Local variation in arctic fox abundance on Svalbard,Norway

Arctic fox (Alopex lagopus) numbers vary greatly, with cyclic fluctuations often associated with fluctuations in microtine rodents. However, in areas where small prey mammals are absent, such as Iceland and Svalbard, such cyclic fluctuations are lacking. Annual fluctuations in the density of the arctic fox population on the Brøggerhalvøya peninsula and Kongsfjorden region on Svalbard, Norway, were studied from 1990 to 2001 by using indices of fox abundance. All indices showed similar trends; fox numbers were low in 1990, increased until 1995 whereupon they decreased sharply, before increasing again and levelling off in 2001. Increasing numbers of foxes during the first part of the study paralleled increasing numbers of Svalbard reindeer (Rangifer tarandus platyrhynchus) carcasses in winter and increasing numbers of nesting barnacle geese (Branta leucopsis) in summer. This study shows that the number of arctic foxes varies greatly even in areas without fluctuating microtine rodents.     

The marine side of a terrestrial carnivore: intra-population variation in use of allochthonous resources by arctic foxes

Inter-individual variation in diet within generalist animal populations is thought to be a widespread phenomenon but its potential causes are poorly known. Inter-individual variation can be amplified by the availability and use of allochthonous resources, i.e., resources coming from spatially distinct ecosystems. Using a wild population of arctic fox as a study model, we tested hypotheses that could explain variation in both population and individual isotopic niches, used here as proxy for the trophic niche. The arctic fox is an opportunistic forager, dwelling in terrestrial and marine environments characterized by strong spatial (arctic-nesting birds) and temporal (cyclic lemmings) fluctuations in resource abundance. First, we tested the hypothesis that generalist foraging habits, in association with temporal variation in prey accessibility, should induce temporal changes in isotopic niche width and diet. Second, we investigated whether within-population variation in the isotopic niche could be explained by individual characteristics (sex and breeding status) and environmental factors (spatiotemporal variation in prey availability). We addressed these questions using isotopic analysis and Bayesian mixing models in conjunction with linear mixed-effects models. We found that: i) arctic fox populations can simultaneously undergo short-term (i.e., within a few months) reduction in both isotopic niche width and inter-individual variability in isotopic ratios, ii) individual isotopic ratios were higher and more representative of a marine-based diet for non-breeding than breeding foxes early in spring, and iii) lemming population cycles did not appear to directly influence the diet of individual foxes after taking their breeding status into account. However, lemming abundance was correlated to proportion of breeding foxes, and could thus indirectly affect the diet at the population scale.     

Predator–prey relationships: arctic foxes and lemmings

1. The number of breeding dens and litter sizes of arctic foxes Alopex lagopus were recorded and the diet of the foxes was analysed during a ship-based expedition to 17 sites along the Siberian north coast. At the same time the cyclic dynamics of co-existing lemming species were examined.
2. The diet of arctic foxes was dominated by the Siberian lemming Lemmus sibiricus (on one site the Norwegian lemming L. lemmus ), followed by the collared lemming Dicrostonyx torquatus .
3. The examined Lemmus sibiricus populations were in different phases of the lemming cycle as determined by age profiles and population densities.
4. The numerical response of arctic foxes to varying densities of Lemmus had a time lag of 1 year, producing a pattern of limit cycles in lemming–arctic fox interactions. Arctic fox litter sizes showed no time lag, but a linear relation to Lemmus densities. We found no evidence for a numerical response to population density changes in Dicrostonyx .
5. The functional or dietary response of arctic foxes followed a type II curve for Lemmus , but a type III response curve for Dicrostonyx .
6. Arctic foxes act as resident specialist for Lemmus and may increase the amplitude and period of their population cycles. For Dicrostonyx , on the other hand, arctic foxes act as generalists which suggests a capacity to dampen oscillations.     

