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Omnivores exploit numerous sources of protein and other nutrients throughout the year, and meat is generally considered a high-quality resource. However, it is unknown if there is any general association between latitude and carnivorous behavior in omnivorous mammals. We examined the relative importance of meat and other dietary components, including anthropogenic food items, in the diet of brown bears (Ursus arctos) in Estonia using conventional scat- and stomach-content analyses as well as stable-isotope (δ15N, δ13C) analyses. When food habits of brown bears in Estonia were compared with those of other populations in central and northern Europe, the proportion of animal prey in the diet was positively correlated with latitude. Further comparison with the data on the diet of two other omnivorous mammals, the European badger (Meles meles) and the European pine marten (Martes martes), provides evidence that increased carnivory towards northern latitudes may be a general adaptation in omnivorous mammals.
Managers are sometimes faced with a situation where one endangered species increases the vulnerability of another one. According to our late-winter helicopter survey of Finland's two small populations of wild-forest reindeer (Rangifer tarandus fennicus), the eastern one decreased by half during the last 7 years. This is probably due to the return of the wolf (Canis lupus) to the area. Our data show that the annual recruitment rate of reindeer is strongly correlated with wolf density. Calf mortality was high and stable during the first months after birth. The wolf is classified as an endangered species in Finland. Thereby, our study area provides an example of a triggered situation in which a locally abundant, endangered predator increases the vulnerability of a threatened prey. There are basically two policy options for avoiding extinction: (1) to directly control the predation risk or (2) to reach further out into the ecosystem to control those factors that have led to high abundance of predators. One potential direct management action is increased wolf control in the primary summer home ranges of female reindeer. In the long term, wolf predation on wild-forest reindeer would decline if the abundance of moose (Alces alces) could be lowered, because high moose density supports high abundance of wolves. Another noteworthy option is the reintroduction of reindeer into regions where the wolf still exists at low densities.
Division of labour is a major feature of insect societies. Behavioural differences can be present also during non-colonial stages of the life cycle, when it is difficult to discriminate between distinct behavioural phenotypes and by-products of differences in overall activity levels. We used the social wasp Polistes dominulus to address this issue. In pre-hibernating aggregations some individuals (helpers) perform external tasks by collecting food and providing it to cluster mates. Such helpers have been so far identified using only a descriptive approach, and their behaviour was not disentangled from a possible higher level of overall activity. Here we provide an operational definition of the helper's trait and we then compare behavioural patterns of helpers and non helpers, verifying that helpers actually represent a peculiar behavioural phenotype. Our result expands knowledge on the caste differentiation issue in Polistes wasps and on the assessment of behavioural phenotypes in a non-colonial context.
We examined whether the body size of mound building wood ant Formica aquilonia workers is affected by forest clear-cutting in a before-after logging field study. Clear-cutting is expected to decrease the availability of tree-living aphids, the main food resource of wood ants. Worker size decreased from one year to the next in clear-cuts but not in forest stands, indicating food limitation in the clear-cuts. Worker size increased with nest size in forest interiors, but not in clear-cuts, which further indicates food limitation in the clear-cuts. In addition, lower body-fat contents in ant workers in the clear-cuts supports previous suggestions of lower food resources after forest logging. Nests were cooler in the clear-cuts, which suggest that they may be poor habitats for forest-dwelling wood ants. Food resource limitation may have an effect on the ability of wood ants to regulate nest temperatures.
There are now a growing number of studies linking environmental conditions operating at different life stages of birds to their arrival on breeding grounds. Here we focus on one of the major fitness determinants; timing of breeding. We examined the influence of climate relevant to different parts of the birds' annual life cycle, and the impact of population size on distribution traits in a central European population of the red-backed shrike Lanius collurio. Timing of breeding was affected by breeding ground climate as well as by population size. In years with higher population densities shrikes started to breed earlier. In contrast to previous studies we did not find that our climatic variables adequately explained the variability of timing of breeding. We argue that density-dependent processes are also important for the reproduction of shrikes and that in phenological studies; attention should also be paid to other factors operating at breeding grounds.
The objective of this study is to investigate whether presence/absence models can be used as surrogates of arthropod abundance, and eventually under which circumstances such surrogacy is guaranteed. Presence/absence data for 48 arthropod species from Terceira Island were modelled using artificial neural networks. Probabilities of occurrence were correlated with abundance data from a standardized arthropod survey programme. Although a tendency was found for vagile species to show relationships, only nine species showed significant positive correlations between probability of presence and abundance. Five of these were exotic spider species with high abundances and wide distributions in several human-modified habitats. The patchy distribution of pristine habitats, the capacity to reach them and the probable low dependence on limiting resources, other than food, enhance the relationship. A lack of significant correlations for the majority of the species may be due to historical events, inappropriate scale, demographic controls of density, or the incapacity of presence/absence models to account for environmental suitability. The difficulty to identify a priori the species for which the relationship will hold advises against the use of species distribution models as surrogates of arthropod abundance.
We investigated the response of predatory spiders, carabids, staphylinids and heteropteran bugs to the age of wildflower areas at twenty 1- to 4-year-old wildflower sites and in wheat fields. Density, biomass and species richness of spiders, carabids and bugs increased with the age of wildflower sites, and were higher at older wildflower sites than in the wheat fields. In contrast, staphylinid density decreased significantly with the age of wildflower sites. Canonical correspondence analysis explained 42.4% and 46.7% of the total variance of spider and carabid assemblages, respectively. Spider and carabid assemblages were best explained by vegetation cover. Mean individual weights of spiders, carabids and staphylinids increased significantly with the age of wildflower sites. The positive response of these three groups of beneficials is of practical relevance because many farmers currently remove wildflower areas after two to three years of establishment. Thus, older stages of succession increase the numbers of most beneficials studied.