Steep Elevation Gradients Research Articles

The simultaneous inducibility of phytochemicals related to plant direct and indirect defences against herbivores is stronger at low elevation

Summary Ecological theory indicates that warmer and more stable climates should result in stronger biotic interactions. Therefore, plant species growing at lower elevations and experiencing greater herbivore pressure should invest in higher levels of defences than those at higher elevations. Nonetheless, there are a number of studies that have found no effect of elevational gradients on plant defensive traits. Several factors might explain the lack of consistency for the altitude–defence relationships, including (i) the reduction of all defensive traits into one measure of resistance; (ii) not considering plant defence as the simultaneous expression of several defensive traits; and (iii) not considering the relative influence of biotic (e.g. herbivory) and abiotic (e.g. climate and soil conditions) factors associated with the ecological gradient. Here, we present a comprehensive test of the effects of elevation and its associated biotic and abiotic factors on the individual and simultaneous expression of constitutive direct and indirect defences and their inducibility (i.e. expression of defences after herbivore attack). Specifically, we estimated climatic and soil variables and measured herbivore damage and constitutive and jasmonic acid‐induced glucosinolate levels in the leaves as a proxy for direct defences, and volatile emission as a proxy for indirect defences in 16 Cardamine species naturally growing along the steep elevational gradient of the Alps. Within a phylogenetic comparative framework, we found that species growing at lower elevations invested more in the simultaneous inducibility of both direct and indirect defences, whereas species growing at higher elevations invested more in constitutive direct defences. Although we found strong elevational gradients in herbivory and climatic and soil variables, these biotic and abiotic factors only partially explained elevational patterns in plant defences. Synthesis. These results highlight that the complex regulation of multiple defence traits strongly vary across elevational gradients and build towards a better understanding of the multiple mechanisms underlying trait evolution and species interactions along ecological gradients.

Phylogenetic diversity of macromycetes and woody plants along an elevational gradient in Eastern Mexico

AbstractPhylogenetic information provides insight into the ecological and evolutionary processes that organize species assemblages. We compared patterns of phylogenetic diversity among macromycete and woody plant communities along a steep elevational gradient in eastern Mexico to better understand the evolutionary processes that structure their communities. Macrofungi and trees were counted and identified in eight sites from 100 to 3500 m asl, and sequence data retrieved from GenBank for the same or closely related species were used to reconstruct their phylogenies. Patterns of species richness and phylogenetic diversity were similar for both macrofungi and trees, but macromycete richness and diversity peaked at mid‐elevations, whereas woody plant richness and diversity did not show significant trends with elevation. Phylogenetic similarity among sites was low for both groups and decreased as elevational distance between sites increased. Macromycete communities displayed phylogenetic overdispersion at low elevations and phylogenetic clustering at high elevations; the latter is consistent with environmental filtering at high elevation sites. Woody plants generally exhibited phylogenetic clustering, consistent with the potential importance of environmental filtering throughout the elevational gradient.

The role of selection and historical factors in driving population differentiation along an elevational gradient in an island bird

Adaptation to local environmental conditions and the range dynamics of populations can influence evolutionary divergence along environmental gradients. Thus, it is important to investigate patterns of both phenotypic and genetic variations among populations to reveal the respective roles of these two types of factors in driving population differentiation. Here, we test for evidence of phenotypic and genetic structure across populations of a passerine bird (Zosterops borbonicus) distributed along a steep elevational gradient on the island of Réunion. Using 11 microsatellite loci screened in 401 individuals from 18 localities distributed along the gradient, we found that genetic differentiation occurred at two spatial levels: (i) between two main population groups corresponding to highland and lowland areas, respectively, and (ii) within each of these two groups. In contrast, several morphological traits varied gradually along the gradient. Comparison of neutral genetic differentiation (FST ) and phenotypic differentiation (PST ) showed that PST largely exceeds FST at several morphological traits, which is consistent with a role for local adaptation in driving morphological divergence along the gradient. Overall, our results revealed an area of secondary contact midway up the gradient between two major, cryptic, population groups likely diverged in allopatry. Remarkably, local adaptation has shaped phenotypic differentiation irrespective of population history, resulting in different patterns of variation along the elevational gradient. Our findings underscore the importance of understanding both historical and selective factors when trying to explain variation along environmental gradients.

