Food Webs最新文献

Microplastics are contaminants that are often ingested, bioaccumulated, and transferred through food chain, affecting aquatic ecosystems. Zooplankton is susceptible to ingesting microplastics, so it is probably a vector that transfers microplastics to higher trophic levels. Cladocerans are a diet of amphibian larvae. Amphibians' survival is under threat worldwide due to their sensitivity to pollution. This work aimed to determine the transfer of zooplankton microplastics to Ambystoma mexicanum larvae (known as axolotl), for which we evaluated two responses in the first five weeks of development: 1) functional response of the larvae and 2) examination of their feces. Cladocerans were exposed to a diet of phytoplankton and microplastics to use them as food for axolotl larvae. Five axolotl larvae were randomly selected each week, each fed with a different concentration of cladocerans, and prey consumption was recorded for each larva. Finally, all the feces of the axolotls expelled after feeding were digested and examined under a light microscope. We found that microplastics were transferred from the cladocerans to A. mexicanum. Microplastics negatively affected the larval feeding behavior since the axolotls fed zooplankton exposed to microplastics consumed less prey than those of the control group. We also observed that microplastics were present in 78% of the feces. Microplastics reduce the feeding of juvenile A. mexicanum, an endemic amphibian of Mexico, in critical danger of extinction.

As human populations continue to expand, urbanization will increase and impact ecosystem processes, contribute to habitat fragmentation, and alter community composition of species. While some species can adapt to the rapidly changing environment, urbanization can favor generalist species and reshape food webs, which may result in ecological instability. Determining how wildlife respond to urbanization is necessary for management and city planning purposes in order to create suburban areas where humans and wildlife can coexist. One area that needs more focus is the effects of suburbanization on scavenging species, and how land development can alter scavenging dynamics and the redistribution of carrion-derived nutrients within food webs. We used motion activated cameras to monitor experimentally placed fish carcasses in riparian zones of suburban and rural areas in northeast Georgia, USA. We conducted 300 trials across both landscapes that were scavenged by 7 mammalian, 2 avian, and 2 reptilian species. Our results revealed fish carrion within riparian areas was readily consumed by terrestrial scavengers. However, carcass fate (whether the carcass was scavenged or not) and carcass persistence differed between suburban and rural landscapes. Carcasses were scavenged by vertebrates less often and persisted longer in rural landscapes. Species richness was similar and mesocarnivores were the predominant scavengers in both landscapes. However, scavenging by the Virginia opossum (Didelphis virginiana) was more prevalent in the suburban landscape relative to the rural landscape (61% and 36% of scavenging events, respectively). While raccoons (Procyon lotor) scavenged carcasses fairly equally across both landscapes, the American black bear (Ursus americanus) and red-shouldered hawk (Buteo lineatus) scavenged more frequently in rural areas. Our data suggest that suburban species, especially opossums, may be highly adapted to foraging in an anthropogenic environment. Additionally, nutrients from aquatic carcasses near water sources can readily move into terrestrial environments through scavenging. These results contribute to the growing body of scavenging ecology and the effects of urbanization on wildlife.

Globally, it is not yet clear whether particular individuals of apex predators with specific body conditions are more likely to attack livestock. In the Andes, attacks on livestock by pumas (Puma concolor) represent a recurring problem that, consequently, leads to the persecution and lethal removal of this predator by ranchers. However, although the anthropic motivations that lead to the lethal removal of pumas are known, the body conditions of the individuals that attack livestock are still unknown. From 2015 to 2016, three pumas were killed by ranchers after attacks on livestock in the department of Cuzco, at an average elevation of 4415 m, in southeastern Peru. The necropsy of these individuals revealed that they were all deviating from normal health and body conditions (cachexia, tarsal fracture, teeth problems and unusual stomach content). Although based on only three individuals, our findings allow us to hypothesize that these individuals did not meet the necessary body conditions for hunting wild prey. This could increase their states of hunger and lead them to forage in livestock landscapes, which in turn could serve as auxiliary foraging sites with more energetically profitable prey. We consider it essential to develop further research efforts to understand what ecological conditions cause pumas to be more vulnerable to human-induced mortality. This information is essential to further understand the characteristics of the ecological niche of these large predators in current anthropic contexts and, therefore, to direct coherent conservation strategies.

