贵州纳雍光叶珙桐群落主要优势种群生态位研究

研究了贵州纳雍光叶珙桐群落11个主要优势种群生态位宽度及重叠,结果表明,在该群落中以西南红山茶、猫儿屎、光叶珙桐的生态位宽度较大;群落中主要种群间生态位重叠的发生比较普遍,但是重叠的程度不是很高,说明物种间存在竞争,群落尚未达到稳定的顶级群落阶段,尚处于演替的进程中。     

Potential distribution and population trends of the smalltail shark Carcharhinus porosus inferred from species distribution models and historical catch data

1. Updated distribution ranges are crucial for conservation status assessments. Comprehensive analyses combining published literature and available data on historical catches and species distribution models (SDMs) are effective tools that could improve the prediction of more realistic scenarios for some species, especially those with limited information available and facing multiple threats.
2. The present study aimed at generating an updated distribution for the smalltail shark Carcharhinus porosus, one of the most threatened and understudied shark species of the western Atlantic Ocean. Estimates of the key areas for this species conservation based on the SDMs, and trends in catch probabilities throughout its distribution range are provided.
3. Four algorithms (BIOCLIM, Domain, Mahalanobis, and Maximum Entropy) were used to model the distribution of C. porosus and calculate its habitat suitability based on marine environmental variables. To assess historical catch probability trends, we built a generalized linear model from published and grey literature data. This analysis was used to estimate catch probability as an indication of population trends.
4. SDMs suggest that the northern coast of South America (NCSA) harbours the most suitable habitats for C. porosus in the world, which was expected given its historically high catch rate in this region. In addition, there was a continuously declining catch probability trend starting in the 1970s. However, the decline was smaller for the NCSA as compared with the Gulf of Mexico and the eastern South America coast.
5. Results indicate that the NCSA should be considered the currently most important area in the world for this species conservation. Furthermore, the lack of data throughout Central and South American marine regions hampers the evaluation of extinction risk throughout its updated distribution. Thus, research in these areas is urgently required for a more comprehensive conservation status assessment.

     

Stable isotope variations in otoliths of Pacific halibut (Hippoglossus stenolepis) and indications of the possible 1990 regime shift

Stable oxygen and carbon isotope ratios (δ¹⁸O and δ¹³C) from archived otoliths of Pacific halibut, Hippoglossus stenolepis, were measured to examine the most recent regime shifts in British Columbia and the Gulf of Alaska. δ¹⁸O values of these otoliths ranged from −1.5 to +2.8‰ VPDB, and were consistent with the life stages and migration behavior of halibut. δ¹³C varied from −3.3 to +0.9‰ VPDB, but did not show a transition from the juvenile to the adult stage as does δ¹⁸O. Evaluation of δ¹⁸O and δ¹³C values of mature halibut (ages 8–12) indicated that the 1977 regime shift might have a warming impact on the northeast Pacific fish stocks. In contrast, a possible regime shift around 1990 with a bottom seawater temperature decrease of about 2 °C might have occurred in both the areas. The connection between stable isotope variations in otoliths and the climate regime shifts is thus potentially useful in studying the population dynamics of Pacific halibut, and decadal scale (e.g., the last 20–30 years) ocean environmental changes.     

Competitive interactions between native and exotic salmonids: a combined field and laboratory demonstration

Abstract –  We studied the impact of two exotic salmonid species (brook trout, Salvelinus fontinalis and rainbow trout, Oncorhynchus mykiss ) on native brown trout ( Salmo trutta fario ) habitat, growth and survival. Habitat selection and vertical distribution between young-of-the-year of the three species were examined in a stream aquarium under different sympatric and allopatric combinations. In addition, similar species combinations were introduced in a Pyrenean mountain stream (southwest France) in order to extend laboratory results to growth and apparent survival. Both laboratory and field results indicated that rainbow trout significantly affected native brown trout habitat selection and apparent survival. On the contrary, brown trout habitat, growth and apparent survival were hardly affected by brook trout. These results support the idea that rainbow trout negatively influence native brown trout, and that competition could influence the outcome of fish biological invasions in freshwater ecosystems.     

