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Fox Population (fox + population)
Selected AbstractsStrength of asymmetric competition between predators in food webs ruled by fluctuating prey: the case of foxes in tundraOIKOS, Issue 1 2010John-André Henden In food webs heavily influenced by multi-annual population fluctuations of key herbivores, predator species may differ in their functional and numerical responses as well as their competitive ability. Focusing on red and arctic fox in tundra with cyclic populations of rodents as key prey, we develop a model to predict how population dynamics of a dominant and versatile predator (red fox) impacted long-term growth rate of a subdominant and less versatile predator (arctic fox). We compare three realistic scenarios of red fox performance: (1) a numerical response scenario where red fox acted as a resident rodent specialist exhibiting population cycles lagging one year after the rodent cycle, (2) an aggregative response scenario where red fox shifted between tundra and a nearby ecosystem (i.e. boreal forest) so as to track rodent peaks in tundra without delay, and (3) a constant subsidy scenario in which the red fox population was stabilized at the same mean density as in the other two scenarios. For all three scenarios it is assumed that the arctic fox responded numerically as a rodent specialist and that the mechanisms of competition is of a interference type for space, in which the arctic fox is excluded from the most resource rich patches in tundra. Arctic fox is impacted most by the constant subsidy scenario and least by the numerical response scenario. The differential effects of the scenarios stemmed from cyclic phase-dependent sensitivity to competition mediated by changes in temporal mean and variance of available prey to the subdominant predator. A general implication from our result is that external resource subsidies (prey or habitats), monopolized by the dominant competitor, can significantly reduce the likelihood for co-existence within the predator guild. In terms of conservation of vulnerable arctic fox populations this means that the likelihood of extinction increases with increasing amount of subsidies (e.g. carcasses of large herbivores or marine resources) in tundra and nearby forest areas, since it will act to both increase and stabilize populations of red fox. [source] Possible contemporary evolution in an endangered species, the Santa Cruz Island foxANIMAL CONSERVATION, Issue 2 2009H. M. Swarts Abstract An ability to mount rapid evolutionary responses to environmental change may be necessary for species persistence in a human-dominated world. We present evidence of the possibility of such contemporary evolution in the anti-predator behaviour of the critically endangered Santa Cruz Island fox Urocyon littoralis. In 1994, golden eagles colonized Santa Cruz Island, CA and devastated the predator-naïve, endemic island fox population by 95% within 10 years. In 1992, just before the arrival of golden eagles, foxes showed substantial diurnal activity, but diurnal activity was 37.0% lower in 2003,2007, after golden eagle colonization; concurrently, overall activity declined and nocturnal activity increased. Moreover, on nearby Santa Catalina Island, where golden eagles were absent but where the fox population recently crashed due to a disease epidemic, remaining foxes were significantly more diurnally active than were those on Santa Cruz Island. The weight of evidence suggests that the change in activity pattern was a response to predation, not to low population density, and that this was probably a heritable rather than a learned behavioural trait. This behavioural change may allow for prolonged island fox persistence, but also potentially represents a loss of behavioural diversity in fox populations. [source] Estimating population parameters in a threatened arctic fox population using molecular tracking and traditional field methodsANIMAL CONSERVATION, Issue 4 2008T. Meijer Abstract Comprehensive population parameter data are useful for assessing effective conservation actions. The Fennoscandian arctic fox Alopex lagopus is critically endangered and the population size is estimated at 120 individuals that are fragmented into four isolated populations. Here, we use molecular tracking and visual observations to estimate population size and survival in one of the populations on the Swedish mountain tundra during a year of low food availability. We collected 98 arctic fox faecal samples during the winter of 2006 and recorded visual observations of ear-tagged individuals during the summer of 2005 and 2006. The faecal samples were analysed for variation in nine microsatellite loci and matched to the genetic profiles of previously ear-tagged individuals from 2001 to 2005. During winter 2006, the minimum number alive was 12 individuals using visual observations, 30 using molecular tracking and 36 by combining the datasets. Population size was estimated through mark,recapture for the molecular tracking and visual observation datasets and through rarefaction analyses for molecular tracking data. The mark,recapture estimate for visual observations was uninformative due to the large confidence interval (CI) (i.e. 6,212 individuals). Based on the molecular tracking dataset combined with the minimum number alive for visual observations and molecular tracking, we concluded a consensus population size of 36,55 individuals. We also estimated the age-specific finite survival rate during 1 year (July 2005 to July 2006) by combining molecular tracking with visual observations. Juvenile survival on a yearly basis was 0.08 (95% CI 0.02,0.18) while adults had a survival of 0.59 (95% CI 0.39,0.82). Juveniles displayed a lower survival than the adults during autumn (P<0.01) whereas no age-specific survival difference during spring was found. The risk of negative effects due to the small population