Trophic ecology of a top predator colonizing the southern extreme of South America: Feeding habits of invasive American mink (Neovison vison) in Tierra del Fuego

The American mink (Neovison vison) is a semi-aquatic, generalist carnivore released onto Tierra del Fuego (TDF) Island in the 1940s, subsequently spreading to adjacent islands in the archipelago with potential effects on native prey populations. Knowledge of this new predator's trophic ecology is essential to identify threats, plan control strategies and conserve native fauna. We studied seasonal mink diet in TDF in different habitats. We identified undigested remains from 493 scats collected between May 2005 and March 2009 along marine coasts and freshwater shores (rivers and lakes). Small mammals and fish were the main mink prey in TDF (over 65% of diet items). Seasonal variations were not detected, but diet did vary significantly between marine and freshwater habitats, where more terrestrial items were consumed. Among mammals, mink consumed more small native rodents than exotic species. Native fish consumption was also important with greater representation of species from the families Nototheniidae and Galaxiidae in marine and freshwater habitats respectively. Birds were the third item in importance, but did not constitute a particularly large part of the mink's diet on TDF. Overall, differences found in mink diet between habitats reflected their generalist/opportunistic feeding behaviour and did not differ greatly from observations in its native range or in other areas where it has been introduced. Our results establish the interactions between this novel predator and its prey and also illustrate the need to continue research on native prey populations to quantify mink impact on them and understand the ecological context of this biotic assemblage.     

The role of migratory ducks in the long‐distance dispersal of native plants and the spread of exotic plants in Europe

Little is known about the role of migratory waterfowl in the long‐distance dispersal (LDD) of seeds. We studied the gut contents of 42 teals Anas crecca collected in the Camargue, southern France, and found intact seeds of 16 species. There was no relationship between the probability that a given seed species was found intact in the lower gut, and the seed hardness or size. The number of seeds found in the oesophagus and gizzard (a measure of ingestion rate) was the only significant predictor of the occurrence of intact seeds in the lower gut, so studies of waterfowl diet can be used as surrogates of dispersal potential. In a literature review, we identified 223 seed species recorded in 25 diet studies of teal, pintail Anas acuta, wigeon A. penelope or mallard A. platyrhynchos in Europe. We considered whether limited species distribution reduces the chances that a seed can be carried to suitable habitat following LDD. Overall, 72% of plant species recorded in duck diets in southern Europe (36 of 50) were also recorded in the north, whereas 97% of species recorded in duck diets in the north (137 of 141) were also recorded in the south. This suggests a great potential for LDD, since most dispersed plants species occur throughout the migratory range of ducks. Migratory ducks are important vectors for both terrestrial and aquatic plant species, even those lacking the fleshy fruits or hooks typically used to identify seeds dispersed by birds. Finally, we show ducks are important vectors of exotic plant species. We identified 14 alien to Europe and 44 native to Europe but introduced to some European countries whose seeds have been recorded in duck diet.     

Pāteke (Anas chlorotis) population trends in response to predator control on Great Barrier Island and Northland,New Zealand

Pāteke, brown teal (Anas chlorotis) were until recently restricted to two key strongholds in northern New Zealand: Great Barrier Island and eastern Northland. In 2000, we applied predator control at two sites within the strongholds. We analysed three decades of summer pāteke flock count data collected at ‘trapped’ and ‘untrapped’ locations to assess numerical pāteke response to predator control. Using piecewise regression, we found that Northland pāteke at trapped sites increased from 130 individuals before predator control, to 341 by 2015. Conversely, pāteke in untrapped areas in Northland remain low. Compared with the Northland trapped site, there was a slower rate of population increase in the predator treated site at Okiwi on Great Barrier Island; 286 individuals at trapped sites before predator control and 390 individuals in 2015. Pāteke numbers at untrapped sites on Great Barrier Island also increased, from 214 to 316 individuals. Cause of death analyses confirm that predation is a significant factor at trapped sites in Northland (87% of pāteke deaths) and Okiwi (56% of deaths), with starvation accounting for an additional 16% of identified causes of death at Okiwi. Access to sufficient food sources may be limiting at Okiwi, but overall the provision of predator control has benefitted pāteke populations.     

