Ambient temperature influences diet selection and physiology of an herbivorous mammal, Neotoma albigula

The whitethroat woodrat (Neotoma albigula) eats juniper (Juniperus monosperma), but the amount of juniper in its diet varies seasonally. We tested whether changes in juniper consumption are due to changes in ambient temperature and what the physiological consequences of consuming plant secondary compounds (PSCs) at different ambient temperatures might be. Woodrats were acclimated to either 20 degrees C or 28 degrees C. Later, they were given two diets to choose from (50% juniper and a nontoxic control) for 7 d. Food intake, resting metabolic rate (RMR), and body temperature (T(b)) were measured over the last 2 d. Woodrats at 28 degrees C ate significantly less juniper, both proportionally and absolutely, than woodrats at 20 degrees C. RMRs were higher for woodrats consuming juniper regardless of ambient temperature, and T(b) was higher for woodrats consuming juniper at 28 degrees C than for woodrats eating control diet at 28 degrees C. Thus, juniper consumption by N. albigula is influenced by ambient temperature. We conclude that juniper may influence thermoregulation in N. albigula in ways that are helpful at low temperatures but harmful at warmer temperatures in that juniper PSCs may be more toxic at warmer temperatures. The results suggest that increases in ambient temperature associated with climate change could significantly influence foraging behavior of mammalian herbivores.     

Ingestion of juniper foliage reduces metabolic rates in woodrat (Neotoma) herbivores

Ingestion of plant secondary compounds by herbivores is predicted to increase resting or basal metabolic rates. We tested this hypothesis with two species of woodrat herbivores, Neotoma stephensi and Neotoma albigula, consuming diets of juniper (Juniperus monosperma), which is rich in plant secondary compounds. In nature, N. stephensi specializes on juniper, whereas N. albigula consumes a variety of plant species including juniper. We measured resting metabolic rates (RMR) of woodrats on control, 25% juniper and a treatment containing the maximum tolerable dose of juniper (50% juniper for N. albigula and 70% juniper for N. stephensi). Ingestion of a juniper diet resulted in decreased RMR in both species of woodrats. We propose several potential mechanisms for metabolic depression of Neotoma on juniper diets. Our novel results underscore the need for more studies utilizing plant-based diets to determine the general effect of plant secondary compounds on metabolic rates of herbivores.     

Juniper fields in Sogn, Western Norway, a man-made vegetation type

Juniperus communis has been used e.g. as poles (posts), haysticks and wall-coating. In some districts it has even been an important export article. The fields of columnar juniper are the result of a long history of cultivation and grazing. In this article the main types of juniper fields in Sogn, Western Norway are presented, and their relationships to soil conditions and traditional use are discussed. According to structure, utilization and development four main types of juniper fields are recognized: I. Traditional juniper fields, II. Semi-cultural juniper fields, III. Secondary juniper fields and IV. Semi-natural juniper fields. Due to changes in agricultural methods, juniper fields are becoming rare.     

Intercanopy community structure across a heterogeneous landscape in a western juniper‐encroached ecosystem

Questions: How does landscape position influence biotic and abiotic attributes of western juniper (Juniperus occidentalis) encroached ecosystems? How does intercanopy plant community structure respond to changes in soil moisture and temperature based on juniper cover and topographic position? Location: Steens Mountain, southeast Oregon, USA. Objectives: Competition with western juniper modifies plant community composition, alters soil hydrology, and reduces plant productivity. Research is needed to understand these influences across heterogeneous landscapes. This study characterizes the relationship between juniper encroachment and soil water, soil temperature, topographic position, and intercanopy plant community structure. Methods: Using a completely randomized block design, plant density and cover, percent bare ground, percent soil moisture, soil temperature, heat accumulation, and elevation were sampled in 10 m² plots representing low (<1%), moderate (～14%), and high (～27%) juniper cover at four aspects. The relationship and difference between vegetation patterns and environmental variables were analyzed using AOV, NMS, and MRPP (α=0.1). Indicator species analysis tested for shifts in dominant species along ecological gradients. Results: Soil moisture remained higher in low juniper cover sites than moderate and high juniper cover sites. North‐facing sites had highest soil moisture at 5 cm depth with low and moderate juniper cover levels. With increasing soil temperature from May to June, soil moisture declined by 19.7% at 5 cm depth. Achnatherum lemmonii and Pseudoreogneria spicata occurred in closed juniper stands while Achnatherum occidentale and Leymus cinereus were common when encroachment was limited. Application: This approach can be used to predict ecosystem response to western juniper encroachment across heterogeneous landscapes.     

