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Consumers are thought to select food resources based on their nutritional content. While laboratory experiments have explored this, the nutritional dynamics of invertebrate predators have been scarcely studied in the field given various methodological constraints. The intersection of these nutritional dynamics with predator traits is also poorly characterised, leading to many gaps in our understanding of how different predators forage and feed in natural systems. Here, we integrate dietary metabarcoding with prey macronutrient (protein, lipid and carbohydrate) content and abundance to assess how nutrients and predator traits (sex, life stage and taxonomy) interactively drive prey preferences in the field, using spider–prey interactions as a model system. Different spider genera, sexes and life stages had nutritionally distinct diets. Our analyses demonstrated disproportionate foraging (selection and avoidance) for prey rich in different macronutrients, with the nature of these relationships differing between spider taxa, life stages and sexes. This may be explained by niche differentiation among spider groups, driven by biases toward prey rich in different nutrients, or nutrient‐specific foraging in which individual spiders vary their nutritional preferences to redress deficits, although further evidence is required to confirm this. This insight into the nutritional dynamics of generalist invertebrate predators extends our understanding beyond lab‐based behavioural assays and provides a novel framework for other complex real‐world systems. [ABSTRACT FROM AUTHOR]

Abstract Background Cydnoseius negevi (Swirski and Amitai) (Acari: Phytoseiidae) is a promising bio-agent in the Mediterranean region. It attacks a wide range of pest species. Two fundamental questions have been raised when C. negevi was a promising candidate for biological control applications in a hydroponic system. This study was carried out to answer the raised questions: (1) how long a predatory female takes to attack its prey in a non-choice biological control application? and (2) what do the predatory females prefer when offered a multiple choice (free-choice) of pest preys?, to understand the potentialities of C. negevi attacking behaviour. Results Two sets of experiments were conducted for 240 min under laboratory conditions of 27 ± 2 °C, 60 ± 5% RH, and 18:6h L:D photoperiod. The tested prey species were Tetranychus urticae Koch, Bemisia tabaci (Gennadius), Frankliniella occidentalis (Pergande), Parlatoria ziziphi (Lucas), and Icerya aegyptiaca (Douglas). Non-choice experiments tested the time (min) needed to the 24 h starved female to attack its prey. The free-choice experiments tested the female’ choices and the time recorded for each female during the full experimental time. Significant differences were recorded in both sets at confidence level of 95%. The spider mite T. urticae recorded the shortest predatory female’s response in both non- and free-choice sets. On the contrary, the insect I. aegyptiaca had the least female’s choice in both sets of experiment. Conclusion The present study discussed the behavioural categories of C. negevi. The female responses showed a list of priorities to the tested herbivore species. Such behavioural simulation is considerable for the future pest control applications to predict the generalist predator’s preferences among a wide range of multiple herbivore species.

We explored the potential of differences in foraging preferences to contribute to long-term species coexistence in aquatic predatory hemipterans. We hypothesized that predatory hemipterans would have distinct foraging preferences informed by their morphology. We used a prey choice experiment to test whether Belostoma flumineum, Pelocoris biimpressus, and Ranatra australis differed in their relative preferences of amphipod, damselfly naiad, and physid snail prey. We discovered that the predators showed complementarity in their foraging preferences with B. flumineum preferring snails, P. biimpressus damselfly naiads and R. australis amphipods as prey. Our results suggest that the disparate foraging preferences of aquatic hemipterans may facilitate their coexistence in aquatic systems but caution that studies need to explore whether patterns uncovered in the laboratory experiment reflect interactions in nature. [ABSTRACT FROM AUTHOR]

The role that humans played in the extinction of Pleistocene proboscideans is highly controversial. Ethnohistoric records of elephant hunting, in concert with theoretical rationales, are often used as proxy evidence to support the view that ancient humans regularly and efficiently targeted large-sized proboscideans to the point of extinction. This paper examines the socioeconomic and technological contexts of elephant hunting in contemporary and ethnohistoric records to show how these circumstances influenced the scale of harvest, productivity, and valuation of elephants. Quantitative and qualitative evidence derived from some of these records are used to analyze the efficiency of elephant capture using traditional hunting technologies (spears, poisoned projectiles, traps, and drives). This analytical framework provides a systematic method for evaluating the productivity of proboscidean predation. Results show that prior to the widespread use of firearms in the eighteenth and nineteenth centuries, the acquisition of elephants, irrespective of the traditional hunting technology used, was a dangerous, high-cost activity often associated with a high-risk of hunting failure. In the ethnographic record, elephant hunting is consistently associated with prestige-seeking among egalitarian hunter-gatherers. Although the analysis presented here is derived from hunting episodes that involved modern elephants, the physical characteristics and abilities that make these animals expensive and risky to hunt were likely manifested by most Pleistocene proboscideans. Using ethnographic data, a framework for recognizing how prestige hunting is manifested under different ecological and sociopolitical circumstances is provided and offers an alternative and compelling explanation for zooarchaeological patterning of costly prey in the past. [ABSTRACT FROM AUTHOR]

The role of vertebrate scavengers in nutrient flow of aquatic ecosystems has recently been emphasized. Evidence is accumulating that scavenging is an alternative tactic for certain predatory fish, but their foraging choices between scavenging and predation under varying environmental conditions have not been studied. In this study, we presented black bullheads, Ameiurus melas (Rafinesque, 1820), with both live and carcass prey of tubenose gobies, Proterorhinus semilunaris (Heckel, 1837), in aquaria with varying levels of turbidity and habitat complexity. Our findings revealed that black bullheads exhibit higher consumption of carcass prey in complex habitat and clear water conditions. We also provide evidence of the active predatory behavior displayed by black bullheads; a greater consumption of live prey was observed in simple habitat and turbid water. We found no relationship between individual exploratory behavior and the choice between carcass and live prey in black bullheads. Our results suggest that the choice between scavenging versus predatory foraging strategy under varying environmental conditions is influenced by the behavior of both consumer and prey. The ability of black bullheads to adapt their foraging strategy in different environments may contribute to their widespread success as an invasive species. [ABSTRACT FROM AUTHOR]

