Pikas (Ochotona princeps : Lagomorpha) as allogenic engineers in an alpine ecosystem

Pikas (Ochotona princeps: Lagomorpha) build caches of vegetation (“haypiles”), which serve as a food source during winter in alpine and subalpine habitats. Haypiles appear to degrade over time and form patches of nutrient-rich soils in barren talus and scree areas. We sampled soils underneath and next to haypiles, and plants growing on and near haypiles in an alpine cirque in northwestern Wyoming, USA, to determine the effects of pika food caches on N, C, and C/N ratios in soils and plants. We found that (1) haypile soils had significantly higher carbon and nitrogen levels and lower C/N ratios than both adjacent soils and soils in the general study area, (2) two of three plant species tested (Polemonium viscosum and Oxyria digyna) had significantly higher levels of tissue percent N when growing on haypile soils, and (3) total standing plant biomass at the study site increased with soil percent N suggesting that vegetation was nitrogen limited. Pikas may therefore function as allogenic ecosystem engineers by modulating nutrient availability to plants. Received: 5 July 1997 / Accepted: 30 November 1997     

Syntaxonomy and chorology of the Vaccinium myrtillus communities in the Monti Reatini (Central Italy)

Abstract

The present paper details the results of a phytosociological study on Vaccinium myrtillus communities in the Monti Reatini (Central Apennines). A comparison is reported with Vaccinium communities from the rest of the Italian peninsula (already described), showing the coenological and syntaxonomical autonomy of the Monti Reatini types. The Authors include the Monti Reatini shrublands with V. myrtillus and Juniperus nana in the Pino-Juniperetea class and secondary vegetation forms dynamically linked to them in two new Poo violaceae-Nardetum subassociations: Poo violaceae-Nardetum brachypodietosum rupestris and Poo violaceae-Nardetum caricetosum kitaibelianae.     

An example of the seasonal impact of sheep on colonisation by deciduous trees

Summary

Seasonal grazing treatments were begun in 1990 on two sites of bilberry moorland that lay 60–200 m from a strip of riverside woodland in Northern England. Treatments were summer grazing, winter grazing, year-round and no grazing, fences being moved in mid April and mid October each year to open or close plots. The main plant species, Calluna vulgaris, Empetrum nigrum and Vaccinium myrtillus, showed negligible response in cover or height to season of grazing, but colonisation by deciduous trees was much affected. On plots given summer protection (total area 2000 m²) 249 Sorbus aucuparia saplings were counted in 2000, together with one Quercus robur sapling, but no saplings were found in summer-grazed and year-round-grazed plots. Each winter the rowan saplings in the summer-protected plots were severely browsed by sheep, but they recovered in the next growing season. Their increasing trunk diameter and shoot increment up to 2000 suggested that some would soon escape herbivore control. But the fence moves did not take place in 2001,and in April 2002 these saplings were found to have been very heavily browsed. Nearly all survived but regrowth was much poorer in summer 2002 than summer 2000, so several more years of recovery are needed before it can be decided if summer protection from grazing allows succession to woodland at these sites.     

Positive interactions between leafrollers and other arthropods enhance biodiversity on hybrid cottonwoods

We examined the potential of a common herbivore to indirectly influence other diverse community members by providing habitat. Larvae of the leafroller Anacampsis niveopulvella commonly construct shelters by rolling leaves of cottonwood trees. These leaf rolls are later colonized by other arthropods. We first documented 4 times greater species richness and 7 times greater abundance on cottonwood shoots that contained a rolled leaf compared to adjacent shoots without leaf rolls. Second, with both removal and addition experiments, we showed that leaf rolls are responsible for these differences in arthropod assemblages. Leaf roll removal caused a 5-fold decline in richness and a 7-fold decline in abundance; leaf roll addition resulted in a 2.5-fold increase in richness and a 6-fold increase in abundance. Third, to determine whether rolled leaves are colonized for food or for shelter, we compared colonization of natural and artificial leaf rolls. Both richness and abundance were approximately 2-fold greater in artificial leaf rolls, indicating that leaf rolls are colonized primarily for shelter. Fourth, in a natural hybrid zone we found that leafroller densities were 2-fold greater on backcross hybrids than on F₁ hybrids. These differences are likely associated with genetically-based differences in leaf morphology and/or leaf chemistry. Ultimately, plant genotype affects positive indirect interactions that have the potential to affect community structure. This study and others demonstrate that shelter builders (i.e., leafrollers and gall formers) enhance biodiversity, while free-feeders are more likely to negatively affect biodiversity. Received: 19 April 1999 / Accepted: 8 November 1999     

