Density-dependent effects on salmonid populations: A review

We reviewed 199 published data sets (21 species) to assess the relative frequency of various density-dependent processes in salmonids. We examined studies for the presence or absence of density-dependence: in growth, mortality, fecundity and recruitment. Based on data from all studies pooled 71% showed density-dependence in growth, 23% found density-dependence in mortality, 2% detected density-dependence in fecundity and 4% displayed density-dependence in recruitment. Most studies at the population level (e.g. changes in abundance or means of growth, mortality or fecundity) demonstrated density-dependence; however, these studies were not common, likely because they require long time series of data (at least 3–4 times mean generation time for the species). Our review indicated there was no evidence that the probability of finding density-dependent effects differed among the 21 species examined, but the number of studies per species varied substantially (5 [minimum for analysis] – 20+); hence, this finding should be viewed as tentative. Most salmonid species showed evidence of density-dependence in growth; however, few studies examined density-dependent effects on fecundity or recruitment, and further study is needed on these phenomena. There was no evidence that density-dependent effects were restricted to a particular habitat type or geographic region.     

Evaluating the relationship between yearling walleye,Sander vitreus,electrofishing catch‐per‐unit‐effort and density in northern Wisconsin lakes

Recruitment declines of walleye, Sander vitreus (Mitchill), observed in some northern Wisconsin lakes have resulted in management actions to evaluate and rehabilitate populations. An effective index for estimating relative abundance of yearling walleye is required. The objectives herein were : (a) to evaluate the relationship between yearling walleye electrofishing CPUE and density in northern Wisconsin lakes; (b) to test for the influence of lake‐specific factors on electrofishing catchability of yearling walleye; and (c) to develop an index whereby electrofishing CPUE can be used to quantify yearling walleye relative abundance. Yearling density was significantly positively related to electrofishing CPUE on a long‐term dataset from Escanaba Lake as well as a dataset including several lakes combined. Electrofishing catchability of yearling walleye was negatively related to lake‐surface area but was not related to other lake‐specific variables. This index can provide an efficient method to continue monitoring natural recruitment and also to evaluate survival of stocked walleye.     

Response of Scotian Shelf silver hake (Merluccius bilinearis) to environmental variability

Commercially‐exploited fish populations are not only shaped by fishing pressure, but also by the dynamics of their environment. By quantifying the influence of environmental variability, fisheries management advice can be improved and uncertainties reduced. To this end, we developed statistical models of the response of Scotian Shelf silver hake stock metrics to variability in zooplankton community composition and phenology over the past 18 years and in the physical environment since 1985. Dominant modes of variability in these pelagic habitat indicators were characterized using principal component analysis, and the relationships of silver hake condition, abundance, and recruitment to pelagic habitat variability were assessed using generalized additive models. Condition was largely modulated by the onset and duration of the spring bloom, which controls food availability. In contrast, adult abundance was governed by composition of the zooplankton community and bottom‐water temperature, which dictates the distribution of silver hake. Finally, recruitment was affected by both thermal conditions and food availability. Our results presented here form the basis for qualitative assessment of ecosystem attributes and the influence on silver hake stock productivity.     

利用红外相机调查五道峡自然保护区鸟兽资源及节律特征

为掌握五道峡国家级自然保护区的鸟兽资源情况,布设62台红外相机进行野生动物资源监测。调查发现,1 433张独立有效照片共记录兽类7目、12科、19种,物种相对丰富度指数前5位的是小麂、中华斑羚、野猪、猪獾和花面狸;记录到鸟类5目、14科、33种,物种相对丰富度前3位的是红腹锦鸡、白冠长尾雉和松鸦。节律特征分析结果表明,夏季物种丰富度显著高于冬季(P<0.05),与春季、秋季差异不明显,野生动物在夏季活动频繁,冬季动物活动频率较低;小麂、中华斑羚和野猪在早晨和黄昏活动频繁,属昼行晨昏型动物,白冠长尾雉和红腹锦鸡活动集中于早晨和黄昏。3种偶蹄目兽类的日活动节律重叠程度的分析结果表明,3个优势物种间日活动节律表现为中等程度的重叠,相互间存在不同程度的竞争。以期掌握五道峡国家级自然保护区鸟兽资源和节律信息,为保护区生物多样性保护与持续监测提供依据。     

勤得利湾浮游植物群落结构特征

2003年5、7、9、11月对勤得利湾浮游植物的种类组成结构特征进行了研究。结果表明:浮游植物共计7门69种,以绿藻、硅藻为主,分别占52.36%和20.11%。近亲鱼腥藻、铜绿微囊藻、普通小球藻、柱形栅列藻、四尾栅列藻、颗粒直链藻、细长锥囊藻、四角十字藻、浮球藻、含糊囊裸藻、针形纤维藻、尺骨针杆藻等为优势种。浮游植物数量为1750.8×104ind./L,以硅藻为主,数量为517.3×104ind./L,占29.55%;生物量为16.082mg/L,硅藻最高,为7.285mg/L。浮游植物季节变化比较明显,数量夏季最高为2801.4×104ind./L,生物量以夏季最高28.235mg/L;水平分布采样点Ⅲ最高,平均为2158.6×104ind./L,采样点Ⅳ生物量最高为12.296mg/L。多样性指数变化是夏季>秋季>冬季>春季。均匀度指数变化是秋季>夏季>冬季>春季。     