In small-scale societies hunting is a high-risk, high-reward activity which impacts status and reproductive success. The question of whether men hunt to provision families or as a costly signal of their phenotypic qualities has been hotly debated in the anthropological literature. To shed new light on this question, we explored audience assessments of a hunter's phenotypic quality and desirability as a function of the composition of prey acquired by the hunter. A combination of ranking and forced-choice tasks were administered to 52 informants (46% female, aged 15–76 years) from the Aché hunter-gatherer tribe of Paraguay between May and July of 2015. Ratings of a hunter's provisioning ability, strength, fighting ability, disease resistance, and desirability as a mate or ally were all positively associated with killing large and hard-to-kill prey, and negatively associated with killing hard-to-find prey. However, killing a single large animal resulted in a worse assessment of hunter phenotype and desirability than killing an equivalent biomass of small animals. These findings highlight the potential of small prey hunting as a mechanism for advertising both quality and consistent provisioning ability. Critically, no conflict was observed between the goal of advertising quality/desirability and the goal of effective provisioning, since hunters who acquired more meat, even if the source of the meat was small game, were generally perceived as having better phenotypes and as more desirable. [ABSTRACT FROM AUTHOR]

Simple Summary: Predator–prey interactions can be influenced by environmental factors and depend on the sensory capabilities of a predator and its prey. Environmental factors influence the prey discrimination of white sharks in Gansbaai during their passive prey predatory behavior. Tide range is the most important factor that influences the white sharks' prey choice, followed by underwater visibility, water temperature, and sea conditions. With high tide, better underwater visibility, cooler water temperature, and better sea conditions, sharks choose the energetical richer prey, the seal-shaped decoy, instead of the tuna bait. This study confirms the importance of visual ability in mature and immature white sharks with dietary shifts in their feeding pattern. The influence of environmental factors on prey discrimination of bait-attracted white sharks was studied over a six-year period (2008–2013) at Dyer Island Nature Reserve (Gansbaai, South Africa). Across 240 bait-attracted feeding events observed in this period, both immature and mature white sharks were attracted by the seal-shaped decoy rather than the tuna bait, except for the years 2008 and 2011. Tide ranges, underwater visibility, water temperature, and sea conditions were, in decreasing order, the factors which drove white sharks to select the seal-shaped decoy. High tide lowered the minimum depth from which sharks could approach seals close to the shore, while extended visibility helped the sharks in making predatory choices towards the more energy-rich prey source, the odorless seal-shaped decoy. On the contrary, warmer water is associated with an increase in phytoplankton that reduces underwater visibility and increases the diversity of teleosts including tuna—a known prey of white sharks—driving the sharks to favor the tuna bait. Overall, sea conditions were almost always slightly rough, ensuring a good average underwater visibility. Recommendations for future research work at this site are presented. [ABSTRACT FROM AUTHOR]

Parental food provisioning is crucial for the growth and survival of offspring. Growth rate depends on food quality and food supplied to offspring may differ from what adults use for their own. In the case of steppe passerine birds, detailed characterization on nestling dietary composition, as well as prey choice and resource partitioning among species, is a pending subject. Dietary differences between nestlings and adults remain also largely unexplored. By using faecal DNA metabarcoding, we described the diet of nestlings and adults of five shrub-steppe passerine species over the 2017–2019 breeding seasons in central Spain. We also monitored arthropod availability in the field to assess dietary selection. We expected interspecific dietary differences to limit competition for food resources among sympatric species, as well as parental selection of high quality prey for nestlings. We also predicted age-related differences, with nestlings being fed nutrient-rich prey more frequently than adults. The main arthropod orders provisioned to nestlings were Orthoptera, Julida, Araneae and Lepidoptera. Nestlings of the different species showed high interspecific diet overlap, indicating both a coincidence in growth needs among bird species and no or little limitation of the most profitable resources during the breeding season. Adults of all species showed higher diet richness than nestlings, and age-related differences in prey composition were mainly driven by the selection of the most easily digestible, larger protein- and calcium-rich prey for nestlings, which may favour their rapid growth, and avoiding highly sclerotized and less nutritional prey such as ants. Our study sheds light on the basic ecology and conservation of these declining steppe birds, indicating that interspecific competition may not be a major factor during the breeding season. Given the current global decline of arthropods, further long-term research would be necessary, along with the implementation of effective conservation measures that ensure a sufficient availability of resources identified as key prey in the diet of steppe bird nestlings.

Distinguishing between selective and opportunistic hunting is a major challenge in Paleolithic archaeology, requiring the comparison of the human hunting record to the usually unknown natural prey abundance. Open-air hunting camps are ubiquitous in the Eurasian Middle Paleolithic (MP) record, alongside cave sites, and are often dominated by large-bodied species. In the Levant, MP faunal records differ between caves and open-air sites: Caves are dominated by mountain gazelle and fallow deer, while open-air sites are more aurochs-dominated. This discrepancy can be explained by transport patterns, but whether the abundance of aurochs in open-air sites is due to deliberate targeting or natural abundance in the landscape is unclear. The Nesher Ramla open-air site is a natural sinkhole in central Israel with an 8-m-deep MP sequence. Detailed zooarchaeological, dental wear, and isotope analyses of the upper sequence fauna found a highly diverse assemblage dominated by medium-sized ungulates in the uppermost phases (Units I and IIa). Results concerning ungulate dietary niches and isotopic signatures demonstrate that animals from different biomes and topographies congregated at the site. Evidence of human butchery is infrequent and fewer than carnivore modifications. Several articulated vertebral columns attest to in situ preservation. Our results demonstrate that the Nesher Ramla's uppermost sequence formed primarily under natural conditions, suggesting that it was a site of opportunistic hunting by humans and carnivores, probably targeting ungulates that came to the sinkhole to drink. Therefore, we consider this assemblage representative of the site's "natural" environment and use it as a benchmark for comparing assemblages and hunting strategies. Thus, we observe a clear difference between our case study and those recovered from the site's lower layers (Unit IIB and below) and other open-air sites. For the first time, we can show that the abundance of large bovines in MP open-air sites is not necessarily due to their abundance in the environment but to deliberate human planning and selective hunting. • Nesher Ramla (NR) is an MIS 5 open-air Levantine site with an 8 m-thick sequence. • Latest phase fauna was deposited by natural deaths, human and carnivore predations. • Ungulates came to the site from afar to drink from the seasonal waterhole. • High ungulate diversity of the faunal assemblage suggests opportunistic hunting. • Aurochs abundance in Levantine MP open-air sites is due to selective human hunting. [ABSTRACT FROM AUTHOR]

