Male weasels decrease activity and energy expenditure in response to high ambient temperatures.

The heat dissipation limit (HDL) hypothesis suggests that the capacity of endotherms to dissipate body heat may impose constraints on their energy expenditure. Specifically, this hypothesis predicts that endotherms should avoid the detrimental consequences of hyperthermia by lowering their energy expenditure and reducing their activity in response to high ambient temperatures (T(a)). We used an extensive data set on the daily energy expenditure (DEE, n = 27) and the daily activity time (AT, n = 48) of male weasels (Mustela nivalis) during the spring and summer breeding season to test these predictions. We found that T(a) was related in a "hump-shaped" (i.e. convex) manner to AT, DEE, resting metabolic rate (RMR) and metabolic scope (the ratio of DEE to RMR). These results support the HDL hypothesis because in response to warm Tas male weasels reduced their AT, DEE, and RMR. Although the activity and energy expenditure of large endotherms are most likely to be constrained in response to warm Tas because they are less able to dissipate heat, our results suggest that small endotherms may also experience constraints consistent with the HDL hypothesis

Appendix S3

Raw data for the model depicted in Figure

Data from: Plant-herbivore interactions: silicon concentration in tussock sedges and population dynamics of root voles

1.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. 2.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. 3.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 one-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. 4.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. 5.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. 6. 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

Data from: Plant-herbivore interactions: silicon concentration in tussock sedges and population dynamics of root voles

1. 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. 2. 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. 3. 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 one-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. 4. 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. 5. 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. 6. 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

Data from: Lower body mass and higher metabolic rate enhance winter survival in root voles, Microtus oeconomus

Although the biological significance of individual variation in physiological traits is widely recognized, studies of their association with fitness in wild populations are surprisingly scarce. We investigated the effect of individual phenotypic variation in body mass, resting (RMR) and peak metabolic rates (PMR) on mortality of the root vole Microtus oeconomus. Body mass and metabolic rates varied significantly among consecutive years and were also age dependent, as individuals born in late summer and autumn were characterized by significantly lower body mass and metabolic rates than animals born earlier. At the beginning of winter voles born in spring and early summer exhibited reduced body mass and metabolic rates, whereas animals born later maintained lower body mass and RMR, which may be interpreted as phenotypic plasticity enhancing the probability of survival. Body mass had no significant effect on vole survival during summer. In contrast, smaller individuals were characterized by lower mortality during early winter, whereas higher body mass was positively associated with survival later in the season. High body-mass-corrected RMR positively affected survival in both summer and winter. The effect of PMR was apparent only during winter, though its direction (and correlation with RMR) varied among years. Deep snow cover negatively affected the survival of voles in both early and late winter. Ambient temperature was positively associated with winter survival, except for late winter, when rising temperature caused flooding of vole habitat. We conclude that the lack of consistency in the directionality and strength of the effects of body mass and metabolic rates on winter survival does not undermine their importance, but rather demonstrates the ability of individuals to adjust metabolic rate to changing environmental conditions

Data from: Plant-herbivore interactions: silicon concentration in tussock sedges and population dynamics of root voles

1. 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. 2. 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. 3. 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 one-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. 4. 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. 5. 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. 6. 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

Microsatelite data of weasels, Bialowieza Forest, Poland

Microsatelites data and mean phenotypic data (body mass and RMR) for weasels Mustela nivalis captured in Bialowieza Forest, Poland