Resource utilization and guild structure of small vertebrates in the Amazon forest leaf litter

Ten species of small vertebrates that occurred together in leaf litter of the Amazon tropical rainforest were studied during the dry season in Rondônia, western Brazil. This vertebrate assemblage consisted of two diurnal lizards, two diurnal frogs, one nocturnal frog, and five frog species that are active by day and night. All species feed on small invertebrates, primarily insects and arachnids. There are significant differences in prey types and sizes eaten, and overlap values among species are relatively low. Niche breadths vary from unity (extremely low) to high (> 9.0). A pseudocommunity analysis using two different algorithms indicated that structure exists in the prey resource matrix of the vertebrate assemblage. The zero structure of the community matrix contributes to the observed structure, i.e. prey items not taken by certain species are important in maintaining structure. Several well-defined feeding guilds are apparent, and the feeding guilds do not appear to follow taxonomic lines.     

Seasonal variation in populations of panamanian litter frogs and their prey: A comparison of wetter and drier sites

Summary Various species of frogs and toads, belonging to the genera Bufo, Atelopus, Dendrobates, Colostethus, and Eleutherodactylus, occur in the leaf litter in rainforest in Panamá. This study compares the litter communities at two sites in Panamá: Pipeline Road, the drier site, and Carti Road, the wetter site. At both sites, frog abundance is greater in the dry season, when abundance of their prey, the litter arthropods, is greater. Species diversity does not change seasonally at either site; however, species diversity differs strikingly between sites, with Carti Road having the greater species diversity. Similarity in diet does not vary consistently with seasonal changes in food abundance at a single site or with differences in species diversity between sites. These results suggest that neither moisture nor food abundance alone influences the abundance or the diversity of litter frogs at these two sites in Panamá.     

Seasonal patterns in the foraging ecology of the harvester ant Pogonomyrmex naegelii (Formicidae, Myrmicinae) in a Neotropical savanna: daily rhythms, shifts in granivory and carnivory, and home range

The temporal dynamics of foraging, diet, and use of space is essential to understand the ecology of harvester ants. Here, we present an account of the foraging ecology of Pogonomyrmex naegelii in Brazilian cerrado savanna. Nests occur on bare ground and contain 166?C580 workers (N?=?3 colonies). Colony activity is unimodal year-round and peaks around the middle of the day. Foragers leave the nest independently and individually search for food in all directions. Ants ventured up to 15?m from nests, with most foraging occurring within 2?m of nests. Colonies tended to have larger home ranges in the dry/cold (April?CSeptember) than in the wet/warm season (October?CMarch). P. naegelii has a generalist and season-dependent diet comprised of many seed species and arthropod prey, and pieces of plant and animal matter. Foragers collected seeds from 34 plant species, predominantly grasses (genera Gymnopogon, Axonopus, Aristida). Over 6,700 seeds can be stored in nest granaries. Ants and termites were the main animal prey retrieved by P. naegelii. The proportion of seeds and arthropods foraged by P. naegelii changes year-round: in the dry/cold season, the diet is predominantly granivorous, whereas in the wet/warm season, seeds and arthropods are retrieved in more balanced proportions. Although food availability was not assessed, year-round diet of P. naegelii matches the pattern of seasonal abundance of grass seeds and arthropod prey in cerrado. Data on harvester ants come mostly from arid habitats; this study is a first assessment of the ecology of a Neotropical Pogonomyrmex from a moderately moist savanna environment.     

Diet seasonality and food overlap among fishes of the upper Orituco stream, northern Venezuela.