Interannual variation in Neocalanus biomass in the Oyashio waters of the western North Pacific

We examined the interannual variation in Neocalanus copepod biomass in the Oyashio waters in spring and summer from 1972 to 1999. In the mid‐1970s, mesozooplankton biomass in spring was high; however, it decreased significantly in the late 1970s. The timing of the decrease in mesozooplankton biomass corresponded to the 1976/77 climatic regime shift. The biomass of N. flemingeri, which dominated the Neocalanus community, was roughly constant from 1980 to 1999. Although species‐level estimates of Neocalanus biomass were not available for the 1970s, a previous study reported that Neocalanus copepods were the predominant mesozooplankton in the Oyashio waters in spring during the 1970s. Neocalanus copepods dominated the mesozooplankton community throughout the 1970s, and their biomass decreased in the late 1970s. Springtime net community production, an index of new production, also decreased in the late 1970s. We suggest that the reduction in new production negatively affected Neocalanus food availability, resulting decreased copepod biomass. New production may have been limited by a combination of subsurface iron supplies, increased vertical density gradient, and reduced vertical water mixing in winter, which resulted in diminished iron entrainment in winter. In summer, mesozooplankton biomass significantly decreased and increased synchronously with the 1976/77 and 1988/89 climatic regime shifts. The biomass of N. plumchrus, which dominated the Neocalanus community, was low in the 1980s and increased in the early 1990s. The biomass of the second‐most dominant copepod, N. cristatus, also increased in the early 1990s. Neocalanus copepods were reported to be a dominant component of the mesozooplankton community in the 1970s; Neocalanus biomass was high in the mid‐1970s and decreased in the late 1970s. Japanese sardine (Sardinops melanostictus), an important predator of Neocalanus copepods, exhibited interannual variation in standing stock that was inversely related to mesozooplankton biomass. At their peak in 1984, sardines consumed 32–138% of the daily Neocalanus production during summer. Therefore, predation pressure on Neocalanus by Japanese sardine is likely to affect interannual variation in mesozooplankton biomass during the summer.     

Diet shift of larval and juvenile landlocked Ryukyu-ayu <Emphasis Type="Italic">Plecoglossus altivelis ryukyuensis</Emphasis> in the Fukuji Reservoir,Okinawa Island,Japan

ABSTRACT:   The diet shift of larval and juvenile Ryukyu-ayu Plecoglossus altivelis ryukyuensis was investigated for the landlocked population stocked in the Fukuji Reservoir, Okinawa Island. Gut contents of 274 specimens (5.1–31.4 mm in body length) including 31 yolk-sac larvae (5.7–8.0 mm) were examined. The diet of larval and juvenile landlocked P. a. ryukyuensis was mainly composed of zooplankton such as dinoflagellates, rotifers, copepods, and cladocerans. Feeding incidence was 48% in total and it gradually increased with growth. Diet analysis clearly demonstrated a diet shift during the larval and juvenile periods. For yolk-sac larvae and 5.0–19.9 mm fish, the diet was dominated by dinoflagellates Gymnodinium sp., and Peridinium sp., both numerically and by frequency, followed by rotifers that mainly consisted of Polyarthra spp. Diet breadth (Levin's standardized index B_A) diversified with growth, and feeding on copepods and cladocerans gradually increased in 10.0–14.9 mm fish. Diet overlap (Morisita's index: C) showed that diet drastically changed in 20.0–24.9 mm fish with a specialization on cladocerans Bosminopsis deitersi and Diaphanosoma brachyurum . This diet shift probably corresponded with an increase of feeding ability resulting from an enlargement of the mouth, increased swimming ability, and the development of sense organs.     

理论换段点下HMCVT换段离合器转矩交接及控制

针对液压机械无级变速器在换段过程中的动力中断和换段冲击问题,该研究以三段式液压机械无级变速器第二段切换第三段为例,通过建立动力学模型分析理论换段点下两段位的液压路功率方向变化规律,提出基于液压路功率方向的两阶段换段离合器转矩交接方法,并使用分段函数对两阶段离合器转矩交接轨迹进行优化,通过仿真对转矩交接方法正确性进行了验证。为了实现转矩的跟踪控制,基于终端滑模控制的方法设计了离合器控制器,通过对油压的跟踪控制实现转矩的跟踪控制,通过试验验证了控制器有效性。仿真和试验结果表明：在负载换段过程中,所提换段离合器转矩交接方法能够实现动力的平稳过渡,终端滑模控制器能够实现离合器油压的跟踪控制,从而实现转矩控制。在输入轴转速1 000 r/min,负载700 N·m工况下,使用终端滑模控制器控制两换段离合器进行换段,输出轴转速的波动范围为-20.6～7.4 r/min,输出轴转矩波动范围为-117.4～107.9 N·m,换段过程中最大冲击度为-6.16 m/s3,换段离合器的最大滑摩功为508.45 J,换段过程中无动力中断。该研究可为液压机械段变速器的换段控制提供参考。     

