Predator Size Research Articles

Green crab (Carcinus maenas (Linnaeus, 1758)) foraging on soft-shell clams (Mya arenaria Linnaeus, 1758) across seagrass complexity: Behavioural mechanisms and a new habitat complexity index

Although many studies have examined foraging success across seagrass complexity, few have identified underlying behavioural mechanisms or examined effects of belowground complexity. Here, I used a new habitat complexity index (IBG), behavioural data, and laboratory manipulations of artificial above- and belowground structures and predator sizes to understand foraging of invasive green crabs (Carcinus maenas) on soft-shell clams (Mya arenaria) in seagrass (Zostera marina) beds. IBG was calculated as interstitial area between rhizomes (i.e., belowground complexity) divided by claw area; belowground complexity was varied while claw area was held constant. This meant that as IBG increased, belowground complexity itself decreased. Belowground complexity strongly affected crab foraging, and a sigmoid function described predation rate across increasing IBG. This relationship was not evident when aboveground complexity was high (i.e., interstitial area between shoots was small), and no patterns in predation across a gradient of aboveground complexity were observed. Important behavioural mechanisms included encounter rate with prey and the probability of capture upon encounter, both of which increased hyperbolically as IBG increased, and handling time per prey, which decreased exponentially as IBG increased. Most handling time was spent excavating prey from the sediments. Predator size did not change these relationships, although larger crabs had more difficulty capturing prey at low IBG than smaller crabs. Clearly, success of crabs feeding on infauna in seagrass beds is limited most by claw size relative to opening size from which prey are extracted. IBG incorporates this limitation, and can be used to predict effects of habitat complexity on foraging success of epibenthic predators in various habitat types.

Feeding ecology of the glacier lanternfish Benthosema glaciale (Actinopterygii, Myctophidae) in the Flemish Cap (North Atlantic Ocean)

The feeding dynamics of the glacier lanternfish Benthosema glaciale were studied during the summer of 2010 in the Flemish Cap. B. glaciale constituted a majority of the deep scattering layer (DSL), which was located between 300 and 650 m during daylight hours; at night, a part of the DSL migrated to the surface. B. glaciale is a zooplanktivore, feeding primarily on copepods (Calanushyperboreus, Pareuchaeta norvegica, Metridia longa and Calanus finmarchicus), followed by amphipods (Themisto compressa) and krill (primarily Nematoscelis spp.). Although crustaceans dominated the diet, other invertebrates, such as chaetognaths, gastropods, polychaetes, ostracods and appendicularians, also contributed. The geographical differences in the composition of the diet resulted from the association of prey with distinct water masses. In the colder water at the north of the bank, Arctic species represented a higher proportion of the diet, but this situation was reversed in areas influenced by the warmer water from the south. B. glaciale fed more intensively towards the centre of the Flemish Cap. The diet of B. glaciale shifted ontogenetically, showing increasing prey size and prey diversity with increasing predator size.

Evasion of Predators Contributes to the Maintenance of Male Eyes in Sexually Dimorphic Euphilomedes Ostracods (Crustacea)

Sexual dimorphisms have long drawn the attention of evolutionary biologists. However, we still have much to learn about the evolutionary, genetic, and developmental drivers of sexual dimorphisms. Here, we introduce ostracods of the genus Euphilomedes (Myodocopida, Ostracoda, and Crustacea) as a promising new system in which to investigate why and how sexual dimorphisms evolve. First, we ask whether male-skewed selective pressure from pelagic predators may help explain a dramatic sexual dimorphism in which male Euphilomedes have compound eyes, but females do not. Manipulative experiments demonstrate that blindfolding reduces the survival rate of male Euphilomedes when they are exposed to predatory fish. Blindfolding of the female rudimentary eyes (rudiments) does not, however, similarly influence the survival rate of brooding females. Further, numerical estimates of sighting distances, based on reasonable extrapolations from Euphilomedes's eye morphology, suggest that the eyes of male Euphilomedes are useful for detecting objects roughly the size of certain pelagic predators, but not conspecifics. We conclude that eyes do not mediate direct interactions between male and female Euphilomedes, but that differences in predation pressure-perhaps associated with different reproductive behaviors-contribute to maintaining the sexually dimorphic eyes of these ostracods. Second, through transcriptome sequencing, we examined potential gene regulatory networks that could underlie sexual dimorphism in Euphilomedes' eyes. From the transcriptome of juvenile male Euphilomedes' eyes, we identified phototransduction genes and components of eye-related developmental networks that are well characterized in Drosophila and other species. The presence of suites of eye regulatory genes in our Euphilomedes juvenile male transcriptome will allow us, in future studies, to test how ostracods regulate the development of their sexually dimorphic eyes.

