Optimal foraging by bacteriophages through host avoidance

Optimal foraging theory explains diet restriction as an adaptation to best utilize an array of foods differing in quality, the poorest items not worth the lost opportunity of finding better ones. Although optimal foraging has traditionally been applied to animal behavior, the model is easily applied to viral host range, which is genetically determined. The usual perspective for bacteriophages (bacterial viruses) is that expanding host range is always advantageous if fitness on former hosts is not compromised. However, foraging theory identifies conditions favoring avoidance of poor hosts even if larger host ranges have no intrinsic costs. Bacteriophage T7 rapidly evolved to discriminate among different Escherichia coli strains when one host strain was engineered to kill infecting phages but the other remained productive. After modifying bacteria to yield more subtle fitness effects on T7, we tested qualitative predictions of optimal foraging theory by competing broad and narrow host range phages against each other. Consistent with the foraging model, diet restriction was favored when good hosts were common or there was a large difference in host quality. Contrary to the model, the direction of selection was affected by the density of poor hosts because being able to discriminate was costly.     

Foraging efficiency of juvenile bluegill, Lepomis macrochirus, among different vegetated habitats

Optimal foraging theory is devoted to understanding how organisms maximize net energy gain. However, both the theory and empirical studies lack critical components, such as effects of environmental variables across habitats. We addressed the hypothesis that energetic returns of juvenile bluegill are affected by environmental variables characteristic of the vegetated habitats. Predicted optimal diet breadths were calculated and compared to prey items eaten by juvenile bluegill to determine if bluegill were foraging to maximize energetic gain. Differences in habitat profitability among vegetated sites were determined by comparing predictions of maximized energetic return rates (cals^-1) with prey contents of bluegill stomachs. Sizes of most prey items eaten by juvenile bluegill throughout the vegetated sites were smaller than the predicted optimal diet breadths. However, inclusion of smaller prey items in the diet did not seem to affect rate of energetic gain. Energetic return rates were maximized at the 1.5 and 2mm prey size classes and declined only slightly with inclusion of smaller prey sizes. Predicted energetic return rates and average mass in bluegill stomachs were related negatively. Average mass in bluegill stomachs also was associated negatively with Elodea canadensis stem densities and percent of light transfer, suggesting that foraging efficiency of bluegill decreased as plant density and percent of light increased. Results of our research indicate that maximization of energetic return rates is dependent upon availability of prey sizes that contribute to optimal foraging. Thus, determination of those habitats that provide the highest availability of benthic invertebrate prey with the least interference by stems is critical. Enhanced foraging capabilities can promote recruitment, faster growth, better body condition and survival.     

Foraging Ecology of Fall-Migrating Shorebirds in the Illinois River Valley

Populations of many shorebird species appear to be declining in North America, and food resources at stopover habitats may limit migratory bird populations. We investigated body condition of, and foraging habitat and diet selection by 4 species of shorebirds in the central Illinois River valley during fall migrations 2007 and 2008 (Killdeer [Charadrius vociferus], Least Sandpiper [Calidris minutilla], Pectoral Sandpiper [Calidris melanotos], and Lesser Yellowlegs [Tringa flavipes]). All species except Killdeer were in good to excellent condition, based on size-corrected body mass and fat scores. Shorebird diets were dominated by invertebrate taxa from Orders Diptera and Coleoptera. Additionally, Isopoda, Hemiptera, Hirudinea, Nematoda, and Cyprinodontiformes contribution to diets varied by shorebird species and year. We evaluated diet and foraging habitat selection by comparing aggregate percent dry mass of food items in shorebird diets and core samples from foraging substrates. Invertebrate abundances at shorebird collection sites and random sites were generally similar, indicating that birds did not select foraging patches within wetlands based on invertebrate abundance. Conversely, we found considerable evidence for selection of some diet items within particular foraging sites, and consistent avoidance of Oligochaeta. We suspect the diet selectivity we observed was a function of overall invertebrate biomass (51.2±4.4 [SE] kg/ha; dry mass) at our study sites, which was greater than estimates reported in most other food selection studies. Diet selectivity in shorebirds may follow tenants of optimal foraging theory; that is, at low food abundances shorebirds forage opportunistically, with the likelihood of selectivity increasing as food availability increases. Nonetheless, relationships between the abundance, availability, and consumption of Oligochaetes for and by waterbirds should be the focus of future research, because estimates of foraging carrying capacity would need to be revised downward if Oligochaetes are truly avoided or unavailable for consumption.     

