Variation In Survival Probability Research Articles

The role of pictorial cues and contrast for camouflage

Shadows that are produced across the surface of an object (self-shadows) are potentially an important source of information for visual systems. Animal patterns may exploit this principle for camouflage, using pictorial cues to produce false depth information that manipulates the viewer’s detection/recognition processes. However, pictorial cues could also facilitate camouflage by matching the contrast (e.g. due to shadows) of 3D backgrounds. Aside from studies of countershading (patterning that may conceal depth information), the role of self-shadows in camouflage patterns remains unclear. Here we investigated whether pictorial cues (self-shadows) increase the survival probability of moth-like prey presented to free-living wild bird predators relative to targets without these cues. We manipulated the presence of self-shadows by adjusting the illumination conditions to produce patterned targets under directional lighting (lit from above or from below; self-shadows present) or diffuse lighting (no self-shadows). We used non-patterned targets (uniform colour) as controls. We manipulated the direction of illumination because it has been linked with depth perception in birds; objects lit from above may appear convex while those lit from below can appear concave. As shadows influence contrast, which also determines detectability, we photographed the targets in situ over the observation period, allowing us to evaluate the effect of visual metrics on survival. We found some evidence that patterned targets without self-shadows had a lower probability of survival than patterned targets with self-shadows and targets with uniform colour. Surprisingly, none of the visual metrics explained variation in survival probability. However, predators increased their foraging efficiency over time, suggesting that predator learning may have overridden the benefits afforded by camouflaging coloration.

Identifying drivers of spatio-temporal variation in survival in four blue tit populations

In a context of rapid climate change, the influence of large-scale and local climate on population demography is increasingly scrutinized, yet studies are usually focused on one population. Demographic parameters, including survival, can vary significantly across populations of a given species, depending on global or local climatic fluctuations but also on many other population-specific parameters such as breeding density, habitat naturalness, predation or parasitism. Such ecological differences between populations could lead to different paces-of-life (POL), whereby populations where individuals display higher reproductive investment and bolder behaviours would have lower survival probabilities. We use here long-term (19 to 38 years) monitoring datasets from four Mediterranean populations of blue tits (Cyanistes caeruleus) to investigate the effects of sex, age class, large-scale and local climate temporal variation and population breeding density, on adult survival, using Capture-Mark-Recapture modelling. Environment heterogeneity in these four populations (two in evergreen and two in deciduous forests) has been linked to strong multi-trait phenotypic variation, suggesting blue tits in deciduous forests display faster POL compared to their conspecifics in evergreen habitats. The present results show heterogeneity in average survival probabilities across the four populations, with, as predicted, lower survival in the fast blue tits occupying deciduous habitats. Interestingly, the year-to-year variation in survival probabilities was synchronous among populations. This suggests that regional environmental conditions could drive survival fluctuations across populations. However, breeding densities were not correlated across populations, and we found no evidence that adult survival is correlated with either large-scale or local, climate temporal variation in these four blue tit populations. Finally, two of the focal populations displayed a linear temporal decrease in adult survival over the study period, calling for further investigation to explain this decline. Overall, this multi-site study shows that blue tit parental survival from one spring to the next can vary substantially across years, in a synchronous way across populations, yet the climate indices we used are not correlated with the temporal variation. This calls for further investigations in other potential drivers such as resource (in particular insect) abundance, predation or parasitism.

Annual survival probabilities of anadromous Arctic Char remain high and stable despite interannual differences in sea ice melt date

Throughout their range, anadromous Arctic Char (Salvelinus alpinus (Linnaeus, 1758)) support commercial, recreational, and subsistence fisheries that are important economically, socially, and culturally. However, drivers of interannual variation in survival in this species remain poorly understood. Here, we aimed to quantify the impact of environmental and biological parameters on the survival probability of anadromous Arctic Char near the community of Cambridge Bay, Nunavut, Canada. To do so, we tracked 183 Arctic Char tagged with acoustic transmitters and used capture–mark–recapture methods to estimate survival probabilities over six years. Annual survival probabilities for individuals was high, varying between 0.79 and 0.88, whereas recapture probabilities varied between 0.64 and 0.90. Interannual variation in survival probability was low and neither the environmental (air temperature and sea ice cover) nor biological (sex) variables influenced survival probability. These estimates suggest that annual survival probability is high for anadromous adult Arctic Char in the Cambridge Bay area, despite clear differences in the ice cover melt date among years. These results further our understanding of the demographic parameters of Arctic Char in the region, which will be important for future assessments of the sustainability of commercial fisheries as well as for predicting population responses to a rapidly changing Arctic.