磷的生物有效性对山地生态系统的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 磷的生物有效性对山地生态系统的影响 DOI: 10.5846/stxb201407111421 作者: 作者单位: 中科院成都山地所,中科院成都山地所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(41272200) Phosphorus bioavailability in mountain ecosystems: characteristics and ecological roles Author: Affiliation: Institute of Mountain Hazards and Environment, CAS,Institute of Mountain Hazards and Environment, CAS Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:磷(P)的生物有效性对山地生态系统的发育和稳定至关重要。由于大气CO2浓度升高和N沉降增加,生态系统C、N和P的化学计量比失衡,P的生物有效性受到更多关注。近年来山地系统中P的研究不断深入,2004-2013年间ISI Web of Knowledge中相关研究论文几乎是此前近百年的3倍。总结了山地生态系统中P的生物有效性的特点及其对植物物种多样性和初级生产力的影响。山地生态系统P的生物有效性因垂直高差和地形梯度空间变异明显,快速物质运移和生物过程是控制山地生态系统P的生物有效性的关键因素。P的生物有效性可以影响山地生态系统物种多样性和初级生产力,其对初级生产力的限制存在于全球范围内的山地生态系统。当P的生物有效性发生改变时,山地生态系统的结构越复杂,其植物物种多样性和初级生产力的响应可能会越平缓。全球变化的重要驱动因子(如增温和N沉降增加)可以直接或间接地改变山地生态系统P的生物有效性,因此需要在山地生态系统中加强长期监测和养分控制实验,并结合新型P分析技术,以期认识山地生态系统P的生物有效性的现状、变化趋势和对生态系统的影响,从而为适应全球变化背景下山地生态系统养分状况的改变提供依据。 Abstract:Phosphorus (P) is an essential element for sustainable development of terrestrial ecosystems. Mountains cover approximately 20% of the land area. The biogeochemical cycle of P in the mountain ecosystems differs from that in lowland ecosystems because of the huge spatial heterogeneity, fast transport of materials, and relatively rich biodiversity. As global changes, the increase in temperature, atmospheric CO2 concentration, and N deposition have disrupted the stoichiometric equilibrium of C, N, and P. In mountain ecosystems, especially alpine regions that are sensitive to global changes, P bioavailability has become a hot area in the field of biogeochemical-cycle research. Nearly three times as many articles on the biogeochemical cycle of P in mountain ecosystems were published in the last decade in comparison with the century before. This review summarizes the characteristics of P bioavailability in mountain ecosystems; its effects on plant biodiversity and primary productivity are comprehensively explored. The P bioavailability in mountain ecosystems differs from that in lowland ecosystems in three ways: (1) there is obvious spatial heterogeneity in P bioavailability (because of steep elevation and topographic gradients), which exists on different spatial scales and in various forms depending on the factors influencing the biogeochemical cycle of P; (2) the P bioavailability in the mountains is significantly affected by the fast P transport, because hydrologic and gravitational processes are accelerated by the steep elevation gradient; and (3) biological processes are the key factors influencing the P bioavailability in the mountains. Plants and microorganisms act both as active pools and regulators in the P cycle. It is generally accepted that diversity of plant species reaches its maximum at moderate P bioavailability. Under conditions of low and high P bioavailability, P limitations and competitive exclusion may suppress the diversity of plant species. Nevertheless, in mountain ecosystems with complex structures, some mechanisms (including disturbance, niche separation, and rich biodiversity) can alleviate this suppression; thus, plant species diversity may be affected to a lesser degree by the changes in P bioavailability. In terms of the primary productivity, limitations on P bioavailability can be found in mountain ecosystems worldwide according to field surveys and nutrient manipulation experiments. In contrast to the croplands featured by single species, the responses of primary productivity in the mountain ecosystems to P bioavailability can be affected by composition of the set of plant species. When P bioavailability decreases, species with high P utilization efficiency can become more dominant; thus, the primary production may not decrease substantially. In addition, environmental factors such as temperature, water, wind, and radiation in mountain ecosystems may further weaken the responses of primary productivity to P bioavailability. Therefore, just as the plant species diversity, the primary productivity in mountain ecosystems with complex structure may be less sensitive to the changes in P bioavailability. The P bioavailability in the mountains is more sensitive to global changes (e.g., an increase in temperature and N deposition) because these regions generally have low temperature and N limitations. An increase in temperature and N deposition can alter the P bioavailability in mountain ecosystems directly or indirectly. Meanwhile, P bioavailability can, to a certain degree, affect the responses of mountain ecosystems to global changes. Long-term field observation and nutrient manipulation experiments, together with the use of new P analysis techniques such as X-ray absorption near-edge structure (XANES) spectroscopy and nuclear magnetic resonance (NMR) open up new opportunities to elucidate the P status, its changing trends, and its influences on mountain ecosystems. On the basis of this knowledge, it is possible to achieve better adaptation to the changing nutrient status in mountain ecosystems. 参考文献 相似文献 引证文献

