Experimental Demonstration of Accelerated Extinction in Source-Sink Metapopulations

Population extinction is a fundamental ecological process which may be aggravated by the exchange of organisms between productive (source) and unproductive (sink) habitat patches. The extent to which such source-sink exchange affects extinction rates is unknown. We conducted an experiment in which metapopulation effects could be distinguished from source-sink effects in laboratory populations of Daphnia magna. Time-to-extinction in this experiment was maximized at intermediate levels of habitat fragmentation, which is consistent with a minority of theoretical models. These results provided a baseline for comparison with experimental treatments designed to detect effects of concentrating resources in source patches. These treatments showed that source-sink configurations increased population variability (the coefficient of variation in abundance) and extinction hazard compared with homogeneous environments. These results suggest that where environments are spatially heterogeneous, accurate assessments of extinction risk will require understanding the exchange of organisms among population sources and sinks. Such heterogeneity may be the norm rather than the exception because of both the intrinsic heterogeneity naturally exhibited by ecosystems and increasing habitat fragmentation by human activity

Species Invasion Shifts the Importance of Predator Dependence

The strength of interference between foraging individuals can influence per capita consumption rates, with important consequences for predator and prey populations and system stability. Here we demonstrate how the replacement of a previously established invader, the predatory crab Carcinus maenas, by the recently invading predatory crab Hemigrapsus sanguineus shifts predation from a species that experiences strong predator interference (strong predator dependence) to one that experiences weak predator interference (weak predator dependence). We demonstrate using field experiments that differences in the strength of predator dependence persist for these species both when they forage on a single focal prey species only (the mussel Mytilus edulis) and when they forage more broadly across the entire prey community. This shift in predator dependence with species replacement may be altering the biomass across trophic levels, consistent with theoretical predictions, as we show that H. sanguineus populations are much larger than C. maenas populations throughout their invaded ranges. Our study highlights that predator dependence may differ among predator species and demonstrates that different predatory impacts of two conspicuous invasive predators may be explained at least in part by different strengths of predator dependence

Feeding rates of the mud shrimp Upogebia pugettensis and implications for estuarine phytoplankton abundance

The suspension-feeding mud shrimp, Upogebia pugettensis, is a common inhabitant of intertidal mudflats in estuaries throughout the Pacific Northwest, where it develops extensive burrows. Also inhabiting the shrimps' burrow is the commensal bivalve, Cryptomya californica. Filtration by dense populations of the shrimp and its commensals may have a negative impact on phytoplankton abundance within these estuaries. The presence of the shrimp introduces three possible sinks for phytoplankton: filtration by the shrimp, filtration by the commensal bivalve, and removal of phytoplankton by the burrow itself. Together, the shrimp, commensal bivalve, and burrow, comprise the shrimp-burrow complex. Laboratory feeding experiments were conducted to measure particle removal rates of the shrimp-burrow complex, and to determine the relative importance of each of the three components of the complex in particle removal. For comparison, the same experiments were conducted with the Pacific oyster, Crassostrea gigas, Retention efficiencies were determined for particles in the size range from 2 to 10 1m in an effort to determine whether shrimp utilize the same size range of particles as other suspension feeders. Using data from our filtration experiments, a simple box model was developed to predict the proportion of the total volume of water in the lower Yaquina Bay, Oregon, that is filtered by shrimp-burrow complexes over a 24-hour period. Results indicate that the burrow wall may be an important factor in removal of phytoplankton (expressed as suspended POC), potentially accounting for 0.7 that removed by the shrimp alone. The model predicts that, for the phytoplankton concentrations tested, the shrimp-burrow complex may potentially remove 0.152-1.667 times the total amount of phytoplankton found in the lower Yaquina each day, depending on tidal-flow dynamics. We conclude that the shrimp-burrow complex is capable of removing large proportions of available phytoplankton, and may potentially deplete phytoplankton in some areas of the lower Yaquina Bay