Seasonal pulses of migratory prey and annual variation in small mammal abundance affect abundance and reproduction by arctic foxes

We examined how large seasonal influxes of migratory prey influenced population dynamics of arctic foxes and how this varied with fluctuations in small mammal (lemming and vole) abundance—the main prey of arctic foxes throughout most of their range. Specifically, we compared how arctic fox abundance, breeding density and litter size varied inside and outside a large goose colony and in relation to annual variation in small mammal abundance. Information-theoretic model selection showed that (1) breeding density and fox abundance were 2–3 times higher inside the colony than they were outside the colony and (2) litter size, breeding density and annual variation in fox abundance in the colony tracked fluctuations in lemming abundance. The influence of lemming abundance on reproduction and abundance of arctic foxes outside the colony was inconclusive, largely because fox densities outside the colony were low, which made it difficult to detect such relationships. Lemming abundance was, thus, the main factor governing reproduction and abundance of arctic foxes in the colony, whereas seasonal influxes of geese and their eggs provided foxes with external subsidies that elevated breeding density and fox abundance above that which lemmings could support. This study highlights (1) the relative importance of migratory prey and other foods on the abundance and reproduction by local consumers and (2) how migratory animals function as vectors of nutrient transfer between distant ecosystems such as Arctic environments and wintering areas by geese thousands of kilometres to the south.     

Prolonging the arctic pulse: long-term exploitation of cached eggs by arctic foxes when lemmings are scarce

1. Many ecosystems are characterized by pulses of dramatically higher than normal levels of foods (pulsed resources) to which animals often respond by caching foods for future use. However, the extent to which animals use cached foods and how this varies in relation to fluctuations in other foods is poorly understood in most animals. 2. Arctic foxes Alopex lagopus (L.) cache thousands of eggs annually at large goose colonies where eggs are often superabundant during the nesting period by geese. We estimated the contribution of cached eggs to arctic fox diets in spring and autumn, when geese were not present in the study area, by comparing stable isotope ratios (delta(13)C and delta(15)N) of fox tissues with those of their foods using a multisource mixing model in Program IsoSource. 3. The contribution of cached eggs to arctic fox diets was inversely related to collared lemming Dicrostonyx groenlandicus (Traill) abundance; the contribution of cached eggs to overall fox diets increased from < 28% in years when collared lemmings were abundant to 30-74% in years when collared lemmings were scarce. 4. Further, arctic foxes used cached eggs well into the following spring (almost 1 year after eggs were acquired) - a pattern that differs from that of carnivores generally storing foods for only a few days before consumption. 5. This study showed that long-term use of eggs that were cached when geese were superabundant at the colony in summer varied with fluctuations in collared lemming abundance (a key component in arctic fox diets throughout most of their range) and suggests that cached eggs functioned as a buffer when collared lemmings were scarce.     

Pulses of movement across the sea ice: population connectivity and temporal genetic structure in the arctic fox

Lemmings are involved in several important functions in the Arctic ecosystem. The Arctic fox (Vulpes lagopus) can be divided into two discrete ecotypes: “lemming foxes” and “coastal foxes”. Crashes in lemming abundance can result in pulses of “lemming fox” movement across the Arctic sea ice and immigration into coastal habitats in search for food. These pulses can influence the genetic structure of the receiving population. We have tested the impact of immigration on the genetic structure of the “coastal fox” population in Svalbard by recording microsatellite variation in seven loci for 162 Arctic foxes sampled during the summer and winter over a 5-year period. Genetic heterogeneity and temporal genetic shifts, as inferred by STRUCTURE simulations and deviations from Hardy–Weinberg proportions, respectively, were recorded. Maximum likelihood estimates of movement as well as STRUCTURE simulations suggested that both immigration and genetic mixture are higher in Svalbard than in the neighbouring “lemming fox” populations. The STRUCTURE simulations and AMOVA revealed there are differences in genetic composition of the population between summer and winter seasons, indicating that immigrants are not present in the reproductive portion of the Svalbard population. Based on these results, we conclude that Arctic fox population structure varies with time and is influenced by immigration from neighbouring populations. The lemming cycle is likely an important factor shaping Arctic fox movement across sea ice and the subsequent population genetic structure, but is also likely to influence local adaptation to the coastal habitat and the prevalence of diseases.     

