Predator-prey Size Relationships Research Articles

Temperature alters the predator-prey size relationships and size-selectivity of Southern Ocean fish

A primary response of many marine ectotherms to warming is a reduction in body size, to lower the metabolic costs associated with higher temperatures. The impact of such changes on ecosystem dynamics and stability will depend on the resulting changes to community size-structure, but few studies have investigated how temperature affects the relative size of predators and their prey in natural systems. We utilise >3700 prey size measurements from ten Southern Ocean lanternfish species sampled across >10° of latitude to investigate how temperature influences predator-prey size relationships and size-selective feeding. As temperature increased, we show that predators became closer in size to their prey, which was primarily associated with a decline in predator size and an increase in the relative abundance of intermediate-sized prey. The potential implications of these changes include reduced top-down control of prey populations and a reduction in the diversity of predator-prey interactions. Both of these factors could reduce the stability of community dynamics and ecosystem resistance to perturbations under ocean warming.

Improving the biological realism of predator-prey size relationships in food web models alters ecosystem dynamics.

Body-size relationships between predators and prey exhibit remarkable diversity. However, the assumption that predators typically consume proportionally smaller prey often underlies size-dependent predation in ecosystem models. In reality, some animals can consume larger prey or exhibit limited changes in prey size as they grow larger themselves. These distinct predator-prey size relationships challenge the conventional assumptions of traditional size-based models. Cephalopods, with their diverse feeding behaviours and life histories, offer an excellent case study to investigate the impact of greater biological realism in predator-prey size relationships on energy flow within a size-structured ecosystem model. By categorizing cephalopods into high and low-activity groups, in line with empirically derived, distinct predator-prey size relationships, we found that incorporating greater biological realism in size-based feeding reduced ecosystem biomass and production, while simultaneously increasing biomass stability and turnover. Our results have broad implications for ecosystem modelling, since distinct predator-prey size relationships extend beyond cephalopods, encompassing a wide array of major taxonomic groups from filter-feeding fishes to baleen whales. Incorporating a diversity of size-based feeding in food web models can enhance their ecological and predictive accuracy when studying ecosystem dynamics.

Feeding Niche and Predator–Prey Size Relationship in the Whiptail Lizard Aspidoscelis lineattissima (Squamata: Teiidae) in Insular and Continental Populations of the Mexican Pacific

We explore the feeding habits of two populations of the lizard Aspidoscelis lineattissima from two localities (Cocinas = island and Xametla = mainland) under the hypothesis that in an insular environment, there is less selection of food, because it is a relatively comfortable environment to forage due to the presence of few competitors and predators. We also examine the predator–prey size relationship in this lizard species with the intention of distinguishing possible ontogenetic changes in the choice of prey sizes in the two localities. In stomach contents of the lizards from mainland, a total of 2,616 prey items were recorded, while on the island, 1,357 prey items were found. This number of prey was divided into 18 categories for the mainland and 20 for the island. In general terms, the most important prey in the diet of lizards from both localities were Isoptera, Coleoptera (adult and larvae), Araneae, Orthoptera, Hymenoptera (ants and others), Blattodea, and Diptera. Island lizards presented a greater amount of plant material in their stomach contents. The breadth of the food niche was greater on the island than on the mainland. Although statistically there were no differences regarding food overlap between localities, the highest overlap values between groups (age classes and sexes) were found on the mainland. We found a positive relationship between morphological variables of the lizards (snout–vent length, head width, and head length) with the maximum and mean values of the prey volume in both localities. This reveals an ontogenetic change that indicates that as lizards grow, they add a greater quantity of large prey to their diet and at the same time eat smaller prey. These results showed that the diet of the lizards from both localities was similar to other species of the genus. The feeding habits of a species in contrasting environments is evidence that is helpful for understanding the foraging patterns more clearly, and the possible connection with its life history characteristics, shedding more light on the hypothesis of niche amplitude and the optimal foraging theory.

