Effects of herbivory on competition intensity in two arctic-alpine tundra communities with different productivity

The effects of long-term (11 yr) exclusion of vertebrate herbivores on competition intensity and plant community structure were studied using manipulative field experiments in two arctic-alpine plant communities with contrasting productivity: an unproductive snowbed and a considerably more productive tall herb meadow. In the snowbed, the exclusion of herbivorous mammals resulted in a significant increase in the biomasses of vascular plants and cryptogams, whereas no corresponding response was observed on the tall herb meadow. The intensity of competition, measured with a neighbour removal experiment, did not differ significantly between three of the four habitat×treatment combinations – snowbed exclosures, meadow exclosures and open meadow plots – but was significantly lower on open snowbed plots. Our results thus suggest that the low competition intensity in the unproductive snowbed is caused by herbivorous mammals, which tend to depress plant biomass in relatively unproductive habitats. When herbivorous mammals have been excluded for a sufficiently long time to allow the build-up of plant biomass even in unproductive habitats, between-habitat differences in competition intensity disappear.     

Signal reliability compromised by genotype-by-environment interaction and potential mechanisms for its preservation

Sexual selection based on signaling requires that signals used by females in mate choice are reliable indicators of a male's heritable total fitness. A signal and the preference for it are expected to be heritable, resulting in the maintenance of genetic covariance between these two traits. However, a recent article has proposed that signals may quickly become unreliable in the presence of both environmental variation and genotype-by-environment interaction (G x E) with crossing reaction norms, potentially compromising the mechanisms of sexual selection. Here we examine the heritability and plasticity of a male dominance advertisement in the bank vole, Clethrionomys glareolus, in stable and changing rearing environments from father to son. The bank vole is naturally exposed to considerable sources of spatial and temporal environmental variation and male reproductive success is determined by both intra- (male-male competition) and inter- (females prefer to mate with dominant males) sexual selection. Significant G x E for male dominance was found with crossing reaction norms. Plasma testosterone level (T), rather than condition, determined a male's dominance and T also showed a significant G x E. Dominance showed a considerable plasticity across environments, but was only heritable under stable conditions. We document a negative between-environments correlation of male dominance, suggesting that when the environment changes between father and son, the dominance signal is unreliable to females and sexual selection may be compromised. We discuss how G x E and environmental variation interacting with other mechanisms may preserve the reliability of signals and thus the mechanism of sexual selection itself.     

The cost of reproduction induced by body size at birth and breeding density

Body size at birth has implications for the quality of individuals throughout their life. Although large body size is generally considered an advantage, the relationship between body size at birth and long-term fitness is often complicated. Under spatial or temporal variation in environmental conditions, such as the seasonally changing densities of Fennoscandian vole populations, selection should favor variation in offspring phenotypes, as different qualities may be beneficial in different conditions. We performed an experiment in which a novel hormonal manipulation method was used to increase phenotypic variance in body size at birth in the bank vole (Myodes glareolus). The effects of body size on the future fitness of young males and females were then studied at varying population densities in outdoor enclosures. Our results show that small body size at birth and high breeding density increase the survival costs of reproduction. However, there was no interaction between the effects of body size and density on survival, which suggests that the fitness effects of body size were strong enough to persist under environmental variation. Moreover, litter size and the probability of breeding were more sensitive to variation in breeding density than offspring size. Therefore, it is unlikely that individual fitness could be optimized by adjusting offspring body size to the prevailing population density through adaptive maternal effects. Our results highlight the significance of the costs of reproduction in the evolution of life-history traits, and give strong experimental support for the long-term fitness effects of body size at birth.     

Persisting chronic gastritis and elevated Helicobacter pylori antibodies after successful eradication therapy

AIM: The persistence of chronic inflammation in gastric mucosa and elevated Helicobacter pylori antibodies after successful eradication therapy are common findings in clinical practice. We studied their possible association with each other and disappearance in long-term follow up, as well as their possible connection with gastric atrophy. PATIENTS AND METHODS: The study population consisted of 108 dyspeptic patients with successful eradication therapy median 6.4 years earlier. The patients underwent gastroscopy, and biopsies from antrum and corpus were evaluated by an experienced pathologist. Serum samples collected from 77 patients were studied for H. pylori antibodies, parietal cell antibodies, as well as for pepsinogen I, pepsinogen II, and gastrin-17 levels. RESULTS: The prevalence of chronic gastric inflammation and elevated H. pylori antibodies after successful eradication therapy decreased by time, but still after 5 years, 17 of 51 (33%) subjects had elevated H. pylori antibodies and 14 of 68 (21%) had a mild inactive chronic inflammation in gastric mucosa. In patients with and without chronic inflammation in gastric mucosa, elevated H. pylori antibodies were detected in three of 10 (30%) and 14 of 41 (34%), elevated parietal cell antibodies in one of 10 (10%) and six of 41 (15%), low pepsinogen I in one of 10 (10%) and none of 41, and elevated gastrin-17 in three of 10 (30%) and six of 41 (15%), respectively. CONCLUSION: More than 5 years after successful H. pylori eradication therapy, mild persistent chronic inflammation may occur in gastric mucosa in up to one-fifth and elevated H. pylori antibodies even in one-third of patients, although these two are independent phenomena.     

