Chitosan‐heparin polyelectrolyte multilayers on cortical bone: Periosteum‐mimetic,cytophilic, antibacterial coatings

Cortical bone allografts suffer from high rates of failure due to poor integration with host tissue, leading to non‐union, fracture, and infection following secondary procedures. Here, we report a method for modifying the surfaces of cortical bone with coatings that have biological functions that may help overcome these challenges. These chitosan‐heparin coatings promote mesenchymal stem cell attachment and have significant antibacterial activity against both S. aureus and E. coli. Furthermore, their chemistry is similar to coatings we have reported on previously, which effectively stabilize and deliver heparin‐binding growth factors. These coatings have potential as synthetic periosteum for improving bone allograft outcomes. Biotechnol. Bioeng. 2013; 110: 609–618. © 2012 Wiley Periodicals, Inc.     

Differential survival among life stages contributes to co‐dominance of Abies mariesii and Abies veitchii in a sub‐alpine old‐growth forest

Questions: Are there interspecific differences in mortality and recruitment rates across life stages between two shade‐tolerant dominant trees in a sub‐alpine old‐growth forest? Do such differences in demography contribute to the coexistence and co‐dominance of the two species? Location: Sub‐alpine, old‐growth forest on Mt. Ontake, central Honshu, Japan. Methods: From 1980 to 2005, we recorded DBH and status (alive or dead) of all Abies mariesii and A. veitchii individuals (DBH ≥ 5 cm) in a 0.44‐ha plot. Based on this 25 year census, we quantified mortality and recruitment rates of the two species in three life stages (small tree, 5 cm ≤ DBH < 10 cm; subcanopy tree, 10 cm ≤ DBH < 20 cm; canopy tree, DBH ≥ 20 cm). Results: Significant interspecific differences in mortality and recruitment rates were observed in both the small tree and sub‐canopy tree stages. In this forest, saplings (< 5 cm DBH) are mostly buried by snow‐pack during winter. As a consequence, saplings of A. mariesii, which is snow and shade tolerant, show higher rates of recruitment into the small tree stage than do those of A. veitchii. Above the snow‐pack, trees must tolerate dry, cold temperatures. A. veitchii, which can more readily endure such climate conditions, showed lower mortality rate at the subcanopy stage and a higher recruitment rate into the canopy tree stage. This differential mortality and recruitment among life‐stages determines relative dominance of the two species in the canopy. Conclusion: Differential growth conditions along a vertical gradient in this old forest determine survival of the two species prior to reaching the canopy, and consequently allow co‐dominance at the canopy stage.     

Association study of FOXO3A SNPs and aging phenotypes in Danish oldest‐old individuals

FOXO3A variation has repeatedly been reported to associate with human longevity, yet only few studies have investigated whether FOXO3A variation also associates with aging‐related traits. Here, we investigate the association of 15 FOXO3A tagging single nucleotide polymorphisms (SNPs) in 1088 oldest‐old Danes (age 92–93) with 4 phenotypes known to predict their survival: cognitive function, hand grip strength, activity of daily living (ADL), and self‐rated health. Based on previous studies in humans and foxo animal models, we also explore self‐reported diabetes, cancer, cardiovascular disease, osteoporosis, and bone (femur/spine/hip/wrist) fracture. Gene‐based testing revealed significant associations of FOXO3A variation with ADL (P = 0.044) and bone fracture (P = 0.006). The single‐SNP statistics behind the gene‐based analysis indicated increased ADL (decreased disability) and reduced bone fracture risk for carriers of the minor alleles of 8 and 10 SNPs, respectively. These positive directions of effects are in agreement with the positive effects on longevity previously reported for these SNPs. However, when correcting for the test of 9 phenotypes by Bonferroni correction, bone fracture showed borderline significance (P = 0.054), while ADL did not (P = 0.396). Although the single‐SNP associations did not formally replicate in another study population of oldest‐old Danes (n = 1279, age 94–100), the estimates were of similar direction of effect as observed in the Discovery sample. A pooled analysis of both study populations displayed similar or decreased sized P‐values for most associations, hereby supporting the initial findings. Nevertheless, confirmation in additional study populations is needed.     

