Role of sources and temporal sinks in a marine amphipod

Spatially structured habitats challenge populations to have positive growth rates and species often rely on dispersing propagules to occupy habitats outside their fundamental niche. Most marine species show two main life stages, a dispersing stage and a sedentary stage affecting distribution and abundance patterns. An experimental study on Corophium acherusicum, a colonial tube-building amphipod, showed the strong influence that a source population can have on new habitats. More importantly, this study shows the effect of temporal sinks where newly established populations can show reduced growth rates if the propagule supply from a source is removed. Sink populations had a reduction in abundance and became male-biased as females left colonies. The consequences arising from short-term dispersal and temporal sinks could be due to different selection pressures at the source and sink populations. These consequences can become reflected in long-term dynamics of marine populations if we shift focus to non-random dispersal models incorporating behaviour and stage-dependent dispersal.     

环境因子对森林净生态系统生产力的影响

净生态系统生产力(net ecosystem production,NEP)是生态系统净的碳积累速率,可以指示生态系统碳汇/碳源的状态,当NEP为正值时指征生态系统为碳汇,反之则为碳源。在全球环境变化背景下,NEP已作为生态系统碳循环的核心概念被深入研究。本文以NEP为出发点,综述了5个主要非生物环境因子(水分、温度、氮沉降、大气CO2浓度增加和时空尺度)对森林生态系统NEP的影响。从文献分析表明NEP受生态系统本身性质和各环境影响因子及其之间相互作用的调控。本文最后指出,合理运用Meta分析、生态学联网研究、设计和开展长期观测、多尺度与多因子的科学试验在未来研究中的重要性和必要性,相关研究的开展将有利于全面理解和正确评估环境因子对净生态系统生产力的影响,对研究和预测全球变化对陆地生态系统碳循环的影响具有重要意义。     

Terrestrial carbon sinks in China and around the world and their contribution to carbon neutrality

Enhancing the terrestrial ecosystem carbon sink (referred to as terrestrial C sink) is an important way to slow down the continuous increase in atmospheric carbon dioxide (CO₂) concentration and to achieve carbon neutrality target. To better understand the characteristics of terrestrial C sinks and their contribution to carbon neutrality, this review summarizes major progress in terrestrial C budget researches during the past decades, clarifies spatial patterns and drivers of terrestrial C sources and sinks in China and around the world, and examines the role of terrestrial C sinks in achieving carbon neutrality target. According to recent studies, the global terrestrial C sink has been increasing from a source of (?0.2±0.9) Pg C yr^?1 (1 Pg=10¹⁵ g) in the 1960s to a sink of (1.9±1.1) Pg C yr^?1 in the 2010s. By synthesizing the published data, we estimate terrestrial C sink of 0.20–0.25 Pg C yr^?1 in China during the past decades, and predict it to be 0.15–0.52 Pg C yr^?1 by 2060. The terrestrial C sinks are mainly located in the mid- and high latitudes of the Northern Hemisphere, while tropical regions act as a weak C sink or source. The C balance differs much among ecosystem types: forest is the major C sink; shrubland, wetland and farmland soil act as C sinks; and whether the grassland functions as C sink or source remains unclear. Desert might be a C sink, but the magnitude and the associated mechanisms are still controversial. Elevated atmospheric CO₂ concentration, nitrogen deposition, climate change, and land cover change are the main drivers of terrestrial C sinks, while other factors such as fires and aerosols would also affect ecosystem C balance. The driving factors of terrestrial C sink differ among regions. Elevated CO₂ concentration and climate change are major drivers of the C sinks in North America and Europe, while afforestation and ecological restoration are additionally important forcing factors of terrestrial C sinks in China. For future studies, we recommend the necessity for intensive and long term ecosystem C monitoring over broad geographic scale to improve terrestrial biosphere models for accurately evaluating terrestrial C budget and its dynamics under various climate change and policy scenarios.