size and low juvenile survival is accordingly considerable. [source] Prevalence of serum antibodies to canine adenovirus and canine herpesvirus in the European red fox (Vulpes vulpes) in AustraliaAUSTRALIAN VETERINARY JOURNAL, Issue 6 2005AJ ROBINSON Objectives: To determine the seroprevalence and aspects of the epidemiology of canine adenovirus (CAdV) and canine herpesvirus (CaHV-1) in European red foxes (Vulpes vulpes) in Australia. Design: Serum samples were collected opportunistically from foxes in 1991,1994 in Western Australia (WA) and South Australia (SA) and in 1980,1984 and 1990,1994 in New South Wales (NSW) and the Australian Capital Territory (ACT). The sera were examined for antibody to CAdV and CaHV-1 using ELISAs. Seroprevalence in the different regions was determined for both viruses and the CAdV data were analysed for interactions between decade of collection, age, season, region and gender using logistic regression. Results: The overall prevalence of antibody to CAdV was 23.2% (308/1326) but was significantly higher in sera collected in the eastern states of Australia (47%: 233/498) than in WA (9%: 75/828). Overall, in NSW and the ACT, there was a significantly lower prevalence in juveniles than in adults and the prevalence in juveniles in the 1990s was significantly lower than in the 1980s. The prevalence was also significantly lower in the autumn than in the winter for juveniles but the reverse held for adults. The NSW and ACT data were subdivided into eastern (including the ACT) and western regions. This revealed a significantly higher prevalence in the winter than in the autumn for the west and the reverse in the east. In WA, the northern rangeland regions of WA had lower prevalence (1.9%) than the southern agriculture regions (10.7%). Seasonally, there was a peak prevalence in the spring dropping through the summer and autumn and rising again in the winter. This seasonal pattern was also found in the combined data for all sites in the 1990s. There was no gender difference in prevalence of CAdV either overall or in different regions. The overall prevalence of antibody to CaHV-1 was 2.2% (28/1300). The small number of positives allowed only limited statistical analysis that did not reveal any differences in decade of collection, age, season or region. Conclusions: CAdV infection is common in the Australian fox population whereas CaHV-1 infection is rare. For CAdV, the age and seasonal patterns of seroprevalence were generally consistent with the recruitment of young susceptible foxes into the population in the spring and the accumulation of infections with age. The differences in regional prevalences correlated with fox density. The low prevalence of antibody to CaHV-1 suggests that CaHV-1 may be a more suitable vector than CAdV for bait delivery of immunocontraceptive antigens to foxes in Australia. [source] Population structure in an isolated Arctic fox, Vulpes lagopus, population: the impact of geographical barriersBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2009KARIN NORÉN The genetic composition of a population reflects several aspects of the organism and its environment. The Icelandic Arctic fox population exceeds 8000 individuals and is comprised of both coastal and inland foxes. Several factors may affect within-population movement and subsequent genetic population structure. A narrow isthmus and sheep-proof fences may prevent movement between the north-western and central part and glacial rivers may reduce movement between the eastern and central part of Iceland. Moreover, population density and habitat characteristics can influence movement behaviour further. Here, we investigate the genetic structure in the Icelandic Arctic fox population (n = 108) using 10 microsatellite loci. Despite large glacial rivers, we found low divergence between the central and eastern part, suggesting extensive movement between these areas. However, both model- and frequency-based analyses suggest that the north-western part is genetically differentiated from the rest of Iceland (FST = 0.04, DS = 0.094), corresponding to 100,200 generations of complete isolation. This suggests that the fences cannot be the sole cause of divergence. Rather, the isthmus causes limited movement between the regions, implying that protection in the Hornstrandir Nature Reserve has a minimal impact on Arctic fox population size in the rest of Iceland. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 18,26. [source] The behavioural ecology of the island fox (Urocyon littoralis)JOURNAL OF ZOOLOGY, Issue 1 2001Gary W. Roemer Abstract Insular populations typically occur at higher densities, have higher survivorship, reduced fecundity, decreased dispersal, and reduced aggression compared to their mainland counterparts. Insularity may also affect mating system and genetic population structure. However, these factors have not been examined simultaneously in any island vertebrate. Here we report on the ecological, behavioural and genetic characteristics of a small carnivore, the island fox Urocyon littoralis, from Fraser Point, Santa Cruz Island, California. Dispersal distances in island foxes are very low (mean 1.39 km, sd 1.26, range 0.16,3.58 km, n=8). Home-range size is one of the smallest (mean annual home range=0.55 km2, sd 0.2, n= 14) and density is nearly the highest recorded for any canid species (2.4,15.9 foxes/km2). Similar to other fox species, island foxes are distributed as mated pairs that maintain discrete territories. Overlap among mated pairs was always high (mean 0.85, sd 0.05), while overlap among neighbours (mean 0.11, sd 0.13), regardless of sex, was low. Despite this high degree of territoriality, island foxes are not strictly monogamous. Four of 16 offspring whose parents were identified by paternity analysis were a result of extra-pair fertilizations. Mated pairs were unrelated, however, suggesting inbreeding avoidance. Substantial