Montane Sites Research Articles

Improving evapotranspiration estimates in Mediterranean drylands: The role of soil evaporation

[1] An adaptation of a simple model for evapotranspiration (E) estimations in drylands based on remotely sensed leaf area index and the Penman-Monteith equation (PML model) (Leuning et al., 2008) is presented. Three methods for improving the consideration of soil evaporation influence in total evapotranspiration estimates for these ecosystems are proposed. The original PML model considered evaporation as a constant fraction (f) of soil equilibrium evaporation. We propose an adaptation that considers f as a variable primarily related to soil water availability. In order to estimate daily f values, the first proposed method (fSWC) uses rescaled soil water content measurements, the second (fZhang) uses the ratio of 16 days antecedent precipitation and soil equilibrium evaporation, and the third (fdrying), includes a soil drying simulation factor for periods after a rainfall event. E estimates were validated using E measurements from eddy covariance systems located in two functionally different sparsely vegetated drylands sites: a littoral Mediterranean semiarid steppe and a dry-subhumid Mediterranean montane site. The method providing the best results in both areas was fdrying (mean absolute error of 0.17 mm day−1) which was capable of reproducing the pulse-behavior characteristic of soil evaporation in drylands strongly linked to water availability. This proposed model adaptation, fdrying, improved the PML model performance in sparsely vegetated drylands where a more accurate consideration of soil evaporation is necessary.

The first Leptanilloides species (Hymenoptera: Formicidae: Leptanilloidinae) from eastern South America

We describe a species of the exclusively Neotropical dorylomorph ant genus Leptanilloides (Leptanilloidinae), Leptanilloides atlantica sp. nov., based on workers collected in the Atlantic Forest, São Paulo, south-eastern Brazil. The 11 species of Leptanilloides described are known from relatively high altitudes in western America (from the Andes foothills in Bolivia to Sierra Morena in Mexico). The discovery of a Leptanilloides species in south-eastern Brazil represents a significant range extension for the genus; this new species shares characters with Leptanilloides biconstricta (Bolivia), Leptanilloides femoralis (Venezuela) and Leptanilloides gracilis (Mexico) and may be distinguished based on a combination of traits. The hypogaeic habits of Leptanilloidinae combined with inefficient collecting techniques may explain the paucity of information and of specimens of this group in most museum collections as well as its present apparent disjunct distribution. We compare Leptanilloides distribution to that of other organisms that show similar disjunct patterns in the Andes and montane sites in the Brazilian Atlantic Forest.http://www.zoobank.org/urn:lsid:zoobank.org:pub:E7E334AA-58C0-455D-A0A6-724D29226DD0

Effects of disturbance scale on soil microbial communities in the Western Cascades of Oregon

To gain a better understanding of how rapidly microbial communities respond to different magnitudes of perturbation that mimic minor or catastrophic disturbances. Two montane sites in the western Cascade Mountains of Oregon with adjacent areas of forest and meadow vegetation were studied. A reciprocal transplant experiment evaluated both minor (soil cores remaining in the same vegetation type) or more severe disturbance (soil cores transferred to a different vegetation type). The biomass and composition of the bacterial and fungal communities were measured for 2 years following the establishment of the experiment. Minor disturbance (coring) had little impact on microbial biomass but transferring between vegetation type showed greater fungal biomass in soil incubated in the forest environment. The composition of bacterial communities was not influenced by coring but responded strongly to transfers between vegetation sites, changing to reflect their new environment after 2 years. Fungal community composition responded somewhat to coring, probably from disrupting mycorrhizal fungal hyphae, but more strongly to being transferred to a new environment. The response of the microbial community to major disturbance was rapid, showing shifts reflective of their new environment within 2 years, suggesting that microbial communities have the capacity to quickly adjust to catastrophic disturbances.

