Dietary Resource Partitioning Research Articles

DNA metabarcoding reveals broad woodpecker diets in fire-maintained forests

Abstract Ecological disturbance is a key agent shaping the spatial and temporal landscape of food availability. In forests of western North America, disturbance from fire can lead to resource pulses of deadwood-associated arthropods that provide important prey for woodpeckers. Although the foraging strategies among woodpecker species often demonstrate pronounced differences, little is known about the ways in which woodpeckers exploit and partition prey in disturbed areas. In this study, we employed DNA metabarcoding to characterize and compare the arthropod diets of 4 woodpecker species in Washington and California, USA—Black-backed Woodpecker (Picoides arcticus), Hairy Woodpecker (Dryobates villosus), Northern Flicker (Colaptes auratus), and White-headed Woodpecker (Dryobates albolarvatus)—primarily using nestling fecal samples from burned forests 1–13 years postfire. Successful sequencing from 78 samples revealed the presence of over 600 operational taxonomic units (OTUs) spanning 32 arthropod orders. The nestling diets of two species in particular—Northern Flicker and Black-backed Woodpecker—proved to be much broader than previous observational studies suggest. Northern Flicker nestlings demonstrated significantly higher diet diversity compared to other focal species, all of which displayed considerable overlap in diversity. Wood-boring beetles, which colonize dead and dying trees after fire, were particularly important diet items for Black-backed, Hairy, and White-headed woodpeckers. Diet composition differed among species, and diets showed limited differences between newer (≤5 yr) and older (>5 yr) postfire forests. Our results show mixed evidence for dietary resource partitioning, with three of the four focal species exhibiting relatively high diet overlap, perhaps due to the pulsed subsidy of deadwood-associated arthropods in burned forests. Woodpeckers are frequently used as management indicator species for forest health, and our study provides one of the first applications of DNA metabarcoding to build a more complete picture of woodpecker diets.

Mechanisms of dietary resource partitioning in large‐herbivore assemblages: A plant‐trait‐based approach

Abstract Sympatric large mammalian herbivore species differ in diet composition, both by eating different parts of the same plant and by eating different plant species. Various theories proposed to explain these differences are not mutually exclusive, but are difficult to reconcile and confront with data. Moreover, whereas several of these ideas were originally developed with reference to within‐plant partitioning (i.e. consumption of different tissues), they may analogously apply to partitioning of plant species; this possibility has received little attention. Plant functional traits provide a novel window into herbivore diets and a means of testing multiple hypotheses in a unified framework. We used DNA metabarcoding to characterize the diets of 14 sympatric large‐herbivore species in an African savanna and analysed diet composition in light of 27 functional traits that we measured locally for 204 plant species. Plant traits associated with the deep phylogenetic split between grasses and eudicots formed the primary axis of resource partitioning, affirming the generality and importance of the grazer–browser spectrum. A secondary axis comprised plant traits relevant to herbivore body size. Plant taxa in the diets of large‐bodied species were lower on average in digestible energy and protein, taller on average (especially among grazers), and tended to be higher in tensile strength, zinc, stem‐specific density, and potassium (and lower in sodium, stem dry matter content, and copper). These results are consistent with longstanding hypotheses linking body size with forage quality and height, yet they also suggest the existence of undiscovered links between herbivore body size and a set of rarely considered food–plant traits. We also tested the novel hypothesis that the leaf economic spectrum (LES), a major focus in plant ecology, is an axis of resource partitioning in large‐herbivore assemblages; we found that the LES was a minor axis of individual variation within a few species, but had little effect on interspecific dietary differentiation. Synthesis. These results identify key plant traits that underpin the partitioning of food–plant species in large‐herbivore communities and suggest that accounting for multiple plant traits (and trade‐offs among them) will enable a deeper understanding of herbivore–plant interaction networks.