     

Temporal variation can facilitate niche evolution in harsh sink environments

We examine the impact of temporal variation on adaptive evolution in "sink" environments, where a species encounters conditions outside its niche. Sink populations persist because of recurrent immigration from sources. Prior studies have highlighted the importance of demographic constraints on adaptive evolution in sinks and revealed that adaptation is less likely in harsher sinks. We examine two complementary models of population and evolutionary dynamics in sinks: a continuous-state quantitative-genetics model and an individual-based model. In the former, genetic variance is fixed; in the latter, genetic variance varies because of mutation, drift, and sampling. In both models, a population in a constant harsh sink environment can exist in alternative states: local maladaptation (phenotype comparable to immigrants from the source) or adaptation (phenotype near the local optimum). Temporal variation permits transitions between these states. We show that moderate amounts of temporal variation can facilitate adaptive evolution in sinks, permitting niche evolution, particularly for slow or autocorrelated variation. Such patterns of temporal variation may particularly pertain to sinks caused by biotic interactions (e.g., predation). Our results are relevant to the evolutionary dynamics of species' ranges, the fate of exotic invasive species, and the evolutionary emergence of infectious diseases into novel hosts.     

生态化学计量学：复杂生命系统奥秘的探索

 20世纪以来,生物科学的发展异军突起,成为发展最快的学科,不仅学科分类逐渐细化,而且研究领域也逐渐深入,然而,这种分化和深入也可能会掩盖生物的一些最普遍特征。地球上的生物是否具有统一的、更本质的特征？能否把不同生物学领域和不同层次的知识联系起来？随着对这些问题的不断探索,一门新兴的学科——生态化学计量学,在最近20年悄然兴起。生态化学计量学结合了生物学、化学和物理学等基本原理,是研究生物系统能量平衡和多重化学元素（主要是C、N、P）平衡的科学。这一研究领域使得生物学科不同层次（分子、细胞、有机体、种群、生态系统和全球尺度）的研究理论能够有机地统一起来。目前,生态化学计量学已经广泛应用于种群动态、生物体营养动态、微生物营养、寄主_病原关系、生物共生关系、消费者驱动的养分循环、限制性元素的判断、生态系统比较分析和森林演替与衰退及全球C、N、P生物地球化学循环等研究中,并取得了许多研究成果。该文概述了生态化学计量的概念、历史起源和基本理论,重点介绍了生态化学计量学理论在消费者驱动的养分循环、限制性养分元素判别以及全球C、N、P循环等方面的应用进展,并对生态化学计量学未来的研究方向进行了展望,期望引起国内同行的重视并有助于推动我国在此领域开展相关研究。     

江西省森林碳蓄积过程及碳源/汇的时空格局

森林碳蓄积是研究森林与大气碳交换以及估算森林吸收或排放含碳气体的关键参数,不同年龄森林的碳源/汇功能差异则体现出森林生态系统碳蓄积过程的时间特征。以森林资源清查的样方数据作为数据源,通过刻画主要树种的林分蓄积生长曲线、林龄与净初级生产力(NPP)之间的关系,驱动区域碳收支模型(InTEC)模拟江西省1950—2008年的森林碳蓄积过程,了解山江湖工程实施以来的森林碳源/汇状况。结果表明,20世纪80年代以前,江西省森林年平均NPP波动于450—813 gCm-2a-1之间,年净增生物量碳26.55—36.23 TgC/a,年净增木质林产品碳0.01—0.3 TgC/a;80年代初,NPP和年净增生物量碳分别降至307.39 gC m-2a-1和17.31 TgC/a,而年净增木质林产品碳却高达0.6 TgC/a,说明森林被大量砍伐进入林产品碳库;1985年山江湖工程实施后,大面积造林使得年净增碳蓄积呈现急剧上升趋势,生物量和木质林产品碳蓄积分别上升至目前的42.37 TgC/a和0.79 TgC/a,而平均NPP值增加缓慢、碳汇功能降低,说明林分质量有待提高;90年代后碳汇功能开始稳步增强,说明造林面积的迅速增加是引起江西省森林碳增汇的主要驱动因素,但未来森林增汇潜力应源于森林生长和有效的经营管理。     

Meta-ecosystems: a theoretical framework for a spatial ecosystem ecology

This contribution proposes the meta‐ecosystem concept as a natural extension of the metapopulation and metacommunity concepts. A meta‐ecosystem is defined as a set of ecosystems connected by spatial flows of energy, materials and organisms across ecosystem boundaries. This concept provides a powerful theoretical tool to understand the emergent properties that arise from spatial coupling of local ecosystems, such as global source–sink constraints, diversity–productivity patterns, stabilization of ecosystem processes and indirect interactions at landscape or regional scales. The meta‐ecosystem perspective thereby has the potential to integrate the perspectives of community and landscape ecology, to provide novel fundamental insights into the dynamics and functioning of ecosystems from local to global scales, and to increase our ability to predict the consequences of land‐use changes on biodiversity and the provision of ecosystem services to human societies.     

