Do Yellow‐Bellied Marmots Perceive Enhanced Predation Risk When they are Farther from safety? An experimental study

Whereas there are many studies of the time allocated to antipredator vigilance while animals forage, the vast majority of these studies remain correlative. This is potentially problematic because a variety of factors other than variation in perceived risk might influence putative antipredator behaviors such as time allocated to vigilance and foraging. We conducted an experimental study of yellow‐bellied marmot (Marmota flaviventris) antipredator behavior while marmots foraged at a replicated set of feeding stations established 1, 5, 10, and 20 m from their main burrows. Marmots appeared to perceive a reduced risk of predation when they foraged in the presence of other marmots; they allocated more time to foraging and decreased the time allocated to vigilance. When they foraged farther from their burrows, marmots initiated foraging after a substantially greater amount of time, tended to increase the frequency of their bouts of vigilance, and decreased the duration of each bout. Yearling marmots took less time to begin foraging than adults. Marmot flight initiation distance at our feeding trays was independent of the distance they foraged away from the burrow. Taken together, these experimental results demonstrate that marmots' perceptions of risk increased with distance to the burrow and decreased when other individuals were within 10 m of them while they foraged.     

Flight Initiation Distance and Starting Distance: Biological Effect or Mathematical Artefact?

In many studies, flight initiation distance (FID, the distance at which a prey starts to flee at the approach of a walker) is positively related to starting distance (SD, the distance at which the walker begins to approach) and alert distance (AD, the distance at which the focal individual becomes alert to the threat). In spite of the fundamental differences between SD, a covariate that may not have any biological effect, and AD, a measure related to the behaviour of the animal, it is common to use SD as a proxy for AD when AD is hard to measure (e.g. in species that do not exhibit distinguishable alert postures). However, the relationship between SD and AD or FID may not have any biological reasons, but may instead simply result from a mathematical artefact because of the constraints SD ≥ AD ≥ FID. Under such constrains, the homoscedasticity assumption is violated, and thus, the classical null hypothesis of linear regression (slope = 0) is invalid. In this study, we first show that using SD as a proxy for AD can strongly affect the results on FID. Using data from FID tests on alpine marmots (Marmota marmota), a linear mixed model with AD as a covariate, suggested that the interaction between previous activity and AD had an effect on FID, while this effect was not detected when SD replaced AD as the covariate in the analysis. We then propose that the actual statistical test of the relationship between SD, AD and FID should be based on a null hypothesis that incorporates the constraint SD ≥ AD ≥ FID ≥ 0 and generate 95% CI of simulated slopes obtained from random values under this constraint. This null hypothesis can be rejected if the observed slope of the relationship between two of these variables is outside the 95% CI. We demonstrated that, for alpine marmots, the observed slope of the relationship between AD and SD was within the 95% CI of the simulated slopes. The absence of a statistically significant biological effect in the relationship between SD and AD raises important questions on the outcome of relationship between SD and FID. In Alpine marmot flight, decision should be studied separating the effect of SD on AD and the effect of AD on FID.     

Does egg competition occur in marine broadcast‐spawners?

When the availability of sperm limits female reproductive success, competition for sperm, may be an important broker of sexual selection. This is because sperm limitation can increase the variance in female reproductive success, resulting in strong selection on females to compete for limited fertilization opportunities. Sperm limitation is probably common in broadcast-spawning marine invertebrates, making these excellent candidates for investigating scramble competition between broods of eggs and its consequences for female reproductive success. Here, we report our findings from a series of experiments that investigate egg competition in the sessile, broadcast-spawning polychaete Galeolaria caespitosa. We initially tested whether the order in which eggs encounter sperm affects their fertilization success at two ecologically relevant current regimes. We used a split-clutch-split--ejaculate technique to compare the fertilization success of eggs from individual females that had either first access (competition-free treatment) or second access (egg competition treatment) to a batch of sperm. We found that fertilization success depended on the order in which eggs accessed sperm; eggs that were assigned to the competition-free treatment exhibited significantly higher fertilization rates than those assigned to the egg competition treatment at both current speeds. In subsequent experiments we found that prior exposure of sperm to eggs significantly reduced both the quantity and quality of sperm available to fertilize a second clutch of eggs, resulting in reductions in fertilization success at high and low sperm concentrations. These findings suggest that female traits that increase the likelihood of sperm-egg interactions (e.g. egg size) will respond to selection imposed by egg competition.     