The diets of four diurnal fish species (Creagrutus bolivari, Knodus deuterodonoides, Knodus sp. and Poecilia reticulata) were examined during a year in the Orituco stream at northern Venezuela. The fishes were sampled monthly from February 1991 to March 1992 (except October 1991 and February 1992) in the stream main channel with a beach seine and a cast net. Diet is reported as frequency of occurrence and numeric proportion because variation in prey sizes was small. Non-parametric statistical tests were applied. A total of 18 distinct prey items were found in stomachs. The diet of these fishes consisted of aquatic insects (Coleoptera, Diptera, Hemiptera, Odonata, Plecoptera and Trichoptera), allochthonous plant matter (fragments of leaves and seeds), microalgae (Chlorophyta and Bacillariophyceae) and terrestrial arthropods (Coleoptera, Diptera, Hymenoptera and Arachnida). The low percentage of empty guts and the high fullness percentage of guts suggest that food was always abundant. Aquatic insects were more important in the dry season (November-April) while plant matter and terrestrial arthropods increased in the wet season (May-October). The Proportional Similarity Measure (PS) was high between characid species and low between characids and P. reticulata in the dry season. PS decreased during the wet season because of a reduction in aquatic insect consumption. The seasonal diet shift indicated the greater importance of allochthonous food only in the wet season.     

Ranging behaviour and habitat preference of a wild marmoset group, Callithrix humeralifer (Callitrichidae, Primates)

The ranging behaviour of a group of marmosets ( Callithrix humeralifer ) in seasonal Amazonian rain forest was studied during one year. Range sizes (monthly and daily), day range lengths and patterns of range use are examined for correlations with feeding behaviour and the distribution of three forest types within the marmoset's range. Seasonal differences in ranging are associated with changes in the abundance and distribution of plant food sources. The marmosets ranged more widely and used more sources of a greater diversity of plant food species, which were distributed over a wider area, in the wet season than in the dry season. In the dry season, they ranged over a smaller area and, although they used fewer sources of a reduced diversity of plant species overall, they exploited a larger number of sources of the five highest ranked plant species in the diet. Throughout the year, they showed a preference for disturbed primary forest, characterized by dense understoreys and abundant second growth patches. Reasons for this preference are discussed, taking into account their use of fruits of typical pioneer species (particularly in the dry season), insect prey abundance, sleeping site availability and defence against predators.     

Feeding habits and seasonal trophic guilds structuring fish community in the bay mouth region of a tropical estuarine habitat

Understanding trophic relationships of fish in estuarine ecosystem is an important element for sustainable resource management. This study examined the feeding habits of 29 dominant fish species, characterized the trophic guilds, assessed the impact of season and clarified the role of diets in structuring the fish community in the mouth region of Pattani Bay, Thailand. Samples of 5792 fishes collected monthly by gillnets from March 2019 to February 2020 were used for stomach content analyses. It was found that the number of food types and fullness index differed between fish taxa (P < 0.001). Most fishes were specialist feeders feeding on specific food components and were categorized into five trophic guilds: piscivore, shrimp-fish feeder, polychaete feeder, zooplanktivore and planktivore. Six species were piscivorous, considered as apex predators, that fed almost entirely on fishes. High diet overlaps among some species (>0.6) were recorded. Not much variation in seasonal guilds was observed: four guilds in the dry season, three in the moderate rainy season and four in the rainy season. Some species remained in the same guild the whole year round, but some fishes changed seasonally. Two fish communities from different regions of the bay were segregated based on feeding habits. The inner bay community comprised mainly copepod and plankton feeders, but there were more piscivores in the deeper bay mouth area. Results from this study help us to understand the feeding habits and trophic guilds of dominant fish species at the mouth of this tropical estuarine bay.     