Dietary resource partitioning among three coeval proboscidean taxa (Anancus capensis, Mammuthus subplanifrons, Loxodonta cookei) from the South African Early Pliocene locality of Langebaanweg E Quarry

The co-existence of megaherbivores in present-day ecosystems is uncommon. During the Early Pliocene, three large proboscidean taxa (Anancus capensis, Mammuthus subplanifrons and Loxodonta cookei) co-existed in the strongly C3-dominated Langebaanweg (LBW) environment, on the southwestern coast of South Africa. It is expected that this would have required at least some resource partitioning. To investigate whether/how dietary resources were partitioned, we have measured δ13C and δ18O in tooth enamel from the molars of A. capensis (n = 13), M. subplanifrons (n = 3) and L. cookei (n = 20). δ13C values for A. capensis are more tightly clustered and the mean more negative than for L. cookei and M. subplanifrons. Anancus capensis probably favoured shady, wooded parts of the LBW environment, where it mainly browsed. Loxodonta cookei and M. subplanifrons spent more time in open habitats and were dietarily flexible. The preference for browse of A. capensis may have contributed to its extinction, whereas the dietary flexibility of the genus Loxodonta meant it was able to survive to the present. We did not find significant differences in δ18O values between the three taxa, which suggests that they drank from the same water sources as expected if they were all resident in the LBW palaeoenvironment. Our study shows that the carrying capacity of the C3- dominated LBW environment was high.

Niche overlap and dietary resource partitioning in an African large carnivore guild

AbstractUnderstanding and quantifying a large carnivores’ feeding behaviour is a key component in determining its functional significance in an ecosystem, both in terms of its top‐down influence on prey species, but also its relationships with sympatric carnivores. Dietary overlap is one of the numerous niche dimensions used to characterize resource partitioning and potential competition within a community. We characterize the diet, potential dietary niche overlap and prey preference of a large African carnivore guild on small fenced protected areas. To quantify the potential inter‐ and intraspecific foraging competition, we analysed 5,128 kills, representing 35 prey species made by African wild dogs Lycaon pictus (n = 553), cheetahs Acinonyx jubatus (1,427), lions Panthera leo (2,648) and leopards P. pardus (500). Our results show that large African carnivores in small protected areas are exposed to considerable overlap in dietary resource utilization. At the interspecific level, African wild dogs and cheetahs displayed the greatest vulnerability to potential dietary competition. Lions exhibited marked differences in prey preference, mass and species utilization compared to the other carnivores. African wild dogs and cheetah females with dependent offspring occupied the greatest potential for dietary competition within the large carnivore guild. Using a case study based on the preferred biomass of prey available, we estimate the sustainable density of large carnivores at a small fenced prospective African wild dog reintroduction site. African wild dogs displayed the lowest mean predicted density compared to all sympatric predators with an expected population size of 7 individuals. Our research highlights the need to assess the influence of competitive forces in structuring and restoring large predators to portions of their historical range by identifying species most vulnerable to a potential reintroduction attempt. In the absence of controlled experiments, elucidating the influences of exploitation competition is challenging, and only through manipulating sympatric species presence and densities can these complex interactions be fully understood.

Dietary resource partitioning among age-sex classes of Agama agama (Squamata: Agamidae) assessed by fecal pellet analysis

Dietary resource partitioning among age-sex classes of Agama agama (Squamata: Agamidae) assessed by fecal pellet analysis. Dietary analysis is critical to understand the ecological roles of lizards, especially of species of Agama that are colonizing continents and islands from which they were previously absent. The foraging habits of four groups—viz., adult females, adult males, and young and juveniles (of both sexes)—of Agama agama in Nigeria were observed to assess the diet of the lizards and the contribution of the diet to separating age-sex classes. The claim that fying arthropods are less likely to be eaten by lizards was tested, and the hypothesis of dietary opportunism was explored. Sets (3–5 pellets) of 1453 fecal pellets collected during a 2-yr period were linked to individual lizards. Multivariate discriminant analysis of individual food items showed 61% lizards were correctly classifed to age-sex. However, items pooled into composite food groups, yielded fewer (43%) correctly classifed lizards. Cluster Analysis indicated that individual foods were less common (46.3%) to lizard classes than composite foods (76.1%). Thus, lizard age-sex classes are better differentiated when prey item is identifed at the lowest possible taxonomic level. Overall, arthropods are the largest, composite food for all lizard classes but, the relative amounts of different arthropod taxa varies signifcantly, and is highest for Diptera. Other foods include plants, seeds, and non-arthropod animal material. Differing coeffcients of variation accentuate dietary disparities within classes. Proportions of most individual and composite diet items differ signifcantly by month, season, and study site. Although consumed by lizards, no traces of white mold were found in the feces; this underscores the value of combining fecal analysis with surveillance of foraging habits of Agama agama.

