A guide to central place effects in foraging

We develop a general patch-use model of central place foraging, which subsumes and extends several previous models. The model produces a catalog of central place effects predicting how distance from a central place influences the costs and benefits of foraging, load-size, quitting harvest rates, and giving-up densities. In the model, we separate between costs that are load-size dependent, i.e. a direct effect of the size of the load, and load-size independent effects, such as correlations between distance and patch qualities. We also distinguish between predictions of between- and within-environment comparisons. Foraging costs, giving-up densities and quitting harvest rates should almost always increase with distance with these effects amplified by increases in metabolic costs, predation risk and load-costs. With respect to load-size: when comparing foraging in patches within an environment, we should often expect smaller loads to be taken from distant patches (negative distance–load correlation). However, when comparing between environments, there should be a positive correlation between average distance and load-size.     

Flight physiology of migrating Urania fulgens (Uraniidae) moths: kinematics and aerodynamics of natural free flight

Summary Air speeds and wing kinematics were determined for the Neotropical moth Urania fulgens in natural migratory flight over Lake Gatun, Republic of Panama. Morphological parameters are presented for the same insects filmed in free flight. A quasi-steady aerodynamic analysis was used to show that unsteady mechanisms of lift generation are probably not necessary to produce the forces necessary for fast forward flight. Mechanical power requirements of forward flight were estimated from the biomechanical and morphological data. Over an airspeed range of 1.5 to 4.5 m/s, the mechanical power required to fly is predicted to increase dramatically with forward speed. A comparison of estimated metabolic rates with endogenous lipid reserves suggests that U. fulgens feeds extensively on flower nectar during migration from Central into South America.     

A meta-analysis of parasite virulence in nestling birds

Parasitism is a common cause of host mortality, but little is known about the ecological factors affecting parasite virulence (the rate of mortality among infected hosts). We reviewed 117 field estimates of parasite-induced nestling mortality in birds, showing that there was significant consistency in mortality among host and parasite taxa. Virulence increased towards the tropics in analyses of both species-specific data and phylogenetic analyses. We found evidence of greater parasite prevalence being associated with reduced virulence. Furthermore, bird species breeding in open nest sites suffered from greater parasite-induced mortality than hole-nesting species. By contrast, parasite specialization and generation time of parasites relative to that of hosts explained little variation in virulence. Likewise, there were little or no significant effects of host genetic variability, host sociality, host migration, host insular distribution or host survival on parasite virulence. These findings suggest that parasite-induced nestling mortality in birds is mainly determined by geographical location and to a smaller extent nest site and prevalence.     

Winter feeding of birds increases productivity in the subsequent breeding season

Supplementary food given to birds can have contemporary effects by reducing the risk of starvation, increasing survival and altering movements and reproductive performance. There is, however, a widely held perception that birds benefit from extra food over winter, but that it is better that they 'look after themselves' during breeding. Here we describe a landscape-scale experiment showing for the first time that the effects of increasing food availability only during the winter can be carried over to the subsequent breeding season. Even though food supplementation stopped six weeks prior to breeding, birds living on sites provisioned over winter had advanced laying dates and increased fledging success compared with birds living on unprovisioned sites. Thus, supplemental feeding of wild birds during winter, in a manner mimicking householders provisioning in gardens and backyards, has the potential to alter bird population dynamics by altering future reproductive performance. With levels of bird feeding by the public continuing to increase, the impacts of this additional food supply on wild bird populations may be considerable.     

社群学习对植食性鸟类和哺乳动物觅食行为的作用

社群学习是动物的一种可塑性行为表现型式。综述了社群学习对植食性鸟类和哺乳动物觅食行为的作用,并述评了其学习机制。社群同伴对动物个体觅食地点、时间和取食方式均有影响,母体摄食的食物信息可通过胎盘和乳汁显著影响幼体的食物选择。动物通过观察学习、嗅闻学习以及味觉厌恶学习,不仅能更快找到食物资源,提高觅食效率,而且能有效降低中毒与被捕食的风险,从而提高其适合度。     

