Geographical variation in body weight and sexual size-dimorphism of Norwegian moose (Alces alces)

Geographical variation in male carcass weight, and sexual dimorphism in size was studied in 19 populations of Norwegian moose ( Alces alces (L.)).
Significant age-specific variation in male carcass weight was found for all the populations studied up to the age of 4 1/2 years, but in some populations maximum weight was not reached until at least 5 1/2 years. Increase in the mean weight of females after the age of 2 1/2 years was not significant. Only a weak relationship existed between mean yearling and adult bull weights in a population. However, within both the southern (< 62°N) and northern (> 62°N) parts of the country, yearling carcass weight was a good predictor of adult bull weight in a region.
Adult bull weight in a region was best predicted from the increment in mean carcass weight observed between 1 1/2 and 3 1/2 years of age. Within a region, variation in age-specific carcass weight between cohorts of bulls from different years was also well predicted from annual variation in growth increment.
Those patterns reveal a sexual difference in strategy of body growth. The adult weight of females is probably strongly determined by the weight gained by the time of onset of reproduction. The males have available a longer period for growth in body weight. They are therefore able to compensate for low weights early in life by increased gain of weight in later years, that provide good conditions for growth.
Geographical variation in the degree of sexual dimorphism in size correlated only poorly with adult male size. We suggest that the sexual size-dimorphism is a result of reproductive constraints of the female, i.e. in populations living in poor conditions and having small body size, the onset of reproduction prevents further gain in body weight.     

Geographical variation of antler morphology of moose (Alces alces) in Russia

We attempt to identify geographical subdivisions within the range of moose according to antler size for a more correct trophy evaluation in the СIC system (The International Council for Game and Wildlife Conservation). Traditionally, this division coincides with subspecific division of trophy animal species. That is why we partially touch upon the problem of the geography of moose subspecies in Eurasia. Catalogs of hunters’ trophies that were available to us served as the research material (1,047 trophies in total). We were choosing the same measurements for moose antlers evaluated by different methods. They are overall spread, circumference of beam, width of palm, and number of tines. We applied multivariate statistic methods to the findings, enlarging the geographical division groups step by step. As a result, we suggest four geographical groups: European, Siberian, the north of the Far East, and the south of the Far East. In principle, this division corresponds to the subspecies: European (Alces alces alces L., 1758), east Siberian (A. a. pfizenmayeri Zukowsky, 1910), Chukotka or Kolyma (A. a. buturlini Chernyavski et. Zhelesnov, 1982), and Ussuri (А. а. cameloides Milne-Edwards, 1867). We consider it incorrect to draw the line between the European and Siberian groups along the river Yenisei. It is more correct to move it to the Urals.     

Geographical variation in the breeding cycles and recruitment of Patella spp.

The effect of geographical differences in breeding cycles on the recruitment variation of the limpets — Patella vulgata L., P. aspera Röding and (to a limited extent) P. depressa Pennant — has been studied over much of their range in Britain and NW. Europe. In spite of considerable annual and local variation in recruitment success, broader patterns can be distinguished, which can be linked to spawning times and factors affecting the survival of newly-settled spat. The breeding cycles of P. vulgata and P. aspera differ across their ranges in that, in both species, spawning begins, and gametogenesis ends, earlier in the north and east than in the south and west. The cause of these differences can be correlated with geographical and annual differences in sea temperature over the potential breeding periods, and can be related to the regional incidence of conditions found experimentally to be necessary for successful settlement and survival of spat during a critical stage of their growth. The significance of this temperature window in determining the littoral and geographical distribution of the species is discussed.     