Individual variation in early-life telomere length and survival in a wild mammal.

Individual variation in survival probability due to differential responses to early-life environmental conditions is important in the evolution of life histories and senescence. A biomarker allowing quantification of such individual variation, and which links early-life environmental conditions with survival by providing a measure of conditions experienced, is telomere length. Here, we examined telomere dynamics among 24 cohorts of European badgers (Meles meles). We found a complex cross-sectional relationship between telomere length and age, with no apparent loss over the first 29months, but with both decreases and increases in telomere length at older ages. Overall, we found low within-individual consistency in telomere length across individual lifetimes. Importantly, we also observed increases in telomere length within individuals, which could not be explained by measurement error alone. We found no significant sex differences in telomere length, and provide evidence that early-life telomere length predicts lifespan. However, while early-life telomere length predicted survival to adulthood (≥1 year old), early-life telomere length did not predict adult survival probability. Furthermore, adult telomere length did not predict survival to the subsequent year. These results show that the relationship between early-life telomere length and lifespan was driven by conditions in early-life, where early-life telomere length varied strongly among cohorts. Our data provide evidence for associations between early-life telomere length and individual life history, and highlight the dynamics of telomere length across individual lifetimes due to individuals experiencing different early-life environments.

Annual variation in recruitment and age-specific survival of Little Penguins, Eudyptula minor

Identifying variation in survival probabilities is fundamental to understanding population dynamics. We quantified variation in survival of Little Penguins (Eudyptula minor) at Oamaru, New Zealand, over 19 years from 1993–2011. Specifically survival in relation to age and breeding status were investigated. We used a multi-state capture-mark-recapture model to examine survival and recapture probabilities of known age penguins flipper-banded as chicks, and breeding penguins of unknown age banded as adults. The survival probability of Little Penguins in their first year averaged 0.42 and was lower than all older ages. The mean annual survival probability of breeding adult penguins was 0.86. The observed proportion of fledglings that later recruited into the breeding population in the study colony mirrored first-year survival estimates from the model. Survival was lower for pre-breeding penguins than for breeding penguins of the same age. We detected no significant effect of age on survival for breeding penguins. The comprehensive, long-term monitoring program in place at Oamaru resulted in very high recapture rates of breeding penguins that generated accurate estimates of survival.

Estimates of Survival Probability from Two Populations of Giant Gartersnakes in California’s Great Central Valley

The loss and modification of freshwater ecosystems has led to high rates of imperilment for freshwater species. The Giant Gartersnake (Thamnophis gigas) is among the species that have suffered declines in abundance and spatial distribution and is currently listed as a threatened species by the U.S. government and the State of California. Conservation and management of populations of T. gigas are hampered by a lack of information on its demography. Without estimates of demographic parameters, the status of the population is difficult to characterize, and identifying the parameters to target in management planning is problematic. We used capture–recapture data from two populations in the Great Central Valley of California to estimate annual survival probability. We also evaluated hypothesized causes of variation in survival probability among individuals and among years. Model-selection results for the population in the American Basin indicated that females have a higher survival probability than males and t...

Designing a Monitoring Program to Estimate Estuarine Survival of Anadromous Salmon Smolts: Simulating the Effect of Sample Design on Inference.