Distribution, diversity gradients and Rapoport's elevational rule in the black scavenger flies of the Swiss Alps (Diptera: Sepsidae)

Abstract Elevational gradients influence the distribution and abundance of species drastically and can lead to variation in community composition. Although coprophagous flies are of ecological and economic importance, their biodiversity and distribution are largely neglected. We studied the impact of steep elevational gradients and geography on the distribution of sepsid flies in the Swiss Alps. Sepsidae are a family of acalyptrate flies strongly associated with decaying organic matter and vertebrate dung, and characterised by a high extent of sympatry in their breeding substrates. Historical, haphazardly sampled specimens from 116 locations covering an elevational range from 200 to 2000 m were available in ethanol collections of various Swiss museums. Nineteen species encompassing all native genera (Meroplius, Nemopoda, Saltella, Sepsis and Themira) were recorded. Local species richness increased linearly with elevation, while area‐corrected regional species richness of elevational belts increased asymptotically. Species occurring at higher altitudes had lower wing loadings and greater elevational ranges than lowland species, supporting Rapoport's elevational rule. Despite compositional similarities, the sepsid communities of the northern lowlands differed significantly from the alpine sepsid fauna. The southern lowlands were particularly differentiated in community composition due to a number of presumably thermophilic species that predominantly occur south of the Alps. Relative abundances of several species were thus strongly affected by elevation and climatic variables. We illustrate the impact of elevational gradients and geography on a community of closely related, often sympatric species, and discuss potential mechanisms of niche partitioning via temporal succession, thermal adaptation and differential resource use.

Species richness and areas of endemism of oryzomyine rodents (Cricetidae, Sigmodontinae) in South America: an ndm/vndm approach

AbstractAimTo infer areas of endemism for the tribe Oryzomyini in South America by employing a database of species richness and geographical distribution, and to compare these results with areas of endemism and species richness proposed in the literature for other taxa.LocationWe analysed specimens of the tribe Oryzomyini distributed throughout South and Central America, which are housed in European, North and South American museums and collections.MethodsWe analysed 2768 occurrence records for 102 species of the tribe Oryzomyini using the ndm/vndm algorithm and three different grid sizes to assess the possible effects of grid cell area on the results.ResultsUsing the overlap of consensus areas in South America, we identified three generalized areas of endemism for the Oryzomyini: north‐western South America (NWSA), eastern South American (ESA), and northern South America (NSA); we also identified the Galápagos archipelago (GA) as an area of endemism.Main conclusionsAreas of endemism detected in the continental portion of South America include its three main mountain chains: the Andes Cordillera, the Guyanan Shields, and an area east of the Brazilian Shield named Serra do Mar. Each of these regions encompasses many different types of vegetation, and the species richness and composition of the areas of endemism of the tribe are directly related to this environmental diversity. Different grid sizes affected the distributional heterogeneity of the consensus areas. The smallest grid cell size identified mainly Andean areas, which contain a higher number of more exclusive species in a small area along a steep elevational gradient. In contrast, the largest grid size identified areas of endemism along an environmental gradient that co‐varied with latitude and longitude. The identified areas of endemism are corroborated by previous studies on other taxa.

