Erling Johan Solberg

A model-driven approach to quantify migration patterns: individual, regional and yearly differences

1.u2002Animal migration has long intrigued scientists and wildlife managers alike, yet migratory species face increasing challenges because of habitat fragmentation, climate change and over-exploitation. Central to the understanding migratory species is the objective discrimination between migratory and nonmigratory individuals in a given population, quantifying the timing, duration and distance of migration and the ability to predict migratory movements. 2.u2002Here, we propose a uniform statistical framework to (i) separate migration from other movement behaviours, (ii) quantify migration parameters without the need for arbitrary cut-off criteria and (iii) test predictability across individuals, time and space. 3.u2002We first validated our novel approach by simulating data based on established theoretical movement patterns. We then formulated the expected shapes of squared displacement patterns as nonlinear models for a suite of movement behaviours to test the ability of our method to distinguish between migratory movement and other movement types. 4.u2002We then tested our approached empirically using 108 wild Global Positioning System (GPS)-collared moose Alces alces in Scandinavia as a study system because they exhibit a wide range of movement behaviours, including resident, migrating and dispersing individuals, within the same population. Applying our approach showed that 87% and 67% of our Swedish and Norwegian subpopulations, respectively, can be classified as migratory. 5.u2002Using nonlinear mixed effects models for all migratory individuals we showed that the distance, timing and duration of migration differed between the sexes and between years, with additional individual differences accounting for a large part of the variation in the distance of migration but not in the timing or duration. Overall, the model explained most of the variation (92%) and also had high predictive power for the same individuals over time (69%) as well as between study populations (74%). 6.u2002The high predictive ability of the approach suggests that it can help increase our understanding of the drivers of migration and could provide key quantitative information for understanding and managing a broad range of migratory species.

CLIMATE CAUSES LARGE‐SCALE SPATIAL SYNCHRONY IN POPULATION FLUCTUATIONS OF A TEMPERATE HERBIVORE

Theoretical analyses have shown that the spatial scaling of environmental autocorrelation, strength of density regulation, and the dispersal of individuals determine the scaling of synchrony in population fluctuations. By modeling the separate effects of density regulation, environmental stochasticity, and demographic stochasticity, we estimate the spatial scaling of the component that is due to environmental stochasticity in the population dynamics of roe deer (Capreolus capreolus) in Norway. The estimated spatial scaling of the environmental noise was ∼200 km. An examination of how different weather variables influenced the scaling indicated that snow depth was the major weather variable affecting the scaling of synchrony in population fluctuations, and was negatively related to population growth rates in 97.4% of the 151 populations included in the study. A large-scale climatic phenomenon, the North Atlantic Oscillation, was positively related to population growth rates in 94.7% of the populations but ...

Annual variation in maternal age and calving date generate cohort effects in moose (Alces alces) body mass.

A general feature of the demography of large ungulates is that many demographic traits are dependent on female body mass at early ages. Thus, identifying the factors affecting body mass variation can give important mechanistic understanding of demographic processes. Here we relate individual variation in autumn and winter body mass of moose calves living at low density on an island in northern Norway to characteristics of their mother, and examine how these relationships are affected by annual variation in population density and climate. Body mass increased with increasing age of their mother, was lower for calves born late in the spring, decreased with litter size and was larger for males than for female calves. No residual effects of variation in density and climate were present after controlling for annual variation in mother age and calving date. The annual variation in adult female age structure and calving date explained a large part (71–75%) of the temporal variation in calf body mass. These results support the hypotheses that (a) body mass of moose calves are affected by qualities associated with mother age (e.g. body condition, calving date); and (b) populations living at low densities are partly buffered against temporal fluctuations in the environment.

Fluctuating Asymmetry in the Antlers of Moose (Alces alces): Does it Signal Male Quality?

We studied fluctuating asymmetry (fa) in the number of antler points from a total of 2126 moose (Alces alces) bulls killed during the hunting season in central Norway over a period of 23 years. All age groups showed a positive relation between fa and the number of antler points on the largest antler (antler size, AS). Based on the assumption that only the highest-quality individuals can produce the largest and most symmetrical sexual traits, the results did not support the hypothesis that FA in sexual traits signals the quality of the possessor. However, a partial correlation analysis revealed a negative relation between FA and carcass mass when controlling for AS. Thus relatively larger bulls in relation to their antler size produce more symmetrical antlers compared with relatively smaller bulls. Similarly, a regression analysis between fa and as in the different age groups revealed a significant age-dependent decrease in the regression coefficients. This suggests that older bulls are more able to cope with environmental stress during the development of the antlers than younger bulls. Thus, for a given antler size, the age of the bull can be signalled through the fa. We therefore suggest that quality signalling by antler size and FA could be an additional component of sexual selection on moose antlers.

