Modelling the long-term sustainability of indigenous hunting in Manu National Park, Peru: landscape-scale management implications for Amazonia

P> Widespread hunting throughout Amazonia threatens the persistence of large primates and other vertebrates. Most studies have used models of limited validity and restricted spatial and temporal scales to assess the sustainability. We use human-demographi

东北农田生态系统排放CH_4和N_2O的研究

本文首次对我国东北地区稻田和旱田（大豆田）中甲烷（CH_4）和氧化亚氮(N_2O)的排放通量进行观测,研究了环境因素对这两种温室效应气体排放的影响。观测结果表明：稻田在作物生长季节是CH_4的排放源(source)，作物被收割之后则成为甲烷的汇(sink)。在作物生长季，稻田的CH_4排放通量变化在2.41-26.1mgCH_4/m~2·h之间，平均通量为14.82mgCH_4/m~2·h。稻田N_2O通量在-116.89-100.69μgN_2O/m~2·h间变化，平均通量为-6.36 μg/m~2·h。旱田完全是N_2O的排放源，通量在3.99-332.3 μg N_2O/m~2·h之间变化，平均通量是88.54 μgN_2O/m~2·h。旱田主要表现为甲烷的汇。稻田中甲烷主要在0-5cm土层中产生。水稻和大豆分别对CH_4和N_2O的排放起着重要作用。稻田甲烷排放通量与温度(特别是气温)有极显著的正相关性，也与土壤中硝态氮含量呈显著正相关／旱田甲烷排放通量与土壤中铵态氮浓度呈显著负相关，而N_2O通量则与铵态氮浓度呈正相关，但有3-4天的时间滞后现象。旱田甲烷和氧化亚氮的排放受土壤含水量的影响。本文还讨论了实验室条件下施肥对稻田土壤CH_4产生作用的影响。厩肥的施入影响较弱，而稻杆的影响则十分强烈。尿素也促进CH_4的产生。100和200μg/g(土)的尿素加入量增大了产甲烷速率和甲烷产量；300μg/g(土)的尿素加入量没有增大产甲烷速率，却延长产甲烷时间，使甲烷产量增加更多。土壤中CH_4和N_2O的产生过程之间似乎呈相互消长关系。

