Predator–prey interactions in anurans of the tropical dry forests of the Colombian Caribbean: A functional approach

Anuran–prey selection might be mediated by traits, either by mismatches in predator and prey traits (preventing interactions) or by predator selection of prey traits (encouraging interactions). These effect traits could be summarized in two contrasting foraging strategies: “active” and “sit-and-wait” foragers. We evaluated whether anurans could be classified into groups of species sharing traits associated with their diet, and what is the relation between particular effect traits of anurans and their prey. We collected anurans and identified their stomach contents once during dry, minor, and major rain seasons in six dry forest sites in the Colombian Caribbean. For each of the 19 anuran species and 436 prey items, we registered six effect traits. We applied RLQ and fourth-corner methodologies to relate predator and prey traits through their interaction matrix. Predators were assigned to five groups according to their differences in locomotion, body shape, proportion of the jaw width, mode of tongue protrusion, and strata preferred. Regarding preys, species were assigned to four groups according to their gregariousness, body shape and hardness, defensive traits, and mobility. Body size of both, predators and prey, had a minor contribution in the group assignment. We found that predators using active search target low-mobility preys, whereas species using sit-and-wait strategy target highly nutritive prey that are difficult to manipulate. By linking amphibian diet with foraging strategies, we hope to contribute to the understanding of mechanisms behind anuran–prey food web patterns and to build more realistic models of functional response to changing environments.     

Effects of prey size and foraging mode on the ontogenetic change in feeding niche ofColostethus stepheni (Anura: Dendrobatidae)

The feeding niche ofColostethus stepheni changes during ontogeny. Small individuals eat small arthropods, principally mites and collembolans, and larger frogs eat bigger prey of other types. The shift in prey types is not a passive effect of selection for bigger prey. There is a strong relationship between electivity for prey types and frog size, independent of electivity for prey size. Four indices of general activity during foraging (number of movements, velocity, total area utilized and time spent moving), which are associated with electivity for prey types in adult frogs and lizards, did not predict the ontogenetic change in the diet ofC. stepheni. Apparently, the behavioral changes that cause the ontogenetic change inC. stepheni are more subtle than shifts in general activity during foraging. Studies of niche partitioning in communities of anurans that do not take into consideration ontogenetic changes in diet and seasonal changes in the size structures of populations present a partial and possibly erroneous picture of the potential interactions among species.     

Anurans as prey: an exploratory analysis and size relationships between predators and their prey

The vertebrate predators of post-metamorphic anurans were quantified and the predator–prey relationship was investigated by analysing the relative size of invertebrate predators and anurans. More than 100 vertebrate predators were identified (in more than 200 reports) and classified as opportunistic, convenience, temporary specialized and specialized predators. Invertebrate predators were classified as solitary non-venomous, venomous and social foragers according to 333 reviewed reports. Each of these categories of invertebrate predators was compared with the relative size of the anurans, showing an increase in the relative size of the prey when predators used special predatory tactics. The number of species and the number of families of anurans that were preyed upon did not vary with the size of the predator, suggesting that prey selection was not arbitrary and that energetic constraints must be involved in this choice. The relatively low predation pressure upon brachycephalids was related to the presence of some defensive strategies of its species. This compounding review can be used as the foundation for future advances in vertebrate predator–prey interactions.     

Diet of Rana cancrivora in fresh water and brackish water environments

Rana cancrivora Gravenhorst inhabits both fresh water and brackish water swamps and ditches in Singapore. Food items in the gut of frogs from both habitats have been examined. The diet of frogs collected near brackish water was predominantly crustacean and included crabs ( Sesarma spp.), while the diet of those collected near fresh water comprised mainly insects. Gut contents of frogs included all the small animal species found in the respective environments, the choice of prey appearing to be limited only by size.     