Woodrat (<Emphasis Type="Italic">Neotoma</Emphasis>) herbivores maintain nitrogen balance on a low-nitrogen,high-phenolic forage, <Emphasis Type="Italic">Juniperus monosperma</Emphasis>

The acquisition of adequate quantities of nitrogen is a challenge for herbivorous vertebrates because many plants are in low nitrogen and contain secondary metabolites that reduce nitrogen digestibility. To investigate whether herbivores maintain nitrogen balance on plant diets low in nitrogen and high in secondary compounds, we studied the effect of juniper (Juniperus monosperma) ingestion on the nitrogen balance of two species of herbivorous woodrats (Neotoma stephensi and N. albigula). These woodrat species feed on the foliage of juniper: N. stephensi is a juniper specialist, whereas N. albigula is a generalist that incorporates some juniper in its diet. Based on the nitrogen contents of the natural diets of these woodrats, we predicted that the generalist would be in negative nitrogen balance on a juniper diet whereas the specialist would not be affected. We found that both species of woodrat had low-nitrogen requirements (334.2 mg N/kg^0.75/day) and that a diet of 50% juniper did not result in negative nitrogen balance for either species. However, excretion patterns of nitrogen were altered; on the 50% juniper diet, fecal nitrogen losses increased ~38% and urinary nitrogen losses were half that of the control diet. The results suggest that absorption and detoxification of juniper secondary compounds may be more important for restricting juniper intake by the generalist than nitrogen imbalance.     

Evidence for mutualist limitation: the impacts of conspecific density on the mycorrhizal inoculum potential of woodland soils

The ability of seedlings to establish can depend on the availability of appropriate mycorrhizal fungal inoculum. The possibility that mycorrhizal mutualists limit the distribution of seedlings may depend on the prevalence of the plant hosts that form the same type of mycorrhizal association as the target seedling species and thus provide inoculum. We tested this hypothesis by measuring ectomycorrhizal (EM) fine root distribution and conducting an EM inoculum potential bioassay along a gradient of EM host density in a pinyon–juniper woodland where pinyon is the only EM fungal host while juniper and other plant species are hosts for arbuscular mycorrhizal (AM) fungi. We found that pinyon fine roots were significantly less abundant than juniper roots both in areas dominated aboveground by juniper and in areas where pinyon and juniper were co-dominant. Pinyon seedlings establishing in pinyon–juniper zones are thus more likely to encounter AM than EM fungi. Our bioassay confirmed this result. Pinyon seedlings were six times less likely to be colonized by EM fungi when grown in soil from juniper-dominated zones than in soil from either pinyon–juniper or pinyon zones. Levels of EM colonization were also reduced in seedlings grown in juniper-zone soil. Preliminary analyses indicate that EM community composition varied among sites. These results are important because recent droughts have caused massive mortality of mature pinyons resulting in a shift towards juniper-dominated stands. Lack of EM inoculum in these stands could reduce the ability of pinyon seedlings to re-colonize sites of high pinyon mortality, leading to long-term vegetation shifts.     

