Crab: snail size-structured interactions and salt marsh predation gradients

We studied size-structured predator-prey interactions between blue crabs (Callinectes sapidus) and marsh periwinkles (Littoraria irrorata) with a combination of field studies, laboratory experiments and individual-based modeling. Size distributions of Littoraria differed among years at the same sites in a salt marsh and could largely be explained by dominance of strong cohorts in the population. At a given site, abundance increased with elevation above tidal datum. Size-selective predation by blue crabs does not appear to be an important regulator of snail size distributions but may have a major effect on local abundance. Laboratory studies indicated that predator-prey interactions between Callinectes and Littoraria are strongly size-dependent. Crabs were generally effective at feeding on periwinkles at size ratios greater than approximately 6 (crab width: snail length). At lower size ratios crabs were far less effective at manipulating the snails, which often survived but with damaged shells. An individual-based model which incorporated information about incidence of snail shell scarring (resulting from non-lethal interactions) and snail density, predicted reduced predation rates and smaller average crab size with distance from the low tide refugium for crabs.     

南亚热带演替群落的边缘效应及其对森林片断化恢复的意义

通过对鼎湖山两个群落及其边缘群落的长期定位研究,探讨南亚热带演替群落的边缘效应与森林片断化恢复,通过１６ａ的定位研究,从测度群落的物种结构,多样性,生物量与生产力等指标的比较表明,马尾松林群落和混交林群落本身经过１６ａ的演变,虽然有所发展,但变化不大,群落性质没有改变;边缘群落原非常接近马尾松林群落,经过６ａ的演变,已经发展成为混交林群落,说明边缘效应的作用。边缘群落总体的边缘效应强度Ｅ值为１．６     

互花米草入侵影响下闽江河口湿地土壤有效硅的时空变化特征

2016年1—12月,选择闽江河口鳝鱼滩的短叶茳芏湿地、互花米草湿地以及二者的交错带湿地为研究对象,采用定位研究方法探讨了互花米草入侵影响下湿地土壤有效硅含量的时空变化特征。结果表明:互花米草入侵影响下3块湿地土壤有效硅含量随时间推移整体呈波动上升趋势;互花米草入侵显著提高了鳝鱼滩湿地30—60 cm土层土壤有效硅含量(P0.01),与短叶茳芏湿地相比,交错带湿地和互花米草湿地30—60 cm土层土壤有效硅含量分别增加了8.56%和19.97%,逐步线性回归分析表明土温和电导是影响其变化的重要因素(P0.01)。研究互花米草入侵影响下湿地土壤有效硅含量的变化特征,对于揭示湿地生态系统生源要素硅生物地球化学循环过程以及互花米草入侵及其扩张机制具有重要意义。     

垦殖对沼泽湿地土壤呼吸速率的影响

三江平原是我国最大的沼泽化低平原,同时也是受人类活动影响最剧烈的区域之一。选取三江平原两类典型湿地-常年积水的毛果苔草(Carex lasiocapa)沼泽和季节性积水的小叶章(Deyeuxia angustifolia)草甸及由其垦殖的水田和旱田为研究对象,利用静态暗箱-气相色谱法对土壤呼吸速率进行了观测。研究结果表明,小叶章草甸与毛果苔草沼泽土壤呼吸速率的季节变化形式相同,为单峰型,在夏季出现排放峰值,而冬季呼吸速率最低。沼泽湿地垦殖为旱田后,土壤呼吸速率的季节变化形式未发生变化,但垦殖为水田后,土壤呼吸速率排放峰值的时间延后在秋季出现。毛果苔草沼泽、小叶章草甸、旱田及水田通过土壤呼吸释放的碳量分别为(3.1±0.4)、(4.8±0.7)、(2.8±0.4)、(2.2±0.3)tC.hm-2.a-1。毛果苔草沼泽土壤呼吸速率低于小叶章草甸是由沼泽湿地的积水环境差异造成的,而沼泽湿地垦殖为农田后土壤呼吸作用减弱,主要是由于垦殖后土壤有机碳含量大幅降低所致。相关分析表明,温度和土壤湿度(或积水深度)是影响土壤呼吸速率的重要因素,温度与小叶章草甸、毛果苔草沼泽以及旱田土壤呼吸速率呈显著指数关系,Q10值分别为2.1、2.5和1.8,沼泽湿地垦殖为旱田后温度敏感性指数降低,主要是由于土壤微生物营养源减少从而对微生物营养供应受限造成的。小叶章草甸、毛果苔草沼泽、旱田以及水田土壤呼吸速率与土壤湿度/积水深度之间的关系可用线性或二次曲线方程来描述。     

