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Predators that target multiple prey types are predicted to switch foraging modes according to prey profitability to increase energy returns in dynamic environments. Here, we use bat-borne tags and DNA metabarcoding of feces to test the hypothesis that greater mouse-eared bats make immediate foraging decisions based on prey profitability and changes in the environment. We show that these bats use two foraging strategies with similar average nightly captures of 25 small, aerial insects and 29 large, ground-dwelling insects per bat, but with much higher capture success in the air (76%) vs ground (30%). However, owing to the 3–20 times larger ground prey, 85% of the nightly food acquisition comes from ground prey despite the 2.5 times higher failure rates. We find that most bats use the same foraging strategy on a given night suggesting that bats adapt their hunting behavior to weather and ground conditions. We conclude that these bats use high risk-high gain gleaning of ground prey as a primary foraging tactic, but switch to aerial hunting when environmental changes reduce the profitability of ground prey, showing that prey switching matched to environmental dynamics plays a key role in covering the energy intake even in specialized predators.

Predation success depends on factors such as hunger, prey size, prey availability and intensity of competition. A neglected factor that may also influence predation success is the proper function of morphological traits related to prey search, capture and manipulation. Injuries that compromise the functionality of these morphological traits may reduce predation success. In many invertebrates, autotomy can compromise predation success because the detached body part may be crucial for hunting. However, empirical evidence linking autotomy and predation success is relatively scarce. We filled this gap using the scorpion Ananteris balzani , which autotomizes the last abdominal segments, known as the 'tail'. This is a unique form of autotomy as 'tail' autotomy implies the loss of the stinger, an organ used for venom inoculation, which is the main form of large prey subjugation. Using a paired experimental design, we found that for both small and large prey, subduing success was higher when individuals were intact than when they were autotomized. After autotomy, subduing success of male scorpions decreased from 90% to 17% for small prey and from 47% to 1% for large prey. Subduing success of female scorpions after autotomy decreased from 98% to 93% for small prey and from 97% to 70% for large prey. Autotomized individuals took longer than intact individuals to subdue both small and large prey, but the effect size was higher for large prey. Considering that the tail does not regenerate, autotomized individuals (especially males) will experience a lifelong reduction in trophic niche breadth because their diet will be mostly composed of small prey. Moreover, autotomized individuals probably move more to enhance the likelihood of finding small prey, which may increase their exposure to predators and consequently the costs related to tail loss. • Some morphological traits are crucial for prey capture and subjugation. • The functionality of these traits is thus crucial for predation success. • 'Tail' autotomy in scorpions causes loss of the stinger used for venom inoculation. • Stinger loss reduced subduing success of both small and large prey. • In conclusion, tail autotomy is costly because it decreases predation success. [ABSTRACT FROM AUTHOR]

Predatory fish structure communities through prey pursuit and consumption and, in many marine systems, the gadoids are particularly important. These predators have flexible feeding behaviours and often feed on large prey items. Digestion times of large prey are usually longer than handling times, and gut processing limits feeding rate at high prey density. Optimizing the gut content mix can therefore be an important behavioural strategy. Here, we develop a foraging model that incorporates gut processing and use the model to disentangle internal and external limitations on feeding in the omnivorous cod (Gadus morhua, Gadidae). We extend the traditional definition of prey profitability to consider prey digestive quality, which we quantify for prey of Northeast Atlantic cod populations. We find an important role for gut limitation; within a range of ecologically relevant temperatures and prey densities, predicted feeding rates were strongly reduced compared to feeding constrained by external factors only, and the optimal diet composition under gut limitation differed from predictions from traditional foraging theory. Capelin, a main prey of Northeast Arctic cod, had the highest digestive quality of all prey across ecosystems, but the cold temperatures in the Barents Sea strongly limited feeding rate by slowing down digestion. Baltic cod fed on a higher proportion of poor‐quality prey compared to the other populations, contributing to its slow growth in relation to water temperature. Gut limitation is particularly important to consider in foraging models for fish with many alternative prey species or fish occupying cold waters where digestion is slow. [ABSTRACT FROM AUTHOR]