Integrating evolutionary and functional tests of adaptive hypotheses: a case study of altitudinal differentiation in hemoglobin function in an Andean Sparrow, Zonotrichia capensis.

In air-breathing vertebrates, the physiologically optimal blood-O2 affinity is jointly determined by the prevailing partial pressure of atmospheric O2, the efficacy of pulmonary O2 transfer, and internal metabolic demands. Consequently, genetic variation in the oxygenation properties of hemoglobin (Hb) may be subject to spatially varying selection in species with broad elevational distributions. Here we report the results of a combined functional and evolutionary analysis of Hb polymorphism in the rufous-collared sparrow (Zonotrichia capensis), a species that is continuously distributed across a steep elevational gradient on the Pacific slope of the Peruvian Andes. We integrated a population genomic analysis that included all postnatally expressed Hb genes with functional studies of naturally occurring Hb variants, as well as recombinant Hb (rHb) mutants that were engineered through site-directed mutagenesis. We identified three clinally varying amino acid polymorphisms: Two in the α(A)-globin gene, which encodes the α-chain subunits of the major HbA isoform, and one in the α(D)-globin gene, which encodes the α-chain subunits of the minor HbD isoform. We then constructed and experimentally tested single- and double-mutant rHbs representing each of the alternative α(A)-globin genotypes that predominate at different elevations. Although the locus-specific patterns of altitudinal differentiation suggested a history of spatially varying selection acting on Hb polymorphism, the experimental tests demonstrated that the observed amino acid mutations have no discernible effect on respiratory properties of the HbA or HbD isoforms. These results highlight the importance of experimentally validating the hypothesized effects of genetic changes in protein function to avoid the pitfalls of adaptive storytelling.

Habitat change and trade explain the bird assemblage from the La Chimba archaeological site in the northeastern Andes of Ecuador

The nature of tree‐line habitats in the Andes has long been a contentious topic in the ecological literature. Palynological studies suggest that a combination of anthropogenic and natural processes throughout the Holocene contributed to its present form and species composition. This is the first study to use zooarchaeological evidence to reconstruct possible prehistoric changes in these alpine habitats. I analysed the remains of birds from the La Chimba archaeological site in northern Ecuador to assess changes in the bird tree‐line community over three distinct phases (Early, 2640–2390 year BP; Middle, 2390–1994 year BP; Late, 1994–1700 year BP) of this prehistoric settlement. The elevation of this site (3200 m) places it near a steep elevational gradient in vegetation, with the modern tree‐line here at 3500–3600 m. Therefore, non‐local specimens of birds from the lowlands would hint at long‐distance trade. The composition of birds changes through time: species associated with high montane forest and shrubby páramos decrease and species from dry or open montane habitats increase. This trend is dominated by the decrease of Curve‐billed Tinamous Nothoprocta curvirostris (current elevational range 3000–3900 m) and a corresponding increase of specimens of Andean Tinamous Nothoprocta pentlandii (current elevational range 1000–2300 m). The large number of Andean Tinamous is surprising given that presently it occurs no closer than 300 km to the south of the La Chimba site. Overall, 18 of the 43 species of birds identified from La Chimba are likely to be the result of trade. This includes species from the eastern and western lowlands of Ecuador and one possible long‐distance transport from Peru. Prehistoric trade of birds and bird parts was probably common, and prehistoric anthropogenic landscape change and trade in birds should be considered as alternative explanations for species with disjunct populations in and across the Andes.

New host and lineage diversity of avian haemosporidia in the northern Andes.

