Food Niche Breadth Research Articles

Role of Body Size in the Diets of Sympatric Gray and Culpeo Foxes

Feeding ecology of sympatric South American gray fox ( Dusicyon griseus ) and culpeo fox ( D. culpaeus ) was studied from 1987 to 1990 in Torres del Paine National Park, Chile, to determine if these canids have different patterns of prey selection. Seasonal and species differences in use of prey were compared with availability of prey to determine prey selection by these foxes. Mammals accounted for 90% of 851 items of vertebrate prey occurring in 890 feces of gray foxes. The European hare ( Lepus capensis ) was the most common vertebrate prey (45%), with lesser amounts of the guanaco ( Lama guanicoe ; 14%) and Akodon (13%). Of 784 items of vertebrate prey in 645 feces of culpeo foxes, 93% were mammalian. The European hare accounted for 69% of the prey items, and rodents 20%. The proportion of vertebrate prey items consumed by gray and culpeo foxes changed seasonally. Yearly diets of gray and culpeo foxes were significantly different, with ungulates and the European hare contributing most to the difference. Gray foxes were more omnivorous than culpeo foxes, feeding more on beetles and plants, especially from spring through autumn. Gray foxes had a significantly higher ( X ± SE) index of food-niche breadth for vertebrates than did culpeo foxes (0.24 ± 0.01 versus 0.09 ± 0.01) and consumed vertebrate prey of a significantly lower mass (2.17 ± 0.07 versus 2.59 ± 0.09 kg). The index of similarity between the diets of the two species was low (0.14). Differences in feeding habits between gray and culpeo foxes evidently are attributable to differences in food availability in their respective habitats.

Resource partitioning in a Mediterranean lizard community

Abstract Some aspects of community ecology in a lizard assemblage composed of three sympatric and diurnal species (Algyroides fitzingeri, Podarcis tiliguerta, Chalcides ocellatus) were studied in a Mediterranean habitat of central Sardinia. The three lizards were characterized by significantly different mean body size. There was no spatial overlap between the smallest species (A. fitzingeri) and the largest one (C. ocellatus), while there was a certain amount of overlap between P. tiliguerta and each of the other two lizards. The three species preyed on a wide variety of invertebrates, but mainly on insects. Food niche breadth was higher in P. tiliguerta, and this could be related to the higher microhabitat heterogeneity of this lizard in the study area. Food niche overlap was high between Chalcides ocellatus and Podarcis tiliguerta, but low between Algyroides fitzingeri and C. ocellatus. Although further data are required before any firm conclusion can be drawn, the results of this investigation seem to indicate that (i) interspecific competition among the three lizards is rather limited, due both to food and spatial resource partitioning, and (ii) the lizard community is organized through the ecological needs of each species.

Community Trophic Structure: The Roles of Diet, Body Size, and Activity Time in Vertebrate Predators

We examined trophic structure in an assemblage of 17 vertebrate predators - two snakes (Pituophis catenifer and Crotalus viridis), six hawks (Circus cyaneus, Buteo jamaicensis, B. regalis, Aquila chrysaetos, Falco sparverius, and F. mexicanus), six owls (Tyto alba, Otus kennicottii, Bubo virginianus, Speotyto cunicularia, Asio otus, and Aegolius acadicus), one passerine (Corvus corax), and two mammals (Canis latrans and Taxidea taxus). These predators fed collectively on prey in nine taxonomic classes. Mammalian prey were numerically most important in 15 diets and contributed the most biomass to all 17 diets. Mean prey mass ranged from 2.2 to 711 g, and correlated with predator mass. No significant differences were apparent in food-niche breadth or mean prey mass between diurnal and nocturnal predators, but dietary overlap among predators with the same diel activity was significantly greater than that among asynchronously-active predators. Mean diet overlap was significantly greater among nocturnal predators than among diurnal predators. Four feeding guilds were defined by dietary similarity. A ground squirrel-eating guild contained one snake, three hawks, and a mammal. A jackrabbit-eating guild consisted of a hawk and a mammal. An arthropod/mammal-eating guild was composed of an owl and the raven. Four owls, one hawk, and one snake formed a small-rodent guild. One owl and one hawk were not members of guilds. Mass ratios of adjacent-sized predators were greatest within guilds.