The Role of Individual Behavior Type in Mediating Indirect Interactions

Trait-mediated indirect interactions (TMII) play an important role in structuring natural communities, and numerous studies have experimentally demonstrated their presence in a variety of systems. However, these studies have largely examined the presence or absence of traits that are responsible for these interactions, without considering natural variation between individuals in the extent to which these traits are manifested. We used a well-documented TMII to investigate the importance of individual behavior type for determining the strength of the TMII. The toadfish Opsanus tau has an indirect positive influence on bivalve survival because the mud crab Panopeus herbstii, a consumer of bivalves, reduces foraging effort in the presence of toadfish. We quantified variation in the strength of persistent individual mud crab responses to toadfish and resulting variation in the strength of TMII. We demonstrate that the strength of this TMII is strongly influenced by mud crab size and behavior type, strengthening with the intensity of response of individual mud crabs to toadfish predator cues. Further, we demonstrate that the spatial distribution within intertidal oyster reefs of crabs with different behavior types is not random; mud crabs inhabiting subtidal areas, where predator cues are more persistent, are significantly less responsive to toadfish cues than mud crabs from intertidal areas. This spatial behavioral structure should lead to spatial variation in the strength of TMII. Given the widespread importance of TMII and the broad occurrence of individual personality or behavior types across numerous taxa, these results should be generally applicable. The distribution of behavior types within a population may therefore be a useful metric for improving our ability to predict the strength of TMII

Significance of Autumn and Winter Food Consumption for Reproduction by Southern Beaufort Sea Polar Bears, \u3ci\u3eUrsus Maritimus\u3c/i\u3e

Polar bears (Ursus maritimus) in the southern Beaufort Sea experience long annual periods when preferred seal prey are scarce or are unavailable. Consumption of bowhead whale (Balaena mysticetus) carcasses from native Alaskan subsistence hunting is increasingly common for onshore polar bears, yet the energetic consequences of this consumption remain unclear. We use data on bears captured repeatedly over periods that encompassed autumn and winter, combined with calculations, to show that adult female bears likely consume an average of at least 4 seal equivalents during both autumn and winter periods and that considerable variation in energy intake exists across individual bears. We further show that subsistence-caught whale carcasses provide an upper threshold of \u3e 4000 seal equivalents, which could potentially meet mean consumption needs of ~ 80% of the southern Beaufort Sea bear subpopulation during autumn and winter periods. Finally, we modify an existing model to show that observed mass changes over autumn and winter could substantially alter spring foraging habitat choice by females with cubs and the chance that a female with reduced energy reserves would abort a pregnancy or abandon cubs in favor of increasing her own survival; these behaviors could potentially influence population vital rates. Our study highlights the importance of mass dynamics over the autumn and winter months, points to the need for additional data on foraging and energetics over this period, and indicates that the recent declines in polar bear body condition in some subpopulations could have complex effects on reproduction

An Artificial Habitat Increases the Reproductive Fitness of a Range-shifting Species within a Newly Colonized Ecosystem

When a range-shifting species colonizes an ecosystem it has not previously inhabited, it may experience suboptimal conditions that challenge its continued persistence and expansion. Some impacts may be partially mitigated by artificial habitat analogues: artificial habitats that more closely resemble a species\u27 historic ecosystem than the surrounding habitat. If conditions provided by such habitats increase reproductive success, they could be vital to the expansion and persistence of range-shifting species. We investigated the reproduction of the mangrove tree crab Aratus pisonii in its historic mangrove habitat, the suboptimal colonized salt marsh ecosystem, and on docks within the marsh, an artificial mangrove analogue. Crabs were assessed for offspring production and quality, as well as measures of maternal investment and egg quality. Aratus pisonii found on docks produced more eggs, more eggs per unit energy investment, and higher quality larvae than conspecifics in the surrounding salt marsh. Yet, crabs in the mangrove produced the highest quality larvae. Egg lipids suggest these different reproductive outcomes result from disparities in the quality of diet-driven maternal investments, particularly key fatty acids. This study suggests habitat analogues may increase the reproductive fitness of range-shifting species allowing more rapid expansion into, and better persistence in, colonized ecosystems

The National Early Warning Score and its subcomponents recorded within ±24 hours of emergency medical admission are poor predictors of hospital-acquired acute kidney injury

