Search

Large terrestrial mammals increasingly rely on human‐modified landscapes as anthropogenic footprints expand. Land management activities such as timber harvest, agriculture, and roads can influence prey population dynamics by altering forage resources and predation risk via changes in habitat, but these effects are not well understood in regions with diverse and changing predator guilds. In northeastern Washington state, USA, white‐tailed deer (Odocoileus virginianus) are vulnerable to multiple carnivores, including recently returned gray wolves (Canis lupus), within a highly human‐modified landscape. To understand the factors governing predator–prey dynamics in a human context, we radio‐collared 280 white‐tailed deer, 33 bobcats (Lynx rufus), 50 cougars (Puma concolor), 28 coyotes (C. latrans), and 14 wolves between 2016 and 2021. We first estimated deer vital rates and used a stage‐structured matrix model to estimate their population growth rate. During the study, we observed a stable to declining deer population (lambda = 0.97, 95% confidence interval: 0.88, 1.05), with 74% of Monte Carlo simulations indicating population decrease and 26% of simulations indicating population increase. We then fit Cox proportional hazard models to evaluate how predator exposure, use of human‐modified landscapes, and winter severity influenced deer survival and used these relationships to evaluate impacts on overall population growth. We found that the population growth rate was dually influenced by a negative direct effect of apex predators and a positive effect of timber harvest and agricultural areas. Cougars had a stronger effect on deer population dynamics than wolves, and mesopredators had little influence on the deer population growth rate. Areas of recent timber harvest had 55% more forage biomass than older forests, but horizontal visibility did not differ, suggesting that timber harvest did not influence predation risk. Although proximity to roads did not affect the overall population growth rate, vehicle collisions caused a substantial proportion of deer mortalities, and reducing these collisions could be a win–win for deer and humans. The influence of apex predators and forage indicates a dual limitation by top‐down and bottom‐up factors in this highly human‐modified system, suggesting that a reduction in apex predators would intensify density‐dependent regulation of the deer population owing to limited forage availability. [ABSTRACT FROM AUTHOR]

Ocean warming and species exploitation have already caused large‐scale reorganization of biological communities across the world. Accurate projections of future biodiversity change require a comprehensive understanding of how entire communities respond to global change. We combined a time‐dynamic integrated food web modeling approach (Ecosim) with previous data from community‐level mesocosm experiments to determine the independent and combined effects of ocean warming, ocean acidification and fisheries exploitation on a well‐managed temperate coastal ecosystem. The mesocosm parameters enabled important physiological and behavioral responses to climate stressors to be projected for trophic levels ranging from primary producers to top predators, including sharks. Through model simulations, we show that under sustainable rates of fisheries exploitation, near‐future warming or ocean acidification in isolation could benefit species biomass at higher trophic levels (e.g., mammals, birds, and demersal finfish) in their current climate ranges, with the exception of small pelagic fishes. However, under warming and acidification combined, biomass increases at higher trophic levels will be lower or absent, while in the longer term reduced productivity of prey species is unlikely to support the increased biomass at the top of the food web. We also show that increases in exploitation will suppress any positive effects of human‐driven climate change, causing individual species biomass to decrease at higher trophic levels. Nevertheless, total future potential biomass of some fisheries species in temperate areas might remain high, particularly under acidification, because unharvested opportunistic species will likely benefit from decreased competition and show an increase in biomass. Ecological indicators of species composition such as the Shannon diversity index decline under all climate change scenarios, suggesting a trade‐off between biomass gain and functional diversity. By coupling parameters from multilevel mesocosm food web experiments with dynamic food web models, we were able to simulate the generative mechanisms that drive complex responses of temperate marine ecosystems to global change. This approach, which blends theory with experimental data, provides new prospects for forecasting climate‐driven biodiversity change and its effects on ecosystem processes. [ABSTRACT FROM AUTHOR]

Viral nervous necrosis (viral encephalopathy and retinopathy) is caused by piscine nodavirus (Nodaviridae, Betanodavirus). Since 1986, this highly infectious virus has caused mass mortalities of up to 100% in farmed saltwater and freshwater fish around the world (with the exception of South America and Antarctica), affecting >60 species across 10 orders. The Atlantic blue marlin (Makaira nigricans Lacépède, 1802) is a top-level predator found throughout the tropical waters of the Atlantic and Indo-Pacific oceans. Despite their popularity as a sportfish, relatively little is known about the Atlantic blue marlin and other billfish. We describe here chronic betanodavirus infection in a juvenile Atlantic blue marlin, which is, to our knowledge, the first report of disease in M. nigricans. [ABSTRACT FROM AUTHOR]

The Giant Sea Bass is an apex predator of southern California kelp forests that historically supported large commercial and recreational fisheries but whose population was drastically reduced due to overfishing. Although regulations have been in place to protect Giant Sea Bass for over 30 years, there is concern for continued allowance of their incidental take in commercial gill net fisheries. Through landing records, logbooks, and federal observer data, we examined the commercial take of Giant Sea Bass to determine the: magnitude, location, age, and disposition of catch; whether this take was incidental or targeted; and its impact on the current population. We found that Giant Sea Bass landings declined since gill netting was banned in state waters in 1994 and their overall landings decreased by 75% since becoming protected in 1981. Over time, a greater proportion of older fish was seen in the landings with an increase in mature individuals over 13 years of age since 2000. We found no evidence that commercial fishers are targeting Giant Sea Bass. On average, Giant Sea Bass were landed on 4.2% of gill net trips from 1994 to 2021. Additionally, over the past decade the majority of Giant Sea Bass landings came from only 15 permit holders, but this made up only ~2% of their total landings in pounds as these are the most active permittees, bringing in the highest landings of White Seabass or California Halibut. Assessing gill net observer data, we found the mortality of released Giant Sea Bass is high at 72%, although despite this level of mortality, multiple fishery independent sources indicate Giant Sea Bass populations are increasing, suggesting that current protection measures may be effective. Despite these findings, it is challenging to interpret the full impact of the commercial fishery on Giant Sea Bass as an accurate measure of total discards is unknown without consistent observer coverage. [ABSTRACT FROM AUTHOR]

Kill rates are a central parameter to assess the impact of predation on prey species. An accurate estimation of kill rates requires a correct identification of kill sites, often achieved by field‐checking GPS location clusters (GLCs). However, there are potential sources of error included in kill‐site identification, such as failing to detect GLCs that are kill sites, and misclassifying the generated GLCs (e.g., kill for nonkill) that were not field checked. Here, we address these two sources of error using a large GPS dataset of collared Eurasian lynx (Lynx lynx), an apex predator of conservation concern in Europe, in three multiprey systems, with different combinations of wild, semidomestic, and domestic prey. We first used a subsampling approach to investigate how different GPS‐fix schedules affected the detection of GLC‐indicated kill sites. Then, we evaluated the potential of the random forest algorithm to classify GLCs as nonkills, small prey kills, and ungulate kills. We show that the number of fixes can be reduced from seven to three fixes per night without missing more than 5% of the ungulate kills, in a system composed of wild prey. Reducing the number of fixes per 24 h decreased the probability of detecting GLCs connected with kill sites, particularly those of semidomestic or domestic prey, and small prey. Random forest successfully predicted between 73%–90% of ungulate kills, but failed to classify most small prey in all systems, with sensitivity (true positive rate) lower than 65%. Additionally, removing domestic prey improved the algorithm's overall accuracy. We provide a set of recommendations for studies focusing on kill‐site detection that can be considered for other large carnivore species in addition to the Eurasian lynx. We recommend caution when working in systems including domestic prey, as the odds of underestimating kill rates are higher. [ABSTRACT FROM AUTHOR]

