Diet shift of a facultative scavenger, the wolverine, following recolonization of wolves

1. Wolves Canis lupus L. recolonized the boreal forests in the southern part of the Scandinavian peninsula during the late 1990s, but so far there has been little attention to its effect on ecosystem functioning. Wolf predation increases the availability of carcasses of large prey, especially moose Alces alces L., which may lead in turn to a diet switch in facultative scavengers such as the wolverine Gulo gulo L. 2. Using 459 wolverine scats collected during winter-spring 2001-04 for DNA identity and dietary contents, we compared diet inside and outside wolf territories while controlling for potential confounding factors, such as prey density. We tested the hypothesis that wolverine diet shifted towards moose in the presence of wolves, while taking into account possible sexual segregation between the sexes. Occurrence of reindeer, moose and small prey was modelled against explanatory covariates using logistic mixed-effects models. Furthermore, we compared diet composition and breadth among habitats and sexes. 3. Occurrence of reindeer, moose and small prey in the diet varied with prey availability and habitat. As expected, diet contained more moose and less reindeer and small prey in the presence of wolves. Their diet in tundra consisted of 40% reindeer Rangifer tarandus L., 39% moose and 9% rodents. In forest with wolf, their diet shifted to 76% moose, 18% reindeer and 5% rodents; compared to 42% moose, 32% reindeer and 15% rodents in forest without wolf. This diet switch could not be explained by higher moose density in wolf territories. Female diet consisted of more small prey than for males, but there was a tendency for females to use the highly available moose carrion opportunistically and to hunt less on small prey within wolf territories. 4. Our study highlights how wolves increase scavenging opportunities for wolverines, and how sexual differences in diet may also apply to large scavengers. Due to their more restricted home range, female wolverines are forced to rely more on hunting small prey. The relatively high occurrence of wolf kills, however, forms an important food source to wolverines in this area. The recolonization of wolves may therefore have contributed to the consequent recolonization of wolverines into the same area.     

Functional responses in habitat selection are density dependent in a large herbivore

Habitat selection is complex due to density dependence and functional responses, defined as variation in relative habitat use depending on availability. In this study we unite these concepts by empirically testing for density‐dependent functional responses in habitat selection using a large herbivore, elk Cervus canadensis manitobensis, as a model species. Theory on density‐dependent habitat selection predicts specialised behaviour when densities are low with a gradual switch to generalist behaviour (more even selection of habitat) as competition intensifies. This suggests that functional responses in habitat selection should be positive when competition is low, but that density may have a negative effect on the functional response due to constraining effects of competition on habitat use and availability. We tested this prediction using data from Global Positioning System (GPS) collared elk (n = 33) and empirical data on spatiotemporal variation in local density during winter in Riding Mountain National Park, Manitoba, Canada (2002–2011). As local density increased, winter home range size decreased and the proportion of mixed forest (providing shelter and forage to elk) used and available within the home range also decreased. Our resource selection function (RSF) revealed clear density‐dependent effects in selection, being strongest (or weakest) for high quality (or low quality) habitat types at lowest observed density leading to more even selection as densities increased. The functional response in mixed forest selection was negatively affected by local density. Increasing availability of mixed forest in the home range was associated with higher selection at low density (positive functional response); no effect of availability on selection at moderate density (no functional response); and lower selection as availability increased at high density (negative functional response). Our study demonstrates that this process is largely driven by the negative effect of density on home range size as it constrains use and availability of habitat.     

Age- and density-dependent reproductive effort in male red deer

Reproductive effort in female ungulates originates from gestation and lactation and has been studied extensively; however, no comparable studies of reproductive effort in males (due to fighting for access to mates) have, to our knowledge, previously been reported. Here, we report on weight loss of male red deer during the annual mating season--a direct measure of male reproductive effort (or somatic reproductive costs). The 'terminal investment' hypothesis predicts that reproductive effort should increase with age, given that costs remain stable. We also propose the 'mating strategy-effort' hypothesis, which predicts that reproductive effort peaks in prime-aged males, since they are most often the harem holders. Consistent with the mating strategy-effort hypothesis, relative weight loss during the rutting season peaked at prime age and was lower in younger and senescent males. Weight loss during the rut was relatively smaller as density increased and more so for older males. This is probably primarily due to males (particularly senescent males) starting their rut in poorer condition at high density. The pattern of reproductive effort in males with regard to age and density therefore differs markedly from the pattern reported for females.     