Estuarine fishes feeding on benthic invertebrates and small fishes: Evidence of fine resource partitioning in a tropical coastal lagoon

The main goal of the present study was to carry out an integrated analysis of the feeding habits of a set of species which use the same general food source (benthic invertebrates and small fishes) in a coastal lagoon of the Mexican Pacific. The specific objectives were to explore the patterns of diet overlap among the 12 species included; to relate the differences in diet composition with differences in species morphology and to measure the predator-prey size relationship across the whole set of species. Original primary data on diet composition were obtained from former research whose results were already published in five separated papers dealing with different species or groups of species. Data included information on stomach content (percentage weight) from a total of 2138 individuals pertaining to 12 species (nine of them further split in size groups) and 3953 pairs of prey's size vs predator's size measurements. Eight prey categories made 74% of all food consumed, namely non-identified fishes, penaeids, gobiids, polychaeta, alpheids, upogebiids and engraulids. Using a combination of diet overlap testing based on a null model approach, multivariate methods and regression analyses (linear and quantile), it is concluded that the existence of a relatively homogenous functional group of 12 fish species consuming invertebrates and small fishes is not a realistic assumption. Indeed, several species-size group subsets are clearly identifiable based on the percentage of different prey categories in their diets. The most plausible explanation for the observed patterns of diet composition are the differences in morphological characteristics of the species involved. Other factors allowing the sharing of food resources are the ontogenic change in the size of main prey consumed, notable differences in the abundance of fish species with higher diet overlap values and, perhaps, a high abundance of food resources.

Community size structure varies with predator-prey size relationships and temperature across Australian reefs.

Climate change and fisheries exploitation are dramatically changing the abundances, species composition, and size spectra of fish communities. We explore whether variation in ‘abundance size spectra’, a widely studied ecosystem feature, is influenced by a parameter theorized to govern the shape of size‐structured ecosystems—the relationship between the sizes of predators and their prey (predator–prey mass ratios, or PPMRs). PPMR estimates are lacking for avast number of fish species, including at the scale of trophic guilds. Using measurements of 8128 prey items in gut contents of 97 reef fish species, we established predator–prey mass ratios (PPMRs) for four major trophic guilds (piscivores, invertivores, planktivores, and herbivores) using linear mixed effects models. To assess the theoretical predictions that higher community‐level PPMRs leads to shallower size spectrum slopes, we compared observations of both ecosystem metrics for ~15,000 coastal reef sites distributed around Australia. PPMRs of individual fishes were remarkably high (median ~71,000), with significant variation between different trophic guilds (~890 for piscivores; ~83,000 for planktivores), and ~8700 for whole communities. Community‐level PPMRs were positively related to size spectrum slopes, broadly consistent with theory, however, this pattern was also influenced by the latitudinal temperature gradient. Tropical reefs showed a stronger relationship between community‐level PPMRs and community size spectrum slopes than temperate reefs. The extent that these patterns apply outside Australia and consequences for community structure and dynamics are key areas for future investigation.

Snow crab (Chionoecetes opilio), a new food item for North-east Arctic cod (Gadus morhua) in the Barents Sea

Abstract The snow crab (Chionoecetes opilio) is a newly established species in the Barents Sea, increasing in both distribution and abundance in recent years. We explore the potential importance of North-east Arctic cod (Gadus morhua) predation in structuring the snow crab population expansion in the Barents Sea, through an analysis of cod stomach content data from 2003 to 2018. Spatio-temporal patterns of snow crab within cod diet are assessed across years, between seasons, as well as ontogenetic trends, including predator–prey size relationships. Snow crab represents a new prey item for cod and in recent years the most dominant demersal crustacean species in cod diet. The proportion of snow crab within cod diet increases over time. Primarily 60–110 cm cod prey upon snow crab, mainly during the summer/autumn season. Our results support the idea that the snow crab is still expanding, shifting distribution north and westwards. Cod has the potential to regulate the snow crab population but is unlikely to be in direct competition with the fishery in the Barents Sea. This work suggests that cod can be used as biological sampling tools together with other monitoring programmes to elucidate how new species may affect predator–prey and food-web dynamics within an ecosystem context.

Foraging habitat determines predator-prey size relationships in marine fishes.

Predator-prey size (PPS) relationships are determined by predator behaviour, with the likelihood of prey being eaten dependent on their size relative to that of the consumer. Published PPS relationships for 30 pelagic or benthic marine fish species were analysed using quantile regression to determine how median, lower and upper prey sizes varied with predator size and habitat. Habitat effects on predator foraging activity/mode, morphology, growth and natural mortality are quantified and the effects on PPS relationships explored. Pelagic species are more active, more likely to move by caudal fin propulsion and grow more rapidly but have higher mortality rates than benthic species, where the need for greater manoeuvrability when foraging in more physically complex habitats favours ambush predators using pectoral fin propulsion. Prey size increased with predator size in most species, but pelagic species ate relatively smaller prey than benthic predators. As pelagic predators grew, lower prey size limits changed little, and prey size range increased but median relative prey size declined, whereas the lower limit increased and median relative prey size was constant or increased in benthic species.