Enamel hypoplasia and dental wear of North American late Pleistocene horses and bison: an assessment of nutritionally based extinction models

AbstractApproximately 50,000–11,000 years ago many species around the world became extinct or were extirpated at a continental scale. The causes of the late Pleistocene extinctions have been extensively debated and continue to be poorly understood. Several extinction models have been proposed, including two nutritionally based extinction models: the coevolutionary disequilibrium and mosaic-nutrient models. These models draw upon the individualistic response of plant species to climate change to present a plausible scenario in which nutritional stress is considered one of the primary causes for the late Pleistocene extinctions.In this study, we tested predictions of the coevolutionary disequilibrium and mosaic-nutrient extinction models through the study of dental wear and enamel hypoplasia ofEquusandBisonfrom various North American localities. The analysis of the dental wear (microwear and mesowear) of the samples yielded results that are consistent with predictions established for the coevolutionary disequilibrium model, but not for the mosaic-nutrient model. These ungulate species show statistically different dental wear patterns (suggesting dietary resource partitioning) during preglacial and full-glacial time intervals, but not during the postglacial in accordance with predictions of the coevolutionary disequilibrium model. In addition to changes in diet, these ungulates, specifically the equid species, show increased levels of enamel hypoplasia during the postglacial, indicating higher levels of systemic stress, a result that is consistent with the models tested and with other climate-based extinction models. The extent to which the increase in systemic stress was detrimental to equid populations remains to be further investigated, but suggests that environmental changes during the late Pleistocene significantly impacted North American equids.

Resource partitioning between two young-of-year cownose rays Rhinoptera bonasus and R. brasiliensis within a communal nursery inferred by trophic biomarkers.

Although interspecific trophic interactions plays a principal role within elasmobranch communal nurseries, little is known over variation in foraging strategies adopted by young-of-year of sympatric species. To test the hypothesis of dietary resource partitioning between batoids within a communal nursery, we investigated two cownose ray species, Rhinoptera bonasus and R. brasiliensis, which occur in heterospecific groups, a strategy predicted to increase survival and foraging success. Using two biochemical tracers, fatty acids (FA) and stable isotopes (δ15 N and δ13 C), the combined effects of maternal investment and the formation of heterospecific groups implying competition for, or partitioning of available food resources were investigated. Through univariate and multivariate analyses of biochemical tracers in several tissues (fin clip, muscle, liver, red blood cells; RBC) and plasma, our results revealed significant interspecific differences in tracers between the two species. Total FAs (∑saturated FA, ∑monounsaturated FA and ∑polyunsaturated FA) and trophic biomarkers (i.e., docosahexaenoic acid, arachidonic acid, oleic acid and δ15 N) were the principle tracers responsible for the differences detected. These data revealed that R. brasiliensis was less enriched in physiologically important essential FAs than R. bonasus. Our findings suggest that these congeneric species differ in maternal investment strategy and moderately partition food resources over relatively fine spatial scales within a single nursery habitat to limit competition. These results provide further knowledge on the foraging strategies adopted by batoids in communal nursery areas, information that is required for improving spatial conservation and management planning.