南黄海浮游植物的固碳强度与污染物胁迫下海水碳源/汇格局的变化

本论文在解析了南黄海生态环境的基础上，首次研究揭示了浮游植物固碳强度的年际变化及生态反馈机制，获得了东中国近海浮游植物固碳强度及对海域源/汇格局的影响程度；同时，用室内模拟实验探讨了重金属和有机污染物胁迫下海水无机碳体系和源汇格局的变化过程，获得了一些新的认识。主要结论如下： 1. 南黄海浮游植物固碳强度具有明显的时空变化特征，与海域光照、流系和水团变化、海水磷的浓度等因素密切相关，并在一定程度上决定海区碳源/汇的性质。2005年秋季浮游植物日固碳量达9.5万吨，1983-2005年间，南黄海浮游植物固碳强度有降低的趋势，与海水关键营养盐－磷的限制有关。东中国近海浮游植物年总固碳量约为2.2亿吨，约占全球近海浮游植物的年固碳量的2.0%。 在综合分析秋季南黄海水文、化学、生物背景的基础上，系统阐明了海域浮游植物固碳体系的生物地球化学机制。结果表明，2005年秋季南黄海浮游植物固碳强度，即初级生产力变化在 97−701 mgC m-2 d-1之间，平均为307 mg C m-2 d-1；与其关系比较密切的环境因子为海水透明度、盐度、pH、氨氮 (NH4-N)、磷酸盐 (PO4-P) 以及Chl a。在这些因素中，PO4-P对初级生产力的影响最大，显然11月份南黄海的磷是浮游植物生长的限制因子，次之的影响因素是Chl a和NH4-N。 对南黄海源汇格局的研究发现，如果除去涌升流较为活跃的站位（A9、B7、B8、B9、C8、C9、 D9和A1），2005年秋季表层海水pCO2与浮游植物固碳强度明显负相关（r=-0.8，n=23, p<0.001）。在南黄海东部浮游植物固碳强度较高，pCO2值较低；而在西部海区浮游植物固碳强度较低的区域，其pCO2值较高。碳源/汇转折点浮游植物固碳强度为230 mgC m-2 d-1，即小于此值，海区为大气二氧化碳的源，反之为汇，并且CO2汇区浮游植物固碳强度平均值约是CO2源区的2倍多；浮游植物固碳作用，在某一时间和空间尺度内，基本决定了海区的源汇格局。估算结果显示，东中国近海浮游植物固碳量约为222×106t a-1，约为东中国近海通过海－气界面总表观碳汇强度每年1369万吨的16.2倍，仅就浮游植物的年固碳量而言，东中国近海约占全球近海浮游植物的年固碳量的2.0%。 研究揭示了近年来南黄海浮游植物固碳强度具有区域与年际变化明显这一显著特点。一般，近岸区（由黄海沿岸水和表层水控制）内，光照是浮游植物固碳的主要限制因子；从2001年后的大多数年份中，中央区（黄海冷水团控制）的浮游植物固碳强度均与磷酸盐浓度显著正相关，但与氮浓度的相关性不大，说明南黄海生态系统普遍存在着磷限制而非氮限制；混合区终年受黄、东海混合水控制，受到光照条件和营养盐浓度同时影响。根据本次观测所获数据，结合以前研究者的调查资料，我们发现从1983年到2005年，南黄海浮游植物优势种由Bacillariophyta变为Pyrrophyta，浮游植物细胞丰度和Chl a明显下降，浮游植物固碳强度几乎下降了二分之一 （由569.50 mgC m-2 d-1下降至306.83 mgC m-2 d-1），说明南黄海在世界边缘海固碳过程中的作用在降低。经过相关水质参数及生态环境变化的分析，以上现象是对关键营养盐磷的限制以及光限制响应的缘故。此外，研究还发现，由于南黄海初级生产者产量下降所引起的一些生态反馈信息，如浮游动物固碳量的下降和鱼类产量的锐减。 2. 室内模拟实验显示，重金属（铅、铜、镉和锌）及有机污染物（乙醇、丙酮、尿素和多灭磷）对水体生物固碳体系有重要影响，较低浓度时可提高水体的固碳能力，相应水体中的DIC、HCO3-和 Pco2 与对照组相比都明显下降 (P<0.01)；当污染物达到一定浓度后，水体生物的固碳能力明显下降，其有机碳可降解转化为无机碳。当污染物小于转折浓度水体为大气二氧化碳的汇，反之为源。 水体固碳体系对于不同种类、不同浓度的污染物质所表现的受胁迫情况不同，低浓度各污染物（包括重金属和有机污染物）添加组中（对于重金属为0.1和1µmol•L-1，醇和酮分别为<0.5 mol L-1和<0.75 mol L-1），藻干重及固碳量均要大于初始值，说明适量的外源污染可能会促进藻类生长，提高水体的固碳能力，相应水体中的DIC、HCO3- 和PCO2与对照组相比都明显下降 (P<0.01)。当污染物达到一定浓度后，由于其毒害作用，使得水体内生物的固碳能力下降，甚至分解并转化为无机碳，从会引起DIC、HCO3- 和PCO2含量的升高，其含量上升幅度会因固碳体系对不同种类污染物耐受程度的差异而不同。对于尿素和多灭磷，二者浓度分别达到80和20mgL-1时，水体中二氧化碳各参数仍呈现下降趋势，说明在该浓度范围内，大型藻类（如石莼）仍可利用添加物中的氮和磷，将其做为氮源或磷源，促进水体总固碳量的增加。 污染物胁迫对水体碳源汇能力及格局可起到一定的调控作用，与污染物的浓度密切相关，污染物存在着一转折浓度，分别为5µmol L-1（铜）、20µmol L-1（镉） 0.75mol L-1（酮），当污染物添加小于转折浓度并排除其他影响因素时，水体表现为大气CO2的汇，并且适量的增加污染物浓度会使海洋碳汇能力有所增强；而当污染物超出转折浓度时，水体成为CO2的源，其CO2的释放量是随着污染物浓度的增加而增大。对与研究中其他种类的污染物，在实验室设计范围内，水体始终表现为大气CO2的汇。