The northern Andes, with their steep elevational and climate gradients, are home to an exceptional diversity of flora and fauna, particularly rich in avian species that have adapted to divergent ecological conditions. With this diversity comes the opportunity for parasites to exploit a wide breadth of avian hosts. However, little research has focused on examining the patterns of prevalence and lineage diversity of avian parasites in the Andes. Here, we screened a total of 428 birds from 19 species (representing nine families) and identified 133 infections of avian haemosporidia (31%), including lineages of Plasmodium, Haemoproteus, and Leucocytozoon. We document a higher prevalence of haemosporidia at higher elevations and lower temperatures, as well as an overall high diversity of lineages in the northern Andes, including the first sequences of haemosporidians reported in hummingbirds (31 sequences found in 11 species within the family Trochilidae). Double infections were distinguished using PHASE, which enables the separation of distinct parasite lineages. Results suggest that the ecological heterogeneity of the northern Andes that has given rise to a rich diversity of avian hosts may also be particularly conducive to parasite diversification and specialization.

High elevation Plantago lanceolata plants are less resistant to herbivory than their low elevation conspecifics: is it just temperature?

Traits that mediate species interactions are evolutionarily shaped by biotic and abiotic drivers, yet we know relatively little about the relative importance of these factors. Herbivore pressure, along with resource availability and ‘third‐party’ mutualists, are hypothesized to play a major role in the evolution of plant defence traits. Here, we used the model system Plantago lanceolata, which grows along steep elevation gradients in the Swiss Alps, to investigate the effect of elevation, herbivore pressure, mycorrhizal inoculation and temperature on plant resistance. Over a 1200 m elevation gradient, the levels of herbivory and iridoid glycosides (IGs) declined with increasing elevation. By planting seedlings at three different elevations, we further showed that both low‐elevation growing conditions and mycorrhizal inoculation resulted in increased plant resistance to herbivores. Finally, using a temperature‐controlled experiment comparing high‐ and low‐elevation ecotypes, we showed that high‐elevation ecotypes are less resistant to herbivory, and that lower temperatures impair IGs deployment after herbivore attack. We thus propose that both lower herbivore pressure, and colder temperatures relax the defense syndrome of high elevation plants.

Elevation-related differences in memory and the hippocampus in mountain chickadees, Poecile gambeli

Harsh environments may lead to increased demands on memory in animals that rely on memory for survival. We previously showed that winter severity is associated with non-experience-based differences in memory and the hippocampus over a large continental scale in food-caching black-capped chickadees, Poecile atricapillus. However, large climatic differences also occur along steep elevational gradients in montane environments over a small geographical scale. Here, we demonstrate for the first time that large differences in memory and the hippocampus exist over extremely short distances (10 km) along the elevation gradient. We found that food-caching mountain chickadees (P. gambeli) from the highest elevations in the Sierra Nevada Mountains had significantly better spatial memory associated with larger hippocampi, with almost twice the number of hippocampal neurons, than individuals only 600 m lower in elevation. We found similarly large differences in hippocampal neurogenesis rates as indicated by the total number of immature neurons. Our study therefore suggests that climate-related environmental differences can produce dramatic differences in memory and the hippocampus in animals within close proximity on small spatial scales and that currently observed trends in global climate may have significant effects on cognition and the brain.

Variation in liana abundance and biomass along an elevational gradient in the tropical Atlantic Forest (Brazil)

AbstractLianas play a key role in forest structure, species diversity, as well as functional aspects of tropical forests. Although the study of lianas in the tropics has increased dramatically in recent years, basic information on liana communities for the Brazilian Atlantic Forest is still scarce. To understand general patterns of liana abundance and biomass along an elevational gradient (0–1,100 m asl) of coastal Atlantic Forest, we carried out a standard census for lianas ≥1 cm in five 1‐ha plots distributed across different forest sites. On average, we found a twofold variation in liana abundance and biomass between lowland and other forest types. Large lianas (≥10 cm) accounted for 26–35% of total liana biomass at lower elevations, but they were not recorded in montane forests. Although the abundance of lianas displayed strong spatial structure at short distances, the present local forest structure played a minor role structuring liana communities at the scale of 0.01 ha. Compared to similar moist and wet Neotropical forests, lianas are slightly less abundant in the Atlantic Forest, but the total biomass is similar. Our study highlights two important points: (1) despite some studies have shown the importance of small‐scale canopy disturbance and support availability, the spatial scale of the relationships between lianas and forest structure can vary greatly among tropical forests; (2) our results add to the evidence that past canopy disturbance levels and minimum temperature variation exert influence on the structure of liana communities in tropical moist forests, particularly along short and steep elevational gradients.

