Ivar Mysterud

Linking climate change to lemming cycles

The population cycles of rodents at northern latitudes have puzzled people for centuries, and their impact is manifest throughout the alpine ecosystem. Climate change is known to be able to drive animal population dynamics between stable and cyclic phases, and has been suggested to cause the recent changes in cyclic dynamics of rodents and their predators. But although predator–rodent interactions are commonly argued to be the cause of the Fennoscandian rodent cycles, the role of the environment in the modulation of such dynamics is often poorly understood in natural systems. Hence, quantitative links between climate-driven processes and rodent dynamics have so far been lacking. Here we show that winter weather and snow conditions, together with density dependence in the net population growth rate, account for the observed population dynamics of the rodent community dominated by lemmings (Lemmus lemmus) in an alpine Norwegian core habitat between 1970 and 1997, and predict the observed absence of rodent peak years after 1994. These local rodent dynamics are coherent with alpine bird dynamics both locally and over all of southern Norway, consistent with the influence of large-scale fluctuations in winter conditions. The relationship between commonly available meteorological data and snow conditions indicates that changes in temperature and humidity, and thus conditions in the subnivean space, seem to markedly affect the dynamics of alpine rodents and their linked groups. The pattern of less regular rodent peaks, and corresponding changes in the overall dynamics of the alpine ecosystem, thus seems likely to prevail over a growing area under projected climate change.

Intrinsic Scaling Complexity in Animal Dispersion and Abundance

Ecological theory related to animal distribution and abundance is at present incomplete and to some extent naïve. We suggest that this may partly be due to a long tradition in the field of model development for choosing mathematical and statistical tools for convenience rather than applicability. Real population dynamics are influenced by nonlinear interactions, nonequilibrium conditions, and scaling complexity from system openness. Thus, a coherent theory for individual‐, population‐, and community‐level processes should rest on mathematical and statistical methods that explicitly confront these issues in a manner that satisfies principles from statistical mechanics for complex systems. Instead, ecological theory is traditionally based on premises from simpler statistical mechanical theory for memory‐free, scale‐specific, random‐walk, and diffusion processes, while animals from many taxa generally express strategic homing, site fidelity, and conspecific attraction in direct violation of primary model assumptions. Thus, the main challenge is to generalize the theory for memory‐free physical, many‐body systems to include a more realistic memory‐influenced framework that better satisfies ecological realism. We describe, simulate, and discuss three testable aspects of a model for multiscaled habitat use at the individual level: (1) scale‐free distribution of movement steps under influence of self‐reinforcing site fidelity, (2) fractal spatial dispersion of intra–home range relocations, and (3) nonasymptotic expansion of observed intra–home range patch use with increasing set of relocations. Examples of literature data apparently supporting the conjecture that multiscaled, strategic space use is widespread among many animal taxa are also described. We suggest that the present approach, which provides a protocol to test for influence from scale‐free, memory‐dependent habitat use at the individual level, may also point toward a guideline for development of a generalized theoretical framework for complex population kinetics and spatiotemporal population dynamics.

The Home Range Ghost

The area (A) covering a sample of non-autocorrelated animal relocations (n) is generally thought to increase asymptotically towards a true home range size with increasing sample size. This should be the case for any home range with a stable centre, whether applying a minimum convex polygon, box counting or some more sophisticated method for area demarcation. We show by simulation that the rate of increase of A is expected to decrease significantly from one m-fold increase of n to the next m-fold increase, for n as low as 100-200 relocations. For larger n the rate of increase of A is expected to be close to zero for last m-fold increase of a subsample of n. This central null hypothesis in ecology is not supported by an extensive, and assumed representative, sample of (n,A) literature data. Even after adjusting for small-n expected underestimates of A, A increases approximately in proportion with the square root of n. Literature examples are given where no area asymptote appeared in sample sizes passing thousands of relocations. The results support an alternative model for home range area use, the multiscaled home range model (MHR).

The diet of the brown bear Ursus arctos in the Pasvik Valley, northeastern Norway

The seasonal composition of and the annual variation in the diet of the brown bear Ursus arctos in the Pasvik Valley, northeastern Norway, were estimated based on the analysis of 137 bear scats. The importance of moose Alces alces and reindeer Rangifer tarandus in the diet was given special attention, because results from Russia suggest that brown bears are generally more carnivorous in the north. Ungulates, especially adult moose, comprised the most important food item for bears in the Pasvik Valley during spring and summer, contributing 85 and 70% of the Estimated Dietary Energy Content (EDEC), respectively. During autumn, when the bears have to build up fat reserves and increase lean body mass for hibernation, berries were the most important food item, contributing 49% of the EDEC, but ungulates were still important, contributing 30% of the EDEC. Insects and vegetation were of low importance in all seasons. The proportion of ungulates in the diet of brown bears in the Pasvik Valley was considerably higher than farther south in Scandinavia, and this regional difference is important concerning bear and moose management in northern areas.

Physical and biological mechanisms in animal movement processes

We have analysed a large set of animal locations from a telemetry study of a herd of domestic sheep, Ovis aries, in order to test an alternative model for area-utilization functions. Our model incorporates the special effects emerging from complex movement patterns, which have made the traditional home range demarcation protocols so difficult to employ. The telemetry location plots approached a statistically self-similar fractal pattern with dimension 1.5 as the overall plot density (n) increased. The home range area expanded on average as a function of n without any apparent asymptotic approach to a «true» home range area. The regression of log(area) versus log(n) was approximately linear, with slope 0.5 for samples of 10-1433 coordinate plots

Summer habitat use and activity patterns of domestic sheep on coniferous forest range in southern Norway.