Food niche overlap and ecological separation in a multi-species community of shrews in the Siberian taiga

An investigation of the feeding habits and prey availability in a community of seven species of shrew (Insectivora: Soricidae) inhabiting the taiga of Central Siberia was carried out with the aim of quantifying levels of niche overlap and elucidating modes of ecological separation amongst these coexisting species. All species took a wide range of invertebrate prey, and overlap in the numbers of shared prey taxa was high, but differences in dietary composition of certain taxa reduced overlap between most species. Small species fed almost exclusively on small arthropods, mostly Araneae, Chilopoda and Coleoptera, while medium and large-sized species took high proportions of oligochaetes. Prey were mostly taken in proportions approximately equal to their availability, although certain prey appeared to be selected. All shrews took prey in a range of sizes, and the high dietary occurrence of small invertebrates reflected their availability and high encounter rate in field samples. Dietary occurrence of small prey was negatively correlated, and large prey positively correlated, with body size of shrew. Smaller shrews were predominantly ground-surface foragers while larger species were more subterranean, with body size and dietary occurrence of soil prey being positively correlated. Differences in prey size and foraging mode reduced niche overlap between shrew species of widely differing sizes. Each shrew species did not occupy a separate, well-defined food niche. Instead, the community was sub-divided into three functional groups: large and small species which tended towards specialization with relatively low levels of overlap, and intermediate, generalist species with higher levels of overlap.     

Leaf surface specializations of birds and Arthropods in a Panamanian forest

Summary Most species of Panamanian lowland forest birds specialize on leaf undersurfaces when hunting foliage insects. The few species of leaf surface generalists and leaf upper surface specialists are omnivorous gleaners. We estimate that while over 90% of the avian understory insectivory is directed towards leaf undersurfaces, only 50% of canopy foliage insectivory is directed towards the undersides of leaves. In the low understory we found 70–80% of the arthropods on leaf undersides. The excess use of leaf-bottoms by understory birds may be a result of their greater visibility. It is hypothesized that less proficient insectivores are unable to take advantage of the greater effective density of underleaf insects because they can only efficiently attack the closest leaf surfaces; these closest surfaces will usually be the leaf tops from the branch on which the bird is perched. Alternatively, leaf-top specialists may have special foraging adaptations for overcoming the disadvantages of leaf-top foraging. These adaptations may involve attack behavior (Tachyphonus luctuosus) or searching behavior (Dacnis cayana). Dacnis often used leaf damage as a foraging cue; this may be the first report of a bird using leaf damage for searching for insects. The greater use of leaf upper surfaces by canopy birds may be influenced by four factors: greater seasonality of insects in the canopy favoring omnivores which may be less efficient insectivores; more insects on leaf tops; fewer planar leaf arrangements in canopy plants; or the greater visibility of leaf upper surfaces of the outer shell of foliage of massive trees. Based on the greater number of arthropods on leaf bottoms in the dry season, the higher abundance of smaller insects on leaf bottoms, as well as the greater proportion of insects on leaf tops at cooler higher elevations, we suggest that arthropods prefer leaf bottoms in tropical areas for physiological, not predator avoidance reasons.     

The energetic advantages of slug specialization in garter snakes (genus Thamnophis)

We tested the hypothesis that dietary specialization by foraging garter snakes is accompanied by increased assimilation efficiency on specialist prey items. Our comparison included two closely related garter snake species considered to be slug specialists (Thamnophis ordinoides and Thamnophis elegans terrestris), one fish specialist (Thamnophis couchii), and one diet generalist (Thamnophis elegans elegans). Our results suggest that slug specialists have an energetic advantage over non-slug-eating snakes when both eat slugs. Slug specialists T. ordinoides and T. e. terrestris both have higher assimilation and net assimilation efficiencies when eating slugs than do generalists T. e. elegans and T. couchii. The slug specialists did not experience decreased efficiency when eating fish. Therefore, there was no apparent digestive trade-off for the slug specialists when eating other prey.     