A number of researchers have attempted to estimate salmonid smolt survival during outmigration through an estuary. However, it is currently unclear how the design of such studies influences the accuracy and precision of survival estimates. In this simulation study we consider four patterns of smolt survival probability in the estuary, and test the performance of several different sampling strategies for estimating estuarine survival assuming perfect detection. The four survival probability patterns each incorporate a systematic component (constant, linearly increasing, increasing and then decreasing, and two pulses) and a random component to reflect daily fluctuations in survival probability. Generally, spreading sampling effort (tagging) across the season resulted in more accurate estimates of survival. All sampling designs in this simulation tended to under-estimate the variation in the survival estimates because seasonal and daily variation in survival probability are not incorporated in the estimation procedure. This under-estimation results in poorer performance of estimates from larger samples. Thus, tagging more fish may not result in better estimates of survival if important components of variation are not accounted for. The results of our simulation incorporate survival probabilities and run distribution data from previous studies to help illustrate the tradeoffs among sampling strategies in terms of the number of tags needed and distribution of tagging effort. This information will assist researchers in developing improved monitoring programs and encourage discussion regarding issues that should be addressed prior to implementation of any telemetry-based monitoring plan. We believe implementation of an effective estuary survival monitoring program will strengthen the robustness of life cycle models used in recovery plans by providing missing data on where and how much mortality occurs in the riverine and estuarine portions of smolt migration. These data could result in better informed management decisions and assist in guidance for more effective estuarine restoration projects.

Exit, Survival, and Competitive Equilibrium in Dealer Markets

AbstractIn this study we analyze dealer exit, survival, and competitive equilibrium in the NASDAQ Stock Market using data from a unique period that entails major changes in regulatory and competitive environments. We decompose the forces that affect dealer survival into market factors and dealer attributes. Market factors encompass those variables that affect the demand for and profitability of dealer services as a whole. Variation in survival probability across dealers results mainly from their competitive advantages in business strategies, information, quote aggressiveness, access to order flow, and economies of scale. On the whole, our results suggest that dealer markets exhibit a Darwinian survival of the fittest.

Prospective antifungal therapy (PATH) alliance®: focus on mucormycosis

Mucormycosis is increasingly encountered in immunosuppressed patients, such as those with haematological malignancies or stem cell transplantation. We present a descriptive analysis of 121 cases of mucormycosis from the Prospective Antifungal Therapy Alliance(®) registry (July 2004 to December 2008). Patients with proven or probable mucormycosis were enrolled and followed prospectively for 12weeks. The most common underlying disease and site of infection were haematologic malignancy (61.2%) and lungs (46.3%) respectively. Rhizopus (n=63; 52.1%) was the most commonly isolated species, followed by Mucor (n=28; 23.1%), other or unknown (n=17; 14.0%), Rhizomucor (n=9; 7.4%) and Lichtheimia (n=4; 3.3%). The 12-week Kaplan-Meier survival probability for all patients was 0.41; however, there was large variation in survival probabilities between species, with highest survival probability observed for Lichtheimia (0.5), followed by Rhizopus (0.47), Mucor (0.40), unknown Mucormycetes species (0.40), other Mucormycetes species (0.17) and Rhizomucor (0.15). Prior use of voriconazole decreased 12-week survival probability. Survival probability was higher in patients receiving amphotericin B by Day 3 (0.72) vs. those who started amphotericin B therapy after Day 3 (0.33). The low survival probability observed underscores the importance of further studies of mucormycosis. Optimal treatment selection and timing may improve prognosis.

Exit, Survival, and Competitive Equilibrium in Dealer Markets

In this study we analyze dealer exit, survival, and competitive equilibrium in the NASDAQ Stock Market using data from a unique time period that entails major changes in regulatory and competitive environments. We decompose the forces that affect dealer survival into market factors and dealer attributes. Market factors encompass those variables that affect the demand for and profitability of dealer services as a whole. Variation in survival probability across dealers results mainly from their competitive advantages in business strategies, information, quote aggressiveness, access to order flow, and economies of scale. On the whole, our results suggest that dealer markets exhibit a Darwinian survival of the fittest.

