Context Animal and plant populations in arid regions fluctuate in size and extent in response to rainfall, fire and predation. Understanding the influence of these drivers on the status and trends of populations is crucial to implementing effective conservation actions.Aims In this study, we quantified the long-term drivers and trends in populations of a threatened lizard, the great desert skink (Liopholis kintorei; Tjakura), in the central and western deserts of Australia.Methods We collated 23 years (2002-2023) of active Tjakura burrow count data from 31 sites clustered in the following four regions: Yulara, Newhaven Wildlife Sanctuary, Uluru-Kata Tjuta National Park and Kiwirrkurra Indigenous Protected Area. We fitted a negative binomial regression model in a Bayesian framework to estimate trends in active burrow counts over time and quantified the effect of rainfall, mean annual normalised difference vegetation index (NDVI), time since fire and fire extent on active burrow counts.Key results Our results showed contrasting trends in Tjakura active burrow counts across the four regions. At Kiwirrkurra, Newhaven Wildlife Sanctuary and Yulara, active burrow counts increased consistently at rates of 35% (0.298; 95% CI 0.099-0.471), 18% (0.168; 95% CI 0.029, 0.314) and 5% per year (0.045; 95% CI 0.017, 0.073) respectively. In contrast, active burrow counts in Uluru-Kata Tjuta National Park increased from 2002 to 2012 before steadily decreasing. Across all sites, fire was the most important predictor of active Tjakura burrow counts, with a significant positive effect of time since fire (0.108; 95% CI 0.014-0.204) and a strong negative effect of fire extent in the previous year (-0.111; 95% CI -0.243 to -0.026).Conclusions Our results have highlighted the importance of delivering ongoing planned fire management programs that avoid burning vegetation directly at and around Tjakura burrow systems, while providing a patch mosaic across the surrounding landscape.Implications We recommend that monitoring of Tjakura burrows be standardised across regions and that site covariates, especially measures of predation pressure, be monitored to further understand drivers of population trends.

Biodiversity monitoring programmes should be designed with sufficient statistical power to detect population change. Here we evaluated the statistical power of monitoring to detect declines in the occupancy of forest birds on Christmas Island, Australia. We fitted zero-inflated binomial models to 3 years of repeat detection data (2011, 2013 and 2015) to estimate single-visit detection probabilities for four species of concern: the Christmas Island imperial pigeon Ducula whartoni, Christmas Island white-eye Zosterops natalis, Christmas Island thrush Turdus poliocephalus erythropleurus and Christmas Island emerald dove Chalcophaps indica natalis. We combined detection probabilities with maps of occupancy to simulate data collected over the next 10 years for alternative monitoring designs and for different declines in occupancy (10–50%). Specifically, we explored how the number of sites (60, 128, 300, 500), the interval between surveys (1–5 years), the number of repeat visits (2–4 visits) and the location of sites influenced power. Power was high (> 80%) for the imperial pigeon, white-eye and thrush for most scenarios, except for when only 60 sites were surveyed or a 10% decline in occupancy was simulated over 10 years. For the emerald dove, which is the rarest of the four species and has a patchy distribution, power was low in almost all scenarios tested. Prioritizing monitoring towards core habitat for this species only slightly improved power to detect declines. Our study demonstrates how data collected during the early stages of monitoring can be analysed in simulation tools to fine-tune future survey design decisions.

Targeted gene flow is an emerging conservation approach which involves introducing a cohort of individuals with particular traits to locations where they can produce a conservation benefit. This technique is being proposed to adapt recipient populations to a known threat, but questions remain surrounding how best to maximize conservation outcomes during periods of continuous directional environmental change. Here we introduce a new management objective—to keep the recipient population extant and with maximum diversity of local alleles—and we explore how varying the timing and size of an introduction can maximise this objective. Our results reveal a trade-off between keeping a population extant and maintaining a high level of genetic diversity, but management levers can often optimize this so that nearly 100% of the allelic diversity is preserved. These optimum outcomes sets are highly sensitive to the predicted rate of environmental shift, as well as the level of outbreeding depression in the system.