Nitrogen and Phosphorus Uptake Stoichiometry Tracks Supply Ratio During 2-year Whole-Ecosystem Nutrient Additions

Ecosystems - Nutrient uptake, storage, and release are critical ecosystem functions that affect carbon processing and food web dynamics. Yet, mechanisms controlling when ecosystems are net sinks or...     

Attractive sinks, or how individual behavioural decisions determine source–sink dynamics

Gundersen et al . (2001 , Source-sink dynamics: how sinks affect demography of sources. Ecol. Lett. , 4, 14–21.) suggested that sinks can severely affect the demography of populations in source habitats. We propose this is a common result when animals lack cues associated with reduced fitness inside sinks and consequently select habitat inappropriately. These attractive sinks can result either from undetected risks of mortality (as in the experiment of Gundersen et al . 2001 ) or from undetected poor breeding probabilities (due to bioaccumulation of pesticides, for instance). Thus, individual habitat choice is a key process underlying source–sink dynamics.     

Reconciling Carbon-cycle Concepts, Terminology, and Methods

Recent projections of climatic change have focused a great deal of scientific and public attention on patterns of carbon (C) cycling as well as its controls, particularly the factors that determine whether an ecosystem is a net source or sink of atmospheric carbon dioxide (CO₂). Net ecosystem production (NEP), a central concept in C-cycling research, has been used by scientists to represent two different concepts. We propose that NEP be restricted to just one of its two original definitions—the imbalance between gross primary production (GPP) and ecosystem respiration (ER). We further propose that a new term—net ecosystem carbon balance (NECB)—be applied to the net rate of C accumulation in (or loss from [negative sign]) ecosystems. Net ecosystem carbon balance differs from NEP when C fluxes other than C fixation and respiration occur, or when inorganic C enters or leaves in dissolved form. These fluxes include the leaching loss or lateral transfer of C from the ecosystem; the emission of volatile organic C, methane, and carbon monoxide; and the release of soot and CO₂ from fire. Carbon fluxes in addition to NEP are particularly important determinants of NECB over long time scales. However, even over short time scales, they are important in ecosystems such as streams, estuaries, wetlands, and cities. Recent technological advances have led to a diversity of approaches to the measurement of C fluxes at different temporal and spatial scales. These approaches frequently capture different components of NEP or NECB and can therefore be compared across scales only by carefully specifying the fluxes included in the measurements. By explicitly identifying the fluxes that comprise NECB and other components of the C cycle, such as net ecosystem exchange (NEE) and net biome production (NBP), we can provide a less ambiguous framework for understanding and communicating recent changes in the global C cycle.     

The Relevance of Conditional Dispersal for Bacterial Colony Growth and Biodegradation

Bacterial degradation is an ecosystem service that offers a promising method for the remediation of contaminated soils. To assess the dynamics and efficiency of bacterial degradation, reliable microbial simulation models, along with the relevant processes, are required. We present an approach aimed at improving reliability by studying the relevance and implications of an important concept from theoretical ecology in the context of a bacterial system: conditional dispersal denoting that the dispersal strategy depends on environmental conditions. Different dispersal strategies, which either incorporate or neglect this concept, are implemented in a bacterial model and results are compared to data obtained from laboratory experiments with Pseudomonas putida colonies growing on glucose agar. Our results show that, with respect to the condition of resource uptake, the model’s correspondence to experimental data is significantly higher for conditional than for unconditional bacterial dispersal. In particular, these results support the hypothesis that bacteria disperse less when resources are abundant. We also show that the dispersal strategy has a considerable impact on model predictions for bacterial degradation of resources: disregarding conditional bacterial dispersal can lead to overestimations when assessing the performance of this ecosystem service.     