Intestinal absorption of hawthorn flavonoids--in vitro, in situ and in vivo correlations

Our previous studies identified hyperoside (HP), isoquercitrin (IQ) and epicatechin (EC) to be the major active flavonoid components of the hawthorn phenolic extract from hawthorn fruits demonstrating inhibitory effect on in vitro Cu(+2)-mediated low density lipoproteins oxidation. Among these three hawthorn flavonoids, EC was the only one detectable in plasma after the oral administration of hawthorn phenolic extract to rats. The present study aims to investigate the intestinal absorption mechanisms of these three hawthorn flavonoids by in vitro Caco-2 monolayer model, rat in situ intestinal perfusion model and in vivo pharmacokinetics studies in rats. In addition, in order to investigate the effect of the co-occurring components in hawthorn phenolic extract on the intestinal absorption of these three major hawthorn flavonoids, intestinal absorption transport profiles of HP, IQ and EC in forms of individual pure compound, mixture of pure compounds and hawthorn phenolic extract were studied and compared. The observations from in vitro Caco-2 monolayer model and in situ intestinal perfusion model indicated that all three studied hawthorn flavonoids have quite limited permeabilities. EC and IQ demonstrated more extensive metabolism in the rat in situ intestinal perfusion model and in vivo study than in Caco-2 monolayer model. Moreover, results from the Caco-2 monolayer model, rat in situ intestinal perfusion model as well as the in vivo pharmacokinetics studies in rats consistently showed that the co-occurring components in hawthorn phenolic extract might not have significant effect on the intestinal absorption of the three major hawthorn flavonoids studied.     

炒焦对山楂中氨基酸含量的影响分析

为探索炒焦对山楂中氨基酸的影响及山楂炒焦过程中氨基酸的变化,对炒焦前后山楂中氨基酸含量的变化进行了分析.测定结果显示,炒焦前后山楂中氨基酸的种类不变,各种氨基酸含量变化不一;方差分析显示炒焦前后氨基酸的含量变化不显著,炒焦对山楂中氨基酸的影响较小.由于山楂在炒焦过程具备发生美拉德反应的物质基础和客观条件,推测山楂中的氨...     

Behavioral evidence for host races in Rhagoletis pomonella flies

Summary One of the most controversial putative cases of host race formation in insects is that of the apple maggot fly, Rhagoletis pomonella (Diptera: Tephritidae). A principal cause of the controversy is lack of relevant data. In laboratory and field enclosure experiments, we compared the host acceptance behavior of sympatric populations of flies originating from naturally infested hawthorn (the native host) and apple (an introduced host) in Amherst, Massachusetts or East Lansing, Michigan. In general, hawthorn fruit were accepted for ovipositional attempts nearly equally by apple and hawthorn origin females, whereas apples were accepted much more often by apple than hawthorn origin females. Similarly, males of apple and hawthorn origin exhibited about equal duration of residence on hawthorn fruits as sites at which to acquire potential mates, while males of apple origin tended to reside substantially longer than males of hawthorn origin on apples. Irrespective of fly origin, both sexes always responded more positively to hawthorn fruit than to apples. Because all flies assayed were naive (ruling out effects of prior host experience of adults) and because tests revealed no influence of pre-imaginal fruit exposure on pattern of host fruit acceptance by females, the combined evidence suggests the phenotypic differences we observed in host response pattern between hawthorn and apple origin flies may have an underlying genetic basis. Further tests showed that while larval progeny of flies of each origin survived better in naturally growing hawthorn fruit than in naturally growing apples, there was no differential effect of fly origin on larval survival ability in either host. We discuss our findings in relation to restriction in gene flow between sympatric populations of R. pomonella and in relation to current models of host shifts in insects.     

Importance of juniper to birds nesting in piñon–juniper woodlands in northwest New Mexico

Piñon–juniper (Pinus spp.–Juniperus spp.) woodlands are common throughout western North America, yet relatively little is known about the habitat use and requirements for many members of its avian community. During summer 2005–2007, we assessed avian nesting substrates within piñon (Pinus edulis)–juniper (Juniperus osteosperma) woodlands in northwestern New Mexico. Of all nests in live trees, 86% were in junipers. The selection of juniper as a nest tree was significantly higher than expected from the region's piñon–juniper ratio (1:1.06) for the community as a whole, for both open cup and cavity nesting species, and for 8 species (of which 6 are piñon–juniper obligate or semi-obligate species). Nest survival, however, was not higher in juniper than in piñon for the nesting community as a whole or for chipping sparrows (Spizella passerina), the single species that was well represented nesting in piñon. The high use of juniper as a nesting substrate differs from previous studies, which have suggested that a presence of piñon is among the most important habitat features for many piñon–juniper species. Because of their importance to nesting birds, managers should avoid preferential thinning of junipers within piñon–juniper woodlands. © 2011 The Wildlife Society.     