Does Weather or Site Characteristics Influence the Ability of Scavengers to Locate Food?

Olfactory predators and scavengers rely on odors to locate food, and they forage primarily at night. We hypothesized that weather (e.g. wind speed, humidity, and temperature), vegetation, and landscape features affect the dissipation of odors in the atmosphere and, thus, impact the foraging efficiency of olfactory predators. We tested this hypothesis by assessing what conditions were correlated with the persistence of bait along the dike surrounding Willard Bay Reservoir, Utah. We distributed 124 chicken eggs and 199 dead European starlings (Sturnus vulgaris) as bait over 21 separate occasions spanning from May 21, 2009, to August 18, 2009. We used timers to record the time of consumption and cameras to identify which species ate the bait. Sixty‐six eggs and 87 dead European starlings were consumed. The bait was consumed mostly at night (83%) and by striped skunks (Mephitis mephitis), raccoons (Procyon lotor), and red foxes (Vulpes vulpes). We used nest survival models in program MARK to determine which covariates influenced bait persistence. We tested nine variables and found that bait persistence was influenced by section of the dike, time since study initiation, temperature, humidity, and wind speed but not bait type (egg or dead European starling), terrain, or visual cover. How quickly scavengers were able to locate food, which was inversely related to rates of bait persistence, decreased with higher temperatures and wind speeds and increased with higher humidity. Our results support the hypothesis that weather and micro‐habitat characteristics impact the ability of olfactory predators and scavengers to locate food.     

Does scale‐dependent feedback explain spatial complexity in salt‐marsh ecosystems?

Complexity theory highlights scale-dependent feedback mechanisms as an explanation for regular spatial patterning in ecosystems. To what extent scale-dependent feedback clarifies spatial structure in more complex, non-regular systems remains unexplored so far. We report on a scale-dependent feedback process generating patchy landscapes at the interface of intertidal flats and salt marshes. Here, vegetation was characterized by Spartina anglica tussocks, surrounded by erosion gullies. To demonstrate the presence of a scale-dependent feedback, we determined if vegetation induced habitat modification resulted in local facilitation and large scale-inhibition of plant growth. Field surveys revealed that larger tussocks have deeper gullies, suggesting that gully erosion is caused by increased water flow around tussocks. This was confirmed by flume experiments, showing that feedback effects vary with current velocity and water depth. Transplantation of small Spartina units inside and just outside present tussocks revealed that the growth of Spartina transplants compared to transplant growth on bare sediment was higher within the raised Spartina tussocks, but lower in the gully just outside Spartina tussocks, providing clear evidence of scale-dependent feedback. Our results emphasize that scale-dependent feedback is a more general explanation for spatial complexity in ecosystems than previously considered.     

Does nitrogen become limiting under high‐P conditions in detritus‐based tropical streams?

1. We examined effects of nutrients on leaf breakdown in interior forest streams at La Selva Biological Station, Costa Rica. We tested the hypothesis that dissolved inorganic nitrogen (DIN) becomes limiting when ambient phosphorus (P) concentration is high. We also compared the breakdown of relatively ‘low quality’ leaves (lower C : N, Trema integerrima) with that of ‘higher quality’ leaves (higher C : N, Ficus insipida) in a high‐P stream. 2. Litterbags were incubated in two streams: one enriched experimentally with P [target concentration 200 μg soluble reactive phosphorus (SRP) L^?1] and one control (naturally low P concentration approximately 10 μg SRP L^?1). Ammonium enrichment was achieved by adding fertiliser upstream of half of the litterbags in each stream. 3. Phosphorus addition stimulated leaf breakdown, microbial respiration, ergosterol and leaf %P. Leaf breakdown rate was consistent with those in La Selva streams with naturally high P concentration. 4. Nitrogen (N) addition had no effect on leaf breakdown, microbial respiration, ergosterol or leaf chemistry in either the P‐enriched or the reference stream, in spite of low N : P ratios. We conclude that N is probably not limiting in streams at La Selva that are naturally high in P. This may be due to moderately high ambient N concentration (>200 μg DIN L^?1) prevailing throughout the year. 5. The species with a lower C : N decomposed more rapidly and supported higher microbial activity than that with a higher C : N. Subtle differences in leaf N content, as well as dissolved P concentration, may be important in determining microbial colonisation and subsequent leaf breakdown.     