The breeding productivity of dark-bellied brent geese and curlew sandpipers in relation to changes in the numbers of arctic foxes and lemmings on the Taimyr Peninsula, Siberia —

There were about three-year cycles in the populations of arctic foxes, and the breeding productivities of brent geese and curlew sandpipers on the Taimyr Peninsula, Russia, The populations of arctic foxes and lemmings changed in synchrony. The breeding productivities of the birds tended to be good when the arctic foxes were increasing in numbers and poor when the arctic foxes were decreasing. There was a negative relationship between arctic fox numbers (or occupied lairs) and the breeding productivity of brent geese in the following year. Although there was evidence of wide-spread synchrony In the lemming cycle across the Taimyr Peninsula, some localities showed differences, However, such sites would still have been influenced by the general pattern of fox abundance in the typical tundra zone of the Taimyr Peninsula, where most of the arctic foxes breed and from which extensive movements of foxes occur after a decline in lemming numbers. The results support a prey-switching hypothesis (also known as the alternative prey hypothesis) whereby arctic foxes, and other predators, feed largely on lemmings when these are abundant or increasing, but switch to birds when the lemming population is small or declining. The relationships between arctic foxes, lemmings and brent geese may be further influenced by snowny owls which create fox-exclusion zones around their nests, thus providing safe nesting areas for the geese.     

Natal den selection by sympatric arctic and red foxes on Herschel Island,Yukon, Canada

In the twentieth century, red fox (Vulpes vulpes) expanded into the Canadian Arctic, where it competes with arctic fox (Vulpes lagopus) for food and shelter. Red fox dominates in physical interactions with the smaller arctic fox, but little is known about competition between them on the tundra. On Hershel Island, north Yukon, where these foxes are sympatric, we focused on natal den choice, a critical aspect of habitat selection. We tested the hypothesis that red fox displaces arctic fox from dens in prey-rich habitats. We applied an approach based on model comparisons to analyse a 10-year data set and identify factors important to den selection. Red fox selected dens in habitats that were more prey-rich in spring. When red foxes reproduced, arctic fox selected dens with good springtime access, notably many burrows unblocked by ice and snow. These provided the best refuge early in the reproductive season. In the absence of red foxes, arctic foxes selected dens offering good shelter (i.e. large isolated dens). Proximity to prey-rich habitats was consistently less important than the physical aspects of dens for arctic fox. Our study shows for the first time that red foxes in the tundra select dens associated primarily with prey-rich areas, while sympatric arctic foxes do not. These results fit a model of red fox competitively interfering with arctic fox, the first detailed study of such competition in a true arctic setting.     

The impact of past climate change on genetic variation and population connectivity in the Icelandic arctic fox

Previous studies have suggested that the presence of sea ice is an important factor in facilitating migration and determining the degree of genetic isolation among contemporary arctic fox populations. Because the extent of sea ice is dependent upon global temperatures, periods of significant cooling would have had a major impact on fox population connectivity and genetic variation. We tested this hypothesis by extracting and sequencing mitochondrial control region sequences from 17 arctic foxes excavated from two late-ninth-century to twelfth-century AD archaeological sites in northeast Iceland, both of which predate the Little Ice Age (approx. sixteenth to nineteenth century). Despite the fact that five haplotypes have been observed in modern Icelandic foxes, a single haplotype was shared among all of the ancient individuals. Results from simulations within an approximate Bayesian computation framework suggest that the rapid increase in Icelandic arctic fox haplotype diversity can only be explained by sea-ice-mediated fox immigration facilitated by the Little Ice Age.     

Sea-ice use by arctic foxes in northern Alaska

The extensive use of sea-ice by three arctic foxes (Alopex lagopus) in northern Alaska was documented using satellite telemetry during the winter of 2005–2006. Here we present the first detailed data on movements of individual foxes while on the sea-ice. Two juvenile males and one juvenile female traveled long distances (904, 1,096, and 2,757 km) and remained on the sea-ice for extended periods of time (76, 120, and 156 days). Average distances traveled per day ranged from 7.5 to 17.6 km and foxes achieved maximum rates of travel of up to 61 km/day. These findings verify the use of sea-ice by arctic foxes and raise concerns that the diminishing arctic ice cover may negatively impact populations by limiting access to marine food sources.     

Movement tactics of a mobile predator in a meta‐ecosystem with fluctuating resources: the arctic fox in the High Arctic

