Stoichiometric theory in optimal foraging strategy.

Understanding how organisms make choices about what to eat is a fascinating puzzle explored in this study, which employs stoichiometric modeling and optimal foraging principles. The research delves into the intricate balance of nutrient intake with foraging strategies, investigating quality and quantity-based food selection through mathematical models. The stoichiometric models in this study, encompassing producers and a grazer, unveils the dynamics of decision-making processes, introducing fixed and variable energetic foraging costs. Analysis reveals cell quota-dependent predation behaviors, elucidating biological phenomena such as "compensatory foraging behaviors" and the "stoichiometric extinction effect". The Marginal Value Theorem quantifies food selection, highlighting the profitability of prey items and emphasizing its role in optimizing foraging strategies in predator-prey dynamics. The environmental factors like light and nutrient availability prove pivotal in shaping optimal foraging strategies, with numerical results from a multi-species model contributing to a comprehensive understanding of the intricate interplay between organisms and their environment.

Influence of Human Hunting Strategies and Large Carnivore Presence on Population Dynamics of European Facultative Scavengers.

Ungulates serve as the primary carrion source for facultative scavengers in European ecosystems. In the absence of large carnivores, such as wolves (Canis lupus), human hunting leftovers are the main source of carrion for these scavengers. Additionally, wild boars (Sus scrofa) are heavily culled in many ecosystems and are both a significant prey species for wolves as well as a key scavenger. Nowadays, wolves and wild boars are re-establishing their historical home ranges. However, it remains unclear how their presence influences the population dynamics of facultative scavengers under different scenarios of human hunting strategies. We simulated the biomass densities of all states in the trophic web including European scavengers and wolves using an ordinary differential equations (ODE) model. The presence of wolves led to a positive trend in scavenger biomass in general. However, in general, we found that plant-based resources were more important for scavenger dynamics than carrion, regardless of whether the carrion originated from human hunting or wolf predation. Only when wolves were absent but boars present, the human hunting strategy became important in determining scavenger dynamics via carrion supply. In conclusion, our model indicates that population dynamics of facultative scavengers are not mainly driven by the availability of carrion, but rather by the presence of and competition for vegetation. Furthermore, our simulations highlight the importance of adapting human hunting strategies in accordance with the re-establishment of wolf and boar as these can cause fluctuating population patterns over the years.

The departure of sperm whales (Physeter macrocephalus) in response to the declining jumbo squid (Dosidicus gigas) population in the central portion of the Gulf of California.

As sperm whales are important predators that control energy flux in the oceans, changes in their population can be used as a sentinel to measure of ecosystem health. The present study conducted a sperm whale survey of the eastern Midriff Islands Region in the Gulf of California over the course of nine years, recording sightings and collecting photographs of the fluke of sperm whale individuals. A photo-identification catalog was compiled, while individual recapture data were used to estimate the population size in the central portion of the Gulf of California, using a Jolly-Seber POPAN open population model. The results obtained show a yearly population of between 20 and 167 sperm whales, with a super population of 354 sperm whales observed between 2009 and 2015. However, from 2016 to 2018, no sightings of the species were recorded, which coincides with the decline observed in landings of their main prey, the jumbo squid, in the region. General additive model conducted on sperm whale sightings per unit of effort vs jumbo squid landings obtained an adjusted R2 of 0.644 and a deviance explained of 60.3%, indicating a good non-linear relationship between sightings of this odontocete and its prey availability. This evidence suggests that sperm whales departed the region between 2016 and 2018, due to a documented fishery collapse alongside changes of their main prey into its small phenotype, possibly as the result of increase warming conditions in surface and subsurface waters in the Gulf of California in the last three decades.

The bio-accumulation and -magnification of microplastics under predator-prey isotopic relationships.