The impact of climate change on the distribution of two threatened Dipterocarp trees

Two ecologically and economically important, and threatened Dipterocarp trees Sal (Shorea robusta) and Garjan (Dipterocarpus turbinatus) form mono‐specific canopies in dry deciduous, moist deciduous, evergreen, and semievergreen forests across South Asia and continental parts of Southeast Asia. They provide valuable timber and play an important role in the economy of many Asian countries. However, both Dipterocarp trees are threatened by continuing forest clearing, habitat alteration, and global climate change. While climatic regimes in the Asian tropics are changing, research on climate change‐driven shifts in the distribution of tropical Asian trees is limited. We applied a bioclimatic modeling approach to these two Dipterocarp trees Sal and Garjan. We used presence‐only records for the tree species, five bioclimatic variables, and selected two climatic scenarios (RCP4.5: an optimistic scenario and RCP8.5: a pessimistic scenario) and three global climate models (GCMs) to encompass the full range of variation in the models. We modeled climate space suitability for both species, projected to 2070, using a climate envelope modeling tool “MaxEnt” (the maximum entropy algorithm). Annual precipitation was the key bioclimatic variable in all GCMs for explaining the current and future distributions of Sal and Garjan (Sal: 49.97 ± 1.33; Garjan: 37.63 ± 1.19). Our models predict that suitable climate space for Sal will decline by 24% and 34% (the mean of the three GCMs) by 2070 under RCP4.5 and RCP8.5, respectively. In contrast, the consequences of imminent climate change appear less severe for Garjan, with a decline of 17% and 27% under RCP4.5 and RCP8.5, respectively. The findings of this study can be used to set conservation guidelines for Sal and Garjan by identifying vulnerable habitats in the region. In addition, the natural habitats of Sal and Garjan can be categorized as low to high risk under changing climates where artificial regeneration should be undertaken for forest restoration.     

Fungal biomass and decomposition in Spartina maritima leaves in the Mondego salt marsh (Portugal)

Spartina maritima (Curtis) Fernald is a dominant species in the Mondego salt marsh on the western coast of Portugal, and it plays a significant role in estuarine productivity. In this work, leaf litter production dynamics and fungal importance for leaf decomposition processes in Spartina maritima were studied. Leaf fall was highly seasonal, being significantly higher during dry months. It ranged from 42 g m^-2 in June to less than 6 g m^-2 during the winter. Fungal biomass, measured as ergosterol content, did not differ significantly between standing-decaying leaves and naturally detached leaves. Fungal biomass increased in wet months, with a maximum of 614 g g^-1 of ergosterol in January in standing-decaying leaves, and 1077 g g^-1 in December, in naturally detached leaves, decreasing greatly in summer. Seasonal pattern of fungal colonization was similar in leaves placed in litterbags on the marsh-sediment surface. However, ergosterol concentrations associated with standing-decaying and naturally detached leaves were always much higher than in litterbagged leaves, suggesting that fungal activity was more important before leaf fall. Dry mass of litterbagged leaves declined rapidly after 1 month (about 50%), mostly due to leaching of soluble organic compounds. After 13 months, Spartina leaves had lost 88% of their original dry weight. The decomposition rate constant (k) for Spartina maritima leaves was 0.151 month^-1.     