Specialist predators are innately and distinctively proficient at targeting specific prey types. This is enabled by behavioural, perceptual and cognitive mechanisms that can only be understood using carefully designed experiments. Evarcha culicivora is an East African jumping spider that feeds on vertebrate blood acquired indirectly by actively targeting blood-carrying female mosquitoes as preferred prey. Here we asked whether these spiders use the colour red to identify this prey. In Objective 1, we used spectrophotometry to document the changing redness of mosquitoes in the first 17 h following blood meals. In Objective 2, we used vision-based choice tests to document how E. culicivora 's preference for blood-carrying mosquitoes changes over time (using an interval comparable to that in Objective 1). We found the strongest preference for blood-carrying mosquitoes during the first 6 h after those mosquitoes had fed on blood and that this time interval corresponded to when mosquitoes exhibit the reddest coloration. Based on this, we then took mosquitoes that had never fed on blood and manipulated their colour using a blend of red food dye to make them appear blood-fed (i.e. by matching their spectral properties to mosquitoes that had fed on blood within the previous 6 h). We also created grey-dyed mosquitoes that matched the spectral properties of those that had never fed on blood. In Objective 3, there was no evidence of E. culicivora visually discriminating between our red-dyed mosquitoes and blood-carrying mosquitoes; this indicates that, to E. culicivora , our red-dyed mosquitoes appropriately resembled blood-carrying mosquitoes. Finally, in Objective 4, we show that E. culicivora consistently preferred red-dyed mosquitoes over grey-dyed mosquitoes, supporting the hypothesis that E. culicivora uses some aspect of red coloration to identify their preferred prey. We discuss how these findings relate to cognitive processes, colour-based communication and sensory exploitation. • Evarcha culicivora, a jumping spider, targets blood-carrying mosquitoes as prey. • They prefer mosquitoes that have had a recent blood meal, with visibly red abdomens. • Tests with artificially coloured mosquitoes show they use red colour to select prey. [ABSTRACT FROM AUTHOR]

Context: Zooplanktivorous fish are a key link between abundant zooplankton and higher trophic levels but the foraging behaviour of zooplanktivorous fish is not fully understood. Selective feeding behaviours have been observed, with many species of planktivorous fish targeting certain species and sizes of zooplankton for prey. However, why certain size classes of zooplankton are preferred remains unclear. Aim: This study investigated prey selection by three zooplanktivorous fish species through the lens of optimal foraging theory. Methods: We assessed the size structure of zooplankton in the environment and compared this with the size distribution of zooplankton in gut contents from three zooplanktivorous fish. Key results: The targeted prey size of Atypichthys strigatus and Scorpis lineolata aligns with the prey size classes in the environment that contain the highest overall biomass. Trachurus novaezelandiae showed little evidence of targeting these size classes. Conclusions: These prey sizes therefore represent the most efficient prey to target because the return on foraging effort is greatest. By contrast, T. novaezelandiae showed only an underselection of large and small prey. Implications: By incorporating this information on this key trophic link between zooplankton and fish, ecosystem models could better resolve the size dependant predation, particularly in size-based models. This paper shows that 2 of 3 species of estuarine fish target specific sizes of zooplankton rather than eating everything they encounter. This pattern is driven by the fish attempting to maximise the biomass consumed by targeting the zooplankton size classes with the most overall biomass in the environment. [ABSTRACT FROM AUTHOR]

Chinese perch (Siniperca chuatsi) larvae prey on other fish species larvae at the beginning of exogenous feeding but do not eat any zooplankton in natural conditions, the mechanism behind this special feeding habit is unclear at present. This study aimed to visualize the development of gill rakers in Chinese perch larvae and observe the ingestion of larvae to different size Artemia in low salinity (5 g/L) water. Our results indicated that Chinese perch larvae demonstrated a slow development in gill rakers, larvae only had some buds from hatching to 7 days post hatching (dph), and the first and second real gill raker was observed at 9 dph and 12 dph respectively. The edar gene expression also consisted with development of gill rakers. Meanwhile, the results of ingestion showed larvae preferred to feed large size Artemia, and larvae fed the large size Artemia also had a higher npy gene expression. Compared with the larvae fed small size Artemia, the larvae which fed the large size Artemia had a higher survival rate. These data inform hypotheses development of gill rakers may influence the prey choice in Chinese perch larvae, no real gill rakers may cause the larvae can not to forage small size zooplankton at first‐feeding stage and, thus, the Chinese perch larvae form the special feeding habit. [ABSTRACT FROM AUTHOR]

Some prey are exceptionally difficult to digest, and yet even non-specialized animals may consume them—why? Durophagy, the consumption of hard-shelled prey, is thought to require special adaptations for crushing or digesting the hard shells to avoid the many potential costs of this prey type. But many animals lacking specializations nevertheless include hard-bodied prey in their diets. We describe several non-mutually exclusive adaptive mechanisms that could explain such a pattern, and point to optimal foraging and compensatory growth as potentially having widespread importance in explaining costly-prey consumption. We first conducted a literature survey to quantify the regularity with which non-specialized teleost fishes consume hard-shelled prey: stomach-content data from 325 teleost fish species spanning 82 families (57,233 stomach samples) demonstrated that non-specialized species comprise ~75% of the total species exhibiting durophagy, commonly consuming hard-shelled prey at low to moderate levels (~10–40% as much as specialists). We then performed a diet survey to assess the frequency of molluscivory across the native latitudinal range of a small livebearing fish, Gambusia holbrooki, lacking durophagy specializations. Molluscivory was regionally widespread, spanning their entire native latitudinal range (>14° latitude). Third, we tested for a higher frequency of molluscivory under conditions of higher intraspecific resource competition in Bahamian mosquitofish (Gambusia spp.). Examining over 5,300 individuals, we found that molluscivory was more common in populations with higher population density, suggesting that food limitation is important in eliciting molluscivory. Finally, we experimentally tested in G. holbrooki whether molluscivory reduces growth rate and whether compensatory growth follows a period of molluscivory. We found that consumption of hard-shelled gastropods results in significantly reduced growth rate, but compensatory growth following prior snail consumption can quickly mitigate growth costs. Our results suggest that the widespread phenomenon of costly-prey consumption may be partially explained by its relative benefits when few alternative prey options exist, combined with compensatory growth that alleviates temporary costs.