Weed seed survival following ensiling and mesophilic anaerobic digestion in batch reactors

Westerman PR, Hildebrandt F & Gerowitt B (2012). Weed seed survival following ensiling and mesophilic anaerobic digestion in batch reactors. Weed Research52, 286–295.SummaryDigestate, the semi‐solid leftover after anaerobic digestion in biogas reactors, is frequently used as a crop fertiliser. The ability of seeds from various weed species to survive anaerobic digestion was tested, because surviving seeds could be spread via the digestate. Experiments were conducted in experimental mesophilic batch reactors, either with or without ensiling as a pre‐treatment to simulate biomass storage in silage prior to use in reactors. The emphasis was on weed species whose seeds have a water‐impermeable layer, because these may be more thermoresistant. Species with hard seeds were more likely to survive ensiling (up to 98%) and mesophilic anaerobic digestion (up to 58%) compared with species whose seeds lack a water‐impermeable layer (≤1%). There was considerable variation in survival probability between and within species, and between silages and reactors. For hard‐seeded species, survival depended on the proportion of hard seeds and on the ability to remain hard‐seeded during treatment. Freshly harvested seeds lost their water impermeability and survived poorly. The survival of tomato seeds, an indicator species used in the sanitation of composts, was comparable with that of the best surviving species without physical dormancy, but was not comparable with that of hard‐seeded species. Tomato could therefore only represent species that are not hard‐seeded.

Spatial heterogeneity in mortality and its impact on the population dynamics of Eurasian woodcocks

AbstractSpatial heterogeneity, especially in mortality risk, is a major factor shaping population dynamics. Here we study the impacts of spatial heterogeneity in hunting pressure on the demography of Eurasian woodcock Scolopax rusticola, a relatively long‐lived migratory game bird. We develop capture–recapture–recovery models in which both seasonality and spatial variation in hunting pressure are accounted for, and fit them to individual‐based data collected across the French wintering range (>44000 banded individuals) as well as recoveries from spring stopovers and breeding grounds in Europe. Our results quantify spatial variation in survival probability in the wintering areas. They highlight the role of source‐sink dynamics involving juvenile settlement decisions, as well as the importance of mortality outside the winter quarters. We also discuss the impact of spatial heterogeneity for demographic parameter estimation and data collection at the range scale.

Mountain goat survival in coastal Alaska: Effects of age, sex, and climate

AbstractEcological theory predicts that individual survival should vary between sex and age categories due to differences in allocation of nutritional resources for growth and reproductive activities. During periods of environmental stress, such relationships may be exacerbated, and affect sex and age classes differently. We evaluated support for hypotheses about the relative roles of sex, age, and winter and summer climate on the probability of mountain goat (Oreamnos americanus) survival in coastal Alaska. Specifically, we used known‐fates analyses (Program MARK) to model the effects of age, sex, and climatic variation on survival using data collected from 279 radio‐marked mountain goats (118 M, 161 F) in 9 separate study areas during 1977–2008. Models including age, sex, winter snowfall, and average daily summer temperature (during Jul–Aug) best explained variation in survival probability of mountain goats. Specifically, our findings revealed that old animals (9+ yr) have lower survival than younger animals. In addition, males tended to have lower survival than females, though differences only existed among prime‐aged adult (5–8 yr) and old (9+ yr) age classes. Winter climate exerted the strongest effects on mountain goat survival; summer climate, however, was significant and principally influenced survival during the following winter via indirect effects. Furthermore, old animals were more sensitive to the effects of winter conditions than young or prime‐aged animals. These findings detail how climate interacts with sex and age characteristics to affect mountain goat survival. Critically, we provide baseline survival rate statistics across various age, sex, and climate scenarios. These data will assist conservation and management of mountain goats by enabling detailed, model‐based demographic forecasting of human and/or climate‐based population impacts. © 2011 The Wildlife Society.