The Gut Bacterial Community of Mammals from Marine and Terrestrial Habitats

After birth, mammals acquire a community of bacteria in their gastro-intestinal tract, which harvests energy and provides nutrients for the host. Comparative studies of numerous terrestrial mammal hosts have identified host phylogeny, diet and gut morphology as primary drivers of the gut bacterial community composition. To date, marine mammals have been excluded from these comparative studies, yet they represent distinct examples of evolutionary history, diet and lifestyle traits. To provide an updated understanding of the gut bacterial community of mammals, we compared bacterial 16S rRNA gene sequence data generated from faecal material of 151 marine and terrestrial mammal hosts. This included 42 hosts from a marine habitat. When compared to terrestrial mammals, marine mammals clustered separately and displayed a significantly greater average relative abundance of the phylum Fusobacteria. The marine carnivores (Antarctic and Arctic seals) and the marine herbivore (dugong) possessed significantly richer gut bacterial community than terrestrial carnivores and terrestrial herbivores, respectively. This suggests that evolutionary history and dietary items specific to the marine environment may have resulted in a gut bacterial community distinct to that identified in terrestrial mammals. Finally we hypothesize that reduced marine trophic webs, whereby marine carnivores (and herbivores) feed directly on lower trophic levels, may expose this group to high levels of secondary metabolites and influence gut microbial community richness.     

Differences in endozoochorous dispersal between aquatic plant species, with reference to plant population persistence in rivers

Summary 1. In river ecosystems, populations are continuously subjected to unidirectional downstream currents resulting in a downstream movement of populations. To ensure long-term population persistence in rivers, organisms must have a mechanism for upstream dispersal, which allows them to re-colonise upstream areas.
2. In this study we assessed differences in the potential for endozoochorous seed dispersal of Sparganium emersum and Sagittaria sagittifolia , two aquatic plant species with different seed morphologies, by mallard ( Anas platyrhynchos ) and teal ( Anas crecca ), two duck species with different body weights.
3. We found no significant differences in seed retrieval (the proportion of ingested seeds retrieved after gut passage) and seed retention time (time between seed ingestion and retrieval), between mallard and teal, despite the difference in body weights. We did find a significantly higher germination (%) over retention time of S. emersum seeds retrieved from teal compared with mallard, most likely related to a more efficient removal of the seed coat during passage through the gut of teal.
4. There were large differences between S. emersum versus S. sagittifolia in: (i) seed retrieval (22.65 ± 20.8% versus 1.60 ± 2.4%, respectively); (ii) seed retention time in duck gut, with a maximum of 60 h versus 12 h; (iii) the effect of gut passage on seed germination, with an increase of approximately 35% versus a decrease of 25%; and (iv) the effect of gut passage on seed germination rate, with an acceleration of 10 days versus a delay of 3 days on average. The results show that S. emersum has a higher potential for endozoochorous dispersal by ducks and postdispersal establishment than S. sagittifolia .
5. We propose that, in rivers, bird-mediated seed dispersal may promote re-colonisation of upstream areas, enabling long-term plant population persistence.     

Convergent evolution of the gut microbiome in marine carnivores

The gut microbiome can help the host adapt to a variety of environments and is affected by many factors. Marine carnivores have unique habitats in extreme environments. The question of whether marine habitats surpass phylogeny to drive the convergent evolution of the gut microbiome in marine carnivores remains unanswered. In the present study, we compared the gut microbiomes of 16 species from different habitats. Principal component analysis (PCA) and principal coordinate analysis (PCoA) separated three groups according to their gut microbiomes: marine carnivores, terrestrial carnivores, and terrestrial herbivores. The alpha diversity and niche breadth of the gut microbiome of marine carnivores were lower than those of the gut microbiome of terrestrial carnivores and terrestrial herbivores. The gut microbiome of marine carnivores harbored many marine microbiotas, including those belonging to the phyla Planctomycetes, Cyanobacteria, and Proteobacteria, and the genus Peptoclostridium. Collectively, these results revealed that marine habitats drive the convergent evolution of the gut microbiome of marine carnivores. This study provides a new perspective on the adaptive evolution of marine carnivores.     