This paper reports occurrence of mason wasp Pison punctifrons Shuckard, 1838 from Noida, Uttar Pradesh, India. This is a new distribution record for the species. This paper examines the nest architecture and prey choices of the wasp and carries the photographic record of a live P. punctifrons Shuckard on her nest with prey. [ABSTRACT FROM AUTHOR]

North American cambarid crayfish have been highly successful in establishing and spreading across Europe and are now over-invading earlier arrivals in many water bodies. Parthenogenetic marbled crayfish (Procambarus virginalis), which originated from aquarium stocks, are relatively recent invaders and have established in lakes previously invaded by spiny-cheek crayfish (Faxonius limosus). However, the feeding ecology of marbled crayfish and consequential impacts on the non-native species' coexistence are largely unexplored. By combining laboratory experiments with stable isotope analyses of field samples, we were able to (1) determine food preferences of both species under controlled conditions and (2) explore their trophic niches in three lakes where both species co-occur. In the food-choice laboratory experiments, the two species showed similar food preferences and consumption rates. Consistently, the stable isotope analyses (δ13C and δ15N) highlighted the intermediate trophic position of both species. Marbled crayfish and spiny-cheek crayfish occupied a wide range of trophic positions corresponding to a very generalist diet. However, marbled crayfish were more relying on arthropod prey than spiny-cheek crayfish which fed more on mollusks. This is the first work providing evidence for trophic plasticity of marbled crayfish in lake food webs. Our results suggest that the addition of marbled crayfish increases grazing pressure on macrophytes and macrophyte-dependent organisms and the allochthonous detritus decomposition in ecosystems already invaded by spiny-cheek crayfish. Since both species are listed as invasive alien species of EU concern, further assessments of potentially endangered food organisms are needed. [ABSTRACT FROM AUTHOR]

The giant willow aphid, Tuberolachnus salignus is an invasive insect in New Zealand for which control measures are being sought due to its detrimental effects on willow cultivation and apiculture. We evaluated the biocontrol potential of the harlequin ladybird beetle, Harmoniaaxyridis, by measuring voracity and feeding preference of larvae and adults in laboratory trials. Results show that H. axyridis consumes T. salignus, with females being more voracious than males and larvae. However, H. axyridis fed T. salignus took longer to develop, gained less weight and had lower survival compared with those fed eggs of the Mediterranean flour moth, Ephestiakuehniella. In a choice test, larval and adult H. axyridis preferred the green peach aphid, Myzuspersicae, as prey item, rejecting T. salignus. We suggest that H. axyridis is likely to use T. salignus only as a facultative prey, and therefore cannot be prioritised as a potential biocontrol agent. [ABSTRACT FROM AUTHOR]

Between the years 2008 and 2013, six annual research expeditions were carried out at Dyer Island (Gansbaai, South Africa) to study the surface behaviour of white sharks in the presence of two passive prey: tuna bait and a seal-shaped decoy. Sightings were performed from a commercial cage-diving boat over 247 h; 250 different white sharks, with a mean total length (TL) of 308 cm, were observed. Of these, 166 performed at least one or more interactions, for a total of 240 interactions with bait and the seal-shaped decoy. In Gansbaai, there is a population of transient white sharks consisting mainly of immature specimens throughout the year. Both mature and immature sharks preferred to prey on the seal-shaped decoy, probably due to the dietary shift that occurs in white sharks whose TL varies between 200 cm and 340 cm. As it is widely confirmed that white sharks change their diet from a predominantly piscivorous juvenile diet to a mature marine mammalian diet, it is possible that Gansbaai may be a hunting training area and that sharks show a discriminate food choice, a strategy that was adopted by the majority of specimens thanks to their ability to visualize energetically richer prey, after having been attracted by the odorous source represented by the tuna bait.

For a vector species, understanding their egg raft predation (consumption) or destruction is essential for both ecological and human health reasons since it directly influences its fitness. In a mesocosm experiment, we assessed differences in Culiseta longiareolata egg raft predation/destruction by three aquatic predators Notonecta maculata (backswimmers), Sympetrum fonscolombii (dragonflies) and Ommatotriton vittatus (newts), both in the presence and absence of an alternate prey (Culex larve). Egg raft predation and destruction significantly differed between predators types, and strongly influenced by the presence of alternate prey. Backswimmers attacked and destroyed (broke down) all egg rafts until they disintegrated and sank in water regardless of whether an alternative prey was present. Egg raft predation by dragonflies was common in the absence of alternative prey, but rare when alternative prey was present. Predation by newts was rare regardless of whether there was an alternative prey. The number of alternate prey consumed also significantly differed between predators (P < 0.001) with backswimmers being the most effective predator. Relatively few studies have tested for egg raft predation/destruction. Hence it is crucial that we conduct similar trials in other landscapes since such predators can prove to be key agents for the biological control of mosquitoes. [ABSTRACT FROM AUTHOR]

Dietary specialization has led to the origin of several ecotypes of killer whales (Orcinus orca). Comparing the feeding habits of different populations within an ecotype is valuable for understanding the evolution of foraging strategies. In this study we investigated the diet of fish-eating killer whales in the Northwest Pacific Ocean (Avacha Gulf, Kamchatka) and compared it to the published data on Northeast Pacific fish-eating killer whales. We collected prey fragments (N = 141) after hunting events in the summer seasons of 2011–2016 and determined the species of prey. Killer whales fed mainly on various species of Pacific salmon in Avacha Gulf. Coho salmon (Oncorhynchus kisutch) (56% of samples) and chum salmon (O. keta) (31% of samples) predominated in the diet. The results are comparable to the peculiarities of the fish-eating killer whale diet in the Northeast Pacific where killer whales prefer Chinook salmon (O. tshawytscha) most of the summer but shift toward coho and chum in late summer. Avacha Gulf could be an area where killer whales come to hunt coho similar to Prince William Sound in Alaska where killer whales prefer coho to other salmon species. We found significant differences in the diet between sex-age categories. Females (N = 42) and juveniles (N = 15) were more selective and hunted mainly coho while males (N = 53) hunted chum equally to coho. Like Chinook in British Columbia, coho in Kamchatka has a prolonged spawning period. Coho is the most nutritious after Chinook. Coho's prolonged abundance and nutritional value probably make it preferable to killer whales especially females. [ABSTRACT FROM AUTHOR]