Wolbachia属共生菌及其对节肢动物宿主适合度的影响

Wolbachia是广泛分布于节肢动物体生殖组织内呈母质遗传的一类共生细菌。近30多年来,大量的研究主要集中于Wolbachia对宿主生殖方式的调控方面;近年来的研究发现,Wolbachia对节肢动物宿主的适合度具有不同程度的影响。现对Wolbachia的宿主分布、存在部位及其对节肢动物宿主种群适合度的影响等方面进行了综述,探讨了Wolbachia在该领域的研究意义和潜在的应用价值。     

A dynamic model of short-term energy management in small food-caching and non-caching birds

The survival of small birds in winter is critically dependenton the birds' ability to accumulate and maintain safe levelsof energy reserves. In some species, food caching facilitatesenergy regulation by providing an energy source complementaryto body fat. We present a dynamic optimization model of short-term,diurnal energy management for both food-caching and non-caching birds in which only short-day, winter conditions are considered.We assumed that birds can either rest, forage and eat, forageand cache, or retrieve existing caches (the two latter optionsare available only to caching birds). The model predicted thatwhen there is variability in foraging success (here modeledstrictly as within-day variability), both caching and non-caching birds should increase their fat reserves almost linearly inthe morning slowing down toward late afternoon, a result consistentwith field data but different than the result of a previousdynamic program. Non-cachers were predicted to carry higherfat levels than cachers especially when the variability inforaging success is high. Probability of death for non-caching birds was predicted to be higher than that for cachers, especiallyat higher levels of variability in foraging success. Amongcaching birds, an increase in number of caches and fat reserveswas also predicted if: (1) mean foraging success was decreased,(2) variability in foraging success was increased, and (3)energy expenditure at night was increased over our baselineconditions. Under the conditions simulated in our model, birdswere predicted to cache only if cache half-life (i.e., timeinterval over which 50% of the caches are forgotten or lostto pilferage) exceeded 2.5 days, indicating that low pilferagerate and long memory favor more caching. Finally, we showedthat such daily patterns of energy management do not necessarilyrequire relaxing assumptions about mass-dependent predationrisk.     

A further note on the estimation of a fitness function from two samples taken from a popolation

A modification is proposed for the moments method for estimating a fitness function that was discussed in an earlier paper (Manly , 1976b). This modification ensures that fitness estimates are always positive. The theory has been worked out for a fitness function of any number of variables and a computer program has been written to carry out the iterative calculations needed for estimation.     

北极的春季:迁徙鸟类抵达的生物学

一旦鸟类抵达北极区,迁徙鸟类必须调整其生理和行为以适应不可预知的雪盖、天气、食物资源和天敌胁迫。换言之,他们必须抵抗环境干扰(压力)以便尽早迁徙到苔原上的巢区并建立领域。然后,一旦外界环境有利时,它们就立即开始繁殖。这些鸟类的繁殖有一部分是利用低雪盖区域的微生境以及雪融较快的苔原斑块(特别是在柳树Salix sp．附近)。在北极地区,地面温度在日照若干小时后急剧上升,同时无脊椎动物开始活动。风速在地面柳枝和生草丛苔原10cm下几乎减弱为零。这些条件结合在一起提供了理想的避难所,对于早春迁徙到此的雀形目鸟类尤其如此。然而,如果环境调节变得更为恶劣,这些鸟类会离开。因为与南方越冬地相比,春季北极区条件具有潜在的严酷性,所以鸟类对于应激时的肾上腺皮质反应有所调整。雄鸟到达北极地区时对于剧烈应激刺激下的肾上腺酮的分泌有所提高,并且伴随着对于负反馈敏感性的下降和肾上腺皮质层细胞对于促肾上腺皮质激素作用反应的变化。同时,肾上腺酮结合蛋白(CBG)的水平也有所提高,以至于肾上腺酮的作用在恶劣的环境条件下得到缓冲。基因组受体水平的调节,尤其是在脑和肝脏中糖皮质类固醇类似受体与肾上腺酮的低亲合性,以及肾上腺酮的非基因组水平的作用,可能是很重要的。换言之,与抵达生物学有关的激素一行为系统是高度可变的[动物学报50(6)：948-960,2004]。     

Lying in wait: Limiting factors on a low-density ungulate population and the latent traits that can facilitate escape from them