Protective effect of olive and juniper leaves extracts on nephrotoxicity induced by thioacetamide in male mice

This study, for the first time, evaluates the effect of olive and juniper leaves extracts and their combination on thioacetamide (TAA)-induced nephrotoxicity in male mice. The experimental mice were divided into eight groups. Group 1 was served as control. Group 2 was exposed to TAA. Group 3 was treated with TAA and olive leaves extract. Group 4 was subjected to TAA and juniper leaves extract. Group 5 was exposed to TAA and olive and juniper leaves extracts. Groups 6, 7 and 8 were treated with olive, juniper, and olive and juniper leaves extracts respectively. In mice treated with only TAA, significant increases of blood urea nitrogen and uric acid were observed after six weeks. Moreover, levels of serum creatinine, blood urea nitrogen and uric acid were statistically increased in mice administrated with only TAA for twelve weeks. Insignificant alterations in levels of these haematobiochemical parameters were noted in other treated groups after six and twelve weeks. Histopathological evaluations of renal sections from mice treated with only TAA for twelve weeks showed severe damage of the renal corpuscles. Furthermore, the renal sections from mice treated with TAA and olive leaves extract, TAA and juniper leaves extract, TAA and olive and juniper leaves extracts, olive leaves extract, juniper leaves extract, and olive and juniper leaves extracts showed normal structures. In addition, it is conceivable therefore, that these extracts exhibit protective influences against TAA-induced nephrotoxicity, probably mediated through the antioxidative pathway roles.     

Consequence of salinity and excess boron on growth, evapotranspiration and ion uptake in date palm (Phoenix dactylifera L., cv. Medjool)

Patches of common juniper (Juniperus communis L.) shrubs potentially facilitate the formation of fertile islands in heath tundra ecosystems thereby influencing the long-term resilience of these ecosystems. Although the role of juniper in the formation of such ‘islands of fertility’ has been studied in semiarid landscapes, there has been little attention paid to the importance of juniper in other ecosystems. In this study we contrast the soil fertility and rates of N fixation under juniper shrubs with that in open heath tundra in northern Sweden. Plots were established at several individual sites in alpine heath tundra in Northern Sweden and mineral soils to a depth of 10 cm were characterized for available N and P and total C, N, P, Ca, Mg, K, Fe, Mn, Zn, and Cu. Nitrogen fixation rates were measured by acetylene reduction in feather mosses under juniper canopies and contrasted with N fixation in both feather mosses and surface soils in the open heath. Soils under juniper had concentrations of total P greatly in excess of P in open heath, furthermore, juniper islands had the highest concentrations of bioavailable P. Nitrogen fixation rates in the feather moss Pleurozium schreberi (Bird.) Mitt were approximately 150 μmol acetylene reduced m⁻² d⁻¹ under the juniper canopy compared to less than 10 μmol acetylene reduced m⁻² d⁻¹ in the open heath. Feather mosses under the juniper canopy also fixed N at a significantly higher rate (on an aerial basis) than that of surface cores from the open heath that included lichen, mosses, and soil crusts. Juniper facilitates the formation of islands of soil fertility that may in turn facilitate the growth of other plants and positively influence the long term recovery of heath tundra ecosystems following disturbance.     

Can the site conditions required for successful natural regeneration of juniper (Juniperus communis L.) be determined from a single species survey?

