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Irruption of herbivore populations due to the extirpation of predators has led to dramatic changes in ecosystem functioning worldwide. Herbivores compete with other species for their primary source of nutrition, plant biomass. Such competition is typically considered to occur between species in closely related clades and functional groups but could also occur with detritivores that consume senescent plant biomass. In this study, we tested predictions that in ecosystems where herbivores are not regulated by predators, their indirect impacts on dead vegetation increase with primary productivity and extend to termites that feed on senescent vegetation. We compared dead vegetation cover and termite activity in herbivore exclosures and associated grazed plots at three locations situated along a rainfall gradient in arid Australia where kangaroo populations have irrupted. Dead vegetation cover and termite activity increased with rainfall in ungrazed plots but showed a negligible response to rainfall in grazed plots. Our results suggest that grazing can disrupt the flow of energy to detritivores and decouple the relationship between termite activity and primary productivity. Such disruption could have far-reaching impacts on arid ecosystems because many organisms sit within "brown food webs" that are sustained by energy derived from the decomposition of senescent plant tissues., (© 2023 The Authors. Ecology published by Wiley Periodicals LLC on behalf of The Ecological Society of America.)

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., (© 2020 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Apex predators can have substantial and complex ecological roles in ecosystems. However, differences in species-specific traits, population densities, and interspecific interactions are likely to determine the strength of apex predators' roles. Here we report complementary studies examining how interactions between predator per capita metabolic rate and population density influenced the biomass, population energy use, and ecological effects of apex predators on their large mammalian prey. We first investigated how large mammal prey resources and field metabolic rates of terrestrial apex predators, comprising large mammals and the Komodo dragon (Varanus komodoensis), influenced their biomass densities and population energy use requirements. We next evaluated whether Komodo dragons, like apex mammalian predators, exerted top-down regulation of their large mammal prey. Comparison of results from field studies demonstrates that Komodo dragons attain mean population biomass densities that are 5.75-231.82 times higher than that of apex mammalian predator species and their guilds in Africa, Asia, and North America. The high biomass of Komodo dragons resulted in 1.96-108.12 times greater population energy use than that of apex mammalian predators. Nevertheless, substantial temporal and spatial variation in Komodo dragon population energy use did not regulate the population growth rates of either of two large mammal prey species, rusa deer (Rusa timorensis) and wild pig (Sus scrofa). We suggest that multiple processes weaken the capacity of Komodo dragons to regulate large mammal prey populations. For example, a low per capita metabolic rate requiring an infrequent and inactive hunting strategy (including scavenging), would minimize lethal and nonlethal impacts on prey populations. We conclude that Komodo dragons differ in their predatory role from, including not being the ecological analogs of, apex mammalian predators., (© 2020 by the Ecological Society of America.)

Rewilding is increasingly recognized as a conservation tool but is often context specific, which inhibits broad application. Rewilding in Australia seeks to enhance ecosystem function and promote self-sustaining ecosystems. An absence of large-bodied native herbivores means trophic rewilding in mainland Australia has focused on the restoration of functions provided by apex predators and small mammals. Because of the pervasive influence of introduced mesopredators, predator-proof fences, and establishment of populations on predator-free islands are common rewilding approaches. This sets Australian rewilding apart from most jurisdictions and provides globally relevant insights but presents challenges to restoring function to broader landscapes. Passive rewilding is of limited utility in arid zones. Although increasing habitat extent and quality in mesic coastal areas may work, it will likely be necessary to undertake active management. Because much of Australia's population is in urban areas, rewilding efforts must include urban areas to maximize effectiveness. Thus rewilding is not synonymous with wilderness and can occur over multiple scales. Rewilding efforts must recognize human effects on other species and benefit both nature and humans. Rewilding in Australia requires development of a shared vision and strategy and proof-of-concept projects to demonstrate the benefits. The repackaging of existing conservation activities as rewilding may confuse and undermine the success of rewilding programs and should be avoided. As elsewhere, rewilding in Australia should be viewed as an important conservation tool., (© 2019 Society for Conservation Biology.)

It is widely assumed that organisms at low trophic levels, particularly microbes and plants, are essential to basic services in ecosystems, such as nutrient cycling. In theory, apex predators' effects on ecosystems could extend to nutrient cycling and the soil nutrient pool by influencing the intensity and spatial organization of herbivory. Here, we take advantage of a long-term manipulation of dingo abundance across Australia's dingo-proof fence in the Strzelecki Desert to investigate the effects that removal of an apex predator has on herbivore abundance, vegetation and the soil nutrient pool. Results showed that kangaroos were more abundant where dingoes were rare, and effects of kangaroo exclusion on vegetation, and total carbon, total nitrogen and available phosphorus in the soil were marked where dingoes were rare, but negligible where dingoes were common. By showing that a trophic cascade resulting from an apex predator's lethal effects on herbivores extends to the soil nutrient pool, we demonstrate a hitherto unappreciated pathway via which predators can influence nutrient dynamics. A key implication of our study is the vast spatial scale across which apex predators' effects on herbivore populations operate and, in turn, effects on the soil nutrient pool and ecosystem productivity could become manifest., (© 2017 The Author(s).)