Influence of predation risk on diet selection: a simple example in the grey squirrel

Current models of the optimal diet are special cases of a more general (and complex) model which incorporates the effects of predation risk on diet selection; this follows from an assumption implicit in current models that all prey items are eaten where they are encountered. Relaxing this assumption so that a forager might carry a prey item to protective cover for consumption leads to the conclusion that the value of a prey item is a function of its distance to cover as well as its energy content and handling time. Such considerations can significantly alter the outcome of diet selection relative to that expected from simple diet theory. We found that grey squirrels (Sciurus carolinensis) may reject more energetically profitable, but small food items in favour of locating larger, less energetically profitable items that can be carried to protective cover for consumption without greatly sacrificing foraging efficiency. The squirrel's tendency to reject a more profitable item is a function of its distance from cover and the size of the less profitable items. Such behaviour is inconsistent with predictions of current diet models, but is consistent with our qualitative predictions based on a previously determined predation-risk-foraging-efficiency trade-off in the grey squirrel.     

Neophobia affects choice of food-item size in group-foraging common ravens (Corvus corax)

Individuals foraging in groups should develop behavioural tactics to optimise their gain. In novel feeding situations, predation risk and pressure of kleptoparasites may be particularly high and hence may constrain optimal foraging. To create a novel feeding situation, we offered common ravens (Corvus corax) equal numbers of either small (40 g) or large (160 g) pieces of meat on successive days, always in combination with the same novel object. During the first weeks, when ravens were still neophobic, small pieces were taken in larger numbers than large pieces. Intraspecific kleptoparasitism was more likely to occur when ravens carried large food items. It seems that initiating foragers were mainly innovative subdominants. Preference for small items might have decreased with increasing habituation because more dominants were then feeding directly at the source and hence were less likely to resort to kleptoparasitism as an alternative foraging tactic. Electronic Publication     

Between-lake differences in the diet and provisioning behaviour of Black-throated Divers Gavia arctica breeding in Scotland

Surveys at 23 Black-throated Diver breeding lakes in Scotland showed large between-lake differences in the species and size range of potential prey. The study lakes were classified into four types according to the main size-taxa prey classes present. Type 1 lakes lacked small fish, Type 4 lacked salmonids < 300 mm and Types 2 and 3 both had all four of the main prey classes. Diver diet for 30 families at the study lakes was quantified from 7943 prey items seen fed to chicks, and 153 items seen eaten by adults, during 662 h of observations. At all lake types adults mostly ate salmonids of 120–240 mm in length, especially Brown Trout Salmo trutta , and European Eels Anguilla anguilla up to c.  350 mm. The prey eaten by chicks ranged widely, from c.  0.03 g to 300 g, with important implications for feeding behaviour. Young chicks (days 1–8) rejected items greater than 70 mm long. The diet of young chicks consisted mostly of small fish, either Three-spined Sticklebacks Gasterosteus aculeatus (Type 2 lakes) or Minnow Phoxinus phoxinus (Type 3 and Type 4 lakes). At other lakes (Type 1) it consisted mostly of mayfly larvae (Ephemeroptera); invertebrates were the only abundant potential small prey in these lakes. At all lakes the chick diet became more similar to that of adults as chicks grew. Adults provisioning chicks used two foraging strategies. In 'excursion foraging', adults hunted away from the chicks and carried prey back for them; in 'attendance foraging', the chicks accompanied the foraging adult(s). Excursion foraging was used mostly before day 4 and was strongly and positively correlated with the abundance of fish < 80 mm in length. This behaviour is probably adaptive, but is probably tenable only where small fish are relatively abundant. Young chicks fed mainly on small fish had higher survival rates than those fed on invertebrates.     