Patterns of natural mortality in stream‐living brown trout (Salmo trutta)

1. We tested the hypothesis that lifetime mortality patterns and their corresponding rates and causal factors differ among populations of stream‐living salmonids. To this end, we examined the lifetime mortality patterns of several successive cohorts of two stream‐living brown trout (Salmo trutta) populations in Spain and Denmark. 2. In the southern population, we observed a consistent two‐phase pattern, in which mortality was negligible during the first half of the lifetime and severe during the rest of the lifetime. In contrast, the northern population demonstrated a three‐phase pattern with an earlier phase varying from negligible to severe, followed by a second stage of weak mortality, and lastly by a third life stage of severe mortality. 3. Despite substantial differences in the mortality patterns between the two populations, the combined effect of recruitment (as a proxy of the density‐dependent processes occurring during the lifetime) and mean body mass (as a proxy of growth experienced by individuals in a given cohort) explained c. 89% of the total lifetime mortality rates across cohorts and populations. 4. A comparison with other published data on populations of stream‐living brown trout within its native range highlighted lifetime mortality patterns of one, two, three and four phases, but also suggested that common patterns may occur in populations that experience similar individual growth and population density.     

Statewide and local recruitment of mourning doves in Missouri

Intensive harvests have the potential to greatly affect local mourning dove (Zenaida macroura) populations, a popular gamebird and songbird. To evaluate if recruitment was commensurate with harvest, we applied a ratio-based method to estimate local and statewide mourning dove recruitment across 7 public hunting areas in Missouri from 2005 to 2011. We estimated recruitment from preharvest adult sex ratios and harvest age ratios that incorporated various methods to address potential inherent biases (e.g., bias in the adults of unknown sex in preharvest samples, bias in unknown age wings, and local differential vulnerability; DV). Data from 356 radio-marked doves revealed a DV rate, where hatch year doves were, on average 2.7× more likely to be harvested than adult doves. Recruitment estimates for local areas were highly variable and in some cases, biologically unrealistic (e.g., >10 offspring/female), because of small preharvest sample sizes. However, data pooled statewide provided recruitment estimates of 3.1 offspring/female (±0.3 SE) or 4.1 offspring/female (±0.3 SE), assuming samples of unknown sex doves were female biased or male biased, respectively. Although statewide estimates agree with directly observed rates, the sex ratios and differential vulnerability comprising them vary considerably from what has been previously assumed. Whether preharvest sex ratios are biased from trapping methods has 2 important implications; either regional approaches have overestimated recruitment or the number of females in Missouri's population is much less than originally thought. Because each of these scenarios are important to understanding the effects of regional harvest management on Missouri's dove population, they highlight the importance of a better understanding of biases involved in estimating recruitment. © 2012 The Wildlife Society.     

Identifying demographic and environmental drivers of recruitment and population growth in a cavity‐nesting sea duck population

Traits with the greatest proportional effects on fitness are typically conserved, and traits with larger temporal variation frequently play a dominant role in population dynamics. We examined recruitment patterns and population growth in common goldeneyes Bucephala clangula (hereafter goldeneye), using Pradel mark–recapture models from a long‐term nest box study (1997–2010). Our objectives were to estimate recruitment (f ) and population growth (λ) relative to recruitment origin group (in‐situ or unknown), investigate environmental and density dependent effects on these parameters, and evaluate potential immigration patterns. We detected group‐specific differences for f (in‐situ: 0.47 ± 0.13 SE, unknown: 0.31 ± 0.04), and the proportion of boxes occupied by goldeneyes the year prior to recruitment had a significant negative effect on recruitment for the in‐situ group (β = –1.04; 85% CI –1.29, –0.78), and a positive effect for the unknown group (β = 0.45; 85% CI 0.30, 0.61). The negative box occupancy effect in the year prior to recruitment, when in‐situ yearling goldeneyes prospect for potential nest sites, suggests that local nesting densities may limit recruitment of locally hatched females. We identified two competitive models for λ, which averaged 1.04 ± 0.03 and included interactions between recruitment origin group and a linear temporal trend, and the proportion of ducklings marked two years prior. By evaluating all levels of marking effort on λ, we determined that even if all hatched ducklings were marked in a given year, the resulting in‐situ λ was consistently lower than all observed population‐level λs during the study, indicating that individuals produced outside of study area nest boxes contributed to λ. Though female goldeneyes are considered highly philopatric, our results suggest that female natal and breeding dispersal may be more prevalent than previously thought, and the spatial scale at which these processes occur requires further investigation.     