Predation, habitat, hunting, and environmental conditions have all been implicated as regulatory mechanisms in ungulate populations. The low-density equilibrium hypothesis predicts that in low-density populations, predators regulate their prey and that the population will not escape unless predation pressure is eased. We evaluated survival of adult and juvenile moose (Alces alces) in north-central Alaska to determine whether or not the population supported the hypothesis. We instrumented adult male and female moose with radiocollars and used aerial observations to track parturition and subsequent survival of juvenile moose. Generalized linear mixed-effects models were used to assess survival. Adult annual survival rates were high (∼89%), but may be negatively influenced by winter conditions. Migratory status did not affect moose survivorship or productivity. Approximately 60% of the calf crop died before 5 months of age. Productivity was significantly lower in the northern section of the study area where there is less high-quality habitat, suggesting that, even in this low-density population, nutrition could be a limiting factor. It appears that predation on young calves, winter weather, and nutritional constraints may be interacting to limit this population. Latent traits, such as overproduction of calves and migratory behavior, which do not currently enhance fitness, may persist within this population so that individuals with these traits can reap benefits when environmental conditions change.     

Feeding and reproductive biology of the currito,Hoplosternum littorale,in the Venezuelan llanos with comments on the possible function of the enlarged male pectoral spines

Synopsis The reproductive biology of roach, Rutilus rutilus, was investigated during 1980–1982 in a small tributary of the eutrophic Lake rungen, southeastern Norway. The upstream migration started in early May with medium or falling water levels and water temperatures of 6–10° C, and lasted until late May or early June. Roach (both males and females) migrating early in the season were larger than roach migrating late in the season. Males matured on average one year younger than females. The first males were mature at age 2 years, the first females were mature at age 3 years. Males were smaller than females in all age groups. There was no significant year to year variation in mean length of male and female roach in the various age-groups. Mean population fecundity during 1980–1982 was estimated to be 19 × 10⁶ eggs or 63300 eggs m^–2 of spawning area. The survival rate of eggs and small roach varied considerably due to rapid and unpredictable changes in water and silt levels. Mean annual survival rates for mature male and female roach were 0.30 and 0.52, respectively. The survival rates did not vary with age.     

The costs of parental care: a meta-analysis of the trade-off between parental effort and survival in birds

A fundamental premise of life-history theory is that organisms that increase current reproductive investment suffer increased mortality. Possibly the most studied life-history phenotypic relationship is the trade-off between parental effort and survival. However, evidence supporting this trade-off is equivocal. Here, we conducted a meta-analysis to test the generality of this tenet. Using experimental studies that manipulated parental effort in birds, we show that (i) the effect of parental effort on survival was similar across species regardless of phylogeny; (ii) individuals that experienced reduced parental effort had similar survival probabilities than control individuals, regardless of sex; and (iii) males that experienced increased parental effort were less likely to survive than control males, whereas females that experienced increased effort were just as likely to survive as control females. Our results suggest that the trade-off between parental effort and survival is more complex than previously assumed. Finally, our study provides recommendations of unexplored avenues of future research into life-history trade-offs.     

A stochastic repair—misrepair model for the effects of radiation on cells

The purpose of this paper is to present a stochastic model for effects of radiation on cells. The model includes provisions for lethal effects and for transformation to malignant status. Empirical findings indicate the presence of some repair mechanism in the cells, and a way to incorporate this idea into the model is discussed. Comparisons of the derived survival and transformation probabilities with actual data are favorable. The interpretation of the estimated values leads to questions to be investigated by the experimenters.Supported in part by the Graduate Research Board, University of Maryland     

Measuring the functional responses of farmland birds: an example for a declining seed-feeding bunting

1. Many farmland bird species have undergone significant declines. It is important to predict the effect of agricultural change on these birds and their response to conservation measures. This requirement could be met by mechanistic models that predict population size from the optimal foraging behaviour and fates of individuals within populations. A key component of these models is the functional response, the relationship between food and competitor density and feeding rate. 2. This paper describes a method for measuring functional responses of farmland birds, and applies this method to a declining farmland bird, the corn bunting Miliaria calandra L. We derive five alternative models to predict the functional responses of farmland birds and parameterize these for corn bunting. We also assess the minimum sample sizes required to predict accurately the functional response. 3. We show that the functional response of corn bunting can be predicted accurately from a few behavioural parameters (searching rate, handling time, vigilance time) that are straightforward to measure in the field. These parameters can be measured more quickly than the alternative of measuring the functional response directly. 4. While corn bunting violated some of the assumptions of Holling's disk equation (model 1 in our study), it still provided the most accurate fit to the observed feeding rates while remaining the most statistically simple model tested. Our other models may be more applicable to other species, or corn bunting feeding in other locations. 5. Although further tests are required, our study shows how functional responses can be predicted, simplifying the development of mechanistic models of farmland bird populations.     