Feeding at early fish life stages is a key determinant of survival to recruitment. To understand the environmental and developmental determinants of early life stage feeding in ESA‐threatened green sturgeon (Acipenser medirostris), we performed a diet study in a highly managed section of California's Sacramento River, where temperature and discharge are controlled by dam releases. Utilising field collections from 2012 to 2016, we assessed the impacts of temperature, discharge and morphological development on the composition and number of prey items in larval green sturgeon diets. Results show that there are more empty stomachs at colder temperatures. Higher discharge conditions decreased prey taxon richness and counts, especially the abundance of cyclopoid copepods in diets. Fish smaller than 30 mm had teeth on the oral jaws and showed a strong reliance on zooplankton prey. The developmental loss of teeth in fish greater than 30 mm was associated with decreased zooplankton consumption and increased richness of benthic macroinvertebrates in diets. Our results show that river management through dam releases has the potential to impact the earliest life stage of green sturgeon by reducing the prevalence of favoured zooplankton prey in diets. [ABSTRACT FROM AUTHOR]

Scorpions are dominant predators in some environments. Nevertheless, most studies of predatory behavior in scorpions have focused on diet composition whereas some other relevant aspects, such as predatory strategy, have been poorly explored. Herein we evaluate the prey acceptance and predatory strategy of the scorpion Bothriurus bonariensis against sympatric prey with different defenses. As prey, we selected earwigs (Forficula cf. auricularia) which use pincer-like defensive appendages, hard-bodied isopods (Armadillium vulgare) known for their conglobation defensive strategy, soft bodied isopods (Porcellio cf. scaber), which secrete noxious substances as defense mechanisms, cockroaches with limited defensive mechanisms (Blatta cf. orientalis.) and spiders (Lycosa cf. poliostoma) which possess venomous fangs. Prey were offered to 21 adults of B. bonariensis in random order until all prey had been offered to all scorpions. Prey consumption and the number of attempts needed for capture were recorded. We also evaluated the effect of sting use on immobilization time as well as the prey capture strategies on the most consumed prey. We found that despite using a similar number of attempts for capturing all prey, spiders and armadillid isopods were less consumed than other prey. Immobilization times were longer for earwigs than for armadillid isopods and cockroaches. Scorpions used alternative predatory strategies against these aforementioned prey, although the stinger was used against all of them. These results show that scorpions are able to use different predatory strategies which might allow them to include prey with diverse defensive strategies in their diet. [ABSTRACT FROM AUTHOR]

During the years 2008-2014, we studied diet composition, the number of breeding pairs, and reproductive output of tawny owls in Central Europe (Czech Republic) in relation to availability of main prey in the field. We also performed a meta-analysis on diet composition of tawny owl in Europe that confirmed the important role of Apodemus mice in tawny owl diet in Central Europe. In concordance, Apodemus mice were the main prey of tawny owl in our study area (38.7%), and Microtus/Myodes voles (15.4%), birds (12.1%) and others (33.8%) were alternative prey. We found a positive relationship between the proportion of Apodemus mice in the diet and their abundance in the field (beta = 0.23, P = 0.001). Availability of main prey (Apodemus mice, Microtus/Myodes voles or Sorex shrews) in the field was not correlated with the number of breeding pairs. Proportion of birds in diet (expressed by scores from multivariate analysis), which was inversely related to proportion of Apodemus mice, was positively correlated with laying date (beta = 0.66, P = 0.012) and negatively correlated with clutch size (beta = − 0.45, P = 0.004) and brood size (beta = − 0.16, P = 0.076). We also found negative relationships between laying date and clutch size (beta = − 0.13, P = 0.014) and brood size (beta = − 0.07, P = 0.057). Our results support the idea that diet and breeding ecology of owls in Central Europe is mainly driven by the availability of Apodemus mice that are suitable prey due to their similar habitat requirements and nocturnal activity. [ABSTRACT FROM AUTHOR]

Describing predation patterns and especially estimating kill and consumption rates is essential for understanding the functional responses of predators. An understanding of the carrying capacity of the landscape, based on prey availability, also helps to formulate recovery plans for persecuted species. We studied the feeding behavior of the Persian leopard (Panthera pardus saxicolor) in Tandoureh National Park (355 km2) in northeastern Iran, near the Turkmenistan border. Between September 2014 and May 2017, we collared and monitored 6 adult leopards (5 males and 1 female) using GPS-satellite Iridium collars. We investigated 310 clusters of fixes as likely to be kill sites. In total, 130 kills were identified to species, suggesting a mean kill rate of approximately 3.3 ± 0.3 (SE) kills/month per adult male leopard, which is higher than reported by most previous studies. The leopards varied considerably in the time they spent outside the national park; only 1 individual appeared to subsist mainly by raiding livestock. The availability of medium-sized ungulates at adequate densities is likely to be important for future leopard conservation efforts. The management of problem individuals also may promote coexistence of humans and leopards, even in prey-rich areas. [ABSTRACT FROM AUTHOR]