Alternative male mating tactics of the endemic Red Sea parrotfish Scarus ferrugineus

The present study shows that small non‐territorial terminal‐phase males of the rusty parrotfish Scarus ferrugineus are reproductively active and are comparable with initial‐phase males in behaviour, rates of participation during group‐spawning and success in streaking into pair spawning. Large territorial terminal‐phase males defend contiguous territories for several hours during the morning where they pair spawn with initial‐phase females.     

Osteoblast recruitment to sites of bone formation in skeletal development,homeostasis, and regeneration

During endochondral bone development, bone‐forming osteoblasts have to colonize the regions of cartilage that will be replaced by bone. In adulthood, bone remodeling and repair require osteogenic cells to reach the sites that need to be rebuilt, as a prerequisite for skeletal health. A failure of osteoblasts to reach the sites in need of bone formation may contribute to impaired fracture repair. Conversely, stimulation of osteogenic cell recruitment may be a promising osteo‐anabolic strategy to improve bone formation in low bone mass disorders such as osteoporosis and in bone regeneration applications. Yet, still relatively little is known about the cellular and molecular mechanisms controlling osteogenic cell recruitment to sites of bone formation. In vitro, several secreted growth factors have been shown to induce osteogenic cell migration. Recent studies have started to shed light on the role of such chemotactic signals in the regulation of osteoblast recruitment during bone remodeling. Moreover, trafficking of osteogenic cells during endochondral bone development and repair was visualized in vivo by lineage tracing, revealing that the capacity of osteoblast lineage cells to move into new bone centers is largely confined to undifferentiated osteoprogenitors, and coupled to angiogenic invasion of the bone‐modeling cartilage intermediate. It is well known that the presence of blood vessels is absolutely required for bone formation, and that a close spatial and temporal relationship exists between osteogenesis and angiogenesis. Studies using genetically modified mouse models have identified some of the molecular constituents of this osteogenic–angiogenic coupling. This article reviews the current knowledge on the process of osteoblast lineage cell recruitment to sites of active bone formation in skeletal development, remodeling, and repair, considering the role of chemo‐attractants for osteogenic cells and the interplay between osteogenesis and angiogenesis in the control of bone formation. Birth Defects Research (Part C) 99:170–191, 2013. © 2013 Wiley Periodicals, Inc.     

Running on empty: recharge dynamics from animal movement data

Vital rates such as survival and recruitment have always been important in the study of population and community ecology. At the individual level, physiological processes such as energetics are critical in understanding biomechanics and movement ecology and also scale up to influence food webs and trophic cascades. Although vital rates and population‐level characteristics are tied with individual‐level animal movement, most statistical models for telemetry data are not equipped to provide inference about these relationships because they lack the explicit, mechanistic connection to physiological dynamics. We present a framework for modelling telemetry data that explicitly includes an aggregated physiological process associated with decision making and movement in heterogeneous environments. Our framework accommodates a wide range of movement and physiological process specifications. We illustrate a specific model formulation in continuous‐time to provide direct inference about gains and losses associated with physiological processes based on movement. Our approach can also be extended to accommodate auxiliary data when available. We demonstrate our model to infer mountain lion (Puma concolor; in Colorado, USA) and African buffalo (Syncerus caffer; in Kruger National Park, South Africa) recharge dynamics.     

