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Vole grazing may be a step-function, with a critical threshold density, at which voles expand their preferred diet to lower quality forage (threshold herbivory hypothesis). Accordingly, we predicted that the establishment of unpalatable woody plants would be more strongly associated with peak herbivore abundances than with cumulative herbivory at lower numbers. We also investigated whether damage level is better explained by actual vole numbers or by numbers adjusted to the carrying capacity of the herbaceous vegetation. Our results did not support the threshold-density hypothesis. Cumulative herbivory explained the probability of sapling damage better than peak herbivory; sapling survival and growth were equally well explained by mean- and peak-vole abundances. Even at low abundances, herbivory was extended to all woody species; the damage level, however, varied according to the palatability of the woody species. Actual herbivore numbers explained sapling damage better than did abundance adjusted to carrying capacity.
Diet reconstruction using mesowear analysis has mainly been applied to extinct species and their paleoenvironments. Little is known regarding the effects of dietary differences on sympatric environments using this analysis and the limited existing knowledge from extant species may introduce errors when applied to fossil assemblages. I aimed to determine the sensitivity of mesowear analysis using extant ungulates with known diets. An interspecific comparison was conducted using wild populations of Japanese serow (Capricornis crispus, n = 37) and sika deer (Cervus nippon, n = 55) living in deciduous broad-leaved forest of the Nikko National Park, central Japan. One of the mesowear variables differed significantly between the two species (Fisher's exact test: p < 0.05). According to hierarchical cluster and principal component analyses, Japanese serow were classified as browsers, while sika deer as mixed feeders. Previous studies support these results; therefore, mesowear analysis can be used to detect dietary differences in sympatric species.
In low-productivity, high-altitude habitats food can become a limiting factor for the occurring amphibians. Common frog eggs deposited in ponds and the developing tadpoles represent energy-rich prey for syntopic Alpine newts that should be advantageous for storing sufficient amounts of energy to survive hibernation and breed the following spring. In our study population in the Zillertal Alps, Austria at 2100 m a.s.l., in two consecutive years we found the body mass of Alpine newts to be significantly higher in ponds containing tadpoles of the common frog than in ponds without tadpoles. As the frogs forage mostly on land, we regard their eggs as an allochtonous nutrient subsidy for ultra-oligotrophic high-altitude ponds that may have a profound effect on the fitness and distribution of Alpine newts and common frogs.
Scavengers can improve their foraging possibilities by associating with predators that provide food. Therefore, the presence of grey wolves (Canis lupus) may increase scavenging opportunities for wolverines (Gulo gulo). There have been many observations of wolverines utilizing wolf-killed moose (Alces alces), but quantitative information is lacking. We analysed wolverine and wolf habitat selection in eastern Finland, where the two species are sympatric. Generalized linear mixed-effect models were constructed to explain the location of wolverines in terms of their distance from settlements, the forest type and the presence of wolves. We found that wolverines favoured wolf presence, coniferous forests, mixed forests and mires; and avoided settlements, young forests and deciduous forests. These findings improve our understanding of wolverine habitat selection by demonstrating the importance of remote forest areas, as well as the presence of other carnivore species, to wolverines in boreal forests in Finland.
Populations should adapt to the climate at their respective localities. Here, we examined differences in thermal biology between two populations of Podarcis hispanica lizards from areas with different climates. Lizards from the cold, northern mountains attained lower field body temperatures than lizards form the warm, southern plains. However, the larger body size and darker coloration of northern lizards resulted in slower cooling rates, which may increase efficiency of thermoregulation. Northern populations selected higher temperatures in a thermal gradient, possibly as an adaptation to heat up before conditions changed, as their mountain environment is unpredictable. Finally, lizards from both populations had similar temperature-dependent locomotor performance curves, although southern lizards were relatively faster considering their smaller body size. We suggest that environmental differences may lead to differences in morphology and locally adapted thermal biology in lizards that might allow maximizing thermoregulation in each local climatic conditions.
Chemical cues released into the environment from injured prey animals provide a rich source of information about ambient risk. However, these cues could also provide information not associated with predation risk. Here we exposed wood-frog tadpoles (Lithobates sylvaticus) to a control diet and one that was soaked in chemical cues released from injured conspecifics, and documented growth and development of the tadpoles. If animals perceive repeated exposure to injured conspecific cues as indicating a high risk environment, then we predict that tadpoles would reduce foraging, prolonging time to metamorphosis, reducing growth rate and initiating adaptive changes in tail morphology. Conversely, if tadpoles interpret repeated exposure to these chemical cues as an indicator of competitor density, they should increase growth rate and body size to become better competitors. We found that tadpoles exposed to chemical cues exhibited significantly larger body width and body length relative to the control. These patterns are inconsistent with a response to risk but correspond with observed responses of wood-frog tadpoles to increased competition.