Nucleopolyhedrovirus Detection and Distribution in Terrestrial,Freshwater, and Marine Habitats of Appledore Island,Gulf of Maine

Viruses in aquatic ecosystems comprise those produced by both autochthonous and allochthonous host taxa. However, there is little information on the diversity and abundance of viruses of allochthonous origin, particularly from non-anthropogenic sources, in freshwater and marine ecosystems. We investigated the presence of nucleopolyhedroviruses (NPV) (Baculovirus), which commonly infect terrestrial lepidopteran taxa, across the landscape of Appledore Island, Gulf of Maine. PCR and qPCR primers were developed around a 294-bp fragment of the polyhedrin (polH) gene, which is the major constituent protein of NPV multivirion polyhedral occlusion bodies. polH was successfully amplified from several aquatic habitats, and recovered polH sequences were most similar to known lepidopteran NPV. Using quantitative PCR designed around a cluster of detected sequences, we detected polH in Appledore Island soils, supratidal freshwater ponds, nearshore sediments, near- and offshore plankton, and in floatsam. This diverse set of locations suggests that NPVs are widely dispersed along the terrestrial—marine continuum and that free polyhedra may be washed into ponds and eventually to sea. The putative hosts of detected NPVs were webworms (Hyphantria sp.) which form dense nests in late summer on the dominant Appledore Island vegetation (Prunus virginiana). Our data indicate that viruses of terrestrial origin (i.e., allochthonous viruses) may be dispersed widely in coastal marine habitats. The dispersal of NPV polH and detection within offshore net plankton (>64 μm) demonstrates that terrestrial viruses may interact with larger particles and plankton of coastal marine ecosystem, which further suggests that viral genomic information may be transported between biomes.     

Application of palynology to describe vegetation succession in estuarine wetlands on Great Barrier Island,northern New Zealand

Question: This paper compares published palynological studies from coastal swamps containing the same suite of species. We ask the following questions: (1) does succession follow the same pathways in different swamp systems, or (2) at different times? If not, (3) how variable are the patterns and (4) what are the likely driving factors? Location: Great Barrier Island, Northern New Zealand. Methods: Eighteen pollen profile diagrams were studied from four estuarine wetlands, ranging from mangroves to swamp forest. Recognition of a transition between vegetation stages was by subjective consideration of the relative abundances of pollen of key indicator species at different depths in the sedimentary sequence. Results: A linear sequence of vegetation communities beginning with mangroves and followed by estuarine marsh communities composed of Juncus kraussii, Leptocarpus similis and Baumea juncea was recognised in almost all pollen diagrams. Further transitions, from Baumea to a terrestrial system of Leptospermum shrubland or Cordyline/Dacry‐carpus swamp forest, followed two main pathways associated with autogenic accumulation of peat and terrigenous sediment input respectively. At Kaitoke and Awana the marine/freshwater transition occurred before the arrival of humans on Great Barrier Island. At Whangapoua, increased sedimentation followed anthropogenic burning of adjacent forest, and this transition was faster and is still in progress. Conclusion: Palynology and current vegetation zonation patterns concur to demonstrate that the marine sedimentation phase of estuarine succession is predictable and linear. Baumea marks the transition to the freshwater phase, in which varied successional patterns are determined by interactions between hydrology, sediment input, and peat accumulation. Natural and human disturbances drive sedimentation rates, and interact with autogenic factors, to dictate vegetation transitions in these later stages. The intensive impact (mainly burning) during Polynesian times had a much greater effect on estuaries and swamps than the pre‐Polynesian natural processes, greatly accelerating plant succession.     

Ontogenetic and seasonal changes in the diet of the halfbeak <Emphasis Type="Italic">Zenarchopterus dunckeri</Emphasis> at Iriomote Island,southern Japan

Ontogenetic and seasonal changes in the diet of the halfbeak Zenarchopterus dunckeri were examined in the Urauchi River estuary, Iriomote Island, southern Japan, using gut content analysis. The diet of this species changed dramatically with growth. Smaller juveniles fed mostly on small zooplankton and small gastropods, with a shift to the consumption of terrestrial insects, such as ants and flies, by larger individuals. Seasonal dietary differences were also apparent in adults. Ants were the most dominant prey item in the spring to fall months, whereas flies were abundant in the diet in the winter and early summer months.     