Sea ice loss is fundamentally altering the Arctic marine environment. Yet there is a paucity of data on the adaptability of food webs to ecosystem change, including predator–prey interactions. Polar bears (Ursus maritimus) are an important subsistence resource for Indigenous people and an apex predator that relies entirely on the under‐ice food web to meet its energy needs. In this study, we assessed whether polar bears maintained dietary energy density by prey switching in response to spatiotemporal variation in prey availability. We compared the macronutrient composition of diets inferred from stable carbon and nitrogen isotopes in polar bear guard hair (primarily representing summer/fall diet) during periods when bears had low and high survival (2004–2016), between bears that summered on land versus pack ice, and between bears occupying different regions of the Alaskan and Canadian Beaufort Sea. Polar bears consumed diets with lower energy density during periods of low survival, suggesting that concurrent increased dietary proportions of beluga whales (Delphinapterus leucas) did not offset reduced proportions of ringed seals (Pusa hispida). Diets with the lowest energy density and proportions from ringed seal blubber were consumed by bears in the western Beaufort Sea (Alaska) during a period when polar bear abundance declined. Intake required to meet energy requirements of an average free‐ranging adult female polar bear was 2.1 kg/day on diets consumed during years with high survival but rose to 3.0 kg/day when survival was low. Although bears that summered onshore in the Alaskan Beaufort Sea had higher‐fat diets than bears that summered on the pack ice, access to the remains of subsistence‐harvested bowhead whales (Balaena mysticetus) contributed little to improving diet energy density. Because most bears in this region remain with the sea ice year round, prey switching and consumption of whale carcasses onshore appear insufficient to augment diets when availability of their primary prey, ringed seals, is reduced. Our results show that a strong predator–prey relationship between polar bears and ringed seals continues in the Beaufort Sea. The method of estimating dietary blubber using predator hair, demonstrated here, provides a new metric to monitor predator–prey relationships that affect individual health and population demographics. [ABSTRACT FROM AUTHOR]

Copyright of Brazilian Journal of Biology is the property of Instituto Internacional de Ecologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Mercury, a toxic metal released by various human activities, exerts environmental stress through its bioaccumulation and biomagnification, particularly in marine habitats. South American fur seals (Arctocephalus australis) and sea lions (Otaria flavescens) reproduce on the Atlantic coast of Uruguay. As top predators, they can accumulate toxic levels of mercury and are often used as sentinel species for monitoring ecosystem health. Fur seals prey on pelagic species, such as fish and squid, while sea lions consume coastal-benthic prey. We analyzed the total mercury concentration (THg) in hair and the trophic habits (δ13C and δ15N) of females from both species. The average THg concentration in adult female sea lions (30.5 ± 9.3 μg/g dry weight) was significantly higher than in fur seals (6.3 ± 2.5 μg/g dry weight). Additionally, the mean δ15N and δ13C values were significantly higher in sea lion (δ15N: 19.2 ± 0.6‰, δ13C: −13.8 ± 0.2‰) compared to fur seals (δ15N: 16.5 ± 0.5‰, δ13C: −15.5 ± 0.6‰). Our results suggest that different trophic levels and feedings areas affect the THg concentration in Uruguayan Otariids. Notably, at the intraspecific level, the THg concentration in sea lions increased with δ13C values, suggesting a link to coastal feeding habits. This indicates that coastal feeding behaviors, compared to feeding in pelagic environments, enhance mercury bioaccumulation in Otariids along the Uruguayan coast, with the discharge of freshwater from the Río de la Plata (one of the largest estuaries in South America) basin identified as a potential mercury source. THg concentrations found in female sea lion hair are the highest reported in Otariids globally. Mercury levels exceeded toxic thresholds observed in other mammals and could pose significant health risks. Our findings may explain why sea lions were particularly affected by the avian influenza outbreak in Uruguay compared to fur seals. Monitoring the declining sea lion population is crucial, making our results significant for integrated conservation and management strategies. [Display omitted] • Marine mammals are good sentinel species for monitoring Hg bioaccumulation. • Fur seals and sea lions prey on pelagic and coastal benthic species, respectively. • Hg accumulation in the hair of female sea lions was higher than in fur seals. • Hg levels in individual female sea lions rose with δ13C, indicating a link to coastal feeding habits. [ABSTRACT FROM AUTHOR]

Understanding the impacts of human actions on marine species and developing mitigation strategies are crucial conservation challenges. Many fish species, especially marine top predators, are already highly depleted and rely on population monitoring and conservation strategies for their maintenance. In this context, Marine Protected Areas can help recover target species and provide crucial information about population trends when human activities are restricted or managed. Here, we used the longest and most complete temporal series of reef fish data in the Southwestern Atlantic, comprising 16 years of underwater visual census sampling. We evaluated temporal trends in the density and biomass of the dusky grouper (Epinephelus marginatus), both inside and outside a no-take and no-entry Marine Reserve. Our findings reveal a consistent decline in density and biomass inside and outside the MPA over time, reaching alarmingly low densities and experiencing a steeper biomass decline in the last five years. Our results contradict global expectations of positive population recovery trends within MPAs. We highlight the adverse impacts of human activities on the dusky grouper population, including illegal fishing and habitat degradation. Additionally, we address the limited understanding of species' life stages, underscoring that their occurrence outside protected boundaries may render the entire population vulnerable to human pressures. Thus, to guarantee population recovery, stakeholders and researchers must take immediate action to increase knowledge of all life stages and improve ongoing strategies. • Despite conservation efforts over decades, the dusky grouper population is declining. • The population is declining in one of the oldest No-Take areas in the Southwestern Atlantic. • The situation worsened in the last 5 years of the 16-year time series studied. • The Reserve might be underperforming due to the disregard of local factors. • Current conservation strategies must be urgently reviewed. [ABSTRACT FROM AUTHOR]

The use of effect biomarkers has contributed to the understanding of the sublethal effects of contaminants on different organisms. However, the analysis of genotoxic markers as an indicator of organism and environmental health in sharks is underexplored. Thus, the present study investigated the relationship between the genomic damage frequency in erythrocytes and metal(loid) concentrations in whole blood of three shark species (Galeocerdo cuvier, Negaprion brevirostris and Ginglymostoma cirratum), taking into account climatic seasonality. The results showed that G. cuvier , an apex predator, presented the highest total erythrocyte genomic damage frequencies together with the highest mean whole blood concentrations of Al, Cd, Cr, Fe, Mn, Ni, Pb and Zn. The shark N. brevirostris also presented high levels of metal(loid), indicating a greater susceptibility to these contaminants in species that preferentially feed on fish. In contrast, G. cirratum , a mesopredator, presented the lowest erythrocyte damage frequencies and whole blood metal(loid) concentrations. The presence of micronuclei was the most responsive biomarker, and Al, As and Zn had an important effect on the genomic damage frequencies for all species evaluated. Zn concentration influenced the binucleated cells frequencies and Al concentration had an effect on the total damage and micronuclei frequencies in G. cuvier and N. brevirostris. Binucleated cells and blebbed nuclei frequencies were affected by As concentration, especially in G. cirratum , while showing a strong and positive correlation with most of the metals analyzed. Nonetheless, baseline levels of metal(loid) blood concentrations and erythrocyte genomic damage frequencies in sharks have not yet been established. Therefore, minimum risk levels of blood contaminants concentrations on the health of these animals have also not been determined. However, the high genomic instability observed in sharks is of concern considering the current health status of these animals, as well as the quality of the environment studied. [Display omitted] • The presence of micronuclei was the most responsive biomarker in sharks. • Al, As and Zn had an important effect on genomic damage frequencies in sharks. • Galeocerdo cuvier showed greater susceptibility to the metal(loid) analyzed. [ABSTRACT FROM AUTHOR]