Larval Performance and Kill Rate of Convergent Ladybird Beetles,Hippodamia convergens, on Black Bean Aphids,Aphis fabae, and Pea Aphids,Acyrthosiphon pisum

Generalist predator guilds play a prominent role in structuring insect communities and can contribute to limiting population sizes of insect pest species. A consequence of dietary breadth, particularly in predatory insects, is the inclusion of low-quality, or even toxic, prey items in the predator's diet. Consumption of low-quality prey items reduces growth, development, and survival of predator larvae, thereby reducing the population sizes of generalist predators. The objective of this paper was to examine the effect of a suspected low-quality aphid species, Aphis fabae (Scopoli) (Hemiptera: Aphididae), on the larval performance of an abundant North American predator, Hippodamia convergens (Guérin-Méneville) (Coleoptera: Coccinellidae). For comparison, H. convergens larvae were also reared on a known high-quality aphid species Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) and on a 50:50 mix of both aphid species. The proportion of H. convergens larvae surviving to the adult stage was dramatically lower (0.13) on the A. fabae diet than on the A. pisum diet (0.70); survival on the mixed diet was intermediate (0.45) to survival on the single-species diets. Similarly, surviving H. convergens larvae also developed more slowly and weighed less as adults on the A. fabae diet than on the A. pisum diet. Despite the relatively poor performance on the A. fabae diet, H. convergens larvae killed large numbers of A. fabae. Furthermore, H. convergens displayed a preference for A. fabae in the mixed diet treatment, most likely because A. fabae was easier to catch than A. pisum. The results suggest that increases in the distribution and abundance of A. fabae in North America may have negative effects on H. convergens population size.

Beak marks on butterfly wings with special reference to Japanese black swallowtail

AbstractBirds are believed to be one of the principal predators of butterflies. The beak marks (BMs) left on the butterfly wings are useful indices of bird predation. We performed 84 collections in grasslands and woodlands during 2002–2006 in Ito, Shizuoka prefecture, and collected 893 specimens belonging to 48 species. In general, the larger was the body size the higher was the BM rate. There were two peaks in the BM rate and the peaks were higher by 13–14 % in autumn than in spring in both grasslands and woodlands. During 2007 and 2008, capture‐mark‐recapture surveys were conducted 82 times in a flight path of black swallowtail butterflies (BSBs). A total of 443 BSB were individually marked and released at a site 400 m away from the flight path after examining for BM, degree of wing damage, body size, sex and species. The BM% of BSB ranged from 40 to 46 %, which was the highest among the observed butterflies. The recapture rate was negatively correlated with the BM rate suggesting that the avian predation was strong enough to affect the survival rate of BSB adults. In addition, the BM rate showed a delayed positive response to BSB density in the previous month. Variation in the BM rate was analyzed with a multivariate model; it indicated that month and wing length were significant explanatory variables. In addition, the highest BM rate was observed at an intermediate wing size. These results strongly suggested that variation in the BM rate was caused by variation in avian life history and predator size. All the evidence suggested that an appreciable predation pressure by birds operated on BSB adult populations.