Recent studies on microplastics (MPs) in marine ecosystems have focused on their bioaccumulation and biomagnification within food chains, emphasizing their potential health risks to humans. However, these bio-effects of MPs in marine ecosystems remain a contentious issue. Employing the "consumer-dietary source" tracking function in stable isotope analysis can enhance our comprehension of how MPs magnify in organisms. In our research conducted in the coastal waters of Haizhou Bay, Jiangsu, China, we examined two commercially important fish species, Larimichthys polyactis and Collichthys lucidus, through stable isotope analysis to investigate the accumulation of MPs in their dietary sources. Results revealed fiber, blue, and PET as the primary shapes, colors, and polymers of MPs in the region. C. lucidus displayed a broader isotopic niche and a higher propensity for MP accumulation than L. polyactis. Biomagnification analysis indicated that dominant MP shapes, colors, and polymers were magnified in both fish species, with MPs smaller than 3 mm exhibiting substantial biomagnification. Factors such as feeding strategies and habitat preferences may influence MP ingestion by fish. We conclude that a high proportion of dietary sources in fish does not necessarily equate to a high concentration of MPs. Neglecting the proportion of dietary sources might lead to underestimating MP biomagnification. Therefore, a multidimensional approach to exploring the biomagnification of MPs is essential to accurately grasp this unique pollutant's impact.

Are Wild Prey Sufficient for the Top Predators in the Lowland Protected Areas of Nepal?

A balanced equilibrium between carnivores and their prey is crucial for maintaining ecosystem sustainability. In this study, we applied the predator-prey power law equation to assess the balance between the biomass densities of carnivores and their wild prey within Nepal's lowland protected areas during 2013, 2018, and 2022. The estimated value of the power law exponent k for predator-prey biomass was 0.71 (95% CI = 0.39-1.05), indicating an approximate threefold increase in predator biomass density for every fivefold increase in prey biomass density. Consequently, this creates a systematically bottom-heavy predator-prey biomass pyramid. This finding, consistent with the k = 3/4 trophic biomass scaling across ecosystems, suggests that predator biomass is proportionally sustained by prey biomass, indicating a balance between top predators and their wild prey in Nepal's lowland protected areas. We further demonstrated it is possible to retain the overall power law exponent while jointly measuring intraguild competition between two predators with canonical correlation analysis. This understanding opens avenues for future research directed toward unraveling the factors that drive these consistent growth patterns in ecological communities.

Behavioural responses to mammalian grazing expose insect herbivores to elevated risk of avian predation.

Large mammalian herbivores (LMH) are important functional components and drivers of biodiversity and ecosystem functioning in grasslands. Yet their role in regulating food-web dynamics and trophic cascades remains poorly understood. In the temperate grasslands of northern China, we explored whether and how grazing domestic cattle (Bos taurus) alter the predator-prey interactions between a dominant grasshopper (Euchorthippus unicolor) and its avian predator the barn swallow (Hirundo rustica). Using two large manipulative field experiments, we found that in the presence of cattle, grasshoppers increased their jumping frequency threefold, swallows increased foraging visits to these fields sixfold, and grasshopper density was reduced by about 50%. By manipulatively controlling the grasshoppers' ability to jump, we showed that jumping enables grasshoppers to avoid being incidentally consumed or trampled by cattle. However, jumping behaviour increased their consumption rates by swallows 37-fold compared with grasshoppers that were unable to jump. Our findings illustrate how LMH can indirectly alter predator-prey interactions by affecting behaviour of avian predators and herbivorous insects. These non-plant-mediated effects of LMH may influence trophic interactions in other grazing ecosystems and shape community structure and dynamics. We highlight that convoluted multispecies interactions may better explain how LMH control food-web dynamics in grasslands.

Asymmetric arms races between predators and prey: a tug of war between the life-dinner principle and the rare-enemy principle.

Antagonistic co-evolution can be asymmetric, where one species lags behind another. Asymmetry in a predator-prey context is expressed by the 'life-dinner principle', a classic informal model predicting that prey should be in some sense ahead in this arms race, since prey are running for their lives, while predators lag as they only run for their dinner. The model has undergone surprisingly little theoretical scrutiny. We derive analytical models that show coevolutionary outcomes do not always align with the life-dinner principle. Our results show that other important asymmetries can easily reverse the outcome, especially the rare-enemy principle: predators are usually outnumbered by their prey, sometimes substantially (trophic asymmetry), which can make selection on prey relatively weak. We additionally show that the antagonists typically exhibit different evolutionary responses to a situation where both predator and prey start out as equally fast runners. Although predators sometimes become so efficient that attacks always succeed, attack success often reaches a stable intermediate value. We conclude that the life-dinner principle has some validity as a metaphor, but its effect is of an 'all else being equal' type, which is surprisingly easily overridden by other features of the evolutionary dynamics.