Influences of the season and the habitat structure on the foraging ecology of two coua species in the western dry forest of Madagascar

I studied the foraging ecology of Coquerel's Coua (Coua coquereli) and Giant Coua (Coua gigas), which occur in the dry forest in west Madagascar. This kind of forest is characterised by an alternating of a dry and a rainy season. The foraging behaviour was described in several dimensions: i.e. height and proportion of perching, rate of capture (estimating the food availability), foraging techniques, substrates used, type and size of the captured prey. Their foraging behaviour was different according to the season and to the proximity of water. Habitat structure was important to take in consideration to study their foraging behaviour. They tended to use the same pattern of techniques and substrates, but differed by the proportions they used these variables and also by the possibility to climb into the dense understorey vegetation. Seasonal variation has probably an important effect on the prey availability and the nature of prey captured. The diet of both species is also discussed. I suggest that change in habitat structure and resources levels could be important to take in consideration for the conservation of these forest birds.     

Specialization and noncompetitive resource partitioning among sponge-eating dorid nudibranchs

Summary Habitat and food resource partitioning ecologically isolate six species of Pacific Northwest dorid nudibranchs. Food resources along a gradient of sponge skeletal structure are partitioned between two exploitive guilds. The guilds are characterized by mutually exclusive predatory and digestive adaptations which allow efficient processing of sponges with poorly- or well-organized skeletons. Habitats along a depth gradient are partitioned within guilds. For a dorid species, feeding rates, extraction efficiencies and food quality are virtually identical for sponges with the appropriate extreme (either poorly- or well-organized) and intermediate skeletal organizations, but growth and reproductive rates supported by the former prey type are twice those supported by the latter prey type. Prey types with the appropriate extreme skeletal organization are thus optimal food and specialization to that food is expected. When two divergent specialist species co-occur, food resource partitioning is demonstrable but arises from self-stabilizing specializations to maximize net energy accumulation and not from competitive interactions. Habitat partitioning is viewed as arising from prey distributions and dorid physiological tolerances. This system represents an example of morphological and behavioral specializations giving rise to resource partitioning as opposed to competition giving rise to resource partitioning and subsequent morphological and behavioral specializations.     

Diet of Physalaemus cf. cicada (Leptodactylidae) and Bufo granulosus (Bufonidae) in a semideciduous forest.

We determined the diet of the two most abundant anuran species which occur in the litter of a semideciduous forest (Len?óis, Bahia, Brazil), Physalaemus cf. cicada and Bufo granulosus in the dry and rainy seasons. Pitfall traps were used to collect anuran and invertebrate fauna, which showed the availability of prey in the environment. Physalaemus cf. cicada was present in both seasons and Bufo granulosus only in the rainy season. Both species fed mainly on Isoptera and Formicidae. However, there is a difference between the rainy and dry seasons concerning the diet of P. cf. cicada. During the rainy season P. cf. cicada consumed less Isoptera and more Formicidae than in the dry season. In the volumetric sense, Orthoptera was the most important alimentary category for P. cf. cicada and B. granulosus. The Jacobs electivity index indicated that Physalaemus cf. cicada and Bufo granulosus were specialists in Isoptera.     

Seasonal and spatial variations of fish trophic guilds in a shallow,semi-enclosed tropical estuarine bay

A study on seasonal and spatial variations of feeding habits and trophic guilds of dominant fish species in Pattani Bay during March 2003 to February 2004 was aimed at classifying diet composition, identifying dominant food components of each species, categorizing trophic guilds of the community and evaluating effects of habitat characteristics and seasonality on guild organization. Most fishes showed high food intake, fed on a diverse range of food items but relied heavily on calanoid copepods and shrimps. All species, with the exception of Epinephelus coioides, were classified as specialist feeders. Four main dietary guilds were classified. Three of these were classified as the guilds dominated by at least two major food items. Significant variations in trophic guilds of 28 fish species based on habitat types and seasons were also identified. They could be divided into three seasonal groups and three site-groups and a single site. Trophic organization for each season and habitat ranged from two to four groups. This information identifies groups of fishes that seasonally and spatially utilize different food resources within a semi-enclosed estuarine bay ecosystem.     