Micro- and mesozooplankton successions in an Antarctic coastal environment during a warm year.

The rapid increase in atmospheric temperature detected in the last decades in the Western Antarctic Peninsula was accompanied by a strong glacier retreat and an increase in production of melting water, as well as changes in the sea-ice dynamic. The objective of this study was to analyze the succession of micro- and mesozooplankton during a warm annual cycle (December 2010-December 2011) in an Antarctic coastal environment (Potter Cove). The biomass of zooplankton body size classes was used to predict predator-prey size relationships (i.e., to test bottom-up/top-down control effects) using a Multiple Linear Regression Analysis. The micro- and mesozooplanktonic successions were graphically analyzed to detect the influence of environmental periods (defined by the degree of glacial melting, sea-ice freezing and sea-ice melting) on coupling/uncoupling planktonic biomass curves associated to possible predator-prey size relationship scenarios. At the beginning of the glacial melting, medium and large mesozooplankton (calanoid copepods, Euphausia superba, and Salpa thompsoni) exert a top-down control on Chl-a and microzooplankton. Stratification of the water column benefitted the availability of adequate food-size (Chl-a <20) for large microzooplankton (tintinnids) development observed during fall. High abundance of omnivores mesozooplankton (Oithona similis and furcilia of E. superba) during sea-ice freezing periods would be due to the presence of available heterotrophic food under or within the sea ice. Finally, the increase in microzooplankton abundance in the middle of spring, when sea-ice melting starts, corresponded to small and medium dinoflagellates and ciliates species, which were possibly part of the biota of sea ice. If glacier retreat continues and the duration and thickness of the sea ice layer fluctuates as predicted by climate models, our results predict a future scenario regarding the zooplankton succession in Antarctic coastal environments.

Effectiveness of small size against drilling predation: Insights from lower Miocene faunal assemblage of Quilon Limestone, India

The nature of drilling predation, although well documented for molluscan fossils, is understudied for micromolluscs (<5 mm). Studying predation in micromolluscs is especially critical in evaluating the adaptive significance of small size against predation and assessing the evolutionary implication of predator-prey size relationship (PPSR). This study documents a drilling predation event in microbivalves from the lower Miocene (Burdigalian) fossil assemblage of Quilon Limestone from Kerala, India. Our sample of over 2000 valves represents nine families with an average drilling frequency (DF) of 0.06 and an incomplete drilling frequency (IDF) of 0.26. The characteristic drillhole morphology and occurrence of five genera of modern drilling gastropods (Naticid: Natica, Tanea and Polinices; Muricid: Triplex and Dermomurex) from the same locality reveal the predator identity. Predation in the studied assemblage is found to be highly selective in terms of prey taxa, size, mobility and site selection. Six out of nine families show predatory drilling indicating taxon selectivity. Poor correlation between DF and abundance further supports this view. Failed attacks are strongly correlated with morphological features such as surface ornamentation (Lucinidae) and presence of conchiolin layers (Corbulidae). Drilling occurs primarily on medium size class; prey outside this size range show lower rates of attack. This indicates the existence of a “negative size refugia” for extremely small prey along with the classical size refugia existing for large prey. Mobility is found to be an effective defense against drilling predation.Microbenthos of the Quilon Limestone shows a lower predation intensity in comparison to the Miocene macrobenthos worldwide including coeval formations of the Kutch Basin. The interaction in the microbenthos is more strongly size-dependent in contrast to the Kutch fauna. Reduced predation intensity in the microfauna and the existence of “negative size refugia” support the claim of micromorphy acting as a defense mechanism and highlights the role of size-dependent predation in marine benthos.