Phylogeny and Cladistic Classification of the Paramonostiliferous Family Plectonemertidae (Phylum Nemertea)

Abstract— Numerical phylogenetic analysis of nemertean species from the genera Plectonemertes, Katechonemertes and Acteonementes (marine), Argonemertes, Antiponemertes and Leptonemertes (terrestrial), Potamonemertes and Campbellonemertes (freshwater) in the family Plectonemertidae was carried out with the following aims. (1) To estimate the evolutionary relationships between and among these species. (2) To lest the hypothesis of Moore and Gibson that the analysed freshwater species originated from a terrestrial ancestor. (3) To classify the species in monophyletic genera. The analysis did not confirm the hypothesis that the freshwater habitat has been colonised via land. Instead, it suggests that both terrestrial and freshwater species within this family have evolved from a marine ancestor. The cladogram suggests that Antiponemetes is paraphyletic, and it is combined with Argonemertes to form a monophyletic genus.     

Variation of bone collagen amino acid δ13C values in archaeological humans and fauna with different dietary regimes: developing frameworks of dietary discrimination

We present bone collagen amino acid (AA) δ(13)C values for a range of archaeological samples representing four "benchmark" human diet groups (high marine protein consumers, high freshwater protein consumers, terrestrial C(3) consumers, and terrestrial C(4) consumers), a human population with an "unknown" diet, and ruminants. The aim is to establish an interpretive palaeodietary framework for bone collagen AA δ(13)C values, and to assess the extent to which AA δ(13)C values can provide additional dietary information to bulk collagen stable isotope analysis. Results are analyzed to determine the ability of those AAs for which we have a complete set, to discriminate between the diet groups. We show that very strong statistical discrimination is obtained for all interdiet group comparisons. This is often obvious from suitably chosen bivariate plots using δ(113)C values that have been normalized to compensate for interdiet group differences in bulk δ(13)C values. Bi-plots of non-normalized phenylalanine and valine δ(13)C values are useful for distinguishing aquatic diets (marine and freshwater) from terrestrial diets. Our interpretive framework uses multivariate statistics (e.g., discriminant analysis) to optimize the separation of the AA δ(13)C values of the "benchmark"' diet groups, and is capable of accurately assigning external samples to their expected diet groups. With a growing body of AA δ(13)C values, this method is likely to enhance palaeodietary research by allowing the "unknown" diets of populations under investigation to be statistically defined relative to the well-characterized or "known" diets of previously investigated populations.     

Pulmonate phylogeny based on 28S rRNA gene sequences: a framework for discussing habitat transitions and character transformation

Pulmonate snails occupy a wide range of marine, estuarine, freshwater and terrestrial environments. Non-terrestrial forms are supposed to be basal in pulmonate evolution but the group's phylogeny is not well resolved either morphologically or on the basis of available DNA sequence data. The lack of a robust phylogeny makes it difficult to understand character polarization and habitat transformation in pulmonates. We have investigated pulmonate relationships using 27 new sequences of 28S rRNA from pulmonates and outgroups, augmented with data from GenBank. The complete alignments comprised about 3.8kb. Maximum parsimony, maximum likelihood and Bayesian analyses of alignments generated under different assumptions are reported. Complete alignments appear to have a degree of substitution saturation so where there is conflict between hypothesised relationships more weight is given to analyses where regions of random similarity are excluded and which are not affected by this complication. Monophyly of the five main pulmonate groups was robustly supported in almost all analyses. The marine group Amphiboloidea and the freshwater Glacidorbidae are the most basal. The remaining pulmonates (Siphonariidae, Hygrophila and Eupulmonata) form a moderately-supported monophyletic group in all analyses bar one probably affected by saturation of substitutions. Siphonariidae, a predominantly marine and intertidal family, and Eupulmonata (mainly terrestrial with marine, estuarine and freshwater species) form a strongly supported clade that is the sister group to Hygrophila (freshwater). Multiple colonizations of freshwater and terrestrial habitats by pulmonate snails are suggested. No analyses strongly support the possibility of habitat reversions. The colonizations of freshwater by Hygrophila and of land by Stylommatophora were apparently phylogenetically independent although it cannot yet be excluded that there were transient terrestrial phases in the history of the former group or freshwater phases in the latter.     

