Karol Zub

KILL RATES AND PREDATION BY WOLVES ON UNGULATE POPULATIONS IN BIAŁOWIEŻA PRIMEVAL FOREST (POLAND)

Wolf (Canis lupus) kill rates, factors affecting their variation, and predation impact on ungulates were studied in the Polish part of Biaowieza Primeval Forest (580 km 2 ). With the mean size of hunting groups being 4.4 individuals, wolves killed, on average, 0.513 6 0.04 prey·(pack) 21 ·d 21 (mean 6 1 SE); 63% of prey were red deer (Cervus elaphus), 28% were wild boar (Sus scrofa), and 4% were roe deer (Capreolus capreolus). Per capita kill rate averaged 0.116 ungulates·(wolf) 21 ·d 21 , and daily food intake was 5.58 6 0.32 kg·(wolf) 21 ·d 21 . Kill rate on red deer was affected by snow cover (P , 0.001). A pack of wolves killed, on average, 0.264 deer/d in seasons with no snow and 0.587 deer/d when snow was 17 cm deep. The increase in kill rates coincided with a decline in the condition of juvenile (but not adult) deer in late winter (mean marrow fat content in the femur 66% in October-January vs. 27% in February-March). Per capita kill rates decreased slightly (not significantly) with the increasing size of wolf hunting group. However, the amount of food acquired per wolf did not differ among groups containing 2-6 individuals, because larger packs killed bigger prey more often and small prey less frequently than did small packs. Wolf kill rates on wild boar were higher in spring-summer (0.242 6 0.06 boar·(pack) 21 ·d 21 ), when piglets were present, than in autumn-winter (0.106 6 0.04 boar·(pack) 21 ·d 21 ). Annually, wolves killed on average 72 red deer, 16 roe deer, and 31 wild boar over a 100-km 2 area. Compared to prey densities, wolves were an important agent of mortality for red deer only, taking annually 12% of spring-summer (seasonally highest) numbers of deer, which was equivalent to 40% of deer annual increase due to breeding and 40% of their annual mortality. Compared to winter densities (3-6 deer/km 2 ), percentage predation by wolves was inversely density dependent; thus wolves limited deer numbers but did not regulate prey population. By eliminating a substantial proportion of the annual production of the deer population, wolves hamper its growth and prolong the time until it reaches carrying capacity of the habitat. However, wolf predation alone is a poor predictor of deer population dynamics, because deer are also subject to lynx (Lynx lynx) predation and hunting harvest.

Europe-Wide Dampening of Population Cycles in Keystone Herbivores

Cycling in Unison Many small mammals, especially voles, display semi-regular cycles of population boom and bust. Given the fundamental importance of small mammals as basal consumers and prey, such cycles can have cascading effects in trophic food webs. Cornulier et al. (p. 63) collated raw data from vole populations across Europe collected over the past 18 years. Reduction in winter growth rate was common across a wide variety of habitats with very different local climates, suggesting the presence of a continental-scale climatic driver of vole populations. Synchronicity in vole population fluctuation across Europe suggests a common climatic driver. Suggestions of collapse in small herbivore cycles since the 1980s have raised concerns about the loss of essential ecosystem functions. Whether such phenomena are general and result from extrinsic environmental changes or from intrinsic process stochasticity is currently unknown. Using a large compilation of time series of vole abundances, we demonstrate consistent cycle amplitude dampening associated with a reduction in winter population growth, although regulatory processes responsible for cyclicity have not been lost. The underlying syndrome of change throughout Europe and grass-eating vole species suggests a common climatic driver. Increasing intervals of low-amplitude small herbivore population fluctuations are expected in the future, and these may have cascading impacts on trophic webs across ecosystems.