Long-term anti-predator learning and memory differ across populations and sexes in an intertidal snail.

Anti-predator behaviours in response to predator cues can be innate, or they can be learned through prior experience and remembered over time. The duration and strength of continued anti-predator behaviour after predator cues are no longer present, and the potential for an enhanced response when re-exposed to predator cues later is less known but could account for the observed variation in anti-predator responses. We measured the carryover effects of past predation exposure and the potential for anti-predator learning and memory in the marine snail Nucella canaliculata from six populations distributed over 1000 km of coastline. We exposed lab-reared snails to cues associated with a common crab predator or seawater control in two serial experiments separated by over seven months. Responses were population- and sex-dependent, with some populations retaining anti-predator behaviours while others showed a capacity for learning and memory. Male snails showed a strong carryover of risk aversion, while females were able to return to normal feeding rates and grow more quickly. These behavioural differences culminated in strong impacts on feeding and growth rates, demonstrating that this variation has implications for the strength of trait-mediated indirect interactions, which can impact entire ecosystems.

Changes in the food selectivity of zooplanktivorous fishes related to the effects of nutrient enrichment in an urban tropical estuary.

Juvenile fish use estuarine ecosystems due to appropriate refuges and food supply found in these environments. The objective of this study was to investigate whether variations in the diet composition of juvenile fishes were mediated by changes in the availability of zooplankton prey in an urban estuary. Changes in fish foraging and prey selectivity were affected by nutrient enrichment. Calanoida and Cyclopoida were the most abundant items present in all zones and seasons, and for this reason, these were the items that most contributed to the fish diet. Shift in feeding strategy associated with eutrophication was registered due to a decrease in water quality. All species showed some contamination with microplastic particles and exhibited selectivity over them. The use of food resources available for fish is likely to be representative of estuarine habitat quality and may provide valuable information on the ecological status of estuaries.

Community Trait Variation Drives Selection on Species Diversity Through Feedback With Predator Density.

Identifying the processes underlying community assembly and dynamics remains a central goal in ecology. Although much research has been devoted to analyzing how environments affect species diversity, fewer studies have resolved the link between the fundamental process of ecological selection and species diversity. It has been suggested that identifying ecological selection by estimating changes in community-weighted variance (CWV) and mean (CWM) of functional traits may help to identify more general rules of community assembly. Here, we asked whether and how selection by predation and competition affect species diversity, and how this is determined by the initial CWV and CWM for traits governing species interactions, as in our case: Competitiveness and defense against a predator. We tracked experimental five-species phytoplankton communities in the presence and absence of a rotifer predator over time. We manipulated the initial community composition so that communities shared at least three of the five species but differed in CWV and CWM for defense against predation. We found that species diversity was highest with higher initial trait distributions and that temporal changes in diversity correlated with trait selection. The initial distributions determined the form of selection over time, with directional selection for defense and competitiveness, followed by reduced selection and an increase in niche availability when the initial trait distribution was low or high. For intermediate initial trait distributions, we observed directional selection in only one trait, followed by stabilizing selection. Differences and changes in selection for defense, competitiveness, and species diversity correlated with the changes in predator density over time. This suggests that the initial trait distribution determined species diversity through a feedback loop with changes in selection on traits and predator density. Overall, our study shows that identifying ecological selection on functional traits can provide a mechanistic understanding of community assembly.

Australia's recently established predators restore complexity to food webs simplified by extinction.

Since prehistory, humans have altered the composition of ecosystems by causing extinctions and introducing species. However, our understanding of how waves of species extinctions and introductions influence the structure and function of ecological networks through time remains piecemeal. Here, focusing on Australia, which has experienced many extinctions and introductions since the Late Pleistocene, we compared the functional trait composition of Late Pleistocene (130,00-115,000 years before present [ybp]), Holocene (11,700-3,000 ybp), and current Australian mammalian predator assemblages (≥70% vertebrate meat consumption; ≥1 kg adult body mass). We then constructed food webs for each period based on estimated prey body mass preferences. We found that introduced predators are functionally distinct from extinct Australian predators, but they rewire food webs toward a state that closely resembles the Late Pleistocene, prior to the megafauna extinctions. Both Late Pleistocene and current-day food webs consist of an apex predator and three smaller predators. This leads to food web networks with a similar total number of links, link densities, and compartmentalizations. However, this similarity depends on the presence of dingoes: in their absence, food webs become simplified and reminiscent of those following the Late Pleistocene extinctions. Our results suggest that recently established predators, even those implicated in species extinctions and declines, can restore complexity to food webs simplified by extinction.

