Connectivity of wood thrush breeding,wintering, and migration sites based on range‐wide tracking

Many migratory animals are experiencing rapid population declines, but migration data with the geographic scope and resolution to quantify the complex network of movements between breeding and nonbreeding regions are often lacking. Determining the most frequently used migration routes and nonbreeding regions for a species is critical for understanding population dynamics and making effective conservation decisions. We tracked the migration of individual Wood Thrushes (Hylocichla mustelina) (n = 102) from across their range with light‐level geolocators and, for the first time, quantified migration routes and wintering regions for distinct breeding populations. We identified regional and species‐level migratory connectivity networks for this declining songbird by combining our tracking results with range‐wide breeding abundance estimates and forest cover data. More than 50% of the species occupied the eastern wintering range (Honduras to Costa Rica), a region that includes only one‐third of all wintering habitat and that is undergoing intensive deforestation. We estimated that half of all Wood Thrushes in North America migrate south through Florida in fall, whereas in spring approximately 73% funnel northward through a narrow span along the central U.S. Gulf Coast (88–93°W). Identifying migratory networks is a critical step for conservation of songbirds and we demonstrated with Wood Thrushes how it can highlight conservation hotspots for regional populations and species as a whole. Conectividad de Sitios de Reproducción, Invierno y Migración del Zorzal con Base en Rastreo de Cobertura Amplia     

Geographical variations in the trophic ecology of Japanese anchovy, Engraulis japonicus, inferred from carbon and nitrogen stable isotope ratios

Carbon and nitrogen stable isotope ratios of Japanese anchovy (Engraulis japonicus) and their stomach contents were examined and compared among various regions around Japan. Geographical variations in the isotope ratios were found between inshore and Pacific offshore regions. While most of the anchovy samples had isotope ratios around −17.6‰ for δ¹³C and 10.0‰ for δ¹⁵N as median values, higher (more enriched) isotope values were found in the anchovy sampled from inshore regions. On the contrary, lower (more depleted) values were found mostly in the anchovy from the Pacific offshore region including the Kuroshio Extension and Kuroshio-Oyashio transition zones. Higher carbon isotope ratios in the inshore regions may reflect a carbon source from benthic primary producers in addition to phytoplankton possibly through the consumption of the larvae of benthic organisms such as bivalves or decapods, which were found in the stomach contents of the inshore anchovy. Variations in the nitrogen isotope ratio may reflect not only differences in the trophic level of prey species, but also variations in the baseline level of food webs. Stable isotope ratios are potentially a useful tool for understanding the stock/population structure and migration of anchovy. The present findings indicate the potential importance of the “inshore–offshore” variations in the biology of Japanese anchovy populations in the northwestern Pacific waters.     

Temporal and spatial variability in stable isotope ratios of SPM link to local hydrography and longer term SPM averages suggest heavy dependence of mussels on nearshore production

Temporal changes in hydrography affect suspended particulate matter (SPM) composition and distribution in coastal systems, potentially influencing the diets of suspension feeders. Temporal variation in SPM and in the diet of the mussel Perna perna, were investigated using stable isotope analysis. The δ¹³C and δ¹⁵ N ratios of SPM, mussels and macroalgae were determined monthly, with SPM samples collected along a 10 km onshore–offshore transect, over 14 months at Kenton-on-Sea, on the south coast of South Africa. Clear nearshore (0 km) to offshore (10 km) carbon depletion gradients were seen in SPM during all months and extended for 50 km offshore on one occasion. Carbon enrichment of coastal SPM in winter (June–August 2004 and May 2005) indicated temporal changes in the nearshore detrital pool, presumably reflecting changes in macroalgal detritus, linked to local changes in coastal hydrography and algal seasonality. Nitrogen patterns were less clear, with SPM enrichment seen between July and October 2004 from 0 to 10 km. Nearshore SPM demonstrated cyclical patterns in carbon over 24-h periods that correlated closely with tidal cycles and mussel carbon signatures, sampled monthly, demonstrated fluctuations that could not be correlated to seasonal or monthly changes in SPM. Macroalgae showed extreme variability in isotopic signatures, with no discernable patterns. IsoSource mixing models indicated over 50% reliance of mussel tissue on nearshore carbon, highlighting the importance of nearshore SPM in mussel diet. Overall, carbon variation in SPM at both large and small temporal scales can be related to hydrographic processes, but is masked in mussels by long-term isotope integration.     