Comparative ecology in sympatricPodarcis muralisandP. sicula(Reptilia: Lacertidae) from the historical centre of Rome: What about competition and niche segregation in an urban habitat?

Abstract Some aspects of comparative ecology in two sympatric Podarcis species, P. muralis and P. sicula, were studied in an urban park of Rome. Both species preyed on a wide variety of invertebrates, but mainly on insects. Food niche breadth was wider in P. muralis, and this is possibly related to the higher microhabitat heterogeneity of the species in the study area. Food niche overlap was relatively high. Activity patterns (annual cycle, daily activity) were rather similar in the two lacertid lizards. Fecundity did not differ significantly between species, female snout‐vent length and clutch size being positively correlated. At least two clutches per year were detected in each species. In each of the two study sites chosen in the urban park the density of both species did not vary significantly amongst years. Podarcis muralis appeared to be the only species inhabiting humid places with dense vegetation, while P. sicula was numerically more abundant than P. muralis in sunny and dry spots. Although concl...

Diet of the House Sparrow in an Intensively Cultivated Area

Diet of adult House Sparrows Passer domestics was studied by gravimetric analysis of gut contents during August 1988 to July 1989 at Ludhiana, India. Cereals dominated the food forming 83.6% of total diet. Weed seeds and animal matter constituted only 6.2 and 4.3%, respectively. Shannon-Wiener index and Levins' index of food-niche breadth were calculated to be 0.75 and 3.90, respectively. Relative percentage by weight of different food types was significantly positively correlated with their occurrence in the guts (r=0.67, n=16, P<0.005). Pearl millet was the most abundant food type during August through November, whereas wheat dominanted the diet during January through April and July. Rice and maize were recorded in the guts in three months each. Weed seeds were eaten by sparrows throughout the year except in September, January and February. Egg-shell pieces were recorded throughout the year (except June) but insects were found only in three months (June, August and December). Grit was recorded in all months constituting 4 to 43% of total gut contents (annual average 21%). The diet of sparrows was comparatively more diverse during March-June, August and November than during rest of the year as revealed by fluctuations in two indices of food-niche breadth.

Biogeographic variation of food habits and body size of the America puma.

The puma (Felis concolor) has the most extensive range of any terrestrial mammal in the Western Hemisphere, covering over 100° latitude. Food habits of different puma subspecies vary with latitude. Subspecies from temperate habitats generally eat larger prey and specialize on a smaller number of prey taxa, whereas, in tropical habitats, they prey on smaller, more varied prey. In North America, ungulates (primarily deer) represented 68% of the puma's diet by frequency of occurrence. Mean weight of vertebrate prey (MWVP) was positively correlated (r=0.875) with puma body weight and inversely correlated (r=-0.836) with food niche breadth in all America. In general, MWVP was lower in areas closer to the Equator. Patterns of puma prey selection are probably influenced by prey availability and vulnerability, habitat characteristics, and potential competition from the jaguar (Panthera onca).

The realized food niches of three species of stream‐dwelling triclads (Turbellaria)

SUMMARY. 1. The diet of Phagocata vitta, Crenobia alpina and Polycelis felina in a Welsh stream was examined, using a serologicat technique, at monthly intervals over 18 months.2. For each triclad species, dietary composition changed little with time or increasing body size, and overall feeding intensity was greatest in summer and least in winter.3. Alt species fed most heavily on oligochaetes, chironomids and Gammarus. Phagocata vitta fed lightly on Plecoptera, Trichoptera and Ephemeroptera whilst the other two triclad species fed substantially on the first two of these prey categories.4. Food niche breadth indices indicated a wide diet for all species with some specialization in some months. Electivity indices showed positive electivity for oligochaetes and chironomids by all species and for Plecoptera by C. alpina and P. felina.5. Diets overlapped and none had a food refuge: therefore the potential for interspecific competition for food exists.