The influence of body size on the foraging behaviour of European hake after settlement to the bottom

The trophic niche width and feeding strategy (FS) of juvenile European hake were studied during three trawl surveys in two different areas of the Mediterranean Sea. Both of these aspects of trophic behaviour were analysed as function of different biotic and abiotic factors. Prey were grouped by factors such as size, swimming behaviour and energy density. The trophic niche breadth values observed (2.25–2.89) were very similar regardless of the geographic area (geomorphology) and season. The FSs analysed were also quite similar regardless of the geographic area (geomorphology) and season, or predation environment (bottom or water column). Conversely, the FSs were linked with predator size. Increased predator size allowed changes in predatory behaviour through the development of preferences for larger and more energy-rich prey. The changes in FS from generalist to specialist began at a total length (TL) of approximately 12cm in both populations analysed. At larger sizes, the juveniles of both populations became more specialised, as confirmed by the reduction in the breadth of the individual trophic niche. The observed simultaneous changes in the FS, which occurred regardless of the geomorphology and seasonal characteristics, suggest that this shift is driven primarily by endogenous factors. The influence of body size on the foraging behaviour of European hake in the early life stages after bottom recruitment is a crucial information for the application of ecosystem mass-balance models.

Increasing zooplankton size diversity enhances the strength of top‐down control on phytoplankton through diet niche partitioning

1. The biodiversity-ecosystem functioning debate is a central topic in ecology. Recently, there has been a growing interest in size diversity because body size is sensitive to environmental changes and is one of the fundamental characteristics of organisms linking many ecosystem properties. However, how size diversity affects ecosystem functioning is an important yet unclear issue. 2. To fill the gap, with large-scale field data from the East China Sea, we tested the novel hypothesis that increasing zooplankton size diversity enhances top-down control on phytoplankton (H1) and compared it with five conventional hypotheses explaining the top-down control: flatter zooplankton size spectrum enhances the strength of top-down control (H2); nutrient enrichment lessens the strength of top-down control (H3); increasing zooplankton taxonomic diversity enhances the strength of top-down control (H4); increasing fish predation decreases the strength of top-down control of zooplankton on phytoplankton through trophic cascade (H5); increasing temperature intensifies the strength of top-down control (H6). 3. The results of univariate analyses support the hypotheses based on zooplankton size diversity (H1), zooplankton size spectrum (H2), nutrient (H3) and zooplankton taxonomic diversity (H4), but not the hypotheses based on fish predation (H5) and temperature (H6). More in-depth analyses indicate that zooplankton size diversity is the most important factor in determining the strength of top-down control on phytoplankton in the East China Sea. 4. Our results suggest a new potential mechanism that increasing predator size diversity enhances the strength of top-down control on prey through diet niche partitioning. This mechanism can be explained by the optimal predator-prey body-mass ratio concept. Suppose each size group of zooplankton predators has its own optimal phytoplankton prey size, increasing size diversity of zooplankton would promote diet niche partitioning of predators and thus elevates the strength of top-down control.

The roles of productivity and ecosystem size in determining food chain length in tropical terrestrial ecosystems

Many different drivers, including productivity, ecosystem size, and disturbance, have been considered to explain natural variation in the length of food chains. Much remains unknown about the role of these various drivers in determining food chain length, and particularly about the mechanisms by which they may operate in terrestrial ecosystems, which have quite different ecological constraints than aquatic environments, where most food chain length studies have been thus far conducted. In this study, we tested the relative importance of ecosystem size and productivity in influencing food chain length in a terrestrial setting. We determined that (1) there is no effect of ecosystem size or productive space on food chain length; (2) rather, food chain length increases strongly and linearly with productivity; and (3) the observed changes in food chain length are likely achieved through a combination of changes in predator size, predator behavior, and consumer diversity along gradients in productivity. These results lend new insight into the mechanisms by which productivity can drive changes in food chain length, point to potential for systematic differences in the drivers of food web structure between terrestrial and aquatic systems, and challenge us to consider how ecological context may control the drivers that shape food chain length.