Breeding success at the range margin of a desert species: implications for a climate‐induced elevational shift

If the breeding range of a species is limited by biotic or abiotic environmental factors that depress breeding success at the range margin, then range expansion is expected when those limiting factors are alleviated. Over a three‐year period, we measured breeding success of a desert species, black‐throated sparrowAmphispiza bilineata, along a steep elevation gradient between the Peninsular Mountains and Colorado Desert (San Diego County, California) that is undergoing a warming trend. We compared breeding success at geographically marginal locations (higher‐elevation chaparral sites) to more central locations (lower‐elevation desert scrub sites) only a short distance apart. Breeding success was measured at the nest level, territory level, and population level. At each level measured, breeding success tended to be greater at higher‐elevation chaparral sites at the distribution margin compared to lower‐elevation sites where the bird was more common. Black‐throated sparrows had 100% reproductive failure at lower‐elevation sites during the two driest years of our study (2006–2007), but did relatively well at higher‐elevation sites. Only in a wetter year (2008) was breeding success improved at lower‐elevation sites. Surprisingly, there was no evidence of an upward elevational shift in distribution over a 26‐year period despite a clear warming trend and drier conditions. Greater territory density at lower‐elevation sites with reproductive failure during dry years suggests the possibility of an ecological trap in this system, which could prevent or delay climate‐induced range shifts. A common presumption has been that desert species will undergo relatively mild negative impacts due to a warming climate, but it is possible that some desert species are already at or near their temperature and aridity tolerance limits within their current range and shifts may not always be possible.

Batrachochytrium dendrobatidis and the Collapse of Anuran Species Richness and Abundance in the Upper Manu National Park, Southeastern Peru

Amphibians are declining worldwide, but these declines have been particularly dramatic in tropical mountains, where high endemism and vulnerability to an introduced fungal pathogen, Batrachochytrium dendrobatidis (Bd), is associated with amphibian extinctions. We surveyed frogs in the Peruvian Andes in montane forests along a steep elevational gradient (1200-3700 m). We used visual encounter surveys to sample stream-dwelling and arboreal species and leaf-litter plots to sample terrestrial-breeding species. We compared species richness and abundance among the wet seasons of 1999, 2008, and 2009. Despite similar sampling effort among years, the number of species (46 in 1999) declined by 47% between 1999 and 2008 and by 38% between 1999 and 2009. When we combined the number of species we found in 2008 and 2009, the decline from 1999 was 36%. Declines of stream-dwelling and arboreal species (a reduction in species richness of 55%) were much greater than declines of terrestrial-breeding species (reduction of 20% in 2008 and 24% in 2009). Similarly, abundances of stream-dwelling and arboreal frogs were lower in the combined 2008-2009 period than in 1999, whereas densities of frogs in leaf-litter plots did not differ among survey years. These declines may be associated with the infection of frogs with Bd. B. dendrobatidis prevalence correlated significantly with the proportion of species that were absent from the 2008 and 2009 surveys along the elevational gradient. Our results suggest Bd may have arrived at the site between 1999 and 2007, which is consistent with the hypothesis that this pathogen is spreading in epidemic waves along the Andean cordilleras. Our results also indicate a rapid decline of frog species richness and abundance in our study area, a national park that contains many endemic amphibian species and is high in amphibian species richness.

Forest structure and live aboveground biomass variation along an elevational gradient of tropical Atlantic moist forest (Brazil)