Large-scale disturbance events are forecast to increase in severity and frequency due to climate change. Onground surveys are crucial for assessing the immediate impact of disturbances on biodiversity and for informing management responses. However, there are few examples where quantitative tools have guided postdisturbance survey design. In this study, we integrated species distribution modelling and spatial prioritisation to identify taxonomic and spatial gaps in surveys for 92 priority vertebrates 6 months after the 2019-20 wildfires in Australia. We predicted the pre-fire distribution of priority species, mapped locations of post-wildfire surveys that were already underway, and integrated this information with remotely-sensed fire severity maps in the tool, Zonation, to prioritise locations for new surveys across three fire severity classes (unburnt, low severity, high severity). Our results suggest that 6 months after the wildfires, surveys by government agencies had targeted 17 of 20 mammals (85%); 11 of 17 birds (65%); 10 of 17 frogs (59%); 10 of 23 reptiles (43%) and 5 of 17 fish (29%). We developed species distribution models for 63 of these species after collating 120,118 occurrence records from 6 data repositories. By predicting their distribution before the wildfires, we most efficiently identified gaps in survey effort while ensuring representation across species and fire severity classes. Our analysis provided an important `stocktake' of the response effort to the 2019-20 wildfires in Australia and helped inform the allocation of government-funded wildfire recovery programs. Although we focus on wildfire, our approach could assess gaps in survey effort following any large-scale disturbance.

Aim Megafire plays a crucial role in driving the distribution of biodiversity around the world. Long-term monitoring is vital for understanding how species are impacted immediately by megafire and subsequently respond over time. However, monitoring should be designed with sufficient statistical power to detect impact and recovery. In this study, we developed a simulation framework for optimizing the design of biodiversity monitoring programmes to detect population recoveries after megafire. Location Victoria, Australia. Time period 2019-2020. Major taxa studied Vertebrates. Methods We collated species distribution models for 45 priority vertebrates most likely to respond to management after the 2019-2020 megafires in Victoria, Australia. We combined these models with fire severity maps to optimize the location of monitoring sites in and around the fire footprint. We simulated the impact of the megafires on species distributions and modelled plausible recoveries over the next 10 years. Using estimates of detectability for a suite of preferred sampling methods, we simulated monitoring at pairs of burnt and unburnt sites to evaluate the statistical power to detect the modelled recoveries. We tested the sensitivity of power to alternative monitoring designs, rates of recovery and monitoring budgets. Results Priority regions to establish monitoring sites varied by taxonomic group. Power to detect population recoveries increased as the monitoring budget increased, as the recovery rate increased and when the proportion of sites in burnt compared with unburnt habitat increased. According to the optimal monitoring design, an AUD $9M budget could detect 90% of recoveries to pre-fire levels in 40% of species with >80% power. Power was highest for mammals, followed by birds, reptiles and amphibians. Main conclusions Our simulation approach allowed us to test the relative performance of alternative post-fire monitoring designs ahead of time. Although we focused on megafire, our approach could easily be applied to detect population recoveries after any large-scale catastrophic disturbance.

The arrival of novel predators can trigger trophic cascades driven by shifts in prey numbers. Predators also elicit behavioral change in prey populations, via phenotypic plasticity and/or rapid evolution, and such changes may also contribute to trophic cascades. Here, we document rapid demographic and behavioral changes in populations of a prey species (grassland melomys Melomys burtoni, a granivorous rodent) following the introduction of a novel marsupial predator (northern quoll Dasyurus hallucatus). Within months of quolls appearing, populations of melomys exhibited reduced survival and population declines relative to control populations. Quoll-invaded populations were also significantly shyer than nearby, quoll-free populations of conspecifics. This rapid but generalized response to a novel threat was replaced over the following 2 yr with more threat-specific antipredator behaviors (i.e., predator-scent aversion). Predator-exposed populations, however, remained more neophobic than predator-free populations throughout the study. These behavioral responses manifested rapidly in changed rates of seed predation by melomys across treatments. Quoll-invaded melomys populations exhibited lower per-capita seed take rates, and rapidly developed an avoidance of seeds associated with quoll scent, with discrimination playing out over a spatial scale of tens of meters. Presumably the significant and novel predation pressure induced by quolls drove melomys populations to fine-tune behavioral responses to be more predator specific through time. These behavioral shifts could reflect individual plasticity (phenotypic flexibility) in behavior or may be adaptive shifts from natural selection imposed by quoll predation. Our study provides a rare insight into the rapid ecological and behavioral shifts enacted by prey to mitigate the impacts of a novel predator and shows that trophic cascades can be strongly influenced by behavioral as well as numerical responses.