Natal dispersal is common in animals but the fitness cost of moving from the natal area is not well understood. One reason for a fitness cost is that foraging skills and prey preference learned early in life may be less efficient if the individual settles in a new, unfamiliar habitat. In a 4-year study, we found that immigrant parent blue tits, Cyanistes caeruleus , and great tits, Parus major , were inferior food providers compared to local recruits. In blue tits, immigrants provided smaller prey items than local recruits, whereas in great tits, the immigrants provided fewer green larvae, but relatively more brown larvae, to the offspring than local recruits. We also found that immigrant females laid later or smaller clutches than females locally recruited. The results are consistent with the hypothesis that natal dispersal carries costs related to the learning of foraging skills. However, alternative explanations are that the differences were caused by genetic and/or quality differences between the two groups of birds. We discuss various ecological and behavioural traits that may influence, and be influenced by, the mismatch of foraging between natal and breeding habitats. In altricial birds, yearlings will not have previous foraging experience during breeding and, in addition, immigrants will not have spent a long postfledging period in the new local habitat with their parents. If there are foraging-habitat mismatches as a result of dispersal, researchers should include natal origin in models of optimal foraging, time budgets, reproductive success and survival because performance may be directly related to the early learning environment rather than genetic differences. [ABSTRACT FROM AUTHOR]

Abstract: Network analysis is increasingly widespread in ecology, with frequent questions asking which nodes (typically species) interact with one another and how strong are the interactions. Null models are a way of addressing these questions, helping to distinguish patterns driven by neutral mechanisms or sampling effects (e.g. relative abundance of different taxa, sampling completeness) from deterministic biological mechanisms (e.g. resource selection and avoidance), but few “off the shelf” tools are available. We present econullnetr, an r package combining null modelling and plotting functions for networks, with data‐export tools to facilitate its use alongside existing network analysis packages. It models resource choices made by individual consumers, enabling it to capture individual‐level heterogeneity and generalising to a wider range of data types and scenarios than models applied directly to network matrices. The outputs can be analysed from the level of individual links to whole networks. We describe the main functions and provide two short examples, along with the results of a benchmarking exercise to provide guidance about the statistical power and error rates. Our hope is that econullnetr provides a basis for more widespread use of null modelling to assist ecological network interpretation. [ABSTRACT FROM AUTHOR]

The use of optimal foraging theory in archaeology has been criticized for focusing heavily on “negative” human-environmental interactions, particularly anthropogenic resource depression, in which prey populations are reduced by foragers’ own foraging activities. In addition, some researchers have suggested the focus on resource depression is more common in the zooarchaeological literature than in the archaeobotanical literature, indicating fundamental differences in the ways zooarchaeologists and archaeobotanists approach the archaeological record. In this paper, we assess these critiques through a review of the literature between 1997 and 2017. We find that studies identifying resource depression occur at similar rates in the archaeobotanical and zooarchaeological literature. In addition, while earlier archaeological applications of optimal foraging theory did focus heavily on the identification of resource depression, the literature published between 2013 and 2017 shows a wider variety of approaches.

Recently, a highly invasive alien species, the zebra mussel Dreissena polymorpha, has colonized Italian aquatic ecosystems that had been previously colonized by another highly invasive alien species-the North American crayfish Procambarus clarkii. This was the first time and world region where these two species met. To evaluate the relative importance of their interactions, we studied prey selection according to its length, as well as prey choice by P. clarkii preying on D. polymorpha in the presence and absence of alternative prey-the freshwater snail Physella acuta. We followed an optimability-based approach, by first estimating the most profitable length of each mollusc and then by conducting a prey choice experiment, on which both species were provided simultaneously to a crayfish with different size combinations. Prey selection was dependent on prey length, handling time and crayfish length for both molluscs. According to our profitability estimates, snails should be more profitable than mussels in the length range 7-10 mm, while for lengths over 11.0 mm, mussels should be more profitable. The results of the prey choice experiment indicated that D. polymorpha length, P. acuta length, and the difference in profitability between the offered individuals were all relevant for the choice of one species over the other by P. clarkii. However, the overall tendency was the choice of the smallest prey, regardless of species, and the estimates of prey profitability were not useful to predict prey choice. Our study shows that D. polymorpha represents a novel prey resource for P. clarkii, even in the presence of an alternative prey, and that zebra mussels may be a preferred prey, especially small-sized individuals (5-10 mm). [ABSTRACT FROM AUTHOR]

Many fishes are planktivorous during early life and switch to piscivory or consume larger food items as ontogeny progresses. In contrast, paddlefish start as particulate feeders and later become filter feeders. Few studies have identified food items essential for paddlefish growth, survival and recruitment surrounding this ontogenetic diet shift. The objectives of this study were to investigate (i) prey types consumed by paddlefish, (ii) variability in prey selection surrounding an ontogenetic diet shift and (iii) whether habitat affected paddlefish prey selection or foraging success. We analysed gut contents of 189 wild age-0 paddlefish from the middle Mississippi River ( MMR) and also conducted a laboratory experiment to address these objectives. We found that paddlefish primarily foraged on benthic macroinvertebrates in the MMR, which differed from previous studies in lentic systems, suggesting young paddlefish prey selection may be labile depending on habitat (i.e., lotic versus lentic). Dominant prey of wild-caught and experimental age-0 paddlefish were caddisfly larvae ( Trichoptera), followed by hemipterans and amphipods. We found little evidence that habitat attributes affected foraging success, but the most common prey items consumed were associated with wing dike habitat and the upstream and downstream tips of alluvial islands. Our experimental study revealed that if provided a mixture of organisms, age-0 paddlefish will primarily consume macroinvertebrates while age-1 paddlefish will mainly filter zooplankton. Overall results suggest young paddlefish prey selection can be highly variable, but also heavily reliant on a narrow group of prey resources. [ABSTRACT FROM AUTHOR]

Prey choice is often evaluated at the species or population level. Here, we analyzed the diet of octopuses of different populations with the aim to assess the importance of individual feeding habits as a factor affecting prey choice. Two methods were used, an assessment of the extent to which an individual octopus made choices of species representative of those population (PSi and IS) and 25% cutoff values for number of choices and percentage intake of individual on their prey. In one population of Octopus cf vulgaris in Bermuda individuals were generalist by IS=0.77, but most chose many prey of the same species, and were specialists on it by >75% intake. Another population had a wider prey selection, still generalist with PSi=0.66, but two individuals specialized by choices. In Bonaire, there was a wide range of prey species chosen, and the population was specialists by IS= 0.42. Individual choices revealed seven specialists and four generalists. A population of Octopus cyanea in Hawaii all had similar choices of crustaceans, so the population was generalist by IS with 0.74. But by individual choices, three were considered a specialist. A population of Enteroctopus dofleini from Puget Sound had a wide range of preferences, in which seven were also specialists, IS=0.53. By individual choices, thirteen were also specialists. Given the octopus specialty of learning during foraging, we hypothesize that both localized prey availability and individual personality differences could influence the exploration for prey and this translates into different prey choices across individuals and populations showed in this study [Current Zoology 58 (4): 597-603, 2012].

