Timescale analyses of fluctuations in coexisting populations of a native and invasive tree squirrel.

Competition from invasive species is an increasing threat to biodiversity. In Southern California, the western gray squirrel (Sciurus griseus, WGS) is facing competition from the fox squirrel (Sciurus niger, FS), an invasive congener.We used spectral methods to analyze 140 consecutive monthly censuses of WGS and FS within a 11.3 ha section of the California Botanic Garden. Variation in the numbers for both species and their synchrony was distributed across long timescales (>15 months).After filtering out annual changes, concurrent mean monthly temperatures from nearby Ontario Airport yielded a spectrum with a large semi-annual peak and significant spectral power at long timescales (>28 months). The cospectrum between WGS numbers and temperature revealed a significant negative correlation at long timescales (>35 months). Cospectra also revealed significant negative correlations with temperature at a six-month timescale for both WGS and FS.Simulations from a model of two competing species indicate that the risk of extinction for the weaker competitor increases quickly as environmental noise shifts from short to long timescales.We analyzed the timescales of fluctuations in detrended mean annual temperatures for the time period 1915-2014 from 1218 locations across the continental USA. In the last two decades, significant shifts from short to long timescales have occurred, from <3 years to 4-6 years.Our results indicate that (i) population fluctuations in co-occurring native and invasive tree squirrels are synchronous, occur over long timescales, and may be driven by fluctuations in environmental conditions; (ii) long timescale population fluctuations increase the risk of extinction in competing species, especially for the inferior competitor; and (iii) the timescales of interannual environmental fluctuations may be increasing from recent historical values. These results have broad implications for the impact of climate change on the maintenance of biodiversity.

The effect of the Safer at Home order on the frequency of DUI breath alcohol tests in Los Angeles County.

With Los Angeles County having a population size of just over 10 million and an additional 471,000 people who commute into Los Angeles County for employment, many drivers are at risk of being injured or killed in an alcohol-impaired driving collision. On March 19, 2020, the County of Los Angeles issued the Safer at Home order as a result of the COVID-19 pandemic. This curtailed driving and decreased the number of breath alcohol tests that were conducted in Los Angeles County. The number of breath tests conducted in January-February of 2019 and 2020 and March-April of 2019 and 2020 were evaluated using Fisher's exact test and analysis of variance. There was a statistically significant decrease in the overall number of breath tests conducted in Los Angeles County in March-April of 2020. There was also a significant decrease in the number of collisions where DUI was a factor. Accounting for changes in traffic volumes, the number of breath tests per vehicle miles driven also decreased significantly. Since the Safer at Home order closed all non-essential services such as bars and restaurants, there is indirect data on the relative contribution of liquor-serving establishments, and to some extent large social gatherings, to the incidence of drunk driving. Taking into account traffic volume, it was determined that the odds of encountering an intoxicated driver decreased by approximately 23% during the Safer at Home period. This information could help policy-makers determine the likely effectiveness of various countermeasures to prevent drunk driving.

Predator-prey dynamics of bald eagles and glaucous-winged gulls at Protection Island, Washington, USA.

Bald eagle (Haliaeetus leucocephalus) populations in North America rebounded in the latter part of the twentieth century, the result of tightened protection and outlawing of pesticides such as DDT. An unintended consequence of recovery may be a negative impact on seabirds. During the 1980s, few bald eagles disturbed a large glaucous-winged gull (Larus glaucescens) colony on Protection Island, Washington, USA, in the Salish Sea. Breeding gull numbers in this colony rose nearly 50% during the 1980s and early 1990s. Beginning in the 1990s, a dramatic increase in bald eagle activity ensued within the colony, after which began a significant decline in gull numbers.To examine whether trends in the gull colony could be explained by eagle activity, we fit a Lotka-Volterra-type predator-prey model to gull nest count data and Washington State eagle territory data collected in most years between 1980 and 2016. Both species were assumed to grow logistically in the absence of the other.The model fits the data with generalized R 2 = 0.82, supporting the hypothesis that gull dynamics were due largely to eagle population dynamics.Point estimates of the model parameters indicated approach to stable coexistence. Within the 95% confidence intervals for the parameters, however, 11.0% of bootstrapped parameter vectors predicted gull colony extinction.Our results suggest that the effects of bald eagle activity on the dynamics of a large gull colony were explained by a predator-prey relationship that included the possibility of coexistence but also the possibility of gull colony extinction. This study serves as a cautionary exploration of the future, not only for gulls on Protection Island, but for other seabirds in the Salish Sea. Managers should monitor numbers of nests in seabird colonies as well as eagle activity within colonies to document trends that may lead to colony extinction.