An exotic species is the favorite prey of a native enemy

Although native enemies in an exotic species'' new range are considered to affect its ability to invade, few studies have evaluated predation pressures from native enemies on exotic species in their new range. The exotic prey naiveté hypothesis (EPNH) states that exotic species may be at a disadvantage because of its naïveté towards native enemies and, therefore, may suffer higher predation pressures from the enemy than native prey species. Corollaries of this hypothesis include the native enemy preferring exotic species over native species and the diet of the enemy being influenced by the abundance of the exotic species. We comprehensively tested this hypothesis using introduced North American bullfrogs (Lithobates catesbeianus, referred to as bullfrog), a native red-banded snake (Dinodon rufozonatum, the enemy) and four native anuran species in permanent still water bodies as a model system in Daishan, China. We investigated reciprocal recognition between snakes and anuran species (bullfrogs and three common native species) and the diet preference of the snakes for bullfrogs and the three species in laboratory experiments, and the diet preference and bullfrog density in the wild. Bullfrogs are naive to the snakes, but the native anurans are not. However, the snakes can identify bullfrogs as prey, and in fact, prefer bullfrogs over the native anurans in manipulative experiments with and without a control for body size and in the wild, indicating that bullfrogs are subjected to higher predation pressures from the snakes than the native species. The proportion of bullfrogs in the snakes'' diet is positively correlated with the abundance of bullfrogs in the wild. Our results provide strong evidence for the EPNH. The results highlight the biological resistance of native enemies to naïve exotic species.     

Diet Composition of Indian Burrowing Frog <Emphasis Type="Italic">Sphaerotheca breviceps</Emphasis> (Anura: Dicroglossidae) in Uttarakhand Region of Western Himalaya

A study encompassing the food and feeding habits of Indian burrowing frog Sphaerotheca breviceps was carried out in Srinagar Garhwal (n = 27) and Joshimath region (n = 21) of Uttarakhand, Western Himalaya, India to establish their feeding nature and diet composition. Gut content analysis of S. breviceps revealed acceptance of a wide range of insects and other invertebrates as their food. They feed extensively on the ground and litter-dwelling prey animals. There exists a slight deviation in the diets of S. breviceps in respect to localities perhaps due to variation in prey faunal species. Analysis of the food items ingested revealed that the size of the prey animals was ranged from 3 to 56 mm. The diet composition and index of relative importance confirm its insectivorous type of feeding habit. The study indicates that these anurans are primarily predators of nocturnal terrestrial arthropods and act as an important biological agent for controlling the harmful pests and thus help in ecosystem management.     

Feeding ecology of thirteen syntopic species of anurans in a seasonal tropical environment

Summary Thirteen species of anurans belonging to three families forage diurnally for arthropods in the leaf litter of the lowland rainforest at the Río Llullapichis in Amazonian Perú. This paper investigates the diets and patterns of coexistence in this group of ecologically similar species. All thirteen species use the forest floor habitat without apparent differentiation. Most species take prey in proportions significantly different from those occurring in the leaf litter and comprise two specialist guilds: dendrobatids and bufonids that eat hard-bodied, slow-moving arthropods such as ants and mites; and leptodactylids that eat soft-bodied, mobile arthropods, primarily orthopterans and large spiders. Dendrobates femoralis (Boulenger) is a generalist, taking prey in proportions not significantly different from those in the leaf litter. Within specialist guilds, body sizes of species vary and are correlated with the size of prey taken. Foraging behavior and predator defense also correlate with the type and sizes of prey taken. Ant specialists tend to be poisonous and active searchers, taking many small prey per day. Non-ant specialists are cryptic, sit-and-wait foragers that take few large prey per day. Similarity in diet within guilds tends tobe lowest in the dry season when food is less abundant, suggesting that food is in short supply in the dry season.     

Diet breadth variability in larval blue whiting as a response to plankton size structure

Diet breadth (measured as the S.D. of the log of prey size per larvae; SLH) of blue whiting micromesistius poutassou larvae followed a quadratic equation with larval size. In small larvae, diet breadth in terms of size (SLH), the mean and the maximum of the log of prey size per larvae (MLH and XLH, respectively) increased with larval size as prey size selection shifted to larger prey. In contrast, large larvae tended to reduce diet breadth of prey sizes ingested, focusing on the larger prey that were abundant, instead of raising the upper limit of prey sizes because of the low abundance of larger prey. Except for larvae at the onset of first feeding, number of prey stayed constant or decreased in relation to larval size. Both patterns (in small and large larvae) maintained a constant rate of increase of gut carbon content with increase in larval size. Large larvae appear to maintain the increase in gut carbon content during ontogenetic development by reducing diet breadth (SLH) and increasing selection towards the larger prey that are abundant.     

