Seabird species‐ and assemblage‐level isotopic niche shifts associated with changing prey availability during breeding in coastal Newfoundland

Shifting prey availability can lead to altered species interactions, indicated by variation in the dietary niche breadth and position of species within an assemblage. On the Newfoundland coast, annual inshore spawning migration of the dominant forage fish, Capelin Mallotus villosus, provides an excellent opportunity to investigate the influence of varying prey availability on dietary niche breadth and position among species. During June–August 2017, we investigated species‐ and assemblage‐level dietary responses to shifting Capelin availability of three Capelin‐eating, sympatrically breeding auk species, the Atlantic Puffin Fratercula arctica, Razorbill Alca torda and Common Murre Uria aalge. The diet of Leach's Storm Petrels Oceanodroma leucorhoa, which breed alongside the three auk species but are not known to rely on Capelin, was also examined to determine dietary shifts throughout breeding that were unrelated to Capelin availability. We quantified stable isotope ratios (δ¹⁵N, δ¹³C) in seabird blood components (plasma, cellular component) collected both before and after spawning Capelin arrived in the study area and compared isotopic niche breadth within a Bayesian framework. At the species level, auk trophic position increased and isotopic niche breadth narrowed after Capelin arrived, suggesting a more Capelin‐based diet. Simultaneously, trophic diversity of the auk assemblage, reflecting the extent of spacing among niches of species, decreased after spawning Capelin arrived inshore. Contrastingly, increased trophic position but broader isotopic niche breadth during higher relative to lower Capelin availability for Leach's Storm Petrel confirm that this species is probably not affected by the inshore arrival of Capelin, but instead that isotopic changes may be more related to a shift in breeding stage to chick‐rearing. Overall, our findings reiterate the importance of Capelin as a prey resource for breeding auks in coastal Newfoundland, but that the degree of reliance on Capelin varies among species, possibly allowing coexistence of these ecologically similar species. The findings highlight potential changing species interactions, such as increased competition, under declines in Capelin biomass.     

New insights into the trophic ecology of blacktip sharks (Carcharhinus limbatus) from a subtropical estuary in the western Gulf of Mexico

As environmental change persists, understanding resource use patterns is of value to predict the consequences of shifting trophic structures. While many sharks are opportunistic predators, some exhibit prey selectivity, putting them at higher risk compared to species with greater trophic plasticity. In the Gulf of Mexico (GOM), Clupeids and Sciaenids comprise 69% of blacktip shark (Carcharhinus limbatus) diets, which is consequential considering potential responses of these prey groups to disturbance and over harvesting. We assessed if blacktips exhibit selectivity for Clupeids and Sciaenids in the western GOM based on stomach contents from sharks in coastal Texas. Clupeids comprised <2% of diets, while striped mullet (Mugil cephalus) and red drum (Sciaenops ocellatus) comprised >70% of identifiable prey. Ontogenetic shifts from smaller (Clupeids, small Sciaenids) to larger, higher trophic level (Ariidae, Elasmobranchii) prey fits our understanding of foraging among coastal sharks, and suggests our regional understanding of blacktip trophic ecology may be limited by the sizes of sampled sharks. Observed increases in blacktip densities coupled with declines in prey (Mugilids, Sciaenids) is concerning if blacktips have limited diet plasticity. Yet GOM blacktips may be more generalized than previously thought, which is promising for conservation and management.     

基于多种同位素模型的侧柏林生态系统蒸散组分定量拆分

为了全面认识森林生态系统蒸散各组分及其对蒸散的贡献率在日尺度上的变化规律,本研究利用同位素稳态和非稳态假设理论结合水同位素分析仪系统,对生长季侧柏林生态系统蒸散各组分进行了定量拆分和比较。结果表明: 4个测定日(2016年8月5、8、10、11日)不同来源水体的¹⁸O都呈现表层土壤水氧同位素组成(δ_S)＞枝条水氧同位素组成(δ_X)＞大气水汽氧同位素组成(δ_V),说明三者可能因同位素分馏效应表现出明显的差异。土壤蒸发水汽氧同位素组成(δ_E)在日尺度上为-26.89‰～-59.68‰,整体上呈现出先上升后下降的变化趋势;森林生态系统蒸散水汽氧同位素组成(δ_ET)为-15.99‰～-10.04‰,稳态(ISS)下植物蒸腾水汽氧同位素组成(δ_T-ISS)为-12.10‰～-9.51‰,而非稳态(NSS)下植物蒸腾水汽氧同位素组成(δ_T-NSS)为-13.02‰～-7.23‰,在日时间尺度上δ_ET与δ_T-NSS全天的变化趋势一致,在11:00—17:00 δ_ET、δ_T-ISS与δ_T-NSS三者的变化趋势近似一致。总体上,植物蒸腾量对蒸散量的贡献率表现为F_T-ISS 79.1%～98.7%,而F_T-NSS 88.7%～93.7%。这表明研究区土壤蒸发耗水远小于植被蒸腾耗水,植被蒸腾在林地蒸散中起主导作用。     