Large carabid beetle declines in a United Kingdom monitoring network increases evidence for a widespread loss in insect biodiversity

SummaryCarabid beetles are important functional components of many terrestrial ecosystems. Here, we describe the first long‐term, wide‐scale and quantitative assessment of temporal changes inUKcarabid communities, to inform nationwide management aimed at their conservation.Multivariate and mixed models were used to assess temporal trends over a 15‐year period, across eleven sites in theUKEnvironmental Change Network. Sites covered pasture, field margins, chalk downland, woodland and hedgerows in the lowlands, moorland and pasture in the uplands, and grassland, heaths and bogs in montane locations.We found substantial overall declines in carabid biodiversity. Three‐quarters of the species studied declined, half of which were estimated to be undergoing population reductions of > 30%, when averaged over 10‐year periods. Declines of this magnitude are recognized to be of conservation concern. They are comparable to those reported for butterflies and moths and increase the evidence base showing that insects are undergoing serious and widespread biodiversity losses.Overall trends masked differences between regions and habitats. Carabid population declines (10‐year trend, averaged across species) were estimated to be 52% in montane sites, 31% in northern moorland sites and 28% in western pasture sites (with at least 80% of species declining in each case). Conversely, populations in our southern downland site had 10‐year increases of 48% on average. Overall, biodiversity was maintained in upland pasture, and populations were mostly stable in woodland and hedgerow sites.Synthesis and applications. Our results highlight the need to assess trends for carabids, and probably other widespread and ubiquitous taxa, across regions and habitats to fully understand losses in biodiversity. Land management should be underpinned by a consideration of how wide‐scale environmental drivers interact with habitat structure. The stability of population trends in woodlands and hedgerows of species that are declining elsewhere puts these habitats at the fore‐front of integrated landscape management aimed at preserving their ecosystem services.

Habitat characteristics, stage structure and reproduction of colline and montane populations of the threatened species Arnica montana

Arnica montana, a characteristic plant of nutrient-poor grasslands, has strongly declined during the last decades, particularly at lower altitudes. To gain insights into the underlying reasons for this decline, we recorded differences in size, stage structure and reproductive traits between 21 colline populations of A. montana in the Ardennes-Eifel region (280–600 m a.s.l.) and 10 montane populations in the Vosges Mountains (1,200 m a.s.l.). Community composition of the Violion caninae vegetation at colline sites and Nardion strictae vegetation at montane sites indicated that temperature and moisture were the main abiotic factors differentiating between low and high altitudinal relevees. The proportion of flowering rosettes decreased with altitude, indicating a shift from sexual reproduction to clonal growth. In contrast to expectation, Ellenberg values for nutrient availability as well as the proportion of young rosettes and population size did not differ between colline and montane populations. However, population size decreased with nutrient availability, indicating eutrophication as the reason for population decline. In small populations, plant density, the proportion of flowering rosettes, the number of flowerheads per rosette and the number of seeds per flowerhead were lower, indicating less suitable conditions. Thus, preventing further eutrophication in both colline and montane populations will be crucial for the conservation of the species. Reduced reproduction may not be important for the population dynamics of this clonal plant in the short term, but could affect genetic diversity and survival in the long term.

Diversity in nighttime transpiration behavior of woody species of the Atlantic Rain Forest, Brazil

Nighttime transpiration (NT) has been documented in many plant species but we do not yet have a thorough understanding of the abiotic and biotic controls of this phenomenon. In this study we examined interspecific variation in NT behaviors in plants with distinct crown exposures (CE) and occurring at lowland (100m) and montane forests (1000m) in the Brazilian Atlantic rainforest to answer the following questions: are there different NT behaviors in plants subjected to distinct conditions associated with degree of CE and/or altitude? Are there higher rates of NT relative to daily maximum values at the montane forest due to higher vapor pressure deficit (VPD)? Taking into account that low VPD should generally produce low relative NT fluxes, should we expect that understory species in both altitudes will have quite uniform low relative rates of NT in comparison to overstory species owing to the buffered nature of within-canopy microclimate? NT did show differences between altitude and species. Of most significance was a prominent non-linear relationship between the NT and VPD, observed at the montane site. This non-linearity is in contrast to most previously published NT kinetics and suggests stomatal and/or leaf energy balance controls on NT. Our findings raise a new perspective concerning thermodynamic contributions to non-linear NT kinetics and some possible reasons for this interesting behavior are discussed.

Altitude affects the reproductive performance in monoicous and dioicous bryophytes: examples from a Brazilian Atlantic rainforest.