A trophic cascade in a macrophyte-based food web at the land–water ecotone

Trophic cascades may purportedly be more common in aquatic than terrestrial food webs, but herbivory on freshwater vascular plants has historically been considered low. Water lilies are an exception, suffering severe grazing damage by leaf beetles. To test whether a central prediction of cascade models—that predator effects propagate downwards to plants—operates in a macrophyte-based food web, we experimentally manipulated predation pressure on a key herbivore of water lilies in the littoral zone of a lake in Michigan, USA. Field experiments comprised combinations of caging treatments to alter the number of predators (larvae of the ladybird beetle Coleomegilla maculata) that hunt the grazers of the macrophytes (larvae of the leaf beetles Galerucella nymphaeae) on the leaves of the water lily Nuphar advena. Predatory larvae of the ladybird beetles significantly reduced grazing damage to water-lily leaves by 35–43%. The predators reduced plant damage chiefly via density-mediated effects, when lower densities of grazers translated to significant declines in plant damage. Plant damage caused by the surviving herbivores was less than predicted from individual grazing rates under predator-free conditions. This suggests that trait-mediated effects may possibly also operate in this cascade. The observed strong effect of predators on a non-adjacent trophic level concurs with an essential component of the trophic cascade model, and the cascade occurred at the ecotone between aquatic and terrestrial habitats: Nuphar is an aquatic macrophyte with emergent and floating leaves, whereas both beetle species are semi-terrestrial and use the dry, emergent and floating leaves of the water lily as habitat. Also, the cascade is underpinned by freshwater macrophytes—a group for which trophic processes have often been underappreciated in the past.     

The interaction of gap age and microsite for herb layer species in a near‐natural spruce forest

Question: To what degree does the regeneration of understorey forest species depend on gaps of different age and on gap‐induced and non‐gap‐induced microsites? Do species preferences for a specific microsite change with the developmental stage of the gap? How do different species in the understorey interact over time? Location: Near‐natural spruce forest on Mt. Brocken in the Harz National Park, Germany. Methods: We established 90 study plots, stratified according to different gap age classes and undisturbed forest, and including subplots with three different gap‐induced types of microsites (logs, stumps and root plates) and two non‐gap‐induced microsites (moss‐covered rocks and ordinary forest ground). Results: Significant interactions of species were encountered with gap age as well as with microsite type, light availability and competition. While shoot densities of Vaccinium myrtillus were highest at intermediate gap age, Calamagrostis villosa and Trientalis europaea showed highest densities in the oldest gaps. The species preferred different microsites but had higher densities on non‐gap‐induced microsites, and their preferences changed over time. Unexpectedly, species shoot densities were not always negatively affected by densities of competing species. Conclusion: The results confirmed the importance of gaps for regeneration of forest herb layer species, but pointed to a much higher importance of microsites that were not induced by gaps compared to gap‐induced microsites. Niche differentiation between different herb layer species can be conceived as species‐specific preferences for microsite types that change with gap age, as a result of light conditions, degree of decay of logs and root plates and presence of competitors.     

Control of Molinia caerulea by cutting management on sub-alpine grassland

There has been a considerable expansion of Moliniacaerulea after the cessation of cutting management of Nardus stricta sub-alpine grasslands in the Giant Mts. (Krkonoše/Karkonosze/Riesengebirge, the Czech Republic) in the last 50 years. The aim of this study was to investigate whether the reestablishment of traditional management (one cut per year in late July) could reverse Molinia encroachment and help to restore the original Nardus grassland.     

Responses to defoliation of species-rich and monospecific tropical plant communities

Summary Floristically rich and monospecific tropical plant communities both responded to partial defoliation with increases in rates of production of new leaf area. Even after 50% of the leaf area had been removed three times, the leaf area increments were still higher in defoliated plots than in controls. Mean leaf area increment after defoliation, on a leaf area per unit ground area basis, was 905 cm² m^-2 d^-1 in diverse successional vegetation and 536 cm² m^-2 d^-1 in a cassava monoculture. Although defoliation stimulated leaf area development, on a per unit ground area basis, in both the cassava monoculture and the successional vegetation, the effect was more pronounced in the successional vegetation. On a per unit leaf area basis, leaf area increments following defoliation in both the diverse successional vegetation and the monoculture were approximately five times those of controls. The diverse plant community continued to respond vigorously after repeated defoliation, while the amount of stimulation of leaf are development in the monoculture declined. Because of their ability to respond even after repeated defoliation, diverse communities may in the long term be more homeostatic with respect to leaf area than are monocultures. The enhanced responsiveness of the species-rich community was due to changes in plant species abundance and very rapid leaf area development by some species.     