Octopus minor is widely distributed along the northern coast of China. To date, there is little information on the prey selection process of this species. To understand this process, several experiments were carried out. Three types of bivalves, namely, Ruditapes philippinarum, Mactra chinensis, and Mytilus galloprovincialis, were used to observe the prey selection of O. minor and to analyze the potential causes of prey selection from three aspects: prey profitability, adductor muscle tension and handling time. Under single-prey conditions, we found that the average (±SD) predation rates of O. minor on R. philippinarum, M. chinensis, and M. galloprovincialis were 1.73±0.50, 1.27±0.42, and 0.8±0.2/d, respectively. Under different prey combinations, octopods actively selected one type of prey over the other(s), and the order of prey preference was R. philippinarum, followed by M. chinensis and lastly M. galloprovincialis. Furthermore, the shells of the consumed prey showed that O. minor only consumed bivalves by pulling them apart since there was no evidence of drill holes on the shells. The prey selection of O. minor was related to the prey profitability and handling time; O. minor appeared to select preys with a higher profitability and a shorter handling time. However, the difficulty in opening the bivalve was not consistent with the prey preference of the octopods. These results suggest that O. minor prefers to consume R. philippinarum possibly due to a high profitability and a short handling time that supports the optimum Foraging Theory. [ABSTRACT FROM AUTHOR]

Prey and predator distributions influence one another. Understanding the scale and the orientation of predator–prey spatial correlations is crucial in foraging ecology. Growing evidence suggests that predator–prey interactions are more constrained by functional characteristics of both the predator and the prey. Unfortunately, in marine pelagic systems, the scale and orientation of spatial correlations between predators and prey have been only little explored from a functional point of view. We tested the existence of fine-scale association between predators and fish functional groups. Visual predator sightings and acoustic fish records were collected synchronously during oceanographic surveys from 2004 to 2014. Prey biomass was integrated by nautical miles and split into four size classes (<10 cm; 10–20 cm; 20–30 cm; >30 cm) and two depth layers (surface, deep). We computed the relative biomass by prey size and depth category from 0 to 12 nm around predator sightings to determine the predators' proximity to local prey biomass. Two cetaceans (common, bottlenose dolphins) and three seabirds (northern gannets, auks, northern fulmars) were studied. No association was found in fulmars, indicating they probably do not feed on considered fishes in the area. Gannets and auks were positively correlated with local prey biomass for sizes <20 cm at both depth layers. Significant negative relationships were found between common dolphins and prey size classes <20 cm at both depth layers, and between bottlenose dolphins and all size ranges at the deeper layer. Our results suggest that the fine-scale spatial overlap of predator and prey is influenced by their functional traits, and that prey exhibit predator avoidance behaviour in presence of swimming predators but not of flying ones. [ABSTRACT FROM AUTHOR]

Energy densities of 670 fishes belonging to nine species were measured to evaluate intraspecific variability. Functional groups based on energy density appeared to be sufficiently robust to individual variability to provide a classification of forage fish quality applicable in a variety of ecological fields including ecosystem modelling. [ABSTRACT FROM AUTHOR]

Abstract: Predation is one of the primary mechanisms that shape aquatic food webs and predator–prey interactions are typically highly dependent on sizes of both forager and its prey. Round goby Neogobius melanostomus is a recent invader to the Great Lakes and can be an important prey item for native predators. However, predation patterns on round gobies have received limited attention. We assessed size-specific predator–prey interactions between invasive round gobies and native yellow perch Perca flavescens by comparing prey preferences for three size classes of adult yellow perch foraging on six size classes of round gobies. Small yellow perch preferred the smallest round gobies available, medium sized yellow perch increased the range of round goby sizes consumed but still preferred smaller prey, whereas large yellow perch consumed larger round gobies and excluded the smallest prey size. Yellow perch foraging behaviors indicated that intermediate sizes of round gobies were struck at most frequently and that pursuit and handling time increased whereas capture efficiency and prey profitability decreased with round goby size. Our results indicate that predator–prey interactions between yellow perch and round gobies may be size dependent and heavily influenced by capture efficiency and prey profitability. [Copyright &y& Elsevier]