Short life cycles and trade-offs linked to breeding systems make bryophytes good models for the study of plant reproductive strategies. Our aim was to test if differences in sexual reproductive performance of bryophytes in tropical rainforests are driven by the breeding system of the species (monoicous or dioicous) or are mainly affected by the habitat. The reproductive performance (sexual branches, gametangia (sex organs), fertilization and sporophyte production) of 11 species was repeatedly monitored and analysed from populations at sea-level and montane sites of a Brazilian Atlantic rainforest over 15 months. Monoicous species had the highest reproductive performance, particularly for sexual branches, fertilized gametangia and sporophyte production. Species at the sea-level site produced more sexual branches and had more female-biased sex ratios of gametangia than species in the montane site. Fertilizations were more frequent at the montane site, but sporophyte frequency was similar between the two sites. Fertilization tended to occur mostly in the periods of heavy rain (October to December). Breeding system is not the only major influence on the reproductive performance of bryophytes. We show that habitat is also an important factor determining life-history differentiation. Female-biased sex ratios and low rates of fertilization are seen to be compensated for by high production of reproductive structures at the initial phases of the reproductive cycle.

Fine root biomass and root length density in a lowland and a montane tropical rain forest, SP, Brazil

Fine roots, <2 mm in diameter, are responsible for water and nutrient uptake and therefore have a central role in carbon, nutrient and water cycling at the plant and ecosystem level. The root length density (RLD), fine root biomass (FRB) and vertical fine root distribution (VRD) in the soil profile have been used as good descriptors of resource-use efficiency and carbon storage in the soil. Along altitudinal gradients, decreases in temperature and radiation inputs (depending on the frequency of fog events) may reduce decomposition rates and nutrient availability what might stimulate plants to invest in fine roots, increasing acquisition of resources. We evaluated the seasonal variation of fine root parameters in a Lowland and Montane forest at the Atlantic Rain Forest. We hypothesized that, due to lower decomposition rates at the Montane site, the FRB and RLD at soil surface will be higher in this altitude, which can maximize the efficiency of resource absorption. FRB and RLD were higher in the Montane forest in both seasons, especially at the 0-5 layer. At the 0-5 soil layer in both sites, RLD increased from dry to wet season independently of variations in FRB. Total FRB in the top 30 cm of the soil at the Lowland site was significantly lower (334 g.m-2 in the dry season and 219 g.m-2 in the wet season) than at the Montane forest (875 and 451 g.m-2 in the dry and wet season, respectively). In conclusion, despite the relevance of FRB to describe processes related to carbon dynamics, the variation of RLD between seasons, independently of variations in FRB, indicates that RLD is a better descriptor for studies characterizing the potential of water and nutrient uptake at the Atlantic Rain Forest. The differences in RLD between altitudes within the context of resource use should be considered in studies about plant establishment, seedling growth and population dynamics at the Atlantic Rain Forest. At the ecosystem level, RLD and it seasonal variations may improve our understanding of the Atlantic rain forest functioning in terms of the biogeochemical fluxes in a possible scenario of climate change and environmental changes.

Small Mammal Inventories in the East and West Usambara and South Pare Mountains, Tanzania. 3. Chiroptera

Whereas the terrestrial mammal fauna of the East and West Usambara Mountains have been the subject of numerous investigations, the local bat fauna remains poorly documented, as is the case for bats of the South Pare Mountains. During mammal surveys of these three massifs, we used mist nets to collect local bats, documenting 20 bat species in total.In the Usambara Mountains, 161 individual bats representing 19 species were documented during the three years of the survey between 1991 and 1993. In the East and West Usambara Mountains, 17 and 12 species, respectively, were recorded. Most animals were taken in net sets placed outside or at the edge of forested habitats. In the South Pare Mountains, 67 bats representing six species were collected during the two surveys, including 62 bats of six species at 1100 m (surveyed 17–29 July 1993) and five bats representing three species at 2000 m (surveyed 19–28 August 2004). Based on our morphological studies, no evidence of undescribed taxa in these collections exists.Species common across all three massifs include two pteropodids (Epomophorus wahlbergi and Lissonycteris angolensis), one rhinolophid (Rhinolophus clivosus), and one vespertilionid (Neoromicia capensis). Taxa only captured on a single massif include Rousettus lanosus and Rhinolophus simulator (South Pare, 10% of total captures), Myonycteris relicta and Nycteris thebaica (West Usambara, 10% of total captures), and Rousettus aegyptiacus, Rhinolophus deckenii, R. fumigatus, R. swinnyi, Nycteris grandis, Myotis bocagei, and Scotophilus viridis (East Usambara, 35% of total captures).Comparisons of capture rates and species richness between these three montane sites to more lowland forest sites indicate a notable reduction in species richness and density with increasing elevation. Our preliminary surveys are at best rough estimates of patterns of species diversity and richness in the montane portions of these massifs; more fieldwork and associated taxonomic work are clearly needed to have more in-depth knowledge of the local bat fauna.