Reports of positive or neutral effects of grazing on plant species richness have prompted calls for livestock grazing to be used as a tool for managing land for conservation. Grazing effects, however, are likely to vary among different response variables, types, and intensity of grazing, and across abiotic conditions. We aimed to examine how grazing affects ecosystem structure, function, and composition. We compiled a database of 7615 records reporting an effect of grazing by sheep and cattle on 278 biotic and abiotic response variables for published studies across Australia. Using these data, we derived three ecosystem measures based on structure, function, and composition, which were compared against six contrasts of grazing pressure, ranging from low to heavy, two different herbivores (sheep, cattle), and across three different climatic zones. Grazing reduced structure (by 35%), function (24%), and composition (10%). Structure and function (but not composition) declined more when grazed by sheep and cattle together than sheep alone. Grazing reduced plant biomass (40%), animal richness (15%), and plant and animal abundance, and plant and litter cover (25%), but had no effect on plant richness nor soil function. The negative effects of grazing on plant biomass, plant cover, and soil function were more pronounced in drier environments. Grazing effects on plant and animal richness and composition were constant, or even declined, with increasing aridity. Our study represents a comprehensive continental assessment of the implications of grazing for managing Australian rangelands. Grazing effects were largely negative, even at very low levels of grazing. Overall, our results suggest that livestock grazing in Australia is unlikely to produce positive outcomes for ecosystem structure, function, and composition or even as a blanket conservation tool unless reduction in specific response variables is an explicit management objective.

Ontogenetic allometries in ecological habits and niche use are key responses by which individuals maximize lifetime fitness. Moreover, such allometries have significant implications for how individuals influence population and community dynamics. Here, we examined how body size variation in Komodo dragons (Varanus komodoensis) influenced ecological allometries in their: (1) prey size preference, (2) daily movement rates, (3) home range area, and (4) subsequent niche use across ontogeny. With increased body mass, Komodo dragons increased prey size with a dramatic switch from small (≤10 kg) to large prey (≥50 kg) in lizards heavier than 20 kg. Rates of foraging movement were described by a non-linear concave down response with lizard increasing hourly movement rates up until ∼20 kg body mass before decreasing daily movement suggesting reduced foraging effort in larger lizards. In contrast, home range area exhibited a sigmoid response with increased body mass. Intrapopulation ecological niche use and overlap were also strongly structured by body size. Thus, ontogenetic allometries suggest Komodo dragon's transition from a highly active foraging mode exploiting small prey through to a less active sit and wait feeding strategy focused on killing large ungulates. Further, our results suggest that as body size increases across ontogeny, the Komodo dragon exhibited marked ontogenetic niche shifts that enabled it to function as an entire vertebrate predator guild by exploiting prey across multiple trophic levels.

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.

Large carnivores face serious threats and are experiencing massive declines in their populations and geographic ranges around the world. We highlight how these threats have affected the conservation status and ecological functioning of the 31 largest mammalian carnivores on Earth. Consistent with theory, empirical studies increasingly show that large carnivores have substantial effects on the structure and function of diverse ecosystems. Significant cascading trophic interactions, mediated by their prey or sympatric mesopredators, arise when some of these carnivores are extirpated from or repatriated to ecosystems. Unexpected effects of trophic cascades on various taxa and processes include changes to bird, mammal, invertebrate, and herpetofauna abundance or richness; subsidies to scavengers; altered disease dynamics; carbon sequestration; modified stream morphology; and crop damage. Promoting tolerance and coexistence with large carnivores is a crucial societal challenge that will ultimately determine the fate of Earth's largest carnivores and all that depends upon them, including humans.