Precision gain versus effort with joint models using detection/non‐detection and banding data

Capture–recapture techniques provide valuable information, but are often more cost‐prohibitive at large spatial and temporal scales than less‐intensive sampling techniques. Model development combining multiple data sources to leverage data source strengths and for improved parameter precision has increased, but with limited discussion on precision gain versus effort. We present a general framework for evaluating trade‐offs between precision gained and costs associated with acquiring multiple data sources, useful for designing future or new phases of current studies.We illustrated how Bayesian hierarchical joint models using detection/non‐detection and banding data can improve abundance, survival, and recruitment inference, and quantified data source costs in a northern Arizona, USA, western bluebird (Sialia mexicana) population. We used an 8‐year detection/non‐detection (distributed across the landscape) and banding (subset of locations within landscape) data set to estimate parameters. We constructed separate models using detection/non‐detection and banding data, and a joint model using both data types to evaluate parameter precision gain relative to effort.Joint model parameter estimates were more precise than single data model estimates, but parameter precision varied (apparent survival > abundance > recruitment). Banding provided greater apparent survival precision than detection/non‐detection data. Therefore, little precision was gained when detection/non‐detection data were added to banding data. Additional costs were minimal; however, additional spatial coverage and ability to estimate abundance and recruitment improved inference. Conversely, more precision was gained when adding banding to detection/non‐detection data at higher cost. Spatial coverage was identical, yet survival and abundance estimates were more precise. Justification of increased costs associated with additional data types depends on project objectives.We illustrate a general framework for evaluating precision gain relative to effort, applicable to joint data models with any data type combination. This framework evaluates costs and benefits from and effort levels between multiple data types, thus improving population monitoring designs.     

Long‐term population dynamics reveal that survival and recruitment of tropical boobies improve after a hurricane

Variability in population numbers is a central issue in evolutionary ecology and also in biodiversity conservation. However, for most seabirds this information is lacking and tropical populations are virtually unstudied. Long‐term studies are warranted because world's seabird populations exhibit an overall declining trend since 1950. Using data spanning 23 yr, we investigated how adult survival, local recruitment, and their relative contributions to population growth (λ) vary over time in the blue‐footed booby Sula nebouxii, a long‐lived locally foraging seabird that breeds in tropical waters. In addition, we investigated whether booby demographic rates exhibit the same declining trend observed in other seabirds, whether these rates are impacted by hurricanes, and whether these potential impacts differ between sexes. Our analysis of 4608 capture–recapture histories revealed that survival and recruitment were nearly equal between males and females, exhibited a declining trend over the last 23 yr, and in both sexes, these vital rates improved after a hurricane. The declining trend in recruitment was slightly more attenuated in males. These results add to the current evidence for an overall declining trend in world's seabird populations and extend its confirmation to the warm eastern tropical Pacific. Moreover, they provide the first evidence that hurricanes may favor natural populations. As a result of the declining trend and variation in survival and recruitment, λ exhibited a slight decline and substantial variation over the 23 yr. However, most λ values were equal to or higher than 1, and the long‐term average indicates population increase. The ability of blue‐footed boobies to maintain a positive population balance despite of negative trends in their vital rates might result from canalization of adult survival (the vital rate that contributes most to λ and shows lower variation compared to recruitment) against environmental variability.     

Tree demography dominates long‐term growth trends inferred from tree rings

Understanding responses of forests to increasing CO₂ and temperature is an important challenge, but no easy task. Tree rings are increasingly used to study such responses. In a recent study, van der Sleen et al. (2014) Nature Geoscience, 8, 4 used tree rings from 12 tropical tree species and find that despite increases in intrinsic water use efficiency, no growth stimulation is observed. This challenges the idea that increasing CO₂ would stimulate growth. Unfortunately, tree ring analysis can be plagued by biases, resulting in spurious growth trends. While their study evaluated several biases, it does not account for all. In particular, one bias may have seriously affected their results. Several of the species have recruitment patterns, which are not uniform, but clustered around one specific year. This results in spurious negative growth trends if growth rates are calculated in fixed size classes, as ‘fast‐growing’ trees reach the sampling diameter earlier compared to slow growers and thus fast growth rates tend to have earlier calendar dates. We assessed the effect of this ‘nonuniform age bias’ on observed growth trends and find that van der Sleen's conclusions of a lack of growth stimulation do not hold. Growth trends are – at least partially – driven by underlying recruitment or age distributions. Species with more clustered age distributions show more negative growth trends, and simulations to estimate the effect of species’ age distributions show growth trends close to those observed. Re‐evaluation of the growth data and correction for the bias result in significant positive growth trends of 1–2% per decade for the full period, and 3–7% since 1950. These observations, however, should be taken cautiously as multiple biases affect these trend estimates. In all, our results highlight that tree ring studies of long‐term growth trends can be strongly influenced by biases if demographic processes are not carefully accounted for.     