Prey size selection in invasive (Hemigrapsus sanguineus and H. takanoi) compared with native (Carcinus maenas) marine crabs

AbstractIntroductions of predators can have strong effects on native ecosystems and knowledge of the prey size selection of invasive predators is pivotal to understand their impact on native prey and intraguild competitors. Here, we investigated the prey size selection of two invasive crabs (Hemigrapsus sanguineus and Hemigrapsus takanoi) recently invading European coasts and compared them with native shore crabs (Carcinus maenas) which are known to feed on similar prey species. In laboratory experiments, we offered different size classes of native blue mussels (Mytilus edulis) to different size classes of the crab species in an effort to identify the respective prey size preferences and potential overlap in prey size range of native and invasive crabs. In all three species, the preferred prey size increased with crab size reflecting general predator–prey size relationships. Prey size preference did not differ among the crab species, i.e. crabs showed similar mussel size preference in relation to carapace width. Given that additional morphological measurements showed that both of the invasive crab species have much larger claws relative to their body size compared with the native species, this finding was surprising and may relate to differential claw morphologies or structural strength. These results suggest that the invasive crabs exert predation pressure on the same size classes of native mussels as the native crabs, with potential effects on mussel population dynamics due to the high densities of the invaders. In addition, the overlap in prey size range is likely to result in resource competition between invasive and native crabs.

Barents Sea cod (Gadus morhua) diet composition: long-term interannual, seasonal, and ontogenetic patterns

Abstract Atlantic cod (Gadus morhua) is an ecologically and commercially important species in the North-Atlantic region. Cod is a top predator and information on its trophic ecology is integral for understanding predator–prey relationships and food-web dynamics. We present an analysis of the trophic patterns of Barents Sea (BS) cod using a unique 33-year time-series of stomach-content data from 1984 to 2016. We assessed patterns in diet (prey) composition across years, between seasons, as well as ontogenetic trends in diet, including predator–prey size relationships. Ontogenetic shifts in diet were observed, with fish becoming more important prey with increasing cod size. A very early onset of piscivory was found in &amp;lt;20 cm cod. Cannibalism was found in cod &amp;gt; 20 cm and increased with size. Juvenile cod exhibit a tendency towards consuming prey up to 33% of their body length, whereas larger cod feed on all prey sizes, resulting in asymmetric predator–prey size distributions. Diet varied significantly during 1984–2016, consistent with changes in both prey, cod abundance, and distribution. Seasonal differences were observed; capelin dominated the winter diet, whereas cod, polar cod, and other fish species were prevalent in summer/autumn months. This work represents an important step towards understanding trophic linkages that determine BS ecosystem dynamics.

Squamates as prey: Predator diversity patterns and predator-prey size relationships

Understanding the relationships between prey and their predators can provide important insights into evolution of defenses, foraging ecology, and functional roles within their ecosystem. Squamates (lizards and snakes) exhibit a wide range of morphological, ecological and behavioral variation and are model organisms for the study of the evolution of anti-predator traits, making them an ideal group to search for general patterns in predator-prey relationships. We compiled a squamate predator database that consisted of 1152 squamate predation-prey interactions representing 396 lizard species from 30 families and 217 snake species from 13 families. We quantified the predator taxonomic diversity and explored the relationship between predator size and prey size. Both lizards and snakes were preyed upon by a greater diversity of squamate predators compared to avian and mammalian predators. Snakes appear to be more vulnerable to a broader size range of predators compared to lizards, which is likely attributed to differences in their body morphology. These results provide further support for the hypotheses that predation pressure may affect the evolutionary trajectory of squamate defenses.

Go big or … don't? A field-based diet evaluation of freshwater piscivore and prey fish size relationships.

Body size governs predator-prey interactions, which in turn structure populations, communities, and food webs. Understanding predator-prey size relationships is valuable from a theoretical perspective, in basic research, and for management applications. However, predator-prey size data are limited and costly to acquire. We quantified predator-prey total length and mass relationships for several freshwater piscivorous taxa: crappie (Pomoxis spp.), largemouth bass (Micropterus salmoides), muskellunge (Esox masquinongy), northern pike (Esox lucius), rock bass (Ambloplites rupestris), smallmouth bass (Micropterus dolomieu), and walleye (Sander vitreus). The range of prey total lengths increased with predator total length. The median and maximum ingested prey total length varied with predator taxon and length, but generally ranged from 10–20% and 32–46% of predator total length, respectively. Predators tended to consume larger fusiform prey than laterally compressed prey. With the exception of large muskellunge, predators most commonly consumed prey between 16 and 73 mm. A sensitivity analysis indicated estimates can be very accurate at sample sizes greater than 1,000 diet items and fairly accurate at sample sizes greater than 100. However, sample sizes less than 50 should be evaluated with caution. Furthermore, median log10 predator-prey body mass ratios ranged from 1.9–2.5, nearly 50% lower than values previously reported for freshwater fishes. Managers, researchers, and modelers could use our findings as a tool for numerous predator-prey evaluations from stocking size optimization to individual-based bioenergetics analyses identifying prey size structure. To this end, we have developed a web-based user interface to maximize the utility of our models that can be found at www.LakeEcologyLab.org/pred_prey.