Snakes often have specialized diets that undergo a shift from one prey type to another depending on the life stage of the snake. Crotalus viridis viridis (prairie rattlesnake) takes different prey at different life stages, and neonates typically prey on ectotherms, while adults feed almost entirely on small endotherms. We hypothesized that elevated rates of tongue flicking to chemical stimuli should correlate with particular prey consumed, and that this response shifts from one prey type to another as individuals age. To examine if an ontogenetic shift in response to chemical cues occurred, we recorded the rate of tongue flicking for 25 neonate, 20 subadult, and 20 adult (average SVL = 280.9, 552, 789.5 mm, respectively) wild-caught C. v. viridis to chemical stimuli presented on a cotton-tipped applicator; water-soluble cues from two ectotherms (prairie lizard, Sceloporus undulatus, and house gecko, Hemidactylus frenatus), two endotherms (deer mouse, Peromyscus maniculatus and lab mouse, Mus musculus), and water controls were used. Neonates tongue flicked significantly more to chemical cues of their common prey, S. undulatus, than to all other chemical cues; however, the response to this lizard’s chemical cues decreased in adult rattlesnakes. Subadults tongue flicked with a higher rate of tongue flicking to both S. undulatus and P. maniculatus than to all other treatments, and adults tongue flicked significantly more to P. maniculatus than to all other chemical cues. In addition, all three sub-classes demonstrated a greater response for natural prey chemical cues over chemical stimuli of prey not encountered in the wild (M. musculus and H. frenatus). This shift in chemosensory response correlated with the previously described ontogenetic shifts in C. v. viridis diet. Because many vipers show a similar ontogenetic shift in diet and venom composition, we suggest that this shift in prey cue discrimination is likely a general phenomenon among viperid snakes [Current Zoology 58 (4): 549–555, 2012].

The use of optimal foraging theory in archaeology has been criticized for focusing heavily on “negative” human-environmental interactions, particularly anthropogenic resource depression, in which prey populations are reduced by foragers’ own foraging activities. In addition, some researchers have suggested the focus on resource depression is more common in the zooarchaeological literature than in the archaeobotanical literature, indicating fundamental differences in the ways zooarchaeologists and archaeobotanists approach the archaeological record. In this paper, we assess these critiques through a review of the literature between 1997 and 2017. We find that studies identifying resource depression occur at similar rates in the archaeobotanical and zooarchaeological literature. In addition, while earlier archaeological applications of optimal foraging theory did focus heavily on the identification of resource depression, the literature published between 2013 and 2017 shows a wider variety of approaches. [ABSTRACT FROM AUTHOR]

1. Predation risk affects interspecific competition by decreasing foraging activity and relative competitive ability. Predation risk is determined by predators' prey choice and prey responses, both of which can be influenced by temperature. Temperature is especially important for larval prey and can result in a trade-off between predator-induced decreases in foraging activity and growth. Interspecific competition must also be examined in relation to intraspecific density-dependent competition; weaker interspecific competition leads to coexistence of competitors. 2. This study explored how temperature (15 and 25 ° C) could affect a focal species, larvae of the mosquito Culex quinquefasciatus, by examining prey choice in a shared predator (mosquitofish; Gambusia holbrooki) and the effects of predation risk on interspecific competition with Limnodynastes peronii tadpoles. Intraspecific density-dependent competition in C. quinquefasciatus at these temperatures was also examined. 3. At 25 ° C, G. holbrooki consumption of both C. quinquefasciatus and L. peronii increased; however, the effects of interspecific competition on mosquito survival did not decrease with L. peronii exposure to predation risk. The relationship between intraspecific density-dependent competition and interspecific competition was temperature-dependent, with competitive dominance of L. peronii at 25 ° C. Male and female mosquitoes had different temperature-dependent responses, indicating sex-specific intrinsic responses to starvation and differential selection pressures. At 25 ° C, females were susceptible to interspecific competition by L. peronii, while males were susceptible to intraspecific competition. 4. The use of competitors as biological controls has implications for mosquito disease transmission, and these results suggest that control effectiveness may be modified by climate change. [ABSTRACT FROM AUTHOR]

Generalist predators have to deal with prey with sometimes very different morphologies and defensive behaviors. Therefore, such predators are expected to express plasticity in their predation strategy. Here we investigated the predatory behavior of the recluse spider Loxosceles rufipes (Araneae, Sicariidae) when attacking prey with different morphologies and defensive mechanisms. We expected L. rufipes to show different prey capture strategies and variable acceptance towards each prey type. Potential prey species were collected directly from the web or in the surroundings of the web-building site of L. rufipes. We collected and used the following in our experiments: termite workers ( Nasutitermes sp.), lepidopteran larvae ( Eurema salome), ants ( Camponotus sp.) and isopods (Tylidae). We paired these prey with L. rufipes and recorded their behavior in captivity, quantifying acceptance rate, immobilization time and the sequence of behaviors by the predator. The acceptance rate was lower for isopods but not different among other prey. The immobilization time was higher for isopods than for termites and similar for the other pairwise comparisons. The behavioral sequence was similar for all prey except for isopods, which were also bit more often. Our combined results show plasticity in the behavior of L. rufipes and also show it subdues a potentially dangerous prey (ant) and an armored prey (isopod). [ABSTRACT FROM AUTHOR]

The food habits of Melanogrammus aeglefinus were explored and contrasted across multiple north-eastern and north-western Atlantic Ocean ecosystems, using databases that span multiple decades. The results show that among all ecosystems, echinoderms are a consistent part of M. aeglefinus diet, but patterns emerge regarding where and when M. aeglefinus primarily eat fishes v. echinoderms. Melanogrammus aeglefinus does not regularly exhibit the increase in piscivory with ontogeny that other gadoids often show, and in several ecosystems there is a lower occurrence of piscivory. There is an apparent inverse relationship between the consumption of fishes and echinoderms in M. aeglefinus over time, where certain years show high levels of one prey item and low levels of the other. This apparent binary choice can be viewed as part of a gradient of prey options, contingent upon a suite of factors external to M. aeglefinus dynamics. The energetic consequences of this prey choice are discussed, noting that in some instances it may not be a choice at all. [ABSTRACT FROM AUTHOR]