Background: Ecological surveys often aim to inform biodiversity conservation policy and practice. Survey types differ; all require clear aims and good design. A survey in Scotland was carried out to measure the distribution and health of juniper (Juniperus communis) and potential for its natural regeneration.

Aims: Explore if one-off national surveys can inform conservation action by examining, as an example, the Scottish juniper data set to: (1) determine site conditions favourable for juniper regeneration, (2) provide recommendations for site management for regeneration.

Methods: Associations between site conditions and juniper occurrence were investigated with principal component analysis (PCA) and using species distribution modelling (SDM). To identify changes in site conditions over time, we compared degree of site suitability for natural regeneration (PCA distance) and population age structure.

Results: Twenty-one per cent of the sites showed juniper regeneration. Compared to all juniper sites, conditions at regenerating sites were different (e.g. climatically wetter, lower site fertility). Change over time in conditions was suggested by patterns in population age structure.

Conclusions: Following the establishment of a juniper population, site conditions may change, becoming unsuitable for natural regeneration. Historical site information to confirm this is lacking. We cannot answer fundamental questions about the causal mechanisms of the natural regeneration of juniper and question whether one-off survey data can inform conservation management.     

不同生境和去趋势方法下的祁连圆柏径向生长对气候的响应

利用青海不同生境祁连圆柏树木年轮样本,采用3种不同去趋势方法建立树轮年表,结合青海30个气象站的气象资料,分析不同生境和去趋势方法下祁连圆柏径向生长对气候的响应差异。结果表明,祁连山区,生长季前期的平均气温是祁连圆柏树木径向生长的主要限制性因子,NEP树轮标准化宽度年表与生长季前期冬季平均气温相关最好;在柴达木盆地,生长季降水量是该地区树木径向生长的限制性因子,SPL树轮年表对生长季降水量相关较好;在青南高原,祁连圆柏径向生长对春季温度响应最为敏感,而SPL年表与春季温度呈现明显的负相关关系,相关系数达-0.606;而在青海东部地区,祁连圆柏树木径向生长对气候的响应总体不显著。位于青海西部和北部的柴达木盆地和祁连山区祁连圆柏径向生长受西风气候的影响显著,尤其是柴达木盆地,其气候受西风主导;而青南高原受西南季风影响更为显著,该地区祁连圆柏径向生长同时受西南季风气候和海拔高度两方面影响;在青海东部,祁连圆柏径向生长受东亚季风影响更为显著。     

Strategies in herbivory by mammals revisited: The role of liver metabolism in a juniper specialist (Neotoma stephensi) and a generalist (Neotoma albigula)

Although herbivory is widespread among mammals, few species have adopted a strategy of dietary specialization. Feeding on a single plant species often exposes herbivores to high doses of plant secondary metabolites (PSMs), which may exceed the animal's detoxification capacities. Theory predicts that specialists will have unique detoxification mechanisms to process high levels of dietary toxins. To evaluate this hypothesis, we compared liver microsomal metabolism of a juniper specialist, Neotoma stephensi (diet >85% juniper), to a generalist, N. albigula (diet ≤30% juniper). Specifically, we quantified the concentration of a key detoxification enzyme, cytochrome P450 2B (CYP2B) in liver microsomes, and the metabolism of α‐pinene, the most abundant terpene in the juniper species consumed by the specialist woodrat. In both species, a 30% juniper diet increased the total CYP2B concentration (2–3×) in microsomes and microsomal α‐pinene metabolism rates (4‐fold). In N. stephensi, higher levels of dietary juniper (60% and 100%) further induced CYP2B and increased metabolism rates of α‐pinene. Although no species‐specific differences in metabolism rates were observed at 30% dietary juniper, total microsomal CYP2B concentration was 1.7× higher in N. stephensi than in N. albigula (p < .01), suggesting N. stephensi produces one or more variant of CYP2B that is less efficient at processing α‐pinene. In N. stephensi, the rates of α‐pinene metabolism increased with dietary juniper and were positively correlated with CYP2B concentration. The ability of N. stephensi to elevate CYP2B concentration and rate of α‐pinene metabolism with increasing levels of juniper in the diet may facilitate juniper specialization in this species.     