Coastlines are susceptible to plastic and heavy metal pollution, which can accumulate from both marine and terrestrial sources. Shorebirds, top-level predators in these fragile ecosystems are considered as indicators of environmental health. Here, we tested the occurrence of microplastics and heavy metals in the droppings of ten regular wintering migrant shorebird species in Kadalundi-Vallikkunnu Community Reserve and adjoining sand beaches during November, December and January, each year, between 2019 and 2021. Heavy metals were analysed by Flame Atomic Absorption Spectrophotometer and the microplastic polymer compositions were identified using ATR-FTIR spectroscopy. We detected high concentrations of heavy metals such as Zinc, Copper, Cobalt, Chromium, Lead and Cadmium in droppings. Polyethylene, Polypropylene, Polystyrene, Poly Vinyl Chloride, Nitrile and Polyethylene terephthalate were the polymers identified. Polystyrene (42.6 %) and chromium (ranges between 7.83 and 88.45 mg/kg) were found to be the most abundant contaminants in most of the species. [Display omitted] • Microplastic and heavy metal co-occurrence observed in conspecific shorebird guano. • Elevated concentration of heavy metals exceeding environmental limits identified. • Six different microplastic polymers identified. • Polystyrene found to be the most abundant microplastic. • Chromium found to be the most abundant heavy metal. [ABSTRACT FROM AUTHOR]

Anticoagulant rodenticides (ARs) are one of the most toxic groups of compounds currently used worldwide for rodent pest control. Toxic baits are often, directly or indirectly, ingested by non-target animals, resulting in secondary poisoning and frequently affecting apex predators. Their presence in many species of raptors is quite common, particularly scavenger species, with some of these acting as sentinels for the presence of these substances in the environment. However, there is less data on the presence of ARs in Bonelli's eagle, one of the most endangered eagle species in Spain and which is experiencing a negative population trend in Europe. This medium-sized eagle feeds predominantly on live species, and rarely consumes carrion. In this study, 17 carcasses of Bonelli's eagles from the Eastern Spain were necropsied. Both first and second generation ARs in their livers were analyzed by HPLC-MS-TOF revealing that all the eagles studied had been exposed to at least 5 ARs, out of a total of 10 ARs analyzed, with 7 being the highest number of ARs detected in a sample. Second generation ARs were the most prevalent, particularly bromadiolone and brodifacoum, with the highest concentrations in 94% of the cases. More than a third of the eagles presented a liver concentration of greater than 200 ng/g ARs, suggesting AR poisoning. The elevated presence of these compounds in Bonelli's eagles could be a new cause of mortality for this species or could explain other causes of death, such as the increased mortality in power lines, and should be taken into account for their conservation. At the same time, the presence of these compounds in the environment also represents a risk to public health, as the most frequent species in the diet of Bonelli's eagle (rabbits and partridges) are also hunted and consumed by hunters and their families. [Display omitted] • Anticoagulant rodenticides (AR) are present in 100% of the Bonelli's eagles analyzed. • AR hepatic levels exceeded the potentially lethal threshold in 35% of the eagles analyzed. • A traumatic cause of death may be favoured by exposure to ARs. • ARs exposure is associated with increasing intensity of urbanization and rainfed agriculture. • Bonelli's eagles may be a good sentinel species of AR risk for humans. [ABSTRACT FROM AUTHOR]

Marine organisms, especially top predators such as sharks, are susceptible to environmental pollutants like microplastics (MPs) and phthalate esters (PAEs), leading to ecosystem risks. Research on contamination in these apex species is, however, still limited. This study investigated MPs and PAEs in multiple shark species (Isurus oxyrinchus , Alopias superciliosus , Alopias pelagicus , Carcharhinus brevipinna , and Sphyrna zygaena) off Taiwan's eastern coast. Gastric tissue analyses revealed ubiquitous microplastics (2–31 particles), which positively correlated with body lengths and weights for Isurus oxyrinchus. Blue, fiber-shaped (1–2 mm), and rayon-based MPs are likely associated with textile fiber pollution. The PAEs concentration mean was 7035 ± 6829 ng/g, ww, having DEHP and DiNP as primary compounds. This study highlights pervasive contamination in Pacific Ocean sharks, emphasizing anthropogenic impact on top oceanic predators and providing essential insights for food safety and MP accumulation. [Display omitted] • Sharks, as top predators, are highly vulnerable to MPs and PAEs, posing significant ecosystem risks. • MPs and PAEs in various shark species off Taiwan's eastern coast. • Gastric tissue analyses revealed ubiquitous MPs (2–31 particles) in sharks • Mean PAE concentration was 7035 ± 6829 ng/g, ww, with DEHP and DiNP as primary compounds [ABSTRACT FROM AUTHOR]

Mercury (Hg) is a naturally occurring heavy metal, but human activities and natural processes have led to increased pollution with Hg in the environment. Organic mercury, such as methyl mercury (MeHg), is considered more toxic than most inorganic mercury compounds. MeHg is rapidly taken up by aquatic organisms and bioaccumulates through the aquatic food web. The bioaccumulation causes high levels of MeHg in apex predators, such as pilot whales. Pilot whale meat is a traditional food source on the Faroe Islands; thus the consumption of pilot whale meat can lead to high Hg exposures in humans. The majority of the total Hg in pilot whale and fish is generally assumed to be MeHg. However, the relative amount of MeHg to total Hg can be highly variable. For risk assessment, it is relevant to know both the MeHg and the total Hg content. This study summarizes the knowledge of muscle MeHg concentrations relative to total Hg concentrations in pilot whales in the Faroe Islands. The pilot whale tissue was sampled during 1977–78, 1986–87, 2009–2010, and 2015. The 2015 samples included two pairs of fetuses/mothers. The results showed that the 1977–78 pilot whale muscle samples had lower relative concentrations of MeHg to total Hg compared to samples from the subsequent years. This discrepancy between early and later years could not solely be explained by increased demethylation related to concentration differences. Instead, the difference is more likely explained by variations in relative amounts of MeHg in prey of the pilot whales. In the fetuses the total Hg concentration was 20% of the Hg concentration in the mother. The relative MeHg concentrations in the fetuses were also lower (∼20%–30%) than in the mother. However, the MeHg to total Hg fraction in the fetus was similar or higher than in the mother. [Display omitted] • MeHg/TotHg ratios were analyzed in pilot whale muscle from Faroe Islands. • Higher relative ratios were observed in 1980's and 2009–2015 than in late 1970's. • Variation was likely related to different MeHg concentrations in prey. • MeHg concentrations were similar or higher in fetus compared to mother. [ABSTRACT FROM AUTHOR]

The ocean's mesopelagic zone (200–1000 m) remains one of the most understudied parts of the ocean despite knowledge that mesopelagic fishes are highly abundant. Apex predators from the surface waters are known to consume these fishes, constituting an important ecological interaction. Some countries have begun exploring the potential harvest of mesopelagic fishes to supply fishmeal and fish oil markets due to the high fish abundance in the mesopelagic zone compared with overfished surface waters. This study explored the economic and ecological implications of a moratorium on the harvest of mesopelagic fishes such as lanternfish off the US West Coast, one of the few areas where such resources are managed. We adapted a bioeconomic decision model to examine the tradeoffs between the values gained from a hypothetical mesopelagic fishery with the potential values lost from declines in predators of mesopelagic fishes facing a reduced prey resource. The economic rationale for a moratorium on harvesting mesopelagics was sensitive both to ecological relationships and the scale of the nonmarket values attributed to noncommercial predators. Using a California Current‐based ecological simulation model, we found that most modeled predators of mesopelagic fishes increased in biomass even under high mesopelagic harvest rates, but the changes (either increases or decreases) were small, with relatively few predators responding with more than a 10% change in their biomass. While the ecological simulations implied that a commercial mesopelagic fishery might not have large biomass impacts for many species in the California Current system, there is still a need to further explore the various roles of the mesopelagic zone in the ocean. [ABSTRACT FROM AUTHOR]

