Food Webs最新文献

Southern flying squirrels (Glaucomys volans) are common omnivorous mammals that rely on hardwood forests of the southeastern United States. Diet assessments may aid in understanding their place within food webs and their interactions with the endangered red-cockaded woodpecker (RCW; Dryobates borealis) of which, flying squirrels are a known kleptoparasite and possible nest predator. We examined foods assimilated by flying squirrels collected within RCW-managed forests of the Sam D. Hamilton Noxubee National Wildlife Refuge in east-central Mississippi, Oakmulgee Ranger District of the Talladega National Forest in west-central Alabama, Coosa Wildlife Management Area in central Alabama, and the Sehoy Plantation in east-central Alabama to explore variation in foods assimilated by flying squirrels across a section of the southeast. We used Bayesian mixing models applying isotopic ratios of ^14/15N (δN¹⁵) and ^12/13C (δ¹³C) measured in flying squirrel livers and used potential food items collected at each site to reconstruct their diet. Our model yielded evidence that hickories (Carya spp.) and oaks (Quercus spp.) contributed the most to the diet of southern flying squirrels at Noxubee, Oakmulgee, and Coosa with insects comprising the bulk of the diet at Sehoy (n = 39 squirrels). The proportion of hardwoods surrounding areas where flying squirrels were collected (10–52%) contributed little to model performance. Trophic positioning analysis showed a 95% confidence interval overlap between all sites indicating that flying squirrels are likely primary consumers and/or secondary consumers (trophic position of 3; 2.60–3.74). Flying squirrels in our study likely consume a mix of plants and insects and are unlikely to be common tertiary consumers (ex. consuming insectivorous-bird eggs). Their omnivorous habit suggests that efforts to exclude flying squirrels from RCW habitat will need a multifaceted approach with diet item management (ex. hardwood removal) as a part of the possible solutions available.

Mammalian carnivores (order Carnivora) occupy higher trophic levels in many terrestrial ecosystems, shaping community structures via direct predation and trophic cascades. The interference competition among sympatric carnivores (i.e., aggression and killing) has a major role in the intraguild interactions in which the large-dominant predators typically constrain behaviors and resource use patterns by exploitative (i.e., resource) competitions as well as the survival of smaller subordinate species by interference (i.e., direct) competitions. The free-roaming dog, Canis lupus familiaris, has been introduced worldwide and the species affects regional biodiversity, including native carnivore species. Using camera trapping, we investigated the temporal and spatial overlaps between the free-roaming dog and two wild canids, the golden jackal (Canis aureus) and the red fox (Vulpes vulpes), in different landscapes of central Bulgaria. We predict their interference interactions, namely that the dog, as the largest competitor, suppresses the golden jackal with intermediate body size, and, in turn, the golden jackal suppresses the smaller red fox. In mountainous forest landscapes where the free-roaming dog was absent or scarce, the golden jackal and red fox partitioned their diel activities, while there were moderate levels of spatial overlap. In agricultural lowlands where dogs were abundant and anthropogenic disturbances were relatively high, all three canids were primarily nocturnal with high temporal overlap, probably owing to human activities (e.g., hunting) in the daytime. The golden jackal was spatially separated from the dog, whereas the red fox spatially overlapped with large dogs. Our results indicated that, in human-modified landscapes with scattered forests and shrubs, spatial partitioning between the free-roaming dog and the golden jackal at fine spatial scales facilitates their sympatry by decreasing the probability of direct encounters. Furthermore, our findings also indicate that spatiotemporal interactions between the golden jackal and the red fox can change in association with various human disturbances, e.g., landscape modifications, human activities, and the introduction of dogs.

Knowledge on the ecology of many Amazonian anuran species is still incipient, especially when it comes to resource partitioning. Here, we studied dietary variation of four Pristimantis species (P. chiastonotus, P. crepitaculus, P. gutturalis and P. zeuctotylus) from Eastern Brazilian Amazonia during the rainy and dry seasons. From 226 stomach contents retrieved through stomach-flushing, we observed that the four sympatric species can explore the generalist, sit-and-wait, and opportunistic foraging strategies, feeding mainly on highly mobile arthropods such as Diptera, Coleoptera, Hymenoptera, Hemiptera and Orthoptera, which were the most important prey categories. We found significant differences among the species for the volumetric composition of prey, and the amount of prey consumed was the main predictor for this condition in most species. The type of microhabitat was also a predictor for feed volumetric composition in some species. We report a higher perching height for P. chiastonotus, and lower perching in P. gutturalis; the first species had a wider dietary spectrum. These findings contribute to the understanding of resource partitioning among sympatric and closely related species.