Soil patchiness in juniper-sagebrush-grass communities of central Oregon

This study compared the sizes, spacings and properties (soil moisture, pH, nitrogen, soil arthropods and VAM) of soil resource islands and bare patches in sagebrush-grass communities invaded by western juniper versus those without juniper. We analyzed 1000 surface soil samples taken from nine 50-m radius circular plots sampled in December of 1991 and May of 1992 on ‘The Island’, one of the few undisturbed areas of sagebrush-grass shrubland in Oregon. Spatial structure was interpreted from correlograms (Moran's I) and standardized semivariograms. The presence of juniper was associated with increased bare area and smaller, more widely spaced grass and sagebrush plants. Soil arthropod numbers and biomass in plots with juniper were only roughly one-fifth of those in sagebrush-grass plots in December. The dominant soil pattern in both sagebrush-grass and juniper-sagebrush-grass plots was regularly-distributed patches spanning a range of sizes and spacings. Plots with juniper had greater patchiness at shorter lags (<3 m), and patchiness was more developed for soil moisture, net nitrification, and net N mineralization, whereas sagebrush-grass plots had greater patchiness at longer lags (3 – 9 m) and patchiness was more developed for NO₃–N, arthropod numbers and biomass. These differences in soil patterns with and without juniper indicate that juniper responds to, or causes, changes in the size of resource islands under sage and grass when it invades sage-grass communities. This revised version was published online in June 2006 with corrections to the Cover Date.     

To burn or not to burn: Comparing reintroducing fire with cutting an encroaching conifer for conservation of an imperiled shrub‐steppe

Woody vegetation has increased on rangelands worldwide for the past 100–200 years, often because of reduced fire frequency. However, there is a general aversion to reintroducing fire, and therefore, fire surrogates are often used in its place to reverse woody plant encroachment. Determining the conservation effectiveness of reintroducing fire compared with fire surrogates over different time scales is needed to improve conservation efforts. We evaluated the conservation effectiveness of reintroducing fire with a fire surrogate (cutting) applied over the last ~30 years to control juniper (Juniperus occidentalis Hook.) encroachment on 77 sagebrush‐steppe sites. Critical to conservation of this imperiled ecosystem is to limit juniper, not encourage exotic annual grasses, and promote sagebrush dominance of the overstory. Reintroducing fire was more effective than cutting at reducing juniper abundance and extending the period of time that juniper was not dominating the plant community. Sagebrush was reduced more with burning than cutting. Sagebrush, however, was predicted to be a substantial component of the overstory longer in burned than cut areas because of more effective juniper control. Variation in exotic annual grass cover was explained by environmental variables and perennial grass abundance, but not treatment, with annual grasses being problematic on hotter and drier sites with less perennial grass. This suggests that ecological memory varies along an environmental gradient. Reintroducing fire was more effective than cutting at conserving sagebrush‐steppe encroached by juniper over extended time frames; however, cutting was more effective for short‐term conservation. This suggests fire and fire surrogates both have critical roles in conservation of imperiled ecosystems.     

An Ecohydrological Cellular Automata Model Investigation of Juniper Tree Encroachment in a Western North American Landscape