Photo 1. Authors Ben Phillips and John Moreen releasing the first batch of northern quolls (Dasyurus hallucatus) on Indian Island (Kabarl), Northern Territory, Australia. This project was a collaborative effort between several stakeholders, including the Flora and Fauna Division, Department of Environment and Natural Resources, Northern Territory Government, the Territory Wildlife Park, Northern Territory Government, and Kenbi Rangers. The study was conducted on Kenbi country with permission from and in collaboration with the Kenbi Traditional Owners (Raylene and Zoe Sigh) and the assistance of Kenbi Rangers. Photo credit: Chris Jolly. Photo 2. Male northern quoll (Dasyurus hallucatus) fitted with a radio-collar immediately following release on Indian Island (Kabarl), Northern Territory, Australia. Photo credit: Chris Jolly. Photo 3. Beach on northern Indian Island (Kabarl) covered in northern quoll (Dasyurus hallucatus) prints in the months following their introduction in 2017. Photo credit: Chris Jolly. These photographs illustrate the article “Trophic cascade driven by behavioral fine-tuning as naïve prey rapidly adjust to a novel predator” by C. J. Jolly, A. S. Smart, J. Moreen, J. K. Webb, G. R. Gillespie, and B. L. Phillips published in Ecology. https://doi.org/10.1002/ecy.3363.

SummaryIslands are increasingly used to protect endangered populations from the negative impacts of invasive species. Quarantine efforts are particularly likely to be undervalued in circumstances where a failure incurs non-economic costs. One approach to ascribe value to such efforts is by modeling the expense of restoring a system to its former state.Using field-based removal experiments on two very different islands off northern Australia separated by > 400 km, we estimate cane toad densities, detection probabilities, and the resulting effort needed to eradicate toads from an island, and use these estimates to examine the financial benefit of cane toad quarantine across offshore islands prioritized for conversation management by the Australian federal government.We calculate density as animals per km of freshwater shoreline, and find striking concordance of density across our two island study sites: a mean density of 353 [286, 446] individual toads per kilometer on one island, and a density of 366 [319, 343] on the second. Detection probability differed between the two islands.Using a removal model and the financial costs incurred during toad removal, we estimate that eradicating cane toads would, on average, cost between $9444 (based on Horan Island; high detectability) and $18093 AUD (Indian Island; low detectability) per km of available freshwater shoreline.Across islands that have been prioritized for conservation benefit within the toads’ predicted range, we provide an estimate of the value of toad quarantine on each island, and estimate the net value of quarantine efforts to be between $27.25 – $52.20 Million AUD. We explore a proposed mainland cane toad containment strategy – to prevent the spread of cane toads into the Pilbara Bioregion, and estimate its potential value to be between $33.79 – $64.74 M AUD.Synthesis and applications. We present a modelling framework that can be used to estimate the value of preventative management, via estimating the length and cost of an eradication program. Our analyses suggest that there is substantial economic value in cane toad quarantine efforts across Australian offshore islands and a proposed mainland toad containment strategy.