A variety of animals have been observed cleaning ectoparasites off of another species. In terrestrial systems, the most common interactions involve birds cleaning mammals. Despite the high density and wide distribution of kangaroos across Australia, there are almost no known records of bird-kangaroo cleaner relationships. Here I report multiple observations of bird-kangaroo interactions recorded with camera traps. This study replicates a previous report of Willie Wagtail (Rhipidura leucophyrs) cleaning, as well as details observations of two new bird species observed perching on Eastern grey kangaroos (Macropus giganteus). These results indicate bird-macropod cleaning interactions may be more common than previously reported.

Carrion removal is a key ecological function of scavengers, and they promptly dispose of carcasses in those large African conservation areas where predator assemblages remain intact. Despite its species richness, the grassland biome is critically threatened in southern Africa, and the predator assemblage is no longer intact in most of the biome. We used camera traps to monitor scavenger activity at five blue wildebeest (Connochaetes taurinus) carcasses on the Telperion Nature Reserve, characterized by rocky highveld grassland. We found that, in absence of larger vertebrate scavengers, black-backed jackals (Canis mesomelas) were unable to access fresh blue wildebeest carcasses, gaining access only once invertebrate action opened the skin. We also observed black-backed jackals eating flies accumulating on grass near to carcasses. These observations show that the avenues of resource provisioning by carcasses are not limited to direct carrion consumption. Moreover, they raise questions about potentially important cascading effects of not having intact predator assemblages, in smaller conservation areas.

• 1.

  Network nestedness describes an interaction pattern, wherein specialist species interact with a subset of partner species. Antagonistic networks are predicted to not be nested, because nestedness indicates a high intensity of interspecific competition, which compromises species coexistence. However, network nestedness is commonly observed in antagonistic networks, and the discrepancy between prediction and observation has not been fully resolved.

• 2.

  One of underlying factors explaining this discrepancy is the imperfection of metrics to detect network nestedness. However, studies comparing network metrics often fail to resolve which metric works best, presumably because they lack specific criteria.

• 3.

  We compared the results of the most commonly used metrics (weighted NODF) and a later proposed metric (spectral radius) to measure the nestedness of a quantitative plant - larval sawfly bipartite (including 8 sawfly species and 66 plant species, identified by gut DNA metabacoding of larvae). We also determined whether the sawfly species can coexist in terms of their dietary differences. Because nested structure is not likely to be compatible with species coexistence, we assumed that the metric identifying a non-nested structure is superior to the other.

• 4.

  The two metrics led to contrasting nestedness levels. Both observational and preference networks were found to be nested using weighted NODF, but was not nested using the spectral radius approach.

• 5.

  The dietary differences were significant among each sawfly species pair for both observational and preference networks, indicating low interspecific competitiveness and a high potential for species coexistence.

• 6.

  These results indicate that the spectral radius metric is superior to weighted NODF to detecting network nestedness and should be used in future network studies.

Discrete landscape features can concentrate animals in time and space, leading to non-random interspecific encounters. These encounters have implications for predator-prey interactions, habitat selection, intraspecific competition, and transmission of parasites and other pathogens. The lifecycle of the parasitic nematode Parelaphostrongylus tenuis requires an intermediate host of a terrestrial gastropod. Natural hosts of P. tenuis are white-tailed deer, and an aberrant host of conservation concern is moose, which are susceptible to high levels of mortality as a naive host to the parasite. Intermediate hosts become infected when P. tenuis larvae are shed in deer feces, then consumed or enter the gastropod through the foot. Incidental (or perhaps intentional) ingestion of infected gastropod intermediate hosts by aberrant or dead-end hosts often results in mortality of that animal. We present photographic evidence depicting a potential mechanism for transmission from infected white-tailed deer to moose, heretofore not examined in the literature. We deployed remote cameras at mineral licks around Grand Portage Indian Reservation in northeastern Minnesota, USA. We observed white-tailed deer defecating at mineral lick sites and geophagous moose at the same sites. We hypothesize that mineral licks may act as a nidus for P. tenuis transmission between deer and moose in this system and call for further research into the potential role of mineral licks in parasite transmission.