过量氮和磷引起的富营养化对海水无机碳源汇强度的影响

过量氮和磷引起的海水富营养化引起了一系列的生态环境效应，探讨二者的耦合关系对阐明全球海洋生态环境变化机制意义重大。本论文首次探讨了过量氮和磷引起的富营养化对海水无机碳体系的影响，通过室内系统模拟实验，构筑了过量氮和磷与无机碳体系变化的定量耦合关系，在此基础上获得了中国近海典型海域特别是南黄海近十年氮和磷演变引起的无机碳源汇格局变化，获得了以下一系列新的结果和认识： 1、不同营养盐（NO3-、NH4+、NO2-和PO43-）对水体溶解无机碳体系均有重要影响，且影响程度有较大的差异。 在模拟实验中，当NO3-<188 μmol/L，NH4+<126 μmol/L，NO2-<39.5 μmol/L时均可明显提高水体的固碳能力，相应水体中的DIC、HCO3-和 pCO2均较空白对照组时有一定程度的下降。当N浓度达到一定值后，其固碳能力减弱，DIC、HCO3-和pCO2出现相反变化。当NH4+>126 μmol/L和NO2->39.5 μmol/L时pCO2增加，向大气释放CO2。在PO43-添加组中，当浓度小于19.5μmol/L时DIC、pCO2较空白对照组下降，水体表现为大气CO2的汇，其固碳能力高于N组。在孔石莼添加组中，各营养盐组水体的固碳能力均高于空白对照组，相应水体中DIC、HCO3-和pCO2的下降明显。其中，同一营养盐浓度水平下，NH4+组中各无机碳组分的变化幅度明显高于NO3-和NO2-组，PO43-组的无机碳体系变化幅度低于N组。其中，当NO3-、NH4+和NO2-浓度分别在71 μmol/L，49.7 μmol/L和11.7 μmol/L时，pCO2下降明显，水体表现为大气CO2的强汇。对无机碳各参数的变化量与营养盐进行多元回归分析，得到以下统计关系： ⊿DIC=-0.937(⊿PO43-)-0.34(⊿NO3-)-0.46(⊿NH4+)+0.11(⊿NO2-)（R2=0.69, n=30，Sig.<0.05） ⊿HCO3-=-1.357(⊿PO43-)-0.35(⊿NO3-)-0.57(⊿NH4+)-0.013(⊿NO2-)（R2=0.76, n=32, Sig.<0.05） ⊿CO32-=0.344(⊿PO43-)+0.16(⊿NO3-)+0.18(⊿NH4+)+0.076(⊿NO2-)（R2=0.69, n=32, Sig.<0.05） ⊿pCO2=-1.321(⊿PO43-)-0.12(⊿NO3-)-0.31(⊿NH4+)-0.032(⊿NO2-)（R2=0.84, n=35, Sig.<0.01） 2．氮、磷对海水无机碳体系的源汇格局影响主要受控于水体浮游藻类对营养盐的利用。 模拟实验各种情况下Chl-a的浓度均有不同程度的变化。在N组中，当NH4+<126 μmol/L，随着NH4+浓度的增加，Chl-a浓度增加，而高浓度（NH4+>126 μmol/L）的实验组中，Chl-a则随浓度的增加而下降。当NO2-和PO43-的浓度分别大于39.5 μmol/L和19.5 μmol/L时，水体中Chl-a随营养盐浓度的增加而出现下降趋势，不同的是NO3-添加组在实验浓度范围内藻类均出现了不同程度的增长，这可能与浮游藻类对过量营养盐的耐受性不同有关。在低浓度时，PO43-组pCO2的下降最为明显，这与 PO43-组Chl-a的含量较高相一致，其次为NH4+，NO3-高于NO2-，可见在实验水体中PO43-对于藻类新陈代谢作用影响明显，从而作用到无机碳上的影响也就最为明显。对各实验水体⊿Chl-a与无机碳各组分作相关性分析发现，⊿Chl-a与⊿pCO2的相关性最为明显（R2=0.75，p<0.0001），这可能是因为浮游藻类光合作用和分解作用消耗或生成的首先是海水中的游离CO2（即pCO2）。在孔石莼组中，由于大藻对过量营养盐的耐受性较强，因此各组中藻类干重均有一定程度的增长。藻类干重的增加以NH4+最为明显，其次为NO3-和NO2-，这可能与其对N盐的优先吸收顺序NH4+>NO3->NO2-有关。加PO43-组中藻类的干重增加量低于NH4+和NO3-组，这与大藻的生理特性有关。对藻类干重增加量⊿m与⊿DIC作相关性发现，二者相关性明显（R2=0.64，p<0.01），这是由于孔石莼光合作用同时吸收HCO3-和CO2为碳源有关。 3、近年来，中国近海由于海水过量氮磷引起的富营养化，可使大部分海域海水无机碳汇强度增加 应用室内模拟获得的无机碳与氮、磷之间的定量耦合关系，估算了过量氮、磷引起的富营养化条件下，中国近海水体无机碳源汇的变化情况。结果表明，近十年来，由于氮、磷浓度的增加而导致渤海、南黄海、北黄海和东海每年从大气中多吸收0.197×106t C、0.302×106t C、0.039×106t C和2.233×106t C，东中国近海营养要素的含量的变化及组成比例的时间性和地区性差异是造成各海区碳通量差异的重要因素；对2006年南黄海水文、化学、生物与无机碳体系之间的相互关系进行综合分析，可知水体无机碳体系与营养盐水平密切相关。