陆地生态系统碳汇评估方法研究进展

“碳中和”是我国作出的一项重大的国家战略决策,陆地生态系统碳汇作为碳增汇的重要组成部分,在碳中和目标实现的过程中发挥着重要的作用。但当前基于不同观测数据和方法的陆地碳汇计算仍有很大的不确定性,为了全面了解陆地生态系统碳汇分布特征,提高陆地生态系统碳汇评估的准确性,梳理了近年来关于陆地生态系统碳汇评估的国内外研究进展,从“自下而上”和“自上而下”两类途径阐述了陆地生态系统碳汇评估的主要方法(样地清查法、涡度相关法、模型模拟法和碳同化反演法)的主要原理和特征,优势和缺陷,及在不同尺度碳汇研究中的应用,并从土地利用/覆盖变化、气候因素(大气CO₂浓度、氮沉降)、环境因素(太阳辐射、温度、降水)等因素阐述了陆地系统碳汇主要驱动因子;分析了我国陆地生态系统碳汇的主要特征及时空变化趋势,并从人类活动(生态工程)和环境因素阐述了中国陆地生态系统碳汇的驱动因素;最后,展望了新的监测手段和评估方法在提升陆地生态系统碳汇评估精度中的作用,从而更好的服务于我国“碳中和”的长远目标。     

Effects of an attractive sink leading into maladaptive habitat selection

Habitat sinks can attract dispersing animals if high mortality or breeding failure are difficult to detect (e.g., when due to human hunting or pollution). Using a simple deterministic model, we explore the dynamics of such source-sink systems considering three scenarios: an avoided sink, no habitat preference, and an attractive sink. In the second two scenarios, there is a threshold proportion of sink habitat above which the whole population decreases to extinction, but this extinction threshold varies with habitat preference and the relative qualities of the two habitat types. Hence, it would be necessary to know the habitat preferences of any species in a source-sink system to interpret data on population increases and declines. In the attractive sink scenario, small changes in the proportion of sink habitat may have disproportionate effects on the population persistence. Also, small changes in growth rates at the source and the sink severely affect the threshold and the time of extinction. For some combinations of demographic parameters and proportion of habitat sink, the decline affects the source first; thus, during some time, it will be hidden to population monitoring at the sink, where numbers can even increase. The extinction threshold is also very sensitive to the initial population sizes relative to carrying capacity. Attractive sinks represent a novel aspect of source-sink dynamics with important conservation and management implications.     

Modelling Recolonization of Second-Growth Forest Stands by the North American Red Squirrel Tamiasciurus hudsonicus

In this paper, we present a model for source–sink population dynamics where the locations of source and sink habitats change over time. We do this in the context of the population dynamics of the North American red squirrel, Tamiasciurus hudsonicus, within a forest environment subject to harvesting and regrowth. Harvested patches of forest are initially sinks, then eventually become source habitat again as the forest regrows. At the same time, each harvested patch is gradually recolonized by squirrels from other forest patches. We are interested in the interaction of forest harvesting dynamics with squirrel population dynamics. This depends on the harvesting schedule, and on the choices squirrels make when deciding whether to settle in a mature forest patch or in a recently harvested patch. We find that the time it takes for a second-growth forest patch to be recolonized at the mature forest level is longer than the time required for the habitat quality to be restored to the mature forest level. We also notice that recolonization pressure decreases squirrel populations in neighbouring patches. The connectivity between forest patches and the cutting schedule used also affect the time course of recolonization and steady-state population levels.     