Circulating serum vitamin D levels and total body bone mineral density: A Mendelian randomization study

Until recently, randomized controlled trials have not demonstrated convincing evidence that vitamin D, or vitamin D in combination with calcium supplementation could improve bone mineral density (BMD), osteoporosis and fracture. It remains unclear whether vitamin D levels are causally associated with total body BMD. Here, we performed a Mendelian randomization study to investigate the association of vitamin D levels with total body BMD using a large‐scale vitamin D genome‐wide association study (GWAS) dataset (including 79 366 individuals) and a large‐scale total body BMD GWAS dataset (including 66,628 individuals). We selected three Mendelian randomization methods including inverse‐variance weighted meta‐analysis (IVW), weighted median regression and MR‐Egger regression. All these three methods did not show statistically significant association of genetically increased vitamin D levels with total body BMD. Importantly, our findings are consistent with recent randomized clinical trials and Mendelian randomization study. In summary, we provide genetic evidence that increased vitamin D levels could not improve BMD in the general population. Hence, vitamin D supplementation alone may not be associated with reduced fracture incidence among community‐dwelling adults without known vitamin D deficiency, osteoporosis, or prior fracture.     

Rainfall during parental care reduces reproductive and survival components of fitness in a passerine bird

Adverse weather conditions during parental care may have direct consequences for offspring production, but longer‐term effects on juvenile and parental survival are less well known. We used long‐term data on reproductive output, recruitment, and parental survival in northern wheatears (Oenanthe oenanthe) to investigate the effects of rainfall during parental care on fledging success, recruitment success (juvenile survival), and parental survival, and how these effects related to nestling age, breeding time, habitat quality, and parental nest visitation rates. While accounting for effects of temperature, fledging success was negatively related to rainfall (days > 10 mm) in the second half of the nestling period, with the magnitude of this effect being greater for breeding attempts early in the season. Recruitment success was, however, more sensitive to the number of rain days in the first half of the nestling period. Rainfall effects on parental survival differed between the sexes; males were more sensitive to rain during the nestling period than females. We demonstrate a probable mechanism driving the rainfall effects on reproductive output: Parental nest visitation rates decline with increasing amounts of daily rainfall, with this effect becoming stronger after consecutive rain days. Our study shows that rain during the nestling stage not only relates to fledging success but also has longer‐term effects on recruitment and subsequent parental survival. Thus, if we want to understand or predict population responses to future climate change, we need to consider the potential impacts of changing rainfall patterns in addition to temperature, and how these will affect target species' vital rates.     

Post‐fire seed predation: Does distance to unburnt vegetation matter?

Human‐induced changes to fire regimes result in smaller, more patchy fires in many peri‐urban areas, with a concomitant increase in potential edge effects. In sclerophyll vegetation, many structurally dominant serotinous plants rely on the immediate post‐fire environment for recruitment. However, there is little information about how fire attributes affect seed predation or recruitment for these species. We examined the influence of distance to unburnt vegetation on post‐dispersal seed predation for five serotinous species from sclerophyll vegetation in the Sydney region, south‐eastern Australia; Banksia serrata L.f., Banksia spinulosa Sm. var. spinulosa, Hakea gibbosa (Sm.) Cav., Hakea teretifolia (Salisb.) Britten (all Proteaceae) and Allocasuarina distyla (Vent.) L. Johnson (Casuarinaceae). We used cafeteria trials and differential exclusion of vertebrates and invertebrates to test whether rates of seed removal for these five species differed among (i) unburnt, (ii) burnt‐edge (approx. 10 m from unburnt vegetation) and (iii) burnt‐interior (approx. 100 m from unburnt vegetation) locations. When all animals had access to seeds, seeds were removed at lower rates from burnt‐interior areas than from other locations. Vertebrates (small mammals) showed this pattern markedly the first time the experiment was run, but in a repeat trial this effect disappeared. Rate of seed removal by invertebrates differed among plant species but we did not detect any such differences for removal by vertebrates. Overall rates of seed removal also differed significantly between the two fires studied. Our results indicate that small mammal seed predation can be substantial for large‐seeded serotinous shrubs, and that differences in the perimeter: area ratio, severity or size of a fire are likely to affect seed predation.     