Carnivore stable carbon isotope niches reflect predator-prey size relationships in African savannas.

Predator-prey size relationships are among the most important patterns underlying the structure and function of ecological communities. Indeed, these relationships have already been shown to be important for understanding patterns of macroevolution and differential extinction in the terrestrial vertebrate fossil record. Stable isotope analysis (SIA) is a powerful remote approach to examining animal diets and paleodiets. The approach is based on the principle that isotope compositions of consumer tissues reflect those of their prey. In systems where resource isotope compositions are distributed along a body size gradient, SIA could be used to reconstruct predator-prey size relationships. We analyzed stable carbon isotope distributions amongst mammalian herbivores in extant and Plio-Pleistocene African savanna assemblages, and show that the range of δ13 C values among mammalian prey species (herbivores and rodents) increases with body mass (BM), because C4 plant feeding (essentially grazing) is more common among larger taxa. Consequently, δ13 C values of mammalian carnivores in these systems are related to species' BM, reflecting a higher average C4 prey component in the diets of larger-bodied carnivores. This pattern likely emerges because only the largest carnivores in these systems have regular access to the C4 prey base, whereas smaller carnivores do not. The δ13 C-BM relationship observed in mammalian carnivores is a potentially powerful approach for reconstructing and parameterizing predator-prey size relationships in contemporary and fossil savanna assemblages, and for interpreting how various behavioral, ecological and environmental factors influence prey size selection.

A Lagrangian study of plankton trophodynamics over a diel cycle in a eutrophic estuary under upwelling influence

A Lagrangian study was conducted in a eutrophic estuary (Guanabara Bay, Brazil) to investigatein situplankton trophodynamics under the influence of the cold, nutrient-rich South Atlantic Coastal Water in a short-term temporal variability (scale of hours). We tested the hypothesis that the base of the plankton food web is composed of small cells and that microzooplankton is the main consumer of this assemblage. Samples of pico-, nano- and microplankton, as well as copepods, were collected during spring, when the entry of upwelling water in the Bay is commonly observed, and near the surface every 3 h during the 1-day sampling period. Potential predation of dinoflagellates, ciliates, copepod nauplii, copepodites and adult copepods was estimated based on predator-prey size relationships. The main trophic links in the Guanabara Bay food web for the period analysed were nanophytoplankton-copepods, nanophytoplankton-ciliates, and autotrophic dinoflagellates-heterotrophic dinoflagellates. According to microphytoplankton availability, adult copepods could not satisfy their food requirement, and nanophytoplankton represented an important supplementary food source. In fact, diel variations of nano- and microplankton biomass were opposite to that of copepods suggesting predation control by the latter on the former. The trophodynamics of Guanabara Bay, under the influence of upwelling water, resulted in marked differences from other eutrophic estuaries around the world.

Size-based approaches to aquatic ecosystems and fisheries science: a symposium in honour of Rob Peters

This special issue honours Rob Peters’ outstanding contributions to the field of aquatic ecology. It focuses on the size spectrum approach — in which individual organisms, rather than species, are the most basic biological unit — and highlights applications of this approach to fisheries management. The 21 papers in this issue cover three subject areas: (i) the use of size spectra to characterize variation in community structure, (ii) the development of size-based models of ecosystem dynamics to address fisheries questions, and (iii) applications of size-based theory to examine the consequences of variation in predator–prey size relationships, body size – trophic level relationships, and body size – life history relationships. The empirical studies herein demonstrate the utility of size spectra as indicators of population or community structure and for detecting impacts associated with environmental change. Future research focused on refining size-based sampling methods, standardizing metrics and analytical methods, understanding model sensitivity to the underlying assumptions, and comparative studies across ecosystems will enhance our ability to reliably interpret changes in size spectrum characteristics, thus facilitating their use as indicators of ecological change.