Recent advances highlight the potential for predators to restore ecosystems and confer resilience against globally threatening processes, including climate change and biological invasions. However, releasing the ecological benefits of predators entails significant challenges. Here, we discuss the economic, environmental and social considerations affecting predator-driven ecological restoration programmes, and suggest approaches for reducing the undesirable impacts of predators. Because the roles of predators are context dependent, we argue for increased emphasis on predator functionality in ecosystems and less on the identities and origins of species and genotypes. We emphasise that insufficient attention is currently given to the importance of variation in the social structures and behaviours of predators in influencing the dynamics of trophic interactions. Lastly, we outline experiments specifically designed to clarify the ecological roles of predators and their potential utility in ecosystem restoration., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Many biological invasions do not occur as a gradual expansion along a continuous front, but result from the expansion of satellite populations that become established at 'invasion hubs'. Although theoretical studies indicate that targeting control efforts at invasion hubs can effectively contain the spread of invasions, few studies have demonstrated this in practice. In arid landscapes worldwide, humans have increased the availability of surface water by creating artificial water points (AWPs) such as troughs and dams for livestock. By experimentally excluding invasive cane toads (Bufo marinus) from AWP, we show that AWP provide a resource subsidy for non-arid-adapted toads and serve as dry season refuges and thus invasion hubs for cane toads in arid Australia. Using data on the distribution of permanent water in arid Australia and the dispersal potential of toads, we predict that systematically excluding toads from AWP would reduce the area of arid Australia across which toads are predicted to disperse and colonize under average climatic conditions by 38 per cent from 2,242,000 to 1,385,000 km(2). Our study shows how human modification of hydrological regimes can create a network of invasion hubs that facilitates a biological invasion, and confirms that targeted control at invasion hubs can reduce landscape connectivity to contain the spread of an invasive vertebrate.

Resources are produced in pulses in many terrestrial environments, and have important effects on the population dynamics and assemblage structure of animals that consume them. Resource-pulsing is particularly dramatic in Australian desert environments owing to marked spatial and temporal variability in rainfall, and thus primary productivity. Here, we first review how Australia's desert mammals respond to fluctuations in resource production, and evaluate the merits of three currently accepted models (the ecological refuge, predator refuge and fire-mosaic models) as explanations of the observed dynamics. We then integrate elements of these models into a novel state-and-transition model and apply it to well-studied small mammal assemblages that inhabit the vast hummock grassland, or spinifex, landscapes of the continental inland. The model has four states that are defined by differences in species composition and abundance, and eight transitions or processes that prompt shifts from one state to another. Using this model as a template, we construct three further models to explain mammalian dynamics in cracking soil habitats of the Lake Eyre Basin, gibber plains of the Channel Country, and the chenopod shrublands of arid southern Australia. As non-equilibrium concepts that recognise the strongly intermittent nature of resource pulsing in arid Australia, state-and-transition models provide useful descriptors of both spatial and temporal patterns in mammal assemblages. The models should help managers to identify when and where to implement interventions to conserve native mammals, such as control burns, reduced grazing or predator management. The models also should improve understanding of the potential effects of future climate change on mammal assemblages in arid environments in general. We conclude by proposing several tests that could be used to refine the models and guide further research.

It has been demonstrated repeatedly that the degree to which regulation operates and the magnitude of environmental variation in an exploited population will together dictate the type of sustainable harvest achievable. Yet typically, harvest models fail to incorporate uncertainty in the underlying dynamics of the target population by assuming a particular (unknown) form of endogenous control. We use a novel approach to estimate the sustainable yield of saltwater crocodile (Crocodylus porosus) populations from major river systems in the Northern Territory, Australia, as an example of a system with high uncertainty. We used multimodel inference to incorporate three levels of uncertainty in yield estimation: (1) uncertainty in the choice of the underlying model(s) used to describe population dynamics, (2) the error associated with the precision and bias of model parameter estimation, and (3) environmental fluctuation (process error). We demonstrate varying strength of evidence for density regulation (1.3-96.7%) for crocodiles among 19 river systems by applying a continuum of five dynamical models (density-independent with and without drift and three alternative density-dependent models) to time series of density estimates. Evidence for density dependence increased with the number of yearly transitions over which each river system was monitored. Deterministic proportional maximum sustainable yield (PMSY) models varied widely among river systems (0.042-0.611), and there was strong evidence for an increasing PMSY as support for density dependence rose. However, there was also a large discrepancy between PMSY values and those produced by the full stochastic simulation projection incorporating all forms of uncertainty, which can be explained by the contribution of process error to estimates of sustainable harvest. We also determined that a fixed-quota harvest strategy (up to 0.2K, where K is the carrying capacity) reduces population size much more rapidly than proportional harvest (the latter strategy requiring temporal monitoring of population size to adjust harvest quotas) and greatly inflates the risk of resource depletion. Using an iconic species recovering from recent extreme overexploitation to examine the potential for renewed sustainable harvest, we have demonstrated that incorporating major forms of uncertainty into a single quantitative framework provides a robust approach to modeling the dynamics of exploited populations.