Prey choice by marten during a decline in prey abundance

Summary We examined variation in diet choice by marten (Martes americana) among seasons and between sexes and ages from 1980–1985. During this period prey populations crashed simultaneously, except for ruffed grouse (Bonasa umbellus) which was common at the beginning and end of the study, and masked shrews (Sorex cinereus) which were abundant in 1983. Marten were catholic in selection of prey and made use of most available mammalian prey, ruffed grouse, passerine birds, berries, and insects. Diet niche was widest during the latter three years when prey was scare, particularly in late winter. Diet niche breadth was negatively correlated with abundance of all common prey species. Proportion of small prey species in the diet was correlated with absolute abundance of those species, but proportion of some large prey was related to their relative abundance. Diet choice varied among years and among seasons. Berries and insects were common in summer diets while large prey, particularly varying hare (Lepus americanus), were more frequent in winter diet than in summer diet. We found little evidence that any small mammal species was a preferred prey. Sexual size dimorphism between the sexes did not affect prey choice, nor did age. Reduced foraging effort in winter resulted in a wider diet niche only when prey was scarce. The only prediction of optimal foraging models fully supported by our data was a wider diet niche with reduced prey abundance. However, among the three most profitable prey species choice was dependent on the absolute abundance of the most profitable type (varying hare). We suggest that marten primarily forage for large prey but employ a strategy which results in encounters with small prey as well. These small prey are eaten as they provide energy at minimal cost, between captures of large prey.     

What you need is what you eat? Prey selection by the bat Myotis daubentonii

Optimal foraging theory predicts that predators are selective when faced with abundant prey, but become less picky when prey gets sparse. Insectivorous bats in temperate regions are faced with the challenge of building up fat reserves vital for hibernation during a period of decreasing arthropod abundances. According to optimal foraging theory, prehibernating bats should adopt a less selective feeding behaviour – yet empirical studies have revealed many apparently generalized species to be composed of specialist individuals. Targeting the diet of the bat Myotis daubentonii, we used a combination of molecular techniques to test for seasonal changes in prey selectivity and individual‐level variation in prey preferences. DNA metabarcoding was used to characterize both the prey contents of bat droppings and the insect community available as prey. To test for dietary differences among M. daubentonii individuals, we used ten microsatellite loci to assign droppings to individual bats. The comparison between consumed and available prey revealed a preference for certain prey items regardless of availability. Nonbiting midges (Chironomidae) remained the most highly consumed prey at all times, despite a significant increase in the availability of black flies (Simuliidae) towards the end of the season. The bats sampled showed no evidence of individual specialization in dietary preferences. Overall, our approach offers little support for optimal foraging theory. Thus, it shows how novel combinations of genetic markers can be used to test general theory, targeting patterns at both the level of prey communities and individual predators.     

To minimize foraging time,use high‐efficiency,energy‐expensive search and capture methods when food is abundant but low‐efficiency,low‐cost methods during food shortages