Ecology of the Podocarpaceae in Tropical Forests

The emergence of angiosperms in tropical forests at the expense of the gymnosperms, their ancestral relatives, was one of the most important events in the evolutionary history of terrestrial plants. Gymnosperms were nearly eliminated from the tropics after the evolution of angiosperms in the early Cretaceous, yet conifers of the Podocarpaceae are among the few gymnosperm families that persist in tropical forests worldwide. Podocarps are often considered to be restricted to montane sites in the tropics, a feature of their biogeography that is used by paleoecologists to reconstruct past forest communities. However, podocarps also occur in the lowland tropics, where they can be the dominant component of forest canopies. Podocarps have proved to be remarkably adaptable in many cases: members of the family have a semi-aquatic lifestyle, exhibit drought tolerance and resprouting, and include the only known parasitic gymnosperm. Other intriguing aspects of podocarp physiology include the mechanism of water transport in the leaves and the conspicuous root nodules, which are not involved in nitrogen fixation but instead house arbuscular mycorrhizal fungi. Perhaps most surprising, paleobotanical evidence indicates that far from being 'relict' members of tropical forest communities, podocarps have been dispersing into the tropics since the late Eocene epoch more than 30 million years ago. These and other aspects of the Podocarpaceae explored in this volume have far-reaching implications for understanding the ecology and evolution of tropical rain forests.

Physiological diversity and biogeography of vascular epiphytes at Río Changuinola, Panama

The taxonomic composition of the vascular epiphyte flora at the Río Changuinola, Panama, was examined and complemented with an analysis of biogeographic affinities and physiological parameters related to plant water and nutrient relations. In an area of ca. 1000 ha, we found a total of 476 species of vascular epiphytes. This marks a new diversity record among lowland rainforest sites. Species composition was closely related to nearby lowland forest sites but not to montane sites. The floristic similarity with lowland sites decreased with distance and relative position towards the Andes. On basis of isotope discrimination, the proportion of species with Crassulacean Acid Metabolism (CAM) was found to be low compared to other studies, and many of these species showed a rather weak expression of this photosynthetic pathway. This observation and distributional shifts in 15% of the species in the study area towards lower elevations suggest that local water availability is high which in turn is arguably responsible for the high species richness.

Adaptation of redband trout in desert and montane environments

Natural populations that evolve under extreme climates are likely to diverge because of selection in local environments. To explore whether local adaptation has occurred in redband trout (Oncorhynchus mykiss gairdneri) occupying differing climate regimes, we used a limited genome scan approach to test for candidate markers under selection in populations occurring in desert and montane streams. An environmental approach to identifying outlier loci, spatial analysis method and linear regression of minor allele frequency with environmental variables revealed six candidate markers (P < 0.01). Putatively neutral markers identified high genetic differentiation among desert populations relative to montane sites, likely due to intermittent flows in desert streams. Additionally, populations exhibited a highly significant pattern of isolation by temperature (P< 0.0001) and those adapted to the same environment had similar allele frequencies across candidate markers, indicating selection for differing climates. These results imply that many genes are involved in the adaptation of redband trout to differing environments, and selection acts to reinforce localization. The potential to predict genetic adaptability of individuals and populations to changing environmental conditions may have profound implications for species that face extensive anthropogenic disturbances.