Predators compete aggressively for resources, establishing trophic hierarchies that influence ecosystem structure. Competitive interactions are particularly important in invaded ecosystems where introduced predators can suppress native prey species. We investigated whether niche partitioning exists within a guild of invasive mammalian predators and determined the consequences for native species. Over 4405 camera‐trap days, we assessed interactions among three invasive predators: two apex predators (feral cats Felis catus and ferrets Mustela furo) and a mesopredator (stoats Mustela erminea), in relation to their primary prey (lagomorphs, rodents and birds) and habitat use. Further, we tested for mesopredator release by selectively removing cats and ferrets in a pulse perturbation experiment. We found compelling evidence of niche partitioning; spatiotemporal activity of apex predators maximized access to abundant invasive prey, with ferrets targeting lagomorphs and cats targeting rodents. Mesopredators adjusted their behavior to reduce the risk of interference competition, thereby restricting access to abundant prey but increasing predation pressure on diurnal native birds. Stoats were only recorded at the treatment site after both larger predators were removed, becoming the most frequently detected predator at 6 months post‐perturbation. We suggest there is spatial and resource partitioning within the invasive predator guild, but that this is incomplete, and avoidance is achieved by temporal partitioning within overlapping areas. Niche partitioning among invasive predators facilitates coexistence, but simultaneously intensifies predation pressure on vulnerable native species. [ABSTRACT FROM AUTHOR]

Effective conservation requires understanding the processes that determine population outcomes. Too often, we assume that protected areas conserve wild populations despite evidence that they frequently fail to do so. Without large‐scale studies, however, we cannot determine what relationships are the product of localized conditions versus general patterns that inform conservation more broadly. Leopards' (Panthera pardus) basic ecology is well studied but little research has investigated anthropogenic effects on leopard density at broad scales. We investigated the drivers of leopard density among 27 diverse protected areas in northeastern South Africa to understand what conditions facilitate abundant populations. We formulated 10 working hypotheses that considered the relative influence of bottom‐up biological factors and top‐down anthropogenic factors on leopard density. Using camera‐trap survey data, we fit a multi‐session spatial capture–recapture model with inhomogenous density for each hypothesis and evaluated support using an information theoretic approach. The four supported hypotheses indicated that leopard density is primarily limited by human impacts, but that habitat suitability and management conditions also matter. The proportion of camera stations that recorded domestic animals, a proxy for the extent of human impacts and protected area effectiveness, was the only predictor variable present in all four supported models. Protected areas are the cornerstone of large felid conservation, but only when the human–wildlife interface is well managed and protected areas shelter wildlife populations from anthropogenic impacts. To ensure the long‐term abundance of large carnivore populations, reserve managers should recognize the ineffectiveness of "paper parks" and promote contiguous networks of protected areas that offer leopards and other large mammal populations greater space and reduced human impacts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Habitat fragmentation drives larger and more complex home-ranges in powerful owls. • Small and isolated habitat is vital for predator survival in fragmented landscapes. • Connected, cohesive habitat patches reduce competition, enabling more territories. • Owls visited different areas nightly, suggesting unpredictable hunting behaviours. • Decision-makers must consider landscape characteristics for effective conservation. Effectively managing apex predators in human-modified landscapes poses considerable challenges. Habitat fragmentation disperses resources across wider expanses and undermines the ability of apex predators to reach isolated habitat patches as they traverse multi-tenured landscapes comprising unsuitable habitat. Understanding a species response to landscape configuration is key to informing effective management strategies, particularly for threatened, mobile and ecologically important species like apex predators. Here we use GPS tracking data collected from 37 powerful owls (Ninox strenua), an Australian threatened apex predator that occurs across the urban-agricultural-forest gradient, to investigate how landscape characteristics influence their spatial and movement behaviour. We demonstrate that as habitat fragmentation increases, the spatial requirements of powerful owls expand, their home-range shape becomes more intricate and individuals travel further each night, significantly adjusting their movement behaviours and spatial configurations to connect remaining habitat. Landscapes with unified and connected habitats, on the other hand, have smaller spatial requirements, likely due to greater habitat availability that minimises competition for essential resources. This facilitates the establishment of smaller home-ranges and consequently, the occurrence of more territories. Interestingly, landscape characteristics did not influence sequential nightly visitation behaviour, suggesting that powerful owls across all landscape types visit different portions of their home-range each night to exert an unpredictable hunting strategy regardless of local landscape conditions. Our research highlights the importance of integrating the influence of local landscape features and visitation behaviours into decision-making processes. This integration is crucial for informing effective conservation strategies aimed at supporting apex predator survival in disturbed landscapes. [ABSTRACT FROM AUTHOR]

• Taxon richness and connectance of food webs are positively correlated with the number of IGP modules. • Scale-free and core-periphery structure contribute to the prevalence of IGP modules. • Contribution to IGP modules can be used as the indicator of keystone taxa. Exploring how food webs are assembled from basic modules is charming and crucial for understanding how communities are self-organized. As one of the basic modules, intraguild predation (IGP) consists of a prey being consumed by both an intermediate and a top predator, with the former also being consumed by the latter (thus encompassing both predation and competition). This interaction has been shown to govern food web stability, and therefore underpin the organization of network structures. While some studies have been made in understanding the factors and mechanisms behind the prevalence of IGP modules in food webs, the specific role of food web topological structures in relation to these modules remains largely unexplored and is not well understood. Here, 103 food webs were analyzed, and we found that the number of modules in each food web was largely determined by taxon richness and connectance. After controlling richness and connectance, the specific scale-free pattern and core-periphery structure of empirical food webs explains the higher prevalence of IGP modules in empirical food webs better than by chance. Lastly, the loss of taxa which supported large number of IGP modules would lead to serious damage to food web robustness, indicating the keystone role of these taxa in maintaining food web structure and stability. Our results provide new insight into the assembly of empirical food webs from the perspective of IGP modules. [ABSTRACT FROM AUTHOR]

Metal and organic pollutants are prominent marine contaminants that disperse widely throughout the environment. Some contaminants biomagnify, leaving long-lived apex predators such as cetaceans at risk of toxicity. Various tissues collected post-mortem from 16 Ziphiidae individuals that stranded on the New South Wales (NSW) coast, Australia, over ∼15 years were investigated for 16 metals/metalloids and 33 organic contaminants. Polychlorinated biphenyls (PCBs) and Dichlorodiphenyltrichloroethanes (DDTs) were commonly detected in blubber and liver tissues. Mercury, cadmium and silver exceeded reported toxicity thresholds in several individuals. The liver tissue of a Mesoplodon layardii specimen had the highest mercury (386 mg/kg dry weight). Liver tissue of a Mesoplodon grayi specimen had the highest silver concentration (19.7 mg/kg dry weight), and the highest cadmium concentration was in Ziphius cavirostris kidney (478 mg/kg dry weight). This study provides important new information for rare Ziphiidae species globally. [Display omitted] • PCBs and DDXs most commonly detected organic contaminants • Elevated mercury, cadmium and silver in several whales • Mercury to selenium toxicity ratios exceeded 1:1 in some individuals • Some of the highest silver concentrations reported in Southern Hemisphere cetaceans [ABSTRACT FROM AUTHOR]