Who needs a forelimb anyway? Locomotor,postural and manipulative behavior in a one‐armed gibbon

Given the predominance of brachiation and other forms of suspension in gibbon locomotion, we compared the locomotor, postural, and manipulative behaviors of a captive, juvenile, one‐armed gibbon to the behavioral profiles of his family members. We expected Kien Nahn, whose arm was amputated in response to an untreatable injury approximately 1 year before observations began, to avoid suspensory locomotion, to spend more time immobile, and to be less likely to exhibit postures involving forelimb suspension. Data were collected using scan sampling to record the behaviors and postures of Kien Nahn, his younger brother, and his parents. Additional postural and manipulative behaviors were recorded ad lib. Kien Nahn and his younger sibling had similar activity levels, and although differences in postural profiles existed, they were surprisingly few. Specifically, Kien Nahn spent significantly less time in motion and in non‐suspensory forms of locomotion than his brother. When compared to his parents, Kien Nahn was found to be both active and in motion more often, but was less likely to exhibit the forelimb suspension posture. Despite the increased energetic demands associated with one‐armed brachiation, Kien Nahn preferred suspensory locomotion to other forms of locomotion. Furthermore, he found unique solutions for foraging and locomoting, often making use of his feet and teeth, and he was generally the first to approach and manipulate enrichment objects. We found no evidence to suggest that Kien Nahn's injury has altered his activity levels. Although the one‐armed gibbon displayed slightly different locomotor, postural, and manipulative behaviors than his family members, he seems to have adapted well to his injury. Zoo Biol 0:1–8, 2007. © 2007 Wiley‐Liss, Inc.     

Does high relatedness promote cheater‐free multicellularity in synthetic lifecycles?

The evolution of multicellularity is one of the key transitions in evolution and requires extreme levels of cooperation between cells. However, even when cells are genetically identical, noncooperative cheating mutants can arise that cause a breakdown in cooperation. How then, do multicellular organisms maintain cooperation between cells? A number of mechanisms that increase relatedness amongst cooperative cells have been implicated in the maintenance of cooperative multicellularity including single‐cell bottlenecks and kin recognition. In this study, we explore how relatively simple biological processes such as growth and dispersal can act to increase relatedness and promote multicellular cooperation. Using experimental populations of pseudo‐organisms, we found that manipulating growth and dispersal of clones of a social amoeba to create high levels of relatedness was sufficient to prevent the spread of cheating mutants. By contrast, cheaters were able to spread under low‐relatedness conditions. Most surprisingly, we saw the largest increase in cheating mutants under an experimental treatment that should create intermediate levels of relatedness. This is because one of the factors raising relatedness, structured growth, also causes high vulnerability to growth rate cheaters.     

Does artificial light pollution impair problem‐solving success in peafowl?

Behavioral innovations allow animals to adjust their behavior to solve novel problems. While innovative behavior can be important for animals living in new environments, anthropogenic pollution may limit their ability to adapt by impairing cognition or motivation. In particular, exposure to light pollution at night can cause sleep deprivation and may, therefore, hinder innovative behavior. To test this hypothesis, we examined experimentally whether exposure to acute light pollution impacts problem‐solving success in peafowl (Pavo cristatus). After peafowl were exposed to artificial light pollution for one night, they were presented with a problem‐solving task in which they could extract food by piercing the lid of an unfamiliar food bowl. Their problem‐solving success was unrelated to short‐term light pollution exposure. Other factors, including persistence, sex of the bird, and moon illumination, influenced their success in solving the task. The results suggest that short‐term exposure to light pollution does not limit behavioral innovation, but long‐term studies are necessary to further probe this question.     