Alterations in source-sink patterns by modifications of source strength

Bean plants, trimmed to a simplified “double source, double sink” translocation system (the paired primary leaves serving as the double source and the paired lateral leaflets of the immature first trifoliate leaf as the double sink) were used to study the magnitude and short-term time course of change in the allocation ratio (partition ratio) of assimilates translocated from the labeled primary leaf to its respective “near” and “far leaflet” sinks in response to an increase or decrease in the source strength of the opposite primary leaf (the “control” leaf). If the rates of net photosynthesis in the two primary leaves were similar, assimilates from the labeled source leaf partitioned to the leaflet sinks in the ratio of 5:1 or higher, the dominant sink being the leaflet “nearer” to the labeled source leaf. If the rate of net photosynthesis in the control leaf was increased substantially above that of the labeled source leaf, the rate of translocation from the labeled source to either the near leaflet sink or far leaflet sink remained unaffected, despite, presumably, a higher translocation rate from the control leaf, and hence a higher phloem pressure gradient (or increased cross-sectional area) in the transport pathway from the control leaf to the leaflet sinks. If the control leaf was excised, thus reducing the source leaf area by about a half, the translocation rate from the remaining source leaf rapidly doubled, the partition ratio becoming equal to unity. If the control leaf was darkened, the partition ratio adjusted to an intermediate value. Although export rates from the labeled source leaf were increased either by excising or darkening the control leaf, the rate of net photosynthesis in the labeled leaf remained constant.     

牡蛎礁生境：海岸带可持续发展的潜在碳汇

牡蛎礁生境是指由聚集的牡蛎和其他生物及环境堆积形成的复合生态系统,其固碳和储碳潜力巨大,在海岸带生态系统中发挥着重要的作用。然而,目前对牡蛎礁生境碳源与汇的认识仍存在不足,主要在于牡蛎钙化和呼吸作用都释放CO₂,而碳源与汇的评估忽视了钙化、同化和沉积过程带来的整体碳汇价值及牡蛎礁生态系统功能带来的碳汇效应。因此,有必要重新认识牡蛎礁生境的碳汇价值。一方面,牡蛎礁生境的碳源和碳汇需要从牡蛎礁自身的整体碳循环中进行评估,包括牡蛎礁系统中的沉积、钙化、呼吸作用及侵蚀、再悬浮和再矿化作用; 另一方面,牡蛎礁生态系统服务引起的碳汇效应需从牡蛎礁的生态系统服务价值角度进行评估,将生态系统服务价值及碳价值进行关联,从而纳入碳汇核算体系。从实现海岸带可持续增汇角度出发,综述了牡蛎礁生境中碳的源与汇;阐述了容易被人们忽视的微生物在牡蛎礁生境碳汇中的作用;以保护和生态修复为目的,进一步提出可实现牡蛎礁生境最大潜在碳汇的策略,以期为实现海洋负排放及践行"国家双碳战略"提供理论和技术支撑。     

Movements and source–sink dynamics of a Masai giraffe metapopulation

Spatial variation in habitat quality and anthropogenic factors, as well as social structure, can lead to spatially structured populations of animals. Demographic approaches can be used to improve our understanding of the dynamics of spatially structured populations and help identify subpopulations critical for the long-term persistence of regional metapopulations. We provide a regional metapopulation analysis to inform conservation management for Masai giraffes (Giraffa camelopardalis tippelskirchi) in five subpopulations defined by land management designations. We used data from an individual-based mark–recapture study to estimate subpopulation sizes, subpopulation growth rates, and movement probabilities among subpopulations. We assessed the source–sink structure of the study population by calculating source–sink statistics, and we created a female-based matrix metapopulation model composed of all subpopulations to examine how variation in demographic components of survival, reproduction, and movement affected metapopulation growth rate. Movement data indicated no subpopulation was completely isolated, but movement probabilities varied among subpopulations. Source–sink statistics and net flow of individuals indicated three subpopulations were sources, while two subpopulations were sinks. We found areas with higher wildlife protection efforts and fewer anthropogenic impacts were sources, and less-protected areas were identified as sinks. Our results highlight the importance of identifying source–sink dynamics among subpopulations for effective conservation planning and emphasize how protected areas can play an important role in sustaining metapopulations.     