PREY SELECTION AND PREDATION BY WOLVES IN BIAŁOWIEŻA PRIMEVAL FOREST, POLAND

Abstract Relationships of wolves (Canis lupus) and ungulates were studied in the Polish part of Białowieża Primeval Forest with high densities of prey. The number of wolves ranged from 7 to 19, and the number of packs ranged from 2 to 4. Average densities were 2.3 wolves/100 km2. Red deer (Cervus elaphus) was the main prey of wolves. Roe deer (Capreolus capreolus), wild boar (Sus scrofa), moose (Alces alces), and European bison (Bison bonasus) were hunted less than expected based on their abundance. Mean mass of ungulates killed by wolves was 55 kg. Prey were consumed quickly, with 57% of kills completely eaten on the 1st day after killing. Average killing rate by wolves was 0.78 ungulate per wolf pack per day (0.14 prey item per wolf per day). Results of this study combined with the data obtained in the Belarussian part of Białowieża Primeval Forest in 1946–1985 allowed for analysis of dietary response of wolves to changes in densities of ungulates. Wolves showed a response to abundance of red deer. The amount of other ungulates in their diet depended on the densities of red deer. From 1991 to 1996, wolves annually removed 57–105 red deer, 19–38 wild boar, 19–25 roe deer, and 0–2 moose per 100 km2. Those amounts were equivalent to 9–13% of spring–summer densities of red deer, 4–8% of wild boar, 3–4% of roe deer, and 0–29% of moose. Additionally, hunters annually harvested 131–140 red deer, 44–114 roe deer, 1–7 moose, and 45–142 wild boar per 100 km2. Effects of predation and harvest by hunters on ungulate mortality were likely additive and caused declines in ungulate populations during our study.

Tawny Owl (Strix aluco) Predation in a Pristine Deciduous Forest (Bialowieza National Park, Poland)

1. Tawny owl Strix aluco predation on its main prey (bank voles Clethrionomys glareolus and yellow-necked mice Apodemus flavicollis) and alternative prey (shrews, birds, and amphibians) was studied in the pristine deciduous forests of eastern Poland during a 7-year period (1985/86-1991/92) that included 5 years of moderate densities of rodents and 2 years of outbreak and crash triggered by a heavy seed crop of oak, hornbeam, and maple. 2. Number of resident owls was rather stable; 45-53 owls per 10km 2 in years of moderate and high rodent numbers, and 33 owls per 10km 2 in a rodent crash year. Numerical response of owls to rodent densities was log shaped. 3. In the cold season, the dietary (functional) response of owls to autumn density of rodents was of type II (logarithmic). No functional response of owls was observed to shrew numbers. Owl hunting rate on amphibians in winter was shaped by the mean temperature of the cold season and, to a lesser extent, by availability of rodents. Owl hunting rate on birds was inversely related to rodent abundance. 4. During the seven cold seasons (1 October-15 April), tawny owls removed 3-19 mice, 2-18 voles, 2-7 shrews, 0-2 birds, and 1-9 frogs from an average hectare of the forest. Total predation on rodents (N prey removed ha -1 ) was lowest during the crash of rodents and highest during the outbreak; it grew logarithmically with increasing density of rodents. On average, in the cold season, tawny owls removed 54% of autumn numbers of mice and 40% of those of bank voles. Percentage predation peaked at 22 rodents ha -1 in autumn. At both higher and lower prey densities, percentage predation declined. 5. The percentage predation curve of tawny owl was compared to the frequency distribution of autumn densities of rodents in Bialowieza (from 23-year trapping). The heaviest predation fell to prey densities that occurred most frequently. 6. In summer seasons (July-September 1988-92), tawny owls (both adults and juveniles) consumed 0.5-19 mice and 0.4-10 voles from an average hectare. Percentage predation varied from 6% to 74% of rodent numbers recorded in July, but rodents bred rapidly and recruitment usually more than compensated for losses due to predation. 7. Total predation by tawny owls on rodents was quite stable as a consequence of high stability of owl numbers. Percentage predation, although heavy in all years except for rodent outbreak, was not density-dependent and therefore tawny owls did not regulate rodent numbers. In the deciduous forests of Bialowieza National Park, the pattern of predation by tawny owl, a resident generalist, did not differ from that by the weasel, a resident specialist.