Does the photosynthetic light‐acclimation need change in leaf anatomy?

There is a strong correlation between leaf thickness and the light‐saturated rate of photosynthesis per unit leaf area (P_max). However, when leaves are exposed to higher light intensities after maturation, P_max often increases without increasing leaf thickness. To elucidate the mechanism with which mature leaves increase P_max, the change in anatomical and physiological characteristics of mature leaves of Chenopodium album, which was transferred from low to high light condition, were examined. When compared with leaves subjected to low light continuously (LL leaves), the leaves transferred from low to high light (LH leaves) significantly increased P_max. The transfer also increased the area of chloroplasts facing the intercellular space (S_c) and maintained a strong correlation between P_max and S_c. The mesophyll cells of LL leaves had open spaces along cell walls where chloroplasts were absent, which enabled the leaves to increase P_max when they were exposed to high light (LH). However, the LH leaves were not thick enough to allow further increase in P_max to the level in HH leaves. Thus leaf thickness determines an upper limit of P_max of leaves subjected to a change from low to high light conditions. Shade leaves would only increase P_max when they have open space to accommodate chloroplasts which elongate after light conditions improve.     

Post‐fire regeneration in alpine heathland: Does fire severity matter?

Fire severity is thought to be an important determinant of landscape patterns of post‐fire regeneration, yet there have been few studies of the effects of variation in fire severity at landscape scales on floristic diversity and composition, and none within alpine vegetation. Understanding how fire severity affects alpine vegetation is important because fire is relatively infrequent in alpine environments. Globally, alpine ecosystems are at risk from climate change, which, in addition to warming, is likely to increase the severity and frequency of fire in south‐eastern Australia. Here we examine the effects of variation in fire severity on plant diversity and vegetation composition, 5 years after the widespread fires of 2003. We used floristic data from two wide‐spread vegetation types on the Bogong High Plains: open heathland and closed heathland. Three alternative models were tested relating variation in plant community attributes (e.g. diversity, ground cover of dominant species, amount of bare ground) to variation in fire severity. The models were (i) ‘linear’, attributes vary linearly with fire severity; (ii) ‘intermediate disturbance’, attributes are highest at intermediate fire severity and lowest at both low‐ and high‐severity; and (iii) ‘null’, attributes are unaffected by fire severity. In both heathlands, there were few differences in floristic diversity, cover of dominant species and community composition, across the strong fire severity gradient. The null model was most supported in the vast majority of cases, with only limited support for either the linear and intermediate disturbance models. Our data indicate that in both heathlands, vegetation attributes in burnt vegetation were converging towards that of the unburnt state. We conclude that fire severity had little impact on post‐fire regeneration, and that both closed and open alpine heathlands are resilient to variation in fire severity during landscape scale fires.     

Does soil type drive social organization in southern hairy‐nosed wombats?

Spatiotemporal distributions of key resources are hypothesized to underpin sociobiological patterns. Burrow availability and quality is of paramount importance to fossorial animals. The southern hairy-nosed wombat (Lasiorhinus latifrons) burrows in both hard and friable soils. Theoretical and empirical studies suggest that the harder substrate should promote closer geographical clustering of burrows than in softer soils. Clustered burrows are expected to be associated with larger group sizes. If sociality is driven by constraint rather than advantage, patterns of spatial and temporal distribution of animals within and among groups may show indications of avoidance or even antagonism, and 'making the best of a bad job' via positive kin associations to offset the disadvantages of high-density living. To test these ideas, we compared warren relatedness and social structure of L. latifrons on friable soils (Nullarbor Plain) and hard calcrete (Brookfield Conservation Park, BCP). Individuals were sampled by noninvasive collection of hairs for genotyping to identify individuals and to estimate their space-use and associative behaviour with respect to relatedness. Burrows in calcrete were indeed more clumped, and warren and group size larger. Differences in spatiotemporal organization and relatedness structure between sites were in the expected direction: (i) Nullarbor males associated and shared warrens less than at BCP; and (ii) Nullarbor spatial relatedness patterning data were not consistent with proposed female breeding dispersal, in contrast to those at BCP. Under Nullarbor (low density) conditions, cooperation or tolerance between males may be less advantageous, and accessing or digging burrows should be less of a constraint for juvenile females.     

