The patch mosaic of an old-growth warm-temperate forest: patch-level descriptions of 40-year gap-forming processes and community structures

Old-growth forests consist of various types of small patches that reflect their own gap-forming process, which includes changes in environmental conditions occurring over several decades. We reconstructed the gap-forming processes that had occurred during a 40-year period for eight representative patches of an old-growth evergreen broad-leaved forest in Japan, and examined the current community structure. The selected patches were based on (1) changes in canopy heights estimated from aerial photographs taken in four different years, (2) long-term ecological research (LTER) monitoring records, and (3) a recent field survey, so that they sufficiently covered characteristic gap-forming processes such as a new gap, an old gap and consistently closed canopy. Height and diameter at breast height (DBH) were measured on all living trees taller than 1.3 m. In their height distributions, currently almost closed patches that were open in 1966 show a rotated sigmoid, whereas their DBH distributions are an inverse J-shape. In contrast, patches that have been consistently under a closed canopy exhibit gentle inverse J-shapes for both distributions. For species composition, there are no clear contrasts associated with the past gap-forming processes except for the existence of fast-growing deciduous species in large currently open patches. Our results suggested that the variation in several decades of gap-forming processes played a central role in the high patch diversity and the complex patch mosaic of the forest. Diverse gap-forming processes created micro-environmental heterogeneity both vertically and horizontally, and contributed to the maintenance of the species-rich, warm-temperate old-growth forest.     

紊流扰动对水华鱼腥藻细胞生理的影响

正三峡水库成库以来,支流回水区频繁出现水华现象,成为近10年来我国水库生态学领域研究热点~([1])。水流条件是水华形成的主要诱导因素之一~([2]),合适的流速条件能给藻类生长营造有利的外部环境~([3])。温度、光照和营养盐是影响藻类生长的重要环境因子,在自然水体中随着深度的变化而变化~([4])。普遍认为,紊流扰动通过改变藻类在水体中的相对位置和分布,从而改变藻类生长的     

太湖生态系统能量闭合特征及其影响因素

地表能量不闭合不仅限制了涡度相关观测数据在陆面模型发展和验证等应用性研究中的价值,还给生态系统CO2源汇特征辨析带来不确定性。基于太湖避风港站2012年涡度相关通量、辐射、气象和水温梯度观测数据,分析了太湖能量闭合的多尺度(小时、日和月)时间变化特征,阐述了大气稳定度、摩擦风速和湖风对太湖能量闭合状况的影响。结果表明:太湖小时尺度的能量闭合度为0.59,且昼夜差异较小;日尺度的能量闭合度为0.73,在内陆水体观测结果中处于中等水平;月平均能量闭合度呈现冬季高、夏季低的季节变化特征;年平均时太湖仍有27%的能量不闭合。因摩擦风速减小,太湖能量闭合度在大气极不稳定条件下要比弱不稳定条件下结果低0.3;对于太湖这类大型浅水湖泊,其能量闭合度全天都受动力湍流交换强度制约,能量闭合度随摩擦风速增大而显著提高;虽然湖风发生使太湖小时尺度的能量闭合度降低了0.1,但其影响在日尺度上并不明显。     

Causes of shear sensitivity of the toxic dinoflagellate Protoceratium reticulatum

Dinoflagellates have proven extremely difficult to culture because they are inhibited by low‐level shear forces. Specific growth rate of the toxic dinoflagellate Protoceratium reticulatum was greatly decreased compared with static control culture by intermittent exposure to a turbulent hydrodynamic environment with a bulk average shear rate that was as low as 0.3 s^?1. Hydrodynamic forces appeared to induce the production of reactive oxygen species (ROS) within the cells and this caused peroxidation of cellular lipids and ultimately cell damage. Exposure to damaging levels of shear rate correlated with the elevated level of lipoperoxides in the cells, but ROS levels measured directly by flow cytometry did not correlate with shear induced cell damage. This was apparently because the measured level of ROS could not distinguish between the ROS that are normally generated by photosynthesis and the additional ROS produced as a consequence of hydrodynamic shear forces. Continuously subjecting the cells to a bulk average shear rate value of about 0.3 s^?1 for 24‐h caused an elevation in the levels of chlorophyll a, peridinin and dinoxanthin, as the cells apparently attempted to counter the damaging effects of shear fields by producing pigments that are potential antioxidants. In static culture, limitation of carbon dioxide produced a small but measureable increase in ROS. The addition of ascorbic acid (0.1 mM) to the culture medium resulted in a significant protective effect on lipid peroxidation, allowing cells to grow under damaging levels of shear rates. This confirmed the use of antioxidant additives as an efficient strategy to counter the damaging effects of turbulence in photobioreactors where shear sensitive dinoflagellates are cultivated. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Effects of turbulence on the feeding rate of a pelagic predator: The planktonic hydroid Clytia gracilis