Effects of prey size structure and turbulence on feeding and growth of anchovy larvae

Foraging processes in plankton and plank- tivorous fish are constrained by relative prey and predator size and therefore, these are important varia- bles to include in a foraging model. The distribution of prey biomass across different size classes can be char- acterized by a size spectrum slope. We present a for- aging model for anchovy larvae including the most relevant processes such as prey encounter, capture- and pursuit success, all influenced by light, turbulence and prey characteristics. We modelled ingestion rates and specific growth rate by coupling the foraging model with an existing bioenergetic model, and per- formed a sensitivity analysis of prey ingestion in tur- bulent environments assuming either hemispherical or conical perceptive volume. Our results suggest that turbulence has no positive effect because of the low capture ability, small prey size and small visual vol- ume for anchovy larvae. The predicted ingestion is too low to sustain the growth potential of larvae when assuming conical perceptive volume even under prey densities substantially higher than normally found in the field. Ingestion rate is sensitive to the total biomass and the slope of the prey size spectra, specifically because it determines the abundance of prey around the optimal size for the larvae. The model also sug- gests that small larvae benefit from a prey size struc- ture with steep prey size-spectra slope while a large larva benefit from less steep slopes. The model can act as a link between size-spectra measurements from the field and the foraging conditions of larval anchovies.

Prenatal Chemosensory Learning by the Predatory Mite Neoseiulus californicus

BackgroundPrenatal or embryonic learning, behavioral change following experience made prior to birth, may have significant consequences for postnatal foraging behavior in a wide variety of animals, including mammals, birds, fish, amphibians, and molluscs. However, prenatal learning has not been previously shown in arthropods such as insects, spiders and mites.Methodology/Principal FindingsWe examined prenatal chemosensory learning in the plant-inhabiting predatory mite Neoseiulus californicus. We exposed these predators in the embryonic stage to two flavors (vanillin or anisaldehyde) or no flavor (neutral) by feeding their mothers on spider mite prey enriched with these flavors or not enriched with any flavor (neutral). After the predators reached the protonymphal stage, we assessed their prey choice through residence and feeding preferences in experiments, in which they were offered spider mites matching the maternal diet (neutral, vanillin or anisaldehyde spider mites) and non-matching spider mites. Predator protonymphs preferentially resided in the vicinity of spider mites matching the maternal diet irrespective of the type of maternal diet and choice situation. Across treatments, the protonymphs preferentially fed on spider mites matching the maternal diet. Prey and predator sizes did not differ among neutral, vanillin and anisaldehyde treatments, excluding the hypothesis that size-assortative predation influenced the outcome of the experiments.Conclusions/SignificanceOur study reports the first example of prenatal learning in arthropods.

Predator biomass determines the magnitude of non-consumptive effects (NCEs) in both laboratory and field environments

Predator body size often indicates predation risk, but its significance in non-consumptive effects (NCEs) and predator risk assessment has been largely understudied. Although studies often recognize that predator body size can cause differing cascading effects, few directly examine prey foraging behavior in response to individual predator sizes or investigate how predator size is discerned. These mechanisms are important since perception of the risk imposed by predators dictates behavioral responses to predators and subsequent NCEs. Here, we evaluate the role of predator body size and biomass on risk assessment and the magnitude of NCEs by investigating mud crab foraging behavior and oyster survival in response to differing biomasses of blue crab predators using both laboratory and field methods. Cues from high predator biomass treatments including large blue crab predators and multiple small blue crab predators decreased mud crab foraging and increased oyster survival, whereas mud crab foraging in response to a single small blue crab did not differ from controls. Mud crabs also increased refuge use in the presence of large and multiple small, but not single small, blue crab predators. Thus, both predator biomass and aggregation patterns may affect the expression of NCEs. Understanding the impact of predator biomass may therefore be necessary to successfully predict the role of NCEs in shaping community dynamics. Further, the results of our laboratory experiments were consistent with observed NCEs in the field, suggesting that data from mesocosm environments can provide insight into field situations where flow and turbulence levels are moderate.