Effects of season and body-size on the distribution and diet of the Iberian chub Leuciscus pyrenaicus in a lowland catchment

Seasonal and ontogenetic variations in space and food use by Leuciscus pyrenaicus were analysed in a Portuguese lowland catchment. Large fish occurred mostly in deep permanent-flowing sites whereas small fish occurred mostly in the shallowest intermittent-flowing site. No seasonal or size-related changes in feeding intensity were found, but the diet changed both across seasons and throughout ontogeny. The diet was dominated by aquatic prey over all seasons, but during winter and summer more plant material and terrestrial prey, respectively, were eaten. Throughout ontogeny fish shifted from soft-bodied to hard-shelled prey and decreased animal prey breadth. Mean prey size increased with fish size but the prey size spectrum was more variable for medium-sized fish than for either small or large fish. It is suggested that: (i) large fish avoid shallow drying areas owing to the risk of mortality, either by thermal and respiratory stresses or increased predation by mammals and birds; (ii) seasonal changes in diet are a response to differences in prey availability; and (iii) morphological constraints, prey handling costs and habitat partitioning are responsible for size-related changes in diet.     

Body size and tree species composition determine variation in prey consumption in a forest‐inhabiting generalist predator

Trophic interactions may strongly depend on body size and environmental variation, but this prediction has been seldom tested in nature. Many spiders are generalist predators that use webs to intercept flying prey. The size and mesh of orb webs increases with spider size, allowing a more efficient predation on larger prey. We studied to this extent the orb‐weaving spider Araneus diadematus inhabiting forest fragments differing in edge distance, tree diversity, and tree species. These environmental variables are known to correlate with insect composition, richness, and abundance. We anticipated these forest characteristics to be a principle driver of prey consumption. We additionally hypothesized them to impact spider size at maturity and expect shifts toward larger prey size distributions in larger individuals independently from the environmental context. We quantified spider diet by means of metabarcoding of nearly 1,000 A. diadematus from a total of 53 forest plots. This approach allowed a massive screening of consumption dynamics in nature, though at the cost of identifying the exact prey identity, as well as their abundance and putative intraspecific variation. Our study confirmed A. diadematus as a generalist predator, with more than 300 prey ZOTUs detected in total. At the individual level, we found large spiders to consume fewer different species, but adding larger species to their diet. Tree species composition affected both prey species richness and size in the spider''s diet, although tree diversity per se had no influence on the consumed prey. Edges had an indirect effect on the spider diet as spiders closer to the forest edge were larger and therefore consumed larger prey. We conclude that both intraspecific size variation and tree species composition shape the consumed prey of this generalist predator.     

Size-related changes in cranial morphology affect diet in the catfish Clariallabes longicauda

Within the catfish family Clariidae, species exist with different degrees of jaw adductor hypertrophy. This jaw adductor hypertrophy has been related to bite performance, in turn suggesting a link to dietary specialization. Thus, an increase in the degree of hypertrophy will likely be reflected in an increase in the amount of hard prey in the diet. In the present study, we examine the ontogenetic scaling of cranial structure and diet in a species of catfish with a moderate degree of jaw adductor hypertrophy, Clariallabes longicauda . Additionally, we investigate whether the observed changes in the morphology of the feeding system during growth are linked to changes in diet. The fish examined demonstrate a strong positively allometric growth of the jaw adductors, of head height and of maximal head width, suggesting that larger fish can feed on larger and harder prey. Dietary data confirm these hypotheses and reveal an increase in maximal prey size consumed, the proportion of large prey in the diet, and average prey hardness during ontogeny. Moreover, the observed changes in the proportion of large prey consumed and prey hardness are correlated with an increase in lower jaw width and maximal head width, respectively. An increase in the amount of evasive prey in the diet with fish size is correlated with an increase in hyoid length. In summary, not only size dependent, but also size-independent variation of the feeding system was associated with ontogenetic changes in diet in C. longicauda .  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 323–334.     

Generalists as sequential specialists: diets and prey switching in juvenile silver perch

Diets of silver perch, Bidyanus bidyanus, in organically fertilised aquaculture ponds were dominated by chironomid larvae, Daphnia and calanoid copepods. Insects and crustaceans contributed approximately 80% and 20% by weight to the diet respectively. Classification of the stomach contents of individual fish revealed 8 diet groups, 4 of which were dominated by planktonic crustaceans and 4 by insects. Each diet group was strongly dominated by a different prey type. Fish from the same sample tended to belong to the same diet group and there was a non-random distribution of diet groups across ponds. Perch diets were influenced by the method of pond fertilisation (livestock effluent or pellet feed). Shifts in the representation of groups indicated that fish switched from one diet group to another over a 2–4 week period. The selection of planktonic prey by perch was related to prey densities in the ponds. Fish preferred Daphnia when these prey were common, but switched to calanoids and insects when Daphnia were scarce. A perfect rank correlation between the mean body size of planktonic prey and their contribution to the diet suggested that prey choice involved comparative decisions based on prey size. These findings indicate that, while classified as dietary generalists, silver perch exhibit consumption patterns which at the individual level are highly specialised at any given time. These patterns can be predicted, given information on prey densities in the environment.     