Stem cell- and scaffold-based tissue engineering approaches to osteochondral regenerative medicine

In osteochondral tissue engineering, cell recruitment, proliferation, differentiation, and patterning are critical for forming biologically and structurally viable constructs for repair of damaged or diseased tissue. However, since constructs prepared ex vivo lack the multitude of cues present in the in vivo microenvironment, cells often need to be supplied with external biological and physical stimuli to coax them toward targeted tissue functions. To determine which stimuli to present to cells, bioengineering strategies can benefit significantly from endogenous examples of skeletogenesis. As an example of developmental skeletogenesis, the developing limb bud serves as an excellent model system in which to study how osteochondral structures form from undifferentiated precursor cells. Alongside skeletal formation during embryogenesis, bone also possesses innate regenerative capacity, displaying remarkable ability to heal after damage. Bone fracture healing shares many features with bone development, driving the hypothesis that the regenerative process generally recapitulates development. Similarities and differences between the two modes of bone formation may offer insight into the special requirements for healing damaged or diseased bone. Thus, endogenous fracture healing, as an example of regenerative skeletogenesis, may also inform bioengineering strategies. In this review, we summarize the key cellular events involving stem and progenitor cells in developmental and regenerative skeletogenesis, and discuss in parallel the corresponding cell- and scaffold-based strategies that tissue engineers employ to recapitulate these events in vitro.     

Regional‐scale dominance of non‐framework building corals on Caribbean reefs affects carbonate production and future reef growth

Coral cover on Caribbean reefs has declined rapidly since the early 1980's. Diseases have been a major driver, decimating communities of framework building Acropora and Orbicella coral species, and reportedly leading to the emergence of novel coral assemblages often dominated by domed and plating species of the genera Agaricia, Porites and Siderastrea. These corals were not historically important Caribbean framework builders, and typically have much smaller stature and lower calcification rates, fuelling concerns over reef carbonate production and growth potential. Using data from 75 reefs from across the Caribbean we quantify: (i) the magnitude of non‐framework building coral dominance throughout the region and (ii) the contribution of these corals to contemporary carbonate production. Our data show that live coral cover averages 18.2% across our sites and coral carbonate production 4.1 kg CaCO₃ m^?2 yr^?1. However, non‐framework building coral species dominate and are major carbonate producers at a high proportion of sites; they are more abundant than Acropora and Orbicella at 73% of sites; contribute an average 68% of the carbonate produced; and produce more than half the carbonate at 79% of sites. Coral cover and carbonate production rate are strongly correlated but, as relative abundance of non‐framework building corals increases, average carbonate production rates decline. Consequently, the use of coral cover as a predictor of carbonate budget status, without species level production rate data, needs to be treated with caution. Our findings provide compelling evidence for the Caribbean‐wide dominance of non‐framework building coral taxa, and that these species are now major regional carbonate producers. However, because these species typically have lower calcification rates, continued transitions to states dominated by non‐framework building coral species will further reduce carbonate production rates below ‘predecline’ levels, resulting in shifts towards negative carbonate budget states and reducing reef growth potential.     