How Does Inflammation‐Induced Hyperglycemia Cause Mitochondrial Dysfunction in Immune Cells?

Inflammatory mediators have an established role in inducing insulin resistance and promoting hyperglycemia. In turn, hyperglycemia has been argued to drive immune cell dysfunction as a result of mitochondrial dysfunction. Here, the authors review the evidence challenging this view. First, it is pointed out that inflammatory mediators are known to induce altered mitochondrial function. In this regard, critical care patients suffer both an elevated inflammatory tone as well as hyperglycemia, rendering it difficult to distinguish between the effects of inflammation and hyperglycemia. Second, emerging evidence indicates that a decrease in mitochondrial respiration and an increase in reactive oxygen species (ROS) production are not necessarily manifestations of pathology, but adaptations taking shape as the mitochondria is abdicating its adenosine triphosphate (ATP)‐producing function (which is taken over by glycolysis) and instead becomes “retooled” for an immunological role. Collectively, these observations challenge the commonly held belief that acute hyperglycemia induces mitochondrial damage leading to immune cell dysfunction.     

Does batrachotoxin autoresistance coevolve with toxicity in Phyllobates poison‐dart frogs?

Toxicity is widespread among living organisms, and evolves as a multimodal phenotype. Part of this phenotype is the ability to avoid self‐intoxication (autoresistance). Evolving toxin resistance can involve fitness tradeoffs, so autoresistance is often expected to evolve gradually and in tandem with toxicity, resulting in a correlation between the degrees of toxicity and autoresistance among toxic populations. We investigate this correlation in Phyllobates poison frogs, notorious for secreting batrachotoxin (BTX), a potent neurotoxin that targets sodium channels, using ancestral sequence reconstructions of BTX‐sensing areas of the muscular voltage‐gated sodium channel. Reconstructions suggest that BTX resistance arose at the root of Phyllobates, coinciding with the evolution of BTX secretion. After this event, little or no further evolution of autoresistance seems to have occurred, despite large increases in toxicity throughout the history of these frogs. Our results, therefore, provide no evidence in favor of an evolutionary correlation between toxicity and autoresistance, which conflicts with previous work. Future research on the functional costs and benefits of mutations putatively involved in BTX resistance, as well as their prevalence in natural populations, should shed light on the evolutionary mechanisms driving the relationship between toxicity and autoresistance in Phyllobates frogs.     

Does High BMI Influence Hospital Charges in Children Undergoing Adenotonsillectomy?

Background: Obesity is a highly prevalent chronic problem with health and fiscal consequences. Data from adults and nonsurgical pediatric patients suggest that obesity has serious implications for the US economy. Objective: Our goal was to describe the impact of BMI on hospital charges in children undergoing adenotonsillectomy (AT). Methods and Procedures: We carried out a retrospective comparative analysis of the electronic anesthesia record and the charges from billing data from a large tertiary institution on children aged 3–18 years who had AT during the year 2005–2007. The main outcome measures were mean total hospital charges, likelihood of admission, and length of hospital stay (LOS). Results: Of 1,643 children, 68.9% were aged <10 years, 76% were whites, and 74.1% had private commercial insurance. Most (75.3%) children were discharged on the day of surgery. Obese and overweight children were more likely to be admitted than their normal‐weight peers (X² = 26.3, P < 0.001). Among those admitted, BMI showed a positive correlation with LOS (r = 0.20, P < 0.001). Obese and overweight patients had significantly higher total hospital charges than their healthy‐weight counterparts (P = 0.001). Anesthesia, postanesthesia care unit (PACU), and pharmacy and laboratory charges were also higher for obese than normal‐weight children (P < 0.05). Discussion: Overweight and obese children undergoing AT accrued higher hospital charges and had longer postoperative LOS than their healthy‐weight peers. If these findings are extendable to other surgical procedures, they could have far‐reaching implications for the US economy.     