Time spent pursuing, capturing, and subduing prey, and time spent preparing and swallowing it all affect profitability of a prey item (net energy gain/handling time). In the diet selection model of classical optimal foraging theory, handling time is constant for each prey type, but several factors affect it in some predators. We studied factors that might cause time spent to capture and handle prey by broad-headed skinks (Eumeces laticeps) to vary between and within prey types. Pursuit time did not vary with prey (cricket) size in experimental conditions. In three experiments using crickets of the same size, handling times for the first prey eaten were shorter when more prey were simultaneously present. Reduced handling time likely maximizes number of prey captured before the remaining prey escape. Preparation time (capture to initiation of swallowing) did not vary with prey number, but swallowing time decreased with number of prey present. This result suggests that lizards must prepare crickets thoroughly for digestion by bites puncturing the exoskeleton, which constrains them from decreasing preparation time. However, lizards can reduce handling time by swallowing more quickly, increasing the likelihood of capturing additional prey. Handling times were shortest for hungry skinks and longest just before satiation. Two factors may contribute to the increase in handling time with degree of satiation: (1) Motivation to capture prey declines as a predator becomes satiated, removing the reason for shortening handling times when groups of prey are present; (2) as the stomach and the esophagus are filled, mechanical constraints may slow swallowing. Preparation time, number bites, swallowing time, and handling time increased with cricket size. Consequently, although it appears that the largest prey were the most profitable for sizes of crickets studied, this may not be true for other ranges of prey size. Preparation time was shorter for prey bitten on the head than on the side or back, but prey orientation during swallowing did not affect swallowing time. In summary, (1) when prey are present simultaneously, total energetic profit may be increased by reducing handling time, and (2) handling for specific prey types vary with satiation and handling method. [ABSTRACT FROM AUTHOR]

Summary 1. We examined the link between handling time (T [sub h] ), adopted feeding techniques, profitability curves and prey size selection to further understand the constraints that influence bivalve prey selection in shore crabs (Carcinus maenas L.). 2. Blue mussels (Mytilus edulis L.) of different sizes were used as prey. Prey size was generalized to the ratio between mussel width and major chela length (MW : MCL) and prey profitability standardized to the ratio between prey mass eaten per unit breaking time and predator mass (1/h T [sub b] ). 3. Crabs either crushed the mussel with their claws or opened the mussel using the more time-consuming cutter technique. The latter technique was employed above a critical MW : MCL ratio (0·24). This threshold appeared to coincide with the ratio where prey profitability is maximal. 4. When a range of prey sizes were offered simultaneously, an observed MW : MCL ratio (0·14–0·16) turned out to be lower than the predicted optimal MW : MCL ratio (0·16–0·22) and lower than the MW : MCL ratio where the first crab switched feeding techniques (0·16). Crabs preferred a MW : MCL ratio of 0·16 over the optimal ratio of 0·24 when given dichotomous choices between different MW : MCL ratios. 5. Although larger and more profitable mussels can be crushed, we suggest that crabs select small crushable mussels to prevent claw wear and tear. Claw damage has a considerable effect on mating success and hence on an individual's fitness. Risk of claw damage may thus be of greater importance to a foraging shore crab than energy maximization. [ABSTRACT FROM AUTHOR]

We report on the effects of previous foraging experience on prey-selection by the bivalve feeding polychaete Halla okudai, including whether there was evidence of frequency-dependent predation. Three separate batches of H.okudai were maintained for 30 days on clams, mussels, or oysters, before being offered a choice among these three prey. Initially individuals from all three treatments consumed more clams than mussels, and no oysters. As the number of clams was depleted the polychaetes shifted their diet to include a greater proportion of mussels, but even after 20 days oysters were only eaten by polychaetes that had been previously acclimated to them. Nevertheless, polychaetes from each treatment inspected significantly more of the prey species to which they had initially been acclimated, suggesting that previous experience may increase the likelihood of certain prey being detected. When individuals of H.okudai were repeatedly offered the same prey species, handling time did not decrease (and therefore prey profitability did not increase) with experience, which may be because H.okudai paralyses its prey with toxic mucus. Since repeated experience of the same prey species gives no advantage in terms of reduced handling time, we suggest this may be why this species does not show frequency-dependent prey-selection. [ABSTRACT FROM AUTHOR]

In the field, Spinachia fed on four types of prey; copepods, isopods, mysids and amphipods. As fish size increased, mysids gradually succeeded amphipods as the most important food type in the diet. Prey dimensions and morphometry of the fish's mouth most accurately predicted capture efficiency for amphipods, whereas for mysids capture efficiency was determined by the prey's escape response and the fish's fast-start capability. Responses to model prey revealed the ability of fish to differentiate among contrasting prey characteristics, resulting in the adoption of appropriate predatory tactics. Amphipods were associated with a shorter gut evacuation time than mysids, although approximately equal proportions of energy were absorbed from each. Similar rations of mysids and amphipods were required to satiate fish. The lower energy content per unit dry mass of amphipods was off set by their lower water content. From pre-digestive behaviour, we predicted that mysids were more profitable than amphipods, and this was reflected in the fish's choice. Conversely, incorporating the net rate of energy uptake by the gut led us to predict that amphipods were more profitable. Although physiological constraints clearly influence the net rate of energy uptake, it appears that dietary preferences are based on pre-digestive predatory behaviour and hence on time minimisation. [ABSTRACT FROM AUTHOR]