Herbivore Effects on Ecosystem Process Rates in a Low-Productive System

Ecosystems - Mammalian herbivores shape the structure and function of many nutrient-limited or low-productive terrestrial ecosystems through modification of plant communities and plant–soil...     

Colonization of a host tree by herbivorous insects under a changing climate

Climate warming has been predicted to increase the abundance of herbivorous insects. Together with concurrent poleward shifts in many insect species this may increase herbivore pressure on plants. However, the manner in which plants at higher latitudes become colonized by herbivorous insects in the future is unknown. We established a translocation experiment using 26 micropropagated silver birch Betula pendula genotypes from six populations originating from 60°N to 67°N, to study the susceptibility of the translocated birches to local herbivores. The birches were planted at three different latitudes in Finland (60°N, 62°N and 67°N). We studied the effect of source population and latitudinal translocation on herbivore density, species richness, and community composition among the genotypes growing in the same environmental conditions in two years; 2011 and 2012. The source population explained the variation in the herbivore density only in 2012, whereas latitudinal translocation did not affect herbivore density. Variation in species richness was not explained by the source population or by the latitudinal translocation. At two of the study sites, the similarity of the herbivore communities among the populations decreased with increasing latitudinal distance of the source populations, possibly because birch populations that grow geographically closer to each other are genetically more similar, and therefore support a more similar composition of the arthropod community. All birch genotypes were colonized by local herbivores, suggesting that as herbivores shift their ranges polewards, they are able to colonize novel host‐plant genotypes. This enables compositional changes in insect communities on their host plants in the future, which in turn, might affect total herbivory and eventually, plant growth.     

Spatial variation in vegetation damage relative to primary productivity,small rodent abundance and predation

The relative importance of top‐down and bottom‐up mechanisms in shaping community structure is still a highly controversial topic in ecology. Predatory top‐down control of herbivores is thought to relax herbivore impact on the vegetation through trophic cascades. However, trophic cascades may be weak in terrestrial systems as the complexity of food webs makes responses harder to predict. Alternatively, top‐down control prevails, but the top‐level (predator or herbivore) changes according to productivity levels. Here we show how spatial variation in the occurrence of herbivores (lemmings and voles) and their predators (mustelids and foxes) relates with grazing damage in landscapes with different net primary productivity, generating two and three trophic level communities, during the 2007 rodent peak in northern Norway. Lemmings were most abundant on the unproductive high‐altitude tundra, where few predators were present and the impact of herbivores on vegetation was strong. Voles were most common on a productive, south facing slope, where numerous predators were present, and the impacts of herbivores on vegetation were weak. The impact of herbivores on the vegetation was strong only when predators were not present, and this cannot be explained by between‐habitat differences in the abundance of plant functional groups. We thus conclude that predators influence the plant community via a trophic cascade in a spatial pattern that support the exploitation ecosystems hypothesis. The responses to grazing also differed between plant functional groups, with implications for short and long‐term consequences for plant communities.     

Long-Term Experiments Reveal Strong Interactions Between Lemmings and Plants in the Fennoscandian Highland Tundra

Both the theory and the observations suggest that, there are strong links between herbivores and plants in terrestrial ecosystems; although, the effect of herbivores on plant community biomass is often attributed to variations in plant palatability. The existence of a strong link is commonly tested by constructing exclosures that exclude herbivores during a period of time. We here present data from two long-term (9 and 20 years, respectively) herbivore exclosure studies in lemming habitats on arctic tundra in northernmost Norway. The exclusion of all mammalian herbivores triggered strong increases in community level plant biomass and substantial changes in plant community composition. Palatable plants like graminoids and large bryophytes, as well as unpalatable plants like evergreen ericoids, deciduous shrubs, and lichens were all favored by excluding lemmings. These results reveal that a substantial increase in community biomass which occurs only when plant species capable of accumulating biomass are present, and palatability is a poor predictor of long-term responses of plants to excluding herbivores.     

Global network of specific virus-host interactions in hypersaline environments

Hypersaline environments are dominated by archaea and bacteria and are almost entirely devoid of eukaryotic organisms. In addition, hypersaline environments contain considerable numbers of viruses. Currently, there is only a limited amount of information about these haloviruses. The ones described in detail mostly resemble head-tail bacteriophages, whereas observations based on direct microscopy of the hypersaline environmental samples highlight the abundance of non-tailed virus-like particles. Here we studied nine spatially distant hypersaline environments for the isolation of new halophilic archaea (61 isolates), halophilic bacteria (24 isolates) and their viruses (49 isolates) using a culture-dependent approach. The obtained virus isolates approximately double the number of currently described archaeal viruses. The new isolates could be divided into three tailed and two non-tailed virus morphotypes, suggesting that both types of viruses are widely distributed and characteristic for haloarchaeal viruses. We determined the sensitivity of the hosts against all isolated viruses. It appeared that the host ranges of numerous viruses extend to hosts in distant locations, supporting the idea that there is a global exchange of microbes and their viruses. It suggests that hypersaline environments worldwide function like a single habitat.