Animal movement is a fundamental process shaping ecosystems at multiple levels, from the fate of individuals to global patterns of biodiversity. The spatio‐temporal dynamic of food resources is a major driver of animal movement and generates patterns ranging from range residency to migration and nomadism. Arctic tundra predators face a strongly fluctuating environment marked by cyclic microtine populations, high seasonality, and the potential availability of sea ice, which gives access to marine resources in winter. This type of relatively poor and highly variable environment can promote long‐distance movements and resource tracking in mobile species. Here, we investigated the winter movements of the arctic fox, a major tundra predator often described as a seasonal migrant or nomad. We used six years of Argos satellite telemetry data collected on 66 adults from Bylot Island (Nunavut, Canada) tracked during the sea ice period. We hypothesized that long‐distance movements would be influenced by spatio‐temporal changes in resource availability and individual characteristics. Despite strong annual and seasonal changes in resource abundance and distribution, we found that a majority of individuals remained resident, especially those located in an area characterized by highly predictable pulse resources (goose nesting colony) and abundant cached food items (eggs). Foxes compensated terrestrial food shortage by commuting to the sea ice rather than using long‐distance tracking or moving completely onto the sea ice for winter. Individual characteristics also influenced movement patterns: age positively influenced the propensity to engage in nomadism, suggesting older foxes may be driven out of their territories. Our results show how these mammalian predators can adjust their movement patterns to favor range residency despite strong spatio‐temporal fluctuations in food resources. Understanding the movement responses of predators to prey dynamics helps identifying the scales at which they work, which is a critical aspect of the functioning and connectivity among meta‐ecosystems.     

Northern nomads: ability for extensive movements in adult arctic foxes

In July 2008 we outfitted reproductively active adult arctic foxes with satellite tracking collars on Bylot Island, Nunavut, Canada and recorded their movements over a complete annual cycle. We present the tracking data from two individuals, one female and one male, who traveled extensively from February to July 2009, covering minimum distances of 4,599 and 2,193 km, respectively. We recorded high and sustained travel rates on both land and sea ice that reached 90 km/day for the female and 88 km/day for the male. Our data confirm that arctic foxes can move extensively and demonstrate sustained travel rates that are 1.5 times those previously measured for the species. Our study is the first presenting detailed year-round satellite tracking of adult arctic foxes and has implications for our understanding of navigational abilities, foraging ecology, trophic interactions with lemming populations, and genetic population structure of arctic foxes.     

Benefiting from a migratory prey: spatio-temporal patterns in allochthonous subsidization of an Arctic predator

1.?Flows of nutrients and energy across ecosystem boundaries have the potential to subsidize consumer populations and modify the dynamics of food webs, but how spatio-temporal variations in autochthonous and allochthonous resources affect consumers' subsidization remains largely unexplored. 2.?We studied spatio-temporal patterns in the allochthonous subsidization of a predator living in a relatively simple ecosystem. We worked on Bylot Island (Nunavut, Canada), where arctic foxes (Vulpes lagopus L.) feed preferentially on lemmings (Lemmus trimucronatus and Dicrostonyx groenlandicus Traill), and alternatively on colonial greater snow geese (Anser caerulescens atlanticus L.). Geese migrate annually from their wintering grounds (where they feed on farmlands and marshes) to the Canadian Arctic, thus generating a strong flow of nutrients and energy across ecosystem boundaries. 3.?We examined the influence of spatial variations in availability of geese on the diet of fox cubs (2003-2005) and on fox reproductive output (1996-2005) during different phases of the lemming cycle. 4.?Using stable isotope analysis and a simple statistical routine developed to analyse the outputs of a multisource mixing model (SIAR), we showed that the contribution of geese to the diet of arctic fox cubs decreased with distance from the goose colony. 5.?The probability that a den was used for reproduction by foxes decreased with distance from the subsidized goose colony and increased with lemming abundance. When lemmings were highly abundant, the effect of distance from the colony disappeared. The goose colony thus generated a spatial patterning of reproduction probability of foxes, while the lemming cycle generated a strong temporal variation of reproduction probability of foxes. 6.?This study shows how the input of energy owing to the large-scale migration of prey affects the functional and reproductive responses of an opportunistic consumer, and how this input is spatially and temporally modulated through the foraging behaviour of the consumer. Thus, perspectives of both landscape and foraging ecology are needed to fully resolve the effects of subsidies on animal demographic processes and population dynamics.     