Eight domestic sheep (r poorer forest types were used more in the evening and at night. As the season progressed, use of the meadow/old-field habitat type declined in favor of the forest types. Activity peaks were at mid-morning and late evening. Animals camped in groups at midday and at night, always further upslope at night than during the day. Sheep were less active in cold, wet weather. Habitat selection and activity patterns observed in this study were similar to those of both wild and domestic sheep studied elsewhere.

Mortality of lambs in free‐ranging domestic sheep (Ovis aries) in northern Norway

Domestic lamb mortality on an open forested and alpine summer range in the municipality of Malselv in northern Norway was investigated. Two hundred and fifty-three lambs in four of the areas six flocks were randomly fitted with mortality transmitters and monitored throughout the summer grazing season from June to September. Total losses in the six flocks were 183 (22.9%) lambs and 20 (4.2%) ewes. The carcasses of 69 lambs, 36 of which had radio-collars, and six ewes were recovered. Of the collared lambs, eight (22%) died as a result of disease and 27 (75%) were killed by predators. Implicated predators included red fox Vulpes vulpes, lynx Lynx lynx, golden eagle Aquila chrysaetos and wolverine Gulo gulo. Diseased animals included those diagnosed with pasteurellosis, disrupted intestinal functions and advanced coccidiosis. The remains of one lamb were too decomposed for necropsy, though there was no evidence that it had been attacked by a predator. Factors associated with losses were identified using logistic regression. Age of lamb at time of release on the summer range and age of dam were statistically associated with lamb losses (P<0.05). Mortality was higher among older lambs and those of year-old ewes. Parameters commonly associated with lamb size and growth were not statistically associated with mortality. The negative association between lamb mortality and age of dam may be related to the quality of maternal care provided by ewes of different ages, particularly vigilance in the habitat of predators. Similarly, the positive association between mortality and age of lamb may be related to changing lamb behaviour, specifically increased distance from ewe, as lambs grow older and more independent. Predators, when present, are a major cause of mortality in free-ranging lambs, as in most wild ungulates.

Extensive ranging by sheep released onto an unfamiliar range

Abstract During radio telemetry studies of domestic sheep on open, forested ranges in Hedmark County in southeastern Norway, several examples of extremely extensive ranging, either by individual sheep introduced into established herds or by herds turned onto unfamiliar ranges, have been recorded. Two such cases are described here. In one herd, two newly purchased Dala ewes strayed nearly 14 km from the herds normal grazing area. In another herd, comprising one main Dala herd and several individuals purchased from other smaller herds, 101 ewes and 152 lambs spread widely during the course of the summer, and eventually occupied an area of at least 150 km 2 . Efficient range use depends upon an animals familiarity with the range and its distribution of resources, and upon an animals social integration into the rest of the herd. This must be considered when attempting to increase herd size by combining sheep from different herds, and when changes in public policy seek to limit the use of traditional sheep ranges.

Status of the brown bear in Norway: Distribution and population 1978–1982

Abstract A century ago, brown bears Ursus arctos L. were common in forested regions throughout Norway, even on the larger islands. Between 1846 and 1850, they were killed in every county, and the steadily mounting pressure of hunting resulted in a drastic reduction of the population during the following years. Bears were given protection by law in Norway in 1973. The status of the population was ascertained through surveys made during 1978–1982. Bears are distributed across large parts of Norway, and the survey yielded 17 definable populations. The national total comprises approximately 160–230 individuals. The term population is used in cases where bears are established in an area. The main criterion for the confirmation of establishment was confirmed breeding during the period. Areas with scattered observations, where reproduction has not been verified, are said to comprise an occurrence . A minimum of 41 instances of confirmed reproduction were recorded, with at least 64 cubs from 13 different populations throughout the country. It is concluded that the population is slowly increasing, and there is no real case for regarding the bear as a threatened species in Norway. But as a result of its distinctive discontinuous distribution, it must still be recognised as vulnerable. The bear population is to some extent shared with Sweden, Finland and the USSR, and is partly dependent on the management and population development in these countries.

Molecular characterization and evaluation of plant litter-associated fungi from the spring ‘grazing corridor’ of a sheep herd vulnerable to alveld disease

This study sample and identify species of fungi on withered vegetation in the spring ‘grazing corridor’ from infields to Narthecium bogs for a sheep herd almost chronically vulnerable to phototoxic disease. Hepatogen photosensitizing disorders like alveld attack grazing sheep, especially lambs, in various parts of the world. It has been hypothesized that saponin metabolites in the monocotyledonous plant Nartheciumossifragum causes the disorder in Norway, however, this has not been verified. Thus, the search for other causal agents or saponin cofactors (the cofactor hypothesis) has been intensified, and endophytic poisonous fungi associated with dead N. ossifragum leaves and grasses are among the prime suspects. The fungal diversity was targeted by obtaining axenic cultures from surface-sterilized plant material, with subsequent DNA isolation, PCR, and sequencing of the ITS nrDNA region. The taxonomic affinities of the obtained sequences were thereafter explored by similarity searches against the public access sequence database EMBL/GenBank/DDBJ. Among the spectrum of identified taxa were representatives of Cladosporium, Fusarium, Penicillium, and Trichoderma, all of which are well known as potential producers of toxins. A possible involvement of these toxic species in the etiology of alveld is evaluated and discussed.