Idiosyncratic responses of Pacific salmon species to land cover,fragmentation, and scale

Salmon are critical to the ecology and livelihood of the Pacific Northwest, and are declining throughout much of their range. While much of their life cycle occurs in open ocean, freshwater conditions also contribute to population trends. Because stream habitats are connected to uplands by water flow, salmon can be influenced by the characteristics of terrestrial systems. We analyzed the relationships between the population trends of Pacific salmon (1953–2006) and land cover, fragmentation, and forest age derived from remotely‐sensed, landscape level datasets. Analyses included 425 populations of all native salmon species in 156 watersheds on Vancouver Island, British Columbia, Canada. Vancouver Island salmon escapements exhibited general patterns of decline, which may be largely controlled by broad‐scale marine conditions. The spatial variation in these population trends was related to landscape variables at watershed and riparian scales with regression trees. Results were found to be species specific, but characteristics indicating a legacy of historic and current forest management (such as fragmented forests and non‐forested or early‐successional forest cover) generally had negative effects, driven by a small subset of highly fragmented watersheds. Chum and coho had strong negative relationships with fragmentation, pink had a strong positive relationship with wetland abundance, and Chinook and sockeye were most closely related to geomorphology. There was no ‘single best’ scale of analysis. Salmon trends were generally more closely related to variables estimated over the entire watershed, however, the relative importances of watershed and riparian level predictors varied by both variable and species. Efforts to restore salmon habitat will be complicated by marine and freshwater processes, terrestrial conditions throughout watersheds, and the idiosyncratic requirements of each species.     

Discovering hidden biodiversity: the use of complementary monitoring of fish diet based on DNA barcoding in freshwater ecosystems

Ecological monitoring contributes to the understanding of complex ecosystem functions. The diets of fish reflect the surrounding environment and habitats and may, therefore, act as useful integrating indicators of environmental status. It is, however, often difficult to visually identify items in gut contents to species level due to digestion of soft‐bodied prey beyond visual recognition, but new tools rendering this possible are now becoming available. We used a molecular approach to determine the species identities of consumed diet items of an introduced generalist feeder, brown trout (Salmo trutta), in 10 Tasmanian lakes and compared the results with those obtained from visual quantification of stomach contents. We obtained 44 unique taxa (OTUs) belonging to five phyla, including seven classes, using the barcode of life approach from cytochrome oxidase I (COI). Compared with visual quantification, DNA analysis showed greater accuracy, yielding a 1.4‐fold higher number of OTUs. Rarefaction curve analysis showed saturation of visually inspected taxa, while the curves from the DNA barcode did not saturate. The OTUs with the highest proportions of haplotypes were the families of terrestrial insects Formicidae, Chrysomelidae, and Torbidae and the freshwater Chironomidae. Haplotype occurrence per lake was negatively correlated with lake depth and transparency. Nearly all haplotypes were only found in one fish gut from a single lake. Our results indicate that DNA barcoding of fish diets is a useful and complementary method for discovering hidden biodiversity.     

Porotic hyperostosis in a marine-dependent California Indian population

A maize-based iron- and protein-deficient diet is commonly cited as the most important cause of porotic hyperostosis among American Indian agriculturalists. An alternative to this maize dependence hypothesis is suggested by the analysis of 432 crania from the nonagricultural, fish-dependent population of the Channel Island area of southern California. Cribra orbitalia, a form of porotic hyperostosis associated with iron deficiency anemia, is just as common among these fisherpeople, whose diet was rich in iron and essential amino acids, as it is among maize-dependent agriculturalists. Northern Channel Island crania have much more cribra orbitalia than those from the California mainland. The highest incidence is on San Miguel, a small geographically isolated island with a shortage of fresh water and terrestrial resources. The Indians who lived on Santa Cruz, the largest of the northern Channel Islands with the greatest diversity of terrestrial plants and animals, have less cribra orbitalia than those who lived on Santa Rosa or San Miguel Island. This geographical distribution appears to be explained by island-mainland and interisland differences in water contamination, exposure to fish-borne parasites, and nutritional adequacy of the diet. The prevalence of porotic hyperostosis in a population with a heavy dietary dependence on marine resources shows that among prehistoric American Indians, this condition is not always associated with an iron- and protein-deficient diet of cultigens. It seems likely that high nutrient losses associated with diarrheal disease are often more significant in the etiology of porotic hyperostosis than a low dietary intake of essential nutrients.     

Stomach contents of adult sea trout caught in six English rivers

The probability of feeding was significantly lower ( P <0.001) for male than for female sea trout in six rivers, and decreased significantly ( P <0.05) for both sexes with increasing distance upstream from the normal tidal limit. The diet changed markedly from marine to freshwater and terrestrial foods with increasing distance upstream, especially among females.     