Extracts of bilberry (Vaccinium myrtillus L.) fruits improve liver steatosis and injury in mice by preventing lipid accumulation and cell death

ABSTRACT

Bilberry has been reported to have anti-oxidant and anti-inflammatory properties. We studied the effect of bilberry (Vaccinium myrtillus L.) fruits extracts (BEs) on the pathogenesis caused by lipid accumulation in fatty liver and non-alcoholic steatohepatitis (NASH). 5 μg/ml of BEs was enough to suppress lipid accumulation in the fatty liver model of the mouse hepatic AML12 cells. BEs increased cell viability and anti-oxidant capacity, presumably by activating (phosphorylating) Akt/STAT3 and inducing MnSOD/catalase. BEs also significantly reduced Rubicon and induced p62/SQSTM1, possibly contributing to reduce cellular lipids (lipophagy). When the mice were fed supplemented with BEs (5% or 10%, w/w), hepatic steatosis, injury, and hypercholesterolemia/hyperglycemia were significantly improved. Furthermore, histological and cytokine studies indicated that BEs possibly suppress hepatic inflammation (hepatitis) and fibrosis. Therefore, BEs improved liver steatosis and injury, and potentially suppress fibrosis by suppressing inflammatory response, which therefore may prevent the progression of fatty liver to NASH.     

Winter herbivory by voles during a population peak: the relative importance of local factors and landscape pattern

1. We studied the relative role of local habitat variables and landscape pattern on vole–plant interactions in a system with grey-sided voles ( Clethrionomys rufocanus (Sund.)) and their favourite winter food plant, bilberry ( Vaccinium myrtillus L.). The study was conducted during a vole peak year (1992–93) in a tundra area in northern Norway.
2. Using Mantel statistics we were able to separate the direct effects of the spatial patterning of habitats and the indirect effects due to spatial aggregations of similar habitats.
3. Results indicate that knowledge about the explicit spatial patterning of patches does not improve our understanding of the system. Instead, two local factors, vegetation height and bilberry biomass, explained more than 50% of the variation in cutting intensity in winter (defined as the proportion of above-ground shoots cut). Increasing vegetation height increased, and increasing bilberry biomass decreased, the cutting intensity.
4. The conclusion that grey-sided voles are able to distribute themselves relative to habitat quality was also partially supported by our estimated over-winter persistence by voles in the various habitats. Vole persistence was uncorrelated with vegetation height, the important predictor of autumn vole density, but tended to correlate with the deviation from the relation between vegetation height and autumn vole density. This conforms to the expectations from the theory of ideal-free habitat distribution.
5. The cue for vole habitat choice, i.e. vegetation height, indicates that either predation or freezing risk is important for voles when selecting over-wintering habitat.     

Long-term exposure to enhanced ultraviolet-B radiation in the sub-arctic does not cause oxidative stress in Vaccinium myrtillus

The aim of this work was to assess whether or not oxidative stress had developed in a dwarf shrub bilberry ( Vaccinium myrtillus L.) under long-term exposure to enhanced levels of ultraviolet-B (u.v.-B) radiation. The bilberry plants were exposed to increased u.v.-B representing a 15% stratospheric ozone depletion for seven full growing seasons (1991–1997) at Abisko, Swedish Lapland (68°N). The oxidative stress was assessed on leaves and stems by analysing ascorbate and glutathione concentrations, and activities of the closely related enzymes ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2). The affects of autumnal leaf senescence and stem cold hardening on these variables were also considered. The results showed that the treatment caused scarcely any response in the studied variables, indicating that u.v.-B flux representing a 15% ozone depletion under clear sky conditions is not sufficient to cause oxidative stress in the bilberry. It is suggested that no strain was evoked since adaptation was possible under such u.v.-B increases. The studied variables did, however, respond significantly to leaf senescence and especially to stem cold hardening.