Environmental variation and moose Alces alces density as determinants of spatio-temporal heterogeneity in browsing

Understanding temporal variation in habitat selection and browsing intensity by large herbivores is fundamental because of their large impact on the ecosystems. I studied the annual variation in winter browsing pressure on young trees and habitat selection by moose Alces alces over a ten year period. Specifically, the relationships between browsing pressure on Scots pine Pinus sylvestris and two birch species ( Betula ssp.) and three explanatory variables – 1) availability of forage, 2) moose density (estimated by pellet group counts) and 3) snow cover was studied. At a larger spatial scale (forest stand level) the relationship between moose habitat selection between three different habitat types (forest <30 yr, forest>30 yr and mire) and two explanatory variables, 1) snow condition and 2) moose density, were studied. Browsing pressure on Scots pine, the dominating food plant, was related to forage availability, moose density and snow condition. No significant relationships between any of the three explanatory variables and browsing pressure on the two birch species were found. Moose selection for certain habitats varied between years and was affected by number of days with >0.10 m of snow.
Habitat selection was not significantly related to moose density and the relationship between overall moose density and habitat specific moose densities was proportional within the studied density range. These findings have implications for understanding varying browsing patterns – and will affect both the ability to predict herbivores' effect on the forest ecosystem. A snow dependent browsing pattern also indicates that one can expect a long term decrease in browsing pressure on the tree and shrub layer as a consequence of the ongoing large-scale climate change.     

The influence of mean climate trends and climate variance on beaver survival and recruitment dynamics

Ecologists are increasingly aware of the importance of environmental variability in natural systems. Climate change is affecting both the mean and the variability in weather and, in particular, the effect of changes in variability is poorly understood. Organisms are subject to selection imposed by both the mean and the range of environmental variation experienced by their ancestors. Changes in the variability in a critical environmental factor may therefore have consequences for vital rates and population dynamics. Here, we examine ≥90‐year trends in different components of climate (precipitation mean and coefficient of variation (CV); temperature mean, seasonal amplitude and residual variance) and consider the effects of these components on survival and recruitment in a population of Eurasian beavers (n = 242) over 13 recent years. Within climatic data, no trends in precipitation were detected, but trends in all components of temperature were observed, with mean and residual variance increasing and seasonal amplitude decreasing over time. A higher survival rate was linked (in order of influence based on Akaike weights) to lower precipitation CV (kits, juveniles and dominant adults), lower residual variance of temperature (dominant adults) and lower mean precipitation (kits and juveniles). No significant effects were found on the survival of nondominant adults, although the sample size for this category was low. Greater recruitment was linked (in order of influence) to higher seasonal amplitude of temperature, lower mean precipitation, lower residual variance in temperature and higher precipitation CV. Both climate means and variance, thus proved significant to population dynamics; although, overall, components describing variance were more influential than those describing mean values. That environmental variation proves significant to a generalist, wide‐ranging species, at the slow end of the slow‐fast continuum of life histories, has broad implications for population regulation and the evolution of life histories.     

Geographical barriers and climate influence demographic history in narrowleaf cottonwoods

Studies of genetic variation can clarify the role of geography and spatio-temporal variation of climate in shaping demography, particularly in temperate zone tree species with large latitudinal ranges. Here, we examined genetic variation in narrowleaf cottonwood, Populus angustifolia, a dominant riparian tree. Using multi-locus surveys of polymorphism in 363 individuals across the species'' 1800 km latitudinal range, we found that, first, P. angustifolia has stronger neutral genetic structure than many forest trees (simple sequence repeat (SSR) F_ST=0.21), with major genetic groups corresponding to large apparent geographical barriers to gene flow. Second, using SSRs and putatively neutral sequenced loci, coalescent simulations indicated that populations diverged before the last glacial maximum (LGM), suggesting the presence of population structure before the LGM. Third, the LGM and subsequent warming appear to have had different influences on each of these distinct populations, with effective population size reduction in the southern extent of the range but major expansion in the north. These results are consistent with the hypothesis that climate and geographic barriers have jointly affected the demographic history of P. angustifolia, and point the importance of both factors as being instrumental in shaping genetic variation and structure in widespread forest trees.     