Based on a mathematical model, I show that the amount of food in the habitat determines which among alternative methods for search of prey, respectively, for pursuit‐and‐capture give the shortest daily foraging time. The higher the locomotor activity, the higher the rate of energy expenditure and the larger the habitat space a predator can search for prey per time unit. Therefore, I assume that the more efficient a foraging method is, the higher its rate of energy expenditure. Survival selection favors individuals that use foraging methods that cover their energy needs in the shortest possible time. Therefore, I take the optimization criterion to be minimization of the daily foraging time or, equivalently, maximization of the rate of net energy gain. When time is limiting and food is in short supply, as during food bottleneck periods, low‐efficiency, low‐cost foraging methods give shorter daily foraging times than high‐efficiency, energy‐expensive foraging methods. When time is limiting, food is abundant and energy needs are large, as during reproduction, high‐efficiency high‐cost foraging methods give shorter daily foraging times than low‐efficiency low‐cost foraging methods. When time is not limiting, food is abundant, and energy needs are small, the choice of foraging method is not critical. Small animals have lower rates of energy expenditure for locomotion than large animals. At a given food density and with similar diet, small animals are therefore more likely than large ones to minimize foraging time by using high‐efficiency energy‐expansive foraging methods and to exploit patches and sites that require energy‐demanding locomotion modes. Survival selection takes place at food shortages, while low‐efficiency low‐cost foraging methods are used, whereas reproduction selection occurs when food is abundant and high‐efficiency energy‐expensive foraging methods do better. In seasonal environments, selection therefore acts on different foraging methods at different times. Morphological adaptation to one method may oppose adaptation to another. Such conflicts select against foraging and morphological specialization and tend to give species‐poor communities of year‐round resident generalists. But a stable year‐round food supply favors specialization, niche narrowing, and dense species packing.     

Omnivory of an Insular Lizard: Sources of Variation in the Diet of Podarcis lilfordi (Squamata,Lacertidae)

Through 17 years and from a sample of 7,790 faecal pellets and 26,346 prey items, we studied the diet of the Balearic lizard Podarcis lilfordi in Aire Island (Menorca, Balearic Islands, Spain). We analysed the diet in terms of prey frequencies, as well as by their volume and biomass contributions. The diet of the Balearic lizard was extremely variable through the years, months and areas under study. The dominance of small clumped prey, particularly ants, was confirmed. However, the main contribution by volume corresponded to beetles, with a relevant role for Diplopoda and terrestrial Isopoda during some months and at particular areas of the island. Several prey items were probably captured at the base of shrubs, under stones or inside rock crevices. Therefore, our estimations of electivity would only be reliable for epigeal and flying prey. The capacity of the Balearic lizard to include marine subsidies in its diet, such as coastal crustaceans, is noteworthy. Also, its consumption of carrion from carcasses of gulls and rabbits and leftovers from human visitors is remarkable. Juvenile conspecifics can also be a sporadic food resource, especially during the second half of summer, whereas the consumption of vegetal matter is constant for each whole year. The shifts of vegetal exploitation among areas of the island and months take place according to availability of different plant species at each area or during a given period. Thus, lizards are able to conduct a thorough monitoring of plant phenology, exploiting a large variety of plant species. Omnivory does not imply the indiscriminate inclusion of any edible food in its diet. Rather, the inclusion of several food items means the adoption of a wide range of foraging behaviours adapted to the exploitation of each food resource.     

Feeding ecology and its influence on social organization in Brown hyenas (Hyaena brunnea, Thunberg) of the Central Kalahari Desert

(1) Observations are presented on the diet, feeding habits, hunting and foraging behaviour of Brown hyaenas of the Central Kalahari. (2) The remains of kills left by other predators are the single most important food item in the Brown hyaena's diet. The diet also consists of small scavenged items, small prey such as rodents which the hyaena itself kills, and wild fruits. (3) Brown hyaenas hunt and scavenge small items solitarily, but congregate for communal scavenging of the large kills left by other predators. (4) Individual hyaenas are not territorial and there is great overlap in home ranges. They use common pathways and frequently meet to socialize while foraging. (5) Resident adults form a group with a social hierarchy maintained through neck-biting, muzzle-wrestling, chasing, and other social interactions. Subadult hyaenas often leave the group when approximately 22 months old. (6) Brown hyaenas have a complex system of communication including visual displays, social interactions, vocalizations, and extensive pasting. These are described. (7) Since carrion is an important source of food, Brown hyaenas have developed distinct relationships with other predators and these are described. (8) In conclusion, the Brown hyaena exhibits a highly flexible social system, foraging and hunting small items solitarily and congregating for the common utilization of a large carcass. The social organization is therefore influenced by the feeding ecology.     

