Community Trait Distribution Across Environmental Gradients

Ecosystems - Variability in community composition is often attributed to underlying differences in physical environments. However, predator–prey interactions can play an equally important...     

Bacterioplankton Community Variation Across River to Ocean Environmental Gradients

Coastal zones encompass a complex spectrum of environmental gradients that each impact the composition of bacterioplankton communities. Few studies have attempted to address these gradients comprehensively. We generated a synoptic, 16S rRNA gene-based bacterioplankton community profile of a coastal zone by applying the fingerprinting technique denaturing gradient gel electrophoresis to water samples collected from the Columbia River, estuary, and plume, and along coastal transects covering 360 km of the Oregon and Washington coasts and extending to the deep ocean (>2,000 m). Communities were found to cluster into five distinct groups based on location in the system (ANOSIM, p < 0.003): estuary, plume, epipelagic, shelf bottom (depth < 150 m), and slope bottom (depth > 650 m). Across all environments, abiotic factors (salinity, temperature, depth) explained most of the community variability (ρ = 0.734). But within each coastal environment, biotic factors explained most of the variability. Thus, structuring physical factors in coastal zones, such as salinity and temperature, define the boundaries of many distinct microbial habitats, but within these habitats variability in microbial communities is explained by biological gradients in primary and secondary productivity.     

Leaf Chemical and Optical Properties of Metrosideros polymorpha Across Environmental Gradients in Hawaii

Leaf chemical, biophysical, and optical properties were measured in 13 populations of Metrosideros polymorpha across gradients of soil fertility and climate in Hawaii. Climate (predominantly temperature) caused large changes in specific leaf area (SLA) and SLA-linked traits, including nitrogen (N) and pigment contents, as did conditions of highest soil fertility on 20 ky old substrates. When averaged by site, chemical constituent ratios containing chlorophyll (Car/Chl, Chl/N) varied more across climate than substrate gradients, while the Chl a/b ratio was similarly influenced by climate and substrate. Variations in Chl a/b ratios and SLA were similar to those found previously in a common garden of M. polymorpha taken from our climate gradient, suggesting strong genetic control over these traits. Optical reflectance indices related to photosynthetic function were closely correlated to pigment changes, varying three times more in response to climate than across substrate ages. Combined, our results suggest that variation in leaf structure, composition, and function of M. polymorpha is a result of genetic and phenotypic adaptation to environmental differences, and that these variations are greater in response to climate (especially temperature) than to soil fertility.     

Classifying Chimpanzee (Pan troglodytes) Landscapes Across Large-Scale Environmental Gradients in Africa

International Journal of Primatology - Primates are sometimes categorized in terms of their habitat. Although such categorization can be oversimplistic, there are scientific benefits from the...     

Lifestyle-Based Approaches Provide Insights into Body Size Variation Across Environmental Gradients in Anurans

Body size of organisms as a fitness-related phenotype has evolved in response to local conditions, often through the size-dependent thermoregulatory mechanisms. The direction and degree of this response should depend on animals’ lifestyle in terms of the preference for terrestrial or aquatic conditions, especially so for adult anurans that differ in lifestyle among species but all must maintain certain body temperatures for metabolism. It may be expected that anuran species frequently exposed to terrestrial environments characterized by fluctuant thermal conditions are more plastic in body size along thermal gradients than those highly relaying on aquatic environments where thermal conditions are relatively stable. We test this prediction using both interspecific and intraspecific data. With anurans in China as the model organisms, we show that across terrestrial species but not aquatic species, body size decreases with increasing ambient temperature. From the published literature worldwide, we summarized that more terrestrial versus fewer aquatic species follow the predicted ecogeographical size patterns. In addition, both interspecific and intraspecific data reveal that arboreal anurans do not exhibit the size cline, probably because relatively warm climates experienced by these species impose weak selective pressures on heat conservation or adaptation to tree-climbing constrains the variation in body size. Our finding highlights the importance of taking lifestyle into account when assessing macroevolutionary trends in body size for anurans in particular and ectothermic taxa in general.     