Analysis of the niche of two sympatric species of Bombus (Hymenoptera, Apidae) in southeastern Brazil

ABSTRACTThe sources of food and the width and overlap of the food niches of Bombus atratus and Bombus morio were determined by field observations and analysis of the pollen loads carried to the colonies by worker bees. The two species together utilized 50 flower species of which 26 were used by both. Solatium paniculatum (Solanaceae) and Psidium guajava (Myrtaceae) were the most frequently visited plants.The food niche width and niche evenness for both species were similar. The correlation between niche width and niche evenness was non-significant showing that evenness does not depend on niche width. In addition, there was no correlation between niche width and overlap, i.e. overlap varied independently of niche width. A high overlap of food sources utilized by the two species was observed in September, October and November. This may be explained in one of two ways: (a) if B. atratus and B. morio compete for resources, competition would be more intense during those three months; (b) the convergency of both species to the same plant species (Solatium paniculatum and Psidium guajava) would only result in more intensive competition if resources were limiting. However, at that period of the year resources are abundant, therefore although the values of overlap were high, competition need not have occurred.

A long-term study of food-niche dynamics in the Common Barn-Owl: comparisons within and between populations

Food niches of Common Barn-Owl (Tyto alba) populations were studied for 8 years in Utah and Idaho. Small mammals dominated the diet as they do in most parts of the barn-owl's range. Mean prey weight was nearly identical between the two owl populations. Food-niche breadth, though, was significantly broader in Idaho than in Utah. Food-niche breadth was also more variable in Idaho than in Utah both within and between years. Voles (Microtus spp.) were predominant prey for both owl populations and were the only prey whose numeric variation in the diet significantly affected mean prey weight and food-niche breadth. Vegetative composition was less varied and more uniformly favorable to voles in Utah. The Idaho area contained a smaller poportion of good vole habitat but had a greater diversity of vegetation including deserts suitable for small mammal species not found in the Utah study area. These vegetative differences and their effects on small mammal species diversity and density were the most apparent causes of food-niche differences between the two owl populations.

Gradients in population fluctuations of Tengmalm's owl Aegolius funereus in Europe.

I studied the importance of geographical location, snow cover and food to the fluctuations in 30 breeding populations of Tengmalm's owl (Aegolius funereu) in Europe. Cyclicity indices were positively related both to latitude and longitude, but within Fennoscandia they were better correlated with snow cover. Population fluctuations increased northward, while food niche breadth and degree of site tenacity decreased northwards.Microtine fluctuations become more pronounced northwards and are more synchronized, while number of alternative prey increases southwards. These factors promote instability in North European and stability in central European owl populations. Furthermore, snow conditions were more important within Fennoscandia, since this small owl cannot hunt voles protected by deep snow. Environmental predictability and diversity of available food for Tengmalm's owl increase southwards in Europe. Thus, the owl is a resident generalist predator of small mammals and birds in central Europe and adopts a partial migration strategy (males being resident and females nomadic) in South and West Finland, changing its habits to nomadic microtine specialist in areas with pronounced vole cycles (in northern Fennoscandia). These changes fit well with the recent suggestion that gradients in density variations of small rodents are related to sustainable numbers of generalist predators.

Feeding Ecology of Sympatric Barn Owls and Long-Eared Owls in Idaho

The diets of Barn Owls and Long-eared Owls were compared during two consecutive nesting seasons in the Snake River Birds of Prey Area in southwestern Idaho, U.S.A. Over 12800 prey items were identified. Both species fed almost exclusively on small mammals. Microtus were the most important Barn Owl prey, while Long-eared Owls fed primarily on Peromyscus and heteromyid rodents. Nesting Barn Owls were more closely associated with irrigated agriculture than were Long-eared Owls. The feeding niche of Barn Owls was narrower than that of Long-eared Owls the first year but wider the next. Dietary overlap was 48.4% the first year and 60.9% the next. In comparison with other North American studies of sympatric Barn Owls and Longeared Owls, the owls in our study had wider feeding niches and a reduced dietary overlap. Mean weights of Barn Owl prey were significantly heavier than those of Long-eared Owl prey thus Barn Owl prey weight distributions were shifted towards heavier prey than were those of Long-eared Owls. Differences in habitat use, food niche breadth and prey size are potentially important coexistence mechanisms.