Effects of forage composition and growing season on methane emission from sheep in the Inner Mongolia steppe of China

Understanding the effects of dietary composition on methane (CH4) production of sheep can help us to understand grassland degradation resulting in an increase of CH4 emission from ruminant livestock and its resulting significance affecting CH4 source/sink in the grazing ecosystem. The objective of this study was to investigate the effect of forage composition in the diet of sheep in July and August on CH4 production by sheep in the Inner Mongolia steppe. The four diet treatments were: (1) Leymus chinensis and Cleistogenes squarrosa (LC), (2) Leymus chinensis, Cleistogenes squarrosa and concentrate supplementation (LCC), (3) Artemisia frigida and Cleistogenes squarrosa (AC), and (4) Artemisia frigida, Cleistogenes squarrosa and concentrate supplementation (ACC). CH4 production was significantly lower in July than in August (31.4 and 36.2 g per sheep-unit per day, respectively). The daily average CH4 production per unit of digestive dry matter (DM), organic matter (OM) and neutral detergent fiber (NDF) increased by 10.9, 11.2 and 42.1% for the AC diet compared with the LC diet, respectively. Although concentrate supplementation in both the AC and LC diets increased total CH4 production per sheep per day, it improved sheep productivity and decreased CH4 production by 14.8, 12.5 and 14.8% per unit of DM, OM and NDF digested by the sheep, respectively. Our results suggested that in degraded grassland CH4 emission from sheep was increased and concentrate supplementation increased diet use efficiency. Sheep-grazing ecosystem seems to be a source of CH4 when the stocking rate is over 0.5 sheep-units ha(-1) during the growing season in the Inner Mongolia steppe.

A stable carbon isotopic approach for understanding the CO2 flux at the Haibei Alpine Meadow Ecosystem - A simple model