YesBackground: Hospital-acquired Acute Kidney Injury (H-AKI) is a common cause of avoidable morbidity and mortality. Aim: To determine if the patients’ vital signs data as defined by a National Early Warning Score (NEWS), can predict H-AKI following emergency admission to hospital. Methods: Analyses of emergency admissions to York hospital over 24-months with NEWS data. We report the area under the curve (AUC) for logistic regression models that used the index NEWS (model A0), plus age and sex (A1), plus subcomponents of NEWS (A2) and two-way interactions (A3). Likewise for maximum NEWS (models B0,B1,B2,B3). Results: 4.05% (1361/33608) of emergency admissions had H-AKI. Models using the index NEWS had the lower AUCs (0.59 to 0.68) than models using the maximum NEWS AUCs (0.75 to 0.77). The maximum NEWS model (B3) was more sensitivity than the index NEWS model (A0) (67.60% vs 19.84%) but identified twice as many cases as being at risk of H-AKI (9581 vs 4099) at a NEWS of 5. Conclusions: The index NEWS is a poor predictor of H-AKI. The maximum NEWS is a better predictor but seems unfeasible because it is only knowable in retrospect and is associated with a substantial increase in workload albeit with improved sensitivity.The Health Foundatio

Proposed mechanism of action of tap water iontophoresis for treatment of hyperhidrosis

Tap water iontophoresis is commonly used to treat hyperhidrosis, yet the mechanism of action for this treatment remains unknown. Here, I propose a plausible mechanism of action based on the biology of the eccrine sweat gland, reported patterns in iontophoresis effectiveness, and known dynamics of small particles in fluid systems. Specifically, I propose that iontophoresis works via the production of a colloid formed between the products of dark (mucin) and clear (aqueous solution) cells, and the jamming of nanomineral particles inside the lumen and/or the duct of the sweat gland, creating a blockage that temporarily prevents further sweat production or secretion. I further outline several feasible tests of this hypothesis

Data from: Reproductive skipping as an optimal life history strategy in the southern elephant seal, Mirounga leonina

Intermittent breeding by which organisms skip some current reproductive opportunities in order to enhance future reproductive success is a common life history tradeoff among long-lived, iteroparous species. The southern elephant seal Mirounga leonina engages in intermediate breeding when body condition is low. While it is anticipated that this strategy may increase the lifetime reproductive output of this species, the conditions under which reproductive skipping are predicted to occur are not clear. Here I develop a dynamic state variable model based on published data that examines when southern elephant seals are predicted to optimally skip reproduction in order to maximize lifetime reproductive output as a function of current body mass, maternal age, and survivorship. I demonstrate that the optimal reproductive strategy for this species can include reproductive skipping, and that the conditions where this is optimal depend on patterns of mass-dependent adult female survival. I further show that intermittent breeding can increase lifetime reproductive output, and that the magnitude of this benefit increases with the ability of individual animals to replenish depleted body mass through foraging. Finally, I show that when the environment is variable and foraging is reduced in bad years, the benefit of adopting an optimal strategy that includes reproductive skipping increases asymptotically with the frequency of bad years. These results highlight the importance of characterizing the pattern of adult survival in this species, as well as the need to identify other factors that may influence the prevalence and benefits of reproductive skipping

Differences in growth within and across the reproductive forms of northern crayfish (Faxonius virilis)

Abstract Complex life histories are frequently associated with biological trade‐offs, as the use of one trait can decrease the performance of a second trait due to the need to balance competing demands to maximize fitness. Here, we examine growth patterns in invasive adult male northern crayfish (Faxonius virilis) that are indicative of a potential trade‐off between energy allocation for body size versus chelae size growth. Northern crayfish undergo cyclic dimorphism, a process characterized by seasonal morphological changes associated with reproductive status. We measured carapace length and chelae length before and after molting and compared these growth increments between the four morphological transitions of the northern crayfish. Consistent with our predictions, reproductive crayfish molting to the non‐reproductive form and non‐reproductive crayfish molting within the non‐reproductive form experienced a larger carapace length growth increment. Reproductive crayfish molting within the reproductive form and non‐reproductive crayfish molting to the reproductive form, on the other hand, experienced a larger growth increment in chelae length. The results of this study support that cyclic dimorphism evolved as a strategy for optimizing energy allocation for body and chelae size growth during discrete periods of reproduction in crayfish with complex life histories