Gradients of Intercellular CO(2) Levels Across the Leaf Mesophyll

Most current photosynthesis models, and interpretations of many wholeleaf CO₂ gas exchange measurements, are based on the often unstated assumption that the partial pressure of CO₂ is nearly uniform throughout the airspaces of the leaf mesophyll. Here we present measurements of CO₂ gradients across amphistomatous leaves allowed to assimilate CO₂ through only one surface, thus simulating hypostomatous leaves. We studied five species: Eucalyptus pauciflora Sieb. ex Spreng., Brassica chinensis L., Gossypium hirsutum L., Phaseolus vulgaris L., and Spinacia oleracea L. For Eucalyptus, maximum CO₂ pressure differences across the leaf mesophyll were 73 and 160 microbar when the pressures outside the lower leaf surface were 310 and 590 microbar, respectively. Using an approximate theoretical calculation, we infer that if the CO₂ had been supplied equally at both surfaces then the respective mean intercellular CO₂ pressures would have been roughly 12 and 27 microbar less than the pressures in the substomatal cavities in these cases. For ambient CO₂ pressures near 320 microbar, the average and minimum pressure differences across the mesophyll were 45 and 13 microbar. The corresponding mean intercellular CO₂ pressures would then be roughly 8 and 2 microbar less than those in the substomatal cavities. Pressure differences were generally smaller for the four agricultural species than for Eucalyptus, but they were nevertheless larger than previously reported values.     

Decadal Changes in the World's Coastal Latitudinal Temperature Gradients

Most of the world''s living marine resources inhabit coastal environments, where average thermal conditions change predictably with latitude. These coastal latitudinal temperature gradients (CLTG) coincide with important ecological clines,e.g., in marine species diversity or adaptive genetic variations, but how tightly thermal and ecological gradients are linked remains unclear. A first step is to consistently characterize the world''s CLTGs. We extracted coastal cells from a global 1°×1° dataset of weekly sea surface temperatures (SST, 1982–2012) to quantify spatial and temporal variability of the world''s 11 major CLTGs. Gradient strength, i.e., the slope of the linear mean-SST/latitude relationship, varied 3-fold between the steepest (North-American Atlantic and Asian Pacific gradients: −0.91°C and −0.68°C lat⁻¹, respectively) and weakest CLTGs (African Indian Ocean and the South- and North-American Pacific gradients: −0.28, −0.29, −0.32°C lat⁻¹, respectively). Analyzing CLTG strength by year revealed that seven gradients have weakened by 3–10% over the past three decades due to increased warming at high compared to low latitudes. Almost the entire South-American Pacific gradient (6–47°S), however, has considerably cooled over the study period (−0.3 to −1.7°C, 31 years), and the substantial weakening of the North-American Atlantic gradient (−10%) was due to warming at high latitudes (42–60°N, +0.8 to +1.6°C,31 years) and significant mid-latitude cooling (Florida to Cape Hatteras 26–35°N, −0.5 to −2.2°C, 31 years). Average SST trends rarely resulted from uniform shifts throughout the year; instead individual seasonal warming or cooling patterns elicited the observed changes in annual means. This is consistent with our finding of increased seasonality (i.e., summer-winter SST amplitude) in three quarters of all coastal cells (331 of 433). Our study highlights the regionally variable footprint of global climate change, while emphasizing ecological implications of changing CLTGs, which are likely driving observed spatial and temporal clines in coastal marine life.     