Feeding habits of small-spotted catshark (Scyliorhinus canicula Linnaeus, 1758) from the eastern central Adriatic Sea

The feeding habits of small-spotted catshark, Scyliorhinus canicula, from the central Adriatic Sea, were investigated with respect to fish size, season and sampling location. Stomach contents of 1200 specimens, collected at monthly intervals (January to December 2010), were analysed. The prey items identified in the stomachs belonged to eight major groups: Cephalopoda, Polychaeta, Stomatopoda, Decapoda, Mysidacea, Euphausiacea, Amphipoda and Teleostei. Decapods were the most important ingested prey in all seasons, for medium sized fish (22–38 cm TL). Euphausiids and mysids constituted the main prey items of small fish (<22 cm TL) while teleosts dominated the stomach contents of larger specimens (>38 cm TL). Two decapods, Alpheus glaber (%IRI = 5.1) and Solenocera membranacea (%IRI = 3.0), were the most numerous prey items identified to species level. The mean weight of stomach contents (relative to predator size) increased significantly for fish larger than 30 cm TL, while the mean number of prey items did not differ significantly among size-classes. The percentage of empty stomachs showed a monthly variation with a maximal occurrence in February (48.0%) and a minimal in August (9.0%). The lowest feeding frequency could be related to low sea temperatures during the winter. The small-spotted catshark could be considered a generalistic predator.

Predators of juvenile sea urchins and the effect of habitat refuges

We evaluated the effects of potential predators from intertidal habitats on Strongylocentrotus purpuratus survival using laboratory experiments and assessed abundances of main predatory species along the Pacific coast of North America. The interactive effects of urchins’ and predators’ sizes in mediating predation were quantified. Habitat complexity (substrate pits, adult spine canopy) was manipulated to examine its effects on predation of most susceptible individuals (<14 mm). Pachygrapsus crassipes was identified as a major predator of urchins up to ≈30 mm. A positive effect of predator size on consumption of progressively larger urchins was detected, probably due to a mechanical limitation on crabs’ ability to consume large prey. Larger claws of males with respect to females of comparable sizes facilitated the handling of larger prey. Substrate refuges significantly reduced mortality on juvenile urchins. These results show that crab predation may be important in organizing intertidal communities, despite multiple ecological mechanisms promoting sea urchin survival.

Modified pheromone traps help reduce bycatch of bark‐beetle natural enemies

Thanasimus formicariusandTemnochila caerulea,two of the main predators ofIps sexdentatus, a well‐known forest pest in Southern Europe, are captured in high numbers when trappingI. sexdentatusas a result of the kairomonal effect of the lures used.A preliminary field trial showed that predators could survive for at least 1 week within trapping containers, although predator mutilation and high predator death rates were observed.Different modifications of conventional multiple funnel and slot traps with the objective of reducing natural enemy entrance into trap containers were bioassayed in field experiments conducted over four seasons. Based on the larger sizes of predators, different designs using welded wire‐mesh screens improved performance to different extents. Providing escape windows just above the screen on multiple funnel traps gave the most promising results, including when effect sizes among all tested designs were compared.Thus, a simple modification of the lowest funnel of the multiple funnel traps would reduce the bycatch ofT. formicariusandT. caerulea, hence improving the efficiency of trapping programmes by lowering the likely impact on natural populations of these predators.

Food web structure and seasonality of slope megafauna in the NW Mediterranean elucidated by stable isotopes: Relationship with available food sources