Although respiration of organisms and biomass as well as fossil fuel burning industrial production are identified as the major sources, the CO2 flux is still unclear due to the lack of proper measurements. A mass-balance approach that exploits differences in the carbon isotopic signature (delta(13)C) of CO2 Sources and sinks was introduced and may provide a means of reducing uncertainties in the atmospheric budget. delta(13)C measurements of atmospheric CO2 yielded an average of - 10.3 parts per thousand relative to the Peedee Belemnite standard; soil and plants had a narrow range from -25.09 parts per thousand to -26.51 parts per thousand and averaged at -25.80 parts per thousand. Based on the fact of steady fractionation and enrichment during respiration of mitochondria, we obtained the emission Of CO2 of 35.451 mol m(-2) a(-1) and CO2 flux of 0.2149 mu mol m(-2) s(-)1. The positive CO2 flux indicated the Haibei Alpine Meadow Ecosystem a source rather than a sink. The mass-balance model can be applied for other ecosystem even global carbon cycles because it neglects the complicated process of carbon metabolism, however just focuses on stable carbon isotopic compositions in any of compartments of carbon sources and sinks. (C) 2005 Elsevier B.V. All rights reserved.

A multidisciplinary approach for puzzling over fish connectivity in the Mediterranean Sea: The role of early life history stages of red mullet (Mullus barbatus)

Integrating connectivity patterns into marine ecosystem management is a fundamental step, specially for stock subjected to the combined impacts of human activities (overfishing, habitat degradation, etc.) and climate changes. Thus, management of marine resources must incorporates the spatial scales over which the populations are connected. Notwithstanding, studying these dynamics remains a crucial and hard task and the predictions of the temporal and spatial patterns of these mechanisms are still particularly challenging. This thesis aims to puzzle over the red mullet Mullus barbatus population connectivity in the Western Mediterranean Sea, by implementing a multidisciplinary approach. Otolith sclerochronology, larval dispersal modelling and genetic techniques were gathered in this study. More particularly, this research project focused on early life history stages of red mullet and their role in the characterization of connectivity dynamics. The results show that M. barbatus larval dispersal distances can reach a range of 200 km. The differences in early life traits (i.e. PLD, spawning and settlement dates) observed between various areas of the Western Mediterranean Sea suggest a certain level of larval patchiness, likely due to the occurrence of different spawning pulses during the reproductive period. The dispersal of individuals across distant areas, even not significant in demographic terms, is accountable for the maintenance of the genetic flow among different demes. Fluctuations in the level of exchange among different areas, due to the variability of the source-sink dynamics, could have major implications in the population connectivity patterns. These findings highlight the reliability of combining several approaches and represent a benchmark for the definition of a proper resource management, with considerable engagements in effectively assuring the beneficial effects of the existent and future conservation strategies.

Towards an integrated forecasting system for pelagic fisheries

First results of a coupled modeling and forecasting system for the pelagic fisheries are being presented. The system consists currently of three mathematically fundamentally different model subsystems: POLCOMS-ERSEM providing the physical-biogeochemical environment implemented in the domain of the North-West European shelf and the SPAM model which describes sandeel stocks in the North Sea. The third component, the SLAM model, connects POLCOMS-ERSEM and SPAM by computing the physical-biological interaction. Our major experience by the coupling model subsystems is that well-defined and generic model interfaces are very important for a successful and extendable coupled model framework. The integrated approach, simulating ecosystem dynamics from physics to fish, allows for analysis of the pathways in the ecosystem to investigate the propagation of changes in the ocean climate and lower trophic levels to quantify the impacts on the higher trophic level, in this case the sandeel population, demonstrated here on the base of hindcast data. The coupled forecasting system is tested for some typical scientific questions appearing in spatial fish stock management and marine spatial planning, including determination of local and basin scale maximum sustainable yield, stock connectivity and source/sink structure. Our presented simulations indicate that sandeels stocks are currently exploited close to the maximum sustainable yield, but large uncertainty is associated with determining stock maximum sustainable yield due to stock eigen dynamics and climatic variability. Our statistical ensemble simulations indicates that the predictive horizon set by climate interannual variability is 2–6 yr, after which only an asymptotic probability distribution of stock properties, like biomass, are predictable.