Fine-scale population structure of estuarine bottlenose dolphins (Tursiops truncatus) assessed using stable isotope ratios and fatty acid signature analyses

Stable isotope ratios and fatty acid signature analyses were employed to examine the fine-scale population structure of a year-round resident population of 600–800 bottlenose dolphins (Tursiops truncatus) in the Indian River Lagoon (IRL), Florida. The IRL, a 250-km-long estuary running along the central east coast of Florida (28.0°N, 80.6°W), is comprised of the northern and southern IRL, Mosquito Lagoon (ML), Banana River (BR), and St. Lucie Estuary. Samples of skin and blubber were collected from dead stranded (n = 61, 1994–2004) and live dolphins (n = 153, 2002–2007, 2010, 2011) from throughout the IRL and surrounding environs. Using stable isotopes (SI), dolphins could be assigned to a ML subpopulation, a St. Lucie Estuary subpopulation, and an IRL subpopulation. Fatty acid signature analysis (FASA) allowed for finer resolution, detecting ML and BR subpopulations, a separation of northern and southern IRL subpopulations, and a St. Lucie Estuary subpopulation. Differences between sexes were detectable within subpopulations using FASA, but not using SI. This may indicate that males and females are foraging in similar locations at a similar trophic level (detected using SI), but are varying in the types or proportions of specific prey (indicated by FASA). The combination of these complementary analyses results in a powerful tool for assessing fine-scale population substructure.     

Quantitative approaches to the analysis of stable isotope food web data

Ecologists use stable isotopes (delta13C, delta15N) to better understand food webs and explore trophic interactions in ecosystems. Traditionally, delta13C vs. delta15N bi-plots have been used to describe food web structure for a single time period or ecosystem. Comparisons of food webs across time and space are increasing, but development of statistical approaches for testing hypotheses regarding food web change has lagged behind. Here we present statistical methodologies for quantitatively comparing stable isotope food web data. We demonstrate the utility of circular statistics and hypothesis tests for quantifying directional food web differences using two case studies: an arthropod salt marsh community across a habitat gradient and a freshwater fish community from Lake Tahoe, USA, over a 120-year time period. We calculated magnitude and mean angle of change (theta) for each species in food web space using mean delta13C and delta15N of each species as the x, y coordinates. In the coastal salt marsh, arthropod consumers exhibited a significant shift toward dependence on Spartina, progressing from a habitat invaded by Phragmites to a restored Spartina habitat. In Lake Tahoe, we found that all species from the freshwater fish community shifted in the same direction in food web space toward more pelagic-based production with the introduction of nonnative Mysis relicta and onset of cultural eutrophication. Using circular statistics to quantitatively analyze stable isotope food web data, we were able to gain significant insight into patterns and changes in food web structure that were not evident from qualitative comparisons. As more ecologists incorporate a food web perspective into ecosystem analysis, these statistical tools can provide a basis for quantifying directional food web differences from standard isotope data.     

Exaggerated orientation scatter of nocturnal passerine migrants close to breeding grounds: comparisons between seasons and latitudes