Stable isotope studies have revealed the importance of microphytobenthos (MPB) in coastal food webs. Microalgae typically have δ¹³C values between depleted C3 wetland/terrestrial macrophytes, and enriched C4 macrophytes and seagrasses. However, the challenges of obtaining clean samples of microalgae from sediments means they are often represented by limited sampling in many food web studies; consequently, we have a limited understanding of spatial and temporal variation in their δ¹³C values. We tested a simple technique to measure the δ¹³C of bulk pigments extracted from surficial sediments to represent MPB and applied it to quantify fine scale spatial variation in MPB δ¹³C around salt marshes. The bulk extraction method is logistically simple, and drives substantial but relatively consistent fractionation in δ¹³C of −3.5 ± 0.13 ‰ (mean ± 1 S.E., range = 2.3–4.4 ‰, n = 18 paired comparisons) compared to whole cell values. The consistency in fractionation suggests that spatial and temporal δ¹³C patterns measured in field samples should reflect real variation in source values, and that measured values could be corrected and incorporated into isotope mixing models. In 88 MPB samples among four marsh sites over two summers, MPB δ¹³C in marsh creeks was lower by an average of 4.4 ± 0.72 ‰ and up to 8.4 ‰ compared to sites along the outer marsh-open water fringe 10's of m away. Few food web studies incorporate this magnitude of variation in their MPB source estimates into mixing models. Over three weekly samplings at one marsh creek site, low tide dissolved inorganic carbon (DIC) δ¹³C was similarly lower by 4.8 ± 0.36 ‰ and up to 6.2 ‰ compared to high tide and adjacent open water DIC values. The significant small-scale variability in MPB δ¹³C appears to be driven by remineralized marsh carbon which depletes the DIC δ¹³C in the marsh creeks, a phenomenon that has long been recognized but is rarely considered in food web studies. Mixing models that assume a narrower range in MPB source values will erroneously attribute isotopically variable MPB contributions to end-member production sources thereby clouding our understanding of energy flows through coastal seascapes.

Shallow semi-enclosed coastal lagoons are recognized as important biodiversity hotspots and nursery areas for many organisms. However, the topology of the complex food web networks therein has never been studied. Highly defined food web networks were assembled for Ria de Aveiro, Ria de Alvor and Ria Formosa. Their structural network properties were analysed and compared to those of large open estuaries, small intermittent estuaries, as well as other marine ecosystems. The main conclusion was that these coastal lagoons are dominated by intermediate species like other estuarine systems, however they present more complex trophic networks (higher connectance) than large open estuaries, even though having shorter food chains. They also have lower mean path length between pairs of species. Shorter chain length means that disturbance is more likely to travel from basal to top species and likewise from the top to the bottom of the food web, while low path between species pairs implies a higher likelihood that disruption of one species affects any other species. These fragilities may be somewhat counterbalanced by the high connectance of these networks. The most connected species (with the highest degree = highest number of links at node) in the networks are crab and shrimp species. The non-indigenous blue crab appears as the most connected species in Ria de Alvor and among the top 5 most connected species in Ria Formosa. Highly commercial Sparid fishes play particularly important roles in the network as both highly connected and generalist predators. Top species are mostly birds. The top 10 species with more predators are all amphipods in Ria de Aveiro, while in Ria de Alvor they encompass insects, crabs, and gastropods, and in Ria Formosa they are all gastropods, with the exception of a non-indigenous polychaete. The particular network topology and inherent potential fragility of coastal lagoon food webs should be taken into account when designing environmental management plans.

Spotted hyenas (Crocuta crocuta) are known for their flexible foraging behavior and trophic interactions with diverse prey species. However, most studies describing their hunting behavior are focused on predation of large prey. Here we describe the capture rates and behavior of adult and subadult spotted hyenas hunting passerine birds. Hyenas were actively chasing, catching and feeding on red-billed queleas (Quelea quelea), a passerine bird gathering in large flocks at a waterhole in the Etosha National Park, Namibia. In total, we observed 38 successful captures with the average individual capture rate of 21 birds caught per hour. It remains unclear if this is a learned behavior of a single hyena clan or if it could be a widespread interaction across Africa, where the two species co-occur. Although it is unlikely that passerines could make up a substantial part of a spotted hyenas diet regardless of the location, our observations provide a rare documented example of trophic interactions between a large carnivore and small birds. It also represents an addition to a diverse repertoire of hyena foraging behaviors, which confirms their adaptability in obtaining food from non-typical sources.