Trophic niche separation in sympatric rocky shore crabs

AbstractWhere two species occupy the same habitat and similar niches, competition is likely to drive small-scale spatial niche separation or resource partitioning that may not be immediately apparent. A stable isotope approach was used to investigate potential trophic niche separation between co-existing rocky shore crabs in the North-West (NW) Arabian Gulf. Leptodius exaratus and Pilumnopeus convexus which occupy similar shore height on the same rocky intertidal habitats. We also investigated conspecific differences between males vs females and adults vs juveniles. δ15N results indicated that adults of both species occupy a high trophic level in the rocky shore community, suggesting similar functional roles and potential for competition for food resources, while significant differences in δ13C values indicated differences in dietary sources between the two species, and also changes in diet between juveniles and adults in both species. MixSIAR analysis of δ15N and δ13C data confirmed field observations that both species are generalist omnivores, with potential for direct competition including adult predation on juveniles, including conspecifics. Differentiation in isotopic niches (SIBER analysis) was mainly driven by the significant differences in δ13C values, suggesting that co-existence of the two crab species is at least in part mediated by trophic niche separation or dietary resource partitioning, with some (unquantified) potential for spatial resource partitioning at the microhabitat level.

Importance of multi‐dimensional analyses of resource partitioning in highly mobile species assemblages

AbstractResource partitioning is an essential mechanism enabling species coexistence. The resources that are used by an animal are linked to its morphology and ecology. Therefore, similar species should use similar resources. The ecological niche of an individual summarizes all used resources and is therefore composed of several dimensions. Many methods are established to study different dimensions of an animal's niche. The aim of this study was to demonstrate that a combination of suitable methods is needed to study spatial and dietary resource partitioning of sympatric species in detail. We hypothesized that, while each individual method might identify differences between species, the combined results of several methods will lead to a more complete picture of spatial and dietary resource partitioning. As model organisms we chose the sympatric insectivorous bat species Myotis bechsteinii, M. nattereri, and P. auritus. We examined horizontal habitat use by telemetry, vertical habitat use by measuring δ13C, trophic position by measuring δ15N in wing membrane, and diet composition by molecular fecal analysis. Our results show that each method is able to provide information about spatial/dietary resource partitioning. However, considering further dimensions by combining several methods allows a more comprehensive assessment of dietary and spatial resource partitioning in bats.

Sympatric breeding auks shift between dietary and spatial resource partitioning across the annual cycle.

When species competing for the same resources coexist, some segregation in the way they utilize those resources is expected. However, little is known about how closely related sympatric breeding species segregate outside the breeding season. We investigated the annual segregation of three closely related seabirds (razorbill Alca torda , common guillemot Uria aalge and Brünnich’s guillemot U . lomvia ) breeding at the same colony in Southwest Greenland. By combining GPS and geolocation (GLS) tracking with dive depth and stable isotope analyses, we compared spatial and dietary resource partitioning. During the breeding season, we found the three species to segregate in diet and/or dive depth, but less in foraging area. During both the post-breeding and pre-breeding periods, the three species had an increased overlap in diet, but were dispersed over a larger spatial scale. Dive depths were similar across the annual cycle, suggesting morphological adaptations fixed by evolution. Prey choice, on the other hand, seemed much more flexible and therefore more likely to be affected by the immediate presence of potential competitors.

Comparison of Diets of Two Syntopic Lizards,Aspidoscelis marmorataandAspidoscelis tesselata(Teiidae), from the Northern Chihuahuan Desert of Texas

Abstract We compared types and volume of prey in the diets of two whiptail lizards (Teiidae), Aspidoscelis marmorata (a bisexual species) and A. tesselata (a unisexual species) that occur syntopically in a Chihuahuan Desert landscape on Indio Mountains Research Station, Hudspeth County, Texas. Because their home ranges overlap extensively, we hypothesized that there would be dietary resource partitioning between the two species. Stomach contents of 69 A. marmorata and 21 A. tesselata included only arthropods. Aspidoscelis marmorata used 14 orders of arthropods for prey, while A. tesselata used eight orders. Isopterans (termites) were the principal food for both species by count (93.5 and 83.8% in male and female A. marmorata, respectively; 94.6% in A. tesselata). By volume, Homoptera (37.8 and 10.3%), Araneae (11.9 and 54.1%), Orthoptera (18.0 and 0.9%), and Isoptera (16.6 and 3.6%) composed 84.3 and 68.9% of the diet of male and female A. marmorata, respectively; whereas Orthoptera (29.8%), Homoptera (29...