Using tracking radars, we investigated the variability of flight directions of long-distance nocturnal passerine migrants across seasons (spring versus autumn migration) and sites at the southern (56° N) and northern (68° N) ends of the Scandinavian Peninsula (Lund versus Abisko). Whilst most migrants at Lund are on passage to and from breeding sites in Fennoscandia, the majority of the migrants at Abisko are close to their breeding sites, and migration at Abisko thus to a large degree reflects initial departure from breeding sites (autumn) or final approach to breeding destinations (spring). The radar data were used to test predictions about differences in orientation and wind drift effects between adult and juvenile birds (a large proportion of autumn migrants consists of juvenile birds on their first journey), between situations far away from or near the goals and between different phases of migration (initial departure, en route passage, final approach to goal). The concentrations (both total and within-night concentrations) of flight directions differed significantly between seasons as well as sites, with the highest concentration at Lund in spring (mean vector length of track directions, r = 0.79) and lowest at Abisko during spring (r = 0.35). Partial wind drift and partial compensation were recorded at Lund, with a similar effect size in spring and autumn, whilst possible wind drift effects at Abisko were obscured by the large directional scatter at this site. The results from Lund support the prediction that the high proportion of juveniles in autumn contributes to increase the directional scatter during this season, whilst there was no support for predictions of differential wind drift effects between seasons and situations with different goal distances. The most striking and surprising result was the exceedingly large scatter of flight directions at Abisko, particularly in spring. We suggest that such an exaggerated scatter may be associated with final approach orientation, where migrants reach their specific goals from all various directions by final navigation within a more wide-ranging goal region. The larger scatter of autumn flight directions at Abisko compared to Lund may be due to exploratory flights in variable directions being more common at initial departure from breeding sites than later during migratory passage. These surprising results highlight the importance of studying and analysing orientation during final approach to (and initial departure from) migratory goals for understanding the orientation systems of migratory birds.     

Changes in nutrient content and stable isotope ratios of C and N during decomposition of seagrasses and mangrove leaves along a nutrient availability gradient in Florida Bay,USA

The decomposition of the mangrove Rhizophora mangle and the seagrass Thalassia testudinum was examined using litterbags along a natural gradient in nutrient availability. Seagrass leaves had a higher fraction of their biomass in the labile pool (57%), compared to mangrove leaves (36%) and seagrass rhizomes (29%); the overall decomposition rates of the starting material reflected the fractionation into labile and refractory components. There was no relationship between the N or P content of the starting material and the decomposition rate.

Nutrient availability had no influence on decomposition rate, and mass was lost at the same rate from litterbags that were buried in the sediment and litterbags that were left on the sediment surface. The dynamics of N and P content during decomposition varied as a function of starting material and burial state. N content of decomposing mangrove leaves increased, but seagrass rhizomes decreased in N content during decomposition while there was no change in seagrass leaf N content. These same general patterns held for P content, but buried seagrass leaves increased in P content while surficial leaves decreased. δ¹³C and δ¹⁵N changed by as much as 2‰ during decomposition.     

Changes in nutrient content and stable isotope ratios of C and N during decomposition of seagrasses and mangrove leaves along a nutrient availability gradient in Florida Bay, USA

The decomposition of the mangrove Rhizophora mangle and the seagrass Thalassia testudinum was examined using litterbags along a natural gradient in nutrient availability. Seagrass leaves had a higher fraction of their biomass in the labile pool (57%), compared to mangrove leaves (36%) and seagrass rhizomes (29%); the overall decomposition rates of the starting material reflected the fractionation into labile and refractory components. There was no relationship between the N or P content of the starting material and the decomposition rate.

Nutrient availability had no influence on decomposition rate, and mass was lost at the same rate from litterbags that were buried in the sediment and litterbags that were left on the sediment surface. The dynamics of N and P content during decomposition varied as a function of starting material and burial state. N content of decomposing mangrove leaves increased, but seagrass rhizomes decreased in N content during decomposition while there was no change in seagrass leaf N content. These same general patterns held for P content, but buried seagrass leaves increased in P content while surficial leaves decreased. δ¹³C and δ¹⁵N changed by as much as 2‰ during decomposition.     

传统稳定同位素技术在环境科学领域的应用及研究进展

本文回顾了同位素技术的发展历史、简介了传统稳定同位素技术的应用原理与主要分析仪器.重点介绍了传统稳定同位素技术在污染物溯源、识别转化历程和指示反应程度,以及重建古环境信息,构建生态系统营养结构和探索生态物质循环等环境科学领域的应用与最新研究进展,提出了当前传统稳定同位素技术面临的挑战并对未来的发展方向进行了展望.     

Aquatic metabolism and ecosystem health assessment using dissolved O2 stable isotope diel curves.