The threatened Gangetic dolphin (Platanista gangetica) and smooth-coated otter (Lutrogale perspicillata) occuring in the Ganga River Basin (GRB), are experiencing a decline in their population and distribution range owing to multiple anthropogenic pressures, including pollution by Potentially Toxic Elements (PTEs). Apex predators primarily encounter contaminants through dietary exposure. Yet, notable gaps persist in our understanding of the risks associated with the ingestion of PTE-contaminated prey for Gangetic dolphins and smooth-coated otters. In this study, we examined the occurrence and spatial variation of PTEs in the prey (fish) of both these riverine mammals across three major rivers of the Basin, while also evaluating the associated risk of ingesting contaminated prey. Our assessment revealed no statistical variation in bioaccumulation profiles of PTEs across the three rivers, attributable to comparable land use patterns and PTE consumption within the catchment. Zn and Cu were the most dominant PTEs in the prey species. The major potential sources of pollution identified in the catchment include agricultural settlements, vehicular emissions, and the presence of metal-based additives in plastics. Zn, As and Hg accumulation vary with the trophic level whereas some PTEs show concentration (Hg) and dilution (As, Cr, Pb and Zn) with fish growth. The Risk Quotient (RQ), based on the dietary intake of contaminated prey calculated using Toxicity Reference Value was consistently below 1 indicating no significant risk to these riverine mammals. Conversely, with the exception of Co and Ni, the Reference Dose-based RQs for all other PTEs indicated a substantial risk for Gangetic dolphins and smooth-coated otters through dietary exposure. This study serves as a pivotal first step in assessing the risk of PTEs for two threatened riverine mammals in a densely populated river basin, highlighting the importance of their prioritization in regular monitoring to reinforce the ongoing conservation efforts. [Display omitted] • Zn and Cu were the most dominant PTEs in prey fish at all sampling sites. • No spatial variation observed in bioaccumulation of PTEs among three rivers. • As And Co levels in benthopelagic fish were higher than in pelagic and demersal fish. • Hg biomagnifies along the food chain, whereas As and Zn show trophic dilution. • As, Hg, Cr, Zn, Cu, and Cd, poses high risk to these threatened species. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds ubiquitous in the environment and known for their toxic, mutagenic, and carcinogenic effects. These compounds can bioaccumulate in the biota and be transferred through trophic webs. The franciscana dolphin (Pontoporia blainvillei), as top predators, can be an environmental sentinels. Thus, this study aimed to provide data about PAHs concentration in their hepatic tissue collected on the coast of Espírito Santo (Franciscana Management Area, FMA Ia), Rio de Janeiro (FMA IIa), and São Paulo states (FMA IIb), in Southeastern Brazil. PAHs were detected in 86 % of franciscana dolphins (n = 50). The highest ∑PAHs Total median concentration was reported in FMA Ia followed by FMA IIb and FMA IIa (1055.6; 523.9, and 72.1 ng.g-1 lipid weight, respectively). Phenanthrene was detected in one fetus and two neonates, showing maternal transfer of PAHs in these dolphins. Evaluating PAHs with potential toxic effects is of utmost importance for the conservation of a threatened species. [Display omitted] • PAHs were detected in 86 % (43/50) of franciscana dolphins analyzed. • Naphthalene, fluorene, phenanthrene, and pyrene were the most frequent compounds. • The potential carcinogenic benzo(a)pyrene was detected in 26 % (13/50) of franciscanas. • Maternal transfer of PAHs to one fetus and two neonates was evidenced. • Mutagenic and carcinogenic PAHs are another threat to a critically endangered species. [ABSTRACT FROM AUTHOR]

Herbivores obtain nutrients mostly from the vegetation they consume, but may obtain additional minerals during periods of nutritional stress by consuming bones (osteophagia), a behavioral strategy that has been reported for many wild ungulate species, including the white-tailed deer (Odocoileus virginianus). Here we document multiple records (n = 183 camera-trap records) of osteophagia by white-tailed deer chewing sea turtle remains (resulting from jaguar [Panthera onca] predation) near a nesting beach in Santa Rosa National Park, Costa Rica during January-September 2017. Females with fawns, males with hard and velvet-covered antlers, and non-spotted fawns reached a peak of sea turtle bone consumption during June to August. We hypothesize that seasonality, sex, age, and individual growth stage influence the frequency of osteophagy as a strategy to cope with environmental changes and food resource scarcity. Finally, these observations highlight the role of an apex predator as indirectly influencing rare but important ecological processes. [ABSTRACT FROM AUTHOR]

Apex predators drive top‐down effects in ecosystems and the loss of such species can trigger mesopredator release. This ecological process has been well documented in human‐modified small areas, but for management and conservation of ecological communities, it is important to know which human factors affect apex predator occurrence and which mediate mesopredators release at large scales. We hypothesized that mesopredators would avoid spatial and temporal overlap with the apex predator, the puma; but that human perturbations (i.e., cattle raising and trophy hunting) would dampen top‐down effects and mediate habitat use. We installed 16 camera traps in each of 45, 10 × 10 km grid cells in the Caldén forest region of central Argentina resulting in 706 total stations covering 61,611 km2. We used single‐season occupancy and two‐species co‐occurrence models and calculated the species interaction factor (SIF) to explore the contributions of habitat, biotic, and anthropic variables in explaining co‐occurrence between carnivore pairs. We also used kernel density estimation techniques to analyze temporal overlap in activity patterns of the carnivore guild. We found that puma habitat use increased with abundance of large prey and with proximity to protected areas. Geoffroy's cats and skunks spatially avoided pumas and this effect was strong and mediated by distance to protected areas and game reserves, but pumas did not influence pampas fox and pampas cat space use. At medium and low levels of puma occupancy, we found evidence of spatial avoidance between three pairs of mesocarnivores. All predators were mostly nocturnal and crepuscular across seasons and mesopredators showed little consistent evidence of changing activity patterns with varying levels of puma occupancy or human interference. We found potential for mesopredator release at large scale, especially on the spatial niche axis. Our results suggest that a combination of interacting factors, in conjunction with habitat features and intervening human activities, may make mesopredator release unlikely or difficult to discern at broad scales. Overall, we believe that promoting the creation of new protected areas linked by small forest patches would likely lead to increased predator and prey abundances, as well as the interactions among carnivores inside and outside of protected areas. [ABSTRACT FROM AUTHOR]

A colony of about 30 000 pairs of Black-tailed Gull Larus crassirostris nest on Kabushima (Kabu Island), which is located on the northeast mainland coast of Japan (Sanriku Coast, Honshu Island). There, the surface-water Hg concentration is higher than in the North Pacific Ocean. We collected carcasses from the breeding colony to assess the level of mercury (Hg) contamination. We measured Hg concentrations in 10 body tissues, including the endocrine glands. The relative mercury concentrations in the tissue samples (µg/g dry weight) were as follows: adrenal glands > livers > kidneys > blood > pituitaries > gonads > breast muscles > thyroid glands > pancreases > brain stems. Correlations existed between blood mercury levels and all body tissues except for the adrenal glands. Based on these results, we suggest that mercury levels in blood may not be a good indicator for hypothalamic-pituitary-adrenal axis impacts in Black-tailed Gulls. [ABSTRACT FROM AUTHOR]

Black bass fishing tournaments with conventional weigh‐ins tend to displace fish from their capture site and often release fish within close proximity to the weigh‐in site. Tournaments often include Largemouth Bass Micropterus salmoides and Smallmouth Bass M. dolomieu and occur throughout fishing seasons; however, there have yet to be any systematic congeneric comparisons across different seasons. Objectives of our study were to (1) assess post‐tournament dispersal of Largemouth Bass and Smallmouth Bass (i.e., short‐term stockpiling—accumulation of fish around weigh‐in site <1 month after tournament) across seasons, and (2) determine the success of return to the main basin. Research took place on Big Rideau Lake in eastern Ontario and included a preseason control (N = 30) where fish were captured, acoustically tagged, and released at the site of tournament weigh‐in (Rideau Ferry). Tournament‐caught bass (N = 88 total) were tagged at three tournaments that spanned June (early season), August (midseason), and October (late season). Our results indicated a brief short‐term stockpiling (within 300 m) in all seasons, and all detected fish eventually returned to the main basin. Tournament‐caught Largemouth Bass tended to take longer to disperse from the release site following the midseason tournament (4.6 d); Smallmouth Bass tended to disperse from release site <1 d following all treatments. Similarly, tournament‐caught Largemouth Bass exposed to the midseason tournament tended to take the longest to redistribute to the main basin (238 d) in comparison to other treatments. Although Smallmouth Bass tended to redistribute to the main basin faster than Largemouth Bass, late‐season Smallmouth Bass tended to redistribute the slowest (101 d) following tournament release. Although fish do survive and eventually return to the main basin, displacement may have broader ecological consequences (i.e., large‐scale displacement of top predators, adverse effects on recruitment) such that there would be merit in more catch–weigh–release formatted events. [ABSTRACT FROM AUTHOR]