Habitat dimensionality and feeding strategies but not temperature as determinants of body size-trophic structure relationship in a marine food web.

Disentangling the determinants of trophic structure is central to ecology. The capacity to capture subjugate and consume a prey (i.e. gape limitation) is a relevant limitation to acquire energy for most organisms, especially those in smaller size ranges. This generates a size hierarchy of trophic positions in which large organisms consume small ones. Body size is tightly correlated to gape limitation and explains a large fraction of variance in the body size-trophic position relationship. However, a considerable fraction of variance still remains to be explained. Consumer search space dimensionality (2D or 3D) and feeding strategies, temperature and the size structure of primary producers can alter the trophic structure, but tests based on information from natural food webs are scarce. We generated specific predictions about the body size trophic position relationship and evaluated them using information from a subtropical South Atlantic coastal marine ecosystem: benthic realm (2D, rocky shore and sandy beach) and the pelagic realm (3D). We characterized this marine coastal food web based on stable isotopes of carbon and nitrogen from 256 samples from primary producers (macroalgae and phytoplankton) to large predators (sand shark) in summer and winter. Consumer body size encompassed six orders of magnitude in weight from 10-2 to 6 × 104 g. Isotopic signal corresponded to an integration of carbon sources from basal consumers to top predators. The body size-trophic position relationship showed a linear positive association with different slopes for the benthic and pelagic environments. This implies a smaller predator prey size ratio for pelagic (3D) with respect to benthic consumers (2D) as theoretically expected. No seasonal differences were found in slopes and most of the overall variance in benthic environments was largely explained by feeding strategies of the different taxonomic groups. We provide an integrated evaluation on the role of body size, consumer search space and feeding strategy to understand the determinants of trophic position. Results demonstrate that integrating gape limitation hypothesis, the dimensionality of consumer search space and feeding strategies into a formal robust framework to understand trophic structure is feasible even in complex natural ecosystems.

Identificar los determinantes de la estructura trófica es central en ecología. El presente trabajo brinda evidencia empírica sobre el rol del tamaño corporal, la dimensión del espacio de búsqueda de los depredadores y la estrategia de alimentación como determinantes de la posición trófica y su relación con el tamaño. La capacidad de capturar y consumir presas limitado por la apertura de boca es una restricción para la obtención de energía, especialmente en aquellos de pequeño tamaño. Este mecanismo genera una jerarquía de tamaños en la posición trófica de los organismos, donde los grandes consumen a los más pequeños, explicando así gran parte de la variación en la relación tamaño corporal­posición trófica. Sin embargo, la dimensión espacial en la búsqueda de presas (2D, 3D), la temperatura, las estrategias alimentarias y la productividad primaria del sistema pueden modificar la relación esperada. Esto ha sido escasamente explorado in situ en tramas tróficas naturales. El presente trabajo estableció predicciones específicas en la relación tamaño corporal posición trófica y lo evaluó en diferentes módulos de un ecosistema subtropical marino­costero de Sudamérica: el ambiente bentónico (2D, costa rocosa y playa arenosa) y pelágico (3D). La estructura trófica se caracterizó mediante isótopos estables de carbono y nitrógeno en 256 organismos, desde productores primarios (macroalgas y fitoplancton) hasta grandes depredadores (tiburón sarda) en verano e invierno. El rango de tamaños corporales abarcó 6 órdenes de magnitud en peso, desde 10−2 a 6 × 104 g. La señal isotópica indicó una integración de fuentes de carbono desde los consumidores primarios hasta los depredadores superiores. Se observó una relación lineal positiva entre el tamaño corporal y la posición trófica, con una pendiente menor para el ambiente pelágico (3D) con respecto al bentónico (2D), coincidente con las predicciones teóricas. No se observaron diferencias estacionales. La relación tamaño corporal y la posición trófica del ambiente bentónico presentó una gran variabilidad, con restricciones diferenciales entre grupos taxonómicos según sus hábitos alimentarios. Esta evaluación basada en el tamaño corporal, el espacio de búsqueda y la estrategia de alimentación permiten comprender los determinantes de la posición trófica. Los resultados demuestran que la integración de la hipótesis de limitación al consumo, el espacio de búsqueda de presas y la estrategia de alimentación es posible, incluso en ecosistemas naturales complejos.