Live aboveground biomass (AGB) is an important source of uncertainty in the carbon balance from the tropical regions in part due scarcity of reliable estimates of live AGB and its variation across landscapes and forest types. Studies of forest structure and biomass stocks of Neotropical forests are biased toward Amazonian and Central American sites. In particular, standardized estimates of aboveground biomass stocks for the Brazilian Atlantic forest are rarely available. Notwithstanding the role of environmental variables that control the distribution and abundance of biomass in tropical lowland forests has been the subject of considerable research, the effect of short, steep elevational gradients on tropical forest structure and carbon dynamics is not well known. In order to evaluate forest structure and live AGB variation along an elevational gradient (0–1100 m a.s.l.) of coastal Atlantic Forest in SE Brazil, we carried out a standard census of woody stems ≥4.8 cm dbh in 13 1-ha permanent plots established on four different sites in 2006–2007. Live AGB ranged from 166.3 Mg ha −1 (bootstrapped 95% CI: 144.4,187.0) to 283.2 Mg ha −1 (bootstrapped 95% CI: 253.0,325.2) and increased with elevation. We found that local-scale topographic variation associated with elevation influences the distribution of trees >50 cm dbh and total live AGB. Across all elevations, we found more stems (64–75%) with limited crown illumination but the largest proportion of the live AGB (68–85%) was stored in stems with highly illuminated or fully exposed crowns. Topography, disturbance and associated changes in light and nutrient supply probably control biomass distribution along this short but representative elevational gradient. Our findings also showed that intact Atlantic forest sites stored substantial amounts of carbon aboveground. The live tree AGB of the stands was found to be lower than Central Amazonian forests, but within the range of Neotropical forests, in particular when compared to Central American forests. Our comparative data suggests that differences in live tree AGB among Neotropical forests are probably related to the heterogeneous distribution of large and medium-sized diameter trees within forests and how the live biomass is partitioned among those size classes, in accordance with general trends found by previous studies. In addition, the elevational variation in live AGB stocks suggests a large spatial variability over coastal Atlantic forests in Brazil, clearly indicating that it is important to consider regional differences in biomass stocks for evaluating the role of this threatened tropical biome in the global carbon cycle.

Small-scale Divergence in Egg Color along an Elevation Gradient in the Mexican Jay (Aphelocoma ultramarina): A Condition-dependent Response?

ABSTRACT. The functional significance of bird egg color and patterning is a continuing subject of interest and debate. Extreme polymorphism in eggshell appearance is often thought to be maintained by frequency-dependent selection operating within populations. However, variation could also be explained by small-scale differentiation combined with limited migration. Here, we report the existence of extreme variation in egg color in a population of Mexican Jays (Aphelocoma ultramarina) inhabiting a steep elevation and habitat gradient within a single mountain range, the Sierra del Carmen of Coahuila, Mexico. We quantified egg color of 143 eggs from 54 nests throughout the mountain range, using digital photos. Color was also quantified for a subset of these eggs, using a spectrometer. Results from both methods support the conclusion that egg color has diverged at a remarkably small spatial scale of 3–15 km. Photo color quantification indicated that eggs at high elevation were greener than those at low elevati...

Modeling environmentally associated morphological and genetic variation in a rainforest bird, and its application to conservation prioritization.

To better understand how environment shapes phenotypic and genetic variation, we explore the relationship between environmental variables across Ecuador and genetic and morphological variation in the wedge-billed woodcreeper (Glyphorynchus spirurus), a common Neotropical rainforest bird species. Generalized dissimilarity models show that variation in amplified fragment length polymorphism markers was strongly associated with environmental variables on both sides of the Andes, but could also partially be explained by geographic distance on the western side of the Andes. Tarsus, wing, tail, and bill lengths and bill depth were well explained by environmental variables on the western side of the Andes, whereas only tarsus length was well explained on the eastern side. Regions that comprise the highest rates of genetic and phenotypic change occur along steep elevation gradients in the Andes. Such environmental gradients are likely to be particularly important for maximizing adaptive diversity to minimize the impacts of climate change. Using a framework for conservation prioritization based on preserving ecological and evolutionary processes, we found little overlap between currently protected areas in Ecuador and regions we predicted to be important in maximizing adaptive variation.