Geographical and latitudinal variation in growth patterns and adult body size of Swedish moose (Alces alces)

We examined the geographical pattern in growth and adult body size among 14 populations of Swedish moose (Alces alces) using data from 4,294 moose (1.5 years old) killed during the hunting season in 1989–1992. In both sexes, adult body mass was significantly positively correlated with latitude. Moose in northern populations had a 15–20% larger adult body mass than moose in the south. Juvenile body mass was correlated with neither latitude nor adult body mass. Thus, variation in time (years) and rate of body growth after the juvenile stage were responsible for most of the variation in adult body mass among populations. Moose in northern populations grew for approximately 2 more years of life than southern moose. In contrast to adult body mass, skeletal size (measured as jawbone length) was not correlated with latitude, suggesting that variation in adult body mass was primarily due to differences in fat reserves. Discrimination between population characteristics, such as moose density, climate, and the amount of browse available to moose, showed climatic harshness to be the most important variable explaining geographical variation in body mass among populations. The results support the notion that in mammals body size increases with latitude in accordance with Bergmann's rule. We conclude that (1) variation in patterns of growth after the juvenile stage is the main cause of the latitudinal trend in adult body size in moose, and (2) climatic conditions are a more important factor than population density and availability of food in explaining geographical variation in growth patterns and adult body mass between populations of Swedish moose.     

Intraspecific variation in the strength of density dependence in aphid populations

Abstract.  1. Experimental evidence is presented for positive, negative, and no density dependence from 32 independent density manipulations of milkweed aphids ( Aphis nerii ) in laboratory and field experiments. This substantial variation in intraspecific density dependence is associated with temperature and host-plant species.
2. It is reported that as population growth rate increases, density dependence becomes more strongly negative, suggesting that the monotonic definition of density dependence used in many common population models is appropriate for these aphids, and that population growth rate and carrying capacity are not directly proportional.
3. For populations that conform to these assumptions, population growth rate may be widely applicable as a predictor of the strength of density dependence.     

Elevational variation in density dependence in a subtropical forest

Density‐dependent mortality has been recognized as an important mechanism that underpins tree species diversity, especially in tropical forests. However, few studies have attempted to explore how density dependence varies with spatial scale and even fewer have attempted to identify why there is scale‐dependent differentiation. In this study, we explore the elevational variation in density dependence. Three 1‐ha permanent plots were established at low and high elevations in the Heishiding subtropical forest, southern China. Using data from 1200 1 m² seedling quadrats, comprising of 200 1 m² quadrats located in each 1‐ha plot, we examined the variation in density dependence between elevations using a generalized linear mixed model with crossed random effects. A greenhouse experiment also investigated the potential effects of the soil biota on density‐dependent differentiation. Our results demonstrated that density‐dependent seedling mortality can vary between elevations in subtropical forests. Species found at a lower elevation suffered stronger negative density dependence than those found at a higher elevation. The greenhouse experiment indicated that two species that commonly occur at both elevations suffered more from soilborne pathogens during seed germination and seedling growth when they grew at the lower elevation, which implied that soil pathogens may play a crucial role in density‐dependent spatial variation.     

Negative density dependence of seed dispersal and seedling recruitment in a Neotropical palm

Negative density dependence (NDD) of recruitment is pervasive in tropical tree species. We tested the hypotheses that seed dispersal is NDD, due to intraspecific competition for dispersers, and that this contributes to NDD of recruitment. We compared dispersal in the palm Attalea butyracea across a wide range of population density on Barro Colorado Island in Panama and assessed its consequences for seed distributions. We found that frugivore visitation, seed removal and dispersal distance all declined with population density of A. butyracea, demonstrating NDD of seed dispersal due to competition for dispersers. Furthermore, as population density increased, the distances of seeds from the nearest adult decreased, conspecific seed crowding increased and seedling recruitment success decreased, all patterns expected under poorer dispersal. Unexpectedly, however, our analyses showed that NDD of dispersal did not contribute substantially to these changes in the quality of the seed distribution; patterns with population density were dominated by effects due solely to increasing adult and seed density.     

