Summary
Migratory animals can enhance ecosystem productivity through the delivery of material subsidies. Among fish, Pacific salmon are well known to deliver large quantities of nutrients to streams ...as they die after spawning, but the input pathways by which iteroparous species provide nutrient subsidies have not been resolved.
Our objective was to determine the importance of excretion, eggs and carcasses as nutrient sources from a large migration of longnose suckers into a stream draining a moderately agricultural catchment. Additionally, we evaluated nutrient limitation in the stream using nutrient‐diffusing substrates and determined the timing of nutrient releases during egg decomposition using a microcosm experiment.
Eggs were the largest component of the nitrogen (N, 57%) and phosphorus (P, 76%) inputs from the migration, followed by excretion by live adults (40% N, 16% P). Carcasses were a minor component of inputs.
Estimated P inputs from fish were over three times larger than the observed export of dissolved P in this P‐limited stream during the 66‐day sampling period. In contrast, sucker N inputs were <2% of dissolved N export, which was dominated by NO3. However, the dynamics of NH4 concentrations through the course of the migration were closely associated with estimated NH4 inputs from excretion and eggs.
Eggs and excretion constitute significant nutrient inputs during migrations, even in catchments with elevated nutrient loads from agriculture. Mass mortality is not required for migratory fish to enhance nutrient availability in their spawning habitats.
Given that sucker excretion rates and female reproductive investment are typical for freshwater fish, our results suggest that spawning migrations of iteroparous species in rivers around the world may deliver important nutrient subsidies when migrations are large.
The rise of novelty in ecosystems Radeloff, Volker C; Williams, John W; Bateman, Brooke L ...
Ecological applications,
December 2015, Letnik:
25, Številka:
8
Journal Article
Recenzirano
Rapid and ongoing change creates novelty in ecosystems everywhere, both when comparing contemporary systems to their historical baselines, and predicted future systems to the present. However, the ...level of novelty varies greatly among places. Here we propose a formal and quantifiable definition of abiotic and biotic novelty in ecosystems, map abiotic novelty globally, and discuss the implications of novelty for the science of ecology and for biodiversity conservation. We define novelty as the degree of dissimilarity of a system, measured in one or more dimensions relative to a reference baseline, usually defined as either the present or a time window in the past. In this conceptualization, novelty varies in degree, it is multidimensional, can be measured, and requires a temporal and spatial reference. This definition moves beyond prior categorical definitions of novel ecosystems, and does not include human agency, self-perpetuation, or irreversibility as criteria. Our global assessment of novelty was based on abiotic factors (temperature, precipitation, and nitrogen deposition) plus human population, and shows that there are already large areas with high novelty today relative to the early 20th century, and that there will even be more such areas by 2050. Interestingly, the places that are most novel are often not the places where absolute changes are largest; highlighting that novelty is inherently different from change. For the ecological sciences, highly novel ecosystems present new opportunities to test ecological theories, but also challenge the predictive ability of ecological models and their validation. For biodiversity conservation, increasing novelty presents some opportunities, but largely challenges. Conservation action is necessary along the entire continuum of novelty, by redoubling efforts to protect areas where novelty is low, identifying conservation opportunities where novelty is high, developing flexible yet strong regulations and policies, and establishing long-term experiments to test management approaches. Meeting the challenge of novelty will require advances in the science of ecology, and new and creative conservation approaches.
We present dye-doped polymer nanoparticles that are able to detect mercury in aqueous solution at parts per billion levels via fluorescence resonance energy transfer (FRET). The nanoparticles are ...prepared by reprecipitation of highly fluorescent conjugated polymers in water and are stable in aqueous suspension. They are doped with rhodamine spirolactam dyes that are nonfluorescent until they encounter mercury ions, which promote an irreversible reaction that converts the dyes to fluorescent rhodamines. The rhodamine dyes act as FRET acceptors for the fluorescent nanoparticles, and the ratio of nanoparticle-to-rhodamine fluorescence intensities functions as a ratiometric fluorescence chemodosimeter for mercury. The light harvesting capability of the conjugated polymer nanoparticles enhances the fluorescence intensity of the rhodamine dyes by a factor of 10, enabling sensitive detection of mercury ions in water at levels as low as 0.7 parts per billion.