Freshwaters are subject to particularly high rates of species introductions; hence, invaders increasingly co-occur and may interact to enhance impacts on ecosystem structure and function. As trophic interactions are a key mechanism by which invaders influence communities, we used a combination of approaches to investigate the feeding preferences and community impacts of two globally invasive large benthic decapods that co-occur in freshwaters: the signal crayfish ( Pacifastacus leniusculus) and Chinese mitten crab ( Eriocheir sinensis)., In laboratory preference tests, both consumed similar food items, including chironomids, isopods and the eggs of two coarse fish species. In a comparison of predatory functional responses with a native crayfish ( Austropotamobius pallipes), juvenile E. sinensis had a greater predatory intensity than the native A. pallipes on the keystone shredder Gammarus pulex, and also displayed a greater preference than P. leniusculus for this prey item., In outdoor mesocosms ( n = 16) used to investigate community impacts, the abundance of amphipods, isopods, chironomids and gastropods declined in the presence of decapods, and a decapod >gastropod >periphyton trophic cascade was detected when both species were present. Eriocheir sinensis affected a wider range of animal taxa than P. leniusculus., Stable-isotope and gut-content analysis of wild-caught adult specimens of both invaders revealed a wide and overlapping range of diet items including macrophytes, algae, terrestrial detritus, macroinvertebrates and fish. Both decapods were similarly enriched in 15N and occupied the same trophic level as Ephemeroptera, Odonata and Notonecta. Eriocheir sinensis δ13C values were closely aligned with macrophytes indicating a reliance on energy from this basal resource, supported by evidence of direct consumption from gut contents. Pacifastacus leniusculus δ13C values were intermediate between those of terrestrial leaf litter and macrophytes, suggesting reliance on both allochthonous and autochthonous energy pathways., Our results suggest that E. sinensis is likely to exert a greater per capita impact on the macroinvertebrate communities in invaded systems than P. leniusculus, with potential indirect effects on productivity and energy flow through the community. [ABSTRACT FROM AUTHOR]

Parental food provisioning is crucial for the growth and survival of offspring. Growth rate depends on food quality and food supplied to offspring may differ from what adults use for their own. In the case of steppe passerine birds, detailed characterization on nestling dietary composition, as well as prey choice and resource partitioning among species, is a pending subject. Dietary differences between nestlings and adults remain also largely unexplored. By using faecal DNA metabarcoding, we described the diet of nestlings and adults of five shrub-steppe passerine species over the 2017–2019 breeding seasons in central Spain. We also monitored arthropod availability in the field to assess dietary selection. We expected interspecific dietary differences to limit competition for food resources among sympatric species, as well as parental selection of high quality prey for nestlings. We also predicted age-related differences, with nestlings being fed nutrient-rich prey more frequently than adults. The main arthropod orders provisioned to nestlings were Orthoptera, Julida, Araneae and Lepidoptera. Nestlings of the different species showed high interspecific diet overlap, indicating both a coincidence in growth needs among bird species and no or little limitation of the most profitable resources during the breeding season. Adults of all species showed higher diet richness than nestlings, and age-related differences in prey composition were mainly driven by the selection of the most easily digestible, larger protein- and calcium-rich prey for nestlings, which may favour their rapid growth, and avoiding highly sclerotized and less nutritional prey such as ants. Our study sheds light on the basic ecology and conservation of these declining steppe birds, indicating that interspecific competition may not be a major factor during the breeding season. Given the current global decline of arthropods, further long-term research would be necessary, along with the implementation of effective conservation measures that ensure a sufficient availability of resources identified as key prey in the diet of steppe bird nestlings. [ABSTRACT FROM AUTHOR]

In this study we investigated predation rates on third instar larvae of Chrysomya putoria and C. megacephala by third instar larvae of C. albiceps in a two-choice situation. The highest predation rate occurred on C. putoria larvae and this result is compared to previous experiments, in which C. macellaria larvae were present. Our results suggest that, when C. macellaria is absent C. albiceps larvae attack more C. putoria than C. megacephala larvae. Prey choice decisions and its implications for introduced and native blowflies are discussed.

A generalist predator's ability to contribute to biological control is influenced by the decisions it makes during foraging. Predators often use flexible foraging tactics, which allows them to pursue specific types of prey at the cost of reducing the likelihood of capturing other types of prey. When a pest insect has low nutritional quality or palatability for a predator, the predator is likely to reject that prey in favour of pursuing alternative, non-pest prey. This is often thought to limit the effectiveness of generalist predators in consuming aphids, which are of low nutritional quality for many generalist predators. Here, we report behavioural assays that test the hypothesis that the generalist predator, Grammonota inornata (Araneae: Linyphiidae), preferentially forages for a non-pest prey with high nutritional quality (springtails), and rejects a pest prey with low nutritional quality (aphids). In no-choice assays, molecular gut-content analysis revealed that spiders continued to feed on the low-quality aphids at high rates, even when high-quality springtails were readily available. When provided a choice between aphids and springtails in two-way choice tests, spiders did not show the expected preference for springtails. Decision-making by spiders during foraging therefore appears to be sub-optimal, possibly because of attraction to the less frequently encountered of two preys as part of a dietary diversification strategy. These results indicate that behavioural preferences alone do not necessarily compromise the pest-suppression capacity of natural enemies: even nutritionally sub-optimal pest prey can potentially be subject to predation and suppression by natural enemies. [ABSTRACT FROM PUBLISHER]

The behavior of Sphex pensylvanicus wasps was observed in the presence of live potential prey items (katydids) under artificial conditions in Sioux City, Iowa, USA. When a prey item was not attacked (17 out of 20 instances) wasps engaged in what looks like "displacement preening" of her antennae using her legs. In the three instances when stinging behavior was noted, the katydid appeared to have been stung ventrally behind the head. One of the three instances is suggestive of a prey item favored over another. [ABSTRACT FROM AUTHOR]