Naiveté and an aquatic-terrestrial dichotomy in the effects of introduced predators

There is much evidence that suggests that freshwater systems are more sensitive to introduced predators than are terrestrial or marine systems. We argue here that this dichotomy reflects widespread naiveté toward introduced predators among freshwater prey. Continental terrestrial animals are seldom naive toward novel predators owing to the homogenizing effects of historical biotic interchanges. Comparable biotic interchanges might have also precluded prey naiveté in most marine systems. By contrast, freshwater systems exhibit persistent large- and small-scale heterogeneity in predation regimes. This heterogeneity promotes naiveté at multiple spatial scales in freshwater prey, thereby producing a systemic vulnerability to introduced predators that is not seen in continental terrestrial or marine systems.     

Dietary–morphological relationships in a fish assemblage of the Bolivian Amazonian floodplain

Morphological correlates of diet were examined in 48 species of freshwater fishes from floodplain lakes in the central part of the Mamoré River (Bolivian Amazon). The species were classified, according to the percentage occurrence of seven food items, into eight broad trophic categories: mud feeders, algivores, herbivores, terrestrial invertivores and omnivores, carnivores, zooplanktivores, aquatic invertivores and piscivores. There were significant relationships between the diet and morphology of the fishes even when the effect of taxonomical relatedness between species was eliminated. Relative gut length was the main morphological variable used to order species on a carnivore to mud feeder gradient. Standard length and head and mouth size were the morphological variables most closely associated with prey size. Mud feeder, algivore and piscivore species appeared as the most dietary and morphologically specialized. These results support both the hypotheses that species morphology influences the diet and that morphological similarity is conserved even in comparison with taxonomically unrelated species.     

Seasonally varying marine influences on the coastal ecosystem detected through molecular gut analysis

Terrestrial predators on marine shores benefit from the inflow of organisms and matter from the marine ecosystem, often causing very high predator densities and indirectly affecting the abundance of other prey species on shores. This indirect effect may be particularly strong if predators shift diets between seasons. We therefore quantified the seasonal variation in diet of two wolf spider species that dominate the shoreline predator community, using molecular gut content analyses with general primers to detect the full prey range. Across the season, spider diets changed, with predominantly terrestrial prey from May until July and predominantly marine prey (mainly chironomids) from August until October. This pattern coincided with a change in the spider age and size structure, and prey abundance data and resource selection analyses suggest that the higher consumption of chironomids during autumn is due to an ontogenetic diet shift rather than to variation in prey abundance. The analyses suggested that small dipterans with a weak flight capacity, such as Chironomidae, Sphaeroceridae, Scatopsidae and Ephydridae, were overrepresented in the gut of small juvenile spiders during autumn, whereas larger, more robust prey, such as Lepidoptera, Anthomyidae and Dolichopodidae, were overrepresented in the diet of adult spiders during spring. The effect of the inflow may be that the survival and growth of juvenile spiders is higher in areas with high chironomid abundances, leading to higher densities of adult spiders and higher predation rates on the terrestrial prey next spring.     

绿翅鸭、琵嘴鸭、斑嘴鸭越冬期的生存能

在野鸭越冬期逐旬测定了绿翅鸭、琵嘴鸭、斑嘴鸭笼养下的生存能。结果表明,三种野鸭越冬期每天摄食量分别为绿翅鸭32.4克,琵嘴鸭54.9克、斑嘴鸭80.2克。食物利用率依次为75.6％;73.7％;73.8％。生存代谢能依次为102.7千卡/只·天;173.6千卡/只·天;248.2千卡/只·天。总能量的摄入有三个高峰,分别出现在秋季迁来后、冬季寒潮后和春季迁飞前。 三种野鸭越冬期体重呈现出二低二高的变化形式。1983年与1963年野外野鸭体重相比较,绿翅鸭平均降低了20％,斑嘴鸭降低了12％,表明太湖湖泊生态系统对野鸭的栖息越冬有恶化的趋势。 本文分三个季节拟合了体重与生存能的关系式,比较了不同季节生存能与静止代谢能的差异,表明野鸭是通过提高体廓的隔热能力,增加体内能量的储存以及减少活动和生产的能量消耗来渡过寒冷又缺少食物的冬季的。