Threats to aquatic biodiversity are expressed at broad spatial scales, but identifying regional trends in abundance is challenging owing to variable sampling designs and temporal and spatial ...variation in abundance. We compiled a regional data set of brook trout (Salvelinus fontinalis) counts across their southern range representing 326 sites from eight states between 1982 and 2014 and conducted a statistical power analysis using Bayesian state-space models to evaluate the ability to detect temporal trends by characterizing posterior distributions with three approaches. A combination of monitoring periods, number of sites and electrofishing passes, decline magnitude, and different revisit patterns were tested. Power increased with monitoring periods and decline magnitude. Trends in adults were better detected than young-of-the-year fish, which showed greater interannual variation in abundance. The addition of weather covariates to account for the temporal variation increased power only slightly. Single- and three-pass electrofishing methods were similar in power. Finally, power was higher for sampling designs with more frequent revisits over the duration of the monitoring program. Our results provide guidance for broad-scale monitoring designs for temporal trend detection.
The non-disabled human ankle joint was examined during walking in an attempt to determine overall system characteristics for use in the design of ankle prostheses. The hypothesis of the study was ...that the quasi-stiffness of the ankle changes when walking at different walking speeds. The hypothesis was examined using sagittal plane ankle moment versus ankle angle curves from 24 able-bodied subjects walking over a range of speeds. The slopes of the moment versus ankle angle curves (quasi-stiffness) during loading appeared to change as speed was increased and the relationship between the moment and angle during loading became increasingly non-linear.
The loading and unloading portions of the moment versus angle curves showed clockwise loops (hysteresis) at self-selected slow speeds that reduced essentially to zero as the speed increased to self-selected normal speeds. Above self-selected normal speeds, the loops started to traverse a counter-clockwise path that increased in area as the speed was increased. These characteristics imply that the human ankle joint could be effectively replaced with a rotational spring and damper for slow to normal walking speeds. However, to mimic the characteristics of the human ankle during walking at fast speeds, an augmented system would be necessary. This notion is supported by the sign of the ankle power at the time of opposite heel contact, which was negative for slow speeds, was near zero at normal speeds, and was positive for fast walking speeds.
Environmental drivers of population vital rates, such as temperature and precipitation, often vary at short time scales, and these fluctuations can have important impacts on population dynamics. ...However, relationships between survival and environmental conditions are typically modeled at coarse temporal scales, ignoring the role of daily environmental variation in survival. Our goal was to determine the importance of fine-scale temporal variation in survival to population dynamics of stream salmonids. We extended the Cormack–Jolly–Seber model to estimate daily survival rates from seasonal samples of individually marked brook trout (Salvelinus fontinalis) in a stream network. Daily variation in temperature and flow were strongly associated with survival, but relationships varied between juvenile and adult trout and among streams. In all streams, juveniles had higher mortality in warm, low-flow conditions, but in the two larger streams, cold, high-flow conditions also reduced juvenile survival. Adult survival decreased during low flows, particularly in the fall spawning period. Differing survival responses among stream network components to short-term environmental events created shifts in optimal location for maximum survival across life stages, seasons, and years.
Defects are often written off as performance limiters. Contrary to this notion, it is shown that controlling the defect configuration in graphene is critical to overcome a fundamental limitation ...posed by quantum capacitance and opens new channels for ion diffusion. Defect‐engineered graphene flexible pouch capacitors with energy densities of 500% higher than the state‐of‐the‐art supercapacitors are demonstrated.
Objective. To examine the hypothesis that roll-over shapes of non-disabled lower limb systems do not change appreciably with walking speed.