典型林区水分氢氧稳定同位素在土壤-植物-大气连续体中的分布特征

土壤-植物-大气连续体(SPAC)中水循环是水文学和生态学研究的重要内容,氢氧稳定同位素在不同水体中组成特征的差异可以指示水分循环过程。本研究通过分析成都平原区亚热带常绿阔叶林中降水、土壤水、植物水的同位素组成,探讨SPAC系统中水分的氢氧稳定同位素演化特征,揭示区域水循环不同界面过程。结果表明: 研究区雨季大气降水线方程为: δD=7.13δ¹⁸O+2.35(R²=0.99),土壤蒸发线方程为: δD=6.98δ¹⁸O-0.32(R²=0.92)。在降水→土壤水→植物水的界面水输送过程中,氢氧同位素逐渐富集。浅层土壤(0～35 cm)水δ¹⁸O受降水的直接影响,响应关系明显,中深层土壤(35～100 cm)水则相对稳定。观测期间,植物木质部水同位素比土壤水略微富集,说明水分在植物体内输送过程中可能通过韧皮部或树皮发生轻微蒸发或蒸腾。采用直接相关法初步估计植物对不同土层土壤水的利用情况,樟树主要利用中层土壤水,构树主要利用浅层土壤水,金星蕨因根系分布浅更倾向于利用浅层土壤水和植物截留的降水。与金星蕨相比,樟树和构树的叶片水分蒸发和同位素动力分馏程度更强。     

生长在超干旱环境下的3种相思树种表现出异常低的叶片、树枝、树干、根中δ13C含量

生长在超干旱环境下的3种相思树种表现出异常低的叶片、树枝、树干、根中δ¹³C含量 在植物生理生态学中,叶片中碳13(¹³C)含量负值较少(富集),表明叶片处于通过气孔的气体交换减少,比如在干旱胁迫下。此外,与叶片相比,13C在非光合组织中的负值也较少。然而,对从叶片(光合器官)到树枝、树干和根(非光合器官)中的δ ¹³C数值的关系知之甚少,特别是缺少在关联密切的多个树种间或者不同器官间,以及对生长在极端高温和干旱胁迫下的树木中进行测定。本研究测定了3种近缘沙漠相思树种(Acacia tortilis、A. raddiana和A. pachyceras)从叶片到根的¹³C含量。我们在以色列南部成树的叶片组织中测定了δ ¹³C含量。与此同时,在试验果园进行了为期7年的3个水平的灌溉试验。在试验结束时,测定了叶片、树枝、树干和根的生长参数和δ ¹³C含量。研究结果表明,叶片组织中δ ¹³C含量约为−27‰,其同位素贫化程度远超过生长在地球上最干燥和最热环境中的沙漠树种的预期值。在不同的相思树种和不同器官中,所有灌溉水平处理中的δ ¹³C含量并没有富集(−28‰到ca. −27‰),证实了在成熟相思树中的测定结果。在不同器官中,叶片δ ¹³C含量与树枝和根的δ ¹³C含量异常相似,甚至比树干的δ ¹³C含量负值更少。高度贫化的叶片δ ¹³C表明,尽管这些树木生长在极端干燥的生境中,但其气孔气体交换较高。非光合组织中缺乏δ ¹³C富集可能与叶片和异养组织生长的季节耦合有关。     

Long‐term increases in intrinsic water‐use efficiency do not lead to increased stem growth in a tropical monsoon forest in western Thailand

Rising atmospheric carbon dioxide [CO₂] can accelerate tree growth by stimulating photosynthesis and increasing intrinsic water‐use efficiency (iWUE). Little evidence exists, however, for the long‐term growth and gas‐exchange responses of mature trees in tropical forests to the combined effects of rising [CO₂] and other global changes such as warming. Using tree rings and stable isotopes of carbon and oxygen, we investigated long‐term trends in the iWUE and stem growth (basal area increment, BAI) of three canopy tree species in a tropical monsoon forest in western Thailand (Chukrasia tabularis, Melia azedarach, and Toona ciliata). To do this, we modelled the contribution of ontogenetic effects (tree diameter or age) and calendar year to variation in iWUE, oxygen isotopes, and BAI using mixed‐effects models. Although iWUE increased significantly with both tree diameter and calendar year in all species, BAI at a given tree diameter was lower in more recent years. For one species, C. tabularis, differences in crown dominance significantly influence stable isotopes and growth. Tree ring Δ¹⁸O increased with calendar year in all species, suggesting that increasing iWUE may have been driven by relatively greater reductions in stomatal conductance – leading to enrichment in Δ¹⁸O – than increases in photosynthetic capacity. Plausible explanations for the observed declines in growth include water stress resulting from rising temperatures and El Niño events, increased respiration, changes in allocation, or more likely, a combination of these factors.     