Temporal scale of environmental correlations affects ecological synchrony.

Population densities of a species measured in different locations are often correlated over time, a phenomenon referred to as synchrony. Synchrony results from dispersal of individuals among locations and spatially correlated environmental variation, among other causes. Synchrony is often measured by a correlation coefficient. However, synchrony can vary with timescale. We demonstrate theoretically and experimentally that the timescale-specificity of environmental correlation affects the overall magnitude and timescale-specificity of synchrony, and that these effects are modified by population dispersal. Our laboratory experiments linked populations of flour beetles by changes in habitat size and dispersal. Linear filter theory, applied to a metapopulation model for the experimental system, predicted the observed timescale-specific effects. The timescales at which environmental covariation occurs can affect the population dynamics of species in fragmented habitats.

Cholesteryl esters are elevated in the lipid fraction of bronchoalveolar lavage fluid collected from pediatric cystic fibrosis patients.

BACKGROUND: Host-derived lipids including cholesteryl esters (CEs) such as cholesteryl linoleate have emerged as important antibacterial effectors of innate immunity in the airways and cholesteryl linoleate has been found elevated in the context of inflammation. Cystic fibrosis (CF) patients suffer from chronic infection and severe inflammation in the airways. Here, we identified and quantified CEs in bronchoalveolar lavage fluid (BALF) from CF patients and non-CF disease controls, and tested whether CE concentrations are linked to the disease. MATERIALS AND METHODS: CEs in BALF from 6 pediatric subjects with CF and 7 pediatric subjects with non-CF chronic lung disease were quantified by mass spectral analysis using liquid chromatography coupled with tandem mass spectrometry and multiple reaction monitoring. BALFs were also examined for total lipid, total protein, albumin, and, as a marker for inflammation, human neutrophil peptide (HNP) 1-3 concentrations. Statistical analysis was conducted after log 10 transformation of the data. RESULTS: Total lipid/protein ratio was reduced in CF BALF (p = 0.018) but the concentrations of CEs, including cholesteryl linoleate, were elevated in the total lipid fraction in CF BALF compared to non-CF disease controls (p < 0.050). In addition, the concentrations of CEs and HNP1-3 correlated with one another (p < 0.050). CONCLUSIONS: The data suggests that the lipid composition of BALF is altered in CF with less total lipid relative to protein but with increased CE concentrations in the lipid fraction, likely contributed by inflammation. Future longitudinal studies may reveal the suitability of CEs as a novel biomarker for CF disease activity which may provide new information on the lipid mediated pathophysiology of the disease.

Effects of aerobic exercise on lipid-effector molecules of the innate immune response.

INTRODUCTION: Consistent, moderate-to-vigorous-intensity exercise has been associated with a lower risk of upper respiratory tract infection (URI). However, the molecular basis for this apparent protection has not yet been fully resolved. Host-derived lipids such as cholesteryl esters (CE) have emerged as important effector molecules of innate defense against infections. Here, we compared antimicrobial CE in nasal fluid before and after moderate-to-vigorous exercise between active and inactive subjects. METHODS: Nasal fluid was collected from 14 healthy, recreationally active subjects (32 ± 11 yr, 7 men and 7 women) and 14 healthy, inactive subjects (25 ± 3 yr, 7 men and 7 women) before and after treadmill exercise at 70% heart rate reserve. Nasal fluid was analyzed for lysozyme, cholesteryl linoleate (CL), cholesteryl arachidonate (CA), and albumin (Alb) concentrations. RESULTS: Baseline concentrations (mean ± SEM, inactive vs active) of lysozyme (117.7 ± 31.1 vs 122.9 ± 15.5 µg·mL), CL + CA (15.3 ± 1.8 vs 26.2 ± 10.05 µg·mL), and Alb (156.6 ± 54.5 vs 126.9 ± 32.8 µg·mL) were similar to previously reported levels and did not differ significantly between study groups. However, postexercise, CL + CA concentration was significantly lower in inactive compared with active subjects (7.8 ± 1.5 vs 20.1 ± 4.8 µg·mL, P = 0.036) dropping below the antimicrobial effective range. Once adjusted to Alb concentrations, the changes were no longer significant, suggesting that plasma transudation accounted for the increased CA + CL concentration postexercise in the active group relative to the inactive group. CONCLUSIONS: Moderate-to-vigorous aerobic exercise acutely decreases the antimicrobial CE response in inactive subjects but does not modify baseline levels of CE between active and inactive subjects. This suggests that compared with active individuals, inactive individuals may be at greater risk for upper respiratory tract infection immediately postexercise.