Dissolved O2 concentration and delta18O-O2 diel curves can be combined to assess aquatic photosynthesis, respiration, and metabolic balance, and to disentangle some of the confounding factors associated with interpretation of traditional O2 concentration curves. A dynamic model is used to illustrate how six key environmental and biological parameters interact to affect diel O2 saturation and delta18O-O2 curves, thereby providing a fundamental framework for the use of delta18O-O2 in ecosystem productivity studies. delta18O-O2 provides information unavailable from concentration alone because delta18O-O2 and saturation curves are not symmetrical and can be used to constrain gas exchange and isotopic fractionation by eliminating many common assumptions. Changes in key parameters affect diel O2 saturation and delta18O-O2 curves as follows: (1) an increase in primary production and respiration rates increases the diel range of O2 saturation and delta18O-O2 and decreases the mean delta18O-O2 value; (2) a decrease in the primary production to respiration ratio (P:R) decreases the level of O2 saturation and increases the delta18O-O2 values; (3) an increase in the gas exchange rate decreases the diel range of O2 saturation and delta18O-O2 values and moves the mean O2 saturation and delta18O-O2 values toward atmospheric equilibrium; (4) a decrease in strength of the respiratory isotopic fractionation (alphaR closer to 1) has no effect on O2 saturation and decreases the delta18O-O2 values; (5) an increase in the delta18O of water has no effect on O2 saturation and increases the minimum (daytime) delta18O-O2 value; and (6) an increase in temperature reduces O2 solubility and thus increases the diel range of O2 saturation and delta18O-O2 values. Understanding the interplay between these key parameters makes it easier to decipher the controls on O2 and delta18O-O2, compare aquatic ecosystems, and make quantitative estimates of ecosystem metabolism. The photosynthesis to respiration to gas exchange ratio (P:R:G) is better than the P:R ratio at describing and assessing the vulnerability of aquatic ecosystems under various environmental stressors by providing better constrained estimates of ecosystem metabolism and gas exchange.     

稳定氢氧同位素在定量区分植物水分利用来源中的应用

全球气候变化下陆地生态系统的适应性是当前科学研究关注的主题之一,了解生态系统如何响应及影响全球气候变化有利于人类对未来生存环境的预测和适应。生态系统中不同来源水分对植物生长相对贡献决的大小一定程度上决定了生态系统对气候变化的响应方式、程度和响应结果,因此跟踪和分析植物利用水分的来源是制定全球气候变化对策的一个重要研究内容。本文介绍了稳定氢氧同位素技术研究历史及其在定量区分植物利用水分的来源研究中的应用原理与具体方法。由于土壤水分在被植物根系吸收及随后沿导管向上传输的过程中,与外界环境不发生水分交换,因此不存在同位素的分馏过程,所以植物茎木质部水分同位素组成能反映出植物利用的来源水分同位素信息。通过比较植物茎木质部水分与植物利用的不同来源水分同位素值,利用二项或三项分隔线性混合模型(two-orthree-compartment linear mixing model),可以估算出植物对不同来源水分的相对使用量。而由于植物叶片水分同位素组成受到周围环境的温度、湿度、降雨和土壤水分的异质性等许多因素的影响,通过比较分析植物茎木质部水分和叶片水分同位素组成的差异可以得到植物周围环境的气候信息。植物利用水分的来源存在显著的季节性差异,并且,不同生活型植物在利用水分来源上存在明显不同。植物根系的分布及根深是决定植物利用水分来源的一个重要的因素,表层和深层根系的相对分布及其活性影响着植物吸收水分的范围。当然,利用线型分隔混合模型定量区分植物利用水分的不同来源,还有许多值得改进的地方,而且,尽管稳定同位素技术在植物科学中的应用正迅速发展起来,但利用稳定氢氧同位素来分析环境因素对植物影响的研究还只是刚刚展开,还有许多方面值得去进一步探索。     

Characterization of environmental water samples using strontium and lead stable isotope compositions

A simple procedure using both cation and anion exchange chromatography has been applied in the study of lead and strontium isotope composition in rain and stream water samples from remote catchments in Scotland. Whereas the soil released strontium to stream waters, lead was removed from rain water and the concentrations in stream waters were very low. Highly precise analysis by thermal ionisation mass spectrometry proved necessary in the determination of strontium isotope composition. The ⁸⁷Sr/⁸⁶Sr ratio in rain water was close to that of marine strontium but the ratios in stream waters were constant and highly characteristic for the stream. In the case of the stream at the Sourhope site, the ratio (0.70798 ± 0.00005) was less than that in rain water and probably resulted from the weathering of one specific mineral. The results suggested that the ⁸⁷Sr/⁸⁶Sr ratios could be used as a stable isotope tracer of waters and to provide information on the weathering processes. Two major anthropogenic components of lead were identified in water samples. One had its origin in petrol additives whereas the other was probably of industrial origin. The low ²⁰⁶Pb/²⁰⁷Pb ratios observed in stream waters confirmed the lead as being of anthropogenic origin and the data suggested that there was a movement, albeit very small, of lead from the soil to waters.     

A seasonal stable isotope survey of the food web associated to a peri-urban rocky shore

We characterized the structure and functioning of the food web associated to an intertidal rocky shore in the harbour of Brest (Western Brittany, France), through a seasonal δ¹³C and δ¹⁵N survey. The dominance of benthic-derived organic matter, and particularly resuspended sediment, in the local pool of suspended organic matter, is highlighted. This benthic-derived organic matter dominates the diet of filter-feeders, including a certain degree of selectivity displayed by various taxa belonging to this trophic group. The food web structure appeared very stable temporally, which suggested the dominance of mixed diets, rather than the consumption of pure sources. It was constituted of 4 trophic levels, including a large diversity of predators, likely favoured by the diversity of microhabitats that characterize this intertidal habitat. From our results, the trophic functioning of this peri-urban rocky shore community does not appear functionally simplified as previously reported for other anthropized and/or artificial rocky ecosystems. We suggest that the topological complexity of rocky habitats, including a diversity of microhabitats, might be responsible of the important animal diversity, in spite of the anthropogenic disturbances characterizing this peri-urban area.     

氯/溴稳定同位素分析技术及其在环境科学研究中的应用

稳定同位素分析被认为是环境污染物溯源和转化途径探究的有效工具.针对氯/溴稳定同位素研究已经开发了一些较为可靠的分析技术,被广泛应用于氯乙烯、氯苯、溴酚、多溴二苯醚和有机氯农药等有机污染物的研究.本文综述了近年来氯/溴同位素分析技术的最新进展,介绍了稳定同位素分析技术在含氯/溴有机污染物的溯源分析和降解途径识别等方面的应...     

Offspring sex ratios reflect lack of repayment by auxiliary males in a cooperatively breeding passerine

The repayment hypothesis posits that primary sex ratios in cooperative species should be biased towards the helping sex because these offspring “repay” a portion of their cost through helping behavior and therefore are less expensive to produce. However, many cooperatively breeding birds and mammals do not show the predicted bias in the primary sex ratio. Recent theoretical work has suggested that the repayment hypothesis should only hold when females gain a large fitness advantage from the presence of auxiliary adults in the group. When auxiliaries provide little or no fitness advantage, competition between relatives should lead to sex ratios biased towards the dispersing (non-helping) sex. We examined the benefits auxiliaries provide to females and corresponding offspring sex ratios in the red-backed fairy-wren (Malurus melanocephalus), a cooperatively breeding Australian bird with male auxiliary helpers. We found that auxiliaries provide little or no benefit to female reproductive success or survival. As predicted, the population primary sex ratio was biased towards daughters, the dispersing sex, and females with auxiliaries produced female-biased broods whereas females without auxiliaries produced unbiased broods. Moreover, offspring sex ratios were more strongly biased toward females in years when auxiliaries were more common in the population. These results suggest that offspring sex ratios are associated with competition among the non-dispersing sex in this species, and also that females may use cues to assess local breeding opportunities for their offspring.