Food-niche relationships and guild structure of diurnal birds of prey: competition versus opportunism

Food-niche relationships of diurnal raptors have been claimed to be shaped by either competitive interactions or opportunistic feeding. We confront these alternatives by analyzing the patterns of prey use of five assemblages of falconiforms. Our results show that food-niche breadth is not a species property but is determined by the food resources locally available; neither does it become narrower in larger assemblages nor is it correlated with raptor size. Food-niche overlaps are frequently very high and do not become smaller in larger assemblages. Mean weight of prey taken is positively correlated with raptor weight within assemblages, but varies widely across assemblages, with a single species showing manyfold differences. Weight ratios between raptors contiguous in the size axis fall well below the 2.2–3.4 expected figures, nor are they negatively correlated with the amount of food-niche overlap. Normalized distance ratios (d/w) of spacing between raptors along the food-size axis are usually smaller than the expected 1. The five assemblages are organized in feeding guilds whose size is larger where fewer prey categories are available per raptor species. In most cases we found little support for predictions based on competition-structured assemblages. This is probably because of the opportunistic feeding behavior of raptors, and perhaps also because food might not be a limiting resource for them.

Food and feeding of small fish in the Rakaia River, New Zealand

Abstract Benthic macroinvertebrates and fish species were collected at monthly intervals during a 12‐month period, from 3 areas of the lower Rakaia River. The composition and abundance of the benthos and stomach contents of the fish were analysed for seasonal trends, food niche breadth and overlap between pairs of fish species, and overlap between the benthos and the diet of each fish species. The diets of bluegilled bully (Gobiomorphus hubbsi), upland bully (G. breviceps), juvenile longfinned eel (Anguilla dieffenbachii), Galaxias brevipinnis, G. paucispondylus, and juvenile brown trout (Salmo trutta) were similar to the proportions of prey species in the benthos. Deleatidium and chironomid larvae dominated the benthos in all seasons and formed the majority of food items in the diet of these species. Food niche overlap between these species was high, indicating potential competition, but preferred habitat and feeding habit differences plus low fish population density and abundance of main prey items probably eliminate the occurrence of any serious competition. The diet of the other fish species differed from this pattern. The common bully (Gobiomorphus cotidianus) ate proportionally more chironomid larvae and fish eggs than occurred in the benthos; torrentfish (Cheimarrichthys fosteri) ate proportionally more chironomid larvae than occurred in the benthos; and quinnat salmon (Oncorhynchus tshawytscha) depended largely upon prey species of terrestial origin, such as adult Deleatidium and dipterans.

Ecological notes on the lizard Tropidurus peruvianus in southern Peru

A population of Tropidurus peruvianus was studied using Barber traps along an elevational transect in the Lomas of southern Peru from April 1974 to May 1975. Most of the specimens were collected in the lowest part of the transect (250–450 m) and during the fall; none was collected in the more humid and vegetated area of Lomas, between 600 and 900 m. Tropidurus peruvianus is omnivorous and captures arthropod prey in proportion to its availability. The more important items in the diet were adult and larval beetles, ants, and flies. Average food niche breadth was 1·07, a little higher than the value for high Andean lizards. It is suggested that T. peruvianus selects habitats according to environmental humidity—it is neither present in the drier desert plateaux nor in the more mesic portions of the Lomas.