Metabolic adaptations for isopod specialization in three species of Dysdera spiders from the Canary Islands

The spider genus Dysdera is considered to comprise specialist isopod feeders, although the degree of specialization varies between species, depending on morphological (shape of chelicerae), behavioural (attack tactics) and metabolic (food quality of prey) adaptations. Dysdera has radiated extensively in the Canary Islands (currently 47 endemic species are described) and codistributed species have different cheliceral shapes and body sizes indicating different feeding niches. In the present study, we investigate the existence of metabolic adaptations to feeding on isopods by three endemic species (Dysdera insulana Simon, Dysdera macra Simon and Dysdera verneaui Simon) from Tenerife. We hypothesize that there is enhanced extraction efficiency of fundamental macronutrients from isopods compared with control prey in species with special morphological and behavioural adaptations for this prey type. We measure quantitatively spider growth, dry mass consumption, lipid and nitrogen consumption, and calculate growth efficiency and efficiency of utilization of dry mass, lipid and nitrogen. The results show that all three species are able to utilize both prey types, indicating that none of them are strict isopod specialist. Dysdera insulana shows enhanced growth efficiency and D. macra shows enhanced nitrogen extraction efficiency compared with D. verneaui when feeding on Porcellio rather than on Musca. Both traits indicate likely adaptations for the utilization of isopods. Spider species, sex and prey type all affect lipid and nitrogen extraction efficiencies, indicating that spiders do not simply extract nutrients in the proportions available. The results support the hypothesis that adaptations for enhanced digestion of focal prey evolve in species that already have adaptations for enhanced capture success.     

Nestling diet variation in an insular Mediterranean population of blue tits Parus caeruleus: effects of years,territories and individuals

Mediterranean evergreen forests of Corsica are characterized by relatively high species diversity of arthropods with low population densities. Food is never superabundant for Corsican blue tits Parus caeruleus. This study focused on the composition of the food of blue tit nestlings and especially on two main components, caterpillars and spiders. The nestling diet was studied for two years using 8-mm cameras that automatically took photographs of adult birds with food. The diet was composed of c. 50% caterpillars and c. 30% spiders. There were between-year and between-individual differences in these proportions. In both years of the study the proportion of caterpillars declined during the course of the breeding season. Individual and time effects on prey sizes were also observed. Pairs and individuals were fairly constant in the proportions of prey over the feeding period. Different food items were not brought in runs. These findings suggest that strong food limitation exists on Corsica, which can considerably influence life-history traits of the blue tit.     

Temporal variation in diets and trophic partitioning by coexisting lizards (Ctenotus: Scincidae) in central Australia

Summary The diets of five syntopic species of Ctenotus were examined over a two-year period on a 60 ha spinifex grassland site in central Australia. The aims of the study were to test predictions that termites were an important part of the food web for syntopic Ctenotus in spinifex grasslands, and to examine seasonal changes in prey use and dietary overlap between the species. Environmental conditions during the first season of the study were dry resulting in generally low invertebrate abundance. In contrast the second season was relatively moist and overall invertebrate abundance was higher than in the first season. Diets of five species of Ctenotus contained a range of terrestrial prey although one species (C. pantherinus) was relatively termite-specialized at all times. Dietary overlap at the ordinal level between the species was generally higher during dry periods when prey abundance was low, and higher for species-pairs that were similar in body size. During the driest period of the study most species of Ctenotus ate a high proportion of termite prey which accounted for the high dietary overlap. However, each species of Ctenotus consumed different genera or foraging guilds of termites. The results suggest that most of these lizards were opportunistic in their selection of prey but that during dry periods when prey are scarce, termites may play a significant role in supporting a high -diversity of Ctenotus.     

Three carnivorous plant species (Drosera spp.) in European Russia: peaceful coexistence?