The Striped Bass Morone saxatilis is an apex predator that supports recreational, commercial, and First Nations traditional fisheries in the Miramichi River, New Brunswick, Canada. Historic exploitation resulted in steep population declines, forcing a complete fisheries moratorium in 2000. After 13 years of recovery, a recreational fishery was reopened (May 2013) followed by a commercial fishery in 2018. These new opportunities for harvesting raised concerns about mercury levels in fish for human consumption as past levels have exceeded Health Canada guidelines of 0.5 mg/kg. We collected Striped Bass from the northwest Miramichi River in spring during the main recreational and commercial fishing seasons. Fish in the legal harvest slot for the recreational (50–65 cm TL) and commercial (50–80 cm TL) fisheries had total mercury in muscle tissue ranging from 0.08 to 0.43 mg/kg and from 0.08 to 0.63 mg/kg wet weight, respectively. Mercury levels in Striped Bass have decreased since the 1990s, but some individuals were close to or exceeded consumption guidelines. In addition, a preliminary angler creel survey revealed that only 8% of anglers retained their legal, three‐fish limit (average harvest = 0.7 fish/angler/day). However, harvest of oversized fish was observed (11%), and a removal of ˜100,000 adults in the first month of the fishery by the recreational, commercial, and Indigenous fisheries is possible and represents a significant portion of the estimated adult population. We conclude that effective management of the Striped Bass fishery in the Miramichi River will require continued and more detailed angler surveys and population size and structure assessments accompanied by communication of current mercury levels in this species. [ABSTRACT FROM AUTHOR]

Outcomes of management efforts to recover or restore populations of harvested species can be highly dependent on environmental and community context. Predator–prey interactions can alter recovery trajectories, and the timing of management actions within multi‐trophic level harvest scenarios may influence the dynamics of recovery and lead to management trade‐offs. Recent work using a generalist predator–prey model suggests that management promoting synchronized recovery of predators and prey leads to faster and less variable recovery trajectories than sequential recovery (predator or prey first). However, more complex communities may require different management actions to minimize recovery time and variability. Here, we use a tri‐trophic level rocky reef community dynamics model with size‐structure and fisheries at multiple trophic levels to investigate the importance of three ecological processes to recovery of fished communities: (1) size‐structured predation, (2) non‐consumptive effects of predators on prey behavior, and (3) varying levels of recruitment. We also test the effects of initiating recovery from community states associated with varying degrees of fishery‐induced degradation and develop a simulation in which the basal resource (kelp) is harvested. In this system, a predator‐first closure generally leads to the least volatile and quickest recovery, whether from a kelp forest, urchin barren, or intermediate community state. The benefits gained by selecting this strategy are magnified when recovering from the degraded community, the urchin barren, because initial conditions in the degraded state lead to lengthy recovery times. However, the shape of the size‐structured predation relationship can strongly affect recovery volatility, where the differences between alternate management strategies are negated with size‐independent predation. External recruitment reduces return times by bolstering the predatory lobster population. These results show that in a tightly linked tri‐trophic level food web with top‐down control, a predator‐first fishery closure can be the most effective strategy to reduce volatility and shorten recovery, particularly when the system is starting from the degraded community state. Given the ubiquity of top predator loss across many ecosystems, we highlight the value of incorporating insights from community ecology into ecosystem management. [ABSTRACT FROM AUTHOR]

Micro/nano-plastics (MPs/NPs) represent an emerging contaminant, posing a significant threat to oceanic halobios. While the adverse effects of joint pollutants on marine organisms are well-documented, the potential biological impacts on the food chain transmission resulting from combinations of MPs/NPs and heavy metals (HMs) remain largely unexplored. This study exposed the microbial loop to combined contaminants (MPs/NPs + HMs) for 48h, bacteria and contaminants are washed away before feeding to the traditional food chain, employing microscopic observation, biochemical detection, and transcriptome analysis to elucidate the toxicological mechanisms of the top predator. The findings revealed that MPs/NPs combined with Cd2+ could traverse both the microbial loop and classical food chain. Acute exposure significantly affected the carbon biomass of the top predator Tigriopus japonicus (75.8% lower). Elevated antioxidant enzyme activity led to lipid peroxidation, manifesting in increased malondialdehyde levels. Transcriptome sequencing showed substantial differential gene expression levels in T. japonicus under various treatments. The upregulation of genes associated with apoptosis and inflammatory responses, highlighting the impact of co-exposure on oxidative damage and necroptosis within cells. Notably, NPs-Cd exhibited stronger toxicity than MPs-Cd. NPs-Cd led to a greater decrease in the biomass of top predators, accompanied by lower activities of GSH, SOD, CAT, and GSH-PX, resulting in increased production of lipid peroxidation product MDA and higher oxidative stress levels. This investigation provides novel insights into the potential threats of MPs/NPs combined with Cd2+ on the microbial loop across traditional food chain, contributing to a more comprehensive assessment of the ecological risks associated with micro/nano-plastics and heavy metals. [Display omitted] • MPs/NPs could be transferred to the food chain through the microbial loop. • Abundance and biomass decreased after the top predators ingest co-pollutants. • Oxidative stress in T. japonicus could be induced by MPs/NPs alone or in mixtures. • NPs-Cd could produce metabolic disorder and necroptosis in T. japonicus. [ABSTRACT FROM AUTHOR]

Natural and anthropogenic pressures exert influence on ecosystem structure and function by affecting the physiology and behavior of organisms, as well as the trophic interactions within assemblages. Therefore, understanding how multiple stressors affect aquatic ecosystems can improve our ability to manage and protect these ecosystems and contribute to understanding fundamental ecological principles. Here, we conducted a mesocosm experiment to ascertain the individual and combined effects of multiple stressors on trophic interactions within species in freshwater ecosystems. Furthermore, we investigated how species respond to such changes by adapting their food resources. To mimic a realistic food web, we selected fish and shrimp as top predators, gastropods, zooplankton and zoobenthos as intermediate consumers, with producers (macrophytes, periphyton and phytoplankton) and detritus as basal resources. Twelve different treatments included a control, nutrient loading only, herbicide exposure only, and a combination of nutrient loading and herbicide exposure, each replicated under ambient temperature, constant warming and multiple heat waves to simulate environmental stressors. Our results demonstrated that antagonistic interactions between environmental stressors were widespread in trophic interactions, with a more pronounced and less intense impact observed for the high trophic level species. The responses of freshwater communities to environmental stressors are complex, involving direct effects on individual species as well as indirect effects through species interactions. Moreover, our results confirmed that the combinations of stressors, but not individual stressors, led to a shift to herbivory in top predators, indicating that multiple stressors can be more detrimental to organisms than individual stressors alone. These findings elucidate how changes in the resource utilization of species induced by environmental stressors can potentially influence species interactions and the structural dynamics of food webs in freshwater ecosystems. [Display omitted] • Evaluating multiple stressors' effects on food webs from a mesocosm experiment. • Environmental stressors lead to a rewiring of the interaction strength of food webs. • Antagonisms are more common than synergies among multiple stressors. • Consumer species shift their relative use of different food resources in response. [ABSTRACT FROM AUTHOR]

[Display omitted] • Research informed policy and decision tools are vital for effective conservation. • Apex predators are critical for structuring ecosystems. • Environmental policy fails to provide protection for a wide-ranging apex predator. • Poor environmental policy is likely to lead to further decline of apex predators. • Environmental policy underestimates habitat importance in modified landscapes. Ecological impact assessments are undertaken in compliance with legislative mandates to evaluate the effects of proposed habitat modification. This task becomes complex when evaluating the impacts on highly mobile species like apex predators. Despite their importance to ecosystem function, environmental policies may inadequately protect apex predator habitat. Here we provide a case study that examines the efficacy of legislation and impact assessment tools in protecting habitat for a wide-ranging and threatened apex predator. The high resource requirements of apex predators, and their utilisation of large areas of high-quality habitat make them ideal conservation surrogates for other less resource demanding species, and as such good case studies in assessing the effectiveness of policy. The powerful owl (Ninox strenua) occurs across many landscape types throughout its distribution, including large tracts of private property and public landholdings, making this species difficult to assess through impact assessments. To examine the level of legislative protection for powerful owls, and how well their habitat use is captured, we compared GPS tracking data to environmental policy and industry impact assessment tools. We found that legislation has limited potential to protect powerful owl habitat and owls are likely dismissed from impact assessments due to their cryptic and wide-ranging behavioural traits. The existing legislative safeguards seem inadequate, and these shortcomings are likely contributing to species decline. There is a critical need for policy to be applicable to both public and private land tenure, and for legislation and impact assessment tools to incorporate research data for effective conservation and management. [ABSTRACT FROM AUTHOR]