Nonparametric spatial regression of survival probability: visualization of population sinks in Eurasian Woodcock

Both evolutionary ecologists and wildlife managers make inference based on how fitness and demography vary in space. Spatial variation in survival can be difficult to assess in the wild because (1) multisite study designs are not well suited to populations that are continuously distributed across a large area and (2) available statistical models accounting for detectability less than 1.0 do not easily cope with geographical coordinates. Here we use penalized splines within a Bayesian state-space modeling framework to estimate and visualize survival probability in two dimensions. The approach is flexible in that no parametric form for the relationship between survival and coordinates need be specified a priori. To illustrate our method, we study a game species, the Eurasian Woodcock Scolopax rusticola, based on band recovery data (5000 individuals) collected over a > 50 000-km2 area in west-central France with contrasted habitats and hunting pressures. We find that spatial variation in survival probability matches an index of hunting pressure and creates a mosaic of population sources and sinks. Such analyses could provide guidance concerning the spatial management of hunting intensity or could be used to identify pathways of spatial variation in fitness, for example, to study adaptation to changing landscape and climate.

Is the Yelkouan shearwater Puffinus yelkouan threatened by low adult survival probabilities?

Many seabird species are experiencing population declines, with key factors being high adult mortality caused by fishery by-catch and predation by introduced predators on nesting islands. In the Mediterranean, both of these pressures are intensive and widespread. We studied the adult survival of an endemic Mediterranean seabird, the Yelkouan shearwater ( Puffinus yelkouan), between 1969–1994 and 2007–2010 in Malta and between 2004–2010 in France using mark–recapture methods. Mean annual survival probabilities for breeding adults were below 0.9 for all colonies and periods. Between 1969–1994, annual survival for adults of unknown breeding status was on average 0.74 (95% confidence interval: 0.69–0.80) in Malta, possibly as a result of various human disturbances (including illegal shooting), light pollution and fisheries by-catch. Over the period 2004–2010, we found strong support for variation in adult survival probabilities between breeders and non-breeders, and islands with and without introduced predators in France. Survival probabilities for non-breeders (0.95, 0.81–1.0) appeared to be higher than for breeders (0.82, 0.70–0.94), but were imprecise partly due to low recapture probabilities. In Malta, we found evidence for heterogeneity in survival probabilities between two unknown groups (probably breeders and non-breeders), and seasonal variation in survival probability. Birds were more likely to survive the period including the peak breeding season than an equally long period during which they roam widely at sea. Although annual adult survival probability was still low (0.85, 0.58–1.0), colony protection measures appear to have reduced mortality at nesting cliffs. A population model indicated that colonies in France and Malta would currently require continuous immigration of 5–12 pairs per year to maintain stable populations. Our estimates of adult survival probabilities over the past four decades are consistent with overall population declines. Threats to Yelkouan shearwaters require immediate management actions to avoid ongoing population declines in the western Mediterranean.

Evaluating population persistence of Delmarva fox squirrels and potential impacts of climate change

In addition to the combined effects of forest fragmentation, habitat loss, and population isolation on the long-term persistence of many species including the endangered Delmarva fox squirrel ( Sciurus niger cinereus), future changes in climate may make existing habitats less productive and more variable. The Palmer Drought Severity Index (PDSI) for the Delmarva Peninsula of the mid-Atlantic USA, reveals a trend for longer durations of potentially unfavorable conditions for fox squirrel population growth. We used a stochastic population matrix model and available life history information to assess population extinction risk for the Delmarva fox squirrel under a number of scenarios of landscape change and environmental variation, including uncertainties in the future range of climate patterns. Patch size (carrying capacity) was the most important factor influencing persistence of isolated populations. Extinction risk increased markedly across all patch sizes when year to year patterns in environmental variability were autocorrelated to match regional patterns in the PDSI. Increased autocorrelation matching the regional PSDI increased extinction risk, ranging from a factor of 5 to a factor of over 100 in some scenarios when compared to uncorrelated patterns in environmental variability. Increasing the range of variation in survival probabilities was less important to persistence, but its effect also increased when year-to-year changes were autocorrelated in time. Comparing model results with the size and landscape configuration of currently occupied patches on the Delmarva Peninsula showed that many existing populations are above the size threshold identified by these simulations for long-term persistence under current conditions, but these may become vulnerable should climate variability increase and adverse conditions persist for several years at a time.