Optimal foraging strategies in the diet of the green monkey,Cercopithecus sabaeus,at Mt. Assirik,Senegal

The feeding behavior of one group of green monkeys (Cercopithecus sabaeus)was observed between October 1978 and December 1979 in the Parc National du Niokolo-Koba, Senegal. Details of the vegetational composition of the habitat and seasonal variation in food availability were also recorded. The green monkeys’ diet was omnivorous and diverse, including over 65 species of plants, many invertebrates, and some eggs and meat. Preference was given to fruits and flowers, although particular species were not selected; rather, these foods were eaten in proportion to their availability. Leaves, gum, seeds, and fungi were secondarily preferred foods, their consumption depending mostly on the availability of fruit or flowers. There was little overlap in the composition of the diet from month to month, reflecting the strong seasonality of the environment, although there was a consistent intake of invertebrates each month. Differences in diet between populations of the superspecies C. aethiopsare related to the floristic composition of the vegetation. Data on seasonal variation in the diet and changing patterns of resource availability are drawn together within the framework of optimal foraging theory to examine the adaptive strategies underlying the monkeys’ behavior. Their choice of diet was optimal in that they were more selective when profitable food items were common: higher proportions of the diet were given over to fruit and flowers when food availability was high. In parallel with this strategy, a nutritive balance was maintained by consistent inclusion of invertebrates and at least some foliage in the diet, regardless of the amount of fruit or flowers available.     

Evolutionary stability of optimal foraging: Partial preferences in the diet and patch models

In this article the patch and diet choice models of the optimal foraging theory are reanalyzed with respect to evolutionary stability of the optimal foraging strategies. In their original setting these fundamental models consider a single consumer only and the resulting fitness functions are both frequency and density independent. Such fitness functions do not allow us to apply the classical game theoretical methods to study an evolutionary stability of optimal foraging strategies for competing animals. In this article frequency and density dependent fitness functions of optimal foraging are derived by separation of time scales in an underlying population dynamical model and corresponding evolutionarily stable strategies are calculated. Contrary to the classical foraging models the results of the present article predict that partial preferences occur in optimal foraging strategies as a consequence of the ecological feedback of consumer preferences on consumer fitness. In the case of the patch occupation model these partial preferences correspond to the ideal free distribution concept while in the case of the diet choice model they correspond to the partial inclusion of the less profitable prey type in predators diet.     

Selective foraging on woody plant species by the Eurasian beaver (Castor fiber) in Telemark, Norway

Beavers Castor spp. are generalist herbivores, feeding on the bark, shoots and leaves of woody plants, terrestrial herbs and forbs, ferns and aquatic vegetation. As central-place foragers, beavers move out from water to select and cut trees and vegetation, and then transport it back to their refuge. These terrestrial forays are energetically costly; therefore, beavers should concentrate their foraging activity near the central place and increase the degree of selectivity for specific sizes or species of food with increasing distance from the water. The aim of this study was to test the predictions of the central place and the optimal foraging theories for the food selection of the Eurasian beaver Castor fiber , and show the foraging preferences of the focal species in the boreal conifer forest zone of Europe. Foraging intensity by beavers and the abundance of woody species were surveyed in transects positioned randomly at seven beaver territories. In compliance with the central-place foraging theory, the foraging intensity declined with increasing distance from the river. Beavers fed preferentially on willows ( Salix ), rowan ( Sorbus ) and birches ( Betula ), although alders ( Alnus ) dominated their diet. Size selectivity showed similar patterns to previous North American studies, which were also carried out in habitats with predominantly small saplings. The probability of selection of small saplings dropped as distance increased, which is consistent with the predictions of optimal foraging models that larger prey items are more likely to be favoured with increasing provisioning distance.     