Expansion of Paneth cell population in response to enteric Salmonella enterica serovar Typhimurium infection.

Paneth cells residing at the base of the small intestinal crypts contribute to the mucosal intestinal first line defense by secreting granules filled with antimicrobial polypeptides including lysozyme. These cells derive from the columnar intestinal stem cell located at position 0 and the transit amplifying cell located at position +4 in the crypts. We have previously shown that Salmonella enterica serovar Typhimurium (ST), a leading cause of gastrointestinal infections in humans, effects an overall reduction of lysozyme in the small intestine. To extend this work, we examined small-intestinal tissue sections at various time points after ST infection to quantify and localize expression of lysozyme and assess Paneth cell abundance, apoptosis, and the expression of Paneth cell differentiation markers. In response to infection with ST, the intestinal Paneth cell-specific lysozyme content, the number of lysozyme-positive Paneth cells, and the number of granules per Paneth cell decreased. However, this was accompanied by increases in the total number of Paneth cells and the frequency of mitotic events in crypts, by increased staining for the proliferation marker PCNA, primarily at the crypt side walls where the transit amplifying cell resides and not at the crypt base, and by apoptotic events in villi. Furthermore, we found a time-dependent upregulation of first ß-catenin, followed by EphB3, and lastly Sox9 in response to ST, which was not observed after infection with a Salmonella pathogenicity island 1 mutant deficient in type III secretion. Our data strongly suggest that, in response to ST infection, a Paneth cell differentiation program is initiated that leads to an expansion of the Paneth cell population and that the transit amplifying cell is likely the main progenitor responder. Infection-induced expansion of the Paneth cell population may represent an acute intestinal inflammatory response similar to neutrophilia in systemic infection.

Mussel bed boundaries as dynamic equilibria: thresholds, phase shifts, and alternative states.

Ecological thresholds are manifested as a sudden shift in state of community composition. Recent reviews emphasize the distinction between thresholds due to phase shifts-a shift in the location of an equilibrium-and those due to alternative states-a switch between two equilibria. Here, we consider the boundary of intertidal mussel beds as an ecological threshold and demonstrate that both types of thresholds may exist simultaneously and in close proximity on the landscape. The discrete lower boundary of intertidal mussel beds was long considered a fixed spatial refuge from sea star predators; that is, the upper limit of sea star predation, determined by desiccation tolerance, fixed the lower boundary of the mussel bed. However, recent field experiments have revealed the operation of equilibrium processes that maintain the vertical position of these boundaries. Here, we cast analytical and simulation models in a landscape framework to show how the discrete lower boundary of the mussel bed is a dynamic predator-prey equilibrium, how the character of that boundary depends on its location in the landscape, and how boundary formation is robust to the scale of local interactions.

Antimicrobial lipids: novel innate defense molecules are elevated in sinus secretions of patients with chronic rhinosinusitis.