Woody plant encroachment over the past 140 years has substantially changed grasslands in western North American. We studied encroachment of western juniper (Juniperus occidentalis var. occidentalis) into a previously mixed shrub–grassland site in central Oregon (USA) using a modified version of Cellular Automata Tree–Grass–Shrub Simulator (CATGraSS) ecohydrological model. We developed simple algorithms to simulate three encroachment factors (grazing, fire frequency reduction, and seed dispersal by herbivores) in CATGraSS. Local ecohydrological dynamics represented by the model were first evaluated using satellite-derived leaf area index and measured evapotranspiration data. Reconstructed pre-encroachment vegetation cover percentages and the National Land Cover Database (NLCD 2006) vegetation map were used to estimate parameters for encroachment factors to represent juniper encroachment in CATGraSS. Model sensitivity experiments examined the influence of each encroachment factor and their combinations on trajectories of modeled percent cover of each plant functional type and emergent spatial vegetation patterns in the modeled domain. Simulation results identified grazing as the key factor leading to juniper encroachment, by reducing shrub and grass cover and promoting the formation of juniper tree clusters. Reduced fire frequency and increased seed dispersal by grazers further amplified juniper encroachment into grassland patches between clusters of juniper trees. Each encroachment factor showed different consequences on modeled vegetation patterns. Time series of modeled plant cover and spatial patterns of plant functional types were found to be consistent with an existing conceptual model described in the literature. The proposed model provides a tool that can be used to improve our understanding of the drivers and processes of woody plant encroachment and vegetation response to global change.     

Epiphytic lichens on Juniperus communis – an unexplored component of biodiversity in threatened alvar grassland

Semi‐natural grasslands, among them thin‐soil calcareous grasslands (alvars), have great conservation value but have become increasingly rare in Europe. The main threat to alvar grasslands is the encroachment by juniper Juniperus communis and therefore it is usually removed during the restoration practice. Juniper can also be a host plant for many epiphytic lichens, but its role as a phorophyte is poorly known. We studied epiphytic lichen diversity on 126 junipers in 17 sites in western Estonia and found 140 lichenized taxa including several rare and red‐listed species. Using indirect and direct multivariate analyses (DCA, pCCA) and general linear models we revealed that both habitat and phorophyte properties affect lichen assemblies on juniper. Lichen species richness per site showed a unimodal relationship with compound factors of site productivity and juniper characteristics (stem circumference and juniper width). Lichen species richness per phorophyte was increasing with its size and with the proportion of dead branches, and was twice higher in plate alvars than in ryhk alvars. Also, the species composition in plate alvars differed from ryhk alvars by having 42 characteristic lichen species in plate alvars vs three indicators of ryhk alvars. The composition of lichens was significantly influenced by encroachment of alvars, e.g. by high juniper cover and shrub layer height, as well as by the proportion of dead branches and stem circumference of juniper. We conclude that the epiphytic lichen assemblies on junipers are threatened by grassland encroachment similarly to ground layer lichen assemblies. We suggest that some old and scencent junipers should be preserved during the restoration of alvar grasslands.     

Differential expression and activity of catechol-O-methyl transferase (COMT) in a generalist (Neotoma albigula) and juniper specialist (Neotoma stephensi) woodrat

Mammalian herbivores, particularly dietary specialists must have an efficient means to metabolize the high doses of plant secondary compounds they consume. We found previously that Neotoma stephensi, a juniper specialist, upregulated catechol-O-methyl transferase (COMT) mRNA almost seven fold in response to an ecologically relevant diet (70% juniper). To further investigate the relevance of this enzyme with respect to juniper metabolism, we compared the protein expression, activity and kinetics of the two forms of COMT, soluble (S-COMT) and membrane bound (MB-COMT), in the blood, kidneys and liver of N. stephensi on its natural juniper diet to that of N. stephensi fed an experimental diet of 70% juniper as well as a non-toxic control diet under laboratory conditions. In addition, we compared these results to that of Neotoma albigula, a generalist species, which consumes a diet of 25% juniper in the wild. The specialist consuming juniper under both field and laboratory conditions had increased S-COMT expression and activity in their livers and kidneys, and increased S-COMT activity in their blood compared to the specialist and generalist fed the control diet. The specialist showed expression and activity of S-COMT in their kidneys that was as high as or higher than that in their livers. The generalist had an elevated V_max for MB-COMT compared to the specialist that resulted in higher activity for MB-COMT than the specialist despite lower expression of MB-COMT in the generalist's livers and kidneys. This high activity MB-COMT may be in part responsible for differences in the behaviors of the generalist compared to the specialist. We conclude that S-COMT is important in the specialist's ability to consume high levels of juniper.