Song Perch Height in Rufous‐and‐White Wrens: Does Behaviour Enhance Effective Communication in a Tropical Forest?

Animal signals are distorted as they transmit through the environment, but many species have evolved strategies to minimize distortion of vocal signals. Song structure can change over evolutionary time, or signallers can modify their behaviour, to reduce attenuation and degradation in a specific habitat. We investigated signalling behaviour in rufous-and-white wrens, Thyothorus rufalbus , a Neotropical songbird in which both sexes sing, with a specific focus on perch height. Based on previous findings, including a detailed sound transmission study, we predicted that rufous-and-white wrens would choose elevated song perches in order to maximize the distance their songs travel, and that males and females would show different perch height choices. We observed 30 birds in 18 territories in a tropical forest in Costa Rica to determine the perch heights of birds when singing, producing non-song vocalizations, collecting nesting material, foraging, and engaging in other behaviours. We found that both activity and sex influenced perch height. Birds sang from a variety of heights, but the highest perches were used as song posts by males. Males minimized singing from within 1 m of the ground, and they generally perched higher than females, which may reflect sex differences in communication strategies. Both sexes foraged on or near the ground. The finding that rufous-and-white wrens vary their perch height with specific activities suggests that they modify their singing behaviour to enhance long-distance communication.     

Does habitat fragmentation promote climate‐resilient phenotypes?

Understanding how individual differences in physiological performance modify behavioral responses to environmental variability and its fitness consequences is key to predicting the vulnerability of species and populations to environmental change. For many species, summit metabolic rate (M_SUM; the upper limit to heat production) and basal metabolic rate (BMR; the lower limit related to energy acquisition and processing) often constrain aspects of physiological performance and behavioral activity. We examined the relationship between metabolic phenotypes, foraging behavior, and survival in overwintering black‐capped chickadees Poecile atricapillus inhabiting contiguous and fragmented forested landscapes. We found that birds with lower summit metabolic rates were generally more sensitive to winter weather and increased their use of supplemental feeding stations as ambient temperatures decreased. In highly fragmented forests, this relationship may have incurred strong survival consequences, as birds with lower summit metabolic rates were less likely to survive the winter season. Additionally, we found that chickadee populations persisting in fragmented landscapes were characterized by slightly higher thermogenic capacity (M_SUM) and lower maintenance metabolic costs (BMR). We suggest that habitat loss and fragmentation present unique selection pressures that alter the relationships between environmental variability, behavior and physiology, and result in context‐specific fitness consequences.     

Does selective logging change ground‐dwelling beetle assemblages in a subtropical broad‐leafed forest of China?

Selective logging with natural regeneration is advocated as a near‐to‐nature strategy and has been implemented in many forested systems during the last decades. However, the efficiency of such practices for the maintenance of forest species are poorly understood. We compared the species richness, abundance and composition of ground‐dwelling beetles between selectively logged and unlogged forests to evaluate the possible effects of selective logging in a subtropical broad‐leafed forest in southeastern China. Using pitfall traps, beetles were sampled in two naturally regenerating stands after clearcuts (ca. 50 years old, stem‐exclusion stage: selectively logged 20 years ago) and two mature stands (> 80 years old, understory re‐initiation stage: selectively logged 50 years ago) during 2009 and 2010. Overall, selective logging had no significant effects on total beetle richness and abundance, but saproxylic species group and some abundant forest species significantly decreased in abundance in selectively logged plots compared with unlogged plots in mature stands. Beetle assemblages showed significant differences between selectively logged and unlogged plots in mature stands. Some environmental characteristics associated with selective logging (e.g., logging strategy, stand age, and cover of shrub and moss layers) were the most important variables explaining beetle assemblage structure. Our results conclude that selective logging has no significant impacts on overall richness and abundance of ground‐dwelling beetles. However, the negative effects of selective logging on saproxylic species group and some unlogged forest specialists highlight the need for large intact forested areas for sustaining the existence of forest specialist beetles.