Diet of stoats (Mustela erminea) in an Alpine habitat:The importance of fruit consumption in summer

The diet of stoat, Mustela erminea, in the Italian Alps was studied from May to October 1996 and 1997 through faecal analysis. Scats were collected along twenty transects and near dens within a 10-km² study area. In the same area, seasonal variation in the available biomass of different prey types was estimated using capture-mark-recapture (small rodents), pitfall trap grids (insects), and fruit counts. About 60 % of scats (n = 734) contained small rodents, indicating that they were the main prey for stoat. However, the frequency of occurrence of fruits in the diet increased significantly in August, after rodent biomass had dropped by more than 50 % in July, but increased again to previous August levels. Fruit consumption decreased in September and October, although available biomass of fruits remained constant. Thus stoat included a large amount of alternative food in their diet when fruits were mature and their availability, and probably their profitability, increased. We were, however, unable to measure absolute consumption of prey. We conclude that primary prey, rodents, is always harvested, suggesting that the costs of harvesting rodents, abundant throughout spring–autumn, are never high. The consumption of alternative prey is independent of its availability, and increases only when relative benefits of harvesting alternative prey (fruits) increases, which is consistent with optimal foraging theory.     

Patterns in foraging and nesting ecology in the neotropical ant, <Emphasis Type="Italic">Gnamptogenys moelleri</Emphasis> (Formicidae,Ponerinae)

Summary This study provides quantitative field data on the natural history and foraging behaviour of the Neotropical bromeliad-nesting ant Gnamptogenys moelleri (Ponerinae) in a sandy plain forest in Southeast Brazil. The ant nested on different bromeliad species and the nests were more frequently found in bigger bromeliads. The species used a wide array of invertebrates in its diet, hunting for live prey and scavenging the majority of the items from dead animals. The food items varied greatly in size (1 to 26 mm). Hunting was always performed by solitary workers. Retrieving was performed by solitary workers (small items), or by a group of 3 to 12 workers recruited to the food source (large items). Almost all G. moelleri foraging activity was restricted to the nest bromeliad. In the warm period more ants left the nest to forage, and foraging trips achieved greater distances compared to the cool season. Trap data revealed that overall availability of arthropod prey is higher in the summer than in the winter. The opportunism in nest site use and in foraging behaviour, the small foraging area, as well as the seasonal differences in foraging activity are discussed and compared with other tropical ants.Received 30 May 2003; revised 22 September 2003; accepted 3 October 2003.     

Coexistence and community structure in a consumer resource model with implicit stoichiometry

We combine stoichiometry theory and optimal foraging theory into the MacArthur consumer-resource model. This generates predictions for diet choice, coexistence, and community structure of heterotroph communities. Tradeoffs in consumer resource-garnering traits influence community outcomes. With scarce resources, consumers forage opportunistically for complementary resources and may coexist via tradeoffs in resource encounter rates. In contrast to single currency models, stoichiometry permits multiple equilibria. These alternative stable states occur when tradeoffs in resource encounter rates are stronger than tradeoffs in elemental conversion efficiencies. With abundant resources consumers exhibit partially selective diets for essential resources and may coexist via tradeoffs in elemental conversion efficiencies. These results differ from single currency models, where adaptive diet selection is either opportunistic or selective. Interestingly, communities composed of efficient consumers share many of the same properties as communities based on substitutable resources. However, communities composed of relatively inefficient consumers behave similarly to plant communities as characterized by Tilman’s consumer resource theory. The results of our model indicate that the effects of stoichiometry theory on community ecology are dependent upon both consumer foraging behavior and the nature of resource garnering tradeoffs.     