BACKGROUND: Airway secretions possess intrinsic antimicrobial properties that contribute to the innate host defense of the respiratory tract. These microbicidal capabilities have largely been attributed to the presence of antibacterial polypeptides. However, recent investigation has indicated that host-derived lipids including cholesteryl esters also exhibit antimicrobial properties. The purpose of this study was to determine whether sinus secretions contain such antimicrobial lipids and to compare the lipid composition in patients with and without chronic rhinosinusitis (CRS). METHODS: Maxillary sinus fluid was obtained via antral lavage from subjects with (seven patients) and without (nine patients) a history of CRS. After specimen collection, total lipid was extracted according to Bligh and Dyer (Bligh EG and Dyer WJ, A rapid method of total lipid extraction and purification, Can J Biochem Physiol 37:911-918, 1959) and lipid profiles were obtained by reverse phase high-performance liquid chromatography on an amide-embedded C18 column. In addition, the neutrophil-specific antimicrobial peptides human neutrophil peptides 1-3 (HNP1-3) were quantified by Western immunoblotting. RESULTS: Lipids, including cholesteryl esters, were identified in the maxillary sinus secretions of patients with and without CRS. However, levels of lipid composition differed between the two groups with CRS patients exhibiting greater amounts of all classes of lipids, reaching over 10-fold higher concentration when compared with non-CRS patients. This increase was independent of HNP1-3 content. CONCLUSION: Sinus secretions of patients with CRS appear to show elevated levels of antimicrobial lipids compared with controls independent from neutrophil influx. This up-regulation suggests that host-derived lipids act as mediators of mucosal immunity in CRS. Further study is necessary to determine if such antimicrobial lipids function alone or synergistically with antibacterial peptides in conferring such inherent microbicidal properties.

Complex equilibria in the maintenance of boundaries: experiments with mussel beds.

Stationary boundaries of sedentary species may belie dynamic processes that form them. Our aim was to test an implication of an evolving body of theory, that such boundaries are manifestations of complex regulatory dynamics. On rocky shores of British Columbia, large-scale field experiments altered the densities of predatory sea stars (Pisaster ochraceus), causing shifts in the location of the lower vertical boundaries of their prey, sea mussels (Mytilus californianus). While control mussel beds remained unchanged, experimental reductions of sea star densities caused the downward extension of the lower boundaries, and experimental increases in sea stars densities caused the upward recession of the lower boundary well into the zone presumed to be a spatial refuge from predation. Cleared plots prepared within the initial boundaries were recolonized to varying degrees, depending on predator densities. After 30 months, plots on sea star removal sites showed high densities of adult mussels, control plots showed intermediate densities, and sea star addition plots showed only a sparse cover of alternative prey. Observations by divers at high tide showed that as small prey were depleted progressively from removal, to control, to addition sites, correspondingly larger mussels were attacked, including very large individuals comprising the lower boundary of addition sites. The findings contradict classic theory of zonation based on static prey refuges and support an alternative theory in which boundaries are maintained by complex, spatially structured equilibria.

Membrane-targeted synergistic activity of docosahexaenoic acid and lysozyme against Pseudomonas aeruginosa.

Antimicrobial polypeptides, including lysozymes, have membrane perturbing activity and are well-documented effector molecules of innate immunity. In cystic fibrosis, a hereditary disease with frequent lung infection with Pseudomonas aeruginosa, the non-esterified fatty acid DA (docosahexaenoic acid), but not OA (oleic acid), is decreased, and DA supplementation has been shown to improve the clinical condition in these patients. We hypothesized that DA may, either alone or in conjunction with lysozyme, exert antibacterial action against Ps. aeruginosa. We found that DA and lysozyme synergistically inhibit the metabolic activity of Ps. aeruginosa, in contrast with OA. Electron microscopy and equilibrium dialysis suggest that DA accumulates in the bacterial membrane in the presence of lysozyme. Surface plasmon resonance with live bacteria and differential scanning calorimetry studies with bacterial model membranes reveal that, initially, DA facilitates lysozyme incorporation into the membrane, which in turn allows influx of more DA, leading to bacterial cell death. The present study elucidates a molecular basis for the synergistic action of non-esterified fatty acids and antimicrobial polypeptides, which may be dysfunctional in cystic fibrosis.

Colour of environmental noise affects the nonlinear dynamics of cycling, stage-structured populations.

Populations fluctuate because of their internal dynamics, which can be nonlinear and stochastic, and in response to environmental variation. Theory predicts how the colour of environmental stochasticity affects population means, variances and correlations with the environment over time. The theory has not been tested for cycling populations, commonly observed in field systems. We applied noise of different colours to cycling laboratory beetle populations, holding other statistical properties of the noise fixed. Theory was largely validated, but failed to predict observations in sufficient detail. The main period of population cycling was shifted up to 33% by the colour of environmental stochasticity. Noise colour affected population means, variances and dominant periodicities differently for populations that cycled in different ways without noise. Our results show that changes in the colour of climatic variability, partly caused by humans, may affect the main periodicity of cycling populations, possibly impacting industry, pest management and conservation.