Communal or competitive? Stable isotope analysis provides evidence of resource partitioning within a communal shark nursery

ABSTRACT: Quantifying the diet of sympatric co-occurring predatory species is a challenging task, made more so when investigations attempt to focus on specific age groups. This is the task that confronts efforts to understand dietary resource partitioning among co-occurring juvenile shark species within nursery areas. Here, stable isotope analysis (δ13C and δ15N) is used to overcome these challenges in describing species dietary resource partitioning strategies within the communal shark nursery area of Cleveland Bay, Queensland, Australia. We analyzed the isotopic composition of 3 distinct tissues, (muscle, blood plasma, and red blood cells), for 7 species of shark and 3 species of large predatory teleost to investigate whether these communal areas support their diverse array of predators without the need for resource partitioning strategies. Clustered δ15N values for all examined species indicated feeding within the same trophic level; however, wide ranging δ13C values denoted exploitation of several primary carbon sources. Our results demonstrate inter-species resource partitioning strategies at work within the examined communal shark nursery, altering the previous interpretation of these areas as resource-rich and/or competition-limited environments.

Blubber fatty acid profiles indicate dietary resource partitioning between adult and juvenile southern elephant seals

When resources are limited or patchy, a species may develop some degree of resource partitioning to reduce intra-specific competition. Development of intra-specific resource partitioning is more pronounced in species with clear phenotypic variation among individuals (e.g. age or sex). Southern elephant seals Mirounga leonina have pronounced sexual dimorphism and range widely in size and foraging range between juvenile and adult stages. However, hypothesized diet-based resource partitioning has been less clear due to difficulties in sampling diet while seals are away from breeding islands. We analysed fatty acids (FAs) from blubber of 122 juvenile seals and compared them to FA profiles from blubber of 52 adult females, and to FA profiles from 51 prey species (grouped as fish and squid) to examine evidence for diet-based resource partitioning in the seals. FA signature analysis revealed physiological and dietary differences between ages. Principle components of the 21 FAs from seal blubber and prey parts distinguished prey from seals, and clearly separated prey species into fish and squid classes. FA profiles from adult females differed to those from juveniles, with the former more 'squid-like' and the latter more 'fish-like'. Variation in FA profiles of seals was also apparent between sexes and during different seasons. Differences in diet between juveniles and adult females suggest resource partitioning occurs in response to large metabolic and physiological differences with age that limit juvenile dispersal and diving abilities. By consuming a different suite of prey species relative to adult females, juvenile southern elephant seals may reduce intra-specific competition.

Dietary resource partitioning in ruminant communities of Miocene wetland and karst palaeoenvironments in Southern Germany