Ecological drivers of guanaco recruitment: variable carrying capacity and density dependence

Ungulates living in predator-free reserves offer the opportunity to study the influence of food limitation on population dynamics without the potentially confounding effects of top-down regulation or livestock competition. We assessed the influence of relative forage availability and population density on guanaco recruitment in two predator-free reserves in eastern Patagonia, with contrasting scenarios of population density. We also explored the relative contribution of the observed recruitment to population growth using a deterministic linear model to test the assumption that the studied populations were closed units. The observed densities increased twice as fast as our theoretical populations, indicating that marked immigration has taken place during the recovery phase experienced by both populations, thus we rejected the closed-population assumption. Regarding the factors driving variation in recruitment, in the low- to medium-density setting, we found a positive linear relationship between recruitment and surrogates of annual primary production, whereas no density dependence was detected. In contrast, in the high-density scenario, both annual primary production and population density showed marked effects, indicating a positive relationship between recruitment and per capita food availability above a food-limitation threshold. Our results support the idea that environmental carrying capacity fluctuates in response to climatic variation, and that these fluctuations have relevant consequences for herbivore dynamics, such as amplifying density dependence in drier years. We conclude that including the coupling between environmental variability in resources and density dependence is crucial to model ungulate population dynamics; to overlook temporal changes in carrying capacity may even mask density dependence as well as other important processes.     

Winter climate, age, and population density affect the timing of conception in female moose (Alces alces)

Phenological events such as conception or parturition dates may have profound impact on several key life-history traits of ungulates at the individual as well as the population level. However, relatively little is known about the causes of variation in the timing of reproduction. Based on a 17-year survey of reproductive tracts, we investigated the effect of climate, population density, and age on the conception date of female moose (Alces alces) harvested in Estonia. Ninety-five percent of studied moose cows were conceived within a period of 9 weeks (29 August–30 October), while more than 45 % of all moose cows were conceived from 19 September to 2 October. Conception date was negatively related to population density and nonlinearly to the regional measure of winter climate reflecting the maximal extent of ice on the Baltic Sea (MIE) in the previous winter. High air temperatures during rut (in September) delayed the conception date. The timing of conception also depended on female age. Yearlings conceived significantly later as compared to females of all other age groups. Our findings corroborate the importance of density-dependent as well density-independent processes on the timing of conception of this ungulate. We also propose that the effect of population density on conception date may be mediated by increasing ecological carrying capacity concurrent with increasing population abundance.     

Patterns and causes of demographic variation in a harvested moose population: evidence for the effects of climate and density-dependent drivers

1.?Better understanding of the mechanisms affecting demographic variation in ungulate populations is needed to support sustainable management of harvested populations. While studies of moose Alces alces L. populations have previously explored temporal variation in demographic processes, managers responsible for populations that span large heterogeneous landscapes would benefit from an understanding of how demography varies across biogeographical gradients in climate and other population drivers. Evidence of thresholds in population response to manageable and un-manageable drivers could aid resource managers in identifying limits to the magnitude of sustainable change. 2.?Generalized additive models (GAMs) were used to evaluate the relative importance of population density, habitat abundance, summer and winter climatic conditions, primary production, and harvest intensity in explaining spatial variation in moose vital rates in Ontario, Canada. Tree regression was used to test for thresholds in the magnitudes of environmental predictor variables that significantly affected population vital rates. 3.?Moose population growth rate was negatively related to moose density and positively related to the abundance of mixed deciduous habitat abundant in forage. Calf recruitment was negatively related to a later start of the growing season and calf harvest. The ratio of bulls to cows was related to male harvest and hunter access, and thresholds were evident in predictor variables for all vital rate models. 4.?Findings indicate that the contributions of density-dependent and independent factors can vary depending on the scale of population process. The importance of density dependence and habitat supply to low-density ungulate populations was evident, and management strategies for ungulates may be improved by explicitly linking forest management and harvest. Findings emphasize the importance of considering summer climatic influences to ungulate populations, as recruitment in moose was more sensitive to the timing of vegetation green-up than winter severity. The efficacy of management decisions for harvested ungulates may require regional shifts in targets where populations span bioclimatic gradients. The use of GAMs in combination with recursive partitioning was demonstrated to be an informative analytical framework that captured nonlinear relationships common in natural processes and thresholds that are relevant to population management in diverse systems.     

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.     