A New Conceptual Model of Nitrogen Saturation Based on Experimental Nitrogen Addition to an Oak Forest

The dominant conceptual model of nitrogen (N) saturation in forests predicts the temporal patterns of key N cycling indicators as an initially N-limited forest is progressively enriched in N. We present the results from a long-term N addition experiment in an oak forest in southeastern New York State, USA, which do not conform to the predictions of the conceptual model in several ways. In contrast to the predictions of the conceptual model, the foliar N concentrations in the N-treated stands of our study increased to about 20% above the levels in the control stands and then remained essentially constant, and nitrogen leaching from the treated stands increased almost immediately after the start of the experiment, prior to the onset of elevated nitrification. Concentrations of N in soil solution of the N-treated stands peaked at over 150-fold greater than the concentrations in the control stands. There were no significant changes in potential net N mineralization. Tree mortality increased in the treated stands, but the tree mortality did not appear to be the primary cause of the excess nitrate leaching. Based on these results and those of other recent studies, we present a new conceptual model of the N saturation process focused on the mass balance of N rather than the temporal dynamics of N cycling indicators. The mass balance is characterized by inputs of N from atmospheric deposition and fertilization, internal sinks in the vegetation and soils, and outputs to leaching and gaseous losses. The key points of the conceptual model are (1) added N can flow simultaneously to all sinks and losses in the system, (2) the fate of the added N and the temporal patterns of flow of N depend on the strength of the sinks and the factors that control them, and (3) the movement of N to the various sinks determines how N saturation is manifested in the ecosystem. We distinguish capacity N saturation, in which the sinks in the vegetation and soil are zero or negative, from kinetic N saturation, in which the sinks are positive but lower than the N input rate. The sink strengths in the vegetation and soil have two components, one due to carbon (C) accumulation in the system and the other due to change in the stoichiometry (C:N ratio) of the pool. Further work quantifying the magnitudes and controlling factors for the N sinks will allow better prediction of the dynamics of N saturation in different types of forested ecosystems.     

甘肃白龙江流域净生态系统生产力时空变化

净生态系统生产力(NEP)是估算区域植被碳源、碳汇的重要指标。以甘肃白龙江流域为研究区,结合MODIS与气象数据对2000—2013年的流域净生态系统生产力时空变化进行了研究,并探讨了典型地形因子对NEP的影响。结果表明:(1)2000—2013年甘肃白龙江流域单位面积NEP平均为226.65 g C m~(-2)a~(-1),碳汇区主要分布在白龙江上游两岸、岷江西岸、白水江南岸、大团鱼河两岸的山地林区,碳源区主要分布在武都区、迭部县北缘的高寒草甸区等。(2)从不同植被类型上看,常绿阔叶林、常绿/落叶阔叶混交林单位面积NEP最高,高寒草地单位面积NEP最小,且耕地单位面积NEP增加最明显,常绿/落叶阔叶混交林单位面积NEP降低最明显。(3)2000—2013年研究区单位面积NEP总体上呈增加的趋势,增加明显的地区分布在流域的中部和西北部,4—9月为流域碳汇季节。(4)地形因子对甘肃白龙江流域NEP有明显影响,海拔4200 m以下多为碳汇区;陡坡区的碳汇能力的增长趋势低于缓坡区;阴坡的碳汇能力高于阳坡区。     

Empirical evidence for source–sink populations: a review on occurrence,assessments and implications

Assessing the role of local populations in a landscape context has become increasingly important in the fields of conservation biology and ecology. A growing number of studies attempt to determine the source–sink status of local populations. As the source–sink concept is commonly used for management decisions in nature conservation, accurate assessment approaches are crucial. Based on a systematic literature review of studies published between 2002 and 2013, we evaluated a priori predictions on methodological and biological factors that may influence the occurrence of source or sink populations. The review yielded 90 assessments from 73 publications that included qualitative and quantitative evidence for either source or sink population(s) for one or multiple species. Overall, sink populations tended to occur more often than source populations. Moreover, the occurrence of source or sink populations differed among taxonomic classes. Sinks were more often found than sources in mammals, while there was a non‐significant trend for the opposite to be true for amphibians. Univariate and multivariate analyses showed that the occurrence of sources was positively related to connectivity of local populations. Our review furthermore highlights that more than 25 years after Pulliam's widely cited publication on ‘sources, sinks, and population regulation’, in‐depth assessments of the source–sink status of populations based on combined consideration of demographic parameters such as fecundity, survival, emigration and immigration are still scarce. To increase our understanding of source–sink systems from ecological, evolutionary and conservation‐related perspectives, we recommend that forthcoming studies on source–sink dynamics should pay more attention to the study design (i.e. connectivity of study populations) and that the assessment of the source–sink status of local populations is based on λ values calculated from demographic rates.