population differentiation was found between the Fraser Point subpopulation and one only 13 km away (Fst= 0.11). We suggest that the primary effect of finite island area is to limit dispersal, which then influences the demography, behaviour and genetic structure of island fox populations. [source] Strength of asymmetric competition between predators in food webs ruled by fluctuating prey: the case of foxes in tundraOIKOS, Issue 1 2010John-André Henden In food webs heavily influenced by multi-annual population fluctuations of key herbivores, predator species may differ in their functional and numerical responses as well as their competitive ability. Focusing on red and arctic fox in tundra with cyclic populations of rodents as key prey, we develop a model to predict how population dynamics of a dominant and versatile predator (red fox) impacted long-term growth rate of a subdominant and less versatile predator (arctic fox). We compare three realistic scenarios of red fox performance: (1) a numerical response scenario where red fox acted as a resident rodent specialist exhibiting population cycles lagging one year after the rodent cycle, (2) an aggregative response scenario where red fox shifted between tundra and a nearby ecosystem (i.e. boreal forest) so as to track rodent peaks in tundra without delay, and (3) a constant subsidy scenario in which the red fox population was stabilized at the same mean density as in the other two scenarios. For all three scenarios it is assumed that the arctic fox responded numerically as a rodent specialist and that the mechanisms of competition is of a interference type for space, in which the arctic fox is excluded from the most resource rich patches in tundra. Arctic fox is impacted most by the constant subsidy scenario and least by the numerical response scenario. The differential effects of the scenarios stemmed from cyclic phase-dependent sensitivity to competition mediated by changes in temporal mean and variance of available prey to the subdominant predator. A general implication from our result is that external resource subsidies (prey or habitats), monopolized by the dominant competitor, can significantly reduce the likelihood for co-existence within the predator guild. In terms of conservation of vulnerable arctic fox populations this means that the likelihood of extinction increases with increasing amount of subsidies (e.g. carcasses of large herbivores or marine resources) in tundra and nearby forest areas, since it will act to both increase and stabilize populations of red fox. [source] Possible contemporary evolution in an endangered species, the Santa Cruz Island foxANIMAL CONSERVATION, Issue 2 2009H. M. Swarts Abstract An ability to mount rapid evolutionary responses to environmental change may be necessary for species persistence in a human-dominated world. We present evidence of the possibility of such contemporary evolution in the anti-predator behaviour of the critically endangered Santa Cruz Island fox Urocyon littoralis. In 1994, golden eagles colonized Santa Cruz Island, CA and devastated the predator-naïve, endemic island fox population by 95% within 10 years. In 1992, just before the arrival of golden eagles, foxes showed substantial diurnal activity, but diurnal activity was 37.0% lower in 2003,2007, after golden eagle colonization; concurrently, overall activity declined and nocturnal activity increased. Moreover, on nearby Santa Catalina Island, where golden eagles were absent but where the fox population recently crashed due to a disease epidemic, remaining foxes were significantly more diurnally active than were those on Santa Cruz Island. The weight of evidence suggests that the change in activity pattern was a response to predation, not to low population density, and that this was probably a heritable rather than a learned behavioural trait. This behavioural change may allow for prolonged island fox persistence, but also potentially represents a loss of behavioural diversity in fox populations. [source] Are dingoes a trophic regulator in arid Australia?AUSTRAL ECOLOGY, Issue 2 2010A comparison of mammal communities on either side of the dingo fence Abstract The direct and indirect interactions that large mammalian carnivores have with other species can have far-reaching effects on ecosystems. In recent years there has been growing interest in the role that Australia's largest terrestrial predator, the dingo, may have in structuring ecosystems. In this study we investigate the effect of dingo exclusion on mammal communities, by comparing mammal assemblages where dingoes were present and absent. The study was replicated at three locations spanning 300 km in the Strzelecki Desert. We hypothesized that larger species of mammal subject to direct interactions with dingoes should increase in abundance in the absence of dingoes while smaller species subject to predation by mesopredators should decrease in abundance because of increased mesopredator impact. There were stark differences in mammal assemblages on either side of the dingo fence and the effect of dingoes appeared to scale with body size. Kangaroos and red foxes were more abundant in the absence of dingoes while Rabbits and the Dusky Hopping-mouse Notomys fuscus were less abundant where dingoes were absent, suggesting that they may benefit from lower red fox numbers in the presence of dingoes. Feral cats and dunnarts (Sminthopsis spp.) did not respond to dingo exclusion. Our study provides evidence that dingoes do structure mammal communities in arid Australia; however, dingo exclusion is also associated with a suite of land use factors, including sheep grazing and kangaroo harvesting that may also be expected to influence kangaroo and red fox populations. Maintaining or restoring populations of dingoes may be useful strategies to mitigate the impacts of mesopredators and overgrazing by herbivores. [source] | ||||||||||