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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]

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]

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]