Feeding ecology of the Bay Goby (Pisces: Gobiidae). Effects of behavioral,ontogenetic, and temporal variation on diet

The ontogenetic, diel, seasonal, and yearly variations in gut fullness, diet, and prey diversity for a California estuarine gobiid (Lepidogobius lepidus Girard) were examined. Also the feeding behavior of this species was described.Small (<50 mm, SL) and large (? 50 mm, SL) gobies consumed similar prey types in different proportions. Major prey items were polychaetes, harpacticoid copepods, gammarid amphipods, molluscs, and other crustaceans. Diets of large and small gobies were not significantly correlated, and larger fish had a more diverse diet. Small fish fed at all times while larger gobies fed primarily at night. Changes in diet may be related to differential prey preferences, feeding chronologies, and increases in fish size.Both large and small gobies displayed seasonal differences in diet and prey diversity. Year-to-year changes in diet also were noted for both size classes. The bay goby uses different feeding behaviors to capture sedentary and motile prey and appears to forage opportunistically. This behavior is probably advantageous in an environment which fluctuates drastically.     

Influence of ontogenetic changes in prey selection on the survival and growth of rohu, Labeo rohita and singhi, Heteropneustes fossilis larvae

When offered a mixed diet of different zooplanktonic items covering a body size range of 75–2200 μm, (a) rohu, Labeo rohita and (b) singhi, Heteropneustes fossilis larvae ingested progressively larger prey as they grew, due to age-related increase in gape. However, a nearly constant prey size/mouth size ratio was maintained for a period of 4wk after hatching. The dominance of rotifers in the diet during the first 2-wk was followed by cladocerans, particularly Moina macrocopa. Significant differences observed in the growth rates of the larvae reared on different diet regimes were related to ontogenetic changes in prey selection. An exclusive copepod diet throughout resulted in the lowest weight gain in the larvae of both species. However, copepods had no apparent adverse effects when present with the preferred rotifers and cladocerans. Although constituting a suboptimal prey size for the older larvae, rotifers alone, when present in sufficient densities, produced growth rates comparable to those obtained on a cladoceran diet. However, a mixed diet regime contributed to the maximum growth. The implications of these findings to rearing larvae of the economically important rohu and singhi are discussed.     

Accelerating the onset of piscivory: intersection of predator and prey phenologies

Piscivorous fishes tend to be able to consume other fishes early in development and generally experience a dramatic increase in growth after the ontogenetic diet shift to piscine prey. Hence, an acceleration of the onset of piscivory may be favoured strongly by natural selection. Temperate freshwater piscivores, for example, becomes piscivorous at a relatively young age by spawning in advance of, and thereby achieving a size advantage over, the young of their piscine prey. Research in various North American estuaries suggests that young-of-the-year (YOY) bluefish Pomatomus saltatrix , an offshore-spawning estuarine-dependent marine fish, may accelerate the onset of piscivory by being advected to higher latitudes and timing their estuarine entry with the appearance of small coastal fishes. This hypothesis was tested by: (i) determining the annual recruitment date of YOY bluefish and their prey; and (ii) examining the diet and prey size preferences, and predator size-prey size relationships, of YOY bluefish in two different estuarine systems: Great South Bay, and the lower Hudson River. Results suggest that the relationships between bluefish and their prey are determined by a complex interplay between recruitment timing of both predator and prey, prey size availability, predator selectivities, and the timing of vernal warming. It is concluded that YOY bluefish migration into northern estuaries at an advanced size provides them with a predatory size advantage over their principal piscine prey thereby facilitating an early diet shift to piscivory white minimizing the time spent as planktivores.     