The interspecific interactions of apex predators are integral to the function of ecological communities, but most studies have focused on understanding their top down effects. Kleptoparasitism (the stealing of procured food) by dominant scavengers can have negative effects on populations and behaviors of apex predators. We captured 7 pumas (Puma concolor) and fitted them with GPS collars to investigate potential kill sites (n = 352), some of which we monitored with camera traps (n = 58). We analyzed whether observed kleptoparasitism by American black bears (Ursus americanus) affected puma energetics and foraging behavior. We found that black bears were the most frequent scavenger of puma kills (72.4%), and we documented bears scavenging puma kills during every month. The top model for bear detection of puma kills included prey size, temperature, and canopy cover, with bears more likely to scavenge from adult black-tailed deer (Odocoileus hemionus columbianus) carcasses in warmer temperatures and under dense canopy cover. When black bear scavenging occurred, pumas spent 22% less time at their kill and incurred energetic losses. In response, pumas shortened their inter-kill intervals by 1.3 days thus increasing their kill rates. Our results demonstrate how a dominant scavenger directly mediates the foraging behavior of an apex predator. These results suggest that community interactions do not necessarily start at the top in top-down systems, and the effects of predators on prey populations can only be understood within their respective ecological communities. [ABSTRACT FROM AUTHOR]

Beach nesting waterbirds are among the most vulnerable groups of birds that are threatened by climate change, habitat loss, predation, and human disturbance. To improve conservation management strategies, causes of nest failure for ground-nesting waterbirds and effectiveness of mammalian predator control were investigated. Changes in breeding population size and hatching success of Royal (Thalasseus maximus) and Sandwich (T. sandvicensis) terns were evaluated based on pre-mammalian removal (2012-2014) vs. post-mammalian removal (2015-2016) breeding data. Video systems were used at colonies in 2015 and 2016 to determine causes of nest failure. No differences in breeding parameters were found between removal periods, however video data confirmed nest predation as the primary cause of nest failure. Laughing Gull (Leucophaeus atricilla) was the top predator and accounted for 63% of all detected predation events. In 2015, video monitoring identified a novel predator, exotic and invasive nutria (Myocastor coypus), that were responsible for 43% of predation events. In 2016, following a 280% increase in nutria removal from 2015, no nutria predation was recorded. [ABSTRACT FROM AUTHOR]

As extreme climate events become more frequent and intense, short-term temperature responses of ectothermic organisms can lead to decreased performance and survival. However, organisms may acclimate to these conditions through behavioural and physiological mechanisms as exposure time increases. We used a reciprocal temperature (16 °C and 24 °C) transplant experiment to determine how feeding rate and body size of an apex soil mite predator (Stratiolaelaps scimitus) (formerly Hypoaspis miles) consuming prey (Carpoglyphus lactis) (dried-fruit-mite) changed along a gradient of acclimation time (1, 3, and 7 days, with control). In the control treatments, mites reared at 24 °C fed more, but were smaller than mites reared at 16 °C. When transferred to new temperature conditions, predators that experienced cooling events had reduced feeding efficiencies driven by decreased feeding performance, despite an absence of metabolic costs, while under warming events, predators also had reduced feeding activity, but feeding increased with acclimation time. Yet predators lost more weight the longer they were exposed to warming, and continued to experience reduced feeding efficiencies (i.e., lack of weight gain after feeding); this result suggests increased metabolic costs at higher temperatures and provides a mechanism for community downsizing under warming. Overall, our results suggest that ectothermic predators can acclimate to warming events with increased exposure time, but both warming and cooling events decrease overall performance. [ABSTRACT FROM AUTHOR]

Species tend to concentrate in areas with high prey availability, which could lead to competitive interactions within a feeding assemblage as resources become depleted. In coastal Newfoundland, Canada, capelin Mallotus villosus is the focal forage fish species that many top predators feed on during the summer; however, inshore availability varies throughout the boreal summer when abundant aggregations migrate inshore to spawn. We investigated the interactions and responses of Great Shearwaters Ardenna gravis and Sooty Shearwaters A. grisea during their non-breeding season to supplemental food supply under changing natural prey availability (higher and lower capelin availability) by conducting an at-sea experiment during July-August (2015/2016) in coastal Newfoundland. Supplemental food was offered every 30 s over 10 min ('experimental period'), which was preceded and followed by 10-min control periods (i.e., no food provided). The number of both species increased during the experimental periods, indicating that both species were attracted to the food supplementation experiment. Great Shearwaters were 7.6-13.8 times more likely than Sooty Shearwaters to land near the experimental platform and 95.2 times more likely than Sooty Shearwaters to fight over supplemental food items with individuals of the same or different species. These species-specific tendencies remained consistent as prey availability varied within years, but both species increased in their abundance and interactions with other species (including Herring Gulls Larus argentatus and Northern Fulmars Fulmarus glacialis) during prey capture at lower relative to higher prey availability, as evidenced by lower proportions of flying birds and a greater likelihood of landing on the water. Overall, we suggest that when Great and Sooty shearwaters feed in close association, Great Shearwaters are the more competitively dominant species, which may lead to higher risks of by-catch mortality, especially when the availability of natural prey decreases. [ABSTRACT FROM AUTHOR]

Climate change has broad ecological implications for species that rely on sensitive habitats. For some top predators, loss of habitat is expected to lead to cascading behavioral, nutritional, and reproductive changes that ultimately accelerate population declines. In the case of the polar bear (Ursus maritimus), declining Arctic sea ice reduces access to prey and lengthens seasonal fasting periods. We used a novel combination of physical capture, biopsy darting, and visual aerial observation data to project reproductive performance for polar bears by linking sea ice loss to changes in habitat use, body condition (i.e., fatness), and cub production. Satellite telemetry data from 43 (1991–1997) and 38 (2009–2015) adult female polar bears in the Baffin Bay subpopulation showed that bears now spend an additional 30 d on land (90 d in total) in the 2000s compared to the 1990s, a change closely correlated with changes in spring sea ice breakup and fall sea ice formation. Body condition declined for all sex, age, and reproductive classes and was positively correlated with sea ice availability in the current and previous year. Furthermore, cub litter size was positively correlated with maternal condition and spring breakup date (i.e., later breakup leading to larger litters), and negatively correlated with the duration of the ice‐free period (i.e., longer ice‐free periods leading to smaller litters). Based on these relationships, we projected reproductive performance three polar bear generations into the future (approximately 35 yr). Results indicate that two‐cub litters, previously the norm, could largely disappear from Baffin Bay as sea ice loss continues. Our findings demonstrate how concurrent analysis of multiple data types collected over long periods from polar bears can provide a mechanistic understanding of the ecological implications of climate change. This information is needed for long‐term conservation planning, which includes quantitative harvest risk assessments that incorporate estimated or assumed trends in future environmental carrying capacity. [ABSTRACT FROM AUTHOR]