The Trophic Structure of Sympatric Assemblages of Diurnal and Nocturnal Birds of Prey

Patterns of food-niche breadth, food-niche overlap and mean prey weight in the diet are used to characterize and compare the trophic structure of five assemblages of diurnal and nocturnal birds of prey. The localities surveyed are in Michigan, Wisconsin, Utah, Spain and Chile. With few exceptions, no significant differences are demonstrated between sympatric assemblages of hawks and owls in the statistical distributions of raptor weights or of the three trophic estimators above-mentioned. Within each hawk and owl assemblage positive correlations are found between raptor weights and mean prey weights but not between raptor weights and food-niche breadths. Parallel geographic variation of diurnal and nocturnal raptor assemblages is observed in species richness (which is always higher for hawks), sizes and trophic statistics. Mean food-niche breadths within assemblages vary inversely with number of prey categories available per raptor species at a given locality. The trophic structure of sympatric assemblages of hawks and owls is very similar and covaries geographically because they are opportunistic predators that vary their trophic relationships according to the available food resources. INTRODUCTION Local assemblages of hawks and owls have been considered as ecological counterparts that hunt at different times of the day (Grossman and Hamlet, 1964; Craighead and Craighead, 1969). Thus far, this claim has been largely based on qualitative or semiquantitative assessments of feeding patterns of these raptors. In fact, few authors have reported adequate data on the food habits of entire raptorial assemblages (Errington, 1932, 1933; Valverde, 1967; Craighead and Craighead,, 1969; Smith and Murphy, 1973; Jaksic et al., 1981), and they have not usually characterized the trophic relations by means of standard statistics widely used in other dietary studies of birds (e.g., Hespenheide, 1973, 1975; Baltz and Morejohn, 1977; Wiens and Rotenberry, 1979). Standard quantitative estimators of the trophic niche are food-niche breadth (Levins, 1968; Petraitis, 1979), food-niche overlap (Colwell and Futuyma, 1971; Linton et al., 1981) and mean prey size (Storer, 1966; Hespenheide, 1973). Although many researchers have used these trophic estimators to test predictions about species diversity and packing, generalization vs. specialization, character displacement, guild structure, niche partitioning and the like (MacArthur, 1972; Cody, 1974; Pianka, 1974; Cody and Diamond, 1975; May, 1976), only rarely have these statistics been used to describe the trophic ecology of hawk and owl populations (Marti, 1974; Herrera and Hiraldo, 1976; Jaksic et al., 1981). Consequently, almost nothing quantitative is known about the food-niche relations of raptorial assemblages or about their spatial variation. To characterize the trophic structure of hawk and owl assemblages, sympatric diurnal and nocturnal raptors are compared and their geographic variation analyzed. Trophic structure is a shorthand term for the patterns of food-niche breadths, overlaps and prey sizes of sympatric raptor populations. I address the following questions: (a) To what extent is the trophic structure of hawk and owl assemblages similar? (b) Are the trophic statistics reasonably constant properties of given raptorial species or do they vary among localities? I hope that in answering these basic questions background information will be provided for more sophisticated analyses of the modes of predation of hawk and owl assemblages.

Resource utilization by bumblebee queens, workers and males in a subarctic area

We studied the seasonal dynamics of food niche width and annual niche relations of queens, workers and males of six abundant bumblebee species living on a slope of a subarctic hill in North Sweden. The basic data consist of analyses of pollen contents in nectar loads of individual foragers. At any given time of the season individual foragers utilized frequently more than one flower species during each trip, concentrating, however, most of their efforts on one species only. These “major” species varied between individuals thus widening the foraging niche of the species. No obvious differences were observed in niche widths of the sexes and castes of the species (neither day‐to‐day nor annual observations). Queens had highest niche overlaps and males the lowest ones. Sexes and castes were separated into groups by their foraging patterns. Differences in proboscis lengths are not obvious niche separating factors at the study area. The environmental uncertainty (in time and space) may occasionally lead to excess of resources, which, in turn, may open possibilities of wide utilization of available flower species, thus rendering close fit between proboscis length and corolla tube depths of the foraged flowers unnecessary.