Power spectra reveal the influence of stochasticity on nonlinear population dynamics.

Stochasticity alters the nonlinear dynamics of inherently cycling populations. The power spectrum can describe and explain the impacts of stochasticity. We fitted models to short observed time series of flour beetle populations in the frequency domain, then used a well fitting stochastic mechanistic model to generate detailed predictions of population spectra. Some predicted spectral peaks represent periodic phenomena induced or modified by stochasticity and were experimentally confirmed. For one experimental treatment, linearization theory explained that these peaks represent overcompensatory decay of deviations from deterministic oscillation. In another treatment, stochasticity caused frequent directional phase shifting around a cyclic attractor. This directional phase shifting was not explained by linearization theory and modified the periodicity of the system. If field systems exhibit directional phase shifting, then changing the intensity of demographic or environmental noise while holding constant the structure of the noise can change the main frequency of population fluctuations.

Experimental support of the scaling rule for demographic stochasticity.

A scaling rule of ecological theory, accepted but lacking experimental confirmation, is that the magnitude of fluctuations in population densities due to demographic stochasticity scales inversely with the square root of population numbers. This supposition is based on analyses of models exhibiting exponential growth or stable equilibria. Using two quantitative measures, we extend the scaling rule to situations in which population densities fluctuate due to nonlinear deterministic dynamics. These measures are applied to populations of the flour beetle Tribolium castaneum that display chaotic dynamics in both 20-g and 60-g habitats. Populations cultured in the larger habitat exhibit a clarification of the deterministic dynamics, which follows the inverse square root rule. Lattice effects, a deterministic phenomenon caused by the discrete nature of individuals, can cause deviations from the scaling rule when population numbers are small. The scaling rule is robust to the probability distribution used to model demographic variation among individuals.

Anatomy of a chaotic attractor: subtle model-predicted patterns revealed in population data.

Mathematically, chaotic dynamics are not devoid of order but display episodes of near-cyclic temporal patterns. This is illustrated, in interesting ways, in the case of chaotic biological populations. Despite the individual nature of organisms and the noisy nature of biological time series, subtle temporal patterns have been detected. By using data drawn from chaotic insect populations, we show quantitatively that chaos manifests itself as a tapestry of identifiable and predictable patterns woven together by stochasticity. We show too that the mixture of patterns an experimentalist can expect to see depends on the scale of the system under study.

Explaining and predicting patterns in stochastic population systems.

Lattice effects in ecological time-series are patterns that arise because of the inherent discreteness of animal numbers. In this paper, we suggest a systematic approach for predicting lattice effects. We also show that an explanation of all the patterns in a population time-series may require more than one deterministic model, especially when the dynamics are complex.

The shifting balance of littoral predator-prey interaction in regimes of hydrodynamic stress.

Above lowshore levels of wave-beaten rocky shores, desiccation from tidal exposure and hydrodynamics stresses from wave action are thought to create refuges from predation, allowing concentrations of sedentary prey such as mussel beds. Underwater time-lapse photography on rocky shores in Southern California revealed that dense aggregations of spiny lobsters prey on mussels during nocturnal high tides. In contradiction of the refuge hypothesis, the densest aggregations occurred on midshore levels of the most wave-exposed site, a semi-protected site showed intermediate densities, and a protected site showed only sparse numbers of lobsters. On wave-beaten shores, the lobsters' high mobility and rapid prey handling allowed them to exploit intertidal prey in the brief period at extreme high tide, when both desiccation and hydrodynamic stresses were at a minimum. The spatial differences in lobster densities were, however, positively related to the recruitment rates of juvenile mussels, the preferred prey. A field experiment demonstrated that predation by lobsters within a mussel bed affects the age/size structure of the bed without changing primary percent coverage. Therefore, concentrations of adult prey on some wave-swept sites appear to result from elevated rates of prey recruitment that surpass rates of predation, rather than absolute refuges from predation.