Exposure modelling to traffic-related air toxic pollutants

Atualmente, a poluição atmosférica constitui uma das principais causas ambientais de mortalidade. Cerca de 30% da população europeia residente em áreas urbanas encontra-se exposta a níveis de poluição atmosférica superiores aos valores- limite de qualidade do ar legislados para proteção da saúde humana, representando o tráfego rodoviário uma das principais fontes de poluição urbana. Além dos poluentes tradicionais avaliados em áreas urbanas, os poluentes classificados como perigosos para a saúde (Hazard Air Pollutants - HAPs) têm particular relevância devido aos seus conhecidos efeitos tóxicos e cancerígenos. Neste sentido, a avaliação da exposição tornase primordial para a determinação da relação entre a poluição atmosférica urbana e efeitos na saúde. O presente estudo tem como principal objetivo o desenvolvimento e implementação de uma metodologia para avaliação da exposição individual à poluição atmosférica urbana relacionada com o tráfego rodoviário. De modo a atingir este objetivo, foram identificados os parâmetros relevantes para a quantificação de exposição e analisados os atuais e futuros potenciais impactos na saúde associados com a exposição à poluição urbana. Neste âmbito, o modelo ExPOSITION (EXPOSure model to traffIc-relaTed aIr pOllutioN) foi desenvolvido baseado numa abordagem inovadora que envolve a análise da trajetória dos indivíduos recolhidas por telemóveis com tecnologia GPS e processadas através da abordagem de data mining e análise geoespacial. O modelo ExPOSITION considera também uma abordagem probabilística para caracterizar a variabilidade dos parâmetros microambientais e a sua contribuição para exposição individual. Adicionalmente, de forma a atingir os objetivos do estudo foi desenvolvido um novo módulo de cálculo de emissões de HAPs provenientes do transporte rodoviário. Neste estudo, um sistema de modelação, incluindo os modelos de transporteemissões- dispersão-exposição, foi aplicado na área urbana de Leiria para quantificação de exposição individual a PM2.5 e benzeno. Os resultados de modelação foram validados com base em medições obtidas por monitorização pessoal e monitorização biológica verificando-se uma boa concordância entre os resultados do modelo e dados de medições. A metodologia desenvolvida e implementada no âmbito deste trabalho permite analisar e estimar a magnitude, frequência e inter e intra-variabilidade dos níveis de exposição individual, bem como a contribuição de diferentes microambientes, considerando claramente a sequência de eventos de exposição e relação fonte-recetor, que é fundamental para avaliação dos efeitos na saúde e estudos epidemiológicos. O presente trabalho contribui para uma melhor compreensão da exposição individual em áreas urbanas, proporcionando novas perspetivas sobre a exposição individual, essenciais na seleção de estratégias de redução da exposição à poluição atmosférica urbana, e consequentes efeitos na saúde.

Étude de dispositifs électroniques moléculaires à l'aide de modèles simples

Cette thèse en électronique moléculaire porte essentiellement sur le développement d’une méthode pour le calcul de la transmission de dispositifs électroniques moléculaires (DEMs), c’est-à-dire des molécules branchées à des contacts qui forment un dispositif électronique de taille moléculaire. D’une part, la méthode développée vise à apporter un point de vue différent de celui provenant des méthodes déjà existantes pour ce type de calculs. D’autre part, elle permet d’intégrer de manière rigoureuse des outils théoriques déjà développés dans le but d’augmenter la qualité des calculs. Les exemples simples présentés dans ce travail permettent de mettre en lumière certains phénomènes, tel que l’interférence destructive dans les dispositifs électroniques moléculaires. Les chapitres proviennent d’articles publiés dans la littérature. Au chapitre 2, nous étudions à l’aide d’un modèle fini avec la méthode de la théorie de la fonctionnelle de la densité de Kohn-Sham un point quantique moléculaire. De plus, nous calculons la conductance du point quantique moléculaire avec une implémentation de la formule de Landauer. Nous trouvons que la structure électronique et la conductance moléculaire dépendent fortement de la fonctionnelle d’échange et de corrélation employée. Au chapitre 3, nous discutons de l’effet de l’ajout d’une chaîne ramifiée à des molécules conductrices sur la probabilité de transmission de dispositifs électroniques moléculaires. Nous trouvons que des interférences destructives apparaissent aux valeurs propres de l’énergie des chaînes ramifiées isolées, si ces valeurs ne correspondent pas à des états localisés éloignés du conducteur moléculaire. Au chapitre 4, nous montrons que les dispositifs électroniques moléculaires contenant une molécule aromatique présentent généralement des courants circulaires qui sont associés aux phénomènes d’interférence destructive dans ces systèmes. Au chapitre 5, nous employons l’approche « source-sink potential » (SSP) pour étudier la transmission de dispositifs électroniques moléculaires. Au lieu de considérer les potentiels de sources et de drains exactement, nous utilisons la théorie des perturbations pour trouver une expression de la probabilité de transmission, T(E) = 1 − |r(E)|2, où r(E) est le coefficient de réflexion qui dépend de l’énergie. Cette expression dépend des propriétés de la molécule isolée, en effet nous montrons que c’est la densité orbitalaire sur les atomes de la molécule qui sont connectés aux contacts qui détermine principalement la transmission du dispositif à une énergie de l’électron incident donnée. Au chapitre 6, nous présentons une extension de l’approche SSP à un canal pour des dispositifs électroniques moléculaires à plusieurs canaux. La méthode à multiples canaux proposée repose sur une description des canaux propres des états conducteurs du dispositif électronique moléculaire (DEM) qui sont obtenus par un algorithme auto-cohérent. Finalement, nous utilisons le modèle développé afin d’étudier la transmission du 1-phényl-1,3-butadiène branché à deux rangées d’atomes couplées agissant comme contacts à gauche et à la droite.