What is the fitness outcome of crossing unrelated fish populations? A meta-analysis and an evaluation of future research directions

Outbreeding has been shown to decrease fitness in a variety of species, including several species of fish. An understanding of the general outcomes following outbreeding is required in order to understand the consequences of conservation-related actions and hybridization in aquaculture. A meta-analysis was conducted on outbreeding studies in fishes using 670 comparisons between parent populations and their hybrid progeny. Five hundred and seventy-six comparisons involved first generation hybrids (F1), and a much smaller number (94) involved second generation hybrids (F2). The overall response to outbreeding in the F1 and F2 generations was positive and significant (F1: d _i+^* = 0.425 ± 0.121; F2: d _i+^* = 0.548 ± 0.295, where d _i+^* is the effect size of studies within generations); however, responses differed when studies were separated into groups describing the experimental environment, taxon, or trait. Findings may be biased by a few studies of large effect. Genetic distance explained little of the variance in effect sizes across studies. Results of the meta-analysis suggest that there is no reliable predictor for the effects of outbreeding in fishes, although inconsistencies in experimental design were noted across studies. Future research should include comparisons in both parental environments in order to detect the underlying mechanisms of outbreeding depression, and should focus on measurement of equivalent sets of fitness-related traits. Experimental design should permit estimation of genetic distances based on quantitative traits, which may in turn be meaningful predictors of the outcomes of outbreeding depression. Concerted and consistent research in this area will provide information of relevance to conservation, aquaculture and evolutionary studies.     

Dispersal and the evolution of specialisation in a two-habitat type metapopulation

Metapopulation theory for the evolution of specialisation is virtually absent. In this article, therefore, we study a metapopulation model for consumers with a fitness trade-off between two habitats. We focus on effects of habitat abundance, dispersal rate and trade-off strength on the evolution of specialisation under two types of trade-off. Adaptation affects either the intrinsic growth rates r or the carrying capacities K. Depending on dispersal rate and trade-off strength, evolution can result in one generalist, one specialist or two specialist types. Higher dispersal rate and a weaker trade-off favour the evolution of a generalist, for both trade-off structures. However, we also find differences between the two trade-off structures. Our results are qualitatively similar to analyses of two-patch models, suggesting that insights from such simpler models can be extrapolated to metapopulation models. Additional effects, however, occur because in classical metapopulations patch lifetime depends on extinction rate. Counterintuitively, this favours the evolution of specialisation when the trade-off affects r.     

Patterns of phenological changes in migratory birds

The phenology of avian migration appears to be changing in response to climate change. Seemingly contradictory differences in the timing of these annual cycles have been reported in published studies. We show that differences between studies in the choice of songbird species, as well as in the measurements of migration phenology, can explain most of the reported differences. Furthermore, while earlier spring arrival is evident across these studies, trends in timing of departure show large variation between species and according to individual timing of migration (early-arriving vs. late-departing individuals). Much of the variation in departure between species could be explained by each species’ migratory status. We present a detailed analysis of migrants recorded at a Danish migration site, and reveal that although shifts in migration timing can be demonstrated for almost all species, these shifts are either most pronounced in the early arriving/late departing individuals or the changes are similar. Thus most individuals do not seem to change their breeding-area residence time (BART). As BART is likely to reflect ecologically important factors, e.g. number of clutches, we expect that only small effects have been exerted on the breeding ecology of the studied species in the time period investigated. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

A random effects model for multistate survival analysis with application to bone marrow transplants

We present an extension of the non-homogeneous Markov model for a bone marrow transplant recovery process which allows for possible associations between the transition intensities. The associations between intensities are modeled by a correlated gamma frailty model. Based on a parametric model for the conditional transition intensities, we obtain estimates of the model parameters. We use these estimates to make predictions of patient’s eventual prognosis given the current medical history of the patient. Estimates of the uncertainty in our predictions are obtained by a modified bootstrap technique.