Genetic discontinuities in a continuously distributed and highly mobile ungulate, the Norwegian moose

Many species with currently continuously distributed populations have histories of geographic range shifts and successive shifts between decline or fragmentation, growth and spatial expansion. The moose (Alces alces) colonised Scandinavia after the last ice age. Historic records document a high abundance and a wide distribution across Norway in the middle ages, but major decline and fragmentation in the eighteenth and nineteenth centuries. After growth and expansion during the twentieth century, the Norwegian population is currently abundant and continuously distributed. We examined the distribution of genetic variation, differentiation and admixture in Norwegian moose, using 15 microsatellites. We assessed whether admixture has homogenised the population or if there are any genetic structures or discontinuities that can be related to recent or ancient shifts in demography or distribution. The Bayesian clustering algorithm STRUCTURE without any spatial information showed that there is currently a genetic dichotomy dividing the population into one southern and one northern subpopulation. Including spatial information, the Bayesian clustering algorithm TESS, which considers gradients of genetic variation and spatial autocorrelation, suggests that the population is divided into three subpopulations along a latitudinal axis, the southern one identical to the one identified with STRUCTURE. Present convergence zones of high admixture separate the identified subpopulations, which are delimited by genetic discontinuities corresponding to geographic barriers against dispersal, e.g. wide fiords and mountain ranges. The distribution of the subpopulations is supported by spatial autocorrelation analysis. However, some loci are not in Hardy–Weinberg equilibrium and the STRUCTURE analysis suggests that a lower hierarchical structure may exist within the southernmost subpopulation. No bottlenecks or founder events are indicated by the levels of genetic variation, rather a high degree of private alleles in the northern subpopulations indicates introgression. Coalescent-based Approximate Bayesian Computation estimates unambiguously suggest that the genetic structure is a result of an ancient divergence event and a more recent admixture event a few centuries ago. This indicates that the central Scandinavian subpopulation constitutes a relatively recent convergence zone of secondary contact.

Plasma lactate concentrations in free-ranging moose (Alces alces) immobilized with etorphine

OBJECTIVEnTo investigate plasma lactate concentrations of etorphine-immobilized moose in relation to environmental, temporal and physiological parameters.nnnSTUDY DESIGNnProspective clinical study.nnnANIMALSnFourteen female and five male moose (Alces alces), estimated age range 1-7 years.nnnMETHODSnThe moose were darted from a helicopter with 7.5 mg etorphine per animal using projectile syringes and a dart gun. Once immobilized, the moose were approached, a venous blood sample was obtained and vital signs including pulse oximetry were recorded. Diprenorphine was administered to reverse the effects of etorphine. Timing of events, ambient temperature and snow depth were recorded. Blood samples were cooled and centrifuged before plasma was harvested and frozen. The plasma was thawed later and lactate analysed. Data were analysed using descriptive statistics and regression analysis.nnnRESULTSnAll animals recovered uneventfully and were alive 12 weeks after immobilization. Mean ± SD plasma lactate was found to be 9.2 ± 2.1 mmol L-1. Plasma lactate concentrations were related positively to snow depth and negatively to time from induction of immobilization to blood sampling. The model that best described the variability in plasma lactate concentrations used induction time (time from firing the dart to the moose being immobilized). The second best model included induction time and snow depth.nnnCONCLUSIONS AND CLINICAL RELEVANCEnPlasma lactate concentrations in these etorphine-immobilized moose were in the range reported for other immobilized wild ruminants. Decreasing induction time, which may be related to a more profound etorphine effect, and increasing snow depth possibly may increase plasma lactate concentrations in etorphine-immobilized moose.

Population properties affect inbreeding avoidance in moose

Mechanisms reducing inbreeding are thought to have evolved owing to fitness costs of breeding with close relatives. In small and isolated populations, or populations with skewed age- or sex distributions, mate choice becomes limited, and inbreeding avoidance mechanisms ineffective. We used a unique individual-based dataset on moose from a small island in Norway to assess whether inbreeding avoidance was related to population structure and size, expecting inbreeding avoidance to be greater in years with larger populations and even adult sex ratios. The probability that a potential mating event was realized was negatively related to the inbreeding coefficient of the potential offspring, with a stronger relationship in years with a higher proportion or number of males in the population. Thus, adult sex ratio and population size affect the degree of inbreeding avoidance. Consequently, conservation managers should aim for sex ratios that facilitate inbreeding avoidance, especially in small and isolated populations.

Fitness consequences of hybridization between house sparrows ( Passer domesticus ) and tree sparrows ( P. montanus )

Gene transfer may occur following hybridization between closely related species if hybrids are viable and able to breed with individuals of one or both of the parental species. House (Passer domesticus) and tree sparrows (P. montanus) occasionally hybridize and produce viable offspring. Previously, we concluded that male treexa0×xa0house sparrow hybrids are most probably fertile based on the observation of a male F1 hybrid feeding the nestlings with a female house sparrow in two consecutive clutches. However, recent DNA analyses based on blood samples revealed that all nestlings (4) in the first clutch were sired by a neighbouring house sparrow male, whereas nestlings in the second clutch (2) were not blood sampled and most probably died before fledging. This indicates that extensive extra-pair fertilization confounded our previous conclusion, and indicates that social partnership and attending behaviour can be imprecise measures of paternity.

Hybridisation between House SparrowPasser domesticus and Tree SparrowPasser montanus

Hybridisation between House and Tree Sparrows is reported from islands off the coast of Northern Norway, including observed mating attempts in two different mixed pairs, and the breeding success in a third mixed pair. The biometrics of hybrid offsprings were intermediate between the parents. The hybridisation probably involve only inexperienced individuals and may have been facilitated by the spatially division of the population into small island subpopulations. Auf Inseln vor der Küste Nordnorwegens gelangen Beobachtungen zur Hybridisation zwischen Haus- und Feldsperling; bei zwei Mischpaaren wurden Kopulationsversuche und bei einem dritten eine erfolgreiche Brut festgestellt. Die Merkmale der F1-Generation waren intermediär. Wahrscheinlich waren nur unerfahrene Vögel an den Mischpaaren beteiligt, die ihrerseits wohl durch die Bildung und räumliche Verteilung von kleinen Inselpopulationen begünstigt wurde.