景观破碎化对东北虎主要猎物种群动态影响的模拟

以完达山东部地区的现实景观为背景,采用空间直观种群模型LAPS和情景模拟相结合的"虚拟实验"途径,模拟了在10个不同破碎化程度的景观情景中东北虎的主要猎物于1992-2011年间的种群动态,评价了完达山东部地区当前的景观破碎化程度对东北虎主要猎物种群动态的影响。结果表明:LAPS模型准确刻画了研究区东北虎主要猎物种群数量急剧下降的趋势,2002年模拟的东北虎主要猎物的种群数量和实测值之间没有显著差异,马鹿、野猪和狍子的P值分别为0.8651、0.9534和0.2836;不同生境类型的种群密度数据与实测值之间均没有显著差异,其中阔叶林生境中的马鹿、野猪和狍子的P值分别为0.8521、0.9447和0.3152;在灌丛生境中的马鹿、野猪和狍子的P值分别为0.8846、0.9576和0.2415。斑块类型和景观水平上的格局指标变化趋势表明由于农田扩张导致10个景观情景的破碎化程度逐渐增加,景观水平的破碎化程度低于斑块类型水平。方差分析显示10个景观情景中的种群数量没有显著差异,马鹿、野猪和狍子的P值分别为0.8516、0.2624和0.7636,说明研究区当前的景观破碎化程度对种群动态影响并不显著。完达山东部地区存在盗猎等人为干扰,导致了东北虎主要猎物的数量远低于环境容纳量,景观破碎化虽然在局部地区较为严重,但完达山东部地区整体上景观破碎化并不强烈,该地区景观破碎化的效应尚未显现。认为控制盗猎等人为干扰是增加该地区东北虎主要猎物的数量、实现东北虎种群恢复所应优先采取的措施。     

周边区域景观破碎对铜鼓岭国家级自然保护区的压力分析

以铜鼓岭自然保护区及其周边地区为研究对象,基于2004年的SPOT-5卫星遥感数据,应用ERDAS、ArcGIS等遥感和GIS软件提取出研究区的景观要素分类信息,并选用斑块密度(PD)、最大斑块指数(LPI)、面积加权平均形状指数(AWMSI)、面积加权平均斑块分维数(AWMPFD)、斑块面积变异系数(PSCOV)等景观指数和ArcGIS空间分析功能对保护区及其周边区域(缓冲区)进行景观指数分析。结果表明,铜鼓岭地区景观破碎化趋于严重,在保护区外1 km的范围内,海防林破坏,红树林锐减,生态压力大;高位养虾池的大量建造是威胁保护区生态健康的主要因素。     

鹅掌楸贵州烂木山居群的微卫星遗传多样性及空间遗传结构

濒危植物鹅掌楸(Liriodendron chinense)目前仅零散分布于我国亚热带及越南北部地区, 残存居群生境片断化较为严重。研究濒危植物片断化居群的遗传多样性及小尺度空间遗传结构(spatial genetic structure)有助于了解物种的生态进化过程以及制定相关的保育策略。本研究采用13对微卫星引物, 对鹅掌楸的1个片断化居群进行了遗传多样性及空间遗传结构的研究, 旨在揭示生境片断化条件下鹅掌楸的遗传多样性及基因流状况。研究结果表明: 鹅掌楸烂木山居群内不同生境斑块及不同年龄阶段植株的遗传多样性水平差异不显著(P>0.05), 居群内存在寨内和山林2个遗传分化明显的亚居群。烂木山居群个体在200 m以内呈现显著的空间遗传结构, 而2个亚居群内的个体仅在20 m的距离范围内存在微弱或不显著的空间遗传结构。鹅掌楸的空间遗传结构强度较低(Sp = 0.0090), 且寨内亚居群的空间遗传结构强度(Sp = 0.0067)要高于山林亚居群(Sp = 0.0053)。鹅掌楸以异交为主, 种子较轻且具翅, 借助风力传播, 在一定程度上降低了空间遗传结构的强度。此外, 居群内个体密度及生境特征也对鹅掌楸的空间遗传结构产生了一定影响。该居群出现显著的杂合子缺失, 近交系数(F_IS)为0.099 (P < 0.01), 表明生境片断化的遗传效应正逐渐显现。因此, 对鹅掌楸的就地保护应注意维护与强化生境的连续性, 促进基因交流。迁地保护时, 取样距离应不小于20 m, 以涵盖足够多的遗传变异。