In spite of the recent improvements in the understanding of carnivorous plants’ biology, some questions have remained unanswered. In this study, the segregation of food niches (i.e. specialization on different categories of prey) for three sympatric carnivorous temperate Drosera species with different shapes of trapping leaves is tested. Potentially available prey was also taken into account, by using artificial traps. Almost all the prey trapped by the three Drosera species and by passive traps belonged to four insect orders: Diptera, Hymenoptera, Coleoptera, Homoptera, as well as Araneae. Diptera specimens were the main prey for all the species. This study demonstrates that arthropods caught by the three temperate sympatric sundew species (D. rotundifolia, D. obovata and D. anglica), belong to the same orders. The proportions of prey from different orders, caught by different sundew species did not differ significantly. The result does not necessarily imply the absence of interspecific competition for prey: arthropods were identified only to order, and competition may have resulted in specialization on prey taxa of lower rank.     

Craniodental indicators of prey size preference in the Felidae

In the present study, we used linear morphometrics of the crania, mandible and dentition to explore the association between craniodental shape and prey size among 35 species of living felids. To accomplish this, felids were divided into three prey-size groups: (1) large prey specialists; (2) small prey specialists; and (3) mixed prey feeders. From these linear measurements, large prey specialist felids can be distinguished from small and mixed prey feeders by their relatively robust canines and incisors and relatively wide muzzles. These cranial characters are advantageous when dispatching large prey, due to the stranglehold that cats employ during this activity. Robust canines resist the bending and torsional forces applied by struggling prey and a wider muzzle helps to stabilize grip and distribute bite forces more evenly during the killing bite. Small prey specialists had smaller canines, narrower muzzles and slightly longer jaws for a speed advantage when catching small, quick prey. Mixed prey feeders were intermediate between large and small prey specialists, indicating they are adapted to killing both sizes of prey. Given the success of this ecomorphological analysis of living felids that specialize on different prey sizes, we look forward to applying this same approach to extinct species.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 784–799.     

Chemical defenses shift with the seasonal vertical migration of a Panamanian poison frog

Dendrobatid poison frogs sequester lipophilic alkaloids from their arthropod prey to use as a form of chemical defense. Some dendrobatid frogs seasonally migrate between the leaf litter of the forest floor in the dry season to the canopy in the wet season, which may yield differences in prey (arthropods) and therefore alkaloid availability over space and time. Here, we document a seasonal vertical migration of Andinobates fulguritus (the yellow‐bellied poison frog) from ground to canopy between dry and wet seasons. We observed turnover in alkaloid composition between seasons and found that dry season frogs contained a lower relative quantity of alkaloids; however, there was no change in alkaloid richness between seasons. The 77 alkaloids of 13 structural classes identified in this population appear to be derived mostly from mites and ants, though the two most common alkaloids were mite derived. Our observed shifts in defensive profiles are consistent with well‐documented turnover in mite and ant communities between seasons and vertical strata. As climate change is expected to lengthen and strengthen dry seasons in many tropical regions, our results suggest that arboreal poison frogs forced to the ground for longer periods of time may see a shift in the abundance of alkaloids, possibly decreasing their defensive potential. This study provides further predictions for the wide‐reaching effects of climate change, even as nuanced as charismatic poison frogs losing their poisons. Abstract in Spanish is available with online material.     

The ecology of tool-use in the woodpecker finch (Cactospiza pallida)

Insects, mammals and birds are known to use tools, but empirical evidence of the ecological importance of tool‐use is scarce. Here, we present the first ecological study of tool‐use by a bird species. Woodpecker finches use twigs or cactus spines to pry arthropods out of tree‐holes. We compared tool‐use during wet and dry seasons in two different vegetation zones: the Arid Zone and the humid Scalesia Zone. In the Scalesia Zone, where food was abundant and easily accessible, woodpecker finches rarely used tools. In contrast, in the Arid Zone, where food was limited and hard to access, they obtained half of their prey using tools during the dry season. Tool‐use enabled the birds to reach particularly large and otherwise inaccessible prey hidden in tree‐holes. Our data suggest that tool‐use in the woodpecker finch has evolved in response to the dry and unpredictable conditions in the coastal zone of the Galápagos Islands.