Is there a linkage between metabolism and personality in small mammals? The root vole (Microtus oeconomus) example

Significant inter-individual variation in the rate of animal metabolism is a widespread phenomenon that has started to accumulate general interest. Here we follow recent calls to focus on linkage between the variation in energy metabolism and animal personality. By using wild caught root voles as a study species, we examined the relationship between the behavioral patterns (assessed in open field test) and resting metabolic rate (RMR), both of which are known to show large individual differences and intra-individual consistency in voles. Our results showed only a weak relationship between personality traits and metabolism, since the most parsimonious model (according to AICc) explaining RMR included only body mass and season as factors (explaining 84.8% of variation in RMR). However, the next two alternative models (within ΔAICc=2) also included the personality trait reflecting proactive behaviors (PC1) in addition to body mass, sex and season (85.2 and 85.8% of RMR variance explained, respectively). In all, our study does not provide compelling support for recent ideas of close linkage between behavior and metabolism. Still, our study highlights that even in the case of wild caught individuals, when behavior and metabolism often carry effects of both intrinsic and extrinsic conditions, the potential metabolic effects of varying energetically costly behaviors cannot be neglected.

Trade-offs between activity and thermoregulation in a small carnivore, the least weasel Mustela nivalis

We studied factors influencing daily energy expenditures (DEE) of male least weasels (Mustela nivalis) using the doubly labelled water technique. The relationship between ambient temperature and DEE formed a triangular pattern, characterized by invariance of the maximum DEE and an inverse relationship between minimum DEE and temperature. A simple energetic model relating the DEE of male weasels to activity time (AT) and ambient temperature predicted that, across seasons, less than 10 per cent of measurements approach the upper bound of observed DEE. Male weasels were able to maintain a relatively constant maximum energy output across varying temperatures by adjusting their AT to changes in temperature. They achieved maximum energy expenditures in winter due to high thermoregulatory costs, and in spring and summer due to high levels of physical activity. This pattern exemplifies a ‘metabolic niche’ of a small mammal having extremely high energy expenditures primarily driven by ambient temperature.

Phylogenetic analysis of mammalian maximal oxygen consumption during exercise

SUMMARY We compiled published values of mammalian maximum oxygen consumption during exercise () and supplemented these data with new measurements of for the largest rodent (capybara), 20 species of smaller-bodied rodents, two species of weasels and one small marsupial. Many of the new data were obtained with running-wheel respirometers instead of the treadmill systems used in most previous measurements of mammalian . We used both conventional and phylogenetically informed allometric regression models to analyze of 77 ‘species’ (including subspecies or separate populations within species) in relation to body size, phylogeny, diet and measurement method. Both body mass and allometrically mass-corrected showed highly significant phylogenetic signals (i.e. related species tended to resemble each other). The Akaike information criterion corrected for sample size was used to compare 27 candidate models predicting (all of which included body mass). In addition to mass, the two best-fitting models (cumulative Akaike weight=0.93) included dummy variables coding for three species previously shown to have high (pronghorn, horse and a bat), and incorporated a transformation of the phylogenetic branch lengths under an Ornstein–Uhlenbeck model of residual variation (thus indicating phylogenetic signal in the residuals). We found no statistical difference between wheel- and treadmill-elicited values, and diet had no predictive ability for . Averaged across all models, the allometric scaling exponent was 0.839, with 95% confidence limits of 0.795 and 0.883, which does not provide support for a scaling exponent of 0.67, 0.75 or unity.

