phenotypes on movement-related survival to some extent co-varied with stressor pervasiveness. Thus, our study demonstrates how the interplay between an individual’s corticosterone phenotype and movement capacity alongside the arising costs of movement and the pervasiveness of the environmental stressor can affect survival outcomes

Experiments in no-impact control of dingoes: Comment on Allen et al. 2013

There has been much recent debate in Australia over whether lethal control of dingoes incurs environmental costs, particularly by allowing increase of populations of mesopredators such as red foxes and feral cats. Allen et al. (2013) claim to show in their recent study that suppression of dingo activity by poison baiting does not lead to mesopredator release, because mesopredators are also suppressed by poisoning. We show that this claim is not supported by the data and analysis reported in Allen et al.'s paper. © 2014 Johnson et al.; licensee BioMed Central Ltd

Spatiotemporal variation in the endangered Thymus decussatus in a hyper-arid environment

Aims: Arid environments are resource limited, with scarcity of water the key limiting factor, but hyper-arid environments are rarely studied. We test for spatial and temporal variation in ecologically important characteristics to deduce plant adaptations to the extreme climate. Methods: The endangered Sinai Thyme (Thymus decussatus) exists as a set of patches on mountaintops within the St Katherine Protectorate, South Sinai, a hyper-arid environment with rare events of good rains (every 10–15 years). Important Findings: From spatial and temporal patterns of plant mortality, size, condition and flowering among 10 patches on the Mt Sinai massif, we deduce that the incidence and amount of flowering responds relatively quickly (1–2 years) to rainfall fluctuations, but plant growth respond only very slowly. Small individuals are most at risk of death during drought, and a high proportion of plants were dead at the end of 8 years of very low or no rainfall. No recruitment of seedlings was observed even in years of good rainfall. Droughts are expected to become increasingly frequent due to climate change; this may have important consequences for Sinai Thyme and also its associated herbivores, such as the Critically Endangered Sinai Baton Blue (Pseudophilotes sinaicus) whose larval stage feeds exclusively upon the flowers of this plant