Long-term livestock exclusion increases plant richness and reproductive capacity in arid woodlands.

Herbivore exclusion is implemented globally to recover ecosystems from grazing by introduced and native herbivores, but evidence for large-scale biodiversity benefits is inconsistent in arid ecosystems. We examined the effects of livestock exclusion on dryland plant richness and reproductive capacity. We collected data on plant species richness and seeding (reproductive capacity), rainfall, vegetation productivity and cover, soil strength and herbivore grazing intensity from 68 sites across 6500 km2 of arid Georgina gidgee (Acacia georginae) woodlands in central Australia between 2018 and 2020. Sites were on an actively grazed cattle station and two destocked conservation reserves. We used structural equation modeling to examine indirect (via soil or vegetation modification) versus direct (herbivory) effects of grazing intensity by two introduced herbivores (cattle, camels) and a native herbivore (red kangaroo), on seasonal plant species richness and seeding of all plants, and the richness and seeding of four plant groups (native grasses, forbs, annual chenopod shrubs, and palatable perennial shrubs). Non-native herbivores had a strong indirect effect on plant richness and seeding by reducing vegetative ground cover, resulting in decreased richness and seeding of native grasses and forbs. Herbivores also had small but negative direct impacts on plant richness and seeding. This direct effect was explained by reductions in annual chenopod and palatable perennial shrub richness under grazing activity. Responses to grazing were herbivore-dependent; introduced herbivore grazing reduced native plant richness and seeding, while native herbivore grazing had no significant effect on richness or seeding of different plant functional groups. Soil strength decreased under grazing by cattle but not camels or kangaroos. Cattle had direct effects on palatable perennial shrub richness and seeding, whereas camels had indirect effects, reducing richness and seeding by reducing the abundance of shrubs. We show that considering indirect pathways improves evaluations of the effects of disturbances on biodiversity, as focusing only on direct effects can mask critical mechanisms of change. Our results indicate substantial biodiversity benefits from excluding livestock and controlling camels in drylands. Reducing introduced herbivore impacts will improve soil and vegetation condition, ensure reproduction and seasonal persistence of species, and protect native plant diversity.

Context and trade-offs characterize real-world threat detection systems: A review and comprehensive framework to improve research practice and resolve the translational crisis.

A better understanding of context in decision-making-that is, the internal and external conditions that modulate decisions-is required to help bridge the gap between natural behaviors that evolved by natural selection and more arbitrary laboratory models of anxiety and fear. Because anxiety and fear are mechanisms evolved to manage threats from predators and other exigencies, the large behavioral, ecological and evolutionary literature on predation risk is useful for re-framing experimental research on human anxiety-related disorders. We review the trade-offs that are commonly made during antipredator decision-making in wild animals along with the context under which the behavior is performed and measured, and highlight their relevance for focused laboratory models of fear and anxiety. We then develop an integrative mechanistic model of decision-making under risk which, when applied to laboratory and field settings, should improve studies of the biological basis of normal and pathological anxiety and may therefore improve translational outcomes.

Biologically meaningful scents: a framework for understanding predator-prey research across disciplines.

Fear of predation is a universal motivator. Because predators hunt using stealth and surprise, there is a widespread ability among prey to assess risk from chemical information - scents - in their environment. Consequently, scents often act as particularly strong modulators of memory and emotions. Recent advances in ecological research and analytical technology are leading to novel ways to use this chemical information to create effective attractants, repellents and anti-anxiolytic compounds for wildlife managers, conservation biologists and health practitioners. However, there is extensive variation in the design, results, and interpretation of studies of olfactory-based risk discrimination. To understand the highly variable literature in this area, we adopt a multi-disciplinary approach and synthesize the latest findings from neurobiology, chemical ecology, and ethology to propose a contemporary framework that accounts for such disparate factors as the time-limited stability of chemicals, highly canalized mechanisms that influence prey responses, and the context within which these scents are detected (e.g. availability of alternative resources, perceived shelter, and ambient physical parameters). This framework helps to account for the wide range of reported responses by prey to predator scents, and explains, paradoxically, how the same individual predator scent can be interpreted as either safe or dangerous to a prey animal depending on how, when and where the cue was deposited. We provide a hypothetical example to illustrate the most common factors that influence how a predator scent (from dingoes, Canis dingo) may both attract and repel the same target organism (kangaroos, Macropus spp.). This framework identifies the catalysts that enable dynamic scents, odours or odorants to be used as attractants as well as deterrents. Because effective scent tools often relate to traumatic memories (fear and/or anxiety) that cause future avoidance, this information may also guide the development of appeasement, enrichment and anti-anxiolytic compounds, and help explain the observed variation in post-traumatic-related behaviours (including post-traumatic stress disorder, PTSD) among diverse terrestrial taxa, including humans.

Does Historical Coexistence with Dingoes Explain Current Avoidance of Domestic Dogs? Island Bandicoots Are Naïve to Dogs, unlike Their Mainland Counterparts.