Long-term monitoring of a population of greater horseshoe bat emphasises the importance of a pest beetle prey on demographic trends.

The global decline in insect biomass has far-reaching implications for terrestrial and freshwater food webs, impacting species reliant on insects as a crucial component of their diet. This issue extends to species traditionally considered agricultural pests, such as the common cockchafer Melolontha melolontha. In the race to combat cockchafers through collection, insecticide use, and other control methods, the repercussions of their numerical fluctuations on predators, including species of high conservation importance like bats, have been largely overlooked. Drawing on 31-years of monitoring data for a greater horseshoe bat Rhinolophus ferrumequinum population in the Aosta Valley (Western Italian Alps), we investigated whether annual fluctuations in bat counts are influenced by cockchafer availability and weather conditions. Despite an overall positive trend in bat abundance, we observed pronounced annual fluctuations, mostly driven by cockchafer availability rather than variations in temperature and precipitation. Furthermore, we found a significant association between cockchafer availability and the median date of birth and birth rate of bats. Births occurred approximately 5 days earlier in cockchafer flight years, with earlier births also linked to warmer spring temperatures and higher numbers of warm days in April. Moreover, the ratio pups/older bats was 0.56 in cockchafer flight years, compared to 0.47 in other years. Our results underscore the importance of considering predator-prey dynamics when examining the long-term population trends of species of conservation concern. We recommend implementing restrictions on the use of chemicals and other potentially harmful practices that may diminish prey abundance or quality, including that of species considered as agricultural pests. In designing conservation strategies, a delicate balance should be struck between the current interests of farmers and the overarching goal of preserving biodiversity against potential future threats.

How do fish miss? Attack strategies of threespine stickleback capturing non-evasive prey.

Most predators rely on capturing prey for survival, yet failure is common. Failure is often attributed to prey evasion, but predator miscalculation and/or inaccuracy may also drive an unsuccessful event. We addressed the latter using threespine stickleback as predators and bloodworms (non-evasive) as prey. High-speed videography of the entire attack allowed us to determine the strike tactics leading to successful or missed strikes. We analyzed movements and morphological traits from 57 individuals. Our results reveal that kinematics drive the strike outcome and that failed strikes primarily arise from incorrect timing of mouth opening, often beginning too far from the prey for suction to be effective. This likely stems from the lack of integration between locomotion and feeding systems. Our study begins to unravel the important link between behavior and success in fish feeding.

Trade-offs between defense and competitive traits in a planktonic predator-prey system.

Predator-prey interactions are crucial components of populations and communities. Their dynamics depend on the covariation of traits of the interacting organisms, and there is increasing evidence that intraspecific trade-off relationships between defense and competitive traits are important drivers of trophic interactions. However, quantifying the relevant traits forming defense-competitiveness trade-offs and how these traits determine prey and predator fitness remains a major challenge. Here, we conducted feeding and growth experiments to assess multiple traits related to defense and competitiveness in six different strains of the green alga Chlamydomonas reinhardtii exposed to predation by the rotifer Brachionus calyciflorus. We found large differences in defense and competitive traits among prey strains and negative relationships between these traits for multiple trait combinations. Because we compared trait differences among strains whose ancestors evolved previously in controlled environments where selection favored either defense or competitiveness, these negative correlations suggest the presence of a trade-off between defense and competitiveness. These differences in traits and trade-offs translated into differences in prey and predator fitness, demonstrating the importance of intraspecific trade-offs in predicting the outcome of predator-prey interactions.

Development and application of chitosan-urea cotton adsorbent as biomimicry technology inspired by natural predator-prey relationships.