Atmospheric phosphorus deposition at a montane site: Size distribution, effects of wildfire, and ecological implications

The dry deposition of atmospheric particulate matter can be a significant source of phosphorus (P) to oligotrophic aquatic ecosystems, including high-elevation lakes. In this study, measurements of the mass concentration and size distribution of aerosol particles and associated particulate P are reported for the southern Sierra Nevada, California, for the period July–October, 2008. Coarse and fine particle samples were collected with Stacked Filter Units and analyzed for Total P (TP) and inorganic P (IP) using a digestion-extraction procedure, with organic P (OP) calculated by difference. Particle size-resolved mass and TP distributions were determined concurrently using a MOUDI cascade impactor. Aerosol mass concentrations were significantly elevated at the study site, primarily due to transport from offsite and emissions from local and regional wildfires. Atmospheric TP concentrations ranged from 11 to 75 ng m −3 (mean = 37 ± 16 ng m −3), and were typically dominated by IP. Phosphorus was concentrated in the coarse (>1 μm diameter) particle fraction and was particularly enriched in the 1.0–3.2 μm size range, which accounted for 30–60% of the atmospheric TP load. Wildfire emissions varied widely in P content, and may be related to fire intensity. The estimated dry depositional flux of TP for each daily sampling period ranged between 7 and 118 μg m −2 d −1, with a mean value of 40 ± 27 μg m −2 d −1. Relative rates of dry deposition of N and P in the Sierra Nevada are consistent with increasing incidence of N limitation of phytoplankton growth and previously observed long-term eutrophication of lakes.

Mosquitoes and West Nile virus along a river corridor from prairie to montane habitats in eastern Colorado

We conducted studies on mosquitoes and West Nile virus (WNV) along a riparian corridor following the South Platte River and Big Thompson River in northeastern Colorado and extending from an elevation of 1,215 m in the prairie landscape of the eastern Colorado plains to 1,840 m in low montane areas at the eastern edge of the Rocky Mountains in the central part of the state. Mosquito collection during June-September 2007 in 20 sites along this riparian corridor yielded a total of 199,833 identifiable mosquitoes of 17 species. The most commonly collected mosquitoes were, in descending order: Aedes vexans, Culex tarsalis, Ae. dorsalis, Ae. trivittatus, Ae. melanimon, Cx. pipiens, and Culiseta inornata. Species richness was higher in the plains than in foothills-montane areas, and abundances of several individual species, including the WNV vectors Cx. tarsalis and Cx. pipiens and the nuisance-biter and potential secondary WNV vector Ae. vexans, decreased dramatically from the plains (1,215-1,487 m) to foothills-montane areas (1,524-1,840 m). Ae. vexans and Cx. tarsalis had a striking pattern of uniformly high abundances between 1,200-1,450 m followed by a gradual decrease in abundance above 1,450 m to reach very low numbers above 1,550 m. Culex species were commonly infected with WNV in the plains portion of the riparian corridor in 2007, with 14 of 16 sites yielding WNV-infected Cx. tarsalis and infection rates for Cx. tarsalis females exceeding 2.0 per 1,000 individuals in ten of the sites. The Vector Index for abundance of WNV-infected Cx. tarsalis females during June-September exceeded 0.5 in six plains sites along the South Platte River but was uniformly low (0-0.1) in plains, foothills and montane sites above 1,500 m along the Big Thompson River. A population genetic analysis of Cx. tarsalis revealed that all collections from the ≈190 km riparian transect in northeastern Colorado were genetically uniform but that these collections were genetically distinct from collections from Delta County on the western slope of the Continental Divide. This suggests that major waterways in the Great Plains serve as important dispersal corridors for Cx. tarsalis but that the Continental Divide is a formidable barrier to this WNV vector.

Population genetic structure, phylogeography, and demographic history ofPlatycrater arguta (Hydrangeaceae) endemic to East China and South Japan, inferred from chloroplast DNA sequence variation