Targeted gene flow is a novel conservation strategy that involves translocating individuals with favourable genes to areas where they will have a conservation benefit. One oft-cited risk of the strategy is the potential for outbreeding depression. Here, we used the northern quoll (Dasyurus hallucatus) as a model to test this possibility for the first time in a field setting. Northern quolls are endangered by the spread of the invasive cane toad (Rhinella marina), which they are fatally poisoned by, if they mistakenly attempt to consume them. There are, however, a small number of quolls that are “toad-smart”—they possess a heritable trait that means they innately do not attack toads. It is this trait we hoped to promote through targeted gene flow. We established a hybrid population (54 toad-smart and toad-naïve northern quolls) and introduced this population onto a small offshore, toad-infested island in 2017. Genetic data suggests an increase in the toad-smart proportion of the genome increasing from 29.4% in the release population to 40.2% in the first island generation (F2). Our data demonstrate successful in situ hybridisation between populations, with viable F2 hybrids and backcrosses observed, and some evidence of heterosis (hybrid vigour) in F1 hybrids. The population experienced significant reductions in size over the two years, however, through a combination of toad-mortality, as well as stochastic processes including fire, a cyclone, predation and ineffective breeding, and so small sample sizes hamper our results. Such establishment problems would not occur were we to attempt targeted gene flow into already established quoll populations, and our observation of successful hybridisation suggests targeted gene flow could be a viable strategy in established quoll populations soon to be impacted by toads.

Islands are increasingly used to protect endangered populations from the negative impacts of invasive species. Quarantine efforts on islands are typically undervalued, however. Using a field-based removal experiment, we estimate the economic value of quarantine efforts aimed at keeping invasive cane toads (Rhinella marina) off Australian islands. We estimate a mean density of 3444 [2744, 4386] individual toads per km2 and a mean per-night detection probability of 0.1 [0.07,0.13]. Using a removal model and estimates of economic costs incurred during toad removal, we estimate that eradicating cane toads would cost AUD$96,556 per km2. Across islands that have been prioritized for conservation benefit across the toads predicted range, we estimate the remaining value of toad quarantine to be more than $1.3 billion. The value of a proposed waterless barrier on the mainland to prevent the spread of toads into the Pilbara was in excess of $26 billion. We conclude that quarantine of toads across Australia provides substantial value in prevented eradication costs.

Summary Environmental DNA (eDNA) sampling can be a highly sensitive method for detecting aquatic taxa; however, the cost‐efficiency of this technique relative to traditional methods has not been rigorously assessed. We show how methods that account for imperfect and stochastic detection can be used to (i) determine the optimal allocation of survey effort with eDNA sampling for a fixed budget (i.e. identify the optimal combination of water samples vs. site visits), and (ii) assess the cost‐efficiency of eDNA sampling relative to traditional survey techniques. We illustrate this approach by comparing eDNA sampling and bottle‐trapping for an exotic newt species (Lissotriton v. vulgaris) recently detected in Melbourne, Australia. Bottle traps produced much lower detection rates than eDNA sampling, but the cost‐efficiency of the two methods can be similar because bottle‐trapping is cheaper per sample. The relative cost‐efficiency of the two sampling methods was sensitive to the available survey budget, the costs of eDNA primer/probe development and sample processing and the number of positive quantitative PCR assays (qPCRs) used to designate a water sample as positive for newt DNA. Environmental DNA sampling was more cost‐efficient than bottle‐trapping for small to intermediate budgets when primer/probe development and sample processing costs were low, and 1/4 or 2/4 positive qPCRs were used to label a water sample as positive for newt eDNA. However, bottle traps were generally more cost‐efficient than eDNA sampling when primer/probe development and sample processing costs were high, regardless of qPCR threshold or survey budget. Traditional sampling methods may achieve lower detection probabilities compared to eDNA sampling, but the totality of costs can make eDNA sampling less efficient than traditional techniques in some circumstances. Our approach provides a quantitative framework for determining how many water samples and site visits are required to maximize detection probabilities with eDNA sampling, and can calculate the cost‐efficiency of any sampling method.