Relatively little is known about the role of turbulence in a predator-prey system where the predator is a passive, pelagic forager. The Campanulariid hydroid Clytia gracilis (Cnidaria, Hydrozoa) is unusual because it occurs as planktonic colonies and is reported to forage passively in the water column on Georges Bank, Massachusetts, USA. In this study, we investigated the role of various turbulence conditions on the feeding rate of C. gracilis colonies in laboratory experiments. We found a positive relationship between turbulence velocities and feeding rates up to a turbulent energy dissipation rate of ca. 1 cm² s^− 3. Beyond this threshold feeding rate decreased slightly, indicating a dome-shaped relationship. Additionally, a negative relationship was found between feeding efficiency and hydroid colony size under lower turbulent velocities, but this trend was not significant under higher turbulence regimes.     

Reconstruction of coral reef fisheries catches in American Samoa, 1950–2002

Fisheries catches from Pacific Island coral reefs are rarely recorded in official statistics. Reconstruction of catch estimates with limited hard data requires interpolation and assumptions, justifiable only by the unsatisfactory alternative of continued substitution of zero catches, a common policy interpretation for ‘no data’. Uncertainties associated with reconstructions are high, requiring conservative estimation. American Samoan domestic fisheries consist of an artisanal, small-boat sector, whose commercial catches are reported, and a shore-based subsistence sector, with no regular reporting. Our catch reconstruction (with large pelagic species removed) suggested a 79% decrease in catches between 1950 (752 t) and 2002 (155 t). Accounting for rapid human population growth on the main island, the per capita catch rate may have declined from 36.3 kg·person⁻¹ year⁻¹ in 1950 to 1.3 kg·person⁻¹ year⁻¹ by 2002, while the catch rate for the inhabited outer islands has been independently reported as 58.6 kg·person⁻¹ year⁻¹. Catch per area of coral reef (to 50-m depth) may have declined from 5.5 to 0.7 t km⁻² year⁻¹ for the main island, and from 9.1 to 4.9 t km⁻² year⁻¹ for the outer islands, for 1950 and 2002, respectively. Summed for 1950–2002, our reconstruction suggested a 17-fold difference between reconstructed estimates and reported statistics.     

A review of fish swimming mechanics and behaviour in altered flows

Fishes suspended in water are subject to the complex nature of three-dimensional flows. Often, these flows are the result of abiotic and biotic sources that alter otherwise uniform flows, which then have the potential to perturb the swimming motions of fishes. The goal of this review is to highlight key studies that have contributed to a mechanistic and behavioural understanding of how perturbing flows affect fish. Most of our understanding of fish behaviour in turbulence comes from observations of natural conditions in the field and laboratory studies employing controlled perturbations, such as vortices generated in the wake behind simple geometric objects. Laboratory studies have employed motion analysis, flow visualization, electromyography, respirometry and sensory deprecation techniques to evaluate the mechanisms and physiological costs of swimming in altered flows. Studies show that flows which display chaotic and wide fluctuations in velocity can repel fishes, while flows that have a component of predictability can attract fishes. The ability to maintain stability in three-dimensional flows, either actively with powered movements or passively using the posture and intrinsic compliance of the body and fins, plays a large role in whether fish seek out or avoid turbulence. Fish in schools or current-swept habitats can benefit from altered flows using two distinct though not mutually exclusive mechanisms: flow refuging (exploiting regions of reduced flow relative to the earth frame of reference) and vortex capture (harnessing the energy of environmental vortices). Integrating how the physical environment affects organismal biomechanics with the more complex issue of behavioural choice requires consideration beyond simple body motions or metabolic costs. A fundamental link between these two ways of thinking about animal behaviour is how organisms sense and process information from the environment, which determines when locomotor behaviour is initiated and modulated. New data are presented here which show that behaviour changes in altered flows when either the lateral line or vision is blocked, showing that fish rely on multi-modal sensory inputs to negotiate complex flow environments. Integrating biomechanics and sensory biology to understand how fish swim in turbulent flow at the organismal level is necessary to better address population-level questions in the fields of fisheries management and ecology.     