Design. Repeated measures (
n=24).
Background. Roll-over ...shapes of three lower limb systems are presented. They are: roll-over shapes of the (1) foot, (2) ankle–foot, and (3) knee–ankle–foot systems. Roll-over shapes show the
effective rocker (or cam) shapes that the lower limb systems conform to during the period in the stance phase of walking between heel contact and opposite heel contact.
Methods. Roll-over shapes were measured by transforming center of pressure data from a laboratory-based coordinate system into each of three body-based coordinate systems. Knee–ankle–foot roll-over shapes were further characterized using a circular arc model.
Results. From a statistical standpoint, the radii of the best-fit circular arcs did not change significantly with walking speed, while the forward shifts of the circular models did change significantly. However, the change in forward shift was not considered to be clinically significant.
Conclusions. The biologic systems involved in developing the roll-over shapes adapt to changing conditions of walking speed, including increased loading amplitudes as speed is increased, to maintain similar effective roll-over geometries.
Relevance
Roll-over shapes provide insight into the workings of various lower limb systems by taking a new look at existing gait data. This insight could provide broad utility, helping to develop a better understanding of able-bodied and disabled human walking, and leading to the design of improved rehabilitation devices, surgeries, and therapies.
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Sphingosine-1-phosphate (S1P) is a ubiquitous, endogenous small molecule that is synthesized by two isoforms of sphingosine kinase (SphK1 and 2). Intervention of the S1P signaling ...pathway has attracted significant attention because alteration of S1P levels is linked to several disease states including cancer, fibrosis, and sickle cell disease. While intense investigations have focused on developing SphK1 inhibitors, only a limited number of SphK2-selective agents have been reported. Herein, we report our investigations on the structure–activity relationship studies of the lipophilic tail region of SLR080811, a SphK2-selective inhibitor. Our studies demonstrate that the internal phenyl ring is a key structural feature that is essential in the SLR080811 scaffold. Further, we show the dependence of SphK2 activity and selectivity on alkyl tail length, suggesting a larger lipid binding pocket in SphK2 compared to SphK1.
Abstract
Migratory animals can have profound impacts on ecosystem structure and function. In streams, salmon are well known for their contrasting influences on primary productivity through nutrient ...delivery, which enhances potential productivity, and substrate disturbance during nest building, which reduces algal biomass and primary production. However, most migratory fish species neither disturb the substrate significantly nor die en masse after spawning, hence their influence on ecosystems may differ from that observed in salmon streams. To determine the influence of nutrient subsidies from migrations of iteroparous fish whose broadcast spawning does not disturb the substrate substantially, we compared nutrient limitation, nutrient concentrations, and stream metabolism during spawning migrations of suckers (
Catostomus
spp.) in Lake Michigan tributaries with and without migration barriers. Although suckers deliver both nitrogen and phosphorus as eggs and waste excretion, only nitrogen concentrations were elevated during the migration (
NH
4
‐N rose 44% relative to sites without a sucker run). Nutrient diffusing substrates demonstrated P‐limitation during the migration at sites spanning a wide range of sucker abundance, suggesting that high demand for likely masked P inputs from fish. Time series analyses indicated that gross primary production (
GPP
) increased with sucker excretion, but not with egg deposition after accounting for abiotic conditions. In contrast, egg deposition, but not excretion, was associated with a slight increase in ecosystem respiration (
ER
), suggesting that sucker gametes provide labile carbon that contributes to
ER
. The effects of suckers contrast with ecosystem responses to salmon migrations, which elevate
ER
but have mixed effects on
GPP
. This disparity reflects the fact that suckers fertilize streams without attendant disturbance effects. Our results suggest that basic differences in life history and behavior of migratory fish determine the direction and magnitude of their ecosystem effects. As a result, broad trait‐based predictions of the ecosystem role of migratory fishes may become possible as more species are studied.
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