Purification and characterization of a nitrilase from Brassica napus

In germinating seedlings of Brassica napus glucosinolate levels decrease and are potentially degraded to nitriles by a myrosinase. Little is known about the metabolism of glucosinolate aglycone products and the objective of this work was to investigate nitrilase activity and carry out a purification of the enzyme from seedlings of B. napus . A nitrilase capable of converting phenylpropionitrile to phenylpropionic acid was purified to apparent homogeneity from seedlings of B. napus . The protein has a molecular mass of approximately 420 kDa made up of 38 kDa subunits. The pI of the native protein was found to be 4.6. Under denaturing conditions on an isoelectric focusing (IEF) gel a major and minor protein was observed with pI in the range of 5.4-5.9, suggesting the presence of isoforms. Apart from the potential role of the nitrilase in indole-3-acetic acid (IAA) synthesis a developmental study with seedlings indicates that the increase in activity observed may be linked to the in vivo degradation of glucosinolates.     

Alzheimer disease: evidence for susceptibility loci on chromosomes 6 and 14

We report the transmission of HLA haplotypes and Gm allotypes in 97 members of a single kindred containing 257 individuals, 45 of whom were determined by clinical examination, autopsy, or historical data to have had Alzheimer disease (AD). Extensive inbreeding suggests that more than one gene may contribute to susceptibility to AD in this family, despite the apparent vertical transmission of illness. The distribution of HLA haplotypes and of Gm allotypes to affected and unaffected siblings is consistent with the possibility that genes in the HLA region of chromosome 6 and perhaps also in the Gm region of chromosome 14 are determinants of susceptibility. Further studies are needed to investigate whether susceptibility to AD may result from an interaction between (immune response?) genes on these two chromosomes.     

Continuous and discrete extreme climatic events affecting the dynamics of a high-arctic reindeer population

Climate at northern latitudes are currently changing both with regard to the mean and the temporal variability at any given site, increasing the frequency of extreme events such as cold and warm spells. Here we use a conceptually new modelling approach with two different dynamic terms of the climatic effects on a Svalbard reindeer population (the Brøggerhalvøya population) which underwent an extreme icing event (“locked pastures”) with 80% reduction in population size during one winter (1993/94). One term captures the continuous and linear effect depending upon the Arctic Oscillation and another the discrete (rare) “event” process. The introduction of an “event” parameter describing the discrete extreme winter resulted in a more parsimonious model. Such an approach may be useful in strongly age-structured ungulate populations, with young and very old individuals being particularly prone to mortality factors during adverse conditions (resulting in a population structure that differs before and after extreme climatic events). A simulation study demonstrates that our approach is able to properly detect the ecological effects of such extreme climate events.     

Effects of sheep grazing and temporal variability on population dynamics of the clonal herb <Emphasis Type="Italic">Geranium sylvaticum</Emphasis> in an alpine habitat

An improved understanding of population-level consequences of grazing on plants can be facilitated by an assessment of grazing effects on all stages in the life-cycle. In this study, 6 years of demographic data for three populations of the perennial herb Geranium sylvaticum were analysed. We examined the effects of sheep grazing (high sheep density, low sheep density and no sheep) and interannual climatic variability on vital rates and population growth rates (λ). Grazing did not affect survival or flowering rates, but reduced rates of growth and increased rates of clonal reproduction. At the population level, high contributions from retrogression and clonal reproduction buffered reduced rates of growth and stasis, and no consistent differences in λ between populations exposed to different sheep densities were found. Instead, large between-year variability in λ, independent of sheep density, was detected, related to variation in the local summer climate. The results indicated, however, that grazing effects on λ were more severe in unfavourable than in normal years. Our study highlights that increased clonal reproduction rates functioned as a tolerance mechanism towards grazing in this herb, which forms a mechanism to explain how moderate population responses to grazing in some herbs can arise.