Species Diversity Across Nutrient Gradients: An Analysis of Resource Competition in Model Ecosystems

The capture and efficient use of limiting resources influence the competitive success of individual plant species as well as species diversity across resource gradients. In simulations, efficient nutrient acquisition or nutrient retention by species were key predictors of success when nutrients were limiting. Increased nutrient supply favored species with characteristics that improved light interception or light use. Ecological theory suggests that low diversity on fertile sites may be a consequence of competitive exclusion by one or a few species with superior light-interception characteristics. On infertile sites, competitive exclusion may be a function of superior nutrient-acquisition characteristics in species. At intermediate fertility, a shift from single-resource specialization to a balanced effort in the acquisition of multiple resources should allow for greater species diversity. Thus, a unimodal relationship between diversity and nutrient supply, vegetation biomass, or productivity is predicted. However, simulations demonstrated alternate relationships depending on the ecosystem characteristic to which diversity was compared. Diversity was greatest at intermediate total biomass but increased monotonically with net primary production and nitrogen (N) supply. The highest diversity occurred midrange on a scale of community-level leaf area to fine-root length ratios, which in the context of the model indicates that the vegetation as a whole was simultaneously limited by both N and light and that effort toward the acquisition of both resources is distributed in such a way that both resources are equally exploited. Diversity was lowered by the presence of species with a superior ability to sequester resources.     

On Sustainability, Estuaries, and Ecosystem Restoration: The Art of the Practical

Ecosystem restoration in highly complex, human‐dominated estuaries rests on a strong conceptual foundation of sustainability, ecosystems, and adaptive management of human‐induced environmental impacts. Successful application involves evaluating uncertainty, incorporating place‐based information, and engaging diverse constituencies in the planning process. That means integration of technical knowledge with an understanding of the “cultural milieu” inherent in all estuaries, that is, the intensity of human activity and impacts plus socioeconomic factors relevant to restoration goals. Operational definitions of what constitutes acceptable ecosystem conditions and current baselines are critical yet rest in large measure on cultural values and socioeconomic considerations. Resources for long‐term monitoring and research to assess performance and ecosystem condition are paramount. Unprecedented population growth promises additional stressors on estuarine environments worldwide, making maintenance of present conditions difficult. The art of good, practical ecosystem restoration as a management tool at multiple geographic scales promises to play a crucial role in sustainability goals.     

生物多样性的生态系统功能

本文从以下几个方面综述了生物多样性对生态系统功能和作用的影响 :第一 ,几个关于物种在生态系统中的不同地位和生物多样性如何影响生态系统功能的假说 ;第二 ,生物多样性与生态系统的稳定性 ;第三 ,生物多样性如何影响生态系统的生产力 ;第四 ,生物多样性对生态系统可持续性的影响。此外还提出了几个需要继续探讨和关注的问题     

生物多样性的生态系统功能

本文从以下几个方面综述了生物多样性对生态系统功能和作用的影响：第一,几个关于物种在生态系统中的不同地位和生物多样性如何影响生态系统功能的假说;第二,生物多样性与生态系统的稳定性;第三,生物多样性如何影响生态系统的生产力;第四,生物多样性对生态系统可持续性的影响。此外还提出了几个需要继续探讨和关注的问题。     

Sensitivity of Spring Phenology to Warming Across Temporal and Spatial Climate Gradients in Two Independent Databases

Disparate ecological datasets are often organized into databases post hoc and then analyzed and interpreted in ways that may diverge from the purposes of the original data collections. Few studies, however, have attempted to quantify how biases inherent in these data (for example, species richness, replication, climate) affect their suitability for addressing broad scientific questions, especially in under-represented systems (for example, deserts, tropical forests) and wild communities. Here, we quantitatively compare the sensitivity of species first flowering and leafing dates to spring warmth in two phenological databases from the Northern Hemisphere. One??PEP725??has high replication within and across sites, but has low species diversity and spans a limited climate gradient. The other??NECTAR??includes many more species and a wider range of climates, but has fewer sites and low replication of species across sites. PEP725, despite low species diversity and relatively low seasonality, accurately captures the magnitude and seasonality of warming responses at climatically similar NECTAR sites, with most species showing earlier phenological events in response to warming. In NECTAR, the prevalence of temperature responders significantly declines with increasing mean annual temperature, a pattern that cannot be detected across the limited climate gradient spanned by the PEP725 flowering and leafing data. Our results showcase broad areas of agreement between the two databases, despite significant differences in species richness and geographic coverage, while also noting areas where including data across broader climate gradients may provide added value. Such comparisons help to identify gaps in our observations and knowledge base that can be addressed by ongoing monitoring and research efforts. Resolving these issues will be critical for improving predictions in understudied and under-sampled systems outside of the temperature seasonal mid-latitudes.     