集水灌溉和施肥对半干旱区春小麦生态位适宜度和产量的影响

为了探讨利用农业集水进行的控制灌溉和施肥对提高春小麦生态位适宜度和增加产量的重要作用,该文采用田间小区试验和建模分析方法,研究了不同供水和不同施肥对春小麦叶面积指数（LAI）、根生物量、生态位适宜度与产量的影响。结果表明：不同灌溉供水量与不同施肥量对春小麦LAI和根生物量都呈现出显著的影响,其中丰水、平水和自然降水比低水处理的LAI最大值（开花期）分别增加56.9%、30.9%和19.1%;根生物量平均值分别增加84.2%、50.4%和26.6%;同时施肥与相应不施肥相比亦有显著增加。春小麦生态位适宜度与产量的结果显示：在丰水、平水、自然降水和低水处理下的适宜度（F(t)）平均值分别为0.6631、0.5670、0.5174和0.4763,籽粒产量平均值分别为3 159.2、2 345.2、1 735.7和1 380.6 kg/hm2;其中丰水、平水和自然降水比低水处理的适宜度值分别提高了39.2%、19.0%和8.6%;平均籽粒产量分别提高了128.8%、69.9%和25.7%,这表明增加供水量具有提高适宜度和增产的显著正面影响。同时,施肥比相应不施肥也有提高适宜度和增产的积极作用。统计分析表明：适宜度与籽粒产量之间呈正线性相关关系。对试验中16种不同水肥组合处理的评价结论为：丰水下施低、中、高肥,平水高肥和自然降水高肥等5种处理下属适宜;其余11种处理下属中等或不适宜。各处理下的最大适宜度值（0.8351）和最高产量（4 275.8 kg/hm2）是在丰水高肥下一致达到,这表明丰水高肥是半干旱区的一种生态适应性和产量最佳的组合处理。     

Hypotheses to explain patterns of population change among breeding bird species in England

Population declines are now evident across many taxa, but within each assemblage there is often considerable variation in constituent population trends. We used bird population trends produced from the BTO/JNCC Common Birds Census (CBC) and the RSPB/BTO/JNCC Breeding Bird Survey (BBS), to test five main hypotheses to explain population changes of 59 breeding species in England (1967-2006): (1) breeding habitat, (2) predation risk to nest sites, (3) species climatic niche, (4) migration strategy, and (5) over-wintering bioclimatic zones of migrants, accounting for additional demographic and ecological traits. In absence of phylogenetic inter-relatedness, farmland species declined more than woodland species, most pronounced prior to 1986, probably reflecting agricultural intensification (1). We found limited support that ground nesters have declined more than above-ground or cavity nesters (2), and there was some indication that species with more northerly European distributions showed larger declines than more southerly-distributed species (3). Larger population declines were recorded for Afro-tropical migrants than species wintering in Europe or in the UK, most notable prior to 1986 (4). However, declines were not uniform across all migrants (5) - species over-wintering in the arid savannah bioclimatic zone of Africa decreased in population between 1967 and 1976, whereas species wintering in humid West African forest and savannah declined more after 1987. These results suggest both breeding and over-wintering factors influenced population trends. European countries signed to the Convention on the Conservation of Migratory Species of Wild Animals are required to protect and conserve populations of migrants. Understanding connectivity between breeding and over-wintering populations, and similar environmental pressures experienced within over-wintering areas may be a useful step towards mitigating against further declines in migrants.     

Contrasting intraspecific dietary shifts in two terapontid assemblages from Australia’s wet‐dry tropics

Abstract – This study assessed the size‐related patterns of dietary resource use in terapontid assemblages from two north Australian wet‐dry tropical river systems exhibiting contrasting long‐term flow regimes. Substantially higher size‐related dietary divergence in the form of additional trophic guilds and lower levels of dietary overlap were evident among terapontids from the comparatively stable Daly River system, particularly during the dry season. Relatively restricted expression of size‐related dietary shifts in conjunction with higher levels of dietary overlap and no significant seasonal effects on dietary overlap were features of assemblage interaction in the highly variable Burdekin River. Results highlight size‐related dietary shifts as a complex aspect of terapontid trophic habits, and one that can exhibit considerable spatial dynamism.