Ruminants made up a major component in Early and Middle Miocene European land mammal faunas. Hypotheses are tested which concern the diversity of feeding niches in Miocene ruminants and their resource partitioning. Because teeth are the basis of taxonomic work in the biota investigated here, the tooth-based mesowear method of dietary evaluation is applied. Dental wear equilibria as evaluated using mesowear analysis represent an immediate taxon-independent habitat interface, which bridges extant and Neogene communities. Two adjacent palaeoenvironments have been selected as models for testing our hypotheses, because ruminants are well recorded, the temporal window represents a long lasting and stable period before the onset of a global and regional environmental change that led to an increase of grass-dominated environments and because both environments represent fundamentally different habitat conditions but are spatially connected and represent the same climatic zone (i.e., the Molasse Basin wetland and the adjacent karstified Jurassic limestone plateau in Southern Germany). The ruminant communities of both biomes are brachydont throughout and a prevalence of browsing ruminants is found in both biomes, which is in accordance with isotope data. Both habitats, however, did also support strategies equalling those of extant mixed feeders. Among these mixed feeders, there are more grass-dominated mixed feeders in the karst habitat than there are in the wetland. The ruminant communities are thus found to apparently support a range of feeding traits, not evidenced by other ecomorphological approaches such as tooth crown height evaluation nor taxonomic uniformitarianism. The presence of these feeding types suggests that niche segregation in Lower and Middle Miocene brachydont ruminants was already fairly pronounced and reflects the hypothesised niche availability in the two palaeobiomes. The comparatively dry karstified landscape of the Jurassic limestone plateau is reflected by a higher diversity in abrasive feeders compared to the Molasse Basin wetland. As a second approach, two cervid species that co-occur in both biomes, Lagomeryx parvulus and L. pumilio have been tested in terms of differences in the abrasiveness of their diet in the two biomes. L. pumilio has a large dietary spectrum, and in the karst biome, it shows a signal equalling that of extant grass-dominated mixed feeders, while in the wetland biome it behaves as a browser as many other taxa also do. L. parvulus is shown to have a much less pronounced flexibility, as its diet consists of browse in both biomes. The coincidence of both, community structure and interspecific variability in dietary traits of the Lagomeryx species is a strong argument to consider the central hypothesis as supported, that drier environments result in more abrasion dominated dietary signals of flexible feeders, and that there is a general relationship between habitat structure, food availability, the abrasiveness of the forage, and tooth wear. The dietary variability of a species therefore seems to be a highly indicative characteristic in any ecological analysis of extant and fossil biomes and the presented approach adds rarely gained information on certain fossil members of a palaeocommunity and their potential role in the ecosystem.

Dietary resource partitioning among sympatric New Zealand and Australian fur seals

Adult male, female and juvenile New Zealand and Australian fur seals Arctocephalus forsteri and A. pusillus doriferus regularly return to colonies, creating the potential for intra- and inter-specific foraging competition in nearby waters. We hypothesise that the fur seals in this study utilise different prey, thereby reducing competition and facilitating coexistence. We analysed scats and regurgitates from adult male, female and juvenile New Zealand fur seals and adult male Aus- tralian fur seals and compared prey remains found in the samples. Most prey consumed by adult male and female fur seals occur over the continental shelf or shelf break, less than 200 km from Cape Gantheaume. Adult female fur seals utilised proportionally more low-energy prey such as large squid and medium-sized fish. The adult female diet reflected that of a generalist predator, dictated by prey abundance and their dependant pups' fasting abilities. In contrast, adult male New Zealand and Aus- tralian fur seals consumed proportionally more energy-rich prey such as large fish or birds, most likely because they could more efficiently access and/or handle such prey. Juvenile fur seals primar- ily consumed small fish that occur in pelagic waters, south of the shelf break, suggesting juveniles cannot efficiently utilise prey where adult fur seals forage. The age and sex groups in this study employ dramatically different strategies to maximise their survival and reproductive success and consequently the prey that they utilise reflect their different physiological constraints and metabolic requirements.

Morphological Correlates of Dietary Resource Partitioning in the African Bovidae

Members of the African Bovidae exhibit dietary resource partitioning, which presumably allows coexistence of many species with herbivorous diets. Levels of resource partitioning based on diet include primary food preference, habitat preference, and feeding-height preference. Morphological correlates of these levels of resource partitioning were sought in the skull and vertebral column of 33 bovid species. A quantitative morphometric study of the mandible, skull, and thoracic vertebrae in a large sample of bovids ( n > 700) explores these correlates using video-image analysis. Results of this study indicate that many significant morphological differences exist among bovids that have a diet of either grass, dicots, or some combination of these two primary resources. In addition, some variables significantly distinguished bovids with different habitat and feeding-height preferences. These morphological correlates crossed taxonomic boundaries and, in many cases, were related to the structural properties of the herbivorous diet.