Plant–herbivore interactions: silicon concentration in tussock sedges and population dynamics of root voles

Summary It has been hypothesized that the induction of silicon (Si)-based plant defence in response to herbivore damage may engender rodent population cycles. Many studies have also considered accumulation of Si as a process controlled by geo-hydrological factors. To test these ideas, we investigated the relationship between concentration of Si in fibrous tussock sedge (Carex appropinquata) and the population density of a major sedge consumer, the root vole (Microtus oeconomus), in field enclosures in natural habitat under a variety of natural water regimes and weather conditions. We found that a high density of voles at the end of summer resulted in the immediate accumulation of Si by rhizomes, followed by accumulation of Si in leaves with a 1-year lag time. The level of river flooding in the same year had an additional impact on Si concentration in rhizomes but did not affect silicification of leaves. Overwinter changes in concentration of Si in sedges were influenced by fluctuations in ambient temperature and the depth of snow cover (multiple freeze–thaw cycles), thus affecting the quality of winter food available for voles. Smaller voles had lower mortality during early winter than large voles, which seemed to be connected with changes in the quality of the autumn rather than the winter food base. Winter survival of voles was not associated with Si concentration in their faeces, however. Our results suggest that changes in Si concentration in fibrous tussock sedge can be induced by changes in vole population density and are also additionally affected by the amount of flooding and weather conditions.

Effect of energetic constraints on distribution and winter survival of weasel males.

1. The absolute energy needs of small animals are generally lower than those of larger animals. This should drive higher mortality of larger animals, when the environmental conditions deteriorate. However, demonstration of the effect of energy constraints on survivals proved difficult, because the range of body mass within species is generally too small to produce enough variation for studying such an effect. An opportunity for an intraspecific study comes from weasels inhabiting the Białowieża Forest (north-eastern Poland), which are characterized by a threefold variation in body mass. 2. We assumed that in summer larger weasel males are favoured by sexual selection, because they are more successful when competing for mates. We then tested whether they suffer higher mortality in winter, because they have difficulty finding sufficient food to satisfy their energy needs and/or because the additional foraging time would result in increased exposure to predation. 3. We measured daily energy expenditures (DEE) of overwintering weasel males using the doubly labelled water (DLW) technique. We constructed an energetic model predicting how individuals of different size are able to balance their energy budgets feeding on large and small prey while minimizing time spent hunting, thereby reducing their own exposure to predation. 4. The range of body mass in overwintering weasels predicted by our model corresponded very well with the distribution of prey body mass in three different habitats within our study area. Larger individuals were able to compensate for higher food requirements by using habitats with larger prey species than those available to smaller male weasels. This effectively offset the expected negative association between body mass and winter survival predicted from considerations of energy balance. 5. Our results show how energetic constraints affect body mass and spatial segregation of a species at the intra-specific level not only across large geographical ranges, but also within a relatively small area.

Environmental and genetic influences on body mass and resting metabolic rates (RMR) in a natural population of weasel Mustela nivalis

Body mass (BM) and resting metabolic rates (RMR) are two inexorably linked traits strongly related to mammalian life histories. Yet, there have been no studies attempting to estimate heritable variation and covariation of BM and RMR in natural populations. We used a marker‐based approach to construct a pedigree and then the ‘animal model’ to estimate narrow sense heritability (h2) of these traits in a free‐living population of weasels Mustela nivalis—a small carnivore characterised by a wide range of BM and extremely high RMR. The most important factors affecting BM of weasels were sex and habitat type, whereas RMR was significantly affected only by seasonal variation of this trait. All environmental factors had only small effect on estimates of additive genetic variance of both BM and RMR. The amount of additive genetic variance associated with BM and estimates of heritability were high and significant in males (h2 = 0.61), but low and not significant in females (h2 = 0.32), probably due to small sample size for the latter sex. The results from the two‐trait model revealed significant phenotypic (rP = 0.62) and genetic correlation (rA = 0.89) between BM and whole body RMR. The estimate of heritability of whole body RMR (0.54) and BM corrected RMR (0.45) were lower than estimates of heritability for BM. Both phenotypic and genetic correlations between BM corrected RMR and BM had negative signals (rP = −0.42 and rA = −0.58). Our results indicate that total energy expenditures of individuals can quickly evolve through concerted changes in BM and RMR.