Foraging capacities and effects of competitive release on ontogenetic diet shift in bream, Abramis brama

Bream (Abramis brama) undergo ontogenetic diet shift from zooplankton to benthic macroinvertebrates, but the switching size may be highly variable. To unravel under what conditions bream are pelagic versus benthic foragers, we experimentally determined size‐dependent foraging capacities on three prey types from the planktivory and benthivory niche; zooplankton, visible and buried macroinvertebrates. From these data we derived predictions of size‐dependent diet preferences from estimates of prey value and competitive ability, and tested these predictions on diet data from the field. Planktivorous foraging capacity described a hump‐shaped relationship with bream length that peaked for small bream of 67 mm total length. Benthivory capacity increased with increasing bream size, irrespective if benthic prey were visible on the sediment surface or buried in the sediment. From the experimental data and relationships of metabolic demand we calculated minimum resource requirement for maintenance (MRR) for each of the prey categories used in experiments. MRR increased with bream size for both zooplankton and visible chironomids, but decreased with bream size for buried chironomids, suggesting that intermediate sized bream (120–300 mm) may be competitively sandwiched between small and large bream that are more competitive planktivores and benthivores, respectively. Prey value estimates and competitive abilities qualitatively predicted diet shift in a bream population being released from competition. Competitive release did not change the diet of the largest size‐class feeding on an optimal diet of benthic invertebrates both before and after competitive release. However, profound diet shifts towards benthic macroinvertebrates were recorded for intermediate size‐classes that fed on a suboptimal diet prior to competitive release. Thus, laboratory estimates of size‐dependent foraging capacity of bream in planktivorous and benthivorous feeding niches provided useful information on size‐specific competitive ability, and successfully predicted diet preference in the field.     

Morphological distance and inter-nest distance account for intra-specific prey overlap in digger wasps (Hymenoptera: Crabronidae)

Although inter-individual diet variation is common in predatory wasp populations, the factors accounting for such variation are still largely unknown. Here, we asked if paired diet dissimilarity in three species of digger wasps correlates with morphological distance and inter-nest distance, two factors previously linked to diet partitioning in vertebrates. Results sharply differed among species and generations. All sampled populations showed significant inter-individual diet variation for prey taxa, but only in half of the cases for prey size. In one generation of two species [Bembix zonata Klug and Stizus continuus (Klug)], similar-sized wasps had similar prey taxonomic spectra (and for S. continuus also similar prey size spectra), a phenomenon which probably reduces intra-specific competition. In addition, B. zonata females nesting closer to each other had more similar prey taxonomic spectra, suggesting that distant females probably hunt on different patches that harbour different prey species. For the females of a further species (Bembix merceti Parker), pairwise size difference and inter-nest distance did not affect prey dissimilarity. Both morphological distance and inter-nest distance are potentially important in shaping the overlap of individual resource use in wasps, though probably only in certain conditions such as a highly clumped distribution of nests and size-related constraints on prey selection.     

Variation in diet of yellow perch (Perca flavescens) in a Quebec reservoir

We determined the diet of 1 to 1 1/2 a old yellow perch (Perca flavescens) in a Quebec reservoir, relative to occurrences of available prey species and size classes of prey. We used Schindler-Patalas trap samples taken over four 24-h intervals between June and September 1981 to determine size distribution of available prey species. Relative abundances and size distribution of ingested prey species were determined from examination of gut contents of perch trapped by gill nets during the same time intervals. Electivity values of different prey species and of different size classes of prey were determined. Larger zooplankton prey (e.g.Epischura andLeptodora) were generally preferred but there was considerable variability in diet among individual fish that cannot be explained by patterns of prey availability. Within particular size classes of prey, perch have definite preferences, e.g. when perch consume small prey, they preferBosmina to other similar-sized prey. These results are discussed in relation to theories attempting to describe and predict feeding patterns of planktivorous fish species.Deceased, June 6, 1983     

Feeding habits of dolphinfish (Coryphaena hippurus) in the southeastern Gulf of California,Mexico

The objective of the study was to identify key elements of the feeding ecology of the dolphinfish, which is a high tropic predator important for sport and artisanal fishing in the Mexican Pacific. Feeding habits were investigated during the years 2000–2003. This species is seasonal in the southern Gulf of California and probably remains there because of the abundant prey. The contents of 232 dolphinfish stomachs were analyzed, identifying 98 prey species, although only eight of these were well‐represented in the diet. The most important prey by weight was the fish Hemiramphus saltator, however by number and frequency of occurrence was the crustacean Hemisquilla californiensis. No differences in the diet were found between males and females, although there was an ontogenic diet shift between seasons. There was no relationship between dolphinfish size and prey size, because dolphinfish fed preferentially on prey with an average size of 4.7 cm.