Independent statistical validation of the New Zealand Seafloor Community Classification

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Pyrosequencing Reveals Significant Changes in Microbial Communities Along the Ecological Succession of Biological Soil Crusts in the Tengger Desert of China

Biological soil crusts (BSCs) have important ecological functions in arid and semiarid lands, but they remain poorly understood in terms of the changes in microbial communities during BSC succession under in situ field conditions. Here, 454 pyrosequencing was used to assess the microbial community composition of four BSC types in the Tengger Desert of China: alga, lichen (cyanolichen and green alga-lichen), and moss crusts, representing early, middle, and final successional stages of BSCs, respectively. The results showed the highest diversity of microbial communities inhabiting lichen crusts, whereas the lowest diversity was observed in moss crusts. Five phyla, Proteobacteria, Actinobacteria, Cyanobacteria, Bacteroidetes, and Acidobacteria, accounted for about 72% to 87% of total prokaryotic sequences in different BSCs. The most abundant eukaryotic microorganism was Ascomycota, accounting for 47% to 93% of the total eukaryotic sequences. Along the succession of BSCs, the abundance of photoautotrophic Cyanobacteria, Chlorophyta, and Bacillariophyta declined, and that of heterotrophic microorganisms such as bacteria and fungi increased. Statistical analysis showed clear divergency of microbial taxa at the class level among the different successional stages of BSCs. The clustering results at class level showed that the moss crusts were the farthest from the rest in prokaryotic composition; the alga crusts were the most different in terms of eukaryotic microorganisms and the two kinds of lichen crusts were relatively closer in both compositions. Ordination analysis showed that the main variations of community structure among BSCs could be explained best by the abundance of Cyanobacteria and Ascomycota and by physiochemical properties of BSCs, including mechanical composition, moisture, and electrical conductivity. In conclusion, our results indicate that Cyanobacteria and Ascomycota likely play an important role in the evolution of BSC structure and functions and highlight the importance of environmental factors in shaping microbial community structures of BSCs in the Tengger Desert of China.     

东北沼泽湿地土壤中氨氧化微生物活性和丰度研究

为了研究东北典型沼泽湿地——三江湿地和扎龙湿地表层土壤中氨氧化微生物的活性和丰度,采用氯酸盐抑制亚硝酸盐氧化菌(Nitrite-oxidizing bacteria,NOB)和氨苄青霉素抑制氨氧化细菌(Ammonia-oxidizing bacteria,AOB)以及荧光定量PCR的方法,分析了生长季和非生长季氨氧化微生物的活性和丰度的关系。结果表明:在不同类型的湿地土壤中,pH值显著地影响湿地土壤中氨氧化古菌(Ammonia-oxidizing archaea,AOA)的潜在氨氧化活性(Potential ammonia oxidation activity,PAO)(P0.01)。AOA的丰度值与PAO_(AOA+AOB)呈显著正相关(r=0.96,P0.05),而与PAO_(AOA)不存在相关性(P0.05)。三江湿地的毛苔草和小叶章土壤中的PAO_(AOA+AOB)、PAO_(AOA)、AOA丰度与AOB丰度,并无显著差异。研究表明植被的差异并没有影响土壤中氨氧化微生物的潜在氨氧化活性以及氨氧化微生物的丰度,但在抑制AOB活性之后毛苔草土壤中的PAO出现了显著的下降(P0.05),表明AOB在毛苔草土壤中的氨氧化过程中发挥着重要作用。     

Estimating symbiotic N2 fixation in Robinia pseudoacacia

Estimating symbiotic di‐nitrogen (N₂) fixation is challenging, especially when working with woody N₂ fixers in field trials. Fortunately, isotope methods based on ¹⁵N natural abundance or on ¹⁵N artificial enrichment (dilution method) make it possible to estimate the proportion of nitrogen derived from the atmosphere (Ndfa) in N₂‐fixing species. These methods have been extensively used in the field for herbaceous species, much less for tree species such as alder and acacia, and rarely for black locust (Robinia pseudoacacia). The objectives of this study were to characterize the fixation potential of black locust in a plantation by using the two ¹⁵N isotope methods in the field, and to document values of isotope fractionation occurring during N₂ fixation (the B value). B values were estimated both by growing trees on an N‐free medium in controlled conditions (B_lab) and by making Ndfa calculated with the natural abundance method converge with Ndfa calculated with the ¹⁵N dilution method in the field (B_field). The two methods gave consistent estimates of the B value. B values ranging between –1.4 and –3.2‰ were found, varying with the age of the plant material. Up to 76% of the N in the black locust trees came from the atmosphere, representing more than 45 kg N ha^?1 over five years and confirming that black locust may be well adapted to N‐poor soils.