21 1. Environmental DNA (eDNA) sampling can be a highly sensitive method for detecting aquatic taxa; 22 however, the cost-efficiency of this technique relative to traditional methods has not been rigorously 23 assessed. 24 2. We show how methods that account for imperfect and stochastic detection can be used to: (i) 25 determine the optimal allocation of survey effort with eDNA sampling for a fixed budget (i.e., 26 identify the optimal combination of water samples vs. site visits); and (ii) assess the cost-efficiency of 27 eDNA sampling relative to traditional survey techniques. We illustrate this approach by comparing 28 eDNA sampling and bottle-trapping for an exotic newt species (Lissotriton v. vulgaris) recently 29 detected in Melbourne, Australia. 30 3. Bottle traps produced much lower detection rates than eDNA sampling, but the cost-efficiency of 31 the two methods can be similar because bottle-trapping is cheaper per sample. The relative cost32 efficiency of the two sampling methods was sensitive to the available survey budget, the costs of 33 eDNA primer/probe development and sample processing, and the number of positive quantitative 34 PCR assays (qPCRs) used to designate a water sample as positive for newt DNA. Environmental 35 DNA sampling was more cost-efficient than bottle-trapping for small-intermediate budgets when 36 primer/probe development and sample processing costs were low, and 1/4 or 2/4 positive qPCRs was 37 used to label a water sample as positive for newt eDNA. However, bottle traps were generally more 38 cost-efficient than eDNA sampling when primer/probe development and sample processing costs 39 were high, regardless of qPCR threshold or survey budget. 40 4. Traditional sampling methods may achieve lower detection probabilities compared to eDNA 41 sampling, but the totality of costs can make eDNA sampling less efficient than traditional techniques 42 in some circumstances. Our approach provides a quantitative framework for determining how many 43 water samples and site visits are required to maximize detection probabilities with eDNA sampling, 44 and can calculate the cost-efficiency of any sampling method. 45 46

We document the successful establishment of a European newt (Lissotriton vulgaris) in south-eastern Australia, the first recorded case of a caudate species establishing beyond its native geographic range in the southern hemisphere. Field surveys in south-eastern Australia detected L. vulgaris at six sites, including four sites where the species had been detected 15 months earlier. Larvae were detected at three sites. Individuals had identical NADH dehydrogenase subunit 2 and cytb mtDNA gene sequences, and comparisons with genetic data from the species' native range suggest that these individuals belong to the nominal subspecies L. v. vulgaris. Climatic conditions across much of southern Australia are similar to those experienced within the species' native range, suggesting scope for substantial range expansion. Lissotriton vulgaris had been available in the Australian pet trade for decades before it was declared a 'controlled pest animal' in 1997, and thus the invasion documented here likely originated via the release or escape of captive animals. Lissotriton vulgaris is the sole member of an entire taxonomic order to have established in Australia, and given the potential toxicity of this species, further work is needed to delimit its current range and identify potential biodiversity impacts.

Effective management of alien species requires detecting populations in the early stages of invasion. Environmental DNA (eDNA) sampling can detect aquatic species at relatively low densities, but few studies have directly compared detection probabilities of eDNA sampling with those of traditional sampling methods. We compare the ability of a traditional sampling technique (bottle trapping) and eDNA to detect a recently established invader, the smooth newt Lissotriton vulgaris vulgaris, at seven field sites in Melbourne, Australia. Over a four-month period, per-trap detection probabilities ranged from 0.01 to 0.26 among sites where L. v. vulgaris was detected, whereas per-sample eDNA estimates were much higher (0.29-1.0). Detection probabilities of both methods varied temporally (across days and months), but temporal variation appeared to be uncorrelated between methods. Only estimates of spatial variation were strongly correlated across the two sampling techniques. Environmental variables (water depth, rainfall, ambient temperature) were not clearly correlated with detection probabilities estimated via trapping, whereas eDNA detection probabilities were negatively correlated with water depth, possibly reflecting higher eDNA concentrations at lower water levels. Our findings demonstrate that eDNA sampling can be an order of magnitude more sensitive than traditional methods, and illustrate that traditional- and eDNA-based surveys can provide independent information on species distributions when occupancy surveys are conducted over short timescales.