Introduced predators have a global reputation for causing declines and extinctions of native species. Native prey naiveté towards novel predators is thought to be a key reason for predator impacts. However, naiveté is not necessarily forever: where coexistence establishes, it is likely that naiveté will be reduced through adaptation, and the once alien predator will eventually become recognised by prey. For example, native marsupial bandicoots in Sydney avoid backyards with domestic dogs (C. lupus familiaris), but not domestic cats (Felis catus), even though cats and dogs were both introduced about 200 years ago (Carthey and Banks 2012). The authors attributed bandicoots' recognition of dogs to long-term exposure to a close relative of dogs, dingoes that arrived in Australia 4000 years ago. Here, we test a prediction of this hypothesis by taking the study to Tasmania, where dingoes have never been present but where domestic dogs also arrived about 200 years ago. We use a similar survey design to that of Carthey and Banks (2012): asking Hobart residents to report on pet-ownership, bandicoot sightings and scats within their backyards, as well as an array of yard characteristic control variables. We predicted that if long term experience with dingoes enabled mainland bandicoots to recognise domestic dogs, then Tasmanian bandicoots, which are inexperienced with dingoes, would not recognise domestic dogs. Our results indicate that Tasmanian bandicoots are naïve to both dogs and cats after only 200 years of coexistence, supporting our hypothesis and the notion that naiveté in native prey towards alien predators (as observed on the mainland) may eventually be overcome.

Correlates of Recent Declines of Rodents in Northern and Southern Australia: Habitat Structure Is Critical.

Australia has experienced dramatic declines and extinctions of its native rodent species over the last 200 years, particularly in southern Australia. In the tropical savanna of northern Australia significant declines have occurred only in recent decades. The later onset of these declines suggests that the causes may differ from earlier declines in the south. We examine potential regional effects (northern versus southern Australia) on biological and ecological correlates of range decline in Australian rodents. We demonstrate that rodent declines have been greater in the south than in the tropical north, are strongly influenced by phylogeny, and are consistently greater for species inhabiting relatively open or sparsely vegetated habitat. Unlike in marsupials, where some species have much larger body size than rodents, body mass was not an important predictor of decline in rodents. All Australian rodent species are within the prey-size range of cats (throughout the continent) and red foxes (in the south). Contrary to the hypothesis that mammal declines are related directly to ecosystem productivity (annual rainfall), our results are consistent with the hypothesis that disturbances such as fire and grazing, which occur in non-rainforest habitats and remove cover used by rodents for shelter, nesting and foraging, increase predation risk. We agree with calls to introduce conservation management that limits the size and intensity of fires, increases fire patchiness and reduces grazing impacts at ecological scales appropriate for rodents. Controlling feral predators, even creating predator-free reserves in relatively sparsely-vegetated habitats, is urgently required to ensure the survival of rodent species, particularly in northern Australia where declines are not yet as severe as those in the south.

Habitat­ and rainfall­dependent biodiversity responses to cattle removal in an arid woodland­grassland environment.

Biodiversity conservation in rangeland environments is often addressed by removing livestock, but inconsistent responses by biota mean that the efficacy of this form of management is hotly debated. Reasons for this inconsistency include the usually short duration and small spatial scale of manipulations compared to the area of grazing properties, as well as divergent responses amongst biota. In low-productivity arid environments, the pulse-reserve dynamic also complicates the outcome of manipulations. Here, we tested and extended these ideas in a heterogeneous desert environment in central Australia that consists of small patches of open woodland (gidgee) in a grassland (spinifex) matrix. Taking advantage of a controlled property-scale removal of cattle, and a rain event that stimulated productivity, we first quantified differences in the vegetation and small vertebrates of these two habitats, and then tracked the diversity, composition, and abundance of these biota for 6­19 months post-rain. We predicted that the two habitats would differ in the structure, composition, and reproductive output of their constituent plant species. We predicted also that the effects of cattle removal would interact with these habitat differences, with the abundance, richness, and diversity of small mammals and reptiles differing across habitats and grazing treatments. As anticipated, plant species composition in woodland was distinct from that in grassland and varied over time. The effects of cattle removal were habitat specific: Plant composition responded to de-stocking in woodland, but not in grassland; flowers were more abundant, and palatable plant cover also was greater following cessation of grazing pressure. The responses of small mammals but not reptiles showed some accord with our predictions, varying over time but inconsistently with treatment, and perhaps reflected high variability in capture success. We conclude that the timing and length of sampling are important when evaluating the responses of biota to livestock removal, as is the inclusion of all key habitats in the sampling regime.

Interactions of grazing history, cattle removal and time since rain drive divergent short-term responses by desert biota.

Arid grasslands are used worldwide for grazing by domestic livestock, generating debate about how this pastoral enterprise may influence native desert biota. One approach to resolving this question is to experimentally reduce livestock numbers and measure the effects. However, a key challenge in doing this is that historical grazing impacts are likely to be cumulative and may therefore confound comparisons of the short-term responses of desert biota to changes in stocking levels. Arid areas are also subject to infrequent flooding rainfalls that drive productivity and dramatically alter abundances of flora and fauna. We took advantage of an opportunity to study the recent effects of a property-scale cattle removal on two properties with similarly varied grazing histories in central Australia. Following the removal of cattle in 2006 and before and after a significant rainfall event at the beginning of 2007, we sampled vegetation and small vertebrates on eight occasions until October 2008. Our results revealed significant interactions of time of survey with both grazing history and grazing removal for vascular plants, small mammals and reptiles. The mammals exhibited a three-way interaction of time, grazing history and grazing removal, thus highlighting the importance of careful sampling designs and timing for future monitoring. The strongest response to the cessation of grazing after two years was depressed reproductive output of plants in areas where cattle continued to graze. Our results confirm that neither vegetation nor small vertebrates necessarily respond immediately to the removal of livestock, but that rainfall events and cumulative grazing history are key determinants of floral and faunal performance in grassland landscapes with low and variable rainfall. We suggest that improved assessments could be made of the health of arid grazing environments if long-term monitoring were implemented to track the complex interactions that influence how native biota respond to grazing.