The Grand Portage Band of Lake Superior Chippewa is a federally recognized Indian tribe in extreme northeastern Minnesota, USA, and proudly exercises its rights to food sovereignty through subsistence hunting and fishing. Mooz (Moose) are a primary subsistence food used by the Anishinaabeg (people) of Grand Portage Band historically and presently. Management for and research on maintaining this moose population as a vital subsistence species thus sets the context for this paper examining potential for disease transmission between white-tailed deer and moose through shared use of mineral licks.

Spatiotemporal variations in food availability represent a challenge to the persistence of specialist species. The American oystercatcher (Haematopus palliatus) is a shorebird regarded as a bivalve specialist, although foraging habitats and prey species may vary along its distribution. Here, we studied American oystercatcher breeding in sites with variable landscapes to test the effect of temporal and spatial variations in food availability and dietary aspects. Between 2017 and 2021, we sampled oystercatchers (n = 100) and macroinvertebrates at the mesolitoral zone in five foraging areas in southern Brazil, three composed by sand and rock substrates (mixed), and two by sandy beach only. We obtained biological samples from oystercatchers and macroinvertebrates for carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope analysis. In addition, we carried out systematic sampling of macroinvertebrates in sandy beaches at foraging areas to assess prey availability. Main findings showed the oystercatcher diet to be influenced both by the heterogeneity of foraging habitats and temporal fluctuations in availability of food resources. Bivalves contributed ∼60% to the diet of oystercatchers, but differences in the preferred bivalve species were detected among areas. In sites with mixed substrates, oystercatchers had a wider isotopic niche, suggesting habitat heterogeneity induced a more varied diet. Finally, we also observed interannual variation in the diet that may be associated with variation in macroinvertebrate availability on sandy beaches, especially for non-bivalve prey. Therefore, both temporal variations in food availability and foraging habitat heterogeneity seem to shape the foraging ecology of oystercatchers in the coastal zone, evidencing trophic plasticity in this specialist shorebird.

Anthropogenic linear features allow wolves to travel faster and more efficiently, which is thought to increase wolf hunting efficiency of ungulates. Most previous studies have evaluated the role of linear features in wolf-ungulate dynamics by relying on indirect observations (e.g., GPS location data). Thus, there remains little direct observational data showing how wolves use linear features to hunt ungulates. Here, we present observational data (29 hunting sequences) of wolves using linear features to hunt ungulates. Linear features have largely been considered travel corridors that facilitate wolf movement and allow wolves to detect prey near (but not necessarily on) linear features. However, we clearly demonstrate wolves also use linear features as active hunting arenas where they detect, pursue, and kill prey that are also traveling directly on linear features. Our observations further suggest one of, if not the, primary way wolves detect ungulates on linear features is via olfactory cues.

The pelagic thresher, Alopias pelagicus, plays a vital role in coastal and marine ecosystems as a top predator that feeds on species from low trophic levels. It is a commercial species relevant in Ecuador. The feeding chain of A. pelagicus was analyzed through carbon and nitrogen stable isotopes in the Southeast Pacific Ocean. Considering the lack of studies regarding this topic, this would elucidate the flow of nutrients and energy from the base up to this predator. Its diet composition included 19 prey species, out of which 10 were cephalopods and nine Osteichthyes. The most relevant species were the squid Ommastrephes bartramii, Dosidicus gigas, Stenoteuthis oualaniensis, and the fish Merluccius gayi peruanus. The pelagic thresher is a carnivore predator, and its prey species belong to tertiary and quaternary trophic levels. The carbon and nitrogen male isotopic ratios were similar to those of females, as were immature and mature organisms. This suggests that this species feeds in oceanic regions of low depths and could be exploiting and sharing an area with similar feeding resources. According to the mixing models, squids were the most important prey group, in which the squid Ommastrephes bartramii contributed most to its diet. Furthermore, this shark was characterized as a specialist predator with a trophic overlap by sex and maturity stages.