Patterns of hunting mortality in Norwegian moose (Alces alces) populations

We used a simple life table approach to examine the age-specific patterns of harvest mortality in eight Norwegian moose populations during the last 15 years and tried to determine if the observed patterns were caused by hunter selectivity. The general opinion among local managers is that hunters prefer to shoot female moose not in company with calves to keep a high number of reproductive females in the population (and because of the emotional stress involved in leaving the calf/calves without a mother), and relatively large males because of the higher return with respect to meat and trophy. In support of the former view, we found the harvest mortality of adult females to be higher among pre-prime (1–3 years old) than prime-aged age classes (4–7 years old). This is probably because prime-aged females are more fecund and, therefore, more likely to be in company with one or two calves during the hunting season. As the season progressed, however, the selection pressure on barren females decreased, probably due to more productive females becoming ‘legal’ prey as their calf/calves were harvested. In males, we did not find any evidence of strong age-specific hunter selectivity, despite strong age-dependent variation in body mass and antler size. We suggest that this was due to the current strongly female-biased sex ratio in most Norwegian moose populations, which leaves the hunters with few opportunities to be selective within a relatively short and intensive hunting season. The management implications of these findings and to what extent the results are likely to affect the future evolution of life histories in Norwegian moose populations are discussed.Electronic Supplementary Material Supplementary material is available for this article at and accessible for authorised users.     

Impact of moose population density on the production and composition of litter in boreal forests

Recent studies of ungulates have revealed that selective foraging seems to be an important mechanism by which they can affect the structure and species composition of the plant community, and thus quantity (dry mass) and quality (chemical composition) of litter available for decomposers. Such changes in litter production may be especially important in N-limited systems like boreal forests. We chose moose ( Alces alces ) as study species to investigate this mechanism. Moose browse mainly in the tree and shrub layers year round, and because of their wide distribution and often high population densities, they can have a significant effect on litter production of trees and shrubs in Swedish boreal forests. The effects of herbivores may also vary along productivity gradients. We therefore simulated browsing and urine and fecal deposition corresponding to 4 different moose densities in exclosures along a pre-existing forest productivity gradient. Both litter quantity (g dry mass per m² and year) and contributions of C and N (g dry mass per m² and year) decreased with increasing level of simulated moose density. High moose densities over extended time can therefore reduce N contributions to soil and therefore eventually reduce site productivity in Swedish boreal forests. This effect of moose was mainly a result of decreased litter quantity, because contradictory to studies from North America, litter quality (C:N ratio and N contribution per mass unit of litter) was not affected by level of simulated moose density.     

Differing contributions of density dependence and climate to the population dynamics of three eruptive herbivores

1. Although both endogenous and exogenous processes regulate populations, the current understanding of the contributions from density dependence and climate to the population dynamics of eruptive herbivores remains limited. 2. Using a 17‐year time series of three cereal aphid species [Rhopalosiphum padi L., Metopolophium dirhodum (Walker), and Diuraphis noxia (Kurdumov)] compiled from a trapping network spanning the northwestern U.S.A., temporal and spatial patterns associated with population fluctuations, and modelled density dependence in aphid abundances were tested. These models were used to analyse correlations between climate and aphid abundances in the presence and absence of residual variance as a result of density‐dependent effects. 3. The temporal dynamics of aphid population fluctuations indicated periodicity, with no clear evidence for a spatial pattern underlying population fluctuations. 4. Aphid abundances oscillated in a manner consistent with delayed density dependence for all three aphid species, although the strength of these feedbacks differed among species. 5. Diuraphis noxia abundances were negatively correlated with increasing temperatures in the absence of density‐dependent effects, whereas M. dirhodum abundances were positively correlated with increasing cumulative precipitation in the presence of density‐dependent effects; yet, R. padi abundances were unrelated to climate variables irrespective of population feedbacks. 6. Our analysis suggests that endogenous feedbacks differentially regulate aphid populations in the northwestern U.S.A., and these feedbacks may operate at an expansive spatial scale. It is concluded that the contributions of density dependence and climate to aphid population dynamics are species‐specific in spite of similar ecological niches, with implications for assessing species responses to climate variability.