Holocene treeline shifts and monsoon variability in the Hengduan Mountains (southeastern Tibetan Plateau), implications from palynological investigations

The upper 8.45 m of a sediment core from Lake Naleng were analysed for its pollen and charcoal content to detect vegetation, climate, and human activity changes on the southeastern Tibetan Plateau (TP) since the Pleistocene–Holocene transition (11.7 cal kyr BP). The application of pollen indicator taxa, pollen sums, biomisation, and multivariate analysis helped to reconstruct environmental conditions during the Holocene. Furthermore, 64 surface samples from the southeastern TP and its foreland were analysed to investigate the relationship between modern pollen assemblages and vegetation. The modern vegetation was recorded in the surface pollen assemblages by pollen indicator types, although sediments also contain pollen spectra extra-regional pollen transported from lower vegetation belts, which is seen as a consequence of steep elevation gradients at the southeastern margin of the TP. The relation between different vegetation belts and temperature from the modern sample sites was used to infer quantitative temperature trends for the Holocene record. Spreading of forests at the beginning of the Holocene marks the transition to warmer conditions. From 10.7 to ∼ 4.4 cal kyr BP open Abies– Betula forests were found at Lake Naleng probably reflecting a stronger-than-present summer monsoon. Temperature range reconstructions suggest a temperature that was about 2–3 °C warmer and a treeline position that was 400–600 m higher than today. A severe climate deterioration with temperatures about 1–2 °C colder than before is documented by a retreating forest between 8.1 and 7.2 cal kyr BP. Forests retreated while subalpine Rhododendron shrubs spread around Lake Naleng indicating colder conditions with temperatures 1–2 °C below early and mid Holocene level after 4.4 cal kyr BP. The forest decline at 4.4 cal kyr BP is considered to reflect climatic conditions as low concentrations of charcoal particles found in this period exclude human-induced fires as reason for the forest retreat. However, grazing indicators imply human influence on the environment since 3.4 cal kyr BP around Lake Naleng. We therefore consider the rapid treeline shift seen at 3.4 cal kyr BP as partly generated by human activity and partly by climatic conditions.

Climate, Rain Shadow, and Human-Use Influences on Fire Regimes in the Eastern Sierra Nevada, California, USA

There have been few fire history studies of eastern Sierra Nevada forests in California, USA, where a steep elevation gradient, rain shadow conditions, and forest stand isolation may produce different fire regimes than those found on the range’s western slope. We investigated historic fire regimes and potential climate influences on four forest types ranging in elevation from 1700 m to 3200 m on the Sierra Nevada’s eastern slope and the White Mountains’ western slope. Sample areas (approximately 15 ha to 45 ha) had mean site fire return intervals ranging from 4.8 yr to 16.9 yr across ten Jeffrey pine (Pinus jeffreyi Balf.) sites, and 13.4 yr to 45.7 yr across four high elevation lodgepole (P contorta Douglas ex Louden), foxtail (P. balfouriana Balf.) and bristlecone (P longaeva D.K. Bailey) pine sites. At most sites (13 of 14), >50% of fire events occurred in late or dormant season wood. Twentieth century fire return intervals increased at some sites, while other sites continued to record frequent fire events into the 1950s. Years where two or more sites recorded fire events on two or more trees were correlated with drought conditions forecast by the Palmer Drought Severity Index (PDSI) in our sample locations at and north of Mammoth Lakes. The lower Sierra Nevada crest due west of these locations may connect weather patterns with western slope conditions more than at our southern eastside sample sites, which were not significantly correlated with PDSI. Our results suggest eastern Sierra Nevada Jeffrey pine forests have similar seasonality and fire return intervals as some western slope forests, but site fire history can be influenced by stand isolation, historical use, and local rain shadow conditions.

Test of an adaptive hypothesis for egg speckling along an elevational gradient in a population of Mexican jays Aphelocoma ultramarina

The adaptive significance of avian egg speckling patterns has been a subject of ongoing debate. We examined speckling in a population of Mexican jays Aphelocoma ultramarina exhibiting extreme eggshell variability. We sampled 167 eggs at 55 nests from sites ranging across a steep elevation gradient within the Sierra del Carmen mountain range in Coahuila, Mexico, in order to test the recent hypothesis that egg speckling lends structural support to eggs and should therefore be more prevalent in females subject to reduced environmental calcium. Although we documented high variation in the amount and distribution of eggshell speckling within the Sierra del Carmen jays, we found no relationship between local soil calcium levels and the pattern of speckling. Our results indicate that explanations in addition to soil calcium levels are necessary to explain extreme variation in eggshell speckling in birds.