The food-web structure and seasonality of the dominant taxa of benthopelagic megafauna (fishes and decapods) on the middle slope of the Catalan Sea (Balearic Basin, NW Mediterranean) were investigated using the carbon and nitrogen stable isotope ratios of 29 species. Macrofauna (infauna, suprabenthos and zooplankton) were also analysed as potential prey. Samples were collected on a seasonal basis from 600 to 1000m depth between February 2007 and February 2008. The fishes and decapods were classified into feeding groups based on the literature: benthic feeders (including suprabenthos) and zooplankton feeders, the latter further separated into migratory and non-migratory species. Decapods exhibited depleted δ15N and enriched δ13C compared to fishes. Annual mean δ13C of fishes ranged from −19.15‰ (Arctozenus risso) to −16.65‰ (Phycis blennoides) and of δ15N from 7.27‰ (Lampanyctus crocodilus) to 11.31‰ (Nezumia aequalis). Annual mean values of δ13C of decapods were from −18.94‰ (Sergestes arcticus) to −14.78‰ (Pontophilus norvegicus), and of δ15N from 6.36‰ (Sergia robusta) to 9.72‰ (Paromola cuvieri). Stable isotopes distinguished well amongst the 3 feeding guilds established a priori, pointing to high levels of resource partitioning in deep-sea communities. The trophic structure of the community was a function of the position of predators along the benthic–pelagic gradient, with benthic feeders isotopically enriched relative to pelagic feeders. This difference allowed the identification of two food webs based on pelagic versus benthic consumption. Prey and predator sizes were also important in structuring the community. The most generalised seasonal pattern was δ13C depletion from winter to spring and summer, especially amongst migratory macroplankton feeders. This suggests greater consumption of pelagic prey, likely related with increases in pelagic production or with ontogenic migrations of organisms from mid-water to the Benthic Boundary Layer (BBL). δ15N enrichment was detected in periods of water column stratification, particularly amongst benthic feeder fishes. Megafauna relied on a single source of nutrition after peaks in surface production, presumably marine snow. Conversely, a larger array of food sources, probably from advection, sustained the community in periods of water column stratification. Benthic feeder δ13C values of both taxa were positively correlated with fluorescence measured 5m above the seabed and negatively correlated with total organic carbon in the sediments, both being food sources for deposit feeding macroinfauna. Macroplankton feeder δ13C values were linked to environmental variables related to vertical transport from surface production, i.e. lipids and chlorophyll and their degradation products, likely due to their stronger reliance on sinking phytodetritus through consumption of planktonic prey.

Size and shape information serve as labels in the alarm calls of Gunnison’s prairie dogs Cynomys gunnisoni

Abstract Some animals have the capacity to produce different alarm calls for terrestrial and aerial predators. However, it is not clear what cognitive processes are involved in generating these calls. One possibility is the position of the predator: Anything on the ground receives a terrestrial predator call, and anything in the air receives an aerial predator call. Another possibility is that animals are able to recognize the physical features of predators and incorporate those into their calls. As a way of elucidating which of these mechanisms plays a primary role in generating the structure of different calls, we performed two field experiments with Gunnison’s prairie dogs. First, we presented the prairie dogs with a circle, a triangle, and a square, each moving across the colony at the same height and speed. Second, we presented the prairie dogs with two squares of differing sizes. DFA statistics showed that 82.6 percent of calls for the circle and 79.2 percent of the calls for the triangle were correctly classified, and 73.3 percent of the calls for the square were classified as either square or circle. Also, 100 percent of the calls for the larger square and 90 percent of the calls for the smaller square were correctly classified. Because both squares and circles are features of terrestrial predators and triangles are features of aerial predators, our results suggest that prairie dogs might have a cognitive mechanism that labels the abstract shape and size of different predators, rather than the position of the predator.

Maximum handling size, prey size and type selection by snakehead (Channaargus) feeding on juvenile Chinese mitten crab (Eriocheir sinensis)

Laboratory predation trials were conducted to investigate maximum handling size, prey size and type selection by small (35-37cm in total length, L-T), medium (43-46cm L-T) and larger (58-60cm L-T) snakehead (Channa argus) when feeding on a wide size (9-34mm in carapace width, C-W) range of juvenile Chinese mitten crab (Eriocheir sinensis). The maximum handling size of predator feeding on crabs monotonically increased with predator L-T and mouth gape width, G(W). Snakehead with at least 16.0cm L-T or 27.7mm G(W) would be capability to consume the smallest size group of crabs, whereas the predator with 72.6cm L-T or 63.4mm G(W) would be capability to consume all size groups of crabs in these trails. Prey-size selection trials showed that snakehead has a high preference to the small-sized crabs, and lower preference to the medium or large size crabs. The preference index was significantly affected by prey size and prey size x predator size interaction, however, was not affected by predator size. In prey type experiments, snakehead consumed lower proportions of juvenile crabs when fed on the crab and crucian carp than when fed on only the crab, which suggests alternative fish prey may reduce predation risk of the crab by snakehead in nature. These results could be useful for improving the fishery management and release strategies for the crab.