The broadnose sevengill shark (Notorynchus cepedianus) is classified as Vulnerable by the IUCN, and its population in the Southwest Atlantic is declining. Despite some progress in understanding the ecological requirements of the sevengill shark, there are still several information gaps. Essential aspects of its trophic ecology, such as main prey items or key feeding grounds, remain uncertain and this information is essential for developing effective conservation strategies. Stable isotopes and spontaneous regurgitations were analyzed to describe the trophic ecology of sevengill sharks within a marine protected area (MPA) of Península Valdés in Patagonia, Argentina. Analysis of spontaneous regurgitations revealed that the southern elephant seal (Mirounga leonina) was the primary prey item (70%) for the sevengill shark, during abundance peaks of both species in the MPA. However, the stable isotope analysis indicated that the teleosts were the main prey item, and the overall contribution of the elephant seal to the diet of the sevengill shark was around 30%. In addition, the contribution of each prey group varied with the size of the individuals. The estimated trophic position was 4.43, placing the species among the apex predators of the region. This study confirmed the use of the MPA as an essential foraging ground and contributed to identifying its main prey items. Also, it reflects the need to expand conservation tools beyond this particular coastal protection.

Spore dispersal by insects (entomochory) is a crucial relationship for phalloid fungi, as mycophagous insects carry large amounts of spores and assist stinkhorns in the colonization of new sites. Phallus indusiatus s.l. is a widely distributed fungal species (Basidiomycota), which recruits generalist mycophagous insects as dispersal agents for their spores. Given the lack of knowledge about the natural history of this relationship, it is assumed that its spores are mostly dispersed by insect feces. This study was conducted in a fragment of Amazon forest in Pará, Brazil, and we (i) identified the insects that visited P. indusiatus s.l., (ii) observed the behavior of the insects during this interaction, and (iii) counted the spores carried both on the body surface and in the stomach of the visiting insects. A total of 333 insects associated with six P. indusiatus s.l. basidiomes were recorded. Stingless bees devoted the most time to foraging and were the insects that carried the largest amount of spores, >83 million spores on the body surface and >60 million in the stomach. Wasps presented low abundance, with five minutes dedicated to foraging, carrying just over 7 million spores on the body surface and >2 million in the stomach. The beetles, although possibly sheltering in the basidiomes before the total maturation of P. indusiatus s.l., were the insects with less carried spores, 189,000 spores on the body surface and about 39,000 spores in the stomach. However, they were the most abundant insects among visitors, surpassing the 100 individuals in a single basidiome. Stinkhorns are very valuable resources for forest insects and these fungi take advantage of this interaction to disperse their spores via feces, but mainly by the body surface of visitors.

Salmoniformes are valuable commercial fish that are high in physiologically important omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), namely eicosapentaenoic (EPA; 20:5n-3) and docosahexaenoic (DHA; 22:6n-3) ones. The content of EPA and DHA and, as a result, the quality of fish for consumers depend on the fish diet. We studied the fatty acid (FA) content and composition of grayling, Thymallus baicalensis, inhabiting six rivers, which differed in food supply for fish. The diet of fish was studied using fatty acid markers in adipose tissue and stomach content. In two rivers, grayling's diet was of aquatic origin, while in four rivers, terrestrial invertebrates constituted a high proportion of the fish diet. The study was conducted to test the following question: How do diets with varying amounts of terrestrial-based food influence the content of EPA and DHA, as well as the fatty acid composition, in various tissues of grayling? Grayling inhabiting shaded rivers had lower nutritional value as a source of LC-PUFAs for consumers compared to those in unshaded rivers. This was reflected in the diets of grayling in shaded rivers, which included more prey relying on terrestrial sources of FAs compared to unshaded rivers, where dietary items relied on autochthonous production. Furthermore, these different diets greatly affected the content of EPA and DHA in muscle and adipose tissue but demonstrated a less significant impact on PUFA content in the brain. These findings are of interest because they suggest that the nutritional value of grayling tissues, consumed by predators, including humans, depends on source material within a river and adjacent terrestrial habitat.

Functional diversity is the heterogeneity in the functional roles of organisms in an ecosystem. Because the morphological traits of species dictate their functional roles, morphological trait diversity has traditionally been used as a proxy for functional diversity. However, species are embedded in a food web and their functional roles also depend on their network positions therein, therefore we argue that functional diversity can also be viewed from a network perspective. We therefore analysed food webs derived from 92 aquatic ecosystems. For every species in a food web, we measured its network position using several indices. Each of the indices emphasize a specific network characteristic, and we consequently call them “species network traits”. We then subjected these network traits to conventional functional diversity analysis to quantify the network-based functional diversity of an ecosystem. We show that high network-based functional diversity is typical of food webs with large network size, sparse in their organization, highly modular structure, or low network cohesion. We further show that our network-based functional diversity correlates weakly with its conventional morphological trait-based counterpart, and thus it provides an additional view on ecological functioning.