Predator-prey interactions play a crucial role in maintaining ecological balance and possibly provide inspiration for strategies to mitigate environmental changes such as harmful algal blooms (HABs). To this end, this study aims to develop a novel strategy to mitigate HABs based on predator-prey interaction, i.e., Daphnia magna and Microcystis aeruginosa interaction. Bio-compounds (urea and 9-octadecenamide) produced by D. magna when encounter M. aeruginosa, were identified, particularly with urea promoting the aggregation of M. aeruginosa. Then, a novel adsorbent against HABs was synthesized by integrating bio-compounds of urea, and its effectiveness in removing M. aeruginosa was demonstrated. Notably, the adsorbent displayed a high removal efficiency of 99.25 % within 6 h. Our eco-friendly strategy holds promise for controlling HABs, representing the successful application of biomimicry principles.

Grazing intensity alters network complexity and predator-prey relationships in the soil microbiome.

Grasslands are recognized as important reservoirs of soil biodiversity. Livestock grazing is implemented as a grassland management strategy to improve soil quality and enhance plant diversity. Soil microbial communities play a pivotal role in grassland ecosystems, so it is important to examine whether grazing practices affect the soil microbiome. Previous studies on grazing have primarily focused on bacteria and fungi, overlooking an important group-protists. Protists are vital in soil microbiomes as they drive nutrient availability and trophic interactions. Determining the impact of grazing on protists and their relationships with bacterial and fungal communities is important for understanding soil microbiome dynamics in grazed ecosystems. In this study, we investigated soil bacterial, fungal, and protist communities under four grazing levels: no grazing, moderate-use grazing, full-use grazing, and heavy-use grazing. Our results showed that heavy grazing led to a greater diversity of protists with specific groups, such as Discoba and Conosa, increasing in abundance. We also found strong associations between protist and bacterial/fungal members, indicating their intricate relationships within the soil microbiome. For example, the abundance of predatory protists increased under grazing while arbuscular mycorrhizal fungi decreased. Notably, arbuscular mycorrhizae were negatively associated with predatory groups. Furthermore, we observed that microbial network complexity increased with grazing intensity, with fungal members playing an important role in the network. Overall, our study reports the impact of temporal grazing intensity on soil microbial dynamics and highlights the importance of considering protist ecology when evaluating the effects of grazing on belowground communities in grassland ecosystems. IMPORTANCE: The significance of this study lies in its exploration of the effects of temporal grazing intensity on the dynamics of the soil microbiome, specifically focusing on the often-neglected role of protists. Our findings provide insights into the complex relationships between protists, bacteria, and fungi, emphasizing their impact on trophic interactions in the soil. Gaining a better understanding of these dynamics is essential for developing effective strategies for grassland management and conservation, underscoring the importance of incorporating protist ecology into microbiome studies in grasslands.

Springing into action: Comparing escape responses between bipedal and quadrupedal rodents.

Predation is a fundamental selective pressure on animal morphology, as morphology is directly linked with physical performance and evasion. Bipedal heteromyid rodents, which are characterized by unique morphological traits such as enlarged hindlimbs, appear to be more successful than sympatric quadrupedal rodents at escaping predators such as snakes and owls, but no studies have directly compared the escape performance of bipedal and quadrupedal rodents. We used simulated predator attacks to compare the evasive jumping ability of bipedal kangaroo rats (Dipodomys) to that of three quadrupedal rodent groups-pocket mice (Chaetodipus), woodrats (Neotoma), and ground squirrels (Otospermophilus). Jumping performance of pocket mice was remarkably similar to that of kangaroo rats, which may be driven by their shared anatomical features (such as enlarged hindlimb muscles) and facilitated by their relatively small body size. Woodrats and ground squirrels, in contrast, almost never jumped as a startle response, and they took longer to perform evasive escape maneuvers than the heteromyid species (kangaroo rats and pocket mice). Among the heteromyids, take-off velocity was the only jump performance metric that differed significantly between species. These results support the idea that bipedal body plans facilitate vertical leaping in larger-bodied rodents as a means of predator escape and that vertical leaping likely translates to better evasion success.

Dynamic primary resources, not just wild prey availability, underpin lion depredation of livestock in a savanna ecosystem.