Linking Canadian Harvested Juvenile American Black Ducks to Their Natal Areas Using Stable Isotope (δD, δ13C, and δ15N) Methods

Understanding source-sink dynamics of game birds is essential to harvest and habitat management but acquiring this information is often logistically and financially challenging using traditional methods of population surveys and banding studies. This is especially true for species such as the American Black Duck (Anas rubripes), which have low breeding densities and extensive breeding ranges that necessitate extensive surveys and banding programs across eastern North America. Despite this effort, the contribution of birds fledged from various landscapes and habitat types within specific breeding ranges to regional harvest is largely unknown but remains an important consideration in adaptive harvest management and targeted habitat conservation strategies. We investigated if stable isotope (δD, δ13C, δ15N) could augment our present understanding of connectivity between breeding and harvest areas and so provide information relevant to the two main management strategies for black ducks, harvest and habitat management. We obtained specimens from 200 hatch-year Black Duck wings submitted to the Canadian Wildlife Service Species Composition Survey. Samples were obtained from birds harvested in Western, Central, and Eastern breeding/harvest subregions to provide a sample representative of the range and harvest rate of birds harvested in Canada. We sampled only hatch-year birds to provide an unambiguous and direct link between production and harvest areas. Marine origins were assigned to 12%, 7%, and 5% of birds harvested in the Eastern, Central, and Western subregions, respectively. In contrast, 32%, 9%, and 5% of birds were assigned, respectively, to agricultural origins. All remaining birds were assigned to nonagricultural origins. We portrayed probability of origin using a combination of Bayesian statistical and GIS methods. Placement of most eastern birds was western Nova Scotia, eastern New Brunswick, Prince Edward Island, and southern Newfoundland. Agricultural birds from the Central region were consistent with the Saguenay region of Québec and the eastern claybelt with nonagricultural birds originating in the boreal. Western nonagricultural birds were associated with broad boreal origins from southern James Bay to Lake of the Woods and east to Cochrane, Ontario. Our work shows that the geographic origins, landscape, and habitat associations of hatch-year Black Ducks can be inferred using this technique and we recommend that a broad-scale isotopic study using a large sample of Canadian and US harvested birds be implemented to provide a continental perspective of source-sink population dynamics.