Non-Native Plant Invasion along Elevation and Canopy Closure Gradients in a Middle Rocky Mountain Ecosystem

Mountain environments are currently among the ecosystems least invaded by non-native species; however, mountains are increasingly under threat of non-native plant invasion. The slow pace of exotic plant invasions in mountain ecosystems is likely due to a combination of low anthropogenic disturbances, low propagule supply, and extreme/steep environmental gradients. The importance of any one of these factors is debated and likely ecosystem dependent. We evaluated the importance of various correlates of plant invasions in the Wallowa Mountain Range of northeastern Oregon and explored whether non-native species distributions differed from native species along an elevation gradient. Vascular plant communities were sampled in summer 2012 along three mountain roads. Transects (n = 20) were evenly stratified by elevation (~70 m intervals) along each road. Vascular plant species abundances and environmental parameters were measured. We used indicator species analysis to identify habitat affinities for non-native species. Plots were ordinated in species space, joint plots and non-parametric multiplicative regression were used to relate species and community variation to environmental variables. Non-native species richness decreased continuously with increasing elevation. In contrast, native species richness displayed a unimodal distribution with maximum richness occurring at mid–elevations. Species composition was strongly related to elevation and canopy openness. Overlays of trait and environmental factors onto non-metric multidimensional ordinations identified the montane-subalpine community transition and over-story canopy closure exceeding 60% as potential barriers to non-native species establishment. Unlike native species, non-native species showed little evidence for high-elevation or closed-canopy specialization. These data suggest that non-native plants currently found in the Wallowa Mountains are dependent on open canopies and disturbance for establishment in low and mid elevations. Current management objectives including restoration to more open canopies in dry Rocky Mountain forests, may increase immigration pressure of non-native plants from lower elevations into the montane and subalpine zones.     

Ecosystem Recovery Across a Chronosequence of Restored Wetlands in the Platte River Valley

Wet meadows in the Platte River valley (PRV) consist of linear wetlands in mesic prairie matrix systems that have been degraded and diminished for agriculture. Restoration in this region is a widespread practice that involves land contouring and seeding native species, however ecosystem recovery following restoration has never been examined. We quantified recovery trajectories and rates of above- and belowground plant biomass, soil physical and chemical properties, and C and N pools in a chronosequence of six restored wet meadows in relation to three natural wetlands. Within each site, we sampled sloughs (deeper habitats) and adjacent margins (slightly higher elevation) for three consecutive years. Varying hydrologic regimes between habitats resulted in differential patterns in ecosystem measurements (bulk density, C mineralization) in both natural and restored wetlands. Total aboveground biomass (TAB), root biomass, root C and N storage, total soil C and N, microbial N, and extractable N increased with years restored in both margins and sloughs. The model predicted rates of increase did not differ between habitats, but elevations of linear regressions were higher in sloughs than margins for root N, total soil C, total soil N, MBN, and extractable total N (P < 0.05). Our results suggest that bulk density and soil organic matter (SOM) represent two useful, easily measured indices of ecosystem recovery, because they were correlated with many pools and fluxes of C and N. Furthermore, we conclude that most change in ecosystem structure and function during the first decade following restoration occurs in shallow soil depths, and ecosystem recovery varies with subtle differences in elevation and associated plant community structure.