Ontogenetic Shifts in the Predatory Habits of the Northern Moonsnail (Lunatia heros) on the Northwestern Atlantic Coast

Naticid gastropods provide a highly tractable system for exploring ontogenetic changes in diet because the telltale boreholes they leave behind in their hard-shell molluscan prey can be linked reliably to naticid size. In this study, ontogenetic changes in diet and size selectivity across 7 common prey species of Lunatia heros (Say, 1822) were explored using a forensic approach based on beach-collected shells from the eastern coast of Nova Scotia, Canada. Laboratory experiments were also undertaken to assess the relationship between predator size and outer borehole diameter (OBD) for 3 of these prey species. The results confirmed a strong relationship between OBD and shell length for L. heros and demonstrated that this relationship was consistent across prey species varying in shell thickness and composition. Analyses of drilled, beach-collected shells revealed that L. heros clearly differentiates among prey with respect to size and species, with ontogenetic changes in prey selection appearing to reflect shifting predator—prey size relationships. Among prey species, larger predators demonstrated the capacity to select larger prey species and avoid smaller prey taxa. Similarly, within prey species, larger predators preyed on larger individuals of a given species, but also exploited a wider selection of prey sizes than smaller moonsnails. The moonsnail L. heros also exhibited borehole site specificity for both bivalve and gastropod prey, but did not discriminate between left versus right valves when drilling bivalve taxa. The results of this study are important for understanding the changing role of L. heros across its life span within soft-sediment communities. This research should now be broadened to encompass the full suite of prey species targeted by this drilling predator.

Geometric factors influencing the diet of vertebrate predators in marine and terrestrial environments.

Predator–prey relationships are vital to ecosystem function and there is a need for greater predictive understanding of these interactions. We develop a geometric foraging model predicting minimum prey size scaling in marine and terrestrial vertebrate predators taking into account habitat dimensionality and biological traits. Our model predicts positive predator–prey size relationships on land but negative relationships in the sea. To test the model, we compiled data on diets of 794 predators (mammals, snakes, sharks and rays). Consistent with predictions, both terrestrial endotherm and ectotherm predators have significantly positive predator–prey size relationships. Marine predators, however, exhibit greater variation. Some of the largest predators specialise on small invertebrates while others are large vertebrate specialists. Prey–predator mass ratios were generally higher for ectothermic than endothermic predators, although dietary patterns were similar. Model-based simulations of predator–prey relationships were consistent with observed relationships, suggesting that our approach provides insights into both trends and diversity in predator–prey interactions.

A new look at the Lake Superior biomass size spectrum

We synthesized data from multiple sampling programs and years to describe the Lake Superior pelagic biomass size structure. Data consisted of Coulter counts for phytoplankton, optical plankton counts for zooplankton, and acoustic surveys for pelagic prey fish. The size spectrum was stable across two time periods separated by 5 years. The primary scaling or overall slope of the normalized biomass size spectra for the combined years was −1.113, consistent with a previous estimate for Lake Superior (−1.10). Periodic dome structures within the overall biomass size structure were fit to polynomial regressions based on the observed sub-domes within the classical taxonomic positions (algae, zooplankton, and fish). This interpretation of periodic dome delineation was aligned more closely with predator–prey size relationships that exist within the zooplankton (herbivorous, predacious) and fish (planktivorous, piscivorous) taxonomic positions. Domes were spaced approximately every 3.78 log10 units along the axis and with a decreasing peak magnitude of −4.1 log10 units. The relative position of the algal and herbivorous zooplankton domes predicted well the subsequent biomass domes for larger predatory zooplankton and planktivorous prey fish.

Predator–prey body size relationships when predators can consume prey larger than themselves

As predator-prey interactions are inherently size-dependent, predator and prey body sizes are key to understanding their feeding relationships. To describe predator-prey size relationships (PPSRs) when predators can consume prey larger than themselves, we conducted field observations targeting three aquatic hemipteran bugs, and assessed their body masses and those of their prey for each hunting event. The data revealed that their PPSR varied with predator size and species identity, although the use of the averaged sizes masked these effects. Specifically, two predators had slightly decreased predator-prey mass ratios (PPMRs) during growth, whereas the other predator specialized on particular sizes of prey, thereby showing a clear positive size-PPMR relationship. We discussed how these patterns could be different from fish predators swallowing smaller prey whole.