Predator size interacts with habitat structure to determine the allometric scaling of the functional response

While both predator body size and prey refuge provided by habitat structure have been established as major factors influencing the functional response (per capita consumption rate as a function of prey density), potential interactions between these factors have rarely been explored. Using a crab predator (Panopeus herbstii) – mussel prey (Brachidontes exustus) system, we examined the allometric scaling of the functional response in oyster (Crassostrea virginica) reef habitat, where crevices within oyster clusters provide mussels refuge from predation. A field survey of mussel distribution showed that mussels attach closer to the cluster periphery at high mussel density, indicating the potential for saturation of the refuge. In functional response experiments, the consumption rate of large crabs was depressed at low prey density relative to small crabs, while at high prey density the reverse was true. Specifically, the attack rate coefficient and handling time both decreased non‐linearly with crab size. An additional manipulation revealed that at low prey densities, the ability of large crabs to maneuver their claws and bodies to extract mussels from crevices was inhibited relative to small crabs by the structured habitat, reducing their attack rate. At high prey densities, crevices were saturated, forcing mussels to the edge of clusters where crabs were only limited by handling time. Our study illuminates a potentially general mechanism where the quality of the prey refuge provided by habitat structure is dependent on the relative size of the predator. Thus anthropogenic influences that alter the natural crab size distribution or degrade reef habitat structure could threaten the long‐term stability of the crab –mussel interaction in reefs.

Feeding Habits and Predator-Prey Size Relationships in the Whiptail LizardCnemidophorus ocellifer(Teiidae) in the Semiarid Region of Brazil

We studied the diet of the whiptail lizard Cnemidophorus ocellifer (Spix, 1825) and the relationships between predator size and prey size in a Caatinga area of northeastern Brazil. Lizards (N = 111) were collected during the day through active search. In the laboratory, we measured them and registered the number of ingested items of each prey category to Order, as well as the dimensions and frequencies of each. The main prey category in the C. ocellifer diet was insect larvae and pupae, followed by Orthoptera, Isoptera, Coleoptera and Araneae. Termites (Isoptera) were important only in numeric terms, having negligible volumetric contribution and low frequency of occurrence, an uncommon feature among whiptail lizards. The types and sizes of prey consumed by adult males and females were similar, despite sexual dimorphism in head size. Adults and juveniles ingested similar prey types, but differed in prey size. Maximum and minimum prey sizes were positively correlated with lizard body size, suggesting that in this population individuals experience an ontogenetic change in diet, eating larger prey items while growing, and at the same time excluding smaller ones.

Contribution of cephalopod prey to the diet of large pelagic fish predators in the central North Atlantic Ocean

Trophic studies documenting the importance of cephalopod prey for large pelagic fish predators have been performed recently for open ocean ecosystems in the Pacific and Indian oceans, but similar data for the central North Atlantic Ocean have been lacking. A series of longline sampling cruises targeting large pelagic fish species was undertaken in the central North Atlantic Ocean in 2001–2002, and stomach samples were analyzed from a variety of tuna, shark, and billfish species to help fill this data gap. Stomach samples were collected from nine species (n=170 non-empty stomachs), with the majority of stomachs from Atlantic swordfish (Xiphias gladius; n=69), yellowfin tuna (Thunnus albacares; n=31), and albacore tuna (Thunnus alalunga; n=28). Ommastrephid squids were the most ubiquitous prey group across predator species and sampling years. Secondary cephalopod prey included octopods, histioteuthids, and architeuthids. Mesopelagic fishes and Sargassum-associated fishes were also identified as important prey. Diet composition varied spatially and prey size increased with predator size for swordfish and yellowfin tuna. Our results support findings in other ocean basins that demonstrate the importance of squid to large pelagic fishes and highlight the need for more research on their ecological and biophysical dynamics.