Landscape gene flow, coexistence and threshold effect: The case of genetically modified herbicide tolerant oilseed rape (Brassica napus)

Globally there have been a number of concerns about the development of genetically modified crops many of which relate to the implications of gene flow at various levels. In Europe these concerns have led the European Union (EU) to promote the concept of 'coexistence' to allow the freedom to plant conventional and genetically modified (GM) varieties but to minimise the presence of transgenic material within conventional crops. Should a premium for non-GM varieties emerge on the market, the presence of transgenes would generate a 'negative externality' to conventional growers. The establishment of maximum tolerance level for the adventitious presence of GM material in conventional crops produces a threshold effect in the external costs. The existing literature suggests that apart from the biological characteristics of the plant under consideration (e.g. self-pollination rates, entomophilous species, anemophilous species, etc.), gene flow at the landscape level is affected by the relative size of the source and sink populations and the spatial arrangement of the fields in the landscape. In this paper, we take genetically modified herbicide tolerant oilseed rape (GM HT OSR) as a model crop. Starting from an individual pollen dispersal function, we develop a spatially explicit numerical model in order to assess the effect of the size of the source/sink populations and the degree of spatial aggregation on the extent of gene flow into conventional OSR varieties under two alternative settings. We find that when the transgene presence in conventional produce is detected at the field level, the external cost will increase with the size of the source area and with the level of spatial disaggregation. on the other hand when the transgene presence is averaged among all conventional fields in the landscape (e.g. because of grain mixing before detection), the external cost will only depend on the relative size of the source area. The model could readily be incorporated into an economic evaluation of policies to regulate adoption of GM HT OSR. (c) 2007 Elsevier B.V. All rights reserved.

Issues in the assimilation of the sources of a trace gas by inverse modelling

The problem of reconstructing the (otherwise unknown) source and sink field of a tracer in a fluid is studied by developing and testing a simple tracer transport model of a single-level global atmosphere and a dynamic data assimilation system. The source/sink field (taken to be constant over a 10-day assimilation window) and initial tracer field are analysed together by assimilating imperfect tracer observations over the window. Experiments show that useful information about the source/sink field may be determined from relatively few observations when the initial tracer field is known very accurately a-priori, even when a-priori source/sink information is biased (the source/sink a-priori is set to zero). In this case each observation provides information about the source/sink field at positions upstream and the assimilation of many observations together can reasonably determine the location and strength of a test source.

Recovery based on plot experiments is a poor predictor of landscape-level population impacts of agricultural pesticides

Current European Union regulatory risk assessment allows application of pesticides provided that recovery of nontarget arthropods in-crop occurs within a year. Despite the long-established theory of source-sink dynamics, risk assessment ignores depletion of surrounding populations and typical field trials are restricted to plot-scale experiments. In the present study, the authors used agent-based modeling of 2 contrasting invertebrates, a spider and a beetle, to assess how the area of pesticide application and environmental half-life affect the assessment of recovery at the plot scale and impact the population at the landscape scale. Small-scale plot experiments were simulated for pesticides with different application rates and environmental half-lives. The same pesticides were then evaluated at the landscape scale (10 km × 10 km) assuming continuous year-on-year usage. The authors' results show that recovery time estimated from plot experiments is a poor indicator of long-term population impact at the landscape level and that the spatial scale of pesticide application strongly determines population-level impact. This raises serious doubts as to the utility of plot-recovery experiments in pesticide regulatory risk assessment for population-level protection. Predictions from the model are supported by empirical evidence from a series of studies carried out in the decade starting in 1988. The issues raised then can now be addressed using simulation. Prediction of impacts at landscape scales should be more widely used in assessing the risks posed by environmental stressors.

Living to die and dying to live: the survival strategy behind leaf senescence

Senescence represents the final developmental act of the leaf, during which the leaf cell is dismantled in a coordinated manner to remobilize nutrients and to secure reproductive success. The process of senescence provides the plant with phenotypic plasticity to help it adapt to adverse environmental conditions. Here, we provide a comprehensive overview of the factors and mechanisms that control the onset of senescence. We explain how the competence to senesce is established during leaf development, as depicted by the senescence window model. We also discuss the mechanisms by which phytohormones and environmental stresses control senescence, as well as the impact of source-sink relationships on plant yield and stress tolerance. In addition, we discuss the role of senescence as a strategy for stress adaptation and how crop production and food quality could benefit from engineering or breeding crops with altered onset of senescence.