Because it can lead to retaliatory killing, livestock depredation by large carnivores is among the foremost threats to carnivore conservation, and it severely impacts human well-being worldwide. Ongoing climate change can amplify these human-wildlife conflicts, but such issues are largely unexplored, though are becoming increasingly recognized. Here, we assessed how the availability of primary resources and wild prey interact to shape large carnivore selection for livestock rather than wild prey (i.e., via prey switching or apparent competition). Specifically, we combined remotely sensed estimates of primary resources (i.e., water availability and primary productivity), wild prey movement, and 7 years (2015-2021) of reports for livestock depredation by African lions (Panthera leo) in the Makgadikgadi Pans ecosystem, Botswana. Although livestock depredation did not vary between wet versus dry seasons, analyses at finer temporal scales revealed higher incidences of livestock depredation when primary production, water availability, and wild prey availability were lower, though the effects of wild prey availability were mediated by water availability. Increased precipitation also amplified livestock depredation events despite having no influence on wild prey availability. Our results suggest that livestock depredation is influenced by the diverse responses of livestock, wild prey, and lions to primary resource availability, a driver that is largely overlooked or oversimplified in studies of human-carnivore conflict. Our findings provide insight into tailoring potential conflict mitigation strategies to fine-scale changes in resource conditions to efficiently reduce conflict and support human livelihoods.

A global assessment of large terrestrial carnivore kill rates.

Through killing and instilling fear in their prey, large terrestrial carnivores shape the structure and function of ecosystems globally. Most large carnivore species have experienced severe range and population declines due to human activities, and many are now threatened with extinction. Consequently, the impacts of these predators on food webs have been diminished or lost completely from many ecosystems. Kill rates provide a fundamental metric for understanding large carnivore ecology and assessing and comparing predation within and across ecological communities. Our systematic review of large terrestrial mammalian carnivore kill rates reveals significant positive geographic (North America, Europe, and Africa) and taxonomic (grey wolf Canis lupus, puma Puma concolor, lion Panthera leo, and Eurasian lynx Lynx lynx) bias, with most studies apparently motivated by human-carnivore conflict over access to ungulate prey and wildlife management objectives. Our current understanding of the behaviour and functional roles of many large carnivore species and populations thus remains limited. By synthesising and comparing kill rates, we show that solitary carnivores (e.g. brown bears Ursus arctos and most felids) exhibit higher per capita kill rates than social carnivores. However, ungulate predation by bears is typically limited to predation of neonates during a short period. Lower per capita kill rates by social carnivores suggests group living significantly reduces energetic demands, or, alternatively, that group-living carnivores defend and consume a greater proportion of large prey carcasses, or may acquire more food through other means (e.g. scavenging, kleptoparasitism) than solitary hunters. Kill and consumption rates for Canidae - measured as kilograms of prey per kilogram of carnivore per day - are positively correlated with body mass, consistent with increasing energy costs associated with a cursorial hunting strategy. By contrast, ambush predators such as felids show an opposite trend, and thus the potential energetic advantage of an ambush hunting strategy for carnivores as body mass increases. Additionally, ungulate kill rates remain relatively constant across solitary felid body sizes, indicative of energetic constraints and optimal foraging. Kill rate estimates also reveal potential insights into trophic structuring within carnivore guilds, with subordinate carnivores often killing more than their larger counterparts, which may be indicative of having to cope with food losses to scavengers and dominant competitors. Subordinate carnivores may thus serve an important role in provisioning food to other trophic levels within their respective ecosystems. Importantly, kill rates also clarify misconceptions around the predatory behaviour of carnivores (e.g. spotted hyaenas Crocuta crocuta and wolverines Gulo gulo are often considered scavengers rather than the capable hunters that they are) and thus the potential impacts of various carnivore species on their ecological communities. Despite the importance of kill rates in understanding predator-prey interactions, their utility is not widely recognised, and insufficient research limits our ability to fully appreciate and predict the consequences of modified predation regimes, justify current management actions affecting carnivores, or inform effective conservation measures. Together with other important research on predator-prey interactions, robust kill rate studies that address the research deficiencies we highlight will provide a deeper understanding of the foraging behaviours and potential ecosystem impacts of many of the world's carnivores, thus aiding effective conservation and management actions.