Foraging and diet of the red fox Vulpes vulpes in relation to variable food resources in Biatowieza National Park, Poland

Feeding ecology of red fox Vulpes vulpes was studied by scat analysis and snow-tracking m primeval temperate forest and adjacent meadows during four years (1985/86-1988/89) Winters varied from mild to unusually severe Main food resources for foxes were rodents of open meadows and river valleys (root vole Microtus oeconomus ). forest rodents (bank vole Clethrionomys glareolus and yellow-necked mouse Apodemus flavicollis ), hare Lepus europaetis and carcasses of wild boar Sus scrofa and red deer Cervus elaphus either killed by wolves and lynx or that had died from inanition Composition of fox diet m four cold seasons (autumn-winter) was compared to the abundance of main food resources Prolonged, sharp decline of Microtus was followed by only a twofold decrease of its share in fox diet Foxes continued to prey on declining Microlus The changes in the proportions of forest rodents and hare in fox diet clearly followed the fluctuations in numbers of these two prey Carcasses were alternative, buffer food to foxes and were taken considerably when Microlus and other prey were in low numbers or poorly accessible The depth of snow was the most important factor restricting foxes access to rodents Snow-tracking revealed that foxes dwelling in the forest widely used adjacent open areas In open meadows foxes mainly hunted for rodents, while in the forest the most significant foraging activity was scavenging Seasonal analysis of fox diet revealed that consumption of Microlus by foxes was stable throughout the year (37-47% of biomass consumed) Bank vole significantly contributed to fox diet in autumn, and hare in summer only Scavenging was most pronounced in winter and spring when carcasses made up 30% of biomass taken     

Farmed arctic foxes on the Fennoscandian mountain tundra: implications for conservation

Hybridization between wild and captive-bred individuals is a serious conservation issue that requires measures to prevent negative effects. Such measures are, however, often considered controversial by the public, especially when concerning charismatic species. One of the threats to the critically endangered Fennoscandian arctic fox Alopex lagopus is hybridization with escaped farm foxes, conveying a risk of outbreeding depression through loss of local adaptations to the lemming cycle. In this study, we investigate the existence of escaped farm foxes among wild arctic foxes and whether hybridization has occurred in the wild. We analysed mitochondrial control region sequences and 10 microsatellite loci in samples from free-ranging foxes and compared them with reference samples of known farm foxes and true Fennoscandian arctic foxes. We identified the farm fox specific mitochondrial haplotype H9 in 25 out of 182 samples, 21 of which had been collected within or nearby the wild subpopulation on Hardangervidda in south-western Norway. Genetic analyses of museum specimens collected on Hardangervidda (1897–1975) suggested that farm fox genotypes have recently been introduced to the area. Principal component analysis as well as both model- and frequency-based analyses of microsatellite data imply that the free-ranging H9s were farm foxes rather than wild arctic foxes and that the entire Hardangervidda population consisted of farm foxes or putative hybrids. We strongly recommend removal of farm foxes and hybrids in the wild to prevent genetic pollution of the remaining wild subpopulations of threatened arctic foxes.     

The arctic fox Alopex lagopus in Fennoscandia: a victim of human-induced changes in interspecific competition and predation?

After a marked decline at the beginning of the 1900s, the arctic fox Alopex lagopus population in Fennoscandia has remained at a very low level. We suggest that the main cause for the population crash was winter starvation caused by (1) over-hunting of reindeer Rangifer tarandus populations, and thus reduced carcass availability in the mountains, and (2) increased interspecific competition for these carcasses because of increased invasion of red foxes Vulpes vulpes from lower altitudes. The failure of arctic fox populations to recover, despite increasing reindeer populations in the mid 1900s, can be explained by a concurrent strong increase in red fox numbers. Analyses of countywide hunting statistics from Norway 1891–1920 suggest that there actually was an increase in red fox numbers in the period of arctic fox decline, and that the increase in reindeer populations from the 1920s to the 1950s was accompanied by a new increase in red fox numbers. We conclude that restoring arctic fox populations most likely will require a substantial and lasting reduction of red fox populations.     

Diet of arctic foxes (Alopex lagopus) in Iceland

Arctic foxes, Alopex lagopus , live in low productivity arctic and northern tundra habitats, where they generally prey heavily on lemmings. In Iceland, however, no lemmings are present, and the foxes have a very varied diet, including plants such as seaweed and black crowberries, a wide range of birds and invertebrates, and carcasses of large mammals such as seals, reindeer, and sheep. Marked seasonal, geographical and inter-annual differences confirm arctic foxes in Iceland as opportunistic feeders. There are coastal and inland foxes: coastal foxes feed mainly on prey derived directly or indirectly from the ocean, particularly various seabirds and seals, while inland foxes feed largely on migrant birds, such as geese, waders and passerines in summer, and ptarmigan in winter. Despite their reputation for killing lambs, in this study, lamb carcasses were found at only 19.4% of 1125 fox dens, 44% of which had only one carcass. The distance to the nearest farm and the physical condition of lambs were major determinants of the number of carcasses found at a den. We discuss the implications of arctic foxes' diet for population dynamics and group formation, and for management practices.     