Density‐dependent mortality in adults,but not juveniles,of stream‐resident brown trout (Salmo trutta)

1. This study investigates when and where density dependence operates on the mortality rates of stream‐resident brown trout Salmo trutta. To this aim, I explored populations in habitats of different quality containing high, low or intermediate densities over broad scales of space and time. The study is based on census data of 170 cohorts quantified from recruitment to the total disappearance at 12 sites in four contrasting tributaries of the Rio Esva drainage (north‐western Spain), over the years 1986–2007. 2. Log₁₀‐transformed survivor density over time highlighted a consistent pattern for the 170 cohorts characterised by the occurrence of only two life stages. An early stage starts at recruitment, lasts about half the lifetime and shows no or negligible mortality. A threshold time at 425–620 days after emergence preceded a second stage of continuous and constant mortality until the final disappearance of the cohorts. Consequently, in all scenarios, mortality only occurred in the adult component and no effect of season, year, age‐class and/or reproductive stage was detected. 3. Substantial spatial and temporal variations typified both recruitment (range R = 0.01–1.62 ind m^?2) and adults’ mortality rates (range Z = 0.03–0.38 day^?1). Nested anova s revealed strong effects of site and year on both recruitment and mortality with sites interspersed along the stream gradients where recruitment and mortality were typically high relative to other sites located either nearby in the same stream or distant in another stream, where both recruitment and mortality rates were typically low or intermediate. 4. Adult mortality rates plotted against recruitment for the 170 cohorts pooled revealed a continuous, positive power relationship that explained 45.3% of variation in mortality rates over the whole range of recruitment values. Similarly, highly significant power relationships were elucidated for site‐specific mortality rates averaged across years and for annual‐specific mortality rates averaged across sites against the corresponding mean recruitment averaged across years and sites, respectively. These relationships support the hypothesis that the operation of density dependence is scale independent and context independent but operates in a continuous manner across all scenarios examined. 5. A chronic effect of density dependence on adult losses induces temporally persistent populations maintained by a low number of spawners. Apparently, the operation of density dependence adjusts the number of spawners to the availability of rearing and spawning habitat. This dynamic process may also help to explain the small effective population size (Ne) recently documented by genetic studies of stream‐living brown trout and other salmonids.     

Shifting dynamic forces in fish stock fluctuations triggered by age truncation?

Accumulating evidence shows that environmental fluctuations and exploitation jointly affect marine fish populations, and understanding their interaction is a key issue for fisheries ecology. In particular, it has been proposed that age truncation induced by fisheries exploitation may increase the population's sensitivity to climate. In this study, we use unique long‐term abundance data for the Northeast Arctic stock of cod (Gadus morhua) and the Norwegian Spring‐Spawning stock of herring (Clupea harengus), which we analyze using techniques based on age‐structured population matrices. After identifying time periods with different age distributions in the spawning stock, we use linear models to quantify the relative effect of exploitation and temperature on the population growth rates. For the two populations, age truncation was found to be associated with an increasing importance of temperature and a relatively decreasing importance of exploitation, while the population growth rate became increasingly sensitive to recruitment variations. The results suggested that the removal of older age classes reduced the buffering capacity of the population, thereby making the population growth rate more dependent on recruitment than adult survival and increasing the effect of environmental fluctuations. Age structure appeared as a key characteristic that can affect the response of fish stocks to climate variations and its consequences may be of key importance for conservation and management.     

Demographic buffering and compensatory recruitment promotes the persistence of disease in a wildlife population

Demographic buffering allows populations to persist by compensating for fluctuations in vital rates, including disease‐induced mortality. Using long‐term data on a badger (Meles meles Linnaeus, 1758) population naturally infected with Mycobacterium bovis, we built an integrated population model to quantify impacts of disease, density and environmental drivers on survival and recruitment. Badgers exhibit a slow life‐history strategy, having high rates of adult survival with low variance, and low but variable rates of recruitment. Recruitment exhibited strong negative density‐dependence, but was not influenced by disease, while adult survival was density independent but declined with increasing prevalence of diseased individuals. Given that reproductive success is not depressed by disease prevalence, density‐dependent recruitment of cubs is likely to compensate for disease‐induced mortality. This combination of slow life history and compensatory recruitment promotes the persistence of a naturally infected badger population and helps to explain the badger's role as a persistent reservoir of M. bovis.