Do light/dark cycles of medium frequency enhance phytoplankton productivity?

It has been suggested that turbulence with the resultant light/dark cycle and light gradient through which phytoplankton move, enhances their productivity. The stationary bottle incubation technique for estimating rates of primary productivity has mainly been criticized because of bottle effects, the elimination of natural turbulence and the presence of photo-inhibition. In a series of experiments where productivity was measured over static profiles and compared to the productivity in a mixed system, no definite conclusion could be reached regarding the effect of varying light/dark cycles of medium frequency (seconds to minutes). It appeared as though the ratio of the euphotic depth to mixing depth (Z _eu/Z _m) influenced productivity more than the duration of the light/dark cycle. The static bottle incubation method gave higher integral productivities than the mixed samples at low ratio's ofZ _eu/Z _m. It is suggested that mixing has two separate, but synergistic effects i.e. it not only moves the phytoplankton cells through a light/dark cycle, but also decreases the boundary layer, which increases the rate of exchange through the cell wall of nutrients and metabolites. In doing so more nutrients are available and light could be utilized more efficiently and therefore, productivity is increased.     

Into turbulent air: size-dependent effects of von Kármán vortex streets on hummingbird flight kinematics and energetics

Animal fliers frequently move through a variety of perturbed flows during their daily aerial routines. However, the extent to which these perturbations influence flight control and energetic expenditure is essentially unknown. Here, we evaluate the kinematic and metabolic consequences of flight within variably sized vortex shedding flows using five Anna''s hummingbirds feeding from an artificial flower in steady control flow and within vortex wakes produced behind vertical cylinders. Tests were conducted at three horizontal airspeeds (3, 6 and 9 m s⁻¹) and using three different wake-generating cylinders (with diameters equal to 38, 77 and 173% of birds'' wing length). Only minimal effects on wing and body kinematics were demonstrated for flight behind the smallest cylinder, whereas flight behind the medium-sized cylinder resulted in significant increases in the variances of wingbeat frequency, and variances of body orientation, especially at higher airspeeds. Metabolic rate was, however, unchanged relative to that of unperturbed flight. Hummingbirds flying within the vortex street behind the largest cylinder exhibited highest increases in variances of wingbeat frequency, and of body roll, pitch and yaw amplitudes at all measured airspeeds. Impressively, metabolic rate under this last condition increased by up to 25% compared with control flights. Cylinder wakes sufficiently large to interact with both wings can thus strongly affect stability in flight, eliciting compensatory kinematic changes with a consequent increase in flight metabolic costs. Our findings suggest that vortical flows frequently encountered by aerial taxa in diverse environments may impose substantial energetic costs.     

Pollination of lark daisy on roadsides declines as traffic speed increases along an Amazonian highway

Ecological disturbances caused by roadways have previously been reported, but traffic speed has not been addressed. We investigate effects of traffic speed on pollination of Centratherum punctatum (Asteraceae) along an Amazonian highway roadside. We hypothesised that frequency of flower visitors, duration of single visits and pollen deposition on stigmas will vary negatively as traffic speed increases. After measuring vehicle velocities, we classified three road sections as low‐, mid‐ and high‐velocity traffic. The main pollinator bee, Augochlora sp., visited C. punctatum inflorescences with decreasing frequency from low‐ to high‐velocity roadside sections, whereas the nectar thief butterflies did the opposite. Duration of single visits by bees and butterflies was shorter, and arrival of pollen on C. punctatum stigmas was lower, in high‐ than in low‐velocity roadside. Air turbulence due to passing vehicles increases with velocity and disturbed the flower visitors. Overall, results support that traffic velocity negatively affects foraging of flower visitors and the pollination of C. punctatum on roadsides.