Genetic Variation and the Role of Insect Life History Traits in the Ability of Drosophila Larvae to Develop in the Presence of a Competing Filamentous Fungus

Competitive interactions between organisms from distantly related phylogenetical branches have been suggested as being one of the most pervasive forms of interspecific competition. However, so-called inter-kingdom competition has rarely been the focus of ecological and evolutionary studies. Thus, a relatively novel hypothesis has been proposed on the basis that saprophagous insects might intensively compete with filamentous fungi for ephemeral resources (e.g. decaying plant tissue). Consideration that life history traits (e.g. developmental time) are adaptive in determining developmental success in the presence of con- or hetero-specifics competitors implies that these traits have been progressively established by natural selection. Because a similar scenario may apply to antagonistic interactions between saprophagous insects and filamentous fungi, one can expect the existence of heritable variation in developmental success when insect larvae are forced to grow in the presence of noxious mould. Therefore, this study aimed at discovering whether a local population of Drosophila melanogaster indeed harbours genetic variation in developmental success in the presence of the mould Aspergillus niger. By using the isofemale line technique, single larvae forced to feed on fungal infected or uninfected substrate were analysed for variation in survival probability to the adult stage, developmental time and body size of emerged adults. I found genetic variation in survival probability in fungal infected substrates but not in uninfected larval food sources. Mean developmental time and body size varied significantly among isofemale lines in both types of larval environment. Survival was negatively correlated with developmental time on fungal infected substrate, but variation in developmental time on fungal-free substrates was not correlated with survival on fungal infected food patches. Within-trait correlation between fungal infected and uninfected substrates was surprisingly weak, and developmental time was not correlated with body size. The results of this study demonstrate (a) the existence of genetic variation for larval developmental success in the presence of A. niger in a Drosophila population, and (b) heritability of important insect life history traits differed as a function of the larval environment (fungal infected or uninfected feeding substrate). I discuss models that might explain heritability differences and the evolutionary consequences of these results.

Evaluation of some random effects methodology applicable to bird ringing data

Existing models for ring recovery and recapture data analysis treat temporal variations in annual survival probability (S) as fixed effects. Often there is no explainable structure to the temporal variation in S 1 , … , S k ; random effects can then be a useful model: Si = E(S) + k i . Here, the temporal variation in survival probability is treated as random with average value E( k 2 ) = σ 2 . This random effects model can now be fit in program MARK. Resultant inferences include point and interval estimation for process variation, σ 2 , estimation of E(S) and var(Ê(S)) where the latter includes a component for σ 2 as well as the traditional component for v ar(S|S). Furthermore, the random effects model leads to shrinkage estimates, S i , as improved (in mean square error) estimators of Si compared to the MLE, S i , from the unrestricted time-effects model. Appropriate confidence intervals based on the S i are also provided. In addition, AIC has been generalized to random effects models. This paper presents results of a Monte Carlo evaluation of inference performance under the simple random effects model. Examined by simulation, under the simple one group Cormack-Jolly-Seber (CJS) model, are issues such as bias of σ 2 , confidence interval coverage on σ 2 , coverage and mean square error comparisons for inference about Si based on shrinkage versus maximum likelihood estimators, and performance of AIC model selection over three models: S i = S (no effects), Si = E(S) + k i (random effects), and S 1 , … , S k (fixed effects). For the cases simulated, the random effects methods performed well and were uniformly better than fixed effects MLE for the S i .

Size-Sex Variation in Survival Rates and Abundance of Pig Frogs, Rana grylio, in Northern Florida Wetlands

During 1991-1993, we conducted capture-recapture studies on pig frogs, Rana grylio, in seven study locations in northcentral Florida. Resulting data were used to test hypotheses about variation in survival probability over different size-sex classes of pig frogs. We developed multistate capture-recapture models for the resulting data and used them to estimate survival rates and frog abundance. Tests provided strong evidence of survival differences among size-sex classes, with adult females showing the highest survival probabilities. Adult males and juvenile frogs had lower survival rates that were similar to each other. Adult females were more abundant than adult males in most locations at most sampling occasions. We recommend probabilistic capture-recapture models in general, and multistate models in particular, for robust estimation of demographic parameters in amphibian populations.