Seasonal variations in basal metabolic rate, lower critical temperature and responses to temporary starvation in the arctic fox (Alopex lagopus) from Svalbard

Metabolic rates of four resting, post-absorptive male adult summer- and winter-adapted captive arctic foxes (Alopex lagopus) were recorded. Basal metabolic rates (BMR) varied seasonally with a 36% increase from winter to summer, while body mass was reduced by 17% in the same period. The lower critical temperature (T _1c) of the winter-adapted arctic fox was estimated to −7°C, whereas T _lc during summer was 5°C. The similarity of these values, which are much higher than hitherto assumed (e.g. Scholander et al. 1950b), is mainly due to a significantly (P<0.05) lower BMR in winter than in summer. Body core (stomach) temperature was stable, even at ambient temperatures as low as −45°C, but showed a significant (P<0.05) seasonal variation, being lower in winter (39.3±0.33°C) than in summer (39.8±0.16°C). The thermal conductivity of arctic fox fur was the same during both seasons, whereas the thermal conductance in winter was lower than in summer. This was reflected in an increase in fur thickness of 140% from summer to winter, and in a reduced metabolic response to ambient temperatures below T _lc in winter. Another four arctic foxes were exposed to three periods of forced starvation, each lasting 8 days during winter, when body mass is in decline. No significant reduction in mass specific BMR was observed during the exposure to starvation, and respiratory quotient was unchanged at 0.73±0.02 during the first 5 days, but dropped significantly (P<0.05) to 0.69±0.03 at day 7. Locomotor activity and body core (intraperitoneal) temperature was unaltered throughout the starvation period, but body mass was reduced by 18.5±2.1% during these periods. Upon re-feeding, locomotor activity was significantly (P<0.05) reduced for about 6 days. Energy intake was almost doubled, but stabilised at normal levels after 11 days. Body mass increased, but not to the level before the starvation episodes. Instead, body mass increased until it reached the reduced body mass of ad libitum fed control animals. This indicates that body mass in the arctic fox is regulated according to a seasonally changing set point.     

Changes in Adélie penguin breeding populations in Lützow-Holm Bay, Antarctica, in relation to sea-ice conditions

The Adélie penguin, Pygoscelis adeliae, an important component of the Antarctic marine ecosystem, is closely associated with sea ice. Using data collected by Japanese Antarctic Research Expeditions since the 1960s, we examined trends in breeding populations of this species around Lützow-Holm Bay. Ten colonies ranging in size from 10 to 2,500 individuals were counted along the Soya Coast. Populations fluctuated synchronously, and overall increased at most colonies, except for two: one located deep inside the bay and another where human disturbance was substantial. Populations tended to increase during, or after, periods of sparse sea ice in summer, a condition that occurred once every decade. An increase in population size also occurred 5 years after a winter of extensive sea ice and after a winter of especially reduced sea ice.     

Interactions of exotic and native carnivores in an ecotone, the coast of the Beagle Channel, Argentina

In coasts bordering highly productive seas, there can be a flux of resources to the terrestrial ecosystem, and terrestrial carnivores can use marine prey extensively. Two native, endangered species (otter Lontra provocax and culpeo fox Pseudalopex culpaeus lycoides) and two exotic species (mink Neovison vison and grey fox Pseudalopex griseus) inhabit the Beagle coast. The objectives of this paper are: (1) to describe the diet, habitat use and distribution of otters, mink and foxes on the coast of the Beagle channel and (2) to discuss the role of marine resources in the ecological interactions among these species. Diet was determined from the analysis of 245 faeces, and distribution was established from sign surveys. Marine prey occurred in the scats of 98.3, 70.4, 35.5 and 18.2% of otters, mink, culpeo and grey foxes, respectively. Other terrestrial species also use marine resources in Southern Patagonia. All this evidence suggests that the Fueguian coastal channels provide an illuminating example of allochthonous food subsidies from the sea. In the community of four sympatric predators, two native (and endangered) and two exotic, coexistence appears to be facilitated by a renewing marine food subsidy.