AbstractPlatycrater arguta (Hydrangeaceae) is a small deciduous shrub of the Sino­Japanese floristic region, where it occurs in montane sites mostly covered with warm­temperate deciduous forest. This sole representative of its genus contains two varieties disjunctly distributed between East China (var. sinensis) and South Japan (var. arguta). To illuminate the biogeographic and demographic history of this rare species, we conducted a survey of chloroplast DNA (cpDNA) sequence variation (trnD­trnE, trnH­psbA) within and among twelve populations (four from China, eight from Japan, 129 individuals in total) representing the overall distributional range of the species. Based on a total of 19 haplotypes identified, P. arguta was found to harbor surprisingly high levels of haplotype and nucleotide diversity (hT = 0.882;T = 0.00475), possibly associated with its long evolutionary history. Spatial analysis of molecular variance found two regional phylogroups, corresponding to var. sinensis and var. arguta, and supported by genealogical (unrooted network) analysis of haplotypes. Using a coalescent­based model of 'divergence by isolation with migration', the likely vicariant origin of these varieties was dated to the mid­Pleistocene (ca. 0.89 mya). Very similar haplotype mismatch distributions indicate that var. sinensis and var. arguta underwent past demographic growth almost simultaneously (dated to ca. 0.43 and 0.45 mya, respectively), suggesting climate­induced expansion. However, var. sinensis likely experienced a mere demographic expansion in a narrowly circumscribed mountain range, while var. arguta underwent a spatial northward expansion that might have consisted of a series of bottlenecks, leading to genetically impoverished populations that most likely derived from initial population(s) in southern Kyushu. Our results endorse the recognition of two 'evolutionarily significant units' within P. arguta, corresponding to var. sinensis from East China and var. arguta from South Japan.

Holocene fire and vegetation dynamics in a montane forest, North Cascade Range, Washington, USA

We reconstructed a 10,500-yr fire and vegetation history of a montane site in the North Cascade Range, Washington State based on lake sediment charcoal, macrofossil and pollen records. High-resolution sampling and abundant macrofossils made it possible to analyze relationships between fire and vegetation. During the early Holocene (> 10,500 to ca. 8000 cal yr BP) forests were subalpine woodlands dominated by Pinus contorta. Around 8000 cal yr BP, P. contorta sharply declined in the macrofossil record. Shade tolerant, mesic species first appeared ca. 4500 cal yr BP. Cupressus nootkatensis appeared most recently at 2000 cal yr BP. Fire frequency varies throughout the record, with significantly shorter mean fire return intervals in the early Holocene than the mid and late Holocene. Charcoal peaks are significantly correlated with an initial increase in macrofossil accumulation rates followed by a decrease, likely corresponding to tree mortality following fire. Climate appears to be a key driver in vegetation and fire regimes over millennial time scales. Fire and other disturbances altered forest vegetation at shorter time scales, and vegetation may have mediated local fire regimes. For example, dominance of P. contorta in the early Holocene forests may have been reinforced by its susceptibility to frequent, stand-replacing fire events.

Did glacials and/or interglacials promote allopatric incipient speciation in East Asian temperate plants? Phylogeographic and coalescent analyses on refugial isolation and divergence in Dysosmaversipellis

To explore the evolutionary consequences of climate-induced fluctuations in presently fragmented temperate forest habitats in continental East Asia we investigated the phylogeography and demographic history of the temperate-deciduous forest endemic Dysosma versipellis from disjunct montane sites in Central-Southeast China. Based on a survey of chloroplast (cp) DNA sequence variation, our analyses show that this perennial herb consists of morphologically indistinguishable western and central/eastern cpDNA lineages. Coalescent analyses under the ‘isolation with migration’ (IM) model support an ancient (Mid-Pleistocene) divergence between these lineages, with the western lineage having persisted without significant population growth in a long-term refuge just east of the Tibetan (Qinghai-Xizang) Plateau. In contrast, for the central/eastern lineage, we found strong evidence for population expansion from a refuge located south of the middle and lower reaches of the Yangtze River, and likely coinciding with the last or penultimate interglacial, followed by considerable population isolation and divergence in situ over (at least) the latest glacial–interglacial cycle. In line with recent evidence from palaeomodeling of East Asian forest biomes, our results suggest that the same vicariance factor, i.e. climate-induced eco-geographic isolation through (a)biotic displacement of temperate-deciduous forested habitats, promoted the divergence of D. versipellis lineages and populations at different spatial–temporal scales and over glacial and interglacial periods. Thus, there is no evidence that populations of D. versipellis merged at lower elevations during the last glacial(s). As such, D. versipellis accords with the premise that Late Quaternary refugial isolation is likely to have enhanced allopatric (incipient) species formation of temperate plants in East Asia.