Niche expansion, body size, and survival in Galápagos marine iguanas

Foraging theory predicts that dietary niche breadth should expand as resource availability decreases. However, Galápagos marine iguanas often die during algae shortages (El Niños) although land plants abound where they rest and reproduce. On Seymour Norte island, a subpopulation of iguanas exhibited unique foraging behavior: they consistently included the succulent beach plant B. maritima in their diet. We investigated the consequences of land-plant feeding for body size and survival. Batis-eaters supplemented their algae diet both before and after intertidal zone foraging, and more Batis was eaten during tides unfavorable for intertidal zone foraging (dawn and dusk). Larger, energy-constrained iguanas fed more on land than did smaller animals. Compared to intertidal zone algae, Batis was 39% lower in caloric content (1.6 vs. 2.6 kcal g^–1 dry mass), 56% lower in protein (8.3 vs. 18.9% dry mass) and 57% lower in nitrogen (1.3 vs. 3.0% dry mass). In spite of its lower nutrient value, iguanas that supplemented their diet with this plant were able to attain nearly twice the body size of other iguanas on the island. Age estimates indicate that many Batis-eaters survived repeated El Niño episodes during which animals of their relative size-class experienced high mortality on other islands. The larger animals were, however, completely dependent upon this supplementary source of food to maintain condition, and all perished in the 1997–1998 El Niño when high tides inundated and killed Batis on Seymour Norte Island. We hypothesize that Batis feeding developed as a local foraging tradition, and that dietary conservatism and strong foraging site fidelity explain why the inclusion of land plants in the diet has been observed in only a single population. Ultimately, a unique algae-adapted hindgut morphology and physiology may limit a switch from marine to terrestrial diet.     

Flexibility in the food selection by the European hare (<Emphasis Type="Italic">Lepus europaeus</Emphasis>) along the altitudinal gradient of the Southern Andean Precordillera (Argentina)

Predictions derived from the optimal foraging theory are interesting to test on wild herbivores living in mountain environments, considering the expected vegetation changes across altitudinal gradients. A lower food richness and a more generalist diet are expected as altitude increases, with higher diet diversity and a shift to browsing as food availability decreases seasonally. With broad diets and ecological adaptability, Lepus europaeus is a non-native herbivore inhabiting Andean altitudinal gradients. Diet and vegetation were analyzed using microhistological analysis and point-quadrat transects at six sampling sites, representative of altitudinal phytogeographic belts. The diet included 67 of the 109 species present in the vegetation. Lepus europaeus proved to be an intermediate feeder with a generalist and selective diet. Following the prediction for altitudinal gradients, dietary generalism increased as plant cover and diversity decreased with altitude. Differences in plant phenology and toxins justified changes in food preferences, from shrubs at the summit to grasses at lower altitudes. Seasonal changes in diet diversity were consistent with different hypotheses depending on altitude. The tundra climate at the summit determined a strong phenological decline and food scarcity during winter, when the less diverse diet was more focused on a preferred shrub, following the selective quality hypothesis. With a milder climate at lower altitudes, the winter increase in diet diversity, with inclusion of avoided shrubs, agrees with the food abundance hypothesis. Climate severity, food shortage, plant phenology, and secondary compounds are relevant for explaining the feeding strategy of European hares in these mountain environments.     

Diet of some species of Neotropical small mammals

Dietary analysis was performed to determine the variations in diet of some small neotropical species of mammals collected in seasonal areas of the cerrado (a savannah-like grassland) and semi-deciduous forest. Food items were determined based on the analysis of stomach contents of 126 animals (one didelphid and five sigmodontine rodent species). Most species presented herbivorous-omnivorous habits, with a preference for the vegetative parts of plants. Akodon montensis Thomas (1913) was the most abundant species in the forest area and demonstrated a uniform consumption of animal and vegetal items through the year, and contained 65.7% plant material in its diet. Necromys lasiurus (Lund, 1841) was the most abundant in the cerrado with 72.6% of vegetation in its diet, but showed a high consumption of animal items during the rainy season. Oligoryzomys nigripes (Olfers, 1818) contained 95.1% of plant material, while Oxymycterus delator (Thomas, 1903) consumed 61.6% invertebrates, mainly insects. The didelphid Philander frenatus (Olfers, 1818) consumed invertebrates (47.7%), small vertebrates (7.3%) and plant material (44.9%).