The proliferation of native, alien, invasive and domestic species offers enough novel and abundant food resources for the common vampire bat, Desmodus rotundus, to potentially alter preferences for prey. By reference to a stable-isotope analysis for carbon and nitrogen, we report here on the choices of introduced mammal prey made by D. rotundus residing on Anchieta Island — a tropical land-bridge island from which domestic animals were removed and 100 individuals of 15 mammal species were introduced intentionally. Our analysis shows that the studied individuals of D. rotundus were more likely to prey upon species of open habitats (mean value of δ13C = -14.8‰), that is, animals with high δ13C values characterising the consumption of C4 resources. The δ15N values for D. rotundus were higher than expected, most likely similar to apex predator species (mean value of 8.2‰) and overlapped the isotopic niche with capybaras (Hydrochoerus hydrochaeris) on the island. Values were in turn distant from those noted for coatis, as well as other potential prey from a preserved area on the mainland (capybaras included), indicating that, from among all the potential mammalian prey species, the studied bats were feeding exclusively on capybaras, which also represent the species with the greatest mammalian biomass on the island. Previous information regarding the time of human occupation suggests that the domestic animals then present on Anchieta Island might have been the main prey of D. rotundus and responsible for maintaining a viable population. As capybaras were introduced only 36 years ago, this suggests a rapid shift in predation preference induced by anthropogenic disturbances that have allowed D. rotundus to exploit these rodents successfully. Records in the literature further show that common vampire bats were not captured in preserved areas of the mainland close to Anchieta Island, indicating that the rate of capture characterising D. rotundus is usually low in natural forested habitats where potential prey are scattered. As three individuals of the introduced population of capybaras were confirmed to have died from bat rabies virus (RABV) in 2020, we advocate periodic monitoring for bat rabies viruses in the D. rotundus population on Anchieta Island (as well as nearby areas), so that the magnitude of the outbreak may be determined and control strategies developed. Such actions are all the more important given that both the island and nearby areas are frequented by tourists. We highlight that the prey choice indicated here is context-dependent, and possibly influenced by the removal of domestic animals, as well as the explosive population growth achieved by the introduced capybaras, in combination with the predictability of their foraging behaviour. [ABSTRACT FROM AUTHOR]

Growing appreciation of biodiversity and the role of apex predators, along with the increasing popularity of multispecies and trophy‐oriented angling, has elevated the status of gars—in particular, the Alligator Gar Atractosteus spatula—among anglers and biologists alike. As a result, considerable effort has been spent in recent years to gain a working knowledge of the biology and ecology of the species in order to advance science‐based management. In January 2019, the Alligator Gar Technical Committee of the Southern Division of the American Fisheries Society hosted a symposium entitled "Advances in the Conservation and Management of North American Gars" to showcase the results of research and management efforts conducted throughout the species' range. Fishery researchers and managers presented a diversity of works, furthering our understanding of population dynamics, stock assessment, genetics, hatchery practices and stocking, habitat use, and angler desires associated with Alligator Gar fisheries. In our introduction to this special section, we introduce these works and provide a synthesis of the current state of scientific knowledge regarding the Alligator Gar. We hope that this will provide context to the works presented in the symposium and will serve to guide the development of future research that addresses the remaining knowledge gaps concerning the species and its growing fishery. [ABSTRACT FROM AUTHOR]

At-sea observations of seabirds and cetaceans provide essential baseline information about their biogeography and behaviour, facilitating marine spatial planning and management. Much of the world's oceans have been surveyed, yet some regions remain particularly data-poor for seabirds and cetaceans, including the Bay of Bengal. We performed 39 d of vessel-based observations within the Bay of Bengal from 2012 to 2014, surveying an overall linear distance of 4722.3 km. We observed 2697 seabirds of 17 species and 1441 cetaceans of at least eight species. Among the seabirds, Sooty Terns Onychoprion fuscatus (n = 2282, 85% of all birds) and Wedge-tailed Shearwaters Ardenna pacifica (n = 327, 12%) predominated, whereas cetacean numbers were dominated by Spinner Dolphins Stenella longirostris (n = 772, 54% of all cetaceans) and Indo-Pacific Bottlenose Dolphins Tursiops aduncus (n = 533, 37%). Other seabirds and cetaceans accounted for only 4% and 7%, respectively, of all sightings. The abundance and diversity of both groups was low compared to other tropical areas. We propose that low seabird and cetacean abundance results from low productivity due to stratification in the Bay of Bengal, as well as long-lasting disturbance, overexploitation of marine resources, possible impacts of longline fisheries, and the near absence of seabird breeding sites. [ABSTRACT FROM AUTHOR]

The rapid pace of environmental change in the Anthropocene necessitates the development of a new suite of tools for measuring ecosystem dynamics. Sentinel species can provide insight into ecosystem function, identify hidden risks to human health, and predict future change. As sentinels, marine apex (top) predators offer a unique perspective into ocean processes, given that they can move across ocean basins and amplify trophic information across multiple spatiotemporal scales. Because use of the terms "ecosystem sentinel" and "climate sentinel" has proliferated in the scientific literature, there is a need to identify the properties that make marine predators effective sentinels. We provide a clear definition of the term "sentinel", review the attributes of species identified as sentinels, and describe how a suite of such sentinels could strengthen our understanding and management of marine ecosystems. We contend that the use of marine predators as ecosystem sentinels will enable rapid response and adaptation to ecosystem variability and change. [ABSTRACT FROM AUTHOR]

Shark and ray tourism is growing in popularity and often necessitates attractants like bait and chum to encourage close encounters. Such practices remain contentious amongst stakeholders as they may affect the species they target. We used lipid and fatty acid profiles to investigate the effects of South Australia's cage-diving industry on the diet and nutritional condition of white sharks Carcharodon carcharias (n = 75). We found no evidence of dietary shifts or reduced nutritional condition after a >3 week period of tourism-exposed residency at the Neptune Islands where the cage-diving industry operates. White sharks fed on a variety of prey groups, similar to other populations around Southern Australia that are not exposed to ecotourism provisioning. These findings indicate that current cage-diving operations in South Australia do not alter white shark diet and nutritional condition where prey resources are abundant. Image 1 • Previous studies suggest white shark cage-diving changes shark behaviour and daily activity. • Lipids and fatty acids in white shark muscle were used to assess the nutritional effects of the cage-diving industry. • White shark nutrition is unaffected by practices of the cage-diving industry. • White sharks do not consume sufficient bait (tuna) to affect their diet. • White sharks foraging ecology at the Neptune Islands is similar to other locations in South Australia. [ABSTRACT FROM AUTHOR]

Forest plantations are increasingly recognized for their role in providing ecosystem services in agroforestry systems. Understanding the habitat preferences of potentially beneficial birds supports effective forest management. Our study focused on identifying breeding habitat preferences of a raptor guild and assessing exotic eucalypt plantations as potential breeding sites. We explored preferences at various spatial scales considering vegetation features, intraspecific territorial behaviour, and interspecific interactions within the guild to determine their importance. We hypothesized that feeding habits and body mass explain differences in habitat preferences among three diurnal raptors (Northern goshawk, Common buzzard, Eurasian sparrowhawk). We employed random forest models to differentiate breeding sites from control plots, assessing factors' relative importance and unravelling the hierarchical process of habitat selection in southwestern Europe's eucalypt plantations. The studied eucalypt plantations emerged as suitable breeding habitats, harbouring dense breeding populations with uniform spatial distribution. Intraspecific territoriality and vegetation significantly influenced breeding habitat selection, while interspecific interactions held lesser influence. Species-specific variations were attributed to feeding habits and body masses. Tall eucalypt trees and mature-like patches were crucial elements driving breeding habitat selection. Raptors' preference for specific woody elements primarily influences areas within a relatively small radius around their nests (including the nest tree, nest site −10 m radius, and nest stand −50 m), with sparrowhawks showing preferences extending to 125 m. Raptors' inclination for mature woody elements and mature forest patches should steer forest management to bolster these apex predators and their contributions in eucalypt plantations within agroforestry systems. • Tall eucalypt trees and mature-like patches are key elements for habitat selection. • Territoriality shapes habitat selection in the most bird-eating raptors. • Interspecific associations benefit small-sized subordinate raptor species. • Our study highlights the importance of long-term planning for habitat restoration. • Intervention plots should be strategically separated considering territoriality. [ABSTRACT FROM AUTHOR]