Life in a Shrinking World: Thermal Physiology and Activity of Diurnal Alpine Mammals in Relation to Climate Change

The effects of increased global temperatures are being measured in many biological systems. Given the complexity of biological systems, their responses to a changing climate are difficult to predict. Physiologic processes are particularly susceptible to temperature, leading to a species specific optimal range of habitable temperatures. As global temperatures increase, species will be exposed to a changing range of potentially stressful temperatures, especially in species currently living at their thermal limits (e.g., alpine mammals). Warming temperatures may force alpine species to move to higher elevations to maintain thermoneutrality. Ultimately, if temperatures increase as predicted, alpine mammals may be unable to move higher and may face localized extinctions. I hypothesize that, many alpine mammals are currently living at the upper range of their thermoneutral zone and, in response to warming temperatures; alpine mammals will experience ambient temperatures above their upper critical temperature which will limit their activity period. I will measure the metabolic thermoneutral zone of small mammals in relation to temperature at four montane sites in the western U.S. We will focus on small diurnal mammals (chipmunks and pikas) as they are prolific and susceptible to high temperatures. The proposed study will not only provide sorely needed information on the basic thermal requirements of numerous alpine small mammals in the U.S., but that information can be used to generate physiologically relevant models to predict future changes in the altitudinal ranges of these species.

Chytridiomycosis and Amphibian Population Declines Continue to Spread Eastward in Panama

Chytridiomycosis is a globally emerging disease of amphibians and the leading cause of population declines and extirpations at species-diverse montane sites in Central America. We continued long-term monitoring efforts for the presence of the fungal pathogen Batrachochytrium dendrobatidis (Bd) and for amphibian populations at two sites in western Panama, and we began monitoring at three new sites to the east. Population declines associated with chytridiomycosis emergence were detected at Altos de Campana National Park. We also detected Bd in three species east of the Panama Canal at Soberanía National Park, and prevalence data suggests that Bd may be enzootic in the lowlands of the park. However, no infected frogs were found further east at Tortí (prevalence <7.5% with 95% confidence). Our results suggest that Panama's diverse and not fully described amphibian communities east of the canal are at risk. Precise predictions of future disease emergence events are not possible until factors underlying disease emergence, such as dispersal, are understood. However, if the fungal pathogen spreads in a pattern consistent with previous disease events in Panama, then detection of Bd at Tortí and other areas east of the Panama Canal is imminent. Therefore, development of new management strategies and increased precautions for tourism, recreation, and biology are urgently needed.

APPLICATION OF TREE-RING ISOTOPIC ANALYSES TO RECONSTRUCT HISTORICAL WATER USE OF RIPARIAN TREES

Historical patterns of water source use by trees inferred from long-term records of tree-ring stable isotopic content could assist in evaluating the impact of human alterations to natural stream flow regimes (e.g., water impoundments, stream flow diversions, and groundwater extraction). Our objective was to assess the utility of the hydrogen stable isotopic composition (SD) of tree rings as an index of historical water source use by riparian trees. We investigated the influence of site conditions that varied in climate and hydrology on the relationship between deltaD of Populus xylem water (deltaD(xyl)) and tree-ring cellulose (deltaD(cell)). deltaD(xyl) and deltaD(cell) were strongly correlated across sites (r2 = 0.89). However, the slope of this relationship was less than 1, indicating that factors other than deltaD(xyl) influenced deltaD(cell). Inverse modeling with an isotopic fractionation model for tree-ring cellulose suggested that the lack of one-to-one correspondence between deltaD(xyl) and deltaD(cell) was due to the influence of the hydrogen isotopic content of the atmospheric water vapor (deltaD(atm)). Empirically measured values of deltaD(cell) were typically within the seasonal range of deltaD(cell) predicted from the fractionation model. Sensitivity analyses showed that changes in deltaD(xyl) generally had a greater influence at high-elevation montane sites, whereas deltaD(xyl) and deltaD(atm) had about equal influence on deltaD(cell) at low-elevation desert sites. The intrasite relationship between deltaD(cell) and deltaD(xyl) among individual trees was poor, perhaps because of the within-site spatial variation in hydrologic conditions and associated tree physiological responses. Our study suggests that historical variation in deltaD(cell) of Populus provides information on historical variation in both time-integrated water source use and atmospheric conditions; and that the influence of atmospheric conditions is not consistent over sites with large differences in temperature and humidity. Reconstruction of xylem water sources of Populus in riparian ecosystems from deltaD(cell) will be more direct at higher elevation mountain sites than at low-elevation desert sites.