Feeding Ecology and Niche Separation in Some Native and Domestic Ungulates on the Shortgrass Prairie

(1) Using the results of diet selection studies and two wild and two domestic species, we compare some aspects of ecology in relation to body size, the recent evolutionary history of the species and current forage conditions. (2) Food niche breadth and inter-species diet overlap seemed dependent upon recent evolutionary history as well as upon body size, but values were strongly influenced by forage quantity and quality. (3) Dietary selectivity appears especially sensitive to seasonal changes in forage quality, e.g. large as well as small animals pursued relatively selective strategies when forage conditions permitted, but body size and related nutritional-energetic demands appeared to set the limits where switches from selective to non-selective tactics took place. (4) Sensitivity to diet composition and quality increased with decreasing size except in the domestic sheep. It is likely that anatomical-physiological adaptations, including a relatively large rumeno-reticulum allow domestic sheep to utilize more forage plant species and inhabit a wider variety of niches and ecosystems than most ungulates. Human selection has made the sheep food and habitat generalists despite their relatively small size.

Seasonal resource partitioning patterns of marine calanoid copepods: Species interactions

Acartia hudsonica (Pinhey) and Temora longicornis (O.F. Muller) differ in many ways, but they exhibit similar feeding patterns. The quantity of spheres ingested by each species decreased seasonally (fall-summer) and was significantly less in the presence of other species. The food niche width of each species was largest in the fall but decreased and overlapped completely in early summer. These results suggest that Acartia hudsonica and Temora longicornis are more sensitive than Pseudocalanus sp. to temporal variation of the food environment. The niche width of these species was affected both by species interactions and by food levels, with Acartia hudsonica being more sensitive to species interactions. Individuals of Pseudocalanus sp. do not respond to seasonal (February–June) changes of the food environment. This is reflected in the narrow food niche width which did not change on a seasonal basis. The average amount of food ingested varied little on a seasonal basis, but increased significantly in the presence of other species. Species interactions with Temora longicornis and Acartia hudsonica as well as food levels affected niche width and the between phenotype component of niche width.

Relations between species diversity and diet in communities of ants

The food collected by all species of ants in eleyen communities was sampled, and the niche breadths and overlaps calculated. In communities of the Mojave Desert, the mean niche breadths were found to be relatively constant, regardless of changes in elevation or species diversity. Niche overlaps, however, were positively correlated with species diversity. With increases in latitude in the Great Basin Desert, the food niche breadths increased and overlaps decreased. Niche breadths were, not significantly correlated with species diversity in the Great Basin communities. The effect of diffuse overlap (amount of overlap in diet received by a species from all other species in the community) was to increase the rate at which overlap increased with species diversity. Running head: diets of ants.

Optimal Food Selection: A Graphic Model

A graphic model for optimal food selection has been developed. The model as analyzed in the present paper applies to herbivores feeding on abundant food items. Contrary to several current approaches to optimal feeding behavior, our model does not require an explicit ranking of food items. The currency to be optimized may be any nutritive element or a combination thereof. The substitution of specific currencies represents potentially rejectable hypotheses. Due to the availability of data the model is most easily applicable with digestable energy as currency. For each food type, an absolute distribution curve (measured in density units) is constructed over the range of food values, i.e., the currency to be optimized. Based on this distribution function, another distribution function is constructed over the same range of food values. This latter function represents the potentially extractable net amount of nutrients as a function of food value. A broad food niche is predicted whenever the optimization function (i.e., the distribution of the total potentially extractable net amount of nutrients from all food types as a function of food value) has a broad peak. In a stable environment, a stable polymorphism is predicted whenever the optimization function has two peaks of equal height. Discussions of how search images may alter the optimization function are presented. Cyclically occurring changes of resources may also produce a polymorphic population. Shifts of diet as a result of changing intra- and interspecific competition as well as changes in the food supply due to other factors are discussed. The conclusions are compared with similar conclusions deduced on the basis of other theories on food selection. The major disagreements between our conclusions and other conclusions reported in literature, are as follows. 1. The optimal diet is determined both by the total food density and the relative food density. Thus, a food item not in the optimal diet may be added to the diet by becoming very abundant. 2. MacArthur and Pianka (1966) deduced that food items worth exploiting in the absence of competition are always worth eating if competition for the item is present. Based on our model, this does not seem to follow; instead the opposite may occur. Other conclusions regarding optimal diets, food niche breadth, etc., are consistent with current thought on the subject.