The legacy of enhanced N and S deposition as revealed by the combined analysis of δ13C, δ18O and δ15N in tree rings

This study aimed to evaluate the effects of long‐term repeated aerial nitrogen (N) and sulphur (S) misting over tree canopies of a Sitka spruce plantation in Scotland. We combined δ¹³C and δ¹⁸O in tree rings to evaluate the changes in CO₂ assimilation (A) and stomatal conductance (g_s) and to assess their contribution to variations in the intrinsic water‐use efficiency (WUE_i, i.e., the A/g_s ratio). Measurements of δ¹⁵N enabled shifts in the ecosystem N cycling following misting to be assessed. We found that: (i) N applications, with or without S, increased the ratio between A and g_s in favour of A, thus supporting a fertilizer effect of added N. (ii) After the treatments ceased, the trees quickly adjusted to the reductions of N deposition, but not to the reduction in S deposition, which had a negative effect on WUE_i by reducing A. This indicates that the beneficial role of N deposition may be negated in forests that previously received a high load of acid rain. (iii) δ¹⁵N in tree rings reflected the N dynamics caused by canopy retention, with the fingerprint also present in the litter, after the experiment stopped. (iv) Both our results (obtained using canopy applications) and a collection of published data (obtained using soil applications) showed that generally WUE_i increased in response to an increase of N applications, with the magnitude of the changes related to soil conditions and the availability of other nutrients. The shifts observed in δ¹⁵N in tree rings also suggest that both the quantity of the applied N and its quality, mediated by processes occurring during canopy N retention, are important determinants of the interactions between N and C cycles. Stable isotopes are useful probes to understand these processes and to put the results of short‐term experiments into context.     

Insights into the spatiotemporal component of feeding ecology: an isotopic approach for conservation management sciences

Aim Bringing new approaches to trace spatiotemporal variations in animals’ feeding ecology, which is fundamental for wildlife management and conservation since the accessibility of animals to trophic resources plays a key role in the dynamics of populations and metapopulations. Location Western Mediterranean coast. Methods The analysis of naturally occurring stable isotopes constitutes an exceptional approach to assess variations in the trophic ecology of species within the spatiotemporal dimensions. Here, we examined the spatiotemporal heterogeneity in resource exploitation of a nuisance and overpopulated gull species with a great feeding plasticity, the Yellow‐legged gull Larus michahellis, by measuring the stable isotope ratios of carbon (¹³C/¹²C, δ¹³C), nitrogen (¹⁵N/¹⁴N, δ¹⁵N) and sulphur (³⁴S/³³S, δ³⁴S) in different wing feathers. Results Tracing isotopic changes among feathers in relation to moulting sequence, we showed that isotopic analyses on first primary feathers were good indicators of breeding trophic ecology, while others, such as eighth secondary feathers, reflected the feeding behaviour during the non‐breeding period. This knowledge was then used to report on estimations of seasonal feeding patterns throughout the year for seven gull populations along the Western Mediterranean coast. Main conclusions The high diversity in the exploitation patterns of the foraging habitats found in the study area both at spatial and at temporal scale indicated the opportunistic feeding behaviour of Yellow‐legged gulls. Proposed isotopic approach has revealed as a useful tool to evaluate spatiotemporal variations in the feeding ecology of populations which may become clue for dealing with the management of wild species, not only nuisance populations but also endangered species. We finally pointed out the relevance of the isotopic variability among individuals to infer diet diversity and food availability of a given population, thereby allowing demographic forecasts when trophic resources vary in abundance.     

动物活体成像生物发光稳定细胞株的构建

目的:构建组成型表达萤光素酶基因的载体,建立稳定高表达萤光素酶的MCF-7乳腺癌细胞株,检测其对细胞增殖的影响及在传代后的表达效果.方法:以载体pGIA.20为模板,PCR扩增萤火虫萤光素酶基因,将其克隆到载体pIRESpuro2上,将获得的pIRESpuro2-Luc经酶切和测序验证后,转染293T、MCF-7及ZR...     

Alien Plant Invasions,Introduced Ungulates,and Alternative States in a Mesic Forest in Hawaii

Restoration by natural successional processes after removal of perturbations may not be feasible for many degraded ecosystems. Controlling major ecological threats such as non‐native ungulates is often a critical first step toward restoring native communities but past degradation, interactions with alien species and abiotic features may create conditions requiring additional intervention to ensure effective conservation. We monitored a series of fenced plots within diverse mesic forest on western Kauai in the Hawaiian Islands from 1998 to 2005 to determine the effects of ungulate removal on native and alien plant species. Relative to unfenced control plots, germination of seedlings and frequency of understory species of both native and alien species increased in the fenced plots. Density of both native and alien canopy and understory species declined more in unfenced than fenced plots, but density of native species declined more than alien species density in both fenced and unfenced plots. In fenced plots, the frequency of larger alien woody species and cover of an alien, mat‐forming fern species increased over time, indicating that fencing may encourage alien species that could interfere with regeneration of native species. Our study suggests that effective conservation of this and other remnant native Hawaiian forests will require both ungulate exclusion, removal of alien plant species with especially detrimental effects on native species, and proactive restoration programs for native species without natural sources of propagules. As the effects